Photothermal formation of copper conductors on multichip module substrates using a Nd:YAG laser

A simple method for laser direct writing of copper from copper formate precursor films has been developed. Unlike previously reported laser processes involving the decomposition of solid precursor films, this process does not require any postprocessing (e.g., plating) to enhance the deposits in thickness or conductivity. Precursor crystallization has been completely eliminated by introduction of glycerol into the precursor. The lateral resolution has been improved by replacing the commonly used CW laser with a 100-kHz Q-switched laser of much lower average power, allowing for deposition of copper lines less than 20-μm wide. Thousands of individual conductors per substrate with thicknesses of 4-6 μm and resistivities below 10 μΩ-cm are routinely obtained with this method