High-Speed Laser Ablation of Micro Via Holes in Nonwoven Aramid Reinforced PWB's to Reduce Interconnection Costs

摘要

High Speed Laser Ablation of Micro Via Holes in Nonwoven Aramid Reinforced PWB's to Reduce Interconnection Costs The introduction of new components with more I/Os has led to an increase in the number of connections on printed wiring boards. This in turn has led to the development of conductor line images with finer lines and spaces. In addition, the number of layers in multilayers has expanded, thus increasing the number of small diameter via holes which are required to interconnect the individual layers. To further increase the routing density, blind surface via holes and buried via holes are needed to connect the outer layers to one or more of the inner layers of the multilayer. Mechanical drilling of these holes has reached its technological limits and is slow, being typically one to three holes per second. Also, since most of these holes are greater than 300 #mu#m in diameter, larger lands are needed to accommodate the holes. These occupy a large board area which cannot be used for conductor routing, so new technologies need to be developed to form the smaller holes. Laser hole formation, in conjunction with Thermount nonwoven aramid reinforced laminate, has proven to be a reliable option for making surface via holes which are two to four layers deep and have diameters of less than 300 #mu#m. Thisis already being done today in a cost-effective manner at a rate of 12 to 500 holes per second. The laser-ablated holes canbe made so small that they can be located in the surface mount lands as well as in the conductor lines.