Fundamental study of 95 high-lead solder bump on substrates pre-soldered with eutectic PbSn

2009 4th International Microsystems, Packaging, Assembly and Circuits Technology Conference Pub Date : 2009-10-01 DOI:10.1109/IMPACT.2009.5382312

Chih-Chiang. Chang, Chun-Cheng Lin, C. Kao

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Abstract

This study investigated the intermixing of 95Pb5Sn solder bumps and 37Pb63Sn pre-solder in flip-chip solder joints. The reaction conditions included multiple reflows (up to 10) at 240 °C, whereby previously solder-coated parts are joined by heating without using additional solder. We found that the molten pre-solder had an irregular shape similar to a calyx (i.e., a cuplike structure) wrapped around a high-lead solder bump. The height to which the molten pre-solder ascended along the solid high-lead solder bump increased with the number of reflows. The molten pre-solder was able to reach the UBM/95Pb5Sn interface after three to five reflows. The molten pre-solder at the UBM/95Pb5Sn interface generated two important phenomena: (1) the molten solder dewetted (i.e., flowed away from the soldered surface) along the UBM/95Pb5Sn interface, particularly when the number of reflows was high, and (2) the molten pre-solder transported Cu atoms to the UBM/95Pb5Sn interface, which in turn caused the Ni-Sn compounds at the chip-side interface to change into (Cu0.6Ni0.4)6Sn5.

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共晶PbSn预焊基板上95高铅凸点的基础研究

研究了95Pb5Sn钎料凸点与37Pb63Sn预焊料在倒装焊点中的混合。反应条件包括在240°C下多次回流(最多10次)，通过加热将先前涂有焊料的部件连接起来，而不使用额外的焊料。我们发现熔融预焊料有一个不规则的形状，类似于一个花萼(即，一个杯状结构)包裹在一个高铅焊料凸起上。随着回流次数的增加，熔融预焊料沿固体高铅焊料凸点上升的高度增加。熔融预焊料经过3 ~ 5次回流后能够到达UBM/95Pb5Sn界面。UBM/95Pb5Sn界面处的预焊液产生了两个重要现象:(1)预焊液沿UBM/95Pb5Sn界面脱湿(即从被焊表面流出)，回流次数多时尤为明显;(2)预焊液将Cu原子输送到UBM/95Pb5Sn界面，从而导致芯片侧界面处的Ni-Sn化合物转变为(Cu0.6Ni0.4)6Sn5。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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2009 4th International Microsystems, Packaging, Assembly and Circuits Technology Conference

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