Environmental Stress Screening and its effectiveness during the

production process.By: Kees Winkel

Managing Director

Weiss Technik Nederland B.V.

Weiss Technik enables a more sustainable future, with it’s Vision:

We are the world leading supplier of Environmental Simulation Equipment, Industrial Ovens, Cleanroom- and Containment Solutions.

Reliability testing

Reliability Challenges

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SiC (Silicon Carbide)GaN (Gallium Nitrate)

Uncertainty of reliability performance of new materials (e.g. SiC and GaN devices) and processes

Harsh environments with high availability:Off shore wind turbinesPhotovoltaic SystemsBuilding automation

Demand for prolonged warranty(Solar panel 20 Years)

Increased complexity of electronic systems,e.g. number of components

Safety critical applications:Electronic car assist / Aircraft automationRailway systems / Medical electronicsData centers etc

Higher design density/level of integration which may invoke new failure mechanisms

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Reliability Challenges

Resource constraintse.g.time/cost for reliability testing

Product development cost

Limited robustness validation due to time-to-market pressure / competitive situation

Accelerated Testing

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Due to economical pressure the trend is to reduce test times while maintaining test result significance(!) by either:

Extended stress parameter

Acceleration based on Physics, Mathematics and Statisticse.g. exposing a product through 1000 cycles to simulate 15 years use conditions

Objective: faster failure analysis

Analysis and test to ensure that the product is free of failure that might be activated during the expected life time of the product

Estimation of expected failures for a defined operating condition in correlation to operating hours

Accelerated Testing

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The objective of accelerated testing is to determine the lifetime of products/components and verify the lifetime reliability within a shortened testing time.

The success of accelerated tests depends on a good understanding of potential failure mechanisms and the operational environmental stresses that a product/system is exposed to.

Failure mechanisms can be identified using the FMEA method.

Actions + Check

Failure Mode &Effect Analysis

Step1: Detect a failure mode

Step2: Severity classification

Step3: Probability classification

Step4: Detection Number

Risk priority number

Corrective measures to improve product.

PPM Level Failure Rate

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To meet customers expectation of ppm level failure rate it is essential to understand the failure mechanisms by drawing the right conclusions!

Analyzing and understanding the nature of why and how products fail

Implement a design for reliability (DFR) and a robustness validation during development & production process

Cooling jacket

Li-Ion Cells

Battery management

Cooling Liquid connector

Power Pick-Up

Cell Voltage Regulator

Intelligent control and condition monitoring to ensure reliable field operation

Acceleration based on Physics, Mathematics and Statistics

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There are a number of acceleration models that are based on physics and statistics:

Arrhenius equation is a formula for thetemperature dependence of reaction rates:

Many common chemical reaction rates (at room temperature) double for every 10 degree Celsius increase in temperature.

Arrhenius

Failu

re /

h

This model can be used for applications where a constant thermal load causes accumulative damage in products.

It is used for lifetime evaluation and survivability prediction MTBF.

Svante Arrhenius, Swedish scientist1859 - 1927

Corrosion is accelerated at higher temperatures

If we increase the temperature, chemical reactions go faster

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Acceleration based on Physics, Mathematics and Statistics

Coffin Manson

Coffin Manson determines the acceleration factor resulting from temperature cycle test as a ratio of the product life at normal operating conditions to the life at accelerated test conditions:

AF = (ΔT test / ΔT use) m

AF = Acceleration FactorΔT test = Test temperature difference (°C)ΔT use = Use temperature difference (°C)m = Fatigue or Coffin-Manson exponent

As an example, assume a product that undergoes 5 daily temperature transitions from +20 °C to +60 °C (ΔT use = 40 °C) while it is normally being used.

AF = (120 / 40) 3 = 27

The following acceleration if the product is temperature cycle tested at a high temperature of +100 °C and a low temperature of -20 °C(ΔT test = 120 °C):

assuming a typical Coffin-Manson exponent of 3

Testing this product for 1000 temperature cycles using the accelerated conditions would therefore be equal to 15 years of life based on the stated use conditions.

Test time: 675 cyclesAcceleration factor 27Simulated cycles = 18225 cycles

18225 cycles

Simulated life time = =10 years5 cycles/day * 365 days/year

The product life and failures

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Time

Failu

re r

ate

Early product life Life time Wear out phase

Constant random failure rate

„Infant mortality“; early failure

Wear out failures

Observed failure rate

The Riemen Model

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Customer Specification

Design Specification

The robustness margin is necessary as stress loads in products cause accumulating damage!

Product Development Cycle

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FMECAFailure mode, effects and criticality analysis is an extension of failure mode and effects analysis. FMEA is a bottom-up, inductive analytical method which may be performed at either the functional or piece-part level. FMECA extends FMEA by including a criticality analysis, which is used to chart the probability of failure modes against the severity of their consequences. The result highlights failure modes with relatively high probability and severity of consequences.

