Abstract:
A method for forming a nozzle plate for an ink jet printer by laser ablation wherein topographical features are formed by laser ablation and additional ablation pulses are applied to remove debris from the nozzle plate.

Description:
FIELD OF THE INVENTION 
     The invention relates to the manufacture of printheads for ink jet printers. More particularly, the invention relates to the removal of debris from nozzle plates during the manufacture of printheads. 
     BACKGROUND 
     Nozzle plates of the type used in ink jet printheads can be made by laser ablating a polyimide material to define ink flow features. During this process, debris, primarily loose polyimide material, may become present on the ablated material and remain after the flow features have been formed. This debris is undesirable, as it may clog the flow features, cause poor adhesion when the nozzle plate is subsequently attached to a heater chip, or be otherwise detrimental to the manufacturing process and function of the resulting printhead. 
     One common method for removing the debris is by adding a water-soluble sacrificial layer to the topside of the nozzle plate material. The debris lands on this layer and is removed by a high-pressure water spray. However, the desire for faster printers has led to the use of longer heater chips and hence, longer arrays of nozzles. Also, the desire for higher quality print has led to smaller flow features on nozzle plates that are very close together, e.g., &lt;10 μm. However, for various reasons, water spray techniques are generally unsuitable for cleaning debris from longer plates and/or plates having flow features that are very close together. 
     Accordingly, there is a need in the art for improvements in the manufacture of printheads and, in particular, in the making of nozzle plates by laser ablation. 
     SUMMARY OF THE INVENTION 
     With regard to the foregoing, the invention provides a method for forming a nozzle plate for an ink jet printer by laser ablation. 
     In a preferred embodiment, the method includes the steps of laser ablating a first portion of a nozzle plate material to partially form topographical flow features on the material. Next, a second portion of the nozzle plate material is ablated to form second topographical features. During this second ablation step, debris generated during ablation can travel to the first portion. Thus, additional ablation is performed to additionally form the first flow features and, in the process, remove debris generated during ablation of the second flow features. 
     An advantage of the invention is that it enables ablation of longer nozzle plates while avoiding the presence of debris on the finished nozzle plate. For example, debris from the first step of partially forming the first flow features which may land on the second portion is removed during formation of the second flow features. Debris from the formation of the second flow features is removed from the first portion when the first flow features are additionally formed. The debris from the additional formation of the first flow features is substantially negligible. If desired, the ablation may be performed in more than three steps, such that each step produces less and less debris. 
     In another aspect, the invention relates to a method for forming a nozzle plate for an ink jet printer by laser ablation. 
     In a preferred embodiment, the method includes the steps of: 
     (a) laser ablating a nozzle plate material to form topographical features on the nozzle plate material; 
     (b) providing a mask having an inner open area surrounded by a outer shielded area and positioning the mask on the nozzle plate material so that the topographical features are within the inner open area and surrounded by the outer shielded area; and 
     (c) additionally laser ablating the inner open area of the mask to clean debris from the nozzle plate material, wherein such additional laser ablation causes debris located between one or more of the topographical features to travel away from the topographical features and the inner open area. 
     This method is particularly suitable for use in removing debris from between flow features of the nozzle plate that are closely spaced relative to one another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention will 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: 
     FIG. 1 is a representational cross-sectional view of a portion of a nozzle plate component of an ink jet printhead showing formation of debris during laser ablation of flow features on the nozzle plate; 
     FIG. 2 is a representational planar view showing the partial formation of flow features on a first portion of a nozzle plate in accordance with a preferred embodiment of the method of the present invention; 
     FIG. 3 is a representational planar view of the nozzle plate of FIG. 2 showing subsequent formation of ink flow features on a second portion of the nozzle plate; 
     FIG. 4 shows the nozzle plate of FIG. 3 after subsequent treatment of the first portion by laser ablation to further form the previously partially formed flow features of the first portion; 
     FIG. 5 is a representational view of a nozzle plate showing flow features formed by laser ablation and the deposit of debris between closely adjacent flow features; 
     FIG. 6 is a representational view showing removal of debris from the nozzle plate of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is directed toward the manufacture of printheads and, in particular, to a method for forming nozzle plate flow features using a laser ablation technique which removes debris generated during laser ablation of the nozzle plate. The removal of such debris is advantageous so that the debris does not remain to clog flow features and affect subsequent attachment of the nozzle plate to a heater chip. 
