Formation of SnAg solder bump by multilayer electroplating

A novel method, multilayer electroplating, was proposed to prepare alloy bumps. It consists to electroplating different structural elements of alloys sequentially and then forming uniform alloy through reflowing. The formation of eutectic SnAg alloy bumps was taken as an example to verify the applicability of the method in this study.Near-eutectic SnAg solder bumps were formed successfully through multilayer electroplating. After reflowing for 1 min at 250 °C, SnAg alloy with homogeneous structure and composition was obtained from multilayer structure. Fine Ag3Sn particles with uniform distribution were precipitated inside the solder and Cu6Sn5 intermetallic compounds (IMCs) in scallop-like shape formed at the SnAg solder/Cu interface. As reflow time increasing, the morphology of Ag3Sn remained unchanged but the thickness of Cu6Sn5 layer increased. The characteristic of multilayer electroplated SnAg solder bumps was similar to that of traditional alloy, which indicated that it was a suitable method to form SnAg alloy solder bumps.

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► A novel method, multilayer electroplating, was proposed to form alloy bumps.
► The method had precise control of composition ratio and simple processing technique.
► After reflowing, SnAg bumps with homogeneous structure and composition were obtained.