Bulge formation and improvement of the polymer in CO₂ laser micromachining

This paper reports a novel approach to eliminate the bulges formed at the rim of a channel in a PMMA polymer substrate during CO₂ laser micromachining by covering a PDMS or JSR photoresist layer on the polymer substrate to get a good quality of smooth surface for the MEMS application. The bulges formed in the conventional laser micromachined polymer result in problems of bonding of the microfluidic chips or the clogging of liquid flow in the channel. Different cover layers of PDMS material and JSR photoresist unexposed or exposed by UV light were used to study the phenomena of formation and elimination of bulges. Also, a different number of passes were performed to investigate the variation of bulge shape and its formation mechanism as well as the profile of the channel. A physical model for the bulge formation during CO₂ laser micromachining based on the photothermal melting mechanism was proposed. The micromachined PMMA polymer without bulges at the rim of the channel has been demonstrated using a cover layer on the substrate by the CO₂ laser technology at low cost and rapid prototyping.