Effect of Cu content on the interfacial reliability of SnAgCu solder joints

K. Zeng, Becky Holdford
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Abstract

NEMI recommended Sn3.9Ag0.6Cu to replace the eutectic SnPb solder, but solder joints of this alloy have poor performance in reliability tests of electronic packages, especially the board level drop test. In this paper, the effect of Cu content in solder is studied on the interfacial reliability of SnAgCu solder joints on the Ni/Au plated pads. After preconditioning (three reflows post package assembly), some solder balls fell off during routine handling of the packages. Cracking occurred between the IMC layers of (Cu,Ni)6Sn5 and Ni3Sn4. Formation of the dual IMC structure is explained from the perspective of interfacial equilibrium. It is suggested that to improve the drop performance of the packages that have Ni/Au plated pads the key is to avoid the formation of the layer-type of (Cu,Ni)6Sn5 at the interface. Approaches to do that are discussed. A rule for selecting solder alloy and surface materials on both sides of the joints is proposed for BGA packages.
Cu含量对SnAgCu焊点界面可靠性的影响
NEMI推荐使用Sn3.9Ag0.6Cu代替共晶SnPb焊料,但该合金的焊点在电子封装可靠性试验中,特别是板级跌落试验中表现较差。本文研究了钎料中Cu含量对镀Ni/Au焊盘上SnAgCu焊点界面可靠性的影响。经过预处理(封装组装后的三次回流),一些焊料球在封装的日常处理过程中脱落。(Cu,Ni)6Sn5和Ni3Sn4的IMC层之间出现裂纹。从界面平衡的角度解释了双IMC结构的形成。结果表明,要提高镀Ni/Au焊盘封装的跌落性能,关键是避免在界面处形成层状的(Cu,Ni)6Sn5。讨论了这样做的方法。提出了BGA封装中焊接合金和表面材料的选择原则。
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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