Laser-Assisted etching and metallisation of via-holes in polyethylene terephthalate



Experimental results are presented on via-hole etching in a thick (100 μm) film of polyethylene terephthalate (PET) with the help of a copper vapour laser (wavelength γ=510 nm, pulse duration 10 ns, repetition rate 8 kHz). The rate of via-hole formation is as high as 100 μms−1. The effective coupling of the polymer film to the laser radiation is due to the formation of highly absorbing graphitised regions in the bulk of the film, which is initially transparent at the laser wavelength. The side walls of the hole can be metallised by simultaneous decomposition of a Pd(acac)2 spun-on layer as a precursor for subsequent electroless Ni deposition. The activation of the inner surface of the hole is achieved as a result of the precursor vapour entering the hole during laser etching. The metallised via-hole provides a good electrical interconnection of the two sides of the PET film.