共晶錫鉛銲錫於覆晶系統中之電遷移研究

Abstract

錫鉛銲錫已經廣泛的被運用在電子封裝技術之中。在某些情況，銲錫接點在高溫與高電流密度的環境之下運作，會產生電子遷移的效應。因此銲錫之電遷移研究為電子構裝之中一項重要的課題。本論文之中，研究了這個覆晶系統中電遷移對於共晶錫鉛銲錫接點的影響。對於銲錫與金屬層之間的介金屬化合物中的銅、鎳原子成分會因為電子流驅動而改變。此外在150℃的環境溫度之下給予共晶錫鉛銲錫接點三種不同的電流密度，分別是5×103A/cm2, 7.5×103A/cm2 和104A/cm2。由不同的電流密度來探討電遷移對於銲錫球的破壞機制。在較高的電流密度之下，電流擁擠效應比較明顯，同時在晶片端的鋁導線也會因為高電流密度而發生電遷移，因而造成共晶錫鉛銲錫球的損壞。在較低的電流密度之下，金屬薄膜的破裂以及銲錫的回流造成共晶錫鉛銲錫球的損壞。

Tin-Lead solders have been widely used to bond chips to their substrates for electrical connection and packaging. In certain applications, solid solder reaction is of serious concern owing to high temperature environment and high current density, especially under the hood of an automobile. Therefore, solder joints under applying current stressing is a required reliability test. The thin film UBM of the chip side is Ti/Cr-Cu (phase-in)/Cu and the pad metallization of the board side is Cu/Ni/Au. Three current densities, 5×103A/cm2, 7.5×103A/cm2 and 104A/cm2, have been tested in eutectic SnPb solder bumps at 150℃. The direction of electron current affects the microstructure evolution. Electromigration tends to promote the dissolution of thin film UMB into solder and drive to the anode due to interstitial diffusion. Current crowding is obviously found in the higher current density of 104 A/cm2 at 150℃. The migration of Al trace also occurs. UBM layer is squeezed out by the diffusion of tin-rich phase in the chip/cathode side.