以奈米複合材料的觀念改善高透明度光學元件封裝膠材性質之研究

Abstract

高透明度、二液型環氧樹脂膠材（Epoxy Molding Compound，EMC）應用於光學元件封裝時發生膠材自鍍金銅引腳架表面剝離（Delamination）之缺陷，初步推斷原因來自於環氧樹脂膠材與銅引腳架間熱膨脹係數（Coefficient of Thermal Expansion，CTE）有所差距，且與鍍金表面黏著強度（Adhesion）不足所致。本研究目的即為改善此一製程缺陷，方法之一為導入有機-無機奈米複合膠材（Organic-Inorganic Nanocomposites）的觀念調變EMC性質，在不嚴重傷害光穿透度之前提下，將二氧化矽（SiO2）奈米粉體添加於EMC中，達到降低其CTE之目的；其二為利用硫醇官能基能與金形成強共價鍵之特點，尋求適當的硫醇化合物（Thiol Compound）塗佈於引腳架上，使一端能與金表面形成金硫鍵結，另一端的官能基與EMC形成鍵結，藉以改善膠材與鍍金引腳架之黏著強度。 實驗首先篩選符合製程需求分散劑與SiO2奈米粉體，透過光穿透度與CTE分析篩選出GPTMS（(3-Glycidoxypropyl)methyldiethoxysilane）為最適分散劑與10 nm之奈米SiO2粉體為無機摻雜物，在所建立的最適比例與最佳製程條件下製成EMC-SiO2奈米複合膠材，實驗分析結果顯示形成奈米複合物確實降低了膠材之CTE，同時對膠材與鍍金引腳架間之黏著強度有小幅改善；在提升黏著強度部分，本研究選用MPTMS（(3-mercaptoproply)trimethoxysilane）硫醇化合物，鍍金引腳架以0.01 wt.%的MPTMS-酒精溶液浸泡60分鐘即能達到黏著度強化的效果，其可使純EMC與EMC-SiO2奈米複合膠材之黏著強度分別提升86.78%與116.74%。

Delamination from the surface of gold (Au)-clad copper (Cu) leadframe occurred when the highly transparent, two-component epoxy molding compound (EMC) was applied to the encapsulation of optical devices. The mismatch of coefficients of thermal expansion (CTE) in between EMC and Cu as well as the relatively poor adhesion of EMC on Au are likely the causes of such a manufacture defect. This study aims to overcome this difficulty by modulating the physical properties of EMC via the concept of nanocomposites. In the prerequisite of preserving the transparency of the EMC, an appropriate amount of nano-scale SiO2 powders serving as the inorganic filler was added in the EMC to reduce its CTE. As to the study of adhesion enhancement, a suitable thiol compound was coated on the leadframe so as to form a strong covalent bond in between Au and the polymeric matrix during the curing treatment of EMC. First, the type of chemical dispersion agents and the size of nano-scale SiO2 powders suitable for the preparation of EMC-SiO2 nanocomposite resin were determined. Via the analyses of transmittance and CTE, GPTMS ((3-glycidoxypropyl)methyldiethoxysilane) and the SiO2 powder with average size of 10 nm were selected as the dispersant agent and inorganic filler for subsequent study. Appropriate amounts of GPTMS and SiO2 were added in EMC precursor under the optimized processing condition and relevant physical properties were characterized. Analytical results indicated the formation of nanocomposite may suppress the CTE of the EMC and mildly increase the adhesion strength on Au-clad leadframe. In the portion of study regarding of the adhesion enhancement, the addition of MPTMS ((3-mercaptoproply)trimethoxysilane) in the EMC was found to efficiently improve the adhesion property. In conjunction with the adhesion enhancement by forming the nanocomposite, more than two-fold increment in adhesion strength of the EMC on Au-clad leadframe was achieved.