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Evaluation of Electroless Nickel Electroless Palladium (ENEP) finish as a replacement for Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) for Gold Wirebonding and SAC305 Solderability
Keywords: Lead Free solder, nickel electroless , wirebonding
Majority of the DRAM industry today has transformed from aluminum to copper based metallization. However this transition came with a price. Due to the high tendency of copper to oxidize, it needs to be protected by an under bump metallurgy (UBM) which not only protects the surface from oxidation but further aids in wire bonding and solder attach. UBM generally comprises of electroless nickel immersion gold (ENIG) finish or electroless nickel electroless palladium immersion gold (ENEPIG) finish. With the sky rocketing price of gold and DRAM becoming a commodity product, OEMs are looking in all directions to reduce manufacturing costs. In that aspect removing the immersion gold layer from the UBM and reducing the finish to ENEP only can provide substantial savings. This study shows the comparison between an ENEPIG and ENEP finish used in a standard wire bonded chip on board (COB) package as well as solder based flip chip interconnection. Side by side comparison is shown for each finish’s interaction with gold wire and 96.5%Tin-3%Silver-0.5%Copper (SAC 305) solder. Mechanical (wire pull, ball shear) and high temperature storage testing was performed to determine the reliability of each finish over time. Micro structural study over multiple reflow times and high temperature aging was also performed using scanning electron microscopy (SEM/EDS) and auger electron spectroscopy (AES). The intermetallic compound (IMC) formation is very well in agreement with the literature. Overall, results show that ENEP finish has a high potential to replace ENEPIG finish. Keywords: Lead Free solder, electroless nickel electroless palladium immersion gold, wirebonding Originally sent to Pb-Free #1
Jaspreet Gandhi, Packaging Materials Engineer
Micron Technology Inc.
Boise, ID

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