Abstract: The relation between solder thickness and the growth behavior of IMC during HTS (high-temperature storage) aging was investigated with Cu/SAC305/Cu sandwich structures at different solder thicknesses (15~50 μm).The results indicated that the solid state diffusion of interfacial elements is greatly dependent upon solder thickness during HTS aging.The thinner the solder layer is,the faster the Cu₃Sn layer grows,which leads to a thickness ratio decrease of Cu₆Sn₅/Cu₃Sn after HTS aging at 160℃.The growth rate of IMC layer (Cu₆Sn₅ layer + Cu₃Sn layer) also decreases with the decrease of solder thickness during HTS aging.The diffusion coefficient is in relation with the size of solder layer.Further data correlating indicates that the alternation regularity between diffusion coefficient and solder thickness is approximately accordance with parabolic correlation.