Effects of coupling agent thickness on residual stress in polyimide/γ-APS/silicon wafer joints

The adhesion strength of and the residual stress in pyromellitic dianhydride-4,4' -oxydianiline polyimide (PMDA-ODA PI)/ gamma-APS / silicon wafer joints were investigated for various coating thicknesses of gamma-aminopropyltriethoxysilane (gamma-APS). The largest adhesion strength (780 N/m) was observed in the joint with 11 nm of gamma-APS coating thickness. The residual stress was measured by a He-Ne laser thin film stress analyzer and calculated by a finite element analysis. The residual bending stresses obtained by finite element calculations agreed very well with the experimental results. Residual stress increased with increasing gamma-APS coating thickness.