Electrical Resistance of Laser Sintered Direct-Write Deposited Materials for Microelectronic Applications

The direct write technology provides an interesting opportunity for plugging blind via holes as a more precise alternative to currently used screen printing processes. This technology provides a complete, void-less filling of the via and fabrication of the interconnects extending from the via in one single step. After deposition, the material is heat treated (sintered) to densify into a highly conductive solid. Sintering is usually accomplished by laser treatment. Some aspects of this relatively new technology, especially these related to the relationships between the laser sintering process and the deposited material properties are still largely unexplored. This paper presents experimental results for the microscale electrical resistance of two silver inks deposited by a direct write method and sintered with a continuous wave Nd:YAG laser. The resistance of the deposited and sintered silver lines and the resistance of the material in the plugged via holes was mapped by the advanced micro four-point probe technique. Results showed that higher laser powers reduce significantly the resistance of the silver inks. The importance of the deposited material sinterability is also emphasized.