Patent Application
20090186293
The disclosure relates to micro-fluid ejection heads, and in particular to improved dry film photoresist materials for laminating to a micro-fluid ejection head structure to provide a substantially planarized, relatively thin photoresist film on the structure.
Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is in an ink jet printer. Ink jet printers continue to be improved as the technology for making the micro-fluid ejection heads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable printers which approach the speed and quality of laser printers. An added benefit of ink jet printers is that color images can be produced at a fraction of the cost of laser printers with as good or better quality than laser printers. All of the foregoing benefits exhibited by ink jet printers have also increased the competitiveness of suppliers to provide comparable printers in a more cost efficient manner than their competitors.
One area of improvement in the printers is in the print engine or micro-fluid ejection head itself. This seemingly simple device is a relatively complicated structure containing electrical circuits, ink passageways and a variety of tiny parts assembled with precision to provide a powerful, yet versatile micro-fluid ejection head. The components of the ejection head must cooperate with each other and with a variety of fluid formulations to provide the desired ejected fluid properties. Accordingly, it is important to match the ejection head components to the fluid and the duty cycle demanded by the ejection device. Slight variations in production quality can have a tremendous influence on the product yield and resulting fluid ejector performance.
In order to improve the quality of the micro-fluid ejection heads, new techniques for assembling components of the heads are being developed. For example, instead of separately forming nozzle holes in a metal or polyimide nozzle plate material that is then adhesively attached to a semiconductor substrate structure, a dry film photoimageable material may be laminated to an imaged and developed thick film layer made of similar materials on the semiconductor substrate.
An advantage of a dry film lamination method for constructing micro-fluid ejection heads is that wafer level processing of multiple ejection heads may be conducted simultaneously rather than assembling individual components to individual ejection head substrates. The material to be laminated to the thick film layer on a substrate to provide the nozzle plate layer is produced in a separate process and then laminated with pressure and/or heat to the thick film layer. However, variations in the thickness, smoothness, and uniformity of the nozzle plate laminate material makes further processing of the nozzle plate difficult and may result in low yields of acceptable micro-fluid ejection head structures.
Accordingly, what are needed are an improved dry film photoresist laminate material and an improved process for making the dry film laminate material to provide more uniform nozzle plate layers.
In view of the foregoing, exemplary embodiments of the disclosure provide a method for making a dry film photoresist layer for a micro-fluid ejection head and a micro-fluid ejection head made by the method. The method includes applying a photoimageable liquid to a moving web of release material to provide a photoimageable layer on the release material using a slot die coater. The layer on the release material has a coating thickness ranging from about 2 to about 50 microns with a thickness variation of no more than about one micron. The photoimageable layer on the web is dried to provide a dry film photoresist layer. A protective web is then applied to the dry film photoresist layer.
In another embodiment, there is provided a method of making a micro-fluid ejection head having a photoimageable nozzle plate. The method includes applying a photoimageable thick film layer to a device surface of a substrate having fluid ejection actuators thereon. The thick film layer is imaged and developed to provide fluid flow features therein. A photoimageable nozzle plate dry film layer made by a slot die coating method is applied to the imaged and developed thick film layer. The dry film layer is imaged and developed to provide nozzles therein for ejection of fluid therethrough.
An advantage of the embodiments described herein is that the dry film photoimageable layer used for the nozzle plate has an essentially uniform thickness and is substantially devoid of air bubbles, streaks, and/or grooves. An exposed surface of the photoimageable layer on the substrate structure may have a surface roughness (Ra) value of less than about 20 nanometers and a maximum peak to value (Rt) value of less than about 1 micron. Since the slot die coating method applies liquid under substantially constant pressure to a moving web from a closed pressure container, air entrapment in the liquid that may cause the air bubbles is avoided. Another advantage of the slot die coating method over conventional coating methods is that evaporation of liquid components of the photoimageable liquid material is minimized. Accordingly, an essentially consistent solids content of the photoimageable liquid material may be maintained during the coating process thereby enabling improved planarity of the coated layer.
Further features and advantages of the disclosed embodiments may become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein:
As set forth above, improved micro-fluid ejection heads may include nozzle members having a substantially uniform thickness that are substantially devoid of air bubbles, streaks, and/or grooves. Conventional processes used to provide dry film photoimageable layers include rotogravure techniques as illustrated in
However, the dry film photoresist layer made by the foregoing method has significant shortfalls that make it unsuitable for use in making photoimageable nozzle plates. For one, the dry film layer may contain streaks or lines caused by the grooves in the roll 14 used to apply the thin film 18 to the backing material 12. Also, the liquid photoresist material in the pool 16 is often exposed to the environment during the coating process. Accordingly, evaporation of liquid components of the composition provides an ever changing solids concentration in the pool 16 of liquid. Because the solids concentration is changing, coating thicknesses may fluctuate significantly causing unwanted variations in dry film thickness.
