Katsuichi Ukita

Development of beam-pointing compensating optical system for aspheric beam shaper of PWB laser drilling system

In a PWB laser drilling system, an aspheric beam shaper, which converts single-mode Gaussian beam into beam with uniform irradiance profile is widely used. This beam shaper is very sensitive to decentering of the input beam, which is caused by the instability of beam pointing. It degrades the irradiance profile uniformity of the output beam and the processing quality. To solve this problem, we develop a beam pointing compensation optical system. This system contains a newly designed collimator which have a function to project the origin of the pointing vector of the laser beam to the input surface of the shaper in addition to the conventional function to control the diameter and the wavefront curvature of the laser beam. We analyzed the performance of the collimator by simulation, and confirmed that the irradiance distribution of output beam was not degraded by the instability of the beam pointing. Also, we confirmed its effects by the optical experiments.

Analysis of laser drilling process for substrate by optical simulation rectified at the ablation rate

The shape of a processed hole is a key factor for laser drilling system. There are many studies to calculate the behavior of heat or the reaction of molecules in a substrate after laser irradiation. These simulations enable calculation of removed volume by laser power. However, there were some difficulties to estimate the shape of processed hole. To solve the problem, the shape of processed hole was calculated by optical simulation and the ablation rate. The laser intensity distribution on the substrate was calculated by optical simulation considered with diffraction of beam and the aberrations of optics. Furthermore the results of optical simulation were rectified by ablation rate. The calculated shape of the processed hole showed good agreement with actual. This simulation can be used to control the laser drilling process to realize high quality holes.

Development of a high-performance UV-DPSS laser drilling system for PWB

A high-performance UV-DPSS (Diode Pumped Solid State) laser drilling system (wavelength 355nm) for PWBs, which can drill a less than 50micrometers diameter via-hole, has been developed. This system has two main features as follows: 1. A vua-hole without smear is possible to be drilled for PWBs with the optimized irradiation conditions of UV laser. 2. High throughput was realized by using a high power UV-DPSS laser and a developed high-speed control method of galvanometric scanning. This paper describes the outline of the developed UV-DPSS laser drilling system. This system has the advantages which are required small via-holes formation less than 50micrometers in diameter, compares with a conventional CO2 laser system currently.