From recent technological backgrounds, packaging materials for semiconductor applications play a significant role in increased number of pins for grid array, miniaturization, high transmission performance and high reliability. In order to achieve such requirement, we have developed an insulation material for build-up layer package with four outstanding properties; high adhesivity between Cu line and substrate with flat surface, extremely low water absorption, low expansion coefficient, and low dielectric constant with low dielectric loss. We made a technological breakmrough for the Cu line formation onto a quite smooth substrate surface, showing that 10μm/10μm pattern in line and space can be formed finely by using a semi-additive method. Insulation reliability tests for the developed material were studied. The developed material show significantly better reliability than that of existing epoxy based material. We also studied high frequency signal propagation properties of the developed material. The developed material realizes substantial reduction of high frequency propagation loss from existing material. We concluded those technological development can contribute to the semiconductor packaging technology trend toward high density, high speed with high reliability.