     With reference to FIG. 1, there is shown a polymeric nozzle plate material preferably a polyimide material  10  as it is being ablated by a laser beam, represented generally by beam B, to form flow features, such as channel  12 , to provide a nozzle plate. Nozzles or apertures  13  are preferably but not necessarily pre-formed in the material  12  as by a previous laser ablation step. 
     The polyimide material  10  has an upper surface  14  opposite a lower surface  16 . An adhesive layer  18  may be provided on the upper surface  14  prior to the ablation step for use in subsequent attachment of the nozzle plate to a heater chip. The adhesive layer  18  may be protected as by a sacrificial layer, preferably a water-soluble layer  20  such as polyvinyl alcohol or polyethylene oxide. 
     During ablation of the flow features  12 , debris  22  is generated and travels generally away from the channel  12 , as represented by arrows A. The debris  22  generally lands on the layer  20 , or the adhesive layer  18 , or the upper surface  14 , whichever is present as the exposed surface. When the sacrificial layer  20  is present, the debris  22  is commonly removed by use of a water spray which removes the sacrificial layer and the debris attached thereto. However, it has been observed that water spray removal alone is not generally suitable to remove debris in the manufacture of nozzle plates having a length greater than about ½ inch and nozzle plates having flow features that are very close together, e.g., generally spaced less than about 10 μm apart from each other. 
     For example, nozzle plates longer than ½ inch do not fit into the footprint of the laser beam. Thus, to make a 1 inch nozzle plate, a first half is preferably ablated and the plate moved so that the other half can then be ablated. However, ablation of the first half removes its sacrificial layer. Some debris from the ablation of the second half lands on the already ablated first half, which now does not have a sacrificial layer, making such areas generally unsuitable for cleaning by water spray. 
     Accordingly, with reference to FIGS. 2-4, there is shown a preferred embodiment for laser ablation of nozzle plates, particularly, nozzle plates longer than ½ inch, which effectively overcomes the disadvantages of conventional techniques. In FIG. 2, there is shown a nozzle plate  24  having a length of about one inch and having partially formed flow features  26  formed on a first half portion  25  thereof, preferably by partially laser ablating the first portion  25  of the nozzle plate  24 . Subsequent to the step of FIG. 2, FIG. 3 shows additional, and fully formed, flow features  28  on a second half portion  27  thereof adjacent to the partially formed features  26 . Subsequent to the step of FIG. 3, FIG. 4 shows further forming of the previously partially formed flow features  26  into fully formed flow features  30  in first half portion  25  of the nozzle plate  24 . Subsequent to fully forming the flow features  28  and  30 , a water spray may be used if desired, to remove any remaining sacrificial layer  20  and/or debris from the exposed surface of the nozzle plate  24 . 
     In each of the steps of FIGS. 2-4, the flow features, partial or complete, are formed by laser ablation techniques. The laser is preferably operated with an energy density of 1 joule/cm 2 , with a laser frequency of up to about 80 Hertz and a wavelength ranging from about 248 to about 308 nanometers (nm). 
     Returning to FIG. 2, it is noted that the features  26  are only partially formed. This is accomplished by ablating with one or more pulses, preferably one, fewer pulse than is needed to fully form the features  26  on the first portion  25  of the nozzle plate  24 . For example n−1 pulses are used to form the flow features shown in FIG. 1, where n ranges from about 200 to about 400 pulses depending on the desired depth of the flow features. Debris formed during this ablation step travels generally away from the first portion  25  and the features  26 , some being directed toward the second portion  27  where the features  28  are to be formed. Next, in FIG. 3, the features  28  on the second portion  27  of the nozzle plates are formed using the full requirement of laser beam pulses, i.e., n pulses where n ranges from about 200 to about 400 pulses. 
