Reliability Guidelines

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SEMATECHTechnology Transfer 92031014A-GEN

Guidelines for Equipment Reliability


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Guidelines for Equipment ReliabilityTechnology Transfer # 92031014A-GEN

SEMATECHMay 5, 1992

Abstract: This guideline was developed by a task force comprised of reliability experts and users ofreliability methodologies from the SEMI/SEMATECH member companies. The document was

written to address the needs of semiconductor equipment manufacturers and their customers. It

includes a description of the principles of a cost-effective reliability program, instructions on how

to get started, and details on what needs to be done. A large portion of the document is dedicated

to analysis and testing methodologies. These include: Failure Modes and Effects Analysis

(FMEA), Fault Tree Analysis (FTA), Component Failure Analysis (CFA), Human Reliability

Analysis (HRA); and Reliability Testing, Component Testing, Accelerated Testing (Sudden Death,

Step-Stress Testing), Burn-in Testing, Life Testing, Environmental Stress Screening, Qualification

Testing, and Acceptance Testing.

Keywords: Life Cycle Phases, Reliability Testing, RAMP, Failure, FRACAS, Failure Modes and EffectsAnalysis, Quality Function Deployment (QFD), Design of Experiment, Cost of Ownership, Infant

Mortality, Reliability Qualification Testing (RQT), Taguchi, Users Groups, Reliability Block

Diagram Modeling (RBD), Environmental Stress Screening (ESS), Fault Tree Analysis (FTA)

Authors: Dhudsia, Vallabh

Approvals: Vallabh Dhudsia, Project Manager & AuthorKeith Erickson, Director

Dan McGowan, Technical Information Transfer Team Leader


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Technology Transfer # 92031014A-GEN SEMATECH

Table of Contents

1 SUMMARY................................................................................................................................. 1

2 THE RELIABILITY IMPROVEMENT PROCESS AND EQUIPMENT LIFE CYCLE........... 2

2.1 Introduction ......................................................................................................................... 2

2.2 The Equipment Life Cycle .................................................................................................. 2

2.3 Life Cycle Phases................................................................................................................ 3

2.4 Life Cycle Cost.................................................................................................................... 9

2.5 The Reliability Improvement Process............................................................................... 13

2.6 Applying the Reliability Improvement Process................................................................. 21

2.7 Summary ........................................................................................................................... 23

2.8 References ......................................................................................................................... 24

3 IMPLEMENTATION OF THE RELIABILITY IMPROVEMENT PROCESS....................... 25

3.1 Introduction ....................................................................................................................... 25

3.2 Managements Role........................................................................................................... 25

3.3 Applying the Reliability Improvement ProcessThe Reliability Improvement Process..... 263.4 Specific Applications of the Reliability Improvement Process......................................... 44

3.4.1 Starting with Equipment in the Design Phasewith Equipment in the Design

Phase .................................................................................................................... 44

3.4.2 Starting with Equipment in the Prototype Phase ................................................... 46

3.4.3 Starting with Equipment in the Pilot Production Phasewith Equipment in the

Pilot Production Phase ......................................................................................... 47

3.4.4 Starting with Equipment in the Production and Operation Phasewith

Equipment in the Production and Operation Phase ............................................. 49

3.4.5 Starting with Equipment in Phase Out Phase with Equipment in Phase Out

Phase .................................................................................................................... 50

3.5 Functional ResponsibilitiesResponsibilities...................................................................... 51

3.6 Where to Begin.................................................................................................................. 52

3.7 Reliability Plans ................................................................................................................ 55

3.8 Application of Resources and Communicating Value ...................................................... 56

3.9 Summary ........................................................................................................................... 57

3.10 References ....................................................................................................................... 58

4 ACTIVITIES AND TOOLS IN THE RELIABILITY IMPROVEMENT PROCESS............... 59

4.1 Introduction ....................................................................................................................... 59

4.2 Reliability ActivitiesActivities.......................................................................................... 59


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SEMATECH Technology Transfer # 92031014A-GEN

List of Figures

Figure 2-1. Percent of Total Life Cycle Costs vs Locked-in Costs................................................ 9

Figure 2-2. Impact of a reliability program on life cycle cost...................................................... 11

Figure 2-3. Optimizing Life Cycle Costs..................................................................................... 12

Figure 2-4. Decrease in Life Cycle Costs in New Generations of Equipment............................. 13

Figure 2-5. The Reliability Improvement Process........................................................................ 14

Figure 2-6. Application of Reliability Improvement Process....................................................... 22

Figure 3-1. Multiple Equipment and Their Life Cycle Phase Status............................................ 53

Figure 4-1. A Block Model Developed in RAMP for the SETEC Generic Wafer Handler

System...................................................................................................................... 125

Figure 4-2. An Estimate of the Cumulative Distribution Function for MTBF .......................... 127

Figure 4-3. A Pareto Diagram for Component Contribution to System Failure........................ 128

Figure 4-4. A Revised Block Diagram for the SETEC Generic Wafer Handler System,

showing the Addition of the Redundant Wafer Sensor............................................ 128

Figure 4-5. An Estimate of the Cumulative Distribution Function for MTBF after

Modifying the Generic Wafer Handler System........................................................ 129

Figure 4-6. A Pareto Diagram for Component Contribution to System Failureafter

Modifying the Generic Wafer System...................................................................... 130

Further analysis reveals that C2 fails if parts 1 and 2 (P1 and P2) fail. C4 fails if parts 3

or 4 (P3 or P4) fail. The block diagram model now looks like:.............................. 135


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List of Tables

Table 3-1. Reliability Improvement Process Applied at Six Different Starting Points................. 27

Table 3-2. Reliability Improvement Process Activities ............................................................... 31

Table 3-3. Reliability Improvement Process Activities2-3. Reliability ImprovementProcess Activities for the Design Phase..................................................................... 34

Table 3-4. Reliability Improvement Process Activities for the Prototype Phase......................... 37

Table 3-5. Reliability Improvement Process Activities for the Pilot Production Phase .............. 40

Table 3-6. Reliability Improvement Process Activities for the Production and Operation

Phase .......................................................................................................................... 42

Table 3-7. Reliability Improvement Process Activities for the PhaseOut Phase2-7.

Reliability Improvement Process Activities for the PhaseOut Phase ...................... 44

Table 3-8. Design Phase Reliability Improvement Process Activities......................................... 45

Table 3-9. Prototype Phase Reliability Improvement Process Activities..................................... 47

Table 3-10. Pilot Production Phase Reliability Improvement Process Activities When

Initiated In Pilot Production Phase............................................................................. 48

Table 3-11. Production and Operation Phase Reliability Improvement Process Activities

When Initiated in Production and Operation Phase................................................... 50

Table 3-12. Phase Out Phase Reliability Improvement Process Activities When Initiated

in Phase-Out Phase..................................................................................................... 51

Table 3-13. Current Product Line Status...................................................................................... 54


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The SEMATECH Perspective

Statement from Bill Spencer, CEO of SEMATECH:

Todays competitive environment demands an increasing level of reliability in semiconductor

manufacturing equipment. The industry has made great strides in the last four years in improvingreliability. In fact, VLSI Research reports that in its annual customer survey, reliability has fallen

to sixth place on the list of biggest problems, after being number one for 10 years. VLSI is quick

to give SEMATECH credit for much of the improvement. And while the existence of

SEMATECH was a key element, the supplier industry should receive added praise for stepping

up and solving a major problem.

