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A ‘Quality’ Test Plan for Pb-Free Products By Keith M. Sellers Managing Scientist NTS Baltimore
A ‘Quality’ Test Plan for Pb-Free ProductsBy Keith M. SellersManaging ScientistNTS Baltimore
Contents
• Background
• Quality Issues
• Quality Testing– Printed Circuit Board (PCB) Analysis– Printed Circuit Assembly (PCA) Analysis
• Discussion
• Reliability Testing– Solder Joint Reliability Analysis– Tin Whisker Evaluation
Background
Legislation (RoHS, WEEE, etc.) is the main issue fueling the current push for the removal of Pb from electronics.
The strength, durability, and reliability of solder joints consisting of Pb-containing solders and finishes have been well studied…however the same data is not available for newly developed Pb-free solders and finishes.
Background
The switch to “Pb-free” production affects…• Solders and Fluxes• Plating finishes• Processing
─ High temperatures─ Longer times
“Pb-free” testing focuses on…• Board (PCB) Level Quality Evaluations• Assembly (PCA) Level Quality Evaluations• Reliability Analysis
Quality vs. Reliability
Reliability information for Pb-free products is relatively unknown so testing should start at the very beginning…with Quality.
These terms are often used interchangeably, however they are two different concepts entirely.
Quality will affect Reliability, but good Quality does not insure good Reliability.
General Quality Issues
Companies competent in SnPb assembly may have issues with Pb-free assembly.
Pb-free assembly requires its own process parameters and inconsistencies can result by way of its own unique defects.
Even if an assembly “process” has not switched to Pb-free, most of the components being purchased have, with or without knowledge.
General Quality Analysis
Reliability Testing is a “long-term” venture.
Before testing for Reliability, one should ensure Quality is acceptable.
Poor Quality will simply add another variable to the Reliability assessment.
There are many ways to assess overall quality.
One can / should examine actual raw materials (PCB, components, etc.) through completion of final product (PCB, PCA, end products, etc.)
General Quality Testing
A test plan for…
• Printed Circuit Boards (PCBs)─ Why Test?─ Recommended Testing─ Some Findings…
• Printed Circuit Assemblies (PCAs)─ Why Test?─ Recommended Testing─ Some Findings…
A ‘Quality’ Based Test Plan for PCBs
Why Test? – To determine a board’s ability to withstand Pb-free processing.
Test Plan…• Visual Examination• Thermal Analysis• Thermal Stress Analysis• Solderability Testing• Peel Strength Testing• Microsection Analysis
PCB Test PlanRecommended Testing…
• Glass Transition Temperature (Tg) and Z-axis Thermal Expansion by Thermomechanical Analysis (TMA)─ IPC-TM-650, method 2.4.24
• Time to Delamination (T288) ─ IPC-TM-650, method 2.4.24.1
• Glass Transition Temperature (Tg) and Cure Factor (∆Tg) by Differential Scanning Calorimetry (DSC)─ IPC-TM-650, method 2.4.25
• As Received & Thermal Stress Analysis @ 300 °C─ IPC-TM-650, methods 2.1.1 & 2.6.8
• Solderability Testing─ ANSI/IPC-J-STD-003
• Peel Strength Testing
PCB Test Plan
Additional Evaluation of the samples is completed via Microsection Analysis…
PCB Test Plan
Some findings…• The possible effects of higher temperatures and longer times…
PCB Test Plan Results Summary
A comparison of board characteristics…
Test ID Possible Requirement Material A Material B Material C
Visual Examination --- No Anomalies No Anomalies No Anomalies
Tg > 150°C 175°C 180°C 180°C
Cure Factor < 5°C 2.6°C 3.5°C 3.6°C
% CTE < 4% 1.6% 1.9% 2.9%
T288 > 10 min > 10 min > 10 min 6.6 min
As Rec'd Microsection IPC-A-600 No Anomalies No Anomalies No Anomalies
Thermal Stress --- No Anomalies No Anomalies No Anomalies
Solderability > 95% coverage 100% 100% 97%
Peel Strength > 8 lbs/in 8.4 lbs/in 8.6 lbs/in 7.5 lbs/in
Sheet1
Test IDRequirementMaterial AMaterial BMaterial C
Visual Examination---No anomaliesNo anomaliesNo anomalies
Tg150-200 °C164.1 °C173.0 °C182.8 °C
CTE< 4%1.20%1.80%3.40%
Time to Delamination> 10 min8.2 min> 10 min> 10 min
Cure Factor< 5°C1.4°C2.1°C1.8°C
Thermal Stress---No anomaliesNo anomaliesNo anomalies
Solderability> 95% coveragePassPassPass
Peel Strength8 lbf/in7.4 lbf/in8.6 lbf/in6.2 lbf/in
Sheet2
Test IDPossible RequirementMaterial AMaterial BMaterial C
Visual Examination---No AnomaliesNo AnomaliesNo Anomalies
Tg> 150°C175°C180°C180°C
Cure Factor< 5°C2.6°C3.5°C3.6°C
% CTE< 4%1.6%1.9%2.9%
T288> 10 min> 10 min> 10 min6.6 min
As Rec'd MicrosectionIPC-A-600No AnomaliesNo AnomaliesNo Anomalies
Thermal Stress---No AnomaliesNo AnomaliesNo Anomalies
Solderability> 95% coverage100%100%97%
Peel Strength> 8 lbs/in8.4 lbs/in8.6 lbs/in7.5 lbs/in
Sheet3
A ‘Quality’ Based Test Plan for PCAs
Why Test? – To compare appearance, structure, and strength of Pb-containing and Pb-free solder joints.
