Interface Structure of Cu Wire Bonding on Cu Substrate with Sn Plating

Abstract

In previous research on copper wire bonding on a copper substrate with tin plating, suitable thickness and binding conditions for the tin plating were chosen using the peel test after the copper wire bonding. These conditions were determined to be a thickness of 10 mm, a stage temperature of 373 K, a bonding power of 500 to 700 mW and a bonding time of 30 to 50 ms. Cross sectional observations of the bonding interface indicated that the tin layer remained between the copper wire and copper substrate after bonding under these conditions. The purpose of the present study was to evaluate the joint interface structure of the bonded copper wire on the copper substrate with the tin plating. Residual Sn exists locally at the initial bonding interface, and the locations bonded to the interstitial Sn are intermixed with the locations where the Cu wire is bonded to a Cu Sn intermetallic compound. No oxide film layer was found at the bonding interface in the joint between the Cu wire and Cu Sn intermetallic compound; TEM images indicated that these have metallic bonding in which Cu and Cu 3 Sn are directly bonded. This is in contrast to ultrasonic bonding between Cu and Sn, wherein the Cu and Sn are bonded by means of the Sn oxide film.