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The electrodeposition behavior of Sn–Cu alloys in a sulfate solution containing three additives, cresol sulfonic acid, benzal acetone, and nonionic alkyl polyethylene glycol ether surfactant, was investigated potentiostatically between +0.3 and � 0:7 V vs. NHE at 298 K. The contact resistance of the alloys deposited on a Cu connector was evaluated. Cu in the alloys behaved as a more noble metal than did Sn, thus showing the typical feature of regular-type codeposition. In solutions containing additives, the difference in deposition potential between Cu and Sn decreased because Cu deposition was significantly suppressed by the additives. The alloys deposited in solutions containing additives exhibited smooth surfaces and were composed of Cu, Sn, Cu6Sn5, and Cu3Sn phases in accordance with the equilibrium phase diagram of a binary Cu–Sn system. The contact resistance of the alloys increased by heating at 433 K, thus indicating that connecting reliability did not improve by plating with the stable metallic compound Cu6Sn5. The connecting reliability of a connector after abrasion was higher in deposited alloy films than in Sn reflow plating. [doi:10.2320/matertrans.M2011022]

Electrodeposition behavior of Sn–Ag alloys was investigated at current density 1–1000 A·m−2 in both sulfate and pyrophosphate-iodide solutions at 298 K, and the contact resistance of Sn–Ag alloys deposited on a Cu connector was evaluated. In both solutions, Ag behaved as a more noble metal than Sn, showing regular codeposition. The difference in deposition potential between Ag and Sn was 0.4 V in the pyrophosphate-iodide solution and 0.2 V in a sulfate solution containing thiourea as a complexing agent for Ag+ ions. The deposits obtained from a pyrophosphate-iodide solution consisted of blocks of a few microns in size, while those from a sulfate solution exhibited grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of an Ag3Sn intermetallic compound and Sn. This is in accordance with the equilibrium phase diagram of the binary Ag–Sn system. The contact resistance of deposited Sn–Ag alloys, after heating at 433 K for 120 h, was slightly smaller at Ag content below 45 mass% than that of reflow Sn plating. The connection reliability of connectors after abrasion was better in deposited films of Sn–Ag alloys than in those with reflow Sn plating.

Electrodeposition behavior of Sn-Ag alloys was investigated at 1 to 1000 A/m2 in both sulfate and pyrophosphate-iodide baths of 298 K, and the contact resistance of Sn-Ag alloys deposited on Cu connector was evaluated. In both baths, Ag behaved as more noble metal than Sn, showing the typical feature of regular type codeposition. The difference of deposition potential between Ag and Sn was 0.4 V in pyrophosphate-iodide bath, while it was 0.2 V in sulfate bath containing thiourea as complexing agent for Ag+ ions. The deposits obtained from pyrophosphate-iodide bath consisted of blocks of a few micron in size, while those from sulfate bath showed grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of Ag3Sn metallic compound and Sn in accordance with the equilibrium phase diagram of binary Ag-Sn system. The contact resistance of deposited Sn-Ag alloys after heating at 433 K for 120 hours was somewhat smaller at Ag contents less than 45 mass% than that of reflow Sn plating. The connecting reliability of connector after abrasion was better in deposited films of Sn-Ag alloys than in reflow Sn plating.