Fast formation of Cu-Sn intermetallic joints using pre-annealed Sn/Cu/Sn composite preform for high-temperature bonding applications

Abstract

This paper presents the interfacial reaction and growth rate of Cu-Sn intermetallic compounds (IMCs) for various aging times in a composite preform for a die-attach material at high temperature. The feasibility of the composite preform we fabricated for power electronic applications to reduce the long bonding time of transient liquid phase (TLP) bonding was evaluated in this work. After the plating process, the composite preform was composed of Sn layers at both sides of the Cu core layer and the Cu layer. In terms of the aging treatment, the IMC layer was formed rapidly at the Cu-Sn interface in the composite preform by consuming the Sn layers, and the reduction and growth rates of Cu and Cu3Sn were calculated, respectively. We performed the TLP bonding process at 270 °C using various aged composite preforms. The Cu-Sn IMC was formed rapidly on both sides adjacent to the Cu core layer. The thickness of Cu decreased as the aging time elapsed. Therefore, the amount of Cu3Sn adjacent to the Cu core layer increased and the amount of Cu6Sn5 rapidly increased, simultaneously. We investigated the thicknesses and variations of the phase of the joint in the composite preform during the aging treatment process and sequential TLP bonding process for various times. We fabricated pre-annealed Sn/Cu/Sn preforms and performed fast Cu-Sn TLP bonding for high temperature power electronic applications.