Solid-liquid reaction-diffusion bonding using tin film was applied to bond copper, which is a candidate for the die-bond process used in assembling next-generation power devices. Sn-Cu intermetallic compounds formed and grew even during temperatures reaching the melting point of Sn. Eventually, a sound bond layer that was composed of Cu3Sn with some small voids was obtained after complete reaction-diffusion. When the Sn phase remained in the bond layer due to insufficient reaction-diffusion, relatively large defects formed there. Spherical defects also formed in the bond layer when the electroplated Sn film was used as an interlayer, owing to the large amount of gas generated from the film.
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