Lead-Indium for Controlled-Collapse Chip Joining

L. Goldmann, R. Herdzik, N. Koopman, V. Marcotte
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引用次数: 27

Abstract

Lead-indium for flip-chip solder ("controlled-collapse") connections has been investigated as a possible alternative to the commonly used 5-95 tin-lead. In thermal cycle tests, lead-indium was substantially mote resistant than tin-lead to fatigue resulting from chipsubstrate mismatch. The lead-indium that has been studied most extensively, 50-50 by weight, gives a 3:1 improvement in lifetime over 595 and is compatible with standard chip and substrate processing. Evaporated above a Cr-Cu-Au pad on the chip surface, the solder is eventually joined to tinned Cr--Cu lands on the ceramic substate. Because of its lower melting point, lead-indium can be joined at a lower temperature than 5-95 tin-lead. In its reactions with copper and gold, which are present in chip and/or substrate metallizations, indium resembles tin. Gold, present only as the protective top film of the chip metallization, dissolves completely during chip joining, whereas copper is present in sufficient quantity to exceed its solubility limit, and thus forms copper-indium intermetallic layers at both interfaces. To ensure terminal strength and reliability, these layers should be stable and adherent both to the solder and to the underlying metnllizations. Lead-indium has been found to be more susceptible than lead-tin to corrosion in high-humidity and hostile environments. This susceptibility must be borne in mind when lead-indium is considered for nonhermetic applications.
铅铟控制塌缩芯片连接
用于倒装芯片焊料(“控制坍塌”)连接的铅铟已被研究作为常用的5-95锡铅的可能替代品。在热循环测试中,由于芯片衬底失配导致的疲劳,铅-铟的耐受性大大优于锡。铅铟的研究最为广泛,重量为50-50,寿命比595提高了3:1,并且与标准芯片和衬底加工相兼容。焊料蒸发在芯片表面的Cr-Cu- au衬垫上,最终与锡化的Cr-Cu结合在陶瓷基态上。由于铅铟的熔点较低,可以在比5-95锡铅更低的温度下结合。在与铜和金(存在于薄片和/或金属化基底中)的反应中,铟类似于锡。金仅作为芯片金属化的保护膜存在,在芯片连接过程中完全溶解,而铜的存在量足够多,超过其溶解度极限,从而在两个界面形成铜铟金属间层。为了确保终端强度和可靠性,这些层应该是稳定的,并附着在焊料和底层的金属化上。在高湿度和恶劣的环境中,铅铟比铅锡更容易受到腐蚀。当考虑将铅铟用于非密封应用时,必须考虑到这种敏感性。
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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