Fabrication of fine and high-density multithread spirals on inner surfaces of small-diameter pipes using laser scan lithography

Dense and fine multithread helical patterns were fabricated on inner surfaces of copper pipes with an inner diameter of 2 mm. Such textures on the inner pipe surfaces will be useful for improving the heat conductivity of the pipes by increasing the surface areas and the mixing ability of liquids flowing inside by spirally stirring them. To fabricate the patterns, helical space patterns were repeatedly delineated using a laser-scan inner exposure system. Next, the inner pipe surface masked by the remaining resist patterns was chemically etched using a ferric chloride etchant. The etchant was infused into the pipe using a tube pump. The patterns were observed and evaluated by cutting half of the pipe off using a milling machine. To delineate and etch multithread patterns successfully, delineation and etching conditions were investigated in detail using ordinary single-thread helical patterns. After selecting optimal conditions, 50-thread helical groove patterns with a pitch of 126 mu m, a lead of 6.3 mm, and a length of 18 mm were fabricated. Although the resist patterns on half-cut specimens were partially damaged by the cutting fragments generated during the mechanical cutting of the pipe, the etched patterns were not damaged by machining, and good patterns without defects were obtained. The pattern pitch depended on the accuracy and repeatability of the stage movement. However, the stage was successfully and smoothly driven, and very homogeneous multithread helical patterns were obtained. The pitch errors were within the measurement error range of +/- 2 mu m, and there were no parts where patterns were irregularly placed. (C) 2014 The Japan Society of Applied Physics