Laser Polishing of Micro-Machined Microfluidic Molds

Abstract

The objective of this paper is to explore the effective-ness of using a pulsed 1064 nm wavelength Nd:YAG laser to polish micro-machined metal molds. Polishing is desired to reduce the surface roughness of Polydimethylsiloxane (PDMS) devices cast with these molds. Reducing the roughness on polymer microfluidic devices is desirable in order to reduce fluidic resistance, control surface friction, improve optical transparency, and improve the bonding of mating surfaces. This study is focused on modifying the surface roughness of molds in order to improve the finish of cast PDMS devices, thereby enhancing their ability to bond to a glass substrate; standard practice to seal channels when manufacturing a microfluidic device.

The results of the laser parameters used in this study showed successful polishing of features with spatial fre-quencies above ~75 mm-1 (i.e., short wavelength features) . Surface features with smaller spatial frequencies (longer wavelength) remained relatively unaffected. Adhesion tests only correlated with the surface roughness metrics that capture the low spatial frequency (<75 mm-1) features. These results demonstrate that adhesion (bond strength) is a function of wavelength (and amplitude) of surface fea-tures. In order to completely describe a bonding interface, roughness metrics need to be obtained across the range of feature sizes; i.e., data collected and analyzed at different magnifications/resolutions. Laser polishing parameters that target longer wavelength features must be applied to the molds in this study in order to enhance the adhesion of the cast PDMS surfaces.