Electromigration in Pb-free bumps with different UBM thickness

Z. Jinsong, Wu Yiping, Wu Feng-shun, An Bing
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引用次数: 3

Abstract

A study of a dummy flip-chip package was conducted to evaluate electromigration failure of different Pb-free bumps with different UBM (under bump metallization) thickness. The applied current density was 2.3/spl times/10/sup 4/ A/cm/sup 2/, and the operating temperatures were 180/spl deg/C and 160/spl deg/C. The UBM consisted of Cu and Ni electroplate with thickness of 20 /spl mu/m and 10 /spl mu/m (or 5 /spl mu/m), respectively. Pb-free solder bumps, SnAg and SnAgCu alloys, were utilized to perform the experiment. An SnPb eutectic solder bump was also tested in contrast to the different Pb-free solder bumps. Electromigration failure was observed only at the solder bump/UBM interface with electron current flow from the chip to the substrate. Mass IMC (intermetallic compound) dissolution and void nucleation near the cathode were observed during current stressing. Failure took place in the region of the UBM and UBM/bump interface in the form of solder cracking or delamination. Otherwise, in different Pb-free bumps, Ni followed by Cu migration along the electron wind direction was observed. Pb-free solder bumps had a longer failure time than that of SnPb bumps at high temperatures. Effects of current crowding and IMC polarity are key factors of flip-chip interconnects' electromigration behavior.
不同UBM厚度无铅凸点的电迁移
通过对一个虚拟倒装芯片封装进行研究,以评估不同UBM(碰撞金属化下)厚度的不同无铅凸点的电迁移失效。施加电流密度为2.3/spl倍/10/sup 4/ A/cm/sup 2/,工作温度为180/spl℃和160/spl℃。UBM由厚度分别为20 /spl mu/m和10 /spl mu/m(或5 /spl mu/m)的Cu和Ni镀层组成。实验采用无铅钎料bump, SnAg和SnAgCu合金。还测试了SnPb共晶焊点与不同的无pb焊点的对比。当电子电流从芯片流向衬底时,仅在焊料凸点/UBM界面处观察到电迁移失效。在电流应力作用下,观察到阴极附近金属间化合物(IMC)的大量溶解和空洞成核。失效发生在UBM和UBM/凹凸界面区域,以焊料开裂或分层的形式发生。另外,在不同的无pb凸起中,观察到Ni和Cu沿电子风向迁移。在高温下,无铅焊点的失效时间比SnPb焊点的失效时间长。电流拥挤和IMC极性是影响倒装互连电迁移行为的关键因素。
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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