Effect of Au Coating on the Electrolytic Migration of Ag Bonding Wires for Electronic Packaging Applications

Abstract

Ag-based bonding wires were generally accepted as the most promising material to substitute for Au bonding wires, however, the electrolytic migration concern of Ag limited its industrial application in electronic packaging, especially in ultra-fine pitch wire bonding. In the present study, the electrolytic migration behaviors of Au-coated Ag bonding wires and Ag wires were studied through water drop tests. The dendrites’ growth and morphology evolution were investigated by in-situ optical microscope observation and the microstructure of the cathodic and anodic bonding wires were characterized by scanning electron microscope test. It could be seen that when comparing Au-coated Ag bonding wires with Ag wires, the dendrite assembled by a large number of Ag nanoparticles grew much more slowly from cathode to anode. The Ag2O particle layer on the anodic wires was thinner, the dendrite contact time was delayed and the current densities at the dendrite contact time were much smaller when the Au coating layer exist. The above results show that Au coating could act as a barrier to inhibit electrolytic migration, which has contributed to electronic packaging applications of Au-coated Ag bonding wires.

Research Progress on Bonding Wire for Microelectronic Packaging

“…For decades, it has been known that Ag + migration can cause short circuits and failure in microelectronic interconnects [ 159 ]. In order to inhibit Ag + migration to improve bonding reliability effectively, the experimental results showed that the addition of 1.5–4.5 wt% Pd can decrease the Ag + migration rate [ 160 ], and the effect is further enhanced due to the Au addition [ 161 , 162 ]. Cho et al [ 163 ] confirmed that a PdO layer forms on the surface Pd-doped Ag wire, which acts as a barrier against Ag + migration and diffusion to prevent Ag from dissolving in the surrounding water, as shown in Figure 15 .…”

A Review of Silver Wire Bonding Techniques

“…For surface atomic diffusion, this phenomenon can be improved by surface treatment, such as coating a layer of Au, Cu and other metals onto the surface or using chemical reactions to passivate the surface. Xiao et al [79] mention that when Au coating is present, the Ag 2 O particle layer on the anode line becomes thinner, the dendrite contact time is delayed, and the current density during dendrite contact is also greatly reduced. These effects can inhibit electrolytic migration and contribute to the application of gold-plated silver bonding wires in electronic packaging.…”