Long-term isothermally aged concerns for SAC lead-free solder in harsh environment applications

Harsh environment industries, such as automotive, aerospace, and military have enjoyed exemptions with the industry conversion from SnPb to lead free solder materials. However, most of these exemptions have expired, and the limited availability of SnPb compatible components have now forced most of these industries into using lead free solders. Previous thermal cycle and vibration testing have shown acceptable levels of reliability for industry standard lead free materials (SAC). However, few of these tests have included long-term isothermal aging within the testing environment. This paper discusses the long-term (over 1-year exposure at temperature) thermal cycle and vibration reliability performance of SAC (lead free) solder when exposed to higher temperature (75°C and above) aging (exceeding one year). The research performed investigates the reliability of a wide variety of grid array and leadless devices when exposed to long-term isothermal aging. ENIG, ImAg, and OSP, surfaces finishes are investigated for their impact on aging and reliability properties. The paper also explores “doping” SAC solders with industry available solder paste to improve solder joint performance for thermal cycling and vibration testing. Specific industry needs and the relationship with the reliability performance are addressed.