Failure Analysis (FA) Introduction (III -Reliability ... · PDF fileFailure Mode Tung-Bao Lu 1...

Failure ModeFailure Mode

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Failure Analysis (FA) IntroductionFailure Analysis (FA) Introduction

((III III -- Reliability Failure Mode)Reliability Failure Mode)


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Reliability Stress

Reliability Geberal Condition Temperature Humidity Electrical Others

Precondition Baking/L3/Reflowing V V - -

Reflowing (SMT) JEDEC 240oC/3X V - - Shock

TCT -65oC/+150oc/15min V - - Shock

TST -65oC/+150oc/15min V - - Shock

PCT +121oC/100%RH/2ATM V V - -

HL-SLT +150oC V - - Time

LT-SLT -65oC V - - Time

TH Storage 85oC/85%RH V V - Time

THB 85oC/85%RH/Vcc V V V -

HAST +130oC/85%RH/Vcc V V V Accleeracted

Stress


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Typical Preconditioning Defect Mode

• Moisture distribution • Weak point

Die surface Delaimintion Die crack Package crack


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Preconditioning

�� Failure found- Precondition L3 found 1st open fail- FS/SS = 11/135 (8%)- LQFP 100L 18M SSDRAM

�� Advanced EFA- Open failed on some corner pins- Die-surface corner delamination

�� Advanced PFA1st bonding lifted by preconditioning stress

�� Root cause confirm- Modify die-attached epoxy- Modify die-pad structure

(Scanning Electrical Microscope)

(slot)


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Preconditioning

�� Failure found- Precondition L3 found 1st open fail- FS/SS > 5%- TSOPII 44L DRAM

�� Advanced EFA- Open failed on random pins- Die-surface delamination

�� Advanced PFABall-neck broken by die surface delamination

�� Root cause confirmSurface Element Non-uniform (Wafer Process)


Delamination layer

(SAT C-SCAN)

(1)

(2) (3)

(4)

(C, N, O, Si)

(C, N, O, Si) (C, N, O, Si)

(C, O, Si)


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Typical TCT/TST Defect Mode

• Stress

• Weak point (expansion/shrinkage)

Die surface delamination to cause EMC lifted, ball-neck broken

TCT TST


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(Scanning Electric Microscope)

TCT

�� Advanced PFAWedge bond broken but still connected

�� Root cause confirmMaterial changed

- Change molding compound to provide

�� Failure found- TCT 500C open fail- FS/SS=4/100- SOJ 40L 4M DRAM

�� Advanced EFA- Open can be recovered and not stable

while testing- SAT shows normal, no delamination


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(Scanning Electric Microscope)

TCT

�� Advanced PFAWedge bond broken to lift

�� Root cause confirmProcess:- Waiting time from W/S->M/D control- Enhance W/B parameterMaterial- Change molding compound- Cleaning Lead-frame before W/B

�� Failure found- TCT 1000C open fail- FS/SS=1/45- QFP 100L

�� Advanced EFA- One pin open, 2nd finger find delamination


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Failed block

Improvement:Change to long-tape LOC tape to balance force

Before improved

Modified (Long-type)

(MOSAID Memory Tester)

After improved

(Optical Microscope, 500X)

TCT

�� Failure found- TCT 1000C function fail- FS/SS=1/200- TSOPII 54L 64M SDRAM

+150oChot air

-65oCcold air

�� Advanced EFAOnly corner special block failed

�� Advanced PFAPassivation damaged under LOC tape

�� Root cause confirmLOC taped damaged (Bonding process)


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TCT

+150oChot air

-65oCcold air

�� Advanced EFATo identify substrate opened by probingsubstrate plating line and solder ball

�� Advanced PFASubstrate crack is found by DPA and SEM

�� Root cause confirmSupplier improve

chip

Substrate (BT laminate)

ball

epoxy

Open

Crack is found by SEMafter top-side DPA made

Open Cu line crack

Poor quality substrate that can’t been stressedafter temperature cycling tests, crack is found and through Cu-line to cause opened.

�� Failure found- TCT 1000C open fail- FS/SS=3/45- miniBGA 8x10 48B



TCT

�� Advanced PFALead broken near to bump

�� Root cause confirm- Inner lead dimension modify- Material/Structure limit

�� Failure found- TCT 300C open fail- FS/SS=40/200- LCD Driver IC, TCP package- Inner Lead Bonding Process (TAB)- Can pass 30C/130C- TCT condition: -65oC/+150oC/30min

�� Advanced EFA- Open located on wide side- Recovery after time aging



TCT

�� Advanced PFASolder crack on package side

�� Root cause confirmModify PCB solder ball opening

�� Failure found- TCT 1000C open fail- FS/SS=2/10 (2%)- 256M SDRAM SODIMM module- Solder ball connected- Condition: -20oC/+90oC/30min

�� Advanced EFA- Open located on random packages- Contact recovery (press package)



TST

+150oChot liq.