Why Compare? – There are few requirements for a solder joint’s mechanical properties… thus use the “known commodity” Pb-containing PCA as a yardstick.
Test Plan…• Non-Destructive Analyses• Destructive Analyses
PCA Test Plan
Non-Destructive Analyses• Visual Examination• Scanning Acoustic Microscopy• Electrical Examination• X-Ray Inspection• Ion Chromatography
PCA Test Plan
Some findings…• Examples of Scanning Acoustic Microscopy and X-Ray
Inspection Imaging…
PCA Test Plan
Destructive Analyses• Solder Joint Pull Strength
─ JEITA EIAJ ED-4702A, Test Method 002, Method 1 or Method 2
• Solder Joint Shear Strength─ JEITA EIAJ ED-4702A, Test Method 002, Method 3
• Dye-n-Pry• Microsection Analysis
─ Evaluation of overall joint integrity,voids, separations, etc.• Scanning Electron Microscopy / Energy Dispersive X-Ray
Spectroscopy (SEM/EDS)─ Examination of intermetallic layer (IMC), elemental
distribution, etc.
PCA Test Plan
Solder Joint Pull / Shear Strength Diagrams
Diagrams from JEITA EIAJ ED-4702A, Test Method 002, Methods 1 thru 3
PCA Test Plan
Some findings…• Dye-n-Pry Analysis
A1
PCA Test Plan
More findings…• Voiding in Pb-free Solder Joints
PCA Test Plan
More findings…• Voiding in Pb-Free Joints
─ Voids and Outgas “trails”
PCA Test Plan
More findings…• Pb-Free BGA Balls in combination with Pb-containing Solder
Paste─ Non-Homogeneity of joint─ Improper reflow profile
PCA Test Plan
More findings…• Sn-Ag IMC (Platelets)
PCA Test PlanMore findings…
• Ternary Intermetallic (Ni-Cu-Sn)─ An undesirable intermetallic formation (increased
brittleness) in comparison to Ni-Sn or Cu-Sn in a binary state
─ Much more prevalent when using Pb-free solders along with dissimilar plating finishes on the board and component
Cu
SnNi
PCA Test Plan
More findings…• Elemental Mapping Analysis SnNi
Cu Ag
PCA Test Plan Results Summary
A comparison of assembly characteristics…
Test ID Possible Requirement Assembly Process AAssembly Process B
Assembly Process C
Visual Examination IPC-A-610 No Anomalies No Anomalies No Anomalies
X-Ray Examination --- No Anomalies No Anomalies Excessive VoidingIon
Chromatography --- Pass Pass High Chloride
Pull Strength > 5 N 5.6 N 4.5 N 6.5 N
Shear Strength > 5 N 5.9 N 4.1 N 7.2 N
Dye-n-Pry No Separations No Separations No Separations Separations
Microsection IPC-A-610 No Anomalies No Anomalies IMC Cracks
SEM/EDS --- No Anomalies No Anomalies Incomplete Reflow
Sheet1
Test IDRequirementMaterial AMaterial BMaterial C
Visual Examination---No anomaliesNo anomaliesNo anomalies
Tg150-200 °C164.1 °C173.0 °C182.8 °C
CTE< 4%1.20%1.80%3.40%
Time to Delamination> 10 min8.2 min> 10 min> 10 min
Cure Factor< 5°C1.4°C2.1°C1.8°C
Thermal Stress---No anomaliesNo anomaliesNo anomalies
Solderability> 95% coveragePassPassPass
Peel Strength8 lbf/in7.4 lbf/in8.6 lbf/in6.2 lbf/in
Sheet2
Test IDPossible RequirementAssembly Process AAssembly Process BAssembly Process C
Visual ExaminationIPC-A-610No AnomaliesNo AnomaliesNo Anomalies
X-Ray Examination---No AnomaliesNo AnomaliesExcessive Voiding
Ion Chromatography---PassPassHigh Chloride
Pull Strength> 5 N5.6 N4.5 N6.5 N
Shear Strength> 5 N5.9 N4.1 N7.2 N
Dye-n-PryNo SeparationsNo SeparationsNo SeparationsSeparations
MicrosectionIPC-A-610No AnomaliesNo AnomaliesIMC Cracks
SEM/EDS---No AnomaliesNo AnomaliesIncomplete Reflow
Sheet3
General Discussion
Testing has shown that studies need to be completed on products using Pb-free solders and finishes
Sn/Pb Products which easily met reliability estimates may no longer be as robust when Pb-free processing and materials have been implemented, i.e. solder joint concerns in respect to brittleness, creep, elasticity, etc.
