Study on epoxy based composites for high temperature molding compounds
Epoxy molding compound (EMC) is one of the most widely used encapsulation materials for electronic packaging. To provide substantial protection for the electronic packages, EMCs are frequently required to work at elevated temperature, especially when high power and high density devices are developing rapidly and more heat is generated during operation. This thesis discussed the study on epoxy based composites for high temperature molding compounds by investigating two components most important in EMC system, namely the polymer resin and the filler system. In order to increase the glass transition temperature (Tg) and thermal stability of epoxy resin, cyanate ester was incorporated into the polymer matrix. The copolymer network formed by epoxy and cyanate ester (CE/EP) exhibited excellent thermal stability and high Tg above 270 ℃ because of the thermally stable s-triazine structures formed by cyanate ester trimerization. However, cyanate ester was affected by the hydrolysis reaction and too much cyanate ester in the system led to blistering and Tg drops in high temperature and high humidity tests. The cyanate ester amount in this copolymer was optimized to be 33-50 %. Polyimide was incorporated into CE/EP system as an additive (CE/EP-PI) to further improve the thermal stability of this epoxy-based resin. Aromatic polyimide exhibited good compatibility with CE/EP for their structural similarity. Improvements in Tg, storage modulus, fracture toughness and long term high temperature performance were observed at 5-10 % polyimide loading. At high polyimide loading level (> 10 %), a secondary phase emerged which deteriorated the resin properties such as storage modulus. The second part of this thesis investigated a modified filler system with surface coated silicon carbide (SiC) for thermal conductivity enhancement. In this part, SiC with high thermal conductivity was adopted as a replacement for conventional silica fillers. After surface treatment by silane coupling agent (SiC-GPTMS) and reactive silicon rubber (SiC-A15), modified SiC increased the thermal conductivity of the composites from 0.11 W/mK to 0.28 W/mK at 30 % filler loading.