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We report on an experimental study of laser microvia percussion drilling of Ajinomoto build-up film (ABF) material using an ultrashort pulsed laser in the ultraviolet region. In order to optimize the drilling quality in terms of the fabricated taper and microvia diameter, the
MHz burst mode is used in combination with both a Gaussian and a top-hat laser intensity distribution. To evaluate the influence of the top-hat beam shape on defocusing, microvias were drilled at different z-positions in the range of 200 μm evenly distributed around the focal plane. The drilling quality was evaluated by laser scanning microscopy and metallography. When using a top-hat beam shape, a reduced taper of down to 26.8 % on average is achieved compared to a Gaussian beam. For the application of 3 intra-burst pulses, we find an improvement of the taper by 11.6% compared to the single pulse mode due to the increasing heat accumulation. Using a top-hat beam shape in combination with the MHz burst mode, an 18.2 % reduction in laser drilling time for a microvia with a similar taper is remarkable, demonstrating the high potential for scaling throughput in electronics manufacturing.
We report on an optical setup for multi Bessel beam processing combining a refractive axicon and a spatial light modulator.
Based on their particular beam profile, Bessel beams exhibit various advantages over conventional Gaussian beams for
ultrashort pulsed laser processing. Especially for micromachining of transparent materials, applications such as micro-hole
drilling or the generation of voids benefit from the increased focal length of the applied Bessel beam. In addition, on
account of the significantly increased average output power of industrial ultrashort pulsed lasers over the last years, there
is a high demand on multi spot applications for using the available laser power in efficient production processes. Our
optical concept combines the dynamic possibilities of beam splitting using spatial light modulator with the benefits of
Bessel beams facilitating multi Bessel beam processing.