*Article* **Metallographic Mechanism of Embrittlement of 15** μ**m Ultrafine Quaternary Silver Alloy Bonding Wire in Chloride Ions Environment**

**Jun-Ren Zhao, Fei-Yi Hung \* and Che-Wei Hsu**

Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan **\*** Correspondence: fyhung@mail.ncku.edu.tw

**Abstract:** Chloride ions contained in the sealing compound currently used in the electronic packaging industry not only interact with intermetallic compounds but also have a serious impact on silver alloy wires. A 15 μm ultrafine quaternary silver-palladium-gold-platinum alloy wire was used in this study. The wire and its bonding were immersed in a 60 ◦C saturated sodium chloride solution (chlorination experiment), and the strength and elongation before and after chlorination were measured. Finally, the fracture surface and cross-section characteristics were observed using a scanning electron microscope and focused ion microscope. The results revealed that chloride ions invade the wire along the grain boundary, and chlorides have been generated inside the cracks to weaken the strength and elongation of the wire. In addition, chloride ions invade the interface of the wire bonding to erode the aluminum substrate after immersing it for enough long time, causing galvanic corrosion, which in turn causes the bonding joint to separate from the aluminum substrate.

**Keywords:** silver wire; wire bonding; chloride ions; ion migration; galvanic corrosion
