臺灣博碩士論文加值系統

覆晶製程在電子產品中被廣泛的應用，具有小尺寸、高密度、信賴度佳及多連接(input/output, I/O)數等優點，覆晶封裝主要是由銲料及UBM所構成，UBM結構中存在一擴散障層，通常以鎳金屬當障層材料，功用為減緩銅層和銲料反應形成IMC，過度反應會使銲點機械性質降低，進而影響到電子元件可靠度。由於銲料本身和基板性質的差異，應力的產生已成為值得關注的問題，應力可能會影響銲點之濕潤性、銲料與基板間的界面反應等，進而造成電子元件可靠度下降。為了解應力應變在覆晶封裝結構中所扮演腳色及模擬不同熱膨脹係數之電子元件，本研究利用模具施加壓縮(compression)及拉伸(tension)應變於矽晶片，結果再與不受應變作比較，模擬矽晶片與不同UBM之搭配的情況下所造成應力對Ni/Sn界面反應的影響。
實驗結果發現Ni/Sn界面反應在200ºC、170 ºC以及150 ºC下生成Ni3Sn4相，受壓縮或拉伸應力皆會影響IMC相厚度，而隨反應時間越長，應力造成影響越大，且受壓縮應力約略等於拉伸應力，而不受應力樣品IMC生成速度最慢，進而造成Ni3Sn4相厚度的不同。且外加應變會影響Ni金屬層晶粒，不受應力之試片中Ni金屬顆粒較沒有一致的方向，且受壓縮應力會使晶粒呈現細長狀，相反地受拉伸應力會使晶粒尺寸較大。
在255 ºC溫度下Ni-Sn迴銲反應生成之IMC為Ni3Sn4相，發現Ni3Sn4晶粒會因所受應變大小不同而使其尺寸有所改變，整體來說受應力最大區域會使生成Ni3Sn4晶粒尺寸較小，受部分應力次之，而後不受應力的試片中生成Ni3Sn4晶粒顆粒最大。但反應時間超過60分鐘後，Ni3Sn4晶粒尺寸的差異漸趨減少，直到迴銲120分鐘樣品後，Ni3Sn4晶粒顆粒並無太大分別。Ni3Sn4晶粒在反應初期生成小圓石狀IMC，而後再於此層狀IMC中以針狀結構成長並突出表面，當針狀結構Ni3Sn4長到一定長度之後，這些細針狀IMC再以晶粒粗化的方式形成多面晶體。

Flip chip in package have been used extensively in electronic product, the advantage of small size, high density, good reliability has been discovered. Flip chip is made by solder joint and under bump metallurgy. To decrease copper atom reacting with solder, a diffusion barrier in UBM that made by nickel is been researched extensively. Because of the difference of coefficient of thermal expansion, thermal stress is become an important issue. The solder joints wetting, interfacial reaction of solder and substrate would be problem in electronic reliability. In order to realize the difference of Coefficient of thermal expansion, we applied compression and tension stress/strain by modules on silicon wafer. With different UBM layer that effect Ni/Sn interfacial reaction.
Ni3Sn4 phase formed between Ni/Sn interfacial at 200, 170, 150ºC. Regardless of compression or tension strain would cause IMC thickness growth thicker. With reaction time increasing, the effect of strain/stress is going to be great. Moreover, the applied strain/stress could force nickel grain growth. In FIB cross section, compression strain would cause grain become long and thin vertically. Tension strain would cause grain growth bigger and got uniform grain boundary.
In reflow experiment, Ni3Sn4 grain morphology grow smaller because of the strain larger. In region M, the Ni3Sn4 grain become smaller. With no bending specimen, the Ni3Sn4 grain become large. Ni3Sn4 grain difference being less until reflow time exceed to 60min. In initial reaction stage, Ni3Sn4 grain would be round shape. Then Ni3Sn4 grain grow from round shape to needle crystal. Finally, needle crystal become to faceted crystal.

致謝------------------------------------------------------------------------------- I
摘要------------------------------------------------------------------------------- II
目次------------------------------------------------------------------------------- III
表目次---------------------------------------------------------------------------- VI
圖目次--------------------------------------------------------------------------- VII
一、 前言------------------------------------------------------------------------- 1
二、 文獻回顧
2.1 覆晶封裝製程------------------------------------------------------ 2
2.2 熱應力--------------------------------------------------------------- 4
2.3 應力應變影響IMC的成長-------------------------------------- 8
2.4 相變化引發的應力----------------------------------------------- 12
2.5 界面反應動力學-------------------------------------------------- 15
2.6 Ni/Sn界面反應--------------------------------------------------- 17
三、 實驗方法------------------------------------------------------------------ 35
3.1 Ni/Sn固固反應
3.1-1電鍍----------------------------------------------------------------- 35
3.1-2模具外加應力應變----------------------------------------------- 35
3.1-3應力計算----------------------------------------------------------- 36
3.1-4固固界面反應樣品製備----------------------------------------- 42
3.1-5電子顯微鏡樣品製備-------------------------------------------- 42
3.1-6 XRD繞射分析---------------------------------------------------- 42
3.2 液固Ni/Sn界面反應
3.2-1迴銲反應----------------------------------------------------------- 44
3.2-2樣品製備與分析-------------------------------------------------- 44
3.3 Cu/Ni/Sn結構於室溫下反應
3.3-1電鍍----------------------------------------------------------------- 46
3.3-2模具外加應力應變----------------------------------------------- 46
3.3-3外加應力對固固界面反應之影響----------------------------- 46
四、結果與討論----------------------------------------------------------------- 48
4.1 外加應力對Ni-Sn固/固界面反應之影響
4.1-1 150 ºC下Ni/Sn界面反應--------------------------------------- 48
4.1-2 170 ºC下Ni/Sn界面反應--------------------------------------- 52
4.1-3 200 ºC下Ni/Sn界面反應--------------------------------------- 56
4.1-4 150ºC、170 ºC與200 ºC活化能Q及k0值計算----------- 60
4.1-5 XRD繞射分析---------------------------------------------------- 64
4.1-6 200ºC熱處理15天 Ni金屬橫截面之FIB分析----------- 65

4.2 外加應力對Ni-Sn液/固迴銲界面反應之影響
4.2-1 迴銲5分---------------------------------------------------------- 71
4.2-2 迴銲10分--------------------------------------------------------- 71
4.2-3 迴銲30分--------------------------------------------------------- 74
4.2-4 迴銲60分--------------------------------------------------------- 76
4.2-5 迴銲90分、120分----------------------------------------------- 76
4.2-6 迴銲界面反應截面SEM圖------------------------------------ 80
4.2-7 受應力影響Ni3Sn4晶粒---------------------------------------- 82
4.2-8 Ni3Sn4晶粒成長------------------------------------------------ 83
4.3 室溫下外加拉伸應力界面反應------------------------------ 85
五、 結論------------------------------------------------------------------------- 90
六、 參考文獻------------------------------------------------------------------- 92

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