Lead-free coatings in high speed electronic connectors

As a result of legislative pressures and customer demands, the connector industry is at a crossroads with respect to the selection of tangible lead-free coatings. The materials, component finishes and processes that make up the backbone of electronic assembly operations pose challenges to connector manufacturing companies. Lead-free solders and coatings require higher assembly processing temperatures. Consequently, plastics, printed circuit boards and connector housings must in turn be evaluated to determine if higher temperatures can be tolerated. Two lead-free coatings, pure tin and tin-copper, have been proposed as possible alternative surface finishes to tin-lead. Whisker formation in these coatings is also a major concern. Higher reflow temperatures pose another concern because of questionable dimensional stability of resin materials. This paper critically examines the application of matte tin and bright tin-copper chemistries with respect to process applications in high-speed reel-to-reel operations. Results of process parameters, metrology, deposit characteristics, solderability, propensity of whisker formation and its mitigation are discussed in detail. In order to cope with higher solder temperatures and meet the challenges that arise from use of lead-free coatings, suitable resins for connector housings are proposed.