Abstract
Semiconductor had become one of the most influential sectors among worldwide industries. Among the modern semiconductor IC packaging technologies, wire bonding is the most efficient technique for connecting Integrated Circuit (IC) to the motherboard. Gold wires have been widely utilized as the wire bonding material for decades. However, the rising gold price hindered further applications in electronic devices. The alternative wire bonding materials, such as Cu and Ag, have become potential candidates to replace Au wires. Ag was reported to have profound electrical and mechanical properties. Nevertheless, not many studies have focused on the halogen induced failure mechanism of the Ag alloy wires. In this study, we investigated the failure mechanism of Ag-4Pd alloy wire bonded on Al metallization under acceleration tests and corrosive environments. The samples were conducted with high temperature storage test (HTST) at 150°C for 500 hours and thermal cycle test (TCT) in the range of -55°C to 125°C per 30 minutes for 250 cycles as acceleration tests. The as-bonded samples and the samples after HTST and TCT were further set in the 5% NaCl salt spray chamber for chlorine corrosion test. The as-bonded encountered the fastest failure in the 48 hours to 60 hours interval of salt spray, which the failure at the Al metallization was caused by galvanic corrosion. The failure of the HTST samples occurred at the Ag-Al IMC layer and the bond detached from the bond pad in the 96 hours to 168 hours interval of salt spray. The crack propagated through the IMC layer and separated the IMC into two layers; the upper layer included Ag2Al and Ag3Al, and the lower layer was detected to be Ag3Al2. The ball bond detachment of the TCT samples took place in the 192 hours to 240 hours interval of salt spray. It is possible that a thin layer of IMC and slight cracks formed at the Ag-Al interface during the thermal cycle process act as a barrier to prevent the galvanic corrosion. As a result, the Al metallization was corroded from the edge to the center in a slow rate.