Download - ELECTRONIC PART FAILURE ANALYSIS TOOLS AND TECHNIQUES Walt Willing Mike Cascio Jonathan Fleisher.

ELECTRONIC PART FAILURE ANALYSIS TOOLS AND TECHNIQUES

Walt Willing

Mike Cascio

Jonathan Fleisher

2010 RAMS –Tutorial 11B – Cassady

Importance of effective Failure Analysis Basic Failure Analysis Process Failure Analysis Techniques

Electrical Testing / Characterization Non-Invasive Tests Invasive Tests

Suggestions for your own failure analysis capabilities Understanding Electronic Part Failure Mechanisms

Excerpts from the 1997 Alan O. Plait Award for Tutorial Excellence

Agenda

2RAMS 2012 – Tutorial 8B – Willing, et al


Importance of Effective Failure Analysis

Effective root cause analysis helps assure proper corrective action can be implemented

When electronic parts fail, it’s important to understand why - the Root Cause

Accurate root cause assessment important for High Reliability systems where failures are very critical: Implantable medical devices Space satellite systems Deep well drilling systems

As well commercial high production products, where the cost of a single failure mode is replicated multiple times

Common term for process of root cause determination and applying corrective action FRACAS (Failure Reporting, Analysis and Corrective Action System)

Failure Analysis is the crucial “Analysis” part of the FRACAS process



Failure Analysis - Caution“Preserve the Failure” / Prevent “RTOKs”

Failure Analysis has to be handled carefully Assure the failure mechanism is preserved, not “Lost” due to

Carelessness Bypassing important tests / measurements Performing destructive analyses in an incorrect sequence.

Example: Once wirebonds are removed, the part may not be able to be electrically tested

Many parts removed for failure analysis may “Re-Test OK” (RTOK) Possibly the wrong part was removed Part level testing performed did not properly capture the failure mode

Subtle parameter shifts, etc. Peculiar failure sensitivity (e.g. gain vs temperature) exists

Important to assure board level fault isolation / troubleshooting performed correctly



Top Reasons for Component Failures (1 of 3)

1) Electrical Overstress Transients related to test setups. Rapid switching to full amplitude voltage / lead to inrush or high transient Human body electrical static discharge (ESD)

2) Solder joint failure Poor solder joints are the most common issue related to board fabrication Commonly responsible for latent failures due to joint fatigue driven by thermal

cycling




3) Contamination Leads to failures stemming from corrosion or electrical leakage paths Can rapidly destroy wire bond interconnects and metallization. Sources of contamination

Human by-products (Spittle) Chemicals used in the assembly process.

4) Cracked Ceramic Packages Ceramics are used for the majority of high reliability military and space

applications Packages are very brittle and are susceptible to cracking

Stress risers from surface anomalies General mounting stresses (exacerbated by thermal cycling

Root causes can be traced to either design implementation or process controls 5) Timing Issues

Intermittent failures often due to Inadequate timing margins Through timing analysis should be part of any design when asynchronous

signals are present




6) Power Sequencing Issues Many IC technologies susceptible to damage if core bias voltages are not

applied prior to control or data input voltages

7) Poor Design Habits Lack of adequate derating (voltage, power, thermal)

Most common of these is due to not managing component temperature

Running parts outside their rated power dissipation specification Leaving CMOS inputs floating Not properly controlling resets Low bias voltage / Step Load “Droop”



Recommended Trouble ShootingPrior to Part Failure Analysis (1 of 3)

Isolate and confirm part failure while still on the board to the extent possible Review initial failure data Exonerate Test Equipment and if necessary:

Use a known good reference unit to check test set-up Confirm failure on different test set and assembly levels

Confirm the following are within spec: Input conditions (bias, addressing, strobe, logic) Output parameters Take DC probe measurements on part (Use micro-clip probes if necessary) Look at all signals with an Oscilloscope to assure no AC oscillations Check Line-to-line & line-to-ground isolation

Lift solder joints as required to isolate part from circuit For RF circuits, consider soldering a coax onto part before removing and confirm

input/output is out-of-spec Use connectorized measurements as much as possible.

