On the application of laser drilling in circuit board industry
In the drilling process of HDI PCB manufacturing process, there are two laser skills that can be used for laser drilling of PCB. The wavelength of CO2 laser is in the far infrared band, and the wavelength of ultraviolet laser is in the ultraviolet band. CO2 laser is widely used in the production of micro through holes in PCB industry, and the diameter of micro through holes should be greater than 100 μ m (Raman, 2001). CO2 laser has a high productivity in the production of these large aperture holes, which is due to the short punching time required for CO2 laser to make large aperture holes. UV laser technology is widely used in the production of micro holes with diameter less than 100 μ M. with the application of micro circuit diagram, the aperture can be even less than 50 μ M. The output of ultra violet laser is very high when it is used to make holes with diameter less than 80 μ M. Therefore, in order to meet the need of increasing micropore productivity, many PCB manufacturers have begun to introduce double head laser drilling system. The following are the three primary types of dual head laser drilling systems available on the market today:
1) Double head ultraviolet drilling system;
2) Double head CO2 laser drilling system;
3) Rod laser drilling system (CO2 and UV).
All the drilling systems in the manufacturing process of hdipcb board have their own advantages and disadvantages. Laser drilling system can be divided into two types: single wavelength system with double drills and dual wavelength system with double drills. Regardless of the type, there are two primary abilities that affect drilling:
1) Laser energy / pulse energy;
2） Beam positioning system.
The energy of laser pulse and the transmission power of laser beam determine the drilling time. The drilling time refers to the time when the laser drilling machine drills a micro through hole. The beam positioning system determines the speed of movement between the two holes. Together, these factors determine the speed of the laser drilling machine to make a micro through hole. The double head UV laser system is most suitable for drilling holes with the integrated circuit smaller than 90 μ m, and its aspect ratio is also very high.
Double head CO2 laser system uses Q-switched RF to encourage CO2 laser. The main advantages of this system are high repeatability (up to 100kHz), short drilling time, wide control surface, only a few shots can drill a blind hole, but its drilling quality will be relatively low.
In the process of making HDI by PCB manufacturers, the most common double head laser drilling system is the hybrid laser drilling system, which consists of an ultraviolet laser head and a CO2 laser head. The hybrid laser drilling method can be used to drill copper and dielectric holes together. That is, to drill copper with ultraviolet ray, the standard and shape of the hole required by nature, followed by CO2 laser to drill the dielectric without concealment. Drilling process is completed by drilling 2inx2in block, which is called domain.
CO2 laser can effectively remove the dielectric, even the right and wrong average glass reinforced dielectric. However, a single CO2 laser can not make small holes (less than 75 μ m) and remove copper. There are also a few exceptions, which is equal to that it can remove the thin copper foil below 5 μ m through pretreatment (lustino, 2002). Ultra violet laser can make very small holes and remove all common copper streets (3-36 μ m, 1oz, even electroplated copper foil). UV laser can also remove the dielectric data alone, only at a slower speed. Moreover, for non-average data, such as reinforced glass FR-4, the effect is generally not good. This is because as long as the energy density increases to a certain extent, the glass can be removed, which will also damage the inner layer of the pad. Because the rod laser system contains UV laser and CO2 laser, it can reach the best in both fields. All copper foil and holes can be completed by UV laser, and the dielectric can be drilled rapidly by CO2 laser.
Nowadays, the distance between the two bits in most double head laser drilling systems is fixed, and they have step repeat beam positioning skills together. Step by step, the advantage of repetitive laser long-distance conditioner is that the conditioning planning of the domain is large (up to (50x50) μ m). The defect is that it is necessary for the long-distance laser conditioner to move step by step in a fixed field, and the distance between the two drills is fixed. The distance between the two bits of a typical dual head long distance laser conditioner is fixed (about 150 μ m). With regard to different panel standards, a fixed distance drill cannot be operated with the best configuration as a programmable distance drill.
Nowadays, the double head laser drilling system has various functions of different specifications, which can be used by both small PCB manufacturers and large-scale PCB manufacturers.
Because of its high dielectric constant, ceramic alumina is used to make printed circuit board. However, due to its fragility, wiring and installation of the drilling process required by the standard things are difficult to finish, because at this moment, it is necessary to reduce the mechanical pressure to the minimum, which is a credit to laser drilling. Rangel et al. (1997) demonstrated that the qnd: YAG laser can be used to drill holes on alumina substrates and alumina substrates covered with gold and anchors. Using the laser with short pulse, low energy and high peak power is helpful to prevent the sample from being damaged by mechanical pressure, and a high-quality through-hole with aperture less than 100 μ M can be made.
Now some large-scale PCB factories have introduced laser drilling machines. For those with a mechanical aperture less than 0.1 mm, only laser drilling machines can be used to complete. In 2014, two new Mitsubishi laser rigs were added to Ganzhou Shenlian circuit, which is equal to four laser rigs in total to meet the needs of HDI, FPC and other fine circuit boards at that time.