SMTA International Conference Proceedings


AN EXPERIMENTAL STUDY OF PRESS-FIT INTERCONNECTION ON LEAD FREE PLATING FINISHES

Authors: Ila Pal and Elena Smolentseva
Company: Ironwood Electronics, Inc.
Date Published: 9/24/2006   Conference: SMTA International


Abstract: Precision machined pins have traditionally been used to interconnect discrete signals and power connection from the device to system and system to system. The pins are machined to specific geometry that allows them to press-fit into the plated through holes of the complex system boards. A major recipient of press-fit pin applications is rigid backplanes and other PCB interconnect products. The fabrications of large, thick PCB panels push the limits of electroplating and solder processing steps. These panels, exceeding 40 layers, and being larger than 50x50 inches in size having a thickness of over half inch, and weighing over twenty five pounds are crying for an alternative to HASL (Hot Air Solder Level) plating finish which is RoHS (Restriction of Hazardous Substances) compliant. The intention of this proposed paper is to compare press-fit interconnect technology on four different lead free plating finishes. A substrate that can withstand higher processing temperature was selected. The substrate thickness and pin geometry used in the experiments were kept constant. Plating thickness and plating composition were considered as variables. The four different plating finishes selected were ENIG (Electro less Nickel over Immersion Gold), Immersion Silver, Immersion Tin, White Tin. Experimental test results include continuity resistance measured using 4- wire setting, thermal cycling, insertion and extraction force characteristics, analysis of micro-sectioned samples and endurance characteristics. Effects of “cold welding” due to similar metals in contact, tin whiskers, gold embrittlement, and black pad scenarios will be addressed also.

Key words: press-fit terminal, RoHS, lead free, plated through hole, interconnection, testing standards, Kelvin measurements, pin retention force.



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