Micro-fluid ejection devices, such as ink jet printers continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. However, the improvement in speed and quality does not come without a price. The micro-fluid ejection heads are more costly to manufacture because of tighter alignment tolerances.
For example, some conventional micro-fluid ejection heads were made with nozzle plates (a form of a nozzle member) containing flow features. The nozzle plates were then aligned, and adhesively attached to a semiconductor substrate. However, minor imperfections in the substrate or nozzle plate components of the ejection head or improper alignment of the parts has a significant impact on the performance of the ejection heads.
One advance in providing improved micro-fluid ejection heads is the use of a photoresist layer applied to a device surface of the semiconductor substrate as a thick film layer. The thick film layer is imaged to provide flow features for the micro-fluid ejection heads. Use of the imaged thick film layer enables more accurate alignment between the flow features and ejection actuators on the device surface of the substrate.
While the use of an imaged photoresist layer improves alignment of the flow features to the ejection actuators, there still exist alignment problems and difficulties associated with a nozzle plate attached to the thick film layer. Misalignment between the ejection actuators and corresponding nozzles (e.g., holes) in a nozzle plate has a disadvantageous effect on the accuracy of fluid droplets ejected from the nozzles when the nozzles are formed in the nozzle plate before attaching the nozzle plate to the thick film layer. Ejector actuator and nozzle alignment also has an effect on the mass and velocity of the fluid droplets ejected through the nozzles.
Conventional nozzle plates were made from metal or a polyimide material that was laser ablated then adhesively attached to the thick film layer. Use of such nozzle plates require an alignment step to assure that the nozzles correspond with the fluid ejector actuators and flow features in the thick film layer. In order to eliminate such alignment steps, photoimageable nozzle plate materials may be applied to the thick film layer by spin coating or lamination techniques. Spin coating techniques may be used to apply the nozzle plate photoresist material to the thick film layer before the flow features are developed in the thick film layer. However, developing the flow features in the thick film layer after applying the nozzle plate materials to the thick film layer requires difficult processing techniques.
In the alternative, lamination techniques may be used to apply the nozzle plate materials to an imaged and developed thick film layer. However, conventional photoresist materials are available only as a relatively thick photoresist layer having a thickness of from about 35 to about 80 microns. Such relatively thick photoresist materials are too thick for use in providing a suitable photoimageable nozzle plate for a micro-fluid ejection head. If the photoresist materials are screened down to an appropriate thickness, the resulting photoresist films becomes too brittle to handle and apply by a lamination process to the thick film layer.
Accordingly, there is a need for, for example, improved photoresist or photoimageable materials that may be used as nozzle materials that may be laminated adjacent a thick film layer of a micro-fluid ejection head structure.
Amongst other embodiments of the present invention, there is provided a nozzle member for a micro-fluid ejection head, a micro-fluid ejection head containing an improved nozzle member, and a method for making a micro-fluid ejection head. One such nozzle member includes a negative photoresist composition derived from a first di-functional epoxy compound, a relatively high molecular weight polyhydroxy ether, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aliphatic ketone solvent. The nozzle member has a thickness ranging from about 10 microns to about 30 microns.
In another embodiment, there is provided a method for making an improved micro-fluid ejection head. The method includes applying a first negative photoresist layer adjacent a device surface of a substrate. The first negative photoresist layer is derived from a composition including a multi-functional epoxy compound, a first di-functional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent. A plurality of flow features are imaged in the first photoresist layer. The imaged first photoresist layer is developed to provide the plurality of flow features therein and a substantially planar thick film layer surface. A second negative photoresist layer is applied adjacent the thick film layer. The second negative photoresist layer has a thickness ranging from about 10 to about 30 microns and is derived from a second photoresist formulation including the first di-functional epoxy compound, a relatively high molecular weight polyhydroxy ether, the photoacid generator devoid of aryl sulfonium salts, the adhesion enhancer, and an aliphatic ketone solvent. A plurality of nozzles are imaged in the second photoresist layer. The imaged second photoresist layer is developed to provide a photoresist nozzle member adjacent the thick film layer.
In yet another embodiment, there is provided a micro-fluid ejection head including a substrate having a device surface. The ejection head includes a photoimaged and developed thick film layer applied adjacent the device surface of the substrate. The thick film layer is provided by a first negative photoresist layer derived from a composition including a multi-functional epoxy compound, a first di-functional epoxy compound, a photoacid generator devoid of aryl sulfonium salts, an adhesion enhancer, and an aryl ketone solvent. A photoimaged and developed nozzle member is adjacent the imaged and developed thick film layer. The photoimaged and developed nozzle member is a second photoresist layer derived from a composition including the first di-functional epoxy compound, a second di-functional epoxy compound, a relatively high molecular weight polyhydroxy ether, the photoacid generator devoid of aryl sulfonium salts, the adhesion enhancer, and an aliphatic ketone solvent. The nozzle member has a thickness ranging from about 10 microns to about 30 microns.
An advantage of at least some of the exemplary embodiments described herein is that lamination of a dry film photoresist layer adjacent a substrate and thick film layer for a micro-fluid ejection head enables wafer level processing of the ejection head. Wafer level processing means that separate processing steps for the nozzle member and the substrate may be eliminated in favor of photoimaging and developing a composite substrate containing materials providing the flow features and nozzles. Accordingly, laser ablation steps for the nozzle member as well as alignment tolerances, adhesives, and/or thermal compression bonding techniques used to attach the nozzle member to the substrate are avoided. Other potential benefits of the disclosed embodiments include reduction in raw materials required, potential improvement in ejection head performance, improvement in adhesion and durability of the composite substrate and nozzle member structure, and significant manufacturing cost savings.
For purposes of the disclosure, “difunctional epoxy” means epoxy compounds and materials having only two epoxy functional groups in the molecule. “Multifunctional epoxy” means epoxy compounds and materials having more than two epoxy functional groups in the molecule.