Development of Flux-Free Reflow Soldering Process Using Hydrogen Radicals
Development of Flux-Free Reflow Soldering Process Using Hydrogen Radicals
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利用氢自由基开发无助焊剂回流焊工艺
DOI：
10.1109/ectc.2005.1441347
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
T. Takeuchi
中科院分区：
文献类型：
--
作者：
M. Suenaga;T. Nakamori;D. Hirakawa;Y. Ohno;T. Hagihara;J. Kagami;T. Takeuchi
研究了一种应用于倒装芯片（FC）和芯片级封装（CSP）的氢自由基无焊剂回流焊工艺。将400 μ m直径的Sn/37 Pb（质量%）共晶焊料和Sn/3.0 Ag/0.5 Cu（质量%）无铅焊料球安装在FR-4板的焊盘镀覆Cu/Ni/Au上，并在不同条件下照射氢自由基，并在230 ℃下回流。为了研究焊球表面氧化膜的最佳去除条件，在铜基板上进行了铺展试验。为了确认氢自由基的影响，比较了无焊剂和使用焊剂的基底。辐照条件是衡量焊料的液相对焊料的固相。结果表明，Sn/37Pb和Sn/3.0Ag/0.5Cu的焊点剪切强度与使用助焊剂的常规氮气回流焊相当，说明氢自由基清除了焊料表面的氧化膜，获得了良好的焊点。然而，在液相氢自由基照射的情况下，即使不使用助焊剂，焊料中也会产生空隙。在此基础上，开发了直径为80 μ m的Sn/3.5Ag（mass %）焊料凸点的单面和双面回流焊工艺。通过氢自由基的辐照，去除了电镀焊料凸点上的氧化膜，得到了形状良好的焊料凸点。在双面回流焊下，氢自由基可以进入封装与基板之间约80 µ m的差距内，成功地实现了回流焊。
A flux-free reflow soldering process using hydrogen radicals was investigated for application to flip chip (FC) and chip scale package (CSP). 400µm diameter Sn/37Pb(mass%) eutectic solder and Sn/3.0Ag/0.5Cu(mass%) lead free solder balls were mounted on the pad plated Cu/Ni/Au of FR-4 board, and were irradiated hydrogen radicals under varying conditions, and were reflowed at 230 deg/C. In order to research the best removal condition of oxide film on solder balls, spread tests were conducted on Cu substrate. To confirm the effect of hydrogen radicals, flux-free and flux used substrates were compared. The irradiation conditions were weighed liquid phase of solder against solid phase of solder. In these results, solder joints in both Sn/37Pb and Sn/3.0Ag/0.5Cu have similar shear strength to conventional nitrogen reflow using flux, which shows that hydrogen radicals remove the oxide film on solder and the sound bonds are got. However, in case of hydrogen radicals irradiation at liquid phase, voids are generated in solder even without usage of flux. Hydrogen radicals irradiation at solid phase did not generate any voids, and the best irradiation condition to get good shape solder ball was found. As an application of this work, single and double side reflow process with 80µm diameter plated Sn/3.5Ag (mass%) solder bump were developed. For the irradiation of hydrogen radicals, the oxide film on plated solder bump were removed, and good shape solder bumps were produced. Under the double side reflow, hydrogen radicals can go into the gap about 80µm between package and substrate, and it was reflowed successfully.