Evolution of curvature under thermal cycling in sandwich assembly bonded by sintered nano-silver Paste

An optical measurement system was developed to study the residual curvature of sandwiched assembly bonded by three different kinds of die-attachment materials, i.e., nano-silver paste, Pb/Sn solder, and SAC305, in this paper. Effect of bondline thickness on thermal residual stress in the assembly was investigated. The curvatures of the assemblies were found significantly decreased when increasing the bondline thickness. We found that all the sandwiched assemblies at ambient temperature concave towards the alumina side and the residual bending was relieved as the temperature rose. It also turned out that the residual curvature in the assembly grew as the joint size increased. The residual bending in nano-silver assembly fell in between those of Pb/Sn solder and lead-free solder, SAC 305 (Sn96.5Ag3.0Cu0.5). The influence of temperature cycling in the range of -40°C to 125 °C on the thermal residual stress of the sintered nano-Ag was also studied. The severity of the residual curvature in all the structures was mitigated to some extent with increasing number of cycles.