Need For Failure Analysis Techniques

M.S.Ramaiah School of Advanced Studies 1

Vinay Divakar CWB0912001, FT2012

M. Sc. (Engg.) in Electronic System Design

Module Leader : Mr. Ugra Mohan Roy

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Power Point Presentation

NEED FOR FAILURE ANALYSIS

TECHNIQUES

M.S.Ramaiah School of Advanced Studies

Overview

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Below are the topics to be discussed, they are as follows:

Introduction

Importance of Failure Analysis

Classification of Tests to Capture Failures

Failure Rate (Bath Tub) Curve

Estimating life of a system or Product

Calculating the Failure Rate and Product Life (MTTF)

Summary

References


Introduction

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Failure Analysis (FA) is a process of collecting and analyzing data to

determine the cause of failure. E.g. Failed components are taken for analysis

and determine cause of the failure using a wide array of methods and

techniques.

Failure analysis engineers often play the lead role in this department

Types of failures can be due to component, manufacturing or during

production processing

Failure analysis (FA) capability supports the development of semiconductor

technology and packaging. Failure analysts need new techniques and

advanced equipment to match the rate of Moore's Law so that problem

solving can remain efficient and accurate.

Moore's Law is the observation made in 1965 by Gordon Moore, co-founder

of Intel, that the number of transistors per square inch on integrated circuits

has doubled every year since the integrated circuit was invented.


Importance of Failure Analysis

•Electronic parts, why they fail?

•Preserve failure mechanism, don’t

loose (Carelessness)

•Failure of Critical applications e.g.

Space satellite systems.

•Big loss due to chain reaction

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Classification of Tests to capture failures

Environmental Tests

Temperature operating conditions, corrosion etc

Mechanical Tests

Packaging, Materials, insulation resistance etc

Electrical Tests

Electrical overstress, ground bounce etc

Test Procedure, analysis and results

Documentation of the overall results, analysis and the desired modifications

(MIL-STD-883F 1996)

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Failure Analysis for Electrical Overstress (EoS)

• EOS- Thermal damage due to V or

I beyond limit specification

•Trace VI curve for i/p’s of each

part “ part characterization”

•Causes:

a. Poor grounding

b. EMI

c. Uncontrolled supply

d. latchup

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FAILURE RATE CURVE

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Estimating Life of a Product

Failure Rate (λ) : Expressed in units of FIT Failure In Time (FIT): No of failures expected in 1 billion (109) device hours

of operation Mean Time To Failure (MTTF): defines warranty period (Product life) and

Reliability i.e. MTTF=1/ λ Acceleration factor (AF): Testing at two different temperature stresses.

AF = exp [Ea/K (1/Tuse – 1/Tstress)]--------1

Ea = Thermal Activation energy K = Boltsman Constant (1.380x10-23 J/K ) or (8.63x10-5 eV/K) Tuse = Use Temperature (oC + 273) Tstress = Life test stress temperature (oC + 273)

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CONTD…

Failure rate in FIT: λ = ∑β

i=1 = [xi/(∑k

j=1TDHj * AFij)]*(M*109/∑βi=1 xi)-------- 2

λ = failure rate in FITs (Number fails in 109 device hours) β = Number of distinct possible failure mechanisms k = Number of life tests being combined xi = Number of failures for a given failure mechanism i = 1, 2,... β TDHj = Total device hours of test time for life test j, j = 1, 2,... k AFij = Acceleration factor for appropriate failure mechanism, i = 1, 2,... k M = Const associated with chi sq factor Χ = chi square factor for 2r + 2 degrees of freedom r = total number of failures (Σ xi)

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CALCULATING THE FAILURE RATE AND PRODUCT LIFE

(MTTF)

Example : Assume that 600 parts where stressed at 150°C ambient for 3000 hours with one failure at 2000 hours for a photoresist flaw (0.7eV) and one failure at 3000 hours for an oxide defect (0.3eV); the internal temperature rise (Tj) of the part is 20°C and the product was tested at 1000, 2000 and 3000 hours. We want to find the FIT rate for the process at with M=6.3 (chi factor distribution for DOF = 2r+2 for r=2) at 55°C.(William J. Vigrass 1997)

Soln : Given Ea = 0.7eV and Eb = 0.3eV Tj = 20°C Tuse = 55 + 20 + 273 = 348K Tstreee= 150 + 20 +273 = 443K r = 2 (total no of failures) M = 6.3 AF1 = exp[0.7/8.63*10-5(1/348 – 1/443)] = 148.2----3 (from eqn 1)

AF2 = exp[0.3/8.63*10-5(1/348 – 1/443)] = 8.52---4 TDH = No of units * Hours under stress

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CONTD….

TDH = 600 × 1000 + 599 × 1000 + 598 × 1000 = 1.797 × 10-6 hours Using equation 2, the failure rate (FIT) for the system tested for 3000 hours

with a no of failures r = 2 and subjected to two different temperature stresses is calculated as follows:

λ = [(1/1.797*106*148.2) + (1/1.797*106*8.52)]*(6.3*109/2) = 218 FIT’s Estimated life time of the product or system is MTTF = 1/ λ = 1/218 FIT’s = 4.59*106 Hours Note : 1 FIT = 1 failure in 109 device hours

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SUMMARY Moore’s problem

FRACAS

Classes of Testing for failure analysis

EOS and its analysis

Product Failure rate curve

Equations for estimating the FIT and MTTF of a system or product

based on some known data

Example for finding failure rate and product life

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REFERENCES 1. Walter Willing, Jonathan Fleisher & Michael Cascio (2012) ,“Electronic

Part Failure Analysis Tools and Techniques” Northrop Grumman

Corporation, USA.

2. ITEM Software, Inc (2007) ,“Reliability Prediction Basics” USA.

3. William J. Vigrass (1997), “Calculation of Semiconductor Failure

Rates” Indianapolis,19-22 October.

4. DEPARTMENT OF DEFENSE TEST METHOD STANDARD

MICROCIRCUITS (2004) ,“MIL-STD-883F” 31 December, USA.

Rajeev Solomon, Peter Sandborn, and Michael Pecht (2000), “Electronic

Part Life Cycle Concepts and Obsolescence Forecasting” University of

Maryland, College Park, December, USA.

Jim Glancey (2006), “Failure Analysis Methods What, Why and How” USA.

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By- Vinay Divakar

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Need For Failure Analysis Techniques

Education

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