and Pb-Free: Current Reliability Concerns Craig Hillman
RoHS Abstract Like the rest of the electronics industry, your products will transition to Removal of Hazardous Substances (RoHS) compliance prior to the deadlines in 2006. This includes the transition to Lead-Free Solder, and at this time, there are significant reliability uncertainties around Lead-Free Solder. Even if your product does not need to be compliant, the materials and processes that make up your product are changing. As one major consumer product team concluded, doing nothing would double the field failure rate of the electronics. During this time of rapid transition, there is a significant new body of knowledge to understand to determine the areas of greatest risk to the reliability of your product. In this presentation, we will highlight a few of these significant risk areas and how to best mitigate these risks during the transition.
Specific OEM Pain We Address We help with Risk Mgmt. of Entire Process We help you determine when to transition (doing nothing can be more risky! Why?) When you decide to transition, we can Set new Metrics and Develop Implementation Plans Identify Areas of Greatest Risk (Focus Resources) Predict the Reliability of your Product (before its ever built!) Develop and Perform RoHS Specific Qualification Plans Work with your Contract Manufacturers Work with your Vendors Review your Vendors Test Reports/Qual Reports On the following pages are some of these risks
Tin Whiskers Problem: Current state of knowledge is limited Inability to predict tin whisker length for a given component after a certain period of time Step 1: Focus Less than 1 mm pitch (0.3 mm spacing) Metal can housing Contact points (connector flex circuitry) Welds (electrolytic capacitors) Step 2: Qualify Ambient (25C/50%RH, 3k-4k hrs) Elevated (60C/93%RH, 3k-4k hrs) Cyclic (-55 to 85C, 1k-1.5k cycles) Consider corrosive environments Step 3: Mitigate Nickel underplate (require SPC!) High temperature anneal Proprietary plating baths (be skeptical)
Moisture Sensitivity Levels and Plastic Encapsulated Capacitors Pb-free reflow is hotter Increased susceptibility to popcorning PECs are the primary risk (MSL 1 is assumed) Approach to labeling is inconsistent Aluminum Polymer are rated MSL 3 Tantalum Polymer are stored in moisture proof bags (no MSL rating) Approach to Tantalum is inconsistent (some packaged with dessicant; some not) Material issues Aluminum Polymer are rated MSL 3 for eutectic (could be higher for Pb-free) Sensitive conductive-polymer technology may prevent extensive changes Solutions Confirm Pb-free MSL on incoming plastic encapsulated capacitors (PECs) More rigorous inspection of PECs during initial build
Kirkendall Voiding Borgensen, UIC Void formation between copper plating and copper/tin intermetallics. Can lead to solder joint separation. Is Kirkendall voiding a problem? Yes! Observed by multiple organizations Published data suggests complete separation in 6-7 yrs at 75C Other reports suggest much more rapid times to failure Overlooked in SnPb? No! TI/UCLA reproduced this behavior with SnPb Kirkendall voiding never known to cause field failures during 20 years with SnPb and surface mount technology (SMT) Do these environments really exist in the field? Mei, Cisco ECTC 2005 Zeng, TI JAP, 2005
Long-Term Reliability of Pb-Free Solder Joints Can we predict time to failure for Pb-free solder joints? YES So, when should you be concerned? Components highly susceptible to solder joint fatigue Large chip resistors, Ceramic BGAs, Leadless ceramic chip carriers, Non-underfilled CSPs, Etc. Max solder joint temperature greater than 80ºC with dwell times greater than 4 hours At least one thermal cycle per day and a desired lifetime of more than 10 years SAC life / SnPb life 10 8 6 4 2 0 (-55) to 125C, 70 minute cycle 2512 Resistor on FR4 (25-80C) Ceramic BGA on FR4 (0-100C) 0 100 200 300 400 500 Dwell Time (min)
Through-Hole Components Significant risk of insufficient hole fill Can lead to single-sided architecture Rectified through increasing solder pot temperature (?) Single-sided Shrinkage cracks found to have severe influence on time to failure Will require new optical inspection criteria Shrinkage Crack
Mechanical Loading (Board Flexing, Shock, Vibration) Post-reflow handling Increased risk of failure? Conflicting results Sensitive to time after reflow Some companies moving to restrict board-level strain From 1000 to 750 to 500 microstrain Shock and Drop Some degradation in performance Board plating seems to play a large role (SnNi weaker than SnCu) Vibration SAC worse under low-cycle fatigue, where most failures occur PWB surface strain 3.0E-03 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 SnPb SnAgCu 0.0E+00 1,000 100,000 10,000,000 Cycles to Failure
Pb-Free and Printed Boards Increased Warpage Epoxy Cracks Land Separation Blistering Solder Mask Discoloration PTH Cracks CAF Delamination Predicting printed board damage can be difficult Driven by size, material, and design Measure board temp., qualify material set (T-280 of 5-10 min.), test and x-section
For More Information For more information on Reliability of Pb-Free Solder, contact Dr. Craig Hillman, Dr. Miky Lee, or Dr. Nathan Blattau of DfR Solutions (301) 474-0607 // chillman@dfrsolutions.com // www.dfrsolutions.com Dr. Nathan Blattau of DfR Solutions (301) 474-0607 // nblattau@dfrsolutions.com // www.dfrsolutions.com Dr. Miky Lee of DfR Solutions (301) 474-0607 // mlee@dfrsolutions.com // www.dfrsolutions.com Fred Schenkelberg of Ops A La Carte (408) 710-8248 // fms@opsalacarte.com // www.opsalacarte.com Mike Silverman of Ops A La Carte (408) 472-3889 // mikes@opsalacarte.com // www.opsalacarte.com We offer Education on the risks, concerns, and best practices for reliability of Pb-Free solder. Assessment of a company's products and determination of areas of significant reliability risk due to the industry component and manufacturing changes due to the European and worldwide legislation. Product Qualification and Risk Minimization through the RoHS transition using our physics-of-failure based approach to product reliability. (see http://www.dfrsolutions.com/pb_free.asp?mstr=2 for more info)