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

摘要

Increasing requirement for lead-replacement in conventional solders for flip-chip applications are the main drivers for development of new materials and processes. In addition to environmental concerns, deposit characteristics, 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 tinsilver- copper (SnAgCu or SAC) have been identified as the most attractive alternatives to tin-lead systems due to their superior solderability and wetting characteristics, as well as comparable mechanical properties to eutectic tin-lead deposits. Electrodeposition is presently known to be the most effective technique for forming wafer bumps for fine pitch applications. Electrodeposition of binary alloys has already been proven in industry to be production viable, however, when it comes to electrodepositing ternary alloys, there are still concerns surrounding its production applicability. The method for forming ternary SAC alloy bumps previously presented in the literature was by sequential plating of binary alloys followed by multiple reflow processing. This paper describes a new process for forming a ternary SAC bump through one step electrodeposition. The development of such a system has already been presented. This paper will provide additional performance and operating data obtained through production scale evaluation which further illustrates the ease of manufacturability, process maintainability and control of such systems.