超声楔键合Al/Ni系统高温存储过程界面扩散行为(英文)

The Diffusion of Ni into Al Wire at the Interface of Ultrasonic Wire Bond During High Temperature Storage

应用电子扫描电镜(SEM)及X射线能谱(EDX)分析了直径为25μm的Al+1％Si引线与 Au／Ni／Cu焊盘键合后以及老化过程中界面间的冶金行为,结果表明:接头形成于键合点塑性流动 最大的周边区域;超声引线键合的连接本质是压力使引线发生塑性流动导致Al元素与Ni元素之 间的扩散,而超声一方面使金属引线软化增强了塑性流动的程度,另一方面超声使引线内部产生大 量的缺陷,成为扩散的通道,大大加速了扩散的进行;短路扩散是键合点形成的主要机制。在170℃ 时,键合点空气中高温存储后X射线能谱线扫描分析结果表明:老化10 d时,有明显的Ni向Al引 线内扩散现象;老化30 d时,引线内部出现孔洞以及裂纹,界面出现云状组织,成份分析为15．55％ Ni和78．82％Al;老化40 d时,引线内部出现大量的孔洞并存在方块岛状的Al-Ni组织,其尺寸和 形状显示与Kirkendall孔洞不同。

The ultrasonic bonds, after bonding and aging, of Al＋1%Si wire with 25 μ m diameter bonded on the Au/Ni/Cu pad, are analyzed by Scanning Electronic Microscopy （SEM） with Energy Dispersive XRay Spectrometer （EDX）. The joints begin at the bond periphery where it is the location of the greatest plastic flow. It is found that the mechanism of ultrasonic bonding is, both the plastic flow of metal wire generated by wedge tool pressure which results in the diffusion of Ni into Al wire, and the effect of ultrasound is that, on the one hand, ultrasonic vibration enhances the metal wire ability of plastic flow and, on the other hand, it generates many defects inside the metal wire which are the fast diffusion channels. The diffusion type is likely the Short-Circuit Diffusion, which is more prominent than the crystal diffusion when the temperature is low. After high temperature storage at 170 ℃ for 10 d, there is evident diffusion of Ni into Al wire, but the microstructure is the same with the bonds after bonding, there is no evident change. Aged for 30 d, the bond interface forms a cloud-like structure, and the major composition is Al and Ni with weight percent of 78.82% and 15.55% respectively. However, the diffusion is not even and some parts of the bond interface are absence of Ni diffusion. When the aging time is 40 d, the cloud-like structure transforms into rectangular island-like structure and there are many cavities inside the bond wire, which are different from the Kirkendall voids because of the shape and dimension.