But, as with so much of this business today, reliability is a race without an end. And the formula

to improved reliability is to build it into every stage of development. This Reliability Guideline

will assist in development of a program to ensure consideration of reliability factors at every

stage of product development from inception through qualification.

The Guideline was developed by a task force comprised of reliability experts and users of

reliability methodologies from the SEMI/SEMATECH member companies. As a result, it offers

best-of-breed concepts and is written to meet the needs of semiconductor equipment

manufacturers and their customers. Im sure it will prove an excellent tool.

William J. Spencer

President and Chief Executive Officer


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Preface

These guidelines have been written for use by semiconductor equipment suppliers and customers.

They are intended as a road map that these groups can refer to for assistance in improving the

reliability of their semiconductor manufacturing equipment as part of a long-term strategy aimedat regaining an increased worldwide market share.

Although there is an abundance of reliability information available in text books, military

handbooks and standards, and guidebooks directed at specific products, there is no concise,

single source document available for the semiconductor equipment industry. The purpose of

these guidelines is to fill this gap. To assist in this effort, a task force consisting of

representatives from the semiconductor industry was assembled to provide guidance in the

structure and content of these guidelines. The guidelines do not provide comprehensive

instruction on the details of reliability engineering; rather they provide a description of the

principles of a cost-effective reliability program, instructions on how to get started, and details on

what needs to be done. Descriptions of necessary program activities and reliability concepts are

provided along with references for those who desire additional information.

The focus of the guidelines is on hardware reliability realizing that software reliability is an

important aspect of reliability for a large segment of semiconductor manufacturing equipment.

However, other guidelines exist that address the issue of software reliability. Thus, the software

reliability topic is discussed only briefly.

The guidelines:

Are intended to be of value to managers, reliability engineers, and designers

Are not a "detailed how-to" document, but rather a "roadmap of how to"

Are centered around a continuous improvement process referred to as the

Reliability Improvement Process

Cover the entire equipment life cycle as it applies to the semiconductor equipmentindustry

Even though emphasis is placed on designing in reliability, the guidelines show how to

incorporate reliability into every phase of the equipment life cycle.


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1 SUMMARY

These guidelines focus on a continuous improvement process referred to as theReliability

Improvement Process, and theEquipment Life Cycle. These two concepts are introduced and

discussed in Section 1.0 of the guidelines. Knowledge of the equipment life cycle is importantbecause it provides a basis for understanding how and where reliability engineering enters into

the process of designing, producing, and operating the equipment. In this document, the life

cycle has been broken into six distinct phases, each representing a unique portion of the life

cycle. These six life cycle phases are:

1. Concept and Feasibility Phase

2. Design Phase

3. Prototype (alpha-site) Phase

4. Pilot Production (beta-site) Phase

5. Production and Operation Phase

6. Phase-out Phase

These phases provide the framework for tracking reliability improvement throughout the

equipment life cycle phases and guidance on when and where to apply resources. Life cycle costs

concepts are introduced to help understand the impact on expenditures and cost of ownership

when reliability is initiated at different phases of the life cycle.

The Reliability Improvement Process provides a means for systematically improving reliability

throughout the equipment life cycle. It is an iterative process of setting goals, evaluating,

comparing, and improving directed toward continuous reliability improvement. It consists of

five basic steps.

1. Establish reliability goals and requirements for equipment2. Apply reliability engineering or improvement activities, as needed

3. Conduct an evaluation of the equipment or equipment design

4. Compare the results of the evaluation to the goals and requirements and make a

decision for the next step

5. Identify problems and root causes

The process then returns to Step 2, and repeats Steps 2 through 5 until goals and requirements are

met.


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The role of management in implementing the Reliability Improvement Process is introduced in

Section 2.0. Management has responsibilities in establishing and implementing the Reliability

Improvement Process. These responsibilities include establishing the right environment and

choosing individuals to champion the effort. Section 2.0 provides details on preparing for and

implementing the Reliability Improvement Process, including a discussion on the various

activities associated with each step of the Reliability Improvement Process and each phase of thelife cycle. The Reliability Improvement Process can be used for a piece of equipment regardless

of its placement in the life cycle. The discussion in Section 2.0 includes information on how to

select equipment for initiating reliability improvement, the importance of data, and the choice of

activities when resources are limited.

Activities and tools used in applying the Reliability Improvement Process are discussed in more

detail in Section 3.0. Three types of activities are listed: engineering, datarelated, and testing.

Many of the activities require tools for implementation. These tools come from various

disciplines such as probability and statistics and reliability engineering. References that have

detailed information on the tool or activity are provided at the end of each activity in Section 3.0.

2 THE RELIABILITY IMPROVEMENT PROCESS AND EQUIPMENT LIFE

CYCLE

2.1 Introduction

The reliability improvement process and the equipment life cycle form the basis for these

guidelines and are introduced in this section. The reliability improvement process is an iterative

process that provides:

An effective and systematic way to include reliability in equipment design

A structure for making reliability improvements throughout the equipment lifecycle

The reliability improvement process provides a means for making revolutionary advancements

when it is applied to equipment early in the design stage, or during major design upgrades, or for

making evolutionary improvements to existing equipment.

Knowledge of the equipment life cycle is important because it provides:

The framework for applying the reliability improvement process

A basis for understanding the best practice for improving equipment reliabilityand the cost of the improvement

Life cycle costs are introduced in this section to provide a perspective on the impact of initiating

the reliability improvement process early in the equipment life cycle. A thorough knowledge of

life cycle costs and life cycle phase relationships helps to achieve better equipment at lower total

costs.

2.2 The Equipment Life Cycle

The equipment life cycle begins when the idea for the equipment is conceived and ends when the

equipment is no longer useful. The life cycle consists ofphases that describe the state of design,

process of development, and production of the equipment. A working knowledge of these phases


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enables proper planning and execution of the activities and functions necessary for designing,

manufacturing, and operating reliable equipment in a cost effective manner.

2.3 Life Cycle Phases

In this document, the life cycle has been divided into the six phases listed below. As indicated,

these six phases can be grouped under three macro phases. The three macro phases aresometimes used in place of the six phases for illustrative purposes; this in no way impacts the

concepts and methodology presented.

1. Concept and Feasibility Concept and Feasibility

2. Design

3. Prototype (alpha (X)-site) Design and Development Macrophases

4. Pilot Production (Beta (B)-site

5. Production and Operations

6. Phase-out Phase Production and Operation

A discussion of each of the six life cycle phases follows.

1. Concept and Feasibility. The life cycle begins with this phase; the need for new

equipment is identified and alternative approaches to fulfilling that need are explored.

The need for new equipment may be based on existing equipment that can no longer

perform its intended function or on customer requirements for which the necessary

equipment does not exist.

Concept/Feasibility

Design

Prototype (-site)

Pilot Production (-site)

Production/Operation

Phase Out

During this phase, marketing and sales personnel, customer service representatives,

design and reliability engineers, and manufacturing engineers work together with the

customer to:

Determine the need for new equipment

Establish reliability goals

Evaluate the feasibility of meeting these goals

Estimate resource requirements

Examine alternative design concepts


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Select those concepts to be studied in more detail during the design phase

Estimate cost trade offs

The concept and feasibility phase, and the design phase that follows, are the optimal

times for using design-for-reliability practices.

