Laser Drill Microvias
With the desire to put more functions into a single device without increasing the size of the device, many features of the printed circuit board have been changed, modified or removed over the years. From the number of layers of PCB to the mounting technology of components, printed circuit boards have gone through enormous advancement to achieve the desired functionality. One area that remained sidelined for many years was the interconnectivity of conducting lines between multiple layers. In a multiple layer circuit, conducting lines are present both on top of the board and between different layers so to provide current path between the layers. These connecting lines are known as “via” i.e. connecting paths. For advance circuitry the need of decreasing the diameter of these vias was felt but it was difficult to achieve through the traditional way of circuit drilling. For the drill bit to be able to make an accurate hole between the layers, a minimum diameter has to be ensured otherwise the drilling procedure could not take place efficiently.
This limitation with the traditional drilling stimulates the need of laser drilling micro vias where the diameter for the vias can be kept as low as 50 µm. The vias created by the use of laser drilling technology are called “Micro vias” because of their micro diameter. Today, all portable electronic and telecommunication have micro vias connection between different layers of their printed circuit boards. Technological edge in the laser technology has allowed the designers to drill the PCB with the ultraviolet laser light in such a manner that the top copper layer i.e. the conducting path and the bottom substrate material made from glass fibers or epoxy material are drilled simultaneously. The laser intensity is controlled such that tough all layers are drilled but the smoothness of the layers is hardly roughened. In the conformal mask drilling technique, copper is etched in the first step directly above the place where microvias are to be drilled. Then the drilling and cleaning of the substrate layer is done in the next steps and this consumes more time and efforts than the UV laser light drilling technology. The results obtained from the laser drilling technology have also shown lesser substrate roughness due to drilling than the conformal mask drilling technique.
As the laser light technology is based on the principle of high frequency radiations, therefore special care is needed for designers in this operation as it contains great risks of life and skin damage. For this reason, a proper room and environment is designed for such laser operations where the emitted radiations are observed by the walls and do not penetrate in the atmosphere. Furthermore, very accurate galvanometer-controlled mirrors and telecentric lenses are required for precisely positioning the laser beam at the place where micro meter drilling has to be performed.