Reliability Properties of Solderable Conductive Adhesives with Low-Melting-Point Alloy Fillers

Abstract

A solderable conductive adhesive (SCA) using low-melting-point alloy (LMPA) filler was developed to overcome the limitations of conventional electrically conductive adhesives (ECAs), which include their low electrical conductivity, increased contact resistance, and low joint strength. The SCA formed good metallurgical conduction path between the corresponding electrodes due to the rheology-coalescence-wetting behaviors of molten LMPA fillers in SCA. This study examined the reliability of SCA assembly through the thermal shock test (218 to 398 K, 1000 cycles) and the high temperature and high humidity test (358K/85% RH, 1000 h). The electrical resistance of the SCA assembly with metallurgical interconnections was much more stable than those with conventional ICAs. Before the reliability tests, a scallop-type Cu6Sn5 (eta-phase) intermetallic compound (IMC) layer was formed on the Sn-plated Cu lead/LMPA and LMPA/Cu metallization interface based on the results of interfacial microstructure observations of quad flat packages (QFPs) that were assembled with SCA. After the reliability tests, the thickness of IMC layer increased with time, and Cu6Sn5 (eta-phase) and Cu3Sn (epsilon-phase) were formed. In addition, the fracture surface exhibited a cleavage fracture mode with the fracture propagating along the Cu-Sn IMC/Sn-Bi interface. These results demonstrate that SCA assembly with metallurgical interconnection has stable electrical and mechanical bonding characteristics.