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A Study on Solderability of Sn-Ag-Cu Solder with Plated Layers in $\mu-BGA$  

신규식 (전자부품연구원 마이크로신연구센터)
정석원 (서울시립대학교 재료공학과)
정재필 (서울시립대학교 재료공학과)
Publication Information
Journal of Welding and Joining / v.20, no.6, 2002 , pp. 783-788 More about this Journal
Abstract
Sn-Ag-Cu solder is known as most competitive in many kinds of Pb-free solders. In this study, effects of solderability with plated layers such as Cu, Cu/Sn, Cu/Ni and Cu/Ni/Au were investigated. Sn-3.5Ag-0.7Cu solder balls were reflowed in commercial reflow machine (peak temp.:$250^{\circ}C$and conveyer speed:0.6m/min). In wetting test, immersion speed was 5mm/sec., immersion time 5sec., immersion depth 4mm and temperature of solder bath was $250^{\circ}C$. Wettability of Sn-3.5Ag-0.7Cu on Cu, Cu/Sn ($5\mu\textrm{m}$), Cu/Ni ($5\mu\textrm{m}$), and Cu/Ni/Au ($5\mu\textrm{m}/500{\AA}$) layers was investigated. Cu/Ni/Au layer had the best wettability as zero cross time and equilibrium force, and the measured values were 0.93 sec and 7mN, respectively. Surface tension of Sn-3.5Ag-0.7Cu solder turmed out to be 0.52N/m. The thickness of IMC is reduced in the order of Cu, Cu/Sn, Cu/Mi and Cu/Ni/Au coated layer. Shear strength of Cu/Ni, Cu/Sn and Cu was around 560gf but Cu/Ni/Au was 370gf.
Keywords
$\mu-BGA$; Pb-free solder; Sn-3.5Ag-0.7Cu; Joint strength; Microstructure;
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