Objective

Legislation has banned the use of lead in solder for the vast majority of microelectronics products, and the complete switch of the consumer industry to lead-free soldering makes an eventual transition by Department of Defense (DoD) suppliers inevitable. However, the necessary quantitative understanding of long-term reliability effects is still missing. The properties of common lead-free solder joints are fundamentally different from those of tin-lead (SnPb). Prediction of the life of lead-free solder joints under even the simplest long-term service conditions cannot be done following current accelerated test protocols or modifying parameters in current models or expressions for SnPb. Quantitative predictions of long-term life under conditions of vibration, shock, and thermal excursions may be off by orders of magnitude. Even qualitative comparisons of alternative lead-free materials, design, or process options can be misleading. Also, indications are that the damage done in environmental stress screening (ESS) may be seriously underestimated. The issue is furthur complicated by the ongoing evolution of solder properties over the entire life, including interactions with solder volume and pad size, pad finishes, and reflow profile, as well as with subsequent thermal and loading history. In addition, suppliers continue to develop new alloys and users have to count on having to deal with numerous combinations of these in a single assembly. While consequences for consumer electronics are negligible or absent, the potential safety repercussions in certain military and aerospace applications may be incalculable.

The objective of this project is to develop a quantitative knowledge and understanding of lead-free solder joints as well as lead-free joints mixed with SnPb. Based on this knowledge, researchers will define test protocols and guidelines for the interpretation of test results in terms of life in long-term service.