Low temperature transient liquid phase bonding of copper

Abstract

This thesis describes a Pb-free solder alternative that is capable of fluxless bonding. The main advantage of this process is that it offers the benefits of low fabrication temperature (125⁰C) while producing a joint capable of withstanding low stresses at very high service temperatures (300⁰C+). The ternary alloy system of Bi-In-Sn was investigated in the bonding of copper substrates. All bonds were made at 125⁰C with 25psi of fixturing pressure. Primary solidification was observed in as little as 15 minutes. The mechanical properties of the joints were shear tested both at room temperature and at 1000C to simulate a conventional service environment. With sufficient dwell time ([approx.] 250h), joints would not fail in shear even at stresses that caused significant substrate deformation. Scanning electron microscopy was used to examine the joints and the evolution of the diffusion process.