Excimer laser microvia-technology in multichip modules

Microelectronics is moving towards smaller and lighter devices with high I/O counts. This involves the development of small via generation processes. Laser ablation technology is available and also compatible with conventional PCB technology. It allows to bring more functionality in the PCB or to utilize components like chip scale packages (CSP) or as flip chip in order to obtain multichip module laminates (MCM-Ls). In the current work, we use a UV laser in order to generate high-density arrays of microvias (well <100 μm in diameter). Microvias are opened in the dielectric of the resin coated copper (RCC) down to the underlying copper by using a controlled pulsed excimer laser. We show that the depth ablation is controlled and that the copper surface is not significantly damaged. This paper will briefly report on our first experimental results of microvia making. Hole plating that results from both electroless and electrodeposition of copper will be discussed. The shape aspect and the shape ratio of the formed vias as determined by means of profile measurements and optical inspection are presented.