Probe based RF measurements are typically not consistent and unreliable




Inspect / Photograph / X-ray part on board Perform general examination under magnification Focus on the following:

Solder joints Connectors Component (cracks, exterior finish) Foreign Object Debris (FOD) Suspect component

Photograph guidelines Minimum of four angles Solder interfaces to board Photograph each side of part

X-ray on board prior to removal as required




Part Removal Guidelines Review removal process if new steps are required Cut leaded wire connections when possible to remove part Witness removal as necessary If heat is required to remove part

Take as much data as available, excessive solder heat may corrupt evidence



Basic Failure Analysis Techniques

Electrical Testing / Characterization Non-Invasive Tests Invasive (Destructive) Tests



Basic Failure Analysis Process FlowElectrical Testing / Characterization

Test / Characterize over temperatureCurve Tracer I-V check of Inputs

Non-Invasive TestsExternal Microscopic Exam / Photo

Fine & Gross LeakVacuum Bake (Non-Hermetic Parts)

X-rayPINDXRF

SAM / C-SAM

Invasive TestsLid Removal / Decapsulate

Die ExaminationDie Probing

IR Microscopic ExamLiquid Crystal

Cross-SectioningSEM

EDS/EDXFIB

AugerSIMSFTIR

TEM/STEM



Electrical Testing / Characterization

First FA Step - Fully Characterize Failure Mode

Test / Characterize / Look for Sensitivities Over temperature Voltage range Clock speed

Perform Curve tracer assessments on all Inputs / Outputs Compare to known good devices Can help isolate which pin may be damaged



Non-Invasive Tests

Second FA Step - Perform Non-Invasive Tests External Microscopic Exam / Photo X-ray (Film, Realtime, 3D) Fine & Gross seal tests for hermetic devices Vacuum Bake & Retest PIND Test XRF X-ray Fluorescence Acoustic tests (SAM / C-SAM)



External Microscopic Exam / Photo

Thorough external visual examination of the suspect part using a stereo microscope should be performed early in the failure analysis process

Typical inspection scopes range from 10X to 30X magnification Magnification levels up to 100X can be employed to further examine any

anomalies identified. The following conditions should be specifically looked for:

External contamination and/or solder balls Possibly shorting out pins on the device

Damaged leads or package seals Seal integrity Lead integrity

Gross cracks in the package Corrosion Thermal or electrical damage

Representative Photos should be taken of the part and any anomalies

Crack



X-Ray - Film / Realtime / 3D

X-Ray (Radiograph) is a very powerful tool for non-invasive failure analysis X-Ray examinations can detect actual or potential defects within enclosed packages There are multiple types of X-Ray equipment available

Basic film X-Rays Real time X-Ray 3-D X-Ray

While film X-Rays can be useful, modern Real Time X-Ray provide extensive capabilities Resolution for film X-Ray = 1 mil particle size, or bond wires down to 1 mil diameter Limitation of film X-Ray - only one exposure level can be taken at a time

Not all characteristics can be observed at a single exposure level Real time X-Rays typically have a resolution range from 1um to 0.4 um Real time allows for a continuous adjustment of exposure levels and conditions, as

well as real time part rotation to obtain the most revealing X-Ray view Special digital filtering / image processing can also be used to detect possible

delinations in the image not otherwise observable on the image screen Refer to Mil-Std-883 Method 2012



X-Ray Examinations

X-Rays allow internal part examination looking for: Internal particles Internal wire bond dress

Make sure the wire bonds are not touching each other or package lids Die attach quality (voiding, die attach perimeter) Solder joint quality for connectors

Insufficient or excessive solder Substrate or printed wiring board trace integrity Obvious voids in the lid seal Foreign metallic particles within the package Internal part orientation, etc.



Real-Time X-ray of Coaxial Connector

Normal X-ray View X-ray with Image Filtering



Acoustic tests (SAM / C-SAM)

Acoustic testing is popular for finding voids / delaminations / cracks Plastic Encapsulated Microcircuits (PEMS) Ceramic capacitors.

