In commercial production, two laser technologies can be used for laser drilling. The wavelength of the CO2 laser is in the far infrared band, and the ultraviolet laser wavelength is in the ultraviolet band. CO2 laser is widely used in the manufacturing of industrial microholes for printed circuit boards. The micropore diameter of the microholes is more than 100 u m (Raman, 2001). For the fabrication of these large aperture holes, the CO2 laser has high productivity, which is because the punching time required by the CO2 laser to make large holes is very short. Ultraviolet laser technology is widely used in microporous fabrication with a diameter of less than 100 m. With the use of microminiature circuit diagram, the aperture is even less than 50 mu m. The production of ultraviolet laser technology is very high when it is made of holes less than 80 m in diameter. Therefore, in order to meet the increasing demand for microporous productivity, many manufacturers have begun to introduce double headed laser drilling systems. The following are three main types of dual head laser drilling systems in the market today:
1) double head ultraviolet drilling system;
2) double head CO2 laser drilling system;
3) stick to laser drilling system (CO2 and UV).
All these types of drilling systems have their own advantages and disadvantages. The laser drilling system can be easily divided into two types, double bit single wavelength system and double bit dual wavelength system. No matter which type, there are two main parts that affect the drilling ability:
1) laser energy / pulse energy;
2) beam positioning system.
The energy of the laser pulse and the transmission efficiency of the beam determine the drilling time. The drilling time is the time for a laser drilling machine to drill a micro hole. The beam positioning system determines the speed of moving between the two holes. These factors jointly determine the speed of the microholes for a given requirement by a laser drilling machine. The dual head ultraviolet laser system is most suitable for using a hole in an integrated circuit of 90 micron m, and its vertical and horizontal ratio is also high.
The dual head CO2 laser system uses a Q RF 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, which consists of an ultraviolet laser head and a CO2 laser head. This hybrid laser drilling method can be carried out simultaneously with the drilling of copper and dielectric. It is to drill the copper with ultraviolet ray to generate the size and shape of the required hole, and then use the CO 2 laser to drill the uncovered dielectric. The drilling process is done by drilling a block of 2in X 2in, which is called a domain.
The CO2 laser effectively removes the dielectric, even the inhomogeneous glass. However, a single CO2 laser can not make small holes (less than 75 m) and remove copper. There are a few exceptions, that is, it can remove the thin copper foil (lustino, 2002) which has been pretreated below 5 m. The ultraviolet laser can make very small holes and remove all the common copper streets (3-36 m, 1oz, or even electroplated copper foil). The ultraviolet laser can also remove the dielectric material alone, but the speed is slower. Furthermore, for non-uniform materials, such as enhanced glass FR -4, the effect is usually not good. This is because only the energy density increases to a certain extent, the glass can be removed, and this will also destroy the inner layer of the plate. As the rod laser system includes UV laser and CO 2 laser, it can achieve the best in two fields. All the copper foil and holes can be finished by ultraviolet laser. The CO 2 laser can be used to drill the dielectric quickly.
Now, the distance between two bits in most double head laser drilling systems is fixed and has a step - and - repeat beam positioning technique. Step by step, the advantage of the repetitive laser remote regulator itself is that the range is adjustable (up to (50 X 50) mu m). The disadvantage is that the laser remote regulator must move in a fixed field, and the distance between the two bits is fixed. The distance between the two bits of a typical double head laser remote regulator is fixed (about 150 m). For different panel sizes, a bit at a fixed distance can not be operated on the best configuration like a programmable spacing bit.
Because the ceramic alumina has a very high dielectric constant, it is used in the manufacture of printed circuit board. However, due to its fragility, wiring and assembly, drilling process is difficult to accomplish with standard tools, because the mechanical pressure must be reduced to a minimum at this time, which is a good thing for laser drilling. Rangel et al. (1997) proved that the QNd: YAG laser can be used to drill the alumina substrate and the alumina substrate with gold and anchor. Short pulse, low energy and high peak power laser can help to avoid mechanical pressure damage to samples, and create high-quality through-hole with aperture less than 100 m.