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  • UV laser drilling of the PCB
    Date :2010-5-4


    Currently used to produce micro-hole printed circuit board there are four types of lasers: CO 2 laser, YAG lasers, excimer lasers and copper vapor laser. CO2 lasers typically used in the production of about 75μm hole, but because of the beam reflected back from the copper surface, it is only suitable for removing dielectric. CO 2 laser is very stable, inexpensive, and does not require maintenance. Excimer laser is producing high quality, the best choice for small diameter holes, the typical aperture value is less than 10μm. These types most suitable for micro ball grid array package (microBGA) devices, plastic substrate, polyester sub-array of high-density drilling. Copper vapor laser development is still early, however, was still in need of high productivity advantage. Copper vapor laser to remove the dielectric and copper, but in the production process will create serious problems, will make the air flow only in a limited environment of production products.


    In the printed circuit board industry is the most common laser is adjusted QNd: YAG laser, whose wavelength is 355nm, in the ultraviolet range. The wavelength of drilling in printed circuit board when the majority of metals (Gu, Ni, Au, Ag) melt, the absorption rate of more than 50% (Meier and Schmidt, 2002), organic material can also be melting. UV laser photon energy up to 3.5-7.5eV, in the melting process can make chemical bonds break, in part through the UV laser photochemical, in part through the effects of light and heat. These properties make UV laser into printed circuit board of choice for industrial applications.


    YAG laser system has a laser source to provide the energy density (flow) over 4J/cm 2, the energy density of micro-hole drilling through the surface of copper required. Melting process of organic material needed energy density only about 100mJ/cm 2, for example epoxy resin and polyester sub-limbs. In order to correct such a wide range of spectrum, you need a very accurate and precise control of laser energy. Micro-hole drilling process requires two steps, first with high-energy density laser open copper foil, the second step with a low energy density laser to remove the dielectric.


    Laser wavelength of 355nm, their typical spot diameter of about 20μm. Pulse time is less than 140ns, the laser frequency in 10 - 50kHz between the time the material will not produce heat.


    Laser system is proposed by the German Mis LPKF, the mechanical design of the base is solid granite, polished surface precision of not less than 3μm. Table placed on gas bearings bearings, controlled by the linear motor. Positioning accuracy of the ruler to control by the glass, its repeatability ensure ± 1μm. Table itself is installed optical sensor, the reflection points at different locations on the precise laser adjustment, compensation of optical distortion and long-term drift of the bias. Adjusted by the software produced by a series of revised data, can cover the entire scanning area. Drift compensation scale approximately lmin time for action. Any change in the substrate, such as location deviated from the baseline, high-resolution CCD camera can detect, through software control to compensate.


    This system is ideal for prototype production, because it can drill and configuration, from flexible to rigid printed circuit board can be used, including metal polymers, such as solder resist, protective layer, dielectric, etc.. Raman, who introduced the most advanced solid-state ultraviolet laser system and high-density interconnects in micro-hole production application.


    Lange and Vollrath explained the UV laser system (micro-drilling of 600 lines system) in drill, configuration and cutting in a variety of applications. The system and the micro-hole drilling, copper layer aperture is reduced to 30μm, and for a range of substrates can be single-step operation, the system can produce the minimum width of 20μm outer conductors of printed circuit boards its production capacity far exceeds the photochemical. This system of production speeds of up to 250 drilling operation, and can allow all the standard input, such as Gerber and HPGL. Its operation area is 640mm x 560mm (25. 2in x 22in), the maximum height of material 50mm (2in), most commonly applied to the substrate. The base of the machine table and its guide are made of natural granite, with an accuracy of ± 3μm. Table driven by linear drives, the air bearing support; position by a glass rod with thermal compensation control, the precision of soil iμm. Operating table substrate by vacuum equipment installation completed.


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