Acoustic tests rely on acoustic energy transfer through the part If there is a void, the acoustic energy is blocked, and therefore voids can be

detected The acoustic tests can also be tuned to attempt to determine the depth of any

void Acoustic tests involve either reflected acoustic energy, or transmitted energy

through the part The energy transmission medium is typically DI water

Parts to be examined need to be able to withstand exposure to water



Acoustic Scan of a Discoidal Ceramic Capacitor

CSAM identified significant void Confirmed to exist via cross-sectioning



Invasive (Destructive) Tests - Last but Not Least

Internal Package Exam / DIE Exam Cross Sectioning Die Probing IR Microscopic Liquid Crystal die thermal mapping SEM Auger EDS/EDX FIB FTIR SIMS (TOF SIMS / D-SIMS) TEM (transmission electron microscopy STEM (scanning transmission electron microscopy) ESD Testing



Microscopic Internal / Die Exam Look for:

Damaged metal traces Die cracks Broken or damaged wirebonds

Typically performed using a microscope at magnifications of 100X up to 1000X Deep UV optical microscopes can reach 16,000 X magnification and are capable of

resolving 10 microns Microscopes equipped with both dark and light field illumination are helpful, as changing

the lighting conditions can help reveal issues. Photographs should be taken to document the condition of the die and to record any

anomalies

Open Wire Bond Disturbed Bonds



Cross Sectioning

Cross-Sectioning is a very important means of failure analysis Often used for:

Connectors Printed wiring board Substrates Solder joints capacitors, resistors, transformer Semiconductors

Prior to cross-sectioning, samples are potted in a hard setting acrylic or polyester rosin

Failed item is literary cut in a cross-sectioned fashion then highly polished for detailed microscopic examination

The potted sample can be cut in half initially to find target the failure site, or the cross-section can commence at one end of the sample and then progressively cross-section up to and through the failure site. This progressive cross-sectioning can provide a “3D” view of the failure site. Photograph at all steps

Solder Joint



Cross-Sectioning of PWB

Blister area above electrically stressed signal traces caused un-

expected resistance <10ohms

Deformation/ Delamination due to excessive heating



Damage located above the trace

Distorted signal trace,Evidence of high current

thru trace

+28V Trace maintains shape,No evidence of over-current

Signs of Overheating of Center Trace

Material appears carbonized



Scanning Electron Microscope (SEM) SEM is an important tool for semiconductor die failure analysis, as well as

metallurgical failure analysis SEM can provide detailed images of up to 120,000X magnification

Typical magnifications of 50,000X to 100,000X Resolve features down to 25 Angstroms NANO SEMs can resolve features down to 10 Angstroms

With a SEM image, the depth of field is fairly large, providing a better overall three-dimensional view of the sample

SEM examinations are often used to verify semiconductor die metallization integrity and quality Refer to Mil-Std-883 Method 2018



Auger Electron Spectroscopy (AES) Sample surfaces are exposed to an electron beam designed to dislodge secondary

electrons (Auger electrons)

Materials identified by energy level spectra unique to each material’s valence bands

Auger useful for detecting organic materials on surfaces

Depth profiling can occur, useful to 2000 Angstroms deep

Auger profile of contamination on the surface of a wire bond pad



Energy Dispersive X-ray analysis (EDS, EDAX or EDX)

EDX is a technique used along with an SEM to identify the elemental composition of a sample

During EDX, a sample is exposed to an electron beam inside the SEM

SEM electrons collide with the electrons within the sample, causing some of them to be knocked out of their orbits

The vacated positions are filled by higher energy electrons which emit X-rays in the process

By a spectrographic analysis of the emitted X-rays, the elemental composition of the sample can be determined

EDS is a powerful tool for microanalysis of elemental constituents



Energy Dispersive X-ray (EDX, EDAX, EDS)

EDS maps of a Cadmium particle



Secondary Ion Mass Spectrometry (SIMS)

SIMS is a technique which can detect very low concentrations of dopants and impurities in semiconductors

By ion milling deeper into the sample, SIMS provides elemental depth profiles from a few angstroms to tens of microns

