鋁導線設計對覆晶銲錫凸塊中的電流與溫度分佈之研究

Abstract

摘要 當電流通過覆晶銲錫凸塊時，嚴重的電流集中效應也隨之出現在銲錫凸塊中。劇烈的電流集中效應附帶著焦耳熱能的產生，在高溫和高電流密交互作用下加速了電遷移的破壞，同時縮短元件的壽命。造成銲錫凸塊內電流集中的原因與導線和銲錫凸塊的幾何結構差異有著極大的關係。一般晶片端導線設計為平板狀而單一方向的結構，這樣的設計無法有效疏通電流。論文中我們設計多組導線，利用多接點且非單一方向的導線設計來分散原本集中在金屬墊（Al pad）中的電流，讓電流在金屬墊層中分佈更均勻而後流入銲錫凸塊，減緩電流集中效應帶來的破壞。本研究中以有限元素分析模擬系統ANSYS為工具，設計且模擬多組導線之電、熱特性，發現在施加1.2安培電流下，電流集中效應因子於平板狀導線設計（slab trace model）和六接點的導線設計（six connections model）中分別為6.4和2.6。在導線總電阻相同的情況下，可忽略兩導線設計的溫度因素，故six connections model的生命週期可為slab trace model的5.6倍。且導線總電阻相同下，six connections model 銲錫凸塊中的溫度也呈線性分佈，相對於slab trace model，前者有著較低較均勻的溫度梯度，因此熱遷移造成的影響也比較輕微。

Abstract

Serious current crowding effect takes place during current stressing in flip-chip solder joints, which also produces significant Joule heating effect. Both effects accelerate electromigration damage and then shorten the lifetime of devices. The line-to-bump structures cause the serious current crowding and Joule heating effects. The typical design for the wiring traces in the chip side is slab shape. Yet, this design is not able to distribute current uniformly. In this thesis, we design different layouts of Al trace, and simulate the current and temperature distributions in the solder joints. Multiple connections are designed to distribute the current uniformly, and thus current crowing can be relieved to some extend. We use finite-element method in ANSYS software to carry out the simulation. We found that multiple connections design can effectively relieve current crowding effect.