PCB007 Magazine

PCB-Jan2017

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16 The PCB Magazine • January 2017 by Don Gudeczauskas, Albin Gruenwald and George Milad UYEMURA INTERNATIONAL CORPORATION Abstract The use of electroless nickel/electroless pal- ladium/immersion gold (ENEPIG) has been steadily increasing the past several years and benefits of the finish have now become well- known throughout the industry. The finish pro- vides both reliable solder joints and wire bonds. In some Asian countries where mass production is performed at many facilities, dedicated pro- duction lines have been installed for plating of ENEPIG using an immersion gold optimized for ENEPIG but not for electroless nickel/immer- sion gold (ENIG). In the North American mar- ket, however, many PWB facilities are producing both ENIG and ENEPIG finishes from the same plating line due to lower overall production volumes and desire to use the same immersion gold for both finishes. Most facilities have nei- ther the room for two separate immersion golds nor the desire to tie up capital with the cost of gold for two separate immersion gold tanks. The challenge for North American manufactur- ers has been in choosing the proper immersion gold chemistry which can suitably deposit gold for ENIG and ENEPIG while providing a robust finish for soldering, wire bonding, and electrical contact with both finishes. This paper presents results of a comparative study on three types of immersion golds which could be used for both ENIG and ENEPIG de- posits in the same production line: standard displacement immersion gold, high efficiency immersion gold which limits nickel dissolution, and a mixed reaction immersion gold which utilizes a mild reducing agent. Comparative results for solder wetting force, solder joint reli- ability and wire bonding will be presented for ENEPIG. Additionally, plated samples will be examined by SEM for evidence of nickel or pal- ladium damage from the immersion gold plat- ing operation. Introduction Recently, it is well-known that the electro- less ENEPIG process has excellent solder joint reliability (SJR) and that it has the same wire bond reliability (WBR) compared to electroless Ni/Au with thicker Au (ENAG) process, even if FEATURE

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