In commercial production, there are two laser technologies available for laser drilling. The CO2 laser wavelength is in the far infrared range, and the ultraviolet laser wavelength is in the ultraviolet range. CO2 lasers are widely used in the fabrication of industrial microvias for printed circuit boards, requiring microvia diameters greater than 100 μm (Raman, 2001). For the production of these large apertures, CO2 lasers are highly productive because the punching time required to make large holes in CO2 lasers is very short. Ultraviolet laser technology is widely used in the production of micropores with a diameter of less than 100μm. With the use of miniature circuit diagrams, the aperture can be even less than 50μm. Ultraviolet laser technology produces very high yields when making holes smaller than 80 μm in diameter. Therefore, in order to meet the increasing demand for microporous productivity, many manufacturers have begun to introduce dual-head laser drilling systems. -The following are the three main types of double-head laser drilling systems available in the market today:
1) Double-head UV drilling system;
2) Double-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 easily divided into two types, a single-bit single-wavelength system and a dual-drill dual-wavelength system. Regardless of the type, there are two main parts that affect the ability to drill:
1) laser energy / pulse energy;
2) Beam positioning system.
The energy of the laser pulse and the efficiency of the beam transfer determine the drilling time. The drilling time is the time that the laser drill drills a microvia. The beam positioning system determines the speed of movement between the two holes. Together, these factors determine the speed at which a laser drill can produce a given microvia.
The dual-head UV laser system is best suited for drilling holes smaller than 90 μm in integrated circuits, and its aspect ratio is also high. The dual-head CO2 laser system uses a Q-switched RF-excited CO2 laser. The main advantages of this system are high repeatability (up to 100 kHz), short drilling time, wide operating surface, and the ability to drill a blind hole with only a few shots, but the quality of the hole is relatively low.
The most common dual-head laser drilling system is a hybrid laser drilling system consisting of an ultraviolet laser head and a CO2 laser head. This comprehensive hybrid laser drilling method allows simultaneous copper and dielectric drilling. That is, the copper is drilled with ultraviolet light to create the size and shape of the desired hole, followed by a non-covered dielectric with a CO 2 laser. The drilling process is done by drilling a 2in X 2in block called a domain.
The CO2 laser effectively removes the dielectric, even the non-uniform glass reinforced dielectric. However, a single CO2 laser cannot make small holes (less than 75 μm) and remove copper, with a few exceptions, which removes pre-treated thin copper foil below 5 μm (lustino, 2002). Ultraviolet lasers can make very small holes and remove all common copper streets (3 - 36μm, 1oz, even electroplated copper foil). Ultraviolet lasers can also remove dielectric materials separately, but at a slower rate. Moreover, for non-uniform materials, such as reinforced glass FR-4, the effect is generally not good. This is because the glass can be removed only if the energy density is increased to a certain extent, and this will also damage the inner pad. Since the stick laser system includes UV laser and CO 2 laser, it is optimal in both fields. All copper foils and small holes can be completed with UV laser, and the dielectric can be drilled quickly with CO 2 laser. hole. The figure shows the structure of a dual-head laser drilling system with programmable drill distance. The spacing between the two drill bits can be adjusted according to the layout of the components, which guarantees the maximum laser drilling capability.