Production Feasiblity of Electrodeposition of Tin-Silver-Copper for Wafer Bump Applications

Increasing requirements for lead-replacement in conventional solders used for flip-chip applications are the main drivers for development of new materials and processes. Besides environmental concerns, deposit characteristics, as well as ease of manufacturability and cost are important factors that need to be taken into consideration when selecting the most appropriate lead-free alternative. A significant amount of work has been done over the last few years in developing lead-free processes. Various tin-rich alloys including pure tin, tin-silver, tin-copper, tin-bismuth and tin-silver copper were already tested. Tin-silver alloys, and especially tin-silver-copper, due to superior solderability and wetting characteristics as well as comparable mechanical properties to eutectic tin-lead deposits, have been identified as the most attractive alternatives to tin-lead systems.

Electrodeposition process is presently known to be the most effective technique of forming wafer bumps for fine pitch applications. Electrodeposition of binary alloys have already been proven in the industry to be production viable, however , when it comes to electrodepositing ternary alloys, there are still concerns surrounding its production applicability. The method of forming ternary tin-silver-copper alloy bumps previously presented in the literature was sequential plating of binary alloys followed by multiple reflow processing.

This paper describes a new process for forming a ternary tin-silver-copper bump through one step electrodeposition. The development of this process has already been presented. This paper will provide additional performance and operating data obtained through production scale evaluation which illustrates the ease of manufacturability, process maintainability and control of such system.