2. Design. The alternative design concepts selected during the concept and feasibility phaseare explored in more detail by the design engineers during this phase of the life cycle. A

design disclosure package is prepared and evaluated by all concerned parties. Reliability

and manufacturing engineers, as well as quality assurance and field service personnel are

generally called on by the design engineers for input concerning parts selection,

components, serviceability, and manufacturing processes. Also, reliability goals set for

the equipment during the concept and feasibility phase are translated into requirements

very early in the design phase. Requirements are useful in making preliminary reliability

allocations to subsystems and components to understand cost impacts.

This phase of the life cycle can be separated into two parts: preliminary design andfinal

design.

Concept/Feasibility

Design

Prototype (-site)



Phase Out

During the preliminary design process, design and reliability engineers:

Modify goals to meet customer requirements

Evaluate a number of design alternatives

Make preliminary reliability allocations to subsystems and components

Prepare a design disclosure package of requirements and specifications

Estimate cost considerations

More than one design alternative may be selected for the final design phase if serious

questions remain about the best choice.

During the final design process, customer and supplier representatives, design andreliability engineers, project managers, field service personnel, manufacturing engineers,

and quality assurance personnel:

Update reliability allocations to subsystems and components

Carry out design reviews

Implement design-for-reliability practices

Update the design disclosure package to reflect these reviews

Select specific designs for prototype construction


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Estimate cost trade offs and considerations

Several iterations of design review and redesign are usually required before a design is

ready for prototype construction. Design reviews are important in measuring the progress

against design requirements and gaining management approval to proceed with the

prototype phase of the life cycle. These reviews are carried out in parallel with the design

process and are often categorized as follows:

Requirements Review - review the equipments design requirements

Preliminary Design Review - evaluate the preliminary design againstrequirements

Critical Design Review - provide design to the customer(s) for review

3. Prototype. Specific designs selected during the design phase are built and tested during

this phase to determine if all design requirements will be met. The prototype phase pro-

vides the first opportunity to validate the entire design, and is therefore commonly called

alpha-site evaluation. Selected customers are included in alpha-site evaluations and are

asked to provide feedback on all aspects of the equipment.

Concept/Feasibility

Design

Prototype (-site)



Phase Out

Multiple design alternatives may require prototyping and testing if serious questions existabout the best overall choice. It is common for reliability engineers to have responsibility

for performing these tests. However, manufacturing personnel will have responsibility

for determining that parts and components conform to specifications within financial

guidelines.

During the prototype phase, design, reliability, test, and manufacturing engineers, as well

as quality assurance personnel:

Build and test one or more prototypes of a design

Present the test results for a pilot production design review

Redesign as needed to fix weaknesses or make other desirable changes Conduct additional design reviews as appropriate

The design reviews should include another critical design review to give the customer an

opportunity to review the latest design being considered.

Concurrent with redesigns and design reviews, reliability engineers, quality assurance

personnel, and manufacturing engineers will develop quality assurance plans, design

inspection and testing programs, set up production facilities, and develop production

plans in preparation for the pilot production phase.


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4. Pilot Production. This phase of the life cycle serves as a bridge between the prototype

phase and the production and operation phase. This is the first opportunity for the

equipment to be evaluated in an extended customer environment, and is therefore

commonly called beta-site evaluation. In fact, it may be the first time that the equipment

is exposed to a customers processes.

Concept/Feasibility

Design

Prototype (-site)



Phase Out

The purpose of the pilot production phase is to help identify and correct problems with

the equipment before full-scale production begins. Design and reliability engineers

should evaluate the actual level of equipment reliability and determine what needs to be

accomplished to meet requirements in a cost effective manner.

During the pilot production phase, project management, reliability engineers, manufactur-

ing and test personnel, and customer service representatives:

Qualify the equipment manufacturing process

Establish field trials and customer applications of equipment

Monitor the equipments performance

Identify root causes of failures

Implement a "corrective action" program for reliability problems

Determine cost of ownership

Prior to the production and operation phase of the life cycle, reliability and design

engineers should evaluate equipment reliability and make the appropriate recommen-

dations. If the actual equipment reliability level is less than desired, specific reliability

improvement activities that were identified in the corrective action program should be

implemented. This is the last opportunity to make design changes and other

improvements before full-scale production.

Design reviews conducted at this point are often broken down into:

Qualification Review - verify that the final design meets requirements Production Readiness Review - to determine the readiness of full

production

Reliability Budget Review - verify the reliability goal allocations

If any design changes were made at this point, another critical design review may be

appropriate.


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5. Production and Operation. This phase of the life cycle represents the time when units

are produced and sold. All major reliability problems should have been identified and

corrected prior to the production and operation phase. A formal program must be in place

for collecting and analyzing field service data and performance data for the customers

unit as well as for the cost impact.

Concept/Feasibility

Design

Prototype (-site)



Phase Out

During the production and operation phase, field service personnel, management, quality

assurance personnel, and reliability engineers:

Implement a field tracking and customer feedback and satisfactionprogram

Provide training and technical assistance to customers

Document and employ installation testing and operation procedures

Identify and report operation and maintenance problems

Record failure data in a formal database

Manage continuous improvement efforts

Determine cost of ownership impacts

Recorded failure data should account for uncertainty due to variations in site, product

vintage, and customer procedures.

After proper review, decisions are made for resource allocation for continuous improve-

ment in the reliability process. The supplier and customer should function as partners in

these efforts and may participate in user groups.

Once equipment is in the field, it is important to continually monitor reliability, analyze

failures and identify root causes, implement corrective actions, and improve known

causes of failures both for the current and the next generation of equipment.

6. Phase Out. The equipment product line is approaching the end of its useful life during

this final phase of the life cycle. The end of useful life naturally occurs earlier for the

supplier than it does for the customer. The end of useful equipment life for the customer

can occur due to obsolescence, wear, or a change in business plans. To remain

competitive, the supplier must make plans for the next generation of equipment before

phasing out current generation production.


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Concept/Feasibility

Design

Prototype (-site)



Phase Out

The information gained during the six phases of the life cycle should be retained so that it

can be used to improve future generations of similar or new equipment.

This completes the life cycle for the current generation of equipment. Each new

generation of equipment would experience basically the same life cycle.

Supplier Cost Implications. The early life cycle phases typically represent the smallest portion

of those total life cycle costs borne by the supplier, yet generally represent the region where the

greatest impact on equipment reliability can be made. As a design moves toward completion,

design details become increasingly fixed. Thus, the cost in time and dollars to correct reliability

problems increases. Figure 1-1 shows that typically, toward the end of the design/development

macro phase of the life cycle, only 15% of the life cycle costs are consumed, but approximately

95% of the total life cycle costs have been determined (i.e., locked in).[2] Thus, changes made to

improve reliability after the design/development macro phase have little impact on overall life

cycle costs, but can be very expensive in terms of costly design changes, retrofits, service calls,

warranty claims, and customer goodwill. This is not meant to imply that equipment already in

the production/operation macro phase should be ignored in terms of improving reliability.

Reliability improvement activities should continue throughout the life cycle.