General Discussion
Processing temperatures and times are critical parameters in Pb-free production, which can cause possible issues with…
• Board integrity• Intermetallic Growth
Mismatched board and component finishes have been found to cause strength issues on Pb-containing products and will be more prevalent with the continued push towards Pb-free alternatives.
Reliability testing for Pb-free products is indeed similar to past testing.
General Reliability Issues
The reliability of a product, whether Pb-free or not, is critical
There are decades of data available concerning Sn/Pb Reliability.
Conclusions concerning Pb-Free Reliability are generally based on little “hard” data.
• Why?…The acquisition of data takes time and currently not enough time has passed and not enough studies have been performed
Solder Joint Reliability Analysis
Accelerated Environmental Exposure• Why Test? – To investigate PCA failure mechanisms on a
shorter time scale by determining the susceptibility of Pb-free joints to nanosecond “opens”
• Recommended Testing─ Event Detection Monitoring with…
Thermal Shock / Temperature Cycling Mechanical Shock Random Vibration / Resonance Dwell Bend / Flex Testing
─ Highly Accelerated Life Test (HALT) & Highly Accelerated Stress Screening (HASS)
Some findings…
Accelerated Environmental Exposure• Pb-free solder joints after Thermal Cycling and Random
Vibration / Resonance Dwell
More findings…
Accelerated Environmental Exposure• Pb-free solder joints after Thermal Cycling and Random
Vibration / Resonance Dwell
Tin Whisker Evaluation
Why Test? – To determine the ability of a Pb-free tin (Sn) based finish to grow whiskers
• Other whisker types, i.e. Zn, Ag, etc…
Applicable Documents…• JEDEC Test Methods and Standards– JESD22A121 (May 2005)– JESD201 (March 2006)• iNEMI Recommendations• Customer Statements of Work
Tin Whisker Evaluation
Recommended Environmental Exposures…• High Temperature / Humidity Storage
─ 60°C / 87%, 85°C / 85%• Low Temperature / Humidity Storage
─ 30°C / 60%, 25°C / 50%• Thermal Cycling
─ -55°C to -40°C / 85°C• Compression Testing
Recommended Test Durations…• Temperature / Humidity Storage Exposures
─ 1000, 3000, 4000 hour durations• Thermal Cycling Exposures
─ 1000, 1500 cycle durations
Some findings…
Tin Whisker Imaging via SEM
More findings…
Tin Whisker Imaging via SEM
More findings…
Tin Whisker Imaging via SEM
For more information, please visit www.nts.com
Or contact:
Keith Sellers, Managing [email protected]
John Radman, Senior Technical [email protected]
(410) 584-9099
mailto:[email protected]:[email protected]
A ‘Quality’ Test Plan for �Pb-Free ProductsContentsBackgroundBackgroundQuality vs. ReliabilityGeneral Quality IssuesGeneral Quality AnalysisGeneral Quality TestingA ‘Quality’ Based Test Plan for PCBsPCB Test PlanPCB Test PlanPCB Test PlanPCB Test Plan Results SummaryA ‘Quality’ Based Test Plan for PCAsPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test PlanPCA Test Plan Results SummaryGeneral DiscussionGeneral DiscussionGeneral Reliability IssuesSolder Joint Reliability AnalysisSome findings…More findings…Tin Whisker EvaluationTin Whisker EvaluationSome findings…More findings…More findings…Slide Number 38
