drill EDM-UV laser drilling of printed circuit
There are four types of lasers for the production of printed circuit drill edm board micro-vias: CO2 lasers, YAG lasers, excimer lasers and copper vapor lasers. CO2 lasers are typically used in the production of about 75μm holes, but due to a beam reflected from the surface of the copper, so it is only suited to remove the dielectric. CO2 laser is very stable, cheap, and does not require maintenance. The excimer laser is the production of high quality, the best choice for small-diameter hole, a typical aperture value is less than 10μm. These types are most suitable for micro-ball grid array package (microBGA) polyester plastic substrate, high-density arrays drilling device. The development of a copper vapor laser is still early, however, still have an advantage when high productivity is required. Copper vapor laser can remove the dielectric and copper, will cause serious problems in the production process, however, will make the air flow to produce products only in a restricted environment.
In the printed circuit board industry is the most common laser adjust the Q-switched Nd: YAG laser wavelength of 355nm in the ultraviolet range. This wavelength in the printed circuit board drilling most metals (Gu, Ni, Au, Ag) melt, the absorption rate of over 50% (Meier and Schmidt, 2002), organic materials can be melted. UV laser photon energy can be as high as 5 -7. 5eV in the melting process will enable bond breaking, in part by the photochemical effect of ultraviolet laser, in part through photothermolysis. These properties make the UV laser to become the first choice for printed circuit boards for industrial applications.
YAG laser system has a laser source, the energy density (traffic) over 4J/cm 2, this energy density is drilled micro-vias surface of copper through the necessary. Energy density of the melting process of the organic material is only about 100mJ/cm 2, such as epoxy and polyester Asia limb. To correct operation in such a wide spectral range, very accurate and precise control of laser energy. Micro through-hole drilling process requires two steps, the first step to open the foil, high energy density laser and the second step with low-energy density laser to remove the dielectric.
Laser wavelength of 355nm when the typical spot diameter of about 20μm. The pulse duration is less than 140ns, the laser frequency between 10 - 50kHz, when the material does not produce heat.
The laser system is German, the Mis The LPKF, the base of the mechanical design will be hard granite, and its polished surface precision of not less than 3μm. The workbench bearing is placed in the gas bearing, controlled by the linear motor. The accuracy of the positioning of the glass scale to control the repeatability to ensure ± 1μm. Workbench itself is installed optical sensor for precise adjustment of the laser position in the different reflex points, to compensate for optical distortion and deviation of long-term drift. Adjusted, a series of revised data generated by the software, you can cover the entire scan area. Drift compensation of scale takes about lmin time operation. Any change in the substrate, for example, the position deviation from the benchmark can be detected by high-resolution CCD camera, be compensated by software control. |