Another disadvantage of the coating methods described above with reference to
In order to overcome the disadvantages of the conventional roll coating methods illustrated in
A suitable liquid photoresist composition 24 includes a difunctional epoxy resin, a multi-functional epoxy resin, and a phenoxy resin, wherein the difunctional epoxy resin contains two epoxy groups and the multi-functional epoxy resin contains more than two epoxy groups. The resin components are provided in a solvent for liquid application to the backing web 12. A particularly suitable formulation for the liquid photoresist composition 24 is set forth in the following table.
As described above, the photoimageable layer 26 is applied to the backing web 12 by the slot die coater 28 and the layer 26 is then dried with heat from a heat source 40 at a temperature ranging from about 110° to about 150° C., typically about 130° to provide a dried photoimageable layer 42. A protective web layer 44 having a thickness ranging from about 25 μm to about 250 μm is then applied by a lamination process to a surface 46 of the dried photoimageable layer 42 to provide a composite structure 48 illustrated in
A comparison of the properties of 14 micron thick photoimageable layers made by the prior art coating processes and the slot die process described above is provided in Table 2.
As shown by the foregoing table, the photoimageable layer 42 made by the slot die coating process is substantially more uniform in thickness and contains fewer air bubbles than photoimageable layers made by the prior art coating processes.
Suitable backing web 12 materials may be selected from a wide variety of flexible resilient films such as organic polymer films and metal foils, or a combination thereof that are commonly used as carrier sheet web materials. Accordingly, the backing web 12 may be selected from polyester films, polyimide films, copper clad polyimide films, copper, aluminum, nickel, brass, or stainless steel foils, and the like. Other useable web materials include polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polymethylmethacrylate (PMMA), and polycarbonate films. A particularly suitable backing web 12 may be selected from oriented polyethylene terephthalate (PET) films and polybutylene terephthalate (PBT) films having a thickness ranging from about 25 to about 250 microns.
However, conventional backing materials 12 to which the layer 42 is applied may have unacceptable surface roughness values that may impart an undesirable surface roughness characteristic to the layer 42. As shown in
The roughness of surface 50, illustrated in
A characteristic of the backing web 12 is that it has a surface that is wettable with the photoimageable layer 42, but is easily released from the photoimageable layer 42 when the photoimageable layer 42 is applied to a micro-fluid ejection head structure. Another characteristic of the backing web 12 is that it provide a relatively smooth surface for application of the photoimageable layer 42 thereto so that an exposed surface 50 of the photoimageable layer 42 on the thick film layer 52 is relatively smooth.
In order to improve the smoothness of an exposed surface 50 of the photoimageable layer 42, a conformal release layer 56 may be interposed between the backing web 12 and the photoimageable layer 42 to provide a composite structure 58 as illustrated in
Upon removal of the backing material 12 and release layer 56 from the photoimageable layer 42, the layer has a surface 50 that may have a surface roughness (Ra) value of less than about 20 nanometers and a maximum peak to valley (Rt) value of less than 1 micron. A comparison of the smoothness properties of backing materials made with and without the conformal release layer 56 is provided in Table 3.
As indicated by the foregoing table, a release liner containing the conformal release layer 56 had significantly lower Ra and Rt values than conventional backing materials. Accordingly, the photoimageable layer 42 applied to the backing material 12 containing the conformal release layer 56 is expected to have much lower Ra and Rt values. The surface 50 of the photoimageable layers 42 having roughness values (Ra) of less than 20 nanometers and maximum peak to valley (Rt) values of less than one micron is defined herein as an “ultra-smooth” surface 50. The ultra-smooth surface 50 of the photoimageable layer 42 may enhance image resolution during an imaging step to form nozzles in the photoimageable layer 42. Also the ultra-smooth surface 50 may reduce flooding potential for fluids on the surface 50 and may decrease mechanical adhesion between the backing material 12 and the photoimageable layer 42, making peeling of the backing material 12 from the photoimageable layer 42 easier. A comparison of peel strengths of coated and uncoated PET films is provided in the following table. Each peel test consisted of five strips of tape having a width of 25 mm and a length of 100 mm attached to uncoated and release layer coated PET film strips.
Accordingly, the average peel strength of the release layer coated PET film ranged from about 356.0 gram-force to about 418.1 gram-force compared to the uncoated PET film having a peel strength of 591.4 gram-force.
