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58 PCB007 MAGAZINE I JUNE 2018 Feature by Tetsuya Sasamura, Ph.D., Tatsushi Someya, Eriko Furuya, Katsuhisa Tanabe, and Shigeo Hashimoto C. UYEMURA & CO., LTD., HIRAKATA, OSAKA, JAPAN Abstract The characteristics of electroless gold/palla- dium/gold (IGEPIG) deposit, which has been newly developed for fine-line application as electroless nickel-phosphorus (EN) free, has been compared with that of conventional elec- troless Ni-P/Pd/Au (ENEPIG) deposit and elec- troless Pd/Au (EPIG) deposit. The IGEPIG deposit had excellent wire bond- ing reliability (WBR) compared with other de- posits even if the gold thickness of IGEPIG at the top surface was less than that of the EPIG and ENEPIG deposits. From the results of AES analysis after heat treatment for 16 hours at 175°C, Pd and Cu was hardly detected at the top surface of Au, and it indicated that IGEPIG deposit prevented Cu and Pd diffusion. Also, it was revealed by EBSD (electron back scat- ter diffraction pattern) analysis that Pd grain size on Au was about ten times bigger than those on a Pd-activated copper surface. It was assumed that the prevention of Pd and Cu dif- fusion was relative with bigger Pd grain size of IGEPIG deposit. Solder joint reliability (SJR) of IGEPIG de- posit with SAC305 (Sn-3.0Ag-0.5Cu) solder ball is better than that of EPIG deposit, and almost the same with that of ENEPIG depos- it. IGEPIG deposit had excellent pattern ability, because of no EN deposit and Pd activator pro- cess compared with ENEPIG and EPIG. Introduction Recently, the pattern of copper lines and spaces on PCBs has become narrower with the miniaturization of the integrated circuit. If using a conventional ENEPIG process with a nickel thickness of 5–6 µm, it will be easy to cause short circuits between each pattern line because of over-plating. Electroless nickel plat- ing grows both vertically and horizontally, thus increasing the chance of bridging traces when the distance between traces is small. Converse-

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