低燒付溫度及高導電率之銀導電膠

Abstract

本論文研究以金屬有機銀鹽類 ( Metal Organic Decomposition,MOD ) 做為添加劑，搭配具有跟黏性之溶劑與經表面處理過之片狀金屬銀粉 ( Flake Silver Powder ) ，以高速混合機及三軸滾輪進行混合及分散等來製備金屬銀膏。此銀膏之燒付條件可藉由金屬有機銀鹽類( Metal Organic Decomposition, MOD ) 於加熱時產生熱裂解反應( Thermal Decomposition Reaction )，致使金屬有機銀鹽類( Metal Organic Decomposition, MOD )還原形成奈米金屬銀後，於加熱進行中再與周遭之片狀金屬銀粉燒結形成金屬膜。 本研究針對所製備出之金屬膜層進行分析與研究，藉由熱重分析 (Thermogravimetric analysis, TGA)、熱差分析 (Differential thermal analysis, DTA) 與 (Derivative thermogravimetry, DTG)等，探討不同金屬有機銀鹽類之熱裂解反應與熱裂解活化能之變化，並藉由掃瞄式電子顯微鏡 ( SEM )分析金屬膜之微結構及燒付現象，並藉由動態流變儀 ( Stress and Strain Rheometers ) 之黏彈性行為 ( Viscoelasticity ) 探討不同金屬有機銀鹽類於膏體中之各項流變特性等。針對其中效益最好之金屬有機銀鹽類添加物，Silver 2-ethylhexanoate進行更組成份及熱裂解反應等深入之探討與研究，找尋出最佳之添加量。 實驗中並藉由氧化銀 (Silver Oxide, AgO and Ag¬2O) 之添加取代，藉由氧化銀之低溫熱還原性質及觸媒效應，加速系統之熱裂解反應與燒付，進而獲得更低溫及更快速燒付行為之金屬膜層。

In this studied, first, six low curing pastes were prepared from silver flake and □-terpineol and with different metallo-organic decomposition (MOD) compounds. The thermal decomposition behaviors of the pastes were performed. The microstructures and resistivities of screen-printed films on alumina substrate after thermally treated were characterized and discussed. Results indicated 2-ethylhexanoate possesses the lowest decomposition temperature at 190.3□C among the MOD agents studied, which forms silver particles to promote the linking of the flake silver powders and thus reduces the resistivity down to <10□□•cm at the temperature as low as 200□C. Second, the effects of the solvent and atmosphere on the thermal decomposition behaviors of the silver 2-ethylhexanoate and □-terpenol were investigated. Low-curing-temperature silver pastes from Ag flake, □-terpineol and various amounts of silver 2-ethylhexanoate were prepared and characterized. The microstructures and resistivities of the cured films screen-printed from the pastes were examined. The results of thermal analysis ( DSC, TGA, and TGA-MS ) in oxidizing and reducing atmospheres reveal that thermal decomposition is the dominating reaction during heating process of silver 2-ethylhexanoate, even though the DSC result reveals exothermic reaction for silver 2-ethylhexanoate heated in air due to oxidation. After thermal decomposition, it leave almost pure Ag particle, which is beneficial to provide the bridging between silver flake particles in the films. Based on the rheological behavior, microstructural evolution and electrical evaluation, it can be concluded that the low-curing-temperature silver paste with 5wt% of silver 2-ethylhexanoate additions is the best formulation evaluated, which possesses shear-thinning and thixotropy properties and the resistivity of 7.8x10-6 □-cm after cured at 250□C, which is relatively close to the bulk resistivity of Ag. Finish, attempts to modify the curing conditions of MOD silver pastes through the part of substitutions of silver flake by silver (I) oxide (Ag2O) and silver (II) oxide (AgO) were performed. DTA, DTG and XRD results indicated that the presence of residual silver oxide, which effectively catalyzes the evaporation of □-terpineol and the decomposition of the silver 2-ethylhexanoate, decreases the curing temperature and shortens the soaking time. The reduced silver and the remaining Ag2O enhance the connectivity and packing density of the silver flake and thus increase the electric conductivity of the films. For films prepared from pastes with 20 wt% Ag2O or AgO substitutions, resistivities of 14x10-6 and 19x10-6 □□•cm, respectively, were successfully achieved after being cured at 200□C for 5 min.