As described above, the composite material 58 also includes the protective web layer 44. The protective web layer 44 is provided as an interleaf layer on the dried photoimageable layer 42 to enable the composite material 58 to be coiled onto a roll or handled without damaging the surfaces 46 and 50 of the photoimageable layer 42. Upon use of the composite material 58, the protective web layer 44 is removed from the photoimageable layer 42 so that surface 46 is exposed as shown in
With reference now to
The device surface 60 of the substrates 54 also contains electrical tracing from the heater resistors 64 to contact pads used for connecting the substrates 54 to a flexible circuit or a tape automated bonding (TAB) circuit for supplying electrical impulses from a fluid ejection controller to activate one or more of the heater resistors 64.
The thick film layer 62 may be provided by a positive or negative photoresist material applied to the wafer as a wet layer by a spin coating process, a spray coating process, or the like. In the alternative the thick film layer 62 may be applied to the wafer as a dry film photoresist material using heat and pressure. Examples of suitable photoresist materials, include, but are not limited to, acrylic and epoxy-based photoresists such as the photoresist materials available from Shell Chemical Company of Houston, Tex. under the trade name EPON SU8 and photoresist materials available from Olin Hunt Specialty Products, Inc. which is a subsidiary of the Olin Corporation of West Paterson, N.J. under the trade name WAYCOAT. Other suitable photoresist materials include the photoresist materials available from Clariant Corporation of Somerville, N.J. under the trade names AZ4620 and AZ1512. A particularly suitable photoresist material includes from about 10 to about 20 percent by weight difunctional epoxy compound, less than about 4.5 percent by weight multifunctional crosslinking epoxy compound, from about 1 to about 10 percent by weight photoinitiator capable of generating a cation, and from about 20 to about 90 percent by weight non-photoreactive solvent as described in U.S. Pat. No. 5,907,333 to Patil et al., the disclosure of which is incorporated by reference herein as if fully set forth.
After coating the thick film layer 62 onto device surface 60 of the substrates 54, flow features may then be formed in the thick film layer 62 using conventional photoimaging techniques such as ultraviolet radiation, indicated by arrows 66 with wavelengths typically in the range of from about 193 to about 450 nanometers. A mask 68 having transparent areas 70 and opaque areas 72 may be used to define the flow features in the thick film layer 62. The imaged thick film layer 62 may be developed using standard photolithographic developing techniques.
Before or after applying the thick film layer 62 to the wafer containing the substrates 54 and before or after imaging and developing the thick film layer 62, one or more fluid supply slots 74 may be formed through the substrates 54 as shown in
Once developed, the thick film layer 52 may contain fluid supply channels, such as supply channel 76 in flow communication with the slot 74 to provide fluid to fluid ejection chambers, such as ejection chamber 78 as shown in
The resulting composite substrate/thick film layer 54/52 is referred to herein as a micro-fluid ejection head structure 80. Next, as shown in
Nozzles are formed in the photoimageable layer 42 using a photo imaging technique similar to the technique described above with respect to imaging the thick film layer 62. Accordingly, ultraviolet radiation indicated by arrow 82 and a mask 84 containing an opaque area 86 and transparent areas 88 is used to form the nozzles in the photoimageable layer 42. After imaging the photoimageable layer 42, a suitable solvent is used to dissolve the non-imaged areas providing a nozzle plate 90 containing nozzles 92 as shown in
Individual ejection heads 94 may be excised from the wafer containing a plurality of ejection heads 94 to provide the ejection head illustrated in plan view in
The micro-fluid ejection head 94 may be attached in a well known manner to a chip pocket in a cartridge body to form micro-fluid ejection cartridge 100 as shown in
The cartridge body of the cartridge 100 may be made of a metal or a polymeric material selected from the group consisting of amorphous thermoplastic polyetherimide available from G.E. Plastics of Huntersville, N.C. under the trade name ULTEM 1010, glass filled thermoplastic polyethylene terephthalate resin available from E. I. du Pont de Nemours and Company of Wilmington, Del. under the trade name RYNITE, syndiotactic polystyrene containing glass fiber available from Dow Chemical Company of Midland, Mich. under the trade name QUESTRA, polyphenylene oxide/high impact polystyrene resin blend available from G.E. Plastics under the trade names NORYL SE1 and polyamide/polyphenylene ether resin available from G.E. Plastics under the trade name NORYL GTX. A suitable polymeric material for making the cartridge body is NORYL SE1 polymer.
As shown in
At numerous places throughout this specification, reference has been made to a number of U.S. patents. All such cited documents are expressly incorporated in full into this disclosure as if fully set forth herein.
Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. As used throughout the specification and claims, “a” and/or “an” may refer to one or more than one. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, percent, ratio, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
The patentees do not intend to dedicate any disclosed embodiments to the public, and to the extent any disclosed modifications or alterations may not literally fall within the scope of the claims, they are considered to be part hereof under the doctrine of equivalents.
