Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joint assembled using a low-temperature reflow process for PoP technology
Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joint assembled using a low-temperature reflow process for PoP technology
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DOI：
10.1016/j.matdes.2019.108144
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发表时间：
2019-12-05
影响因子：
8.4
通讯作者：
Nishikawa, Hiroshi
中科院分区：
文献类型：
--
作者：
Shen, Yu-An;Zhou, Shiqi;Nishikawa, Hiroshi
层叠封装（PoP）是用于制造加速处理单元的芯片组的流行技术。然而，硅芯片和聚合物衬底之间的热膨胀系数失配在回流过程中引起热翘曲。因此，焊点的回流温度和可靠性是PoP的关键方面。虽然Sn-58 Bi是低温工艺的良好候选材料，但其脆性会导致其他可靠性问题。在本研究中，对由Sn-3.0Ag-0.5Cu（SAC 305）焊料和Sn-58 Bi焊料制成的复合焊料（CS）在回流期间在170 ° C（CS-170）、180 ° C（CS-180）和190 ° C（CS-190）的温度下进行了原位观察。混合焊料区域的体积大小顺序为CS-190 > CS-180 > CS-170。采用计算的Sn-Ag-Cu-Bi四元体系的Sn 58 Bi-SAC 305等值线截面来阐明CS-190的熔融行为。用电子背散射衍射证实了CS-190具有Sn环状孪晶界和Bi相[0001]择优取向。此外，形成了剪切强度为46 MPa的Cu/CS-190/Cu接头。CS-190可降低Sn-Bi钎料的脆性，这是由于随着Bi含量的降低，固溶硬化减少。这些因素可以提高PoP技术的可靠性。(C)2019作者爱思唯尔有限公司出版
Package-on-Package (PoP) is a popular technology for fabricating chipsets of accelerated processing units. However, the coefficient of thermal expansion mismatch between Si chips and polymer substrates induces thermal warpage during the reflow process. As such, the reflow temperature and reliability of solder joints are critical aspects of PoP. Although Sn-58Bi is a good candidate for low-temperature processes, its brittleness causes other reliability issues. In this study, an in-situ observation was performed on composite solders (CSs) made of an Sn-3.0Ag-0.5Cu (SAC305) solder and an Sn-58Bi solder that were mixed during reflow at temperatures of 170 degrees C (CS-170), 180 degrees C (CS-180), and 190 degrees C (CS-190). The volumes of the mixed-solder regions were in the order of CS-190 > CS-180 > CS-170. A calculated Sn58Bi-SAC305 isoplethal section of the Sn-Ag-Cu-Bi quaternary system was employed to elucidate the melting behavior of CS-190. CS-190 with Sn cyclic twin boundary and Bi phase preferred orientation of [0001] was demonstrated by electron backscatter diffraction. Moreover, Cu/CS-190/Cu joints with a shear strength of 46 MPa were formed. CS-190 can reduce the brittleness of Sn-Bi solder owing to the reduced solid-solution hardening with the decrease in the Bi content. These factors can improve the reliability of PoP technology. (C) 2019 The Authors. Published by Elsevier Ltd.