| There are some advantages belong to piezo inkjet printhead, such as long operating life, and many kinds of ink can be used, for example, high viscosity resin, conductive material, protein and so on. In recent several years, a substantial amount of application on the inkjet printhead has been reported, such as printing, printed circuit board (PCB), bio-microarray, medical and 3D printing. Chamber is an important part of piezo inkjet printhead, while the present fabrication methods of chamber suffer from long manufacturing cycle, low alignment resolution between nozzles and piezoelectric structure and residual removing from chamber problem during fabricating process. In this paper, a SU-8 chamber for piezo inkjet printhead was fabricated by using ultraviolet (UV) photolithography and SU-8 thermal bonding method. By this method, the infilling problem of the chamber during thermal bonding process was solved, and low alignment resolution problem of conventional UV exposure system during assembly process was avoided. The following is the main research contents in the paper.(1) Fabrication method of chamber for inkjet printhead was reviewed for the first time. Diameter of nozzle and dimension of restrictor was optimized based on the theory of the incompressible Newtonian laminar flow fluid and simulation by Comsol. The dimension of pressure chamber is 200 ×110 ×1000μm, the restrictor’s is 30 ×110 ×135 μm, the nozzle’s isΦ50×40μm.(2) New fabrication method of chamber for inkjet printhead by SU-8 photolithography technology and bonding method was presented. Some material for chamber was compared, such as polyimide, isopropenyl methyl ketone, copolymer consists of methacrylic acid and polymethylmethaerylate, mixture consists of mibk methyl isobutyl ketone and diglyme, SU-8. Finally, SU-8 was selected as chamber material for piezo inkjet printhead.(3) Visco-elastic attribute and rheological characterization of amorphous polymer, bonding principle and bonding quality evaluation index system for chamber was researched. In addition, bonding parameter was optimized, the optimal bonding parameters are bonding temperature of 50 ℃, bonding pressure of 160 KPa and bonding time of 6 min. By using the optimized bonding parameter, bonding rate is 100%, and maximum chamber deformation is 5.256 μm in 2 inch diameter area fabricating process, and a single chamber dimension is 200 ×110×1000μm.(4) Fabricating process of chamber for piezo inkjet printhead was illustrated in detail. SU-8 2075 photoresist was firstly spin-coated on the substrate. The first SU-8 layer was crosslinked after UV exposure and post-bake. After developing the uncrosslinked SU-8 and hard-bake, the first patterned SU-8 layer with open pressure chamber and restrictor was fabricated. And the SU-8 spin-coated on the PDMS was thermal bonded with the first patterned SU-8 layer. After thermal bonding, the PDMS was removed and the second SU-8 layer was transferred onto the first patterned SU-8 layer, forming sealed pressure chamber and restrictor. The second SU-8 layer was exposed to 365nm UV light with nozzle plate mask, then post-baked on the hotplate to crosslink the exposed SU-8. Polydimethylsiloxane was used as substrate for spin-coating a 10 μm thin SU-8 layer. The mixed ratio of the silicone elastomer and curing agent was 12:1. Quality of nozzle was developed by adding anti-reflect layer and compensation method during mask design process.(5) Quality of chamber for piezo inkjet printhead by SU-8 photolithography technology and bonding method was tested, for example, tensile strength testing, ink-charge testing and ink drop testing. The bonding strength of the chamber bonded under the optimal bonding parameter is 2.1MPa, chamber was charged by ink successfully and ink drop was got through in-house test system.It is significant and commercially-viable to fabricate chamber for piezo inkjet printhead by SU-8 photolithography technology and bonding method, because it is low-cost and high-quality. |
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