     In the process of forming the features  28 , the debris present thereon from the formation of the features  26  on the first portion  25  are removed by the laser beam pulses which form the features  28  in the second portion  27 , with some of the debris from the formation of the features  28  traveling to the first portion  25 . To remove the debris landing on the first portion  25  and, at the same time, to transform the partially formed features  26  into the fully formed features  30 , an additional pulse or pulses sufficient to fully form the features  30  is applied to the first portion  25 . As will be appreciated, some debris from the formation of the features  30  may travel to the second portion  27  of the nozzle plate adjacent the features  28 . However, it has been observed that such debris is substantially negligible when the member of pulses needed to complete flow features  30  is minimized. 
     In this regard, and in another aspect of the invention, the features  26  could be even less fully formed and the features  28  likewise less than fully formed, with each of the flow features  28  and  30  being additionally ablated in one or more subsequent steps in the described sequence, until all features are fully formed. Increasing the total number of steps would result in a reduction in the amount of debris remaining after the features  30  are fully formed on the first portion  25 . However, in each case, the features on the first portion  25  (features  30  for the described embodiment) require at least one more treatment step than do the features on the second portion  27  (features  28  for the described embodiment). 
     It is further noted that the features  26  could initially be fully formed and then a cleaning pulse applied following the formation of the features  28 . However, this is not preferred, as the additional pulse or pulses as represented in the step of FIG. 4 would tend to over-ablate the features  30  in first portion  25  and render them of non-uniform topography with respect to the flow features  28  in the second portion  27 . 
     As mentioned previously, it has been observed that water spray removal alone is not generally suitable to remove debris in the manufacture of nozzle plates  24  having flow features that are very closely spaced together, e.g., generally flow features spaced apart less than about 10 μm. With reference now to FIGS. 5 and 6, and in accordance with another aspect of the invention, there is shown a method for removing debris  40  from closely spaced flow features  42 , which are spaced apart a distance d of less than about 10 μm, and formed on polymeric material preferably on polyimide material  44 . The debris  40  results from the laser ablation of the features  42  and the close proximity of the flow features  42  renders conventional water spray techniques generally unsuitable for removal of debris  40  from these areas. 
     Accordingly, and with further reference to FIG. 6, a preferably rectangular mask  46  having an inner transparent or open area  48  and an outer shielded or opaque area  50  is provided. The mask  46  is positioned to surround the flow features  42  and a cleaning pulse from the laser is applied to ablate the flow features  42  and the spaces  43  between the features where the debris  40  may be located. As set forth above, the flow features are formed with a laser having an energy density of 1 joule/cm 2  with from about 200 to about 400 laser pulses at a frequency of up to 80 Hertz and a wavelength ranging from about 248 to about 308 nm. The cleaning step uses the same laser with the same operating conditions, but with only from 1 to about 5 pulses. This has been observed to effectively remove debris  40  may be from the closely adjacent areas between flow features  42 . New debris  40  generated from the cleaning pulse tends to land outside the transparent or inner open area  48  of the mark  46  (as represented generally by arrows A′). The area outside of the transparent or inner open area  48  is less likely to affect the performance of the nozzle plate and more likely to be removed with a water spray cleaning process than debris falling within the open area  48 . 
     The cleaning pulse is sufficiently low level so as to ablate a very thin amount of the flow features  42  preferably less than about 1 micron. Thus, it is suitable to fully form the features prior to the cleaning step. However, if desired, the features may initially be less than fully formed, with their full formation occurring during the cleaning step. 
     Having described various aspects and embodiments of the invention and several advantages thereof, it will be recognized by those of ordinary skills that the invention is susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.