Microvia Drilling With A Green Laser

Microvias drilling in polymer-copper-polymer multilayer substrate for high density electronic packaging applications is studied in this paper. Frequency doubled Nd:YAG laser (532 nm) is used for the simulation and experiment. Numerical thermal model is built to simulate the drilling process. Volumetric heating and laser self defocusing due to drilling front profile are considered in the model. Due to the low absorption coefficient of the polymer material for the green laser, the polymer-copper interface absorbs a great portion of the laser energy. Thus the drilling mechanism involves thermal phase change, chemical decomposition, and possibly explosion due to rapid thermal expansion and vaporization inside the polymer material. Experimental results show that the material is removed explosively due to high internal pressures