Formation and Growth of Intermetallics in an Annealing-Twinned Ag-8Au-3Pd Wire Bonding Package During Reliability Tests

Wire bonding on Al pad packages with an innovative annealing twinned Ag-8Au-3Pd alloy wire results in a sufficient interfacial intermetallic layer at the initial as-bonded stage, while its growth during the further temperature cycling test and pressure cooker test is very slow. Even after prolonged high-temperature storage at 150°C for 500 h, the thickness of its intermetallics is only around 1.7 μm. In contrast, a very thin CuAl₂ intermetallic layer appears at the interface of the Pd-coated Cu wire bonded package, and a thick layer of Au₈Al₃ intermetallic compounds forms in the Au wire package, which grows to a thickness of around 4.0 μm after high-temperature storage at 150^°C for 500 h. Energy dispersive X-ray spectrometry analyses indicate that AgAl₂, Au₈Al₃, and CuAl₂ are the main intermetallic phases formed in the packages bonded with Ag-8Au-3Pd, and Au and Pd-coated Cu wires, respectively. However, an additional Pd-containing Ag₂Al layer found at the AgAl₂/Al interface of Ag-8Au-3Pd wire bonded package can interrupt its intermetallic reaction, and the annealing twins can further slow the intermetallic growth.