The investigation of high temperature joint generated by low temperature process

A number of new bonding techniques are emerging with the development of three dimensional (3D) stacking packaging. High temperature joint generated by low temperature process with traditional soldering process was one of the approaches to meet the bonding requirement for 3D packaging. Cu/Cu was bonded with joint gap of 100 micros and 60 micros via a layer of Sn plated on the Cu surface. Coupons were fluxed and reflowed at 250°C with different times. The effect of relative IMC thickness on the shear properties was studied. It was revealed that a lacking of ductility for all the Cu/Sn/Cu bondings even IMC was extremely thin. When intermetallic compound grew thicker and gradually dominated the interface, a corresponding increase of shear strength was observed. The shear on IMC (60 micros gap, reflow 12 hours) showed the highest shear strength but a brittle rupture feature. This work enlightened an approach on the evaluation of thin film interfacial strength and also provided an insight into 3-D stacking packaging design.