Effects of metallization characteristics on gold wire bondability of organic printed circuit boards

Abstract

Organic printed circuit boards (PCBs) with Au/Ni plates on bond pads are widely used in chip-on-board (COB), ball grid array (BGA), and chip-scale packages. These packages are interconnected using thermosonic gold wire bonding. The wire bond yield relies on the bondability of the Ni/Au pads. Several metallization parameters, including elemental composition, thickness, hardness, roughness, and surface contamination, affect the success of the solid state joining process. In this study, various characterization and mechanical testing techniques are employed to evaluate these parameters for different metallization schemes with varying Ni and Au layer thicknesses. The pull force of Au wires is measured as a function of plasma treatment applied before wire bonding to clean the bond pads. Close correlations are established between metallization characteristics and wire bond quality.