Thermotropic liquid crystalline polyimides toward high heat conducting materials for 3D chip stack

Novel thermotropic liquid crystalline semi-aliphatic polyimide containing polysiloxane unit has been developed. The polyimide film exhibits high thermal stability and liquid crystallinity with lower transition temperature. Poly(amic acid) solution used as a precursor of the polyimide has very good surface wetting properties for a silicon wafer, resulting in homogeneous polyimide thin film formation on the wafer after thermal imidization below 200degC. The silicon wafer coated with the polyimide thin film can be bonded to another silicon wafer, or to another polyimide film on heating at 270degC with relatively low pressure. Moreover the bonding is repairable on heating again. It is proposed that the polyimide can be utilized as a polymer adhesive for three dimensional chip stack.