铝/镍/铜UBM厚度对SnAgCu焊点的力学性能及形貌影响

Effects of UBM Thickness on Shear Strength and Morphology in Solder Joints between SnAgCu Solder and Al/Ni/Cu Thin Films

研究了倒装芯片中UBM制备和焊球回流工艺流程。通过改变阻挡层Ni和浸润层Cu的厚度,结合推拉力测试实验,探究了SnAgCu焊点剪切强度的变化规律。研究结果表明,UBM中阻挡层Ni对SnAgCu焊点的力学性能影响最大,而浸润层Cu厚度的增加也能提高SnAgCu焊点的力学性能。进一步对推拉力实验后的焊点形貌进行了SEM观察和EDS分析,得到了焊盘剥离、脆性断裂、焊球剥离、韧性断裂四种不同的焊点失效形式,代表着不同的回流质量,而回流质量主要由UBM的成分和厚度决定。研究结果为倒装焊工艺的优化提供了理论指导。

The flip chip processes of UBM fabrication and solder reflow were studied. By varying the thicknesses of Ni barrier layer and Cu wetting layer, the variation of the mechanical strength of the solder joints at the interface between SnAgCu solders and A1/Ni/Cu thin films was investigated. The results prove that the mechanical strength of the solder joints between SnAgCu solders and A1/Ni/Cu thin films is influenced mostly by the thickness of Ni barrier layer. And the mechanical strength can also be enhanced as the thickness of Cu wetting layer increases. After ball shear tests, the morphologies of the solder joints, observed by SEM and analyzed by EDS, were concluded as four modes of failure, that is, pad lift, brittle break, ball lift and ductile break. Each mode represents different reflow quality, mainly determined by the thickness and composition of UBM. The research results provide a theoretical guidance for the flip chip process optimization.