覆晶錫銀銲錫接點 (5-μm Cu 金屬墊層)之電遷移研究

Abstract

在消費性電子產品走向輕、薄、短、小的趨勢中，需要高密度銲錫接點輸入/輸出數目。伴隨著錫球尺寸縮小，覆晶銲錫接點內的電流密度增加，電遷移現象成為元件可靠度的影響關鍵。 含鉛銲錫會對環境造成污染，且歐盟及美國已經通過法令在西元2006年前禁止使用含鉛銲錫，故在電子工業界便積極的研究無鉛銲錫以取代傳統的共晶錫鉛銲錫。目前較受矚目的無鉛銲錫為Sn-Ag為主的合金。Sn-Ag合金的熔點較高約為220°C，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150℃的溫度下，通電電流0.8A，通電平均電流密度8.4 x 103 A/cm2 之電遷移行為及其破壞機制。觀察到孔洞生成主要發生在電子流從Al導線進入bump的地方，亦即陰極/晶片端。且孔洞生成伴隨著電阻上升，有沿著介金屬化合物與共晶錫銀銲錫的介面的逐漸向右趨勢；同時在觀察到不同的電阻上升狀況下的銲錫接點破壞機制或失效模式，討論對應的電遷移破壞機制。

As the consumer electronic products move toward lightly, thin, short and smaller, we need higher solder input/output joint density. Therefore, the evolution of the bonding technology has moved from “Wire Bonding” to “Flip Chip technology”. Along with the solder bump shrinking and current density increased, electromigration phenomenon had become a crucial reliability concern.

Pb-containing solder bump will cause environment pollution, and European Union and the US already forbade to use the Pb-containing solder bumps through the law at Y2006. Thus, the electrical industry is hurry to find the substitute to replace eutectic SnPb solder bump. Pb free solders become the basic requirement for the future electronic product. In recent years, Pb free solder bump research and development as become an important part of the electrical industry. SnAg is one of potential Pb free solder alloys. The Sn-Ag alloy's melting point is about 220°C, 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 150℃. The electromigration behavior and the failure mechanism of the bump are monitored at various stages of electromigration. The microstructure of the solder bumps were observed as the bump resistance increased 20%, 50%, 100%, and 500% of its original value. It is found that void formation is mainly responsible for the increase in bump resistance.