UF對覆晶接合結構熱傳導行為影響的研究

Abstract

UF（Underfill，UF）是提升覆晶接合（Flip-chip Bonding，FC）可靠度的重要技術，而隨著積體電路晶片散熱需求的增加，填充入高熱傳導係數（Thermal Conductivity，）的UF以提升FC接合結構散熱行為遂成為重要研究題目之一。本研究依據傅立葉熱傳導定律（Fourier’s Law of Heat Conduction）建立一套以白金（Platinum）薄膜電極為加熱器與測溫器的材料值與界面熱阻值（Thermal Boundary Resistance，RTBR）的量測系統，其先以Pyrex玻璃與氧化鋁為參考試片驗證其量測之可行性，並分析摻雜無機填充物對環氧樹脂的值的影響，實驗結果顯示無機物之填充能提升膠材的值，且在RTBR值相同的條件下，RTBR值對試片整體溫降比例的影響會隨試片值之升高和試片厚度之降低而變大。本研究亦分析填入UF的FC接合試片之熱傳導行為，實驗結果顯示填入UF能將熱傳遞模式由輻射轉換為傳導，從而提升試片的整體值，並降低Si/UF界面的RTBR值。將材料量測結果代入不同錫球陣列密度之FC接合試片之熱傳導性質計算結果顯示，隨著錫球陣列密度的增加，UF的值與TBR效應對FC接合試片的總熱阻值（Rtotal）及溫度梯度（Temperatrue Gradient，TG）的影響逐漸降低，故使用高值的UF可提升低錫球陣列密度FC試片的熱傳導性質，但在高錫球陣列密度的FC試片中，高值的錫球抑制了UF的值與TBR效應對Rtotal值及TG的影響，填入高值UF對其熱傳導性質的提升並無助益。

Underfill (UF) may promote the reliability of flip-chip (FC) bonding by the providing adhesion in between integrated circuit chip and substrate. As the increasing demand of heat dispersion of electronic components, the UFs with high thermal conductivities () attracts a lot of research interests. Nevertheless, our previous study found that such high-heat-conduction UFs might not necessarily be a crucial issue for FC technology. In order to clarify this controversy, this study adopts the Fourier’s law of heat conduction to establish a thermal conductivity measurement system in which the platinum (Pt) thin-film electrodes serve as the thermal heater and the temperature sensor. First, the feasibility of established system was verified by the measurement of  values of Pyres glass and Al2O3 plates. Afterward, the  values of prestine epoxy resins and commercially available UF were evaluated and the results indicated the incorporation of inorganic fillers benefits the thermal conduction of polymeric resins. Analytical results also revealed the influence of thermal boundary resistance (RTBR) at Pt/sample interface increases with the increase of  value and the decrease of thickness of sample subjected to the test. Further, this study prepares the FC samples without and with the UF to investigate their thermal conduction behaviors. It was found that the UF changes the thermal transfer mode from radiation to conduction, leading to the thermal conduction improvement of FC sample and reduction of TBR property at Si/UF interface. Moreover, the thermal properties of materials obtained by above measurements were implanted in the calculation of thermal conduction behaviors of FC samples containing various solder bump arrays. With the increase of solder bump density, the influence of UF’s  value and TBR property on the total thermal resistance and temperature gradient of FC sample gradually diminished. The utilization of high- UF might promote the thermal conduction of FC samples with low solder bump densities whereas it becomes insignificant in improving the thermal conduction of FC samples with relatively high solder bump densities.