錫銀覆晶銲錫中金屬墊層電遷移與熱遷移行為之研究

Abstract

高接腳密度與縮減封裝體積的優勢下，覆晶封裝成為進階元件的主流封裝形式。但是覆晶封裝中受到鋁導線到銲錫的結構影響，產生的電子聚集效應與焦耳熱效應所造成的電遷移現象成為影響元件封裝可靠度的關鍵。覆晶封裝廣泛地使用鉛為銲錫材料，隨著環保意識的重視，歐盟與美國皆陸續通過法令禁止鉛的使用。錫銀合金熔點較高約220oC，且其優異的機械性質使其成為無鉛銲錫的候選材料之一。 本文探討無鉛覆晶錫銀銲錫接點於150oC與160oC的溫度下，通電電流0.8安培之電遷移行為。破壞模式皆為銅金屬墊層消耗、介金屬成長、孔洞生成、擴大至試片的完全破壞。

Flip-chip technology has become a mainstream trend in advance electronic package because of its capability of higher I/O density and smaller package size. Electromigration phenomenon had become a crucial reliability concern, due to the effect for current crowding and Joule heating effect in the flip-chip solder joints for its unique line-to-bump structure. Pb is widely used to be the solder bump in the flip-chip package. As the awareness of environmental protection is more attentive, European Union and the US already forbade to use the Pb-containing solder bump through the law. The melting point of Sn-Ag alloy is about 220oC, and its good mechanical property makes it become a candidate of Pb free solder bump materials. In this study, we investigate the electromigration behavior stressed by 0.8A at 150oC and 160oC in the Sn-Ag solder joints. We found that the electromigration failure mode in the solder specimens is the dissolution of copper UBM, the growing of IMC layer, the generation of void and the void extending into the rest of the contact open.