-65oCcold liq.

�� Advanced EFA

�� Advanced RAAfter TST 200C, about 50% all open

�� Root cause confirmChange tape design, and all pass

�� Failure found- Customer find after SMT process- TCP package- fixed pin open V1

V2

Previous Design Revised Design



Typical Moisture (PCT, THB, HAST) Defect Mode

• Stress

• Weak point

- Die surface delamination to cause EMC lifted, ball-neck broken

- Al-pad corrosion

- Metal migration



PCT

�� Failure found- PCT 240H open fail- FS/SS=1/45- PLCC 32L Flash

�� Advanced EFA- Open failed around corner special pins- Serious die surface delamination

�� Advanced PFABall lightly lifted around corner pins

�� Root cause confirmChange molding compound

(Scanning Acoustic Tomograph)




PCT

�� Failure found- PCT 216H open fail- FS/SS=1/45- mBGA 48B (Substrate)

�� Advanced EFA- Open failed- Die-surface delamination

�� Advanced PFA1st bonding lifted from device pad

�� Root cause confirm- Change molding compound



chip


ball

epoxy



PCT

�� Failure found- PCT 96H open fail- FS/SS=3/45- mBGA 48B (Substrate)

�� Advanced EFA- Open failed around corner special pins- Substrate surface delamination

�� Advanced PFA2nd Bonding finger lifted from substrate

�� Root cause confirm- Change molding compound- Change substrate solder resistance



chip


ball

epoxy



Failed Pin:LCASB

Normal Pin

-3.2m

(Curve Tracer)

For Normal Pin: Vcc=5.5V, VI=0~5.5V, Leakage Current≅ 0For Failed Pin: Vcc=5.5V, VI=0V, Leakage Current= -3.2mA

Hot-spot

( Liquid Crystal Microscope)(Scanning Electrical Microscope)

PCT

�� Failure found- PCT 240H leakage failed- FS/SS=1/45- TSOPII 40L 4M DRAM

�� Advanced EFALeakage failed on Pin 31 (LCAS)

�� Advanced PFAHot-spot is found around failed pin

�� Root cause confirmGate oxide damaged (Wafer Process)



THB

�� Failure found- THB 500H Open/Leakage failed- FS/SS=7/32- SOJ 40L 4M DRAM

�� Advanced EFA- Open/leakage failed on random pins- Serious die surface delamination

�� Advanced PFABall lightly lifted around failed pins

�� Root cause confirmReliability ovens over-stressed


THB passed THB failed




Typical HT/LT-SLT Defect Mode

•••• IMC Layer Crack (Au-Ball Lift)

Kirkendall Void



Un-predicting Reliability Failure Mode – Ion Migration

Copper Migration

Solder Migration

Temperature-Humidity-Voltage/Bias

Evaluation: Tandem pattern + Dew Cycling Test



Un-predicting Reliability Failure Mode – Tin Whisker

EIA JESD22-A12, May, 2005“Measuring Whisker Growth on Tin and Tin Alloy… “This document is not qualification standard !!!



Process Step Failure Mechanism Failure Mode Detect R. Test

Implantation - Junction leakage due to crystal defects Degradation of BV HTOL, LTOL

- Implantation effects (Isolation & Channel) Leakage or Short ESD, EOS

- Hot carrier effect

Oxidation - Silk bulk defect - thin oxide Short curcuit HTOL

- Particle contamination Si surface Increase in Leakage ESD, EOS

& on oxide layer

- Dielectric breakdown

Photolithography - Photoresist particle defect & pinholes Open curcuit HTOL, LTOL

- Photoresist contamination Increase in Leakage THB

- Masking problem

Wire bonding - Ball missing & intermetallic Open curcuit TCT, TST, PCT

- Compound, bonding problem Intermitant open THB

- Pad contamination Leakage Resistance

- Over bonding condition

- Underlayer cracking

- Loop & wire sagging problem

Package - Corrosion due to bulk or lead-to-EMC Open TCT, TST, PCT

gap moisture pentetration Surface leakage THB

- Poor material solderability

(refer to: Samsung/quality assurance/reliability)

Reliability and Failure Mechanism

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