SIMS works by sputtering the sample surface with a beam of primary ions Secondary ions formed during the sputtering are analyzed using a mass

spectrometer These secondary ions can range down to sub-parts-per-million trace

levels Advanced SIMS analyses such as Time-of-Flight SIMS (TOF-SIMS) and

Dynamic SIMS (D-SIMS) provide additional means of elemental detection and resolution



Focused Ion Beam FIB FIB uses an ion beam to microscopically mil / ablate material away to allow for

cross-sectioning of semiconductor die (ion milling) Gallium or Tungsten ion sources are used

FIB cross-sections are examined by SEM to see features such as Die metallization construction Pinhole in dielectrics (oxides/nitrides) EOS or ESD damage sites

FIB cross sections are very “polished” revealing features down to 200 to 250 Angstroms

FIB can also be used to cut semiconductor metallization lines to isolate circuitry on the die, and if necessary, a Platinum ion beam can be used to actually deposit metallization creating new circuit traces

In this case, die level design changes (known as “Device Editing”) can be implemented to allow for a design “try-out”



Focused Ion Beam (FIB)

FIB cross-sectionof a Schottky diode

FIB cross-sectionof a MOSFET GATE



Transmission Electron Microscopy (TEM/STEM)TEM (Transmission Electron MicroscopySTEM (Scanning Transmission Electron Microscopy)

TEM and STEM use a high energy electron beam to image through an ultra-thin sample allowing for image resolutions on the order of 1 - 2 Angstroms

S/TEM has better spatial resolution then a standard SEM and is capable of additional analytical measurements

S/TEM and requires significantly more sample preparation as very thin samples need to be prepared, often using FIB techniques

S/TEM provides outstanding image resolution and it is possible to characterize crystallographic phase and orientation as well as produce elemental maps



TEM of a gold ball bond on an Aluminum pad confirmed Good Bond Intermetallics

TEM analysis of a gold/aluminum interface of a wire bondData from the TEM provided assurance that the gold/aluminum

stoichiometry was correct even after extensive life aging



Suggestions for Your Own Failure Analysis Capabilities

Suggestions are provided for Failure Analysis capabilities for a typical electronics firm Three levels of Failure Analysis capabilities are suggested

Basic Moderate Advanced

Beyond these three levels, one might consider using commercial failure analysis laboratories for the more esoteric capabilities such as TEM / STEM SIMS

Usually its more cost effective to subcontract out those types of analyses vs. establishing them in-house



Basic Failure Analysis Lab

Basic Meters (DVMMs) Stereo Microscope (10X to 30X) (Preferably with digital camera) Cross Sectioning Equipment Power Supplies / Signal generator Curve Tracer

Cross-Section Equipment

Curve Tracer showingI/V Curve



Moderately Equipped Failure Analysis lab

Metallurgical Microscope (1000X) (Preferably with digital camera) Film X-Ray SEM Chemical Hood with De-capsulating chemicals Die Probe Station Liquid Crystal Acoustic Scan

Metallurgical Microscope withDigital Camera



SEM and Acoustic Testing (CSAM)


Scanning Electron Microscope

Acoustic Testing (CSAM)


Advanced Failure Analysis lab

Real-time X-ray SEM/EDS Auger Analysis System FIB IR Thermal Imaging RF Test Equipment (If necessary)



Real-time X-ray

Comparison Between Film & Real-time X-ray

Film X-ray Real Time X-ray



Scanning Electron Microscope with EDS

EDX used for Spectral

Element Analysis



Focused Ion Beam (FIB) Cross-Sectioning


FIB Cross-Section – Contact Windows

FIB Cross-Section – MOSFET Gates


Thermal Imaging


A hotspot in a CMOS gate is indicated by the liquid crystal technique at 1000X

IR Thermal Imaging System


Understanding Electronic Part Failure MechanismsExcerpts from the 1997 Alan O. Plait Award for Tutorial Excellence

Five subjects covered:

Interconnects

Semiconductor elements

Passive elements

Substrates

Packages.



