Maskless photolithography using UV LEDs

A UV light emitting diode (LED) with a maximum output of 372 nm was collimated using a pinhole and a small plastic tube and focused using a microscope objective onto a substrate for direct lithographic patterning of the photoresist. Movement of the substrate with a motorised linear stage (syringe pump) allowed lines in SU-8 to be pattered with a width down to 35 {micro}m at a linear velocity of 80 {micro}m s-1, while in the dry film resist Ordyl SY 330, features as narrow as 17 {micro}m were made at a linear velocity of 245 {micro}m s-1. At this linear velocity, a 75 mm long feature could be patterned in 5 min. Functional microfluidic devices were made by casting PDMS on a master made by LED lithography. The results show that UV LEDs are a suitable light source for direct writing lithography, offering a budget friendly, and high resolution alternative for rapid prototyping of features smaller than 20 {micro}m