Patent Abstract:
A fluid ejection device capable of ejecting fluid onto media. The device includes a carrier having an upper surface that defines a recess. The device further includes a fluid ejecting substrate disposed therein that is configured for establishing electrical and fluidic coupling with the carrier. The fluid ejecting substrate has a generally planar orifice layer defining a plurality of orifices therein and a generally planar contact surface positioned below the orifice layer. The device further includes an encapsulant that at least partially encapsulates the fluid ejecting substrate and the carrier to form a substantially co-planar surface with the orifice layer.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of copending application Ser. No. 09/556,026 filed on Apr. 20, 2000, now abandoned which is hereby incorporated by reference herein. 
     This invention is a continuation in part of U.S. patent application Ser. No. 09/430,534 filed on behalf of Marvin Wong, et al., on Oct. 29, 1999 now U.S. Pat. No. 6,188,414 entitled “Inkjet Printhead With Preformed Substrate” and assigned to the assignee of the present invention, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to inkjet printers, and more particularly to printing systems that include an inkjet printhead. Thermal inkjet printers have experienced a great deal of commercial success since their inception in the early 1980&#39;s. These printing systems have evolved from printing black text and graphics to full color, photo quality images. Inkjet printers are typically attached to an output device such as a computer. The output device provides printing instructions to the printer. These instructions typically are descriptions of text and images to be printed on a print media. A typical inkjet printer has a carriage that contains one or more printheads. The printhead and print media are moved relative to each other to accomplish printing. 
     The printhead typically consists of a fluid ejecting substrate which is electrically and fluidically coupled to the printing system. The fluid ejecting substrate has a plurality of heater resistors disposed therein which receive excitation signals from the printhead. The heater resistors are disposed adjacent a plurality of orifices formed in an orifice layer. Ink is supplied to the heater resistors from an ink source affixed to the printhead or from an ink source that is replaceable separate from the printhead. Ink supplied to the heater resistors is selectively ejected, in the form of ink droplets, through the orifices and onto the print media. The ink on the print media dries forming “dots” of ink that, when viewed together, create a printed image representative of the image description. The printed image is sometimes characterized by a print quality metric which may encompass dot placement, print resolution, color blending and overall appearance such as freedom from artifacts. Inkjet printer manufacturers are often challenged by an increasing need to improve print quality as well as increasing the reliability of the printhead. 
     The orifice layer and print media are ideally arranged in a parallel orientation to each other. An ink droplet ejected from an orifice in the orifice layer can be represented as a vector that is, ideally, directed orthogonal to the plane of the print media. Thus, when ink is ejected from the orifice layer of an “ideal printhead” the difference between where an ink droplet is placed on the print media and where it should have been placed is zero, thus the trajectory error is zero. In actuality, however, variations in the orifice layer manufacturing process result in ink droplets being ejected from an orifice at an angle which typically ranges between 0 and 2 degrees. These variations in the orifice layer are due to variation tolerances in the orifice formation as well as variation in the planarity of the orifice layer, to name a few. 
     The effect of trajectory error is exacerbated by separation distance between the printhead and print media. For example, a conventional printhead is separated from the print media by 1.5 mm. If ink is ejected from the orifice layer at an error angle of 2 degrees from the ideal or orthogonal direction, the ink droplet will be displaced 0.052 mm from where it should have been placed on the printing. If however, the printhead and print media are 0.7 mm apart and ink is ejected at the same 2 degree error angle, the ink droplet will be displaced by only 0.024 mm. This trajectory error tends to reduce or degrade the quality of the printed image because this error affects the positioning of ink on the print media. 
     The degradation in print quality resulting from trajectory error in conventional printheads is most prevalent where colors of ink are blended to produce “photographic” quality printed images. Here, displaced ink droplets will tend to cause the printed image to appear grainy and streaky. Furthermore, parasitic effects such as air current, tend to further influence trajectory error of the printing system. These parasitic effects tend to be reduced by lessening the printhead to print media spacing. 
     The printhead in a typical printing system is separated from the print media by a distance which may range from 1 millimeters to 1.5 millimeter (mm). This distance between the printhead and print media tends to be limited by the electrical coupling between the fluid ejecting substrate and the printhead body that supports the fluid ejecting substrate. For example, a disposable print cartridge includes a fluid ejecting substrate mounted in a pen body. An encapsulating material is often dispensed on top of the electrical coupling or interconnect to protect or shield the interconnect from ink. Inks used in thermal inkjet printheads tend to have salt constituents that tend to be corrosive and conductive. Once these inks leak into the electrical interface they tend to produce electrical shorts or corrosion that tend to reduce printhead life. The encapsulant disposed over the interconnect is commonly referred to as an encapsulant bead. The encapsulant bead protrudes beyond the orifice layer of the fluid ejecting substrate and tends to limit the spacing between the printhead and print media. Consequently, there tends to be a limit to the reduction of trajectory error. 
     In addition to print quality, the printing systems should have high reliability. Two common failure modes that may decrease the reliability of the printhead are: (1) exposure of the interconnect to ink and (2) ink leakage during the shelf life of the printhead. The encapsulant bead may be eroded thereby exposing the interconnect to ink if the printhead is positioned so close to the print media that the encapsulant bead rubs against the print media during printing. The ink tends to corrode the interconnect which ultimately leads to an electrical failure of the printhead thus, making the printhead less reliable. 
     Conventional inkjet printers employ a cleaning mechanism which includes a wiper that routinely wipes ink residue from the printhead orifice plate. This residue, if sufficient, can either clog the orifices thereby preventing drop ejection or cause misdirected drops. The cleaning mechanism has a predetermined tolerance so that the wiper does not damage the printhead during the cleaning process. However, the wiper tends to be less effective if it is obstructed by a protruding encapsulant bead and could possibly contribute to the erosion of the bead. 
     A second reliability factor that tends to reduce printhead life relates to environmental conditions that the printhead experiences. Printheads are often exposed to extreme environmental conditions before they are used in a printing system. For example, printheads are often stored in shipping warehouses where temperatures may range from 0-60 degrees Celsius. Or, printheads may be exposed to varying atmospheric pressures during shipping if the printheads are shipped via airplane. In general, conventional printheads are designed to accommodate these extreme conditions without leaking. However, under extreme environmental conditions as previously described, printheads may leak prior to being used in the printing system. In an attempt to remedy this problem, a tape-like material is placed over the orifice layer to further guard against ink leakage and drying of the ink in the orifices. Ideally, the tape-like material adheres evenly to the orifice layer. However, in conventional printheads, the encapsulant bead previously described may inhibit the tape-like material from uniformly adhering to the orifice layer. If the tape-like material does not uniformly adhere to the orifice layer, ink may leak through the orifice layer and damage surrounding objects. Additionally, ink leaking from the printhead may, over time, harden and clog the orifices as well as contaminate other colors of ink contained within the printhead. Furthermore, leaky printheads are perceived by consumers as being defective and inferior. 
     Accordingly, there is an ever present need for continued improvements to printing systems that are more reliable and capable of producing even higher quality images. These printing systems should be well suited for high volume manufacturing as well