Accelerated tests can be divided into 3 types:

Type A : accelerated tests to identify failure mechanisms

Type B: accelerated tests to identify failure distribution and rate of occurrence (for designated use conditions)

Type C: time compressed tests to predict failure distribution and rate of occurrence (for designated use conditions)

Verify product design/ identify production weaknesses

Induce accumulative damage to determine product reliability and robustness at end of life

Evaluate life time of components that are mainly subject to wearout(e.g switches, relays etc)

Type Design Draft

Integration Validation Confirmation of design

Manufacturing Maintenance

A (qualitative)

FMECA HALT HALT/ESS HALT/ESS HASS/ESS

B & C (quantitative)

Develop Product readiness Confirm Product readiness

Evaluation of Product readiness

robustness

Tools for accelerated testing

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Highly Accelerated Limit Test HALT

Objective: Determine the maximal stress limits and identification of failure mechanism

Highly Accelerated Stress Screening HASS / ESS

Objective: Identify potential weak spots inproduct or design

Production Quality Verification

Change Management (Manufacturing process / components)

Tools for accelerated testing

Effectiveness of temperature ramp tests

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Improvement in Product Reliability

This optimization should be continued until technical/commercial limits are reached

The “weakest” component fails and can be replaced with a more resilient part

Accumulative Damage

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Accelerated tests are based on the principle that stress loads in products cause accumulating damage during the life time of a product (whether that leads to a failure or not).

Accumulated damage simulates the expected life time stress load to determine the (remaining) robustness margin

The robustness margin determines the product reliability!

Soldering Faults / Cracks

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Thermal stress causes failure due todifferences in thermal expansioncoefficients between materials

Stress on printedwiring assembly

e.g. solder point strength / metallic interface strength

Stress on Wire Bonding

And what about humidity?

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A humidity test often follows a temperature cycle test, e.g. accelerated testing at 85°C / 85%r.H.

This test generates chemical failures and is applied to a combination of devices and materials that constitutes units and parts.

The combination of those different materials, or even a combination of chemicals that are used in manufacturing processes induce chemical reactions, which both temperature and humidity may accelerate.

End of line ESS testing

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The product stress must not exceed its design limit and must not reduce the products life time!

e.g. expose the same product to 10 test cycles

Advantage: • Fast feedback on product quality, correction measures, new components or manufacturing processes

• Induced failure that would not occur during “normal” operationDisadvantage:

• No feedback on product reliability

• Limited stress factors (temperature, humidity, vibration)

Detectable Defects

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•Reduced Field Repair Expenses•Fewer Defects and Waste•Early Flaw Detection•Improved Productivity•Lower Unit Cost•Increased Product Value•Improved Customer Satisfaction•Better Return on Investment• …..

And the benefits are:

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ESS Tests beyond product reliability and robustness

Defects that do not necessarily expose themselves and they can skip by all the manufacturing tests

However, with electrical and thermal stresses during use, they will eventually degrade to cause a significant functionality problem and will result as a failed system in the field

► Detect latent defects – convert them into detectable failures

Infant Mortality

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► Infant mortality

From a customer satisfaction viewpoint, infant mortalities are unacceptable. They cause "dead-on-arrival" products and undermine customer confidence.

Cost to correct a fault

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The costs to correct a fault increases typically with approximately one order of magnitude for every step in the integration process, which is from component to circuit board to apparatus to system.

Receiving Check

Circuit Board

Sub System

System Integration

Operational Use

Time to correction/detectionC

ost

Lessons learned?

Vragen?

• Bedrijfsnaam: Weiss Technik Nederland B.V.

• Adres: Newtonstraat 5, Tiel

• Telefoonnummer:

• 0344-6704400

• 06-11333413

• E-mailadres: kees.winkel@weiss-technik.com

• Standnummer: 7D121

Executive Summary

Reliability of electronics components and systems has become more and more important in a world where product life cycles are getting shorter, compliance to legislation is a must, user requirements are getting stricter and social media can make or break your product. Thorough analysis and testing from individual components to complete systems from the initial conception till the end of line product & system testing is todays norm and standard. In our presentation we will try to demonstrate which kind of tests and tools are available to execute just this and reach our common goal of this happy customer sharing his new purchase on social media.

References

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DIN EN 62506 Methods for product accelerated testing

IEC 60068 Environmental TestingIEC 60605-2 Equipment reliability testing – Part 2: Design of test cyclesIEC 60721 Classification of environmental conditionsIEC 60812 FEMA ProcedureIEC 61014:2003 Program’s for reliability growthIEC 61164:2004 Reliability growth – Statistical test and estimation methodsIEC 61124:2012 Reliability testing – Compliance tests for constant failure rate and constant failure intensityIEC 61163-2 Reliability stress screening – Part 2: Electronic componentsIEC 61649:2008 Weibull analysisIEC 61709 Electronic components – Reliability – Conditions for failure rates and stress modelsIEC/TR 62380 Reliability data handbook – Universal model for reliability prediction of electronicsIEC 62429 Reliability growth – Stress testing for early failures in unique complex systems