A study of residual stress effects due to adhesive bonding of MEMS components

Residual stress effects in MEMS wafer adhesive bonding were investigated. A wafer-level finite element (FE) modelling approach was used, which accounted for wafer configuration and allowed the deformation of individual devices across a wafer to be considered. A specific test was carried out to determine the adhesive's viscoelastic response, through an effective time-dependent Young's modulus, so that initial and longer-term post-curing responses could be estimated. These results are compared with predictions based on modulus values obtained from Dynamic Mechanical Analysis (DMA) testing. The predicted wafer deformations are compared with optical surface profile measurements of actual specimens. Initial response predictions using the effective modulus show excellent agreement with measurements, while the DMA modulus gives a significant underestimate. On the other hand, difficulty was found in modelling long-term relaxation, due to non-linear mechanisms such as polymer "ageing" which are harder to model.