For insulting layers in multi-layer printed circuit boards, Ajinomoto build-up film (ABF) is one of the most crucial component in manufacturing of high-performance electronic devices. The ongoing demand for miniaturized electronic components with advanced functionalities requires a higher power density in packaging and interconnect technology, in turn demanding for a reduction of the diameter of laser drilled microvias.
Recently, ultrashort pulsed lasers have gained considerable attention for microdrilling owing to a negligible heat material interaction and the possibility of small focal diameters by a wavelength in the ultraviolet regime. In order to evaluate its full potential for laser microvia fabrication, we report on a comprehensive study of laser microvia percussion drilling of ABF using a high-power laser system with a wavelength of 355 nm and a laser pulse duration of 10 ps. For the optimization of the laser drilling quality, which in turn is defined by the fabricated taper and the diameter of the microvia as being evaluated by laser scanning microscopy and materialography, laser bursts containing of a number of intra-burst pulses between 1-6 at an intra-burst pulse repetition rate of 82 MHz, different number of laser pulses, laser pulse fluence and laser burst repetition rates, respectively, are varied. In addition, diffractive optical elements are used to transform the Gaussian beam into a round uniform-intensity laser spot within the focal plane of the telecentric f-theta lens to influence the drilling process.