Silica/Epoxy Hybrid Encapsulation with High Heat-Resistance and Low Coefficient of Thermal Expansion
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Article www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673
Silica/Epoxy Hybrid Encapsulation with High Heat-Resistance and Low Coefficient of Thermal Expansion Sung Bum Lee1,2 Ho Sik Lee2 Chang Bum Son3 Sung Hee Kim1 Jun Young Lee*,1
1
School of Chemical Engineering, Sungkyunkwan University, Suwon, Gyeonggi 16419, Korea KUKDO Chemical, 61, Gasandigital 2-ro, Geumcheon-gu, Seoul 08588, Korea 3 Hyundai Motor Group 150, Hyundaiyeonguso-ro, Hwaseong-si, Gyeonggi 18280, Korea 2
Received May 13, 2020 / Revised June 14, 2020 / Accepted June 17, 2020
Abstract: As a matrix resin of silica/epoxy hybrid encapsulation material with high heat resistance and low coefficient of thermal expansion, a tri-functional triglycidyl p-aminophenol (TGPAP) epoxy was successfully synthesized with the desired chemical structure by reacting epichlorohydrin with p-aminophenol using sodium hydroxide catalyst. In order to produce highly pure TGPAP with lower viscosity, a physical thin film vacuum distillation was carried out after synthesis, resulting in 97% purity with the viscosity of 700 cps at room temperature. Silica/TGPAP hybrid was fabricated using two kinds of ground fumed silica with different sizes of 20 μm and 9 μm. Glass transition temperature of the hybrid was found to be as high as 185 oC. Viscosity of the hybrid was 30,000 cps at room temperature before curing, implying good processability. When two different sizes of silica were used with 1 to 1 weight ratio, very low coefficient of thermal expansion of 22.79 ppm/ oC was obtained. From thermal shock test, no cracks were observed even after 1,000 cycles of thermal shock between -40 oC and 125 oC when 67 wt% (45.8 vol%) of silica was involved in the hybrid. In conclusion, silica/TGPAP hybrid with improved processability, superior thermal shock resistance and low thermal expansion coefficient could be fabricated as electronic device encapsulation. Keywords: pure tri-functional epoxy resin, thin film distillation process, silica, hybrid encapsulation, high heat-resistance, low coefficient of thermal expansion.
1. Introduction Since more than 60 years thermosetting epoxy resin systems have found widespread industrial applications in transportation and industrial machinery.1-4 Epoxy materials have been also widely used as encapsulation materials in the electrical and electronic industry because of their excellent mechanical and electrical properties, thermal durability, chemical resistance and easy processability.5 In general, inorganic filler/epoxy resin hybrid materials are often used to improve heat resistance, thermal shock resistance and mechanical properties of the encapsulation of the electronic devices.6-9 In order to utilize silica/epoxy hybrid as encapsulation material of electrical parts, high glass transition temperature (Tg), low coefficient of thermal expansion (CTE) and low viscosity for processability are extremely important properties of the hybrid materials. Generally, viscosity of silica/epoxy hybrid should be low so that filling-up of the hybrid material c
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