Development of micro-alloying method for Cu pillar solder bump by solid liquid interaction

Wen Yin, Daquan Yu, Fengwei Dai, Chongshen Song, Zhang Bo, L. Wan, Han Yu, J. Sun
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引用次数: 1

Abstract

Fine pitch micro bump is one of the key technology for 3D packaging since it can greatly improve the interconnect density. In this paper, we describe a new micro-alloy method for joining Cu pillars by forming solder bump alloys. The alloy composition is controlled by thin metal layer deposition and subsequent solid-liquid interactions. Four elements, e. g., Ag, Cu, Ni and Cr, were selected for micro-alloying Cu/Sn bumps and compositions of Sn-(1~2)Ag, Sn-2Ag-0.5Cu, Sn-(0.03~0.07)Ni, and Sn-(0.03~0.07)Cr were formed on Cu pillars. The microstructure of the solder bumps was studied before and after temperature cycling. The alloying process, and the effect of alloying on the interfacial microstructure and the growth of the intermetallic compounds (IMC) were investigated. The results suggest that the dissolution rate of additional metal in the molten Sn is sufficiently rapid to form solder bumps of varying compositions during a single reflow step. With Ag alloying, Ag3Sn crystals formed and were finely dispersed in the solder. With trace Ni doping, Ni was dissolved into the solder and the IMC layer thickness increases since the Cu solubility in molten Sn increases in the presence of Ni. In comparison, it is quite interesting that with trace Cr alloying, Cr2Sn3 crystals were detected in the solder and that a thinner IMC layer resulted in comparison to Ni-alloying solder and pure Sn on Cu pillars. The susceptibility to whisker growth during alloying was also investigated. No Sn whisker formation or growth was observed on the solder bumps after 1000 thermal cycles. The thickness of IMC layer became thicker after temperature cycling. In decreasing order, the thickness of the IMC layer on the Cu pillar was observed to be: Sn-0.07Ni>;Sn-2Ag>;Sn-0.07Cr>;Sn-2Ag-0.5Cu.
固液相互作用微合金化铜柱凸锡方法的研究
细间距微凸点是三维封装的关键技术之一,它可以大大提高互连密度。本文介绍了一种新的微合金连接铜柱的方法——形成凸点合金。合金成分由薄金属层沉积和随后的固液相互作用控制。选择Ag、Cu、Ni、Cr 4种元素进行微合金化Cu/Sn凸点,在Cu柱上形成Sn-(1~2)Ag、Sn- 2ag -0.5Cu、Sn-(0.03~0.07)Ni、Sn-(0.03~0.07)Cr等成分。研究了温度循环前后焊点的微观结构。研究了合金化过程,以及合金化对界面组织和金属间化合物生长的影响。结果表明,锡液中附加金属的溶解速度足够快,可以在一次回流过程中形成不同成分的焊料凸起。随着银的合金化,形成了Ag3Sn晶体,并在钎料中分散。在钎料中掺入微量Ni后,钎料中Ni的溶解度增加,IMC层厚度增加。相比之下,非常有趣的是,与微量Cr合金化相比,在钎料中检测到Cr2Sn3晶体,并且更薄的IMC层导致了与ni合金化钎料和纯锡在Cu柱上的比较。还研究了合金中晶须生长的敏感性。经过1000次热循环后,钎料凸起处未观察到锡晶须的形成和生长。温度循环后IMC层厚度变厚。Cu柱上IMC层厚度由大到小依次为Sn-0.07Ni>;Sn-2Ag>;Sn-0.07Cr>;Sn-2Ag-0.5Cu。
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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