Challenges for the prediction of solder joint life in long term vibration

In the absence of manufacturing defects the ultimate life of a microelectronics assembly in long-term vibration is likely to be limited by solder joint fatigue. So far relatively limited efforts have been dedicated to the quantitative prediction of this life. However, even day to day `engineering tests' may not be very useful if they do not offer at least a ranking of alternative materials, designs or processes in terms of performance in service.The assessment of solder joint life in long term vibration under realistic service conditions is complicated by effects of cyclic loading on the solder and, in accelerated testing, the PCB deformation properties. Cycling induced damage to the PCB often goes unnoticed but may have profound consequences for the solder fatigue. Also, preliminary isothermal cycling results suggest that variations in cycling amplitude may lead to a change in creep properties. This would invalidate attempts at Finite Element Modeling and is believed to be the reason for the dramatic break-down of Miner's Rule of linear damage accumulation. A preliminary test was conducted to show that this applies to vibration to millions of cycles, at least. These issues are of major concern for the ESS testing commonly required in military and aerospace electronics manufacturing, and they may have consequences for the interpretation of random vibration test results.