In commercial production, there are two laser technologies available for laser drilling.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 industrial micro through-holes on printed circuit boards, which requires a micro through-hole diameter greater than 100 micrometers (Raman, 2001).For the fabrication of these large holes, CO2 laser has high productivity, because the punching time required for CO2 laser fabrication of large holes is very short.Ultraviolet laser technology is widely used in the production of microholes with diameter less than 100 mm. With the use of microcircuit diagram, the aperture can even be less than 50 mm.Uv laser technology produces a very high yield when holes with a diameter of less than 80 housings.As a result, many manufacturers have begun to introduce two-headed laser drilling systems to meet the increasing demand for micro-hole productivity.- here are three main types of two-headed laser drilling systems currently on the market:
1) dual-head ultraviolet drilling system;
2) two-head 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.Laser drilling systems can be simply divided into two types, dual bit single-wavelength system and dual bit dual-wavelength system.Regardless of the type, there are two main components that affect the ability to drill holes:
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. Drilling time refers to the time when the laser drilling machine drills a micro-through-hole. The beam positioning system determines the speed of moving between the two holes.These factors together determine the speed at which the laser drilling mechanism can make a given micropass hole.Dual-head uv laser systems are best suited for boreholes smaller than 90 anode in integrated circuits, and have a high aspect ratio.
The dual-head CO2 laser system USES q-switched rf excitation CO2 laser.The main advantages of this system are high repeatability (up to 100kHz), short drilling time and wide operating surface. It only needs a few shots to drill a blind hole, but its drilling quality will be relatively low.
The most commonly used two-headed laser drilling system is a hybrid laser drilling system consisting of an ultraviolet laser head and a CO2 laser head.The combined laser drilling method can be used to drill copper and dielectric simultaneously.Use the ultraviolet ray to drill the copper, the size and shape of the required hole, followed by a CO 2 laser drill without covering the dielectric.The drilling process is done by drilling the block 2in X 2in, which is called the domain.
CO2 laser effectively removes the dielectric, even non-uniform glass reinforced dielectric.However, a single CO2 laser cannot make a small pore (less than 75 mm) and remove copper, with a few exceptions, by removing the pretreated thin copper foil below 5 mm (lustino, 2002).Uv lasers can make very small holes and remove all the usual copper streets (3-36 current m, 1oz, even electroplated copper foil).Ultraviolet lasers can also remove dielectric material alone, but at a slower rate.And, for non-uniform materials, such as reinforced glass fr-4, the effect is generally not good.This is because the glass can only be removed if the energy density increases to a certain level, which also destroys the inner solder pan.Since the stick laser system includes both the ultraviolet laser and the CO 2 laser, it is the best in both fields. With the ultraviolet laser, all copper foil and holes can be completed. With the CO 2 laser, the dielectric can be drilled rapidly.FIG. 10-14 shows the structure of the dual-head laser drilling system with programmable drill spacing. The spacing between the two bits can be adjusted according to the layout of the components, which ensures the maximum capacity of laser drilling.
Nowadays, the spacing between two bits in most two-headed laser drilling systems is fixed, and there is a step-repeat beam positioning technique.Step by step, the advantage of the repeating laser remote adjuster itself is that the range is wide (up to (50 X 50) current m).The drawback is that the laser remote adjuster must be moved in a fixed domain and the spacing between the two bits is fixed.The distance between two bits of a typical two-headed laser remote regulator is fixed (approximately 150 current m).For different panel sizes, a bit with a fixed distance cannot be configured to operate as optimally as a bit with programmable spacing.
Today, the two-headed laser drilling system has various specifications, which can be applied to both small PCB manufacturers and mass PCB manufacturers.
Ceramic alumina is used to make printed circuit boards because of its high dielectric constant.However, because of its fragility, wiring and assembly, the drilling process is difficult to complete with standard tools, as the mechanical pressure must be reduced to a minimum, which is a good thing for laser drilling.Rangel et al. (1997) demonstrated that the tunable QNd: YAG laser can be used to drill holes for alumina substrates and aluminum oxide substrates coated with gold and anchors.Using a short pulse, low energy, peak power laser helps to avoid mechanical pressure damage to the sample and to create a good through-hole with an aperture of less than 100 volts m.This technique has been successfully used in low-noise microwave amplifiers with a frequency range of 8-18ghz (Betancourt et al., 1996)