Finite element simulation of the fatigue behaviour of a MEMS package

Finite element analysis (FEA) was carried out to analyse the reliability of the solder sealing of a ceramic based vacuum package under the combined effect of atmospheric pressure loading and thermal cycling. The study focused on the effect of cooling history and geometry on the fatigue life of the solder estimated using Engelmaier's correlation [1] involving shear strain range. The fatigue life predictions suggest a very slight effect of atmospheric pressure exerted on the package lid on fatigue life, suggesting that fatigue life is still largely determined by the thermal mismatch between silicon and ceramic. However, fatigue life was found to be significantly affected by the length of time the solder was left to creep before thermal testing, and this is often an overlooked factor in fatigue life estimation. Another interesting result is that the two sides of the package have similar fatigue lives.