Effect of Au Addition on the Microstructure and Properties of Ag-4Pd Bonding Wires

• DOI: 10.1007/s11661-018-4841-7
• Publication Date: 2018-07-26T18:07:50Z
• Authors: Bing-Hau Kuo; Du-Cheng Tsai; Yen-Lin Huang; Po-Chun Hsu; Tung-Han Chuang; Hsing-Hua Tsai; Fuh-Sheng Shieu
• Keywords: 0103 physical sciences; 01 natural sciences

Silver-based bonding wires such as Ag-4Pd and Ag-8Au-3Pd have drawn remarkable attention in the packaging industry because they are cheaper and more conductive than Au- and Cu-based wires, respectively. This study aimed to investigate the intermetallic compound (IMC) formation and growth at the bonding interface between Ag-4Pd wire and Al-pads and between Ag-8Au-3Pd wire and Al-pads. The as-bonded and reliability-tested Ag-4Pd/Al and Ag-8Au-3Pd/Al specimens were then investigated by transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (STEM-EDS). The bonding properties were examined by ball shear and wire pull tests. In the as-bonded state, hexagonal close-packed (HCP) (Ag, Pd)2Al and HCP Ag2Al were formed at the Ag-4Pd/Al interfaces, whereas dual phase consisting of face-centered cubic Ag alloy with HCP precipitates (Ag, Au, Pd)2Al crystals and HCP Ag2Al layers were observed at the Ag-8Au-3Pd/Al interfaces. The IMCs showed significant growth and oxidation during reliability tests at 130 °C and 85 pct relative humidity for 192 hours. Alloying Au in Ag-4Pd wires promoted the growth of the IMC layer and it also enhanced the mechanical properties in the as-bonded material. By contrast, overgrowth of the IMCs in the Ag-8Au-3Pd/Al system induced microcrack formation in bonding and thus degraded the reliability of the material.