Interlayer Material Design Reducing Transient Liquid Phase Bonding Time

Abstract

Power semiconductors require a large bonding area for die attachment. For this purpose, transient liquid phase bonding (TLPB) was applied using fabricated interlayers, namely Sn–3Cu and Sn–10Cu, to study the intermetallic compound (IMC) formation, and the results were compared with those obtained with a pure-Sn interlayer. The Sn–3Cu and Sn–10Cu interlayers exhibited primary IMC fraction of 0.06 and 0.24, respectively, before the TLPB. For a Cu/interlayer/Cu sandwich structure, the TLPB was applied at 250 °C over various time periods (1–4 h). A reduction in the bonding time was more significant for a Sn–10Cu interlayer with a larger amount of primary IMCs than for the Sn–3Cu interlayer. The time exponent of the IMC fraction with respect to the bonding time was approximately 0.3 for all interlayers. This implies that the IMC growth mechanism is governed by a liquid channel or wet grain boundary diffusion. The nearly constant fraction and increasing size of the primary IMCs produced during the TLPB indicate that the primary IMCs coalesced during this process. The primary IMCs preferentially coalesced with the interface IMCs produced during the TLPB when they had the same crystalline orientation.