Fabrication And Dimensional Control Of Nickel Mould Based On SU-8 Thick Photoresist Techniques

UV-LIGA technology based on SU-8 photoresist is widely used in MEMS, because of its advantages such as microstructures moulding, complex structures moulding, mass production and obtaining high aspect rato and near-vertical sidewall microstructures. However, thermal swelling of SU-8 photoresist may lead to deformation of photoresist and width reduction of electroformed parts, which has become the key factor affecting dimensional precision of micro electroformed parts. Dimensional precision demand of microdevices is increasingly higher, with the microminiaturization of devices, while thermal swelling of SU-8 photoresist limits the development of this technology.With the UV-LIGA thchnology based on SU-8 thick photoresist, in this thesis, a new method that improves dimensional precision of electroformed parts by means of adding an isolation area was proposed and thermal swelling of SU-8 rectangular photoresist was investigated in order to obtain thermal swelling offset of SU-8 photoresist with different dimensions. Combining with adding isolation area and linewidth compensation, hot embossing nickel mould forμDMFC polymer flow field plates was fabricated.Taking the 200μm height snake-channle nickel mould with intensive graphics as the research object, this thesis proposed a new method that improves dimensional precision of electroformed parts via adding a closed and equally spaced isolation area around the mask graphics, aiming at the problem that the deformation caused by thermal swelling will increase with the rise of SU-8 photoresist thickness. Experiment results indicated this method improved dimensional precision of electroformed parts, while mask width was designed as 220μm, the width of electroformed parts reached to 212.3μm and the dimension error was merely 7.7μm.Thermal swelling of SU-8 rectangular photoresist was investigated in order to obtain thermal swelling offset of three different width resist with different thickness. Experiment results shown that consistency and repeatability of thermal swelling of SU-8 photoresist with the same size proved to be excellent. When the photoresist thickness was lower than 40μm, offset increased with the rise of thickness and there exited linear relationship between them, while the thickness was higher than 40μm, offset varied slowly. Thermal swelling offset can be considered as the linewidth compensation quantity of mask patterns. Finally, combining with adding an isolation area and linewidth compensation, this thesis fabricated hot embossing nickel mould including four different flow field structures forμDMFC polymer flow field plates, utilizing UV-LIGA technology based on SU-8 thick photoresist. Experiment results indicated that linewidth average error of straight channels was merely 4μm compared with design value, relative error of opening ratio and equivalent hydraulic diameter were about 2.0% and 1.5% repectively, and this method said above improved dimensional precision of nickel mould and also guaranteed the consistency of flow field parameters of this mould.