In commercial production, two laser technologies are available for laser drilling. The CO2 laser wavelength is in the far infrared band, and the ultraviolet laser wavelength is in the ultraviolet band. CO2 laser is widely used in the fabrication of industrial micro vias for printed circuit boards, requiring micro vias with diameters greater than 100 um. For these large aperture apertures, the CO2 laser is very productive because the punching time required for the fabrication of large holes by CO2 laser is very short. Ultra violet laser technology is widely used in the manufacture of micro pores with diameters less than 100 m. With the use of miniature wiring diagrams, the pore size can be even less than 50 m. Therefore, many manufacturers have begun to introduce dual head laser drilling systems to meet the increasing demand for microporous productivity. Here are three main types of double headed laser drilling systems in today's market:
1) double head ultraviolet drilling system;
2) double headed CO2 laser drilling system;
3) stick laser drilling system (CO2 and UV).
All of these types of drilling systems have their own advantages and disadvantages. The laser drilling system can be simply divided into two types, dual drill single wavelength systems and dual drill dual wavelength systems. Either way, there are two main parts that affect the ability to drill holes:
1) laser energy / pulse energy;
2) beam positioning system.
The time of drilling is decided by the energy of laser pulse and the transfer efficiency of beam. The drilling time is the time when a laser drilling machine drills a micro through-hole. The beam positioning system determines the speed of moving between two holes. These factors together determine the speed at which the laser drilling machine produces the required micro vias.
The twin head CO2 laser system uses a modulated Q radio frequency excited CO2 laser. The main advantage of this system is high repetition rate (up to 100kHz), drilling time is short, wide, only need to shoot a few can drill a hole, but the hole quality will be relatively low.
The most common double head laser drilling system is a hybrid laser drilling system consisting of an ultra violet laser head and a CO2 laser head. The combined use of a hybrid laser drilling method allows drilling of copper and dielectric simultaneously. Drill the copper with ultraviolet light to produce the size and shape of the required hole, then drill the non covered dielectric with the CO 2 laser. The drilling process is accomplished by drilling 2in, X, and 2in blocks, which are called domains.
The CO2 laser effectively removes dielectric and even inhomogeneous glass reinforced dielectrics. However, a single CO2 laser can not make small holes and remove copper, and there are a few exceptions, that is, it removes thin copper foil that has been pretreated 5 m below. Ultra violet laser can make very small holes, and can remove all the ordinary copper street. Ultraviolet lasers can also remove dielectric materials alone, but only at a slower rate. Moreover, for inhomogeneous materials, such as reinforced glass FR -4, the effect is usually not good. This is because only the energy density increases to a certain extent can remove the glass, and this will also destroy the inner layer of the pad. The hybrid laser system including ultraviolet laser and CO 2 laser, which in two areas to achieve the best, using ultraviolet laser can complete all the copper foil and a small CO 2 laser can fast drilling of dielectric. Fig. 10-14 shows the structure of a double head laser drilling system with programmable drill spacing. The spacing between the two bits can be adjusted according to the layout of the components, thus ensuring the maximum laser drilling ability.
Most of the double head laser drilling systems now have fixed spacing between the two drills and have step - by - step beam positioning technology. The advantage of stepping and repeating laser remote regulators is that their range of regulation is large. The disadvantage is that the laser remote regulator must move in a fixed field, and the spacing between the two bits is fixed. A typical double head laser remote regulator, the distance between the two bit is fixed. For different panel sizes, the fixed distance drill can not operate as optimally as a programmable spacing drill.
Today, the twin head laser drilling system features a wide range of specifications, both for small printed circuit board manufacturers and for high-volume printed circuit board manufacturers.
Because ceramic alumina has a high dielectric constant, it is used to make printed circuit boards. However, due to its fragility, the drilling process required for routing and assembly is difficult to achieve with standard tools because the mechanical pressure must be minimized to this point, which is a good thing for laser drilling.