3D封装芯片瞬时液相键合的记忆焊点改性机理及可靠性研究

Transient liquid phase bonding with intermetallic compounds (IMC) solder joints formed can realize the 3D chips stacking, which is one of kernel technology in 3D packaging. However, two drawbacks can be found in the solder joints, namely voids and stress concentration, they can decrease the reliability of 3D chips stacking. In this project, concept of "memory solder joints" is advanced, submicron CuZnAl memory particles will be selected as additives into low temperature materials such as Sn and In, these materials will be utilized in transient liquid phase bonding to form IMC memory solder joints containing submicron memory particles, which can improve the structure reliability. Four aspects of the project will be studied as follows: ①it is imperative to develop the paste containing submicron memory particles for 3D packaging, solve the preparation technology of paste and bump, and optimize the transient liquid phase bonding processing; ②the IMC interfacial reaction, growth kinetic, voids growth and the properties of solder joints will be investigated, which can be used to explain the effect law of submicron particles; ③the stress-strain response and fatigue failure of solder joints, and phase transformation of memory particles under alternating loadings will be discussed, which can describe the modification mechanism of solder joints; ④the thermal fatigue failure behavior of memory solder joints will be studied, the mechanical data of memory solder joints will be tested, the microstructure evolution of solder joints will be analyzed, and the fatigue life of memory solder joints will be predicted.Meanwhile,the results of this project can be used in transient liquid phase bonding of MEMS, CMOS and 3D MCM chips stacking.

瞬时液相键合形成金属间化合物(IMC)焊点易于实现3D封装芯片堆叠互连，成为3D封装芯片互连的核心技术之一，但是IMC焊点存在空洞和应力集中两大致命的缺点，导致芯片堆叠的可靠性急剧下降。本项目提出"记忆焊点"的概念，拟采取在Sn/In等低熔点材料中添加适量的亚微米CuZnAl记忆颗粒，通过瞬时液相键合形成以IMC为基体内镶嵌记忆颗粒的记忆焊点，提高结构可靠性。拟开展以下四方面研究：①开发含亚微米记忆颗粒焊膏、解决焊膏-凸点制备技术、优化瞬时液相键合工艺；②研究IMC界面反应、生长动力学、空洞生长和焊点性能，探讨亚微米记忆颗粒影响规律；③研究交变载荷条件下焊点的应力-应变响应、疲劳失效和记忆颗粒相变行为，揭示焊点改性机理；④研究记忆焊点热疲劳失效行为，测试记忆焊点力学数据，分析焊点组织演化，预测记忆焊点疲劳寿命。本研究成果同时可以用于MEMS、CMOS和3DMCM等芯片堆叠的瞬时液相键合。

瞬时液相键合形成金属间化合物焊点易于实现3D封装芯片堆叠互连，但是 焊点存在空洞和应力集中两大致命的缺点，导致芯片堆叠的可靠性急剧下降。因此选择CuZnAl记忆合金颗粒提高三维封装互连焊点的可靠性。本文研究CuZnAl记忆合金颗粒对SnBi、Sn、SnAgCu三种钎料及焊点性能的影响，获得高可靠性的互连焊点。发现CuZnAl颗粒的添加显著提升SnBi钎料的润湿性和焊点力学，获得CuZnAl颗粒的最佳添加量为0.5%，润湿性最大幅度提高13.1%，力学性能最大幅度提高22.8%。CuZnAl的添加对Sn-58Bi钎料的熔化温度影响较小，Sn-58Bi 组织得到明显的细化，当添加量为0.5%，组织得到最大程度细化。0.5%CuZnAl颗粒可以显著抑制金属间化合物的快速生长。采用有限元模拟研究CSP器件Sn-58Bi/Sn-58Bi-0.5CuZnAl两种焊点的应力-应变响应，计算焊点疲劳寿命，证实添加0.5%CuZnAl颗粒焊点疲劳寿命增加17.6%。证实在250℃加热9个小时即可实现Cu/Sn-58Bi-0.5CuZnAl/Cu焊点转化为全金属间化合物(24μm)。研究了0.5%亚微米CuZnAl记忆颗粒对黄铜/锡/黄铜焊点改性机制，焊点界面和基体组织得到明显的细化，焊点力学性能提高20%~25%。另外压力过大会恶化焊点的性能及形成大量空洞。通过0.2N压力、250℃保温10min，随后200℃保温1100h可以将黄铜/锡-CuZnAl/黄铜焊点完全转化为金属间化合物。对三维封装组件进行有限元模拟，发现在金属间化合物焊点阵列对角线第二个焊点处发现了应力-应变集中区域Sn-3.9Ag-0.6Cu焊点阵列中心焊点的应力-应变最弱，拐角焊点为整个组件最危险部位，和实验裂纹图吻合。实现了Cu/Sn-Ag-Cu/Cu瞬时液相键合，发现焊点厚度的降低可以显著细化金属间化合物颗粒，提高焊点的抗拉强度，减小焊点服役期间的von Mises应力。发现在深腐蚀过程中焊点内部出现明显的Ag3Sn纤维和Cu6Sn5棒，部分Cu6Sn5棒呈现六角状。焊后Cu6Sn5棒可以提高焊点的抗拉强度和延伸率，服役期间会降低焊点的性能。0.5%CuZnAl颗粒的添加可以抑制Cu/Sn-Ag-Cu/Cu焊点界面层金属间化合物的生长，证实CuZnAl颗粒的添加可以抑制全金属间化合物焊点的柯肯达尔空洞的形成。