自動車接点材料用の Sn-Cu 合金電析とその電気的接続性

Abstract

Electrodeposition behavior of Sn-Cu alloys was investigated potentiostatically at 0.3 to −0.7 V vs. NHE and 298 K in sulfate bath containing additives of cresol sulfonic acid, benzal acetone and nonionic alkyl polyethylene glycol ether surfactant, and the contact resistance of Sn-Cu alloys deposited on Cu connector was evaluated. Cu behaved as more noble metal than Sn, showing the typical feature of regular type codeposition. In solution containing additives, the difference of deposition potential between Cu and Sn became small because Cu deposition was suppressed by the additives. The Sn-Cu alloys deposited from solution containing additives showed smooth surface. The deposited Sn-Cu alloys were composed of Cu, Sn, Cu6Sn5 and Cu3Sn phases in accordance with the equilibrium phase diagram of binary Cu-Sn system. The contact resistance of deposited Sn-Cu alloys increased by heating at 433 K, showing no improvement of connecting reliability by plating the stable metallic compound of Cu6Sn5. The connecting reliability of connector after abrasion was better in deposited films of Sn-Cu alloys than in reflow Sn plating.