There are four types of lasers :CO 2 laser, YAG laser, excimer laser and copper vapor laser.CO2 lasers are typically used to produce holes of about 75 fins, but because the beam is reflected back from the copper surface, it is only suitable to remove the dielectric.CO 2 lasers are very nonmessy, inexpensive, and do not require maintenance.The excimer laser is the best choice for producing high quality, small diameter holes with a typical aperture of less than 10 diameters.These types are best suited for high density array drilling in microBGA packaging equipment.The development of the copper vapor laser is still in its infancy, but it still has the upper hand when higher yield is required.The copper vapor laser can remove the dielectric and copper, but it can cause serious problems in the production process, making the air flow only able to produce in a restricted environment.
The most commonly used laser in the PCB industry is the QNd: YAG laser, which has a wavelength of 355nm within the ultraviolet range.This wavelength can cause most metals (Gu, Ni, Au, Ag) to melt when the printed circuit board is drilled, with an absorption rate of more than 50% (Meier and Schmidt, 2002), and organic materials can also be melted.The photon energy of ultraviolet laser can be as high as 3.5-7.5 eV, which can make the chemical bond break during melting.These functions make uv laser the first choice for PCB industry application.
The YAG laser system has a laser source that provides energy density (flow rate) over 4J/cm 2, which is necessary to drill the copper circulation on the surface of the micro-through-hole.The energy density required for the melting process of organic materials is only about 100mJ/cm 2, such as epoxy resin and poly coola.In order to operate accurately in such a wide spectrum range, very accurate and precise control of laser energy is required.The drilling process of micro-through-hole requires two steps. The first step is to open the copper foil with a high-energy density laser, and the second step is to remove the dielectric with a low-energy density laser.
At a wavelength of 355nm, the typical spot of light is about 20 m.When the pulse time is less than 140ns and the laser frequency is between 10-50khz, the material does not generate heat.
Figure 10-13 shows the basic schematic diagram of the system.The laser beam is located by a computerized scanner/reflection system and focused by a focal lens at a focal aperture, allowing the beam to be drilled at an exact Angle.The scanning process generates a vector pattern through the software to compensate for deviations in material and design.The scanning area is 55 x55mm.The system is compatible with CAM software and supports all common data patterns.
The laser system was put forward by German Mis LPKF, whose mechanical design base is made of hard granite, and its surface polishing accuracy is not lower than 3 vehicles.Table supports are placed on gas bearings controlled by a linear impulse.The correct positioning is controlled by a glass ruler, whose repeatability is guaranteed to be plus or minus 1 plus or minus m.The table itself is equipped with optical sensors that can accurately adjust the laser position at different reflection points to compensate for optical distortion and long-term drift.After adjustment, a series of correction data generated by the software can cover the whole scanning area.Drift scale compensation requires approximately lmin for manipulation.Any changes to the substrate, such as position deviation from the baseline, can be detected by a high-resolution CCD camera and compensated by software control.
The system is well suited for prototype production because it can drill holes and configurations that can be used on everything from flexible to rigid printed circuit boards, including metallic polymers such as resistance solders, protective coatings, dielectric, etc.Raman et al. have incorporated the most advanced solid-state uv laser systems of their predecessors and their applications in the production of high-density interconnected micro-through-holes.
Lange and Vollrath explained the various applications of the ultraviolet laser system (microwire drilling 600 system) in drilling, configuration and cutting.The system can drill and micro through holes, the copper layer aperture is reduced to 30 micrometers m, and the base material within a certain range can be operated in a single step. This system can also produce the printed circuit board outer lead with a minimum width of 20 micrometers, and its production capacity is much higher than that of photochemistry.The system can be manufactured at speeds of up to 250 drill and allows all scale inputs such as Gerber and HPGL.Its operating area is 640mm x 560mm (25.2in x 22in), and the maximum material height is 50mm (2in), which can be used in common substrates of large departments.The pedestal of the machine table and its guide rail are made of natural granite to a precision of plus or minus 3 m.The table is driven by a linear driver and supported by an air bearing.The position is controlled by a glass ruler with heat compensation, and the precision is soil I displacement m.The installation of the base plate of the control table is done by vacuum equipment.