Thickness effects of coupling agent on residual bending stress were investigated in $Polyimide/SiO_2$ joints during thermal cycling. Thickness and peel strength of $gamma$-APS coupling agent were measured and correlated with solution concentration and residual bending stress. The variation of residual bending stress with temperature was also measured for various thicknesses of the coupling agent. Finite element results were compared with experimental data for residual bending stress in $Polyimide/SiO_2$ joints.