A Quality Test Plan for Pb-Free Products. By Keith M. Sellers Managing Scientist NTS Baltimore

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1 A Quality Test Plan for Pb-Free Products By Keith M. Sellers Managing Scientist NTS Baltimore

2 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

3 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.

4 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

5 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.

6 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.

7 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.)

8 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

9 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

10 PCB Test Plan Recommended Testing Glass Transition Temperature (Tg) and Z-axis Thermal Expansion by Thermomechanical Analysis (TMA) IPC-TM-650, method Time to Delamination (T 288 ) IPC-TM-650, method Glass Transition Temperature (Tg) and Cure Factor ( Tg) by Differential Scanning Calorimetry (DSC) IPC-TM-650, method As Received & Thermal Stress 300 C IPC-TM-650, methods & Solderability Testing ANSI/IPC-J-STD-003 Peel Strength Testing

11 PCB Test Plan Additional Evaluation of the samples is completed via Microsection Analysis

12 PCB Test Plan Some findings The possible effects of higher temperatures and longer times

13 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

14 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

15 PCA Test Plan Non-Destructive Analyses Visual Examination Scanning Acoustic Microscopy Electrical Examination X-Ray Inspection Ion Chromatography

16 PCA Test Plan Some findings Examples of Scanning Acoustic Microscopy and X-Ray Inspection Imaging

17 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.

18 PCA Test Plan Solder Joint Pull / Shear Strength Diagrams Diagrams from JEITA EIAJ ED-4702A, Test Method 002, Methods 1 thru 3

19 PCA Test Plan Some findings Dye-n-Pry Analysis A 1

20 PCA Test Plan More findings Voiding in Pb-free Solder Joints

21 PCA Test Plan More findings Voiding in Pb-Free Joints Voids and Outgas trails

22 PCA Test Plan More findings Pb-Free BGA Balls in combination with Pb-containing Solder Paste Non-Homogeneity of joint Improper reflow profile

23 PCA Test Plan More findings Sn-Ag IMC (Platelets)

24 PCA Test Plan More 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 Sn Ni Cu

25 PCA Test Plan More findings Elemental Mapping Analysis Ni Sn Cu Ag

26 PCA Test Plan Results Summary A comparison of assembly characteristics Test ID Possible Requirement Assembly Process A Assembly Process B Assembly Process C Visual Examination IPC-A-610 No Anomalies No Anomalies No Anomalies X-Ray Examination --- No Anomalies No Anomalies Ion Chromatography Excessive Voiding --- 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

27 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.

28 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.

29 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

30 Solder Joint Reliability Analysis Accelerated Environmental Exposure Why Test? To investigate PCA failure mechanisms on a shorter time scale by determining the susceptibility of Pbfree 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)

31 Some findings Accelerated Environmental Exposure Pb-free solder joints after Thermal Cycling and Random Vibration / Resonance Dwell

32 More findings Accelerated Environmental Exposure Pb-free solder joints after Thermal Cycling and Random Vibration / Resonance Dwell

33 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

34 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

35 Some findings Tin Whisker Imaging via SEM

36 More findings Tin Whisker Imaging via SEM

37 More findings Tin Whisker Imaging via SEM

38 For more information, please visit Or contact: Keith Sellers, Managing Scientist John Radman, Senior Technical Director (410)