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標題: 外加應力對錫鬚生長及銲點界面反應之影響
Effects of mechanically applied stress on tin whisker growth and interfacial reactions at solder joints
作者: 陳郁仁
Chen, Yu-Jen
關鍵字: whisker;錫鬚;hillock;interfacial reaction;錫/銅介面反應
出版社: 化學工程學系所
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半導體封裝過程中,銅導線架上廣泛地利用電鍍錫作為表面處理層,因為在導線架腳表面電鍍錫可以增加架腳的潤濕性及避免氧化,有助於架腳與印刷電鍍板(printed circuit board, PCB)的接合,但錫層表面會自發性成長錫鬚,導線架腳會因錫鬚成長相連接造成短路,降低電子產品的可靠度。然而在覆晶產品製作過程或使用期間,由於材料本身性質與外在環境的影響,會造成應力(stress)之產生。矽晶片與薄膜間由於熱膨脹係數(coefficient of thermal expansion, CTE)差異較大,容易造成銲點熱應力之生成,而應力之生成可能會影響覆晶及表面處理層在許多可靠度之表現。本研究設計黃銅模具,模擬矽晶片基材與鍍膜間熱膨脹係數差異所造成的應力對於錫鬚生長及錫/銅界面反應之影響。本研究主要在銅/錫薄膜上加入應力及溫度之因素,進而探討對錫鬚生長及錫/銅界面反應之影響。
於高溫熱處理研究中,將樣品置於80℃與150℃下進行熱處理30天~80天,溫度對於錫鬚成長也有很大的影響,在高溫80 ℃及150 ℃錫鬚的型態由細絲狀(whisker)轉變為小丘狀(hillock)。但在高溫熱處理下外加拉伸應力對於小丘狀錫鬚的成長影響不如室溫下細絲狀錫鬚那麼顯著。
錫/銅界面反應中,(45μm Sn/10μm Cu)在高溫熱處理下150℃、170℃、200℃下介金屬化合物(intermetallic compound, IMC)隨著時間增長而增厚,先生成Cu6Sn5再生成Cu3Sn。受拉伸應力及壓縮應力在相同時間下IMC生長速率均較不受應力快速,所以整體的IMC(Cu6Sn5+Cu3Sn)也較厚。IMC生長速率為受壓縮應力最快,受拉伸應力其次,不受應力生長速率最慢,所以受到外加壓縮及拉伸應力均會促進IMC生長。

In this study, for simplicity, externally applied tensile stress was exerted on a Sn thin film electrodeposited on a Cu substrate using three-point bending to simulate the condition of a Sn thin film subjecting to a tensile stress due to CTE (coefficient of thermal expansion) effect. To perform the bending experiments, a specifically designed three-point bending module made of brass was used to bend the samples.
Filamentary Sn whiskers were formed on an electrodeposited Sn thin film aged at room temperature. Sn whisker growth was significantly mitigated on the Sn thin film subjected to a tensile stress in bending. This mitigation growth suggests that part of the compressive stress in the Sn thin film was neutralized by the mechanically applied tensile stress. The growth orientation of Sn whiskers formed on the high tensile stress region was random but directional on the low tensile stress region. A potential mechanism was proposed to explain the directional growth of Sn whiskers. The vacancy concentration at the high tensile stress region is higher than that at the low tensile stress region. Driven by the vacancy concentration gradient, the Sn atoms migrate from the low tensile stress region to the high tensile stress region, making the Sn whiskers grow in a preferential orientation.
No Sn whisker growth took place as the aging temperature was raised to 80 and 150℃, while Sn hillocks grew instead. More surprisingly, no noticeable Sn hillock(or whisker) growth was observed on the tensily-bent Sn film aged at 80 and 150℃, indicating that the combined effects of tensile stress and aging can effectively inhibit the Sn hillock(or whisker) growth.
Effects of applied stresses on the copper/tin thin film interfacial reaction were investigated. A three-point bending was used and in-plane bending induced compressive and tensile stresses. The sample was solid-state aged at temperatures of 150℃, 170℃ and 200℃ for 2days to 17days. The results revealed that mechanically applied stress can influence the IMC (intermetallic compound) growth behavior. Both compressive and tensile stresses can accelerate the IMC growth, and the IMC thickness under compressive stress is the thickest.
其他識別: U0005-1507200914342700
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