Three practically important reliability-related questions for solder joint interconnections (SJIs) in automotive electronics, and particularly in its actuator and sensor electron devices, are addressed in this analysis: Could inelastic strains in the solder material be avoided by a rational physical design of the IC package, and, if not, could the sizes of the peripheral inelastic strain areas be predicted and minimized? It is clear that the low cycle fatigue lifetime is inversely proportional to the sizes of the inelastic zones and that the material's fatigue lifetime could be improved dramatically, if the induced strains remain within the elastic range. The Palmgren-Miner rule of linear accumulation of damages can be used, instead of Coffin-Manson relationships, in such a situation. Realizing that, because of the inevitable uncertainties, the difference between highly reliable and an insufficiently robust electronic products is “merely” in the levels of their never-zero probabilities of failure, could these probabilities be assessed, and could this be done at the design stage? A possibility of doing that is particularly critical for SJIs, the most vulnerable structural elements in the today's IC package designs. Reliability of an electronic material or a product cannot be assured, if it is not quantified, and, because of the inevitable and critical uncertainties, this should be done on the probabilistic basis. Should SJI accelerated testing based on costly, time- and labor-consuming and, because of temperature dependency of material properties, possibly even misleading temperature cycling, be replaced by a more physically meaningful, less expensive and more trustworthy accelerated test vehicle, and could low-temperature/random-vibrations bias be employed in this capacity? The rationale behind such a question has to do with the facts that the highest thermal stresses take place at the lowest temperature conditions, and that fatigue cracks, whether elastic or inelastic, propagate most rapidly, when the material experiences random vibrations. This technique has been already reduced to practice in an industrial lab two years ago.
The objective of the analysis is to shed light, by using analytical (“mathematical”) modeling, rather than widely spread computer simulation, on the mechanical behavior and the underlying physics of failure in the SJI. Future work should focus primarily on experimentations to confirm theoretical findings and recommendations.