Effect of the direct current on microstructure, tensile property and bonding strength of pure silver wires

Abstract

In the microelectronics assembly and packaging industry, the wire bonding has become an important process to connect lead frames and pads. In the past, gold and copper were the main materials of wire bonding. However, the cost of gold wires is getting higher nowadays and yet wire bonding cannot be wholly replaced by copper wire; thus silver wires become a novel bonding material in recent years. The reliability test of wires was a static method; this study leads electrical current into the wires to estimate the structural changing and interface properties of Al pads (positive and negative pad). After leading 90% critical fusing current density (CFCD) into a 23μm silver wire, some grains of silver wire had grown up and formed into equal-diameter grains (EDG). After the current test, the fracture position of bonded wires moved from heat affect zone (HAZ) of electric flame-off (EFO) to the neck of HAZ. Otherwise, the current test would reduce the tensile strength of wire. The bonding strength of the positive pad was lower than that of the negative pad. The intermetallic compound (IMC) of bonding interface was AgAl2.