A New Die Attach Material for High Power Electronic Devices

Solder paste is selected as one of the most widely used die attach materials in high power electronic devices. It plays the role to connect die on the substrate or connect copper clip on the die. It is important to get a uniform solder distribution and low void to ensure good electrical conductivity, excellent thermal conductivity as well as mechanical support for the high-power electronic devices, especially for the package with high current density and high operating temperature. Due to the wetting effect of the molten solder during reflow, the die will move and may result into non-uniform solder distribution between die and substrate. In addition, molten solder is not strong enough against the weight of heavy copper clip applied on it to achieve a desired bond line thickness (BLT). To improve the solder distribution uniformity and get desired bond line thickness, a novel die attach material will be discussed in this paper. This novel die attach material is a solder paste with addition of Cu sphere. The existence of the Cu sphere in solder paste will ease the unbalanced wetting force of liquidus solder during reflow process, the die tilt was reduced significantly compared to the solder paste without Cu sphere. At the same time, the addition of Cu sphere will increase the strength of the molten solder and reduce the spreading caused by the heavy copper clip, it is helpful to obtain a higher bond line thickness for copper clip application.