鎳金屬墊層及SOP銅銲墊結構的共晶錫鉛銲錫接點之電遷移研究

Abstract

近年來由於電子產品對攜帶性以及效能的要求不斷的提升，元件發展的也走向輕、薄、短、小的趨勢，因此接點的密度也隨之提升， 在銲錫接點中的電遷移也成為一熱門的研究領域。本研究使用鎳金屬墊層，基板端為銅墊層，並經過SOP(solder on pad)的表面處理，銲錫和預錫的成分都是共晶錫鉛。電遷移研究結果可以看到經過通電測試後，晶片端的陰極沒有明顯的孔洞生成，但是可以觀察到錫原子回填的現象；在基板端的陰極則可以觀察到沿著銅墊層與銲錫接點介面產生環狀的孔洞，是整個迴路中破壞最嚴重之處。會造成此種破壞是因為當電子流進入銅銲墊時，由於銅有較低的電阻率，電子流會在銅銲墊內散佈，當電子流入銲錫接點時，電子流聚集形成一環狀電流密度較高的區域，加上銅原子在銲錫內較容易被電子流推動，於是在陰極基板端的銲錫接點造成孔洞的生成。

As the performance and device density of electronic products continuous to increase, electromigration has become an important reliability issue.In this study, electromigration study is conducted in eutectic SnPb solder joints with Ni under-bump-metallization and solder on pad (SOP) surface finish. We observed that there is severe damage on the substrate side, and the damage on chip side is not obvious. The damages on substrate side included void formation, dissolution of copper, and intermetallic compound formation. The voids almost separated Cu pad from the solder. We used microstructure analysis and 3-dimension simulation to investigate the electromigration mechanism in the area between SOP/ Cu surface finishes and solder. The higher diffusion rate of Cu in the eutectic SnPb solder was responsible for the serious void formation in the surface of the SOP and the solder layers. Therefore, the surface becomes the weakest region during electromigration.