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Concept/Feasibility Design/Development Production/Operation

Production

3%

12%

85%

(35%)

% Locked-In Costs

%Locked-In

Costs

20

40

60

80

100

0

%TotalCosts

0

20

40

60

80

10095%

Operation (50%)

Source: Arsenault and Roberts, Reliability and Maintainability of Electronic Systems

Figure 2-1. Percent of Total Life Cycle Costs vs Locked-in Costs

Although reliability improvements made earlier in the life cycle can increase initial supplier

costs, they generally result in lower support costs for the supplier and lower operational costs for

the customer. Also, early improvement could reduce the suppliers costs of production, warranty,

and service.

2.4 Life Cycle Cost

Two criteria used by semiconductor manufacturers to select equipment for a manufacturing step

or process are:

1. Technical

2. Economical[1]

The question asked for the technical criterion is, "Can a particular piece of equipment or

equipment line do the manufacturing step or process required?" The question asked for the

economical criterion is, "Does the result of the manufacturing process justify or support the cost

and on-going expense of a particular piece of equipment or equipment line?" It is increasingly

common for several pieces of equipment to be able to meet the technical criterion. Thus, theeconomical criterion is becoming increasingly important. Customers consider not only the initial

purchase price, but the costs associated with equipment operations over its entire life (i.e., life

cycle costs).


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Life cycle costs include both equipment supplier costs, which are passed on to the customer in

the purchase price of the equipment, and all costs incurred by the customer over the equipment

life. Supplier costs plus the suppliers gross profit margin are referred to asacquisition costs, and

include:

Research and development

Marketing and sales

Testing and manufacturing

Supplier shipping and installation

Supplier training and support

Supplier service and spare parts

Warranty costs

Continuous improvement

Costs incurred by the customer are referred to as operational costs, and include:

Customer installation and training Operating costs

Customer service costs and spares inventory

Customer performed maintenance

Customer space costs

Scheduled maintenance

Equipment improvements and upgrades

Down time and scrap costs

Disposal costs

Life cycle costs implications to both the supplier and the customer are discussed in the following

paragraphs.


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Customer Cost Implications. Improvements in reliability made by the supplier early in the

equipment life cycle may result in higher development costs being passed on to the customer in

the equipment acquisition costs. However, this can be more than offset as the customer benefits

by having lower operational costs with increased reliability and up time that results in greater

productivity.

Figure 1-2 illustrates how a reliability program impacts acquisition and operational costs. As thisfigure indicates, acquisition costs may increase due to efforts to improve reliability.

TotalLife

CycleCosts

No FormalReliabilityProgram

With Formal

Operational

CostsOperational

Costs

Acquisition

Costs

Acquisition

Costs

ReliabilityProgram

Total

Life

Cycle

Costs

Figure 2-2. Impact of a reliability program on life cycle cost

However, operational costs, and even more important, total life cycle costs decrease. It is

important for the customer to make equipment purchase decisions based on total life cycle costs

and not just on initial purchase price.


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Optimizing Life Cycle Costs. Increasing acquisition costs to improve equipment reliability and

lower operational and total life cycle costs is clearly a recommended practice. However, there is

a point at which increasing acquisition costs to obtain higher levels of reliability is no longer

beneficial. Figure 1-3 shows an optimal point beyond which total life cycle costs begin

increasing with further improvements in reliability.

LifeCycleCosts

Reliability

Optimized CostPoint

Acquisition

Costs

Operational

Costs

Life CycleCosts

Figure 2-3. Optimizing Life Cycle Costs

When this occurs, a more reliable technology is required for further improvement.

Reliability insights from a technology used in one generation of equipment should be

documented so they can be used to improve the next generation. Improvements in technology

transfer between equipment generations will generally produce a decrease in the life cycle costs

in each succeeding generation of equipment as shown in Figure 2-4.


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Generation 1

Generation 2

Generation 3

Generation 4

Life

CycleCosts

Reliability

Figure 2-4. Decrease in Life Cycle Costs in New Generations of Equipment

2.5 The Reliability Improvement Process

The reliability improvement process is an iterative process that is applied at each phase of the

equipment life cycle. It consists of five basic steps:

1. Establish reliability goals and requirements for equipment

2. Apply reliability engineering or improvement activities, as needed

3. Conduct an evaluation of the equipment or equipment design


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4. Compare the results of the evaluation to the goals and requirements and make a

decision to move either to the next step or the next phase

5. Identify problems and root causes

The process then returns to Step 2, and Steps 2 through 5 are repeated until goals and

requirements are met.

The reliability improvement process steps are shown in the flowchart in Figure 1-5.

Establish Goals/Requirements

Step 2.

Reliability Engineering/Improvements

Step 3.

Conduct Evaluation

Step 4.

Step 5.

Identify Problems & Root Causes

No

Go/No GoDecision on

Next Phase

YesAreGoals/Requirements Met?

Figure 2-5. The Reliability Improvement Process


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1. Establish Reliability Goals and Requirements. The first step in the reliability improve-

ment process is to establish reliability goals and requirements. A distinction is made be-

tween goals and requirements. Goals are more internally driven and may or may not be

met. Requirements, on the other hand, are more specific and are customer driven.

Requirements are usually included as deliverables in contractual agreements. Goals arethe starting point, but are modified to satisfy customer requirements early in the equip-

ment life cycle.


Step 2.


Step 3.

Conduct Evaluation

Step 4.

Step 5.


No

Go/No GoDecision on

Next Phase

YesAreGoals/Requirements Met?

All goals have certain common characteristics. The following criteria can be used to

assist in establishing goals[3]:

Attainability: Goals should be set at levels reasonably attainable within

the available time span. Large goals over long periods should be avoidedto maintain interest and commitment. Subgoals over shorter times are

more attainable and more cost effective.

Supportability: Support and resources must be available at the time theyare needed to achieve goals. Advance planning is needed to determine the

resources and the extent to which they can or will be provided.

Acceptability: Goals must be acceptable to those who will be activelyinvolved in pursuing these goals. Acceptance is influenced by relevance,

perceived importance, reasonableness, and desirability of outcome.

Measurability: Goals provide standards against which performance may

be assessed and, therefore, should be selected for suitability and defined ina way that enables measurement. To make them measurable, goals must

be defined qualitatively, quantitatively, and in terms of performance

parameters, values, and time scales.


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2. Reliability Engineering and Improvements. Once goals and requirements have been

established, design-for-reliability practices, or reliability improvement activities are

applied to enhance the reliability of equipment that is in any phase of the life cycle, or for

equipment already in existence.


Step 2.


Step 3.

Conduct Evaluation

Step 4.

Step 5.


No

Go/No GoDecision on

Next PhaseGoals/Requirements Met?

Are

There are some basic practices that can be applied to improve reliability. These include:

Simplicity. Simplification of equipment configuration is one of the basicprinciples of designing-for-reliability. Added parts or features increase the

number of failure modes. A common practice in simplification is referred

to as component integration (the use of a single component to perform

multiple functions).

Redundancy. Another reliability improvement practice is to include morethan one way to accomplish a function by having certain components or

subassemblies in parallel, rather than in series. Beyond a certain point,redundancy may be the only cost-effective way to design reliable

equipment.

Proven Components and Methods. To the extent possible, designersshould use components and methods that have been shown to work in

similar applications. Using proven components can minimize analyses

and testing to verify reliability, thus reducing time and costs of

demonstrating reliability of the equipment.

Derating. Derating is the practice of using components or materials atenvironmental conditions or loads that are less severe than their limiting

condition. Under these conditions, the component or material is expectedto be more reliable.

