以表面處理控制自發性晶鬚生長及殘留應力對晶鬚生長動力學之影響;Control of Spontaneous Tin Whisker Growth by Surface Treatment and the Effect of Residual Stress on Growth Kinetics

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題名:	以表面處理控制自發性晶鬚生長及殘留應力對晶鬚生長動力學之影響;Control of Spontaneous Tin Whisker Growth by Surface Treatment and the Effect of Residual Stress on Growth Kinetics
作者:	蘇建豪;Su,Chien-Hao
貢獻者:	化學工程與材料工程學系
關鍵詞:	錫晶鬚;同步輻射;介金屬化合物;Tin whisker;synchrotron radiation;intermetallic compounds
日期:	2014-05-01
上傳時間:	2014-08-11 18:13:31 (UTC+8)
出版者:	國立中央大學
摘要:	電子封裝產業利用電鍍方式將錫薄膜鍍製銅導線架的表面，因銅與錫反應生成之介金屬化合物(Cu6Sn5)會於錫薄膜中產生壓應力，應力藉由自發性錫晶鬚生長釋放。晶鬚可能造成短路或因尖端放電形成火花，而劣化電子元件之可靠度，故研究晶鬚成長機制及其抑制方法為一重要課題，但因生長位置難以預測，造成研究之困難。本論文嘗試控制晶鬚生長位置，利用微影技術與濺鍍方式於錫薄膜表面創造圓形陣列的氧化層弱點，成功控制錫晶鬚僅可見於弱點區域，再以電子顯微鏡觀察並追蹤錫晶鬚於不同退火時間下的尺度變化，可計算錫晶鬚實際生長速率。實驗中利用同步輻射X光精準量測薄膜之殘留應力，並利用數學模型探討薄膜應力與晶鬚成長之動力學。本實驗亦改變表面弱點之密度，欲探究氧化層之緻密性與晶鬚生長之關係，研究結果呈現晶鬚之總體積不因表面氧化層的狀態改變，但其長度與弱點密度成反比，實驗進一步以聚焦離子束及電子顯微鏡量測介金屬化合物之體積，證實晶鬚與介金屬化合物之生長習習相關，且皆為與反應時間之平方根(t1/2)成正比。由於在錫/銅界面鍍製鎳-磷金屬阻障層為一常見之抑制晶鬚生長的方法，本實驗亦結合表面弱點與應力量測探究其原因。實驗發現錫/鎳-磷界面緩慢生成平板狀的介金屬化合物(Ni3Sn4)，使其殘留應力非常小，從表面形貌觀測得知錫/鎳-磷系統的確無生長晶鬚。由本論文之結果可知，表面氧化層越不緻密，可有效減少長而有害之晶鬚生長，降低元件損壞之風險，利用微結構觀察與晶鬚形貌之量測，推導出一晶鬚生成之數學模型：晶鬚指數，可提供研究晶鬚成長之基礎，亦可供業界於元件設計之參考。;In electronic package industry, the spontaneous growth of whiskers on tin thin films poses a threat to the reliability of electronic devices. These whiskers are produced by the continuous generation and relaxation of compressive stresses within the tin. The primary driving forces involved in Sn thin films grow on a Cu leadframe are the formations of intermetallic compounds (IMCs) resulting from the reaction between Cu and Sn and a dense oxide layer on Sn surfce. This study sought to overcome the unpredictable nature of whisker growth and achieve accurate quantitative analysis of the growth kinetics. The purpose of this research was to control the location of whisker growth, which occurs in the weak spots created by the lithographic processes associated with the application of tin oxide coatings. Scanning Electron Microscopy (SEM) was adopted to examine each whisker at every step to record the dimensions at different annealing time to calculate the real growth rate of whisker. This study employed synchrotron radiation X-ray diffractometery to identify variations in stress associated with whisker growth that fitted appropriately to the mathematical model. The results of this study could prove that the formation of a surface oxide layer is a necessary condition for controlling where whisker growth will occur. We also investigated the relationship between cracks in the surface oxide layer and the growth of whiskers. The results represented that total volume of whisker growth was independently of the interval between weak spots. But the length of whisker and density of weak spots on surface oxide were disproportionate. This study employed statistical methods based on focused ion beam (FIB) observation to characterize the relationship between the total volume of the whisker growth and Cu6Sn5 IMCs. These results clearly demonstrate that the growth of whisker was the square root of annealing time (t1/2). Our results verify the effectiveness of a Ni-P underlayer as a barrier to the inter-diffusion between Sn film and a Cu substrate that was a general mitigated method for whisker growth. The combination of weak spots on surface and measurement of residual stress were studied in the experimental. The results presented thin and layered Ni3Sn4 IMCs grew only and the residual stress was very small. As a result, no whisker growth occurred in the Sn/Ni-P/Cu specimens. The creation of a weak oxide layer or taking steps to prevent the formation of intermetallic compounds could be very important for reducing the threat of short circuit. A “Whisker Index” was proposed to evaluate the effect of microstructure and surface treatments on the kinetics of whisker growth for providing the fundamental knowledge of whisker growth and the future design of devices.
顯示於類別:	[化學工程與材料工程研究所] 博碩士論文

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