使用薄膜鈦/鎳(釩)/銅金屬墊層以及銅銲墊的錫銅銲錫接點之電遷移研究

Abstract

但是近年來因為環保議題而使用無鉛銲錫，其破壞模式就與以往所熟悉在錫鉛銲錫內部的模式不同。本實驗使用試片為鋁/鎳(釩)/銅的薄膜金屬墊層(UBM)以及錫銅銲錫作為銲料，板端銅墊層(Cu pad)。研究發現靠近晶片端的陰極並沒有往常一般的破壞，反而是靠近板端的陰極端有嚴重的破壞，其破壞包含孔洞生成、板端銅墊層消耗以及介金屬化合物的生成。其成因是因為板端銅墊層良好的分散電流使得電流進入銲錫凸塊之後會匯集在銲錫凸塊周圍，導致周圍一圈的電流密度增高，讓破壞從銲錫凸塊與銅墊層介面周圍開始生長，成為主要的破壞地點。在具有薄膜金屬墊層的錫銅銲錫中使用銅墊層讓此處成為銲錫接點在電遷移中最脆弱的點。

In this study, electromigration study in SnCu lead-free solder joints with thin-film under-bump-metallization and Cu substrate pad was conducted. We found that there was sever damage on the substrate side (anode side), and the damage on chip side (cathode side) was little. The damage 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 Cu pad and solder. The higher diffusion rate of Cu in the SnCu solder was responsible for the serious void formation in the interface between Cu pad and the solder layers. Therefore, the surface becomes the weakest region during electromigration.