The paper reports about fabrication process, characterizations and transmission properties of screen printed transmission lines Large area joining between a substrate and a heat sink is desirable for high performance power modules. We found that intermetallic compound (IMC) pillar dispersed solder is highly durable joint to achieve large area joining. The aim of this study is to clarify the mechanism of the strength reinforcement by IMC pillars. The structural characteristic of the solder joint was examined by cross-sectional observation, and the durability characterization was examined by FEM analysis. IMC pillars restrained cracks by obstructing crack propagation in the solder layer.