Owing to the trend of faster and denser circuit design, the dielectric properties of packaging materials for semi-conductors will have greater influence on performance and reliability. Also, as chips become more densely packaged, thermal dissipation becomes a critical reliability issue. Consequently, four important properties for manufacturing semi-conductor packaging are: low values of dielectric constants, high values of thermal conductivity, relatively low values of thermal expansion coefficients, and low cost. Thus, in this study, AW (Aluminum Nitride) was selected as the filler for an epoxy matrix to achieve increased performance of an EMC. As a result, the thermal conductivity of an EMC filled with 70 vol% of AlN increased as much as 7-8 times compared with the EMC filled with a crystalline silica (vol. 70 %). When more than 60 vol% of AlN was added to the EMC, the dielectric constants and thermal expansion coefficient decreased rapidly.