Synthesis and properties of novel liquid ester-free reworkable cycloaliphatic diepoxides for electronic packaging application

Four novel liquid cycloaliphatic diepoxides, with two epoxycyclohexyl moieties linked via -O- (EpoI), -OCH₂CH₂O- (EpoII), -OCH (CH₃)CH₂O- (EpoIII), -OCH(CH₃)CH₂CH(CH₃)O- (EpoIV), respectively, and their diene precursors were synthesized and characterized. These diepoxides could be readily cured with hexahydro-4-methylphthalic anhydride (HMPA) using Iron (III) acetylacetonate as curing accelerator. The thermal and mechanical properties of cured products were examined by differential scanning calorimetry (DSC), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA). The thermogravimetric analysis (TGA) data revealed that, the cured EpoI and EpoII had similar thermal decomposition onset temperature to the commercial ERL-4221™ (> 300 °C), whereas the cured EopIII and EpoIV, having secondary or tertiary carbon-ether linkages, started to decompose at obviously lower temperature (around 220 °C), which just lay in the desired reworkability temperature range (200-300 °C). The higher glass transition temperature (> 120 °C) and moderately low thermal decomposition temperature made EpoIII and EpoIV suitable candidates for future reworkable flip chip electronic packaging application.