Update on Pb-free Electronics in Military Systems David Locker

COTS Pb-free Management Contractual Requirements Define Responsibility of COTS User Establish COTS requirements allocated from system requirements Verify COTS items meet their allocated requirements EIA-933 provides COTS Management framework Defense Acquisition Guidebook identifies general concerns Leverage Robust Parts, Materials, and Processes Engineering Effort Apply GEIA-STD and GEIA-STD COTS User must address Pb-free issues COTS Manufacturer data or generate assessment Tin Whiskers and Pb-free Solder MIL-STD and EIA-STD-4899 provide framework for PM&P Management COTS User: Entity responsible for assuring COTS item meets system requirements Contractual Requirements supported by Management Plans

Tin Whiskers GEIA-STD concerns must be addressed Need Parts List, Conformal Coating, Self-mitigation Data, Tin Finish replacement use information Access to this information should affect selection decision Parylene Conformal Coating preferred Parylene provides truly conformal coating by process Parylene CAN BE REWORKED Parylene greatly reduces level of effort for tin whisker risk mitigation Coverage verification affirmed by process Negligible risk of shorts even if coating broken through Limited spacing analysis required Reduces risk of part damage by hot solder dip Reduces need for Parts List access and change monitoring Reduces risk of whiskers induced by residues/moisture/oxidation Mitigations Require Verification

Pb-free Solder Assemblies Apply Sound Design Practices Pads per Part manufacturer recommendations Stress analysis for Thermal Expansion mismatch and Board flexure strain Apply strain relief measures Assure device/assembly compatibility with reflow thermal stress Test Protocol for <10 year applications (reference GEIA-STD ) Address aging, CTE mismatch, vibration/shock Isothermal and humidity aging: 336 hrs at 85°C; 1000 hrs 85°C/85% RH Temperature cycling: 750 cycles, -40°C/+85°C Vibration/shock per application for System effects Longer test times required for >10 years Thermal Aging Humidity Temp Cycling Humidity Temp Cycling Vibe Shock Several Successes with some Routers and “Single Board Computers” Some Less Than Successful

Pb-free Moving Forward Re-balling: We need the Standard! Assess risk of re-balling compared to higher reflow temperature Conformal coating coverage verification Need consistent urethane application processes Need to apply non-destructive coverage verification methods SAE ARP? Self-mitigation ARP? In-Service Reliability of Pb-free Assemblies Will be trying to accumulate data on current experiences to share Aerospace Vehicle Systems Institute Project key effort Daisy-chain circuit cards Functioning circuit card with SAC305 and Copper wire bond parts Questions?