Microstructural evaluation and failure analysis of Ag wire bonded to Al pads

• The phases of Ag–Al IMCs were characterized as Ag2Al and Ag3Al.
• The growth rates of IMCs were measured.
• The moisture and Cl− ion in EMC caused micro-crack and resistive layer.

We found the failure mechanisms in Ag wire bonded to Al pads during the high-temperature-storage lifetime test (HTST) and the unbiased highly-accelerated temperature and humidity storage test (uHAST). The native oxide layer on the Al pads caused a ball lift. The moisture and the thermal energy during uHAST along with the Cl− ion in epoxy molding compounds (EMCs) induced repetitive oxidation and reduction reactions of the Ag–Al intermetallic compounds (IMCs) with the Al pads. These repetitive reactions formed H2 gas as a by-product causing the formation of a micro-crack. In addition, the alumina layer acted as a resistive layer in the Ag–Al IMCs. The phases of the Ag–Al IMCs were identified as Ag2Al and Ag3Al, and the growth rates of those IMCs were measured at 150 and 175 °C for 2000 h.