The reaction between Br resins and Au_4Al intermetallic compound layer at the Au-Al bond interface has been observed when the semiconductor device is used at high temperatures. Au_4Al is annealed at 573 K for 2 hours with Br resin encapsulation, and microstructures and chemical compositions of the corroded layer have been investigated with TEM and EDX. In the corrosion layer, black island-shape phase with fcc structure and white amorphous phase have been found out. The former one was considered to be Au phase and the latter one amorphous phase of Al-Br-O system. The hardness of the corrosion layer and the Au_4Al are 98 Hv and 192 Hv, respectively. Therefore, it can be considered that the formation of the Au phase and the Al-Br-O amorphous phase contribute to the reduction of the mechanical property during the annealing.
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