Purpose of Failure Mechanisms Section

Understanding common part failure mechanisms for various technologies necessary to provide effective corrective action to avoid failures

Typical Hybrid, Transistor, and IC



Wire Bonds

ISSUES: Bond placement

Wire dress

Bonding energy

Bonding temperature

Bondability

Dissimilar metals

Corrosion

Contamination

Electrical overstress

Mis-Placed bonds caused shorts



Wire Bonds


Wire dress

Bonding energy

Bonding temperature

Bondability

Dissimilar metals

Corrosion

Contamination



Poor Stress Relief


Wire Bonds


Wire dress

Bonding energy

Bonding temperature

Bondability

Dissimilar metals

Corrosion

Contamination




Wire Bonds

Gold / Aluminum Intermatallic“Purple Plague”


Wire dress

Bonding energy

Bonding temperature

Bondability

Dissimilar metals

Corrosion

Contamination




Wire Bonds


Wire dress

Bonding energy

Bonding temperature

Bondability

Dissimilar metals

Corrosion

Contamination




Solders

ISSUES

Die and substrate attach voiding

Corrosion

Intermetallic formation

Reflow

Good and Poor Solder Coverage

10X



Solders

Poor Die Attachment

ISSUES


Corrosion


Reflow



Corrosion of Indium Solder

25X

Solders

ISSUES


Corrosion


Reflow



Solders

ISSUES


Corrosion


Reflow



Epoxies

ISSUES:

Outgassing

Poor adhesion

Electrical resistance

Electrolyic corrosion



Epoxies

ISSUES:

Outgassing

Poor adhesion





Detached Diode Mounted With Conductive Epoxy

Epoxies

ISSUES:

Outgassing

Poor adhesion





Electrotyic Corrision Between Conductive Epoxy and Gold Track

Epoxies

ISSUES:

Outgassing

Poor adhesion





Semiconductor Elements

ISSUES:

Metallization

Overstress

Electrical overstress (EOS)

Electrostatic discharge (ESD)

Oxide



Open in Metallization Stripe Due to Poor Step Coverage

Metallization

ISSUES:

Step coverage

Misalignment

Mechanical damage

Corrosion

Electromigration

Stress voiding



Metallization

ISSUES:

Step coverage

Misalignment

Mechanical damage

Corrosion

Electromigration

Stress voiding



Damaged Metallization

200X

Metallization

ISSUES:

Step coverage

Misalignment

Mechanical damage

Corrosion

Electromigration

Stress voiding



Metallization

ISSUES:

Step coverage

Misalignment

Mechanical damage

Corrosion

Electromigration

Stress voiding



Metallization

ISSUES:

Step coverage

Misalignment

Mechanical damage

Corrosion

Electromigration

Stress voiding

Aluminum Metal - Electromigration



Semiconductor Elements

ISSUES:

Metallization

Overstress



Oxide



Electrical Overstress

Overstress



Over Voltage electrical overstress resulted in G-S-D Short in FET

Not visible at 100XDamage only visible with SEM



Overstress



Electrical Overstress due to Voltage Transient Spike on input to RF Schottky Diode

FIB Through The Short Site Pin Pointed with

Liquid Crystal Analysis



Overstress


Electrostatic discharge

(ESD)

Electrical Overstress due to Intentional ESD Exposure on input to RF Schottky Diode

Not as much damage as a high voltage transient

~500V Human Body Model Exposure



Oxide

ISSUES:

Ionic impurities

Oxide defects

Hot carrier effects



Ceramic Capacitors

ISSUES: Cracking Barrier metals Base Metal Electrodes

• Cracking

50X



Film Resistors

ISSUES: Overstress Corrosion (Nichrome) Cracks ESD Physical Damage


Overstressed Thick Film Resistor


Substrates

ISSUES:

Cracking

Metallization failures

Multilayer failures



Substrates

ISSUES:

Cracking

Metallization failures

Multilayer failures


Incomplete Via Fill


Packages

ISSUES:

Hermeticity

Insulation resistance

Loose particles



Packages

ISSUES:

Hermeticity


Loose particles



Questions?
