Mechanical behavior and reliability of solder joint interconnections in thermally matched assemblies

It is pointed out that matched thermal expansion (contraction) between soldered components should result in a more reliable solder joint interconnection. The author investigates, both theoretically and experimentally, the mechanical behavior and reliability of such interconnections in application to silicon-on-silicon flip-chip technology. The study is limited to the case of the uniform change in temperature (thermal cycling conditions), so that the stresses and strains in the solder joints are caused exclusively by the mismatch between the solder material and silicon. In the theoretical analysis the author considers an axially symmetric elastic problem for a finite circular cylinder whose end planes are subjected to identical radial deformations. The solution obtained is used to evaluate the magnitude and the distribution of the low-temperature strains and stresses in solder joints in a flip-chip package design and to assess the effect of the diameter-to-height ratio on the strains and stresses. The main objectives of the experimental investigations were to identify the potential reliability problems, as well as to accumulate reliability statistics. It is concluded that application of thermally matched assemblies results in a rather reliable interconnection, although it should be be regarded as a panacea for mechanical problems