Eliminating Known Causes of Failure (Fault Avoidance). This can beaccomplished through screening and burn-in procedures to eliminate weak

components before equipment is actually shipped to the customer.


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Failure Detection Techniques. Reliability of equipment can be improvedby incorporating failure detection methods or self-healing devices such as

periodic maintenance schedules, monitoring procedures, automatic sensing

and switching devices.

Ergonomics or Human Factors Engineering. The activities of humans can

be very important to equipment reliability. The equipment design mustconsider human factors aspects such as the person-machine interface,

human reliability, and maintainability.

Conduct Evaluation. The next step in the reliability improvement process is to conduct

an evaluation of the equipment or equipment design to assess its reliability level. A

powerful tool for conducting this evaluation is reliability modeling. For equipment in the

early phases of the life cycle, reliability modeling can be used to predict the equipments

performance to provide information for design changes or for evaluating design alterna-

tives. For equipment that is already in production or is operational in the field, reliability

modeling, combined with testing and failure data analysis, can be used to identify critical

components and help guide resource allocation and reliability improvement decisions.


Step 2.


Step 3.

Conduct Evaluation

Step 4.

Step 5.


No

Go/No GoDecision on

Next Phase

Are

Goals/Requirements Met?

There are a number of reliability prediction models. These include:

Block diagram models. A block diagram is used to logically represent theequipment being modeled by breaking it down into subsystems and

components. Equipment reliability is modeled using failure data on the

subsystems and components.

State transition (Markov) models. Equipment reliability is modeled byidentifying the various operating conditions (states) that the equipment,

subsystem, or component can experience, and the probability of transition

from one state to another.

Other techniques for evaluating equipment reliability and identifying design weaknesses

include:


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Fault tree analysis (FTA). A "top down" approach beginning with anundesirable event (usually equipment failure) at the top or system level

and identifying the events at subsequent lower levels that can cause the

undesirable top event.

Failure modes and effects analysis (FMEA). A technique for

systematically identifying, analyzing, and documenting the possible failuremodes within a design and the effects of such failures on equipment

performance.

Testing is another tool for evaluating equipment reliability. Typically, three different

categories of testing are applied:

1. Component tests - useful in flushing out basic weaknesses in critical

components

2. Systems tests - intended to explore effects of component interactions

3. Reliability demonstration tests - used to demonstrate equipment capability

The above concepts are discussed in more depth in Section 2.0 and 3.0.


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4. Are Goals and Requirements Met? Results of the evaluation process are compared to

reliability goals and requirements. If goals and requirements are not met, the problems

and root causes should be identified as described in Step 5, and reliability improvement

activities should be initiated. If goals and requirements are met or exceeded, then approv-

al can be given to move to the next phase of the life cycle, or goals and requirements canbe updated and additional analyses carried out. For example, if the equipment is in the

concept and feasibility or design phase of the life cycle, sensitivity analyses can be

conducted to evaluate design and cost trade-offs such as:

Design complexity versus reliability

Maintainability versus reliability

Increased costs versus reliability

Esbablish Goals/Requirements

Step 2.


Step 3.

Conduct Evaluation

Step 5.


No

Go/No Go

Decision on

Next Phase

Step 4.

Are


If goals are, or can be exceeded by a significant margin, then the supplier should

capitalize on the situation by turning it into a competitive leadership position.

Upon completing design trade-off studies, approval can be given to move to the next

phase of the equipment life cycle where the reliability improvement process is again

initiated.

5. Identify Problems and Root Causes. If reliability goals and requirements are not met,

the reasons need to be identified and corrective actions should be taken. Test data on

prototypes or actual equipment in the field can be used to supplement information on

equipment reliability generated from predictive modeling. Testing can also help to

identify causes of failure and any potential reliability problems.


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2.6 Applying the Reliability Improvement Process

Optimal benefits from use of the reliability improvement process are clearly realized when the

process is applied to equipment in the concept and feasibility phase of the life cycle and then

continuously applied thereafter. Benefits can also be realized when the improvement process isapplied to equipment that is in some advanced phase of its life cycle. It is important to address

equipment reliability throughout the life cycle. For example, reliability improvements may be

necessary:

Following the Prototype Phase, because of design deficiencies or parts problemsuncovered during prototype testing

Beginning the Pilot Production Phase, due to reliability related issues resultingfrom manufacturing a new equipment line

During the Production and Operation Phase, because feedback from fieldpersonnel and customers indicate reliability problems due to unanticipated failure

mechanisms.

Activities

Activities associated with applying the reliability improvement process to the equipment life

cycle remains basically the same from one phase of the life cycle to the next. Others, however,

vary because of the change in focus from phase to phase. For example, focus in the concept and

feasibility macro phase is primarily on "planning and allocating;" focus in the design and

development macro phase is primarily on "predicting and verifying;" and focus in the production

and operation macro phase is primarily on "evaluating and improving."

The activities also vary depending on whether the improvement process has been continuously

applied to equipment as it moved through its life cycle from concept and feasibility to phase out,or whether it is being applied for the first time to equipment that is in some advanced phase. For

example, consider equipment in the prototype phase: If the reliability improvement process has

been applied continuously to the equipment in the concept and feasibility phase and in the design

phase, then the reliability goals and requirements already exist. Thus, the reliability goals and

requirements activity consists, primarily, of updating the goals and requirements; the primary

focus would be on prototype testing and corrective action activities. However, if the reliability

improvement process was applied to equipment for the first time during the prototype phase, then

developing reliability goals and requirements should be a major focus because these goals and

requirements do not exist. These concepts are discussed in more detail in Section 2.0.

Figure 1.6 provides a high-level view of the main activities associated with applying the

reliability improvement process to each of the three macro phases of the life cycle. This is

provided primarily to illustrate the flow from one macro phase to the next. A more detailed

discussion of applying the reliability improvement process to all six phases of the life cycle, and

a list of the associated activities, is presented in Section 2.0. Some of the activities will vary as

the reliability improvement process is tailored to a particular need or equipment line. However,

the reliability improvement process remains unchanged.


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Step 2.Reliability Engineering/Improvements

Step 3.

Conduct Evaluation

Step 4.

Step 5.


No

Go/No GoDecision onNext Phase


Are


Concept/Feasibility

-Set Reliability Goals

-Create Reliability Program Plan

-Develop Conceptual Designs

-Develop Preliminary Model

-Evaluate Conceptual Designs

-Next Phase Go/No Go Approval

-Identify Problems and Root

Causes

-Develop Corrective Actions


Step 3.

Conduct Evaluation

Step 4.

Step 5.


No



Are


Concept/Feasibility

-Translate Goals into Requirements

-Apply Design-For-Reliability Practices

-Carry out Design Reviews

-Upgrade Reliability Model

-Predict Equipment Performance

-Next Phase Go/No Go Approval

-Identify Problems and Root Causes



Step 3.

Conduct Evaluation

Step 4.

Step 5.


No



Are


Concept/Feasibility

-Revise Goals/Requirements

-Implement Field Tracking System

-Begin Customer Feedback Program

-Start Corrective Action Program

-Upgrade Reliability Model

-Identify Problems and Root Causes


-Begin Phase Out Activities

Figure 2-6. Application of Reliability Improvement Process


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2.7 Summary

Knowledge of the equipment life cycle is important because it provides a basis for understanding

how and where reliability engineering enters into the process of designing, producing, andoperating the equipment. The equipment life cycle is broken into distinct phases, each

representing a unique portion of the equipment life. These phases provide the framework for

tracking reliability throughout the life cycle of the equipment and guidance on when and where to

apply resources. Awareness of life cycle costs help equipment owners understand the impact on

expenditures and cost of ownership when reliability is initiated at different life cycle phases.

