Investigation on thermal stress of bondline based on Cu@Sn preform at high temperature application

Abstract

This paper is devoted to study the thermal stress of a novel bondline based on Cu@Sn preform and analyze the failure mode of solder joint and SiC module. The 2D simplified model of chip-DBC substrate was created, according to the stress evaluating equations, the interfacial peel stress of chip-solder and solder-substrate was numerically calculated, and the stress distribution was imitated by ANSYS software, the results revealed that the peel stress mostly concentrated on the corners of the joint, and decreased with increased joint thickness, the peel stress could be negligible when joint thickness was greater than 50μm. Compared to the high-lead alloy system and sinter nano-silver system, the three-dimensional network structure bondline based on Cu@Sn possessed the minimum tensile stress (3MPa) and compress stress (15MPa). The multi-layer model of SiC module was built to study the influence of bondline layer thickness variation on module reliability, the result indicated that the chip stress was little dependent on the soldering layer thick, and the module stress bonded by the novel bondline was slightly larger than that of high lead system and sintered Ag system. The favorable thick bondline based on Cu@Sn preform was experimentally proved to have better mechanical strength. Shearing strength of the joint at room temperature was up to 49.5MPa, thermal cycling from -70 to 200 for 100cycles, there was no crack available on the joint, due to the pore volume got bigger, shear strength got smaller, the bondline could still function well for mechanical support.