Moldless electroplating for cylindrical microchannel fabrication

A conventional replication master made of photoresist for microchannel fabrication does not have reproducibility for the repeated replica molding, high temperature and high pressure processes. This paper presents how to fabricate cylindrical microfluidic channels easily, cheaply, and endurably by electroplating process. A hemispherical surface, instead of a rectangular surface, is achieved on an extremely thin metal seed layer by moldless electroplating. Without mold, exposed edges have abnormal growth rate and bad adhesion caused by high current density. However, with reduced thickness of the seed layer, the edge effect, converging electric field at the edge point, becomes negligible. A 5-μm wide gold strip was patterned on a glass wafer as seed layers. After the copper electroplating, a long and semicircular pole grew on the wafer. This copper protrusion played a role for the channel when poly(dimethylsiloxane) was poured. A depressed piece and a flat one built up a semicircular channel. Simulation results show that the tendency for metal to be semi-circle strongly depends on the aspect ratio of seed layers. Reversed connections to the power supply resolved copper into ions, which resulted in a dwindling of the radius of the copper pole when electroplating. Based on this fact, various diameters of channels were made by an electroplated replication master on a single wafer.