The reliability improvement process provides a means for systematically improving reliability

throughout the equipment life cycle. Optimal benefits are realized when reliability is designed

into a piece of equipment. However, it is important to improve reliability throughout the life of

the equipment to meet reliability goals and objectives.

The reliability improvement process is an iterative process of setting goals, then evaluating(predicting), comparing, and improving those goals. Central to the reliability improvement

process is data collection and analysis; design improvements; and operations and maintenance

procedure improvements.

About Section 3.0

The next section provides details on preparing for and implementing the reliability improvement

process. It includes a discussion of the various activities associated with each step of the

improvement process and each phase of the life cycle. In preparation for this discussion, the

following questions may assist in assessing current reliability practices and focus.

1. Is the importance of reliability conveyed throughout the company?

2. Is the approach to reliability improvement reactive or proactive?

3. Is the equipment development process life cycle oriented?

4. Have specific goals and requirements been established for equipment

reliability and its growth?

5. Does the organization have technical and executive managers who

champion the reliability cause?

6. Is demonstrated achievement of reliability goals a part of the criteria for

deciding when equipment is ready for release to market?

7. Does the organization collect data that can readily be used in measuring and

providing guidance for equipment reliability performance?

8. Do indicators of reliability performance exist for all equipment?

9. Are these indicators routinely monitored to ensure achievement of

improvement goals?

10. Is a closedloop failure reporting and corrective action system in place?


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2.8 References

1. SI Staff, "Selecting a Product: The Task at Hand," Semiconductor International,

March 1991, pages 7-8.

2. J. E. Arsenault and J. A. Roberts,Reliability and Maintainability of Electronic

Systems, Potomac, MD:Computer Science Press, 1980.3. W. Grant Ireson and Clyde F. Coombs, Jr.,Handbook of Reliability Engineering

and Management, Editors in Chief, McGraw-Hill, 1988.


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3 IMPLEMENTATION OF THE RELIABILITY IMPROVEMENT PROCESS

3.1 Introduction

To ensure that maximum benefits are achieved when implementing the reliability improvement

process, it is important to have an understanding of:

Managements role in the implementation process

The activities associated with applying the process

Functional responsibilities in the implementation process

Where to start the process

How to use limited resources and communicate the value of the process

Each of these topics is discussed in this section. Primary focus is given to applying the

reliability improvement process. Activities associated with applying the reliability improvementprocess to equipment in the concept and feasibility phase and continuing throughout its life cycle

are discussed first. Later, the discussion focuses on activities associated with applying the

reliability improvement process to equipment in an advanced phase (other than concept and

feasibility) of the life cycle.

3.2 Managements Role

Management plays a vital role in implementing the reliability improvement process. It has the

responsibility for establishing the right environment, and in choosing individuals to champion the

effort. The champions provide leadership and are accountable for the success of the reliability

improvement process.Managements Responsibility

One of managements primary responsibilities is to convey the importance of reliability

throughout the company. Institutionalizing the reliability improvement process may require a

cultural change and even an organizational change. Therefore, management leadership and

commitment to this change is essential to ensure success. Success also depends on managements

understanding of the activities involved in the reliability improvement process and on their

support of these activities.

Reliability Champions

Selection of reliability champions is critical to the success of the reliability improvement process.

Two reliability champions are recommended for moderate-to-large sized companies: an

executive champion and a technical champion. In a small company, these two roles may be

combined for one person.

Executive Champion. The role of the executive champion is to:

Provide executive leadership in reliability improvement matters

Promote reliability improvement throughout the company

Provide assurance that the reliability improvement process is supported


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Table 3-1. Reliability Improvement Process Applied at Six Different Starting Points

Starting Points/Life Cycle Phase in Which

The Process Applied For The First Time

Reference Sections

Concept and Feasibility Section 3.3.1

Design Section 3.4.1

Prototype Section 3.4.2

Pilot Production Section 3.4.3

Production/Operation Section 3.4.4

Phase Out Section 3.4.5


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Starting with Equipment in the Concept and Feasibility Phase

The following paragraphs discuss the activities that are performed when the reliability

improvement process is first applied to equipment in the concept and feasibility phase and then

continuously applied in subsequent phases. The discussion for each life cycle phase concludes

with a list of objectives that will have been met as a result of applying the reliability

improvement process, and a table summarizing the activities associated with applying the processto that phase of the life cycle.

Concept and Feasibility

Step 1. Establish Goals and Requirements. In the concept and feasibility phase, the focus of

Step 1 is on establishing goals to meet customer requirements. Later these goals may be revised,

and are eventually modified to reflect changes in customer requirements, or in response to

observations regarding equipment performance level.

Concept/Feasibility

Design

Prototype (a-site)

Pilot Production (b-site)


Phase Out

Goals can be established based on:

Customer Voice

. When establishing reliability goals, it is important to considerwho the customers are and what aspects of reliability they regard as most

important. The supplier must fully understand customers needs, and be able to

translate these needs into equipment-specific information for setting goals.

Competitive Benchmarking. Competitive benchmarking is a process used bysuppliers to measure and compare their products, services, and operations against

competitors and world class performers.

Reverse Engineering. The systematic dismantling of equipment with a highreliability ranking is referred to as reverse engineering. The information obtained

provides information about the actual reliability of similar equipment and the

technology used to achieve that reliability.

Warranty Requirements. To remain competitive, the reliability goals mustsupportthe established warranty requirements.

Equipment Maintenance. It is essential to discuss maintenance aspects of theequipment with field personnel when establishing reliability goals. Improperly

addressing maintenance issues can lead to a design with very high user-perceived

reliability, but prohibitive maintenance costs.


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Once goals have been established, a reliability program plan is created that documents how these

goals will be achieved. It defines:

Activities to be performed

Resources required to fulfill the activities

Schedule for these activities Procedures by which the activities will be performed

Organizations and interfaces required to perform the activities

The program plan provides management and the customer with a means of measuring progress

and assuring that requirements will be accomplished.

Step 2. Reliability Engineering and Improvements. In the concept and feasibility phase, Step

2 of the reliability improvement process focuses first on developing alternative design concepts.

All possible alternatives should be identified and evaluated to ensure that those selected for the

design phase are capable of fulfilling goals and requirements. Functional block diagrams are

used to develop the basic concepts for the equipment and to evaluate their feasibility. The

functional block diagram is updated as the concept changes.

The next step is to develop a preliminary model of the equipmentusing the functional block

diagrams. The initial model is created at a gross level; that is, the equipment is broken into a few

(approximately 10 to 20) major subsystems. This model is used to make initial predictions of the

equipment reliability (Step 3).

A reliability allocation is conducted to allocate the equipment reliability goal into the individual

major subsystems. This is done to make equipment reliability requirements more manageable and

to establish individual reliability requirements for each major subsystem. Since no detailed

information on the equipment is yet available, the allocation process is approximate; it is used to

guide the designer when developing various concepts.

In this phase, the equipment has not been built, so other sources of data are required.Historical

data can be used for those subsystems that are similar to previous generations of equipment. For

those subsystems for which no historical data is available, expert judgementcan be used. Expert

judgement takes the opinion of individuals that are considered to be knowledgeable about a

subsystem or component and uses this knowledge to create initial reliability values.

Another reliability engineering activity available for identifying conceptual design weaknesses is

afailure modes and effects analysis (FMEA). This is a technique for systematically identifying,

analyzing and documenting the possible failure modes within a design and the effects of such

failures on equipment performance.

The process of setting up an FMEA is initiated in this step, but it is used later in Step 5 to helpidentify problems and root causes.


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Step 3. Conduct Evaluation. The subsystem failure data and the reliability prediction model

are used to evaluate the reliability of the conceptual design. A reality check assures that the

predicted reliability value makes sense. Evaluate the following:

Predicted versus the anticipated reliability value

Historical and expert opinion data used to calculate equipment reliability

Reliability prediction model

Conceptual design review(s) of the concepts that will be carried to the design phase are

conducted at this point. These design reviews are also useful in evaluating the current level of

the predicted reliability of the concepts being considered.

Step 4. Are Goals and Requirements Met? A comparison is made between established goals

and the predicted reliability values. If the goals are not met, continue to Step 5 where problems

and root causes are identified. If the goals are met or exceeded, approval is eventually given to

move to the design phase of the life cycle, where goals may be modified to meet customer

requirements.

Step 5. Identify Problems and Root Causes. If goals are not met, problems and root causesshould be identified. Sensitivity analyses can be conducted to direct attention to those

subsystems that have the greatest impact on the equipment reliability.

If an FMEA was developed in Step 2, use it to examine the potential failure modes identified and

to establish possible root causes.

The reliability improvement process now returns to Step 2 (reliability improvement and growth

activities are initiated). These might include:

Adding high-level redundancy

Using proven high reliability components and parts

Forming partnerships with sub-tier suppliers Derating

Once the conceptual design improvements have been selected and incorporated, both the

functional block diagram and the reliability prediction model are re-evaluated. The model and the

data used in the model are changed to reflect the conceptual design improvements. If an FMEA

was initiated, it is also updated to reflect design changes.

Steps 2 through 5 are repeated until goals are met and approval is given to move to the design

phase of the life cycle.

At the end of concept and feasibility phase, the following objectives have been met:

Reliability goals have been established and allocated to major subsystems A reliability program plan has been initiated

Conceptual designs that form the basis of the equipment design are determined

Feasibility that selected conceptual designs will meet goals is demonstrated

Table 3-2 summarizes the activities associated with applying the reliability improvement process

to the concept and feasibility phase. There are three designators used for the activities:


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E(engineering), D(data), T(testing). These designators followed by a number provides the

location of the activity in Section 3.0.

Table 3-2. Reliability Improvement Process Activities

Reliability

Improvement

Process Step

Activities

1. Establish Goals and

Requirements

- Establish reliability goals (E1)

- Create reliability program plan (E2)

2. Reliability

Engineering and

Improvements

- Develop functional block diagrams (E3)

- Create preliminary reliability model (E4)

- Allocate reliability goals (E5)

- Collect historical failure data (D1)- Develop preliminary FMEA (E14)

- Develop preliminary Life Cycle Cost (AT19)

3. Conduct Evaluation - Preliminary prediction of equipment reliability (E6)

- Conceptual design review(s) (E7)

4. Are Goals and

Requirements Met?

- Compare goals to predicted reliability values

- If goals are not met, continue to Step 5

- If goals are met move to design phase of life cycle

5. Identify Problems

and Root Causes

- Perform sensitivity analyses using reliability model (E8)

Design

Step 1. Establish Goals and RequirementsGoals and Requirements. The reliability goals

established in the concept and feasibility phase of the life cycle are modified and become

reliability requirements in the design phase. Requirements need to be well-defined so that they

are understandable by design engineers and manufacturers. Requirements should be broad in

nature and be both qualitative (e.g., definition of responsibilities and program requirements) and

quantitative (e.g., mean time between failures and uptime).

Concept/Feasibility Design

Prototype (-site)



Phase Out


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System level requirements are allocated to major subsystems and components.

Once reliability requirements have been established, the reliability program plan is updated to

reflect these requirements.

Step 2. Reliability Engineering and ImprovementsEngineering and Improvements.Design-for-reliability practices are applied at this step in the improvement process. Application

of design-for-reliability practices creates a proactive environment for the design team. Some of

the more basic practices include:

Simplicity. Simplification of equipment configuration is one of the basicprinciples of designing-for-reliability. Added parts or features increase the

number of failure modes. A common practice in simplification is referred to as

component integration, which is the use of a single component to perform

multiple functions.

Proven Components. To the extent possible, designers should use components

that have been shown to work in similar applications. Using proven componentscan minimize analyses and testing to demonstrate reliability of equipment.

Derating. Derating is the practice of using components or materials at environ-mental conditions or loads that are less severe than their limiting condition.

Under these conditions, the component or material is expected to be more reliable.

Redundancy. Another reliability improvement practice is to include more thanone method for accomplishing a function by having certain components or

subassemblies in parallel, rather than in series. Beyond a certain point,

redundancy may be the only cost-effective way to design reliable equipment.

Failure Detection. Reliability of equipment can be improved by incorporating

failure detection methods such as automatic sensing and switching devices. Ergonomics or Human Factors Engineering. The equipment design must

consider human factors aspects such as the person-machine interface, human

reliability, and maintainability.

The functional block diagram is updated as the design develops. The gross reliability model,

which consists of major subsystems, is expanded. Each subsystem is broken into more detail.

For example, a wafer handler subsystem could be categorized into software, electronics, arm, and

casing components. The reliability allocated to a subsystem is further allocated to the component

level. As was the case in the concept and feasibility phase, this allocation is based on limited

information available during the early phases of the life cycle; it is used as a guide when

developing the various designs. As the design progresses, the allocation becomes finalized.If an FMEA was not developed in the concept and feasibility phase of the life cycle, initiate it in

this phase.

As was the case in the concept and feasibility phase, equipment in the design phase has not yet

been built, so actual component failure data may not be available. Here again, historical data can

be used for those components that are similar to previous generations of equipment. Use

standard handbooks (such as MIL-HDBK-217[1] or NPRD-91 Handbook[2]), or expert opinion

to obtain data for those components where no historical data is available.


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If a critical component is used for the first time and the life data is not available, run a simulated

life test to generate the life data under the expected use conditions.

Step 3. Conduct Evaluation. Use the subsystem and component failure data, and the updated

reliability prediction model, to evaluate the reliability of the current equipment design. As wasthe case in the concept and feasibility phase, evaluate the following:

Data sources and their validity

Predicted versus the anticipated reliability value

Historical and expert opinion data used in determining equipment reliability

Reliability prediction model

Conduct design review(s) of the design(s) that will be carried to the prototype phase at this time.

These reviews are often broken down into:

Requirements Review - review the equipments design requirements

Preliminary Design Review - evaluate the preliminary design against requirements Critical Design Review - provide design to the customer(s) for review

Step 4. Are Goals and Requirements Met? Compare the reliability requirements and the

predicted reliability values. If requirements are not met, continue to Step 5 where problems and

root causes are identified. If requirements are met, approval is given to move to the prototype

phase of the life cycle.

Step 5. Identify Problems and Root Causes. If requirements are not met, sensitivity analyses

can be conducted to direct attention to those subsystems and components that have the greatest

impact on the equipment reliability. Evaluate the FMEA that was developed in Step 2 todetermine potential failure modes of the subsystems and components.

The process now returns to Step 2, where reliability improvement activities are initiated.

Steps 2 through 5 are repeated until requirements are met. Approval can then be given

to move to the prototype phase of the life cycle.

At the end of the design phase, the following objectives have been met:

The core architecture of the equipment design has been finalized

Design(s) have been chosen for prototype


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The actual failure modes that are uncovered during testing, should be recorded in the FRACAS,

and compared to the predicted failure modes established in the FMEA. Where difference occur,

the reasons should be identified.

Step 3. Conduct EvaluationEvaluation. Reliability of the various prototypes is evaluated

based on the test data.

Results of the prototype test are then presented for a design review prior to pilot production.

Step 4. Are Goals and Requirements Met?Goals and Requirements Met? Compare the

results of the testing of the prototype(s) to the requirements to see if they have been met. If the

requirements are not met, move to Step 5, where problems and root causes are identified. If

requirements are met, then a design review is performed, including a management go/no go

decision to continue to the pilot production phase of the life cycle.

Step 5. Identify Problems and Root CausesProblems and Root Causes. A sensitivity

analysis is conducted to direct attention to those subsystems and components that have the

greatest impact on the equipment reliability. Root causes of the failures recorded in the

FRACAS are identified and corrective actions implemented. A more detailed failure analysismight also be performed on those subsystems and components that are failing at a significantly

higher rate than previously anticipated.

The process now returns to Step 2, where improvement activities are initiated. If a FRACAS was

initiated, it might identify corrective actions that could be implemented to eliminate failures.

Other possibilities include:

Derating

Procedural changes

Process changes

Apreventive maintenance (PM) program can be developed for subsystems and components thatdegrade equipment performance. Partnerships established with suppliers are continually

nurtured and purchased subsystems and components are continually evaluated. Human

capabilities and limitations are considered and changes are made to the equipment to eliminate

failures due to human errors. The software reliability program is continued. For critical

subsystems and components, the optimal operating range is found and the impact of the optimal

range on other components is evaluated.

Steps 2 through 5 are repeated until requirements are met. Approval can then be given to move

to the pilot production phase of the life cycle.

At the end of the prototype phase, the following objectives have been met:

The prototype(s) has been tested and evaluated to determine its capability ofachieving the requirements. This includes redesigning and re-evaluating until a

go/no go decision is reached

The core subsystem and component designs are finalized.

Table 3-4 summarizes the activities associated with applying the reliability improvement process

to the prototype phase.


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Table 3-4. Reliability Improvement Process Activities for the Prototype Phase

Reliability Improve-

ment Process Step Activities

1. Establish Goals

and Requirements

- Update reliability requirements (E1)

- Update reliability program plan (E2)

2. Reliability

Engineering and

Improvements

- Update functional block diagram (E3)

- Expand reliability model, as needed (E4)

- Re-allocate subsystem and component reliability requirements (E5)

- Establish test plan (T1)

- Conduct Prototype test (T2)

- Establish FRACAS (E17)

- Perform human reliability analysis (D2)

- Develop preventive maintenance program (E10)

- Continue to evaluate the reliability of purchased components (E11)

- Perform ergonomics studies (E12)

- Conduct software reliability studies (E13)

- Update Life Cycle Cost (AT19)

3. Conduct

Evaluation

- Evaluate prototype reliability (T2)

- Conduct design review(s) (E7)

4. Are Goals and

Requirements Met?

- Compare reliability requirements to predicted values

- If requirements are not met, continue to Step 5

- If requirements are met move to pilot production phase of life cycle

5. Identify Problems

and Root Causes

- Perform sensitivity analyses (E8)

- Evaluate FRACAS to identify problems and root causes (E17)- Evaluate FMEA to identify potential failure modes (E14)

- Perform failure analyses on critical components (E16)

Pilot ProductionProduction

Step 1. Establish Goals and RequirementsGoals and Requirements. During the pilot

production phase, upgrades are made to goals and requirements, as appropriate, and the reliability

program plan is updated to reflect these, as well as other, changes. Modeling and failure data

analyses are used to assess current and potential levels of equipment performance.

Concept/FeasibilityDesign

Prototype (-site)



Phase Out


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Step 2. Reliability Engineering and ImprovementsEngineering and Improvements.

Functional block diagrams and the reliability model are once again updated to reflect any changes

that occurred during the prototype phase. If a FRACAS was not implemented during the

prototype phase, then it should be done at this time.

The test program is evaluated and updated as needed. Any aspects of the test program that are

not clearly defined during the prototype phase should be established here. Additional tests that

should be implemented at this time are:

Burn-in tests

Reliability qualification tests (RQT)

Burn-in tests are useful in identifying weak components or subsystems prior to field use.

An RQT is useful in initial customer applications of the equipment to evaluate equipment

performance in actual operating environments. The RQT is also useful in verifying compliance

with contractual objectives; whereby, equipment is tested according to a predetermined plan

under specified environmental conditions and pass/fail criteria prior to a full-scale productiondecision[3]. Testing equipment in an environment that represents usage throughout its service

life allows for establishing reasonable correlations between test results and actual field

experience.

The manufacturing processes should be qualified at this time to avoid the manufacturing

problems identified during the pilot production. Qualifying manufacturing processes before

full-scale production reduces manufacturing costs and prevents equipment performance

degradation[4]. Qualifying manufacturing processes includes:

Performing a process capability study

Establishing process control

Monitoring the defect level Reducing the defect level

Periodically assessing and controlling the processes[5]

Both new and existing manufacturing processes should be requalified periodically to ensure

requirements are maintained. Personnel involved in the manufacturing process should be

properly trained before introduction of the equipment.

Step 3. Conduct EvaluationEvaluation. The pilot production phase of the life cycle is

generally the first time equipment is evaluated in a customer environment. Thus, reliability

modeling and prototype testing, engineers should work closely with customer service and field

service personnel to evaluate initial customer applications of the equipment to evaluate its

performance in actual operating environments. A reliability qualification test (RQT) isperformed to verify compliance with contractual objectives.

Problems and failures occurring during testing should be carefully analyzed, and

recommendations for corrective action should be issued as part of the FRACAS. Failure modes

identified in the FMEA are compared to reported failures during testing. Differences that occur

should be analyzed.

Definitions of failures should be issued, and pass-fail criteria should be established. Failures

generally fall into four categories[5]:


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Table 3-5. Reliability Improvement Process Activities for the Pilot Production Phase

Reliability

Improvement

Process StepActivities

1. Establish Goals

and Requirements

- Update reliability requirements, as needed (E1)

- Update reliability program plan (E2)

2. Reliability

Engineering and

Improvements

- Update functional block diagram, if needed (E3)

- Update reliability model, if needed (E4)

- Re-allocate reliability requirements, as needed (E5)

- Upgrade testing program, as needed (T1)

- Implement FRACAS, if not already done (E17)

- Perform human reliability analyses (D2)

- Perform software reliability studies (E13)

- Perform ergonomic studies (E12)

- Update preventive maintenance program, as needed (E10)- Continue to evaluate reliability of purchased components (E11)

- Update Life Cycle Cost (AT19

Reliability Guidelines

Documents

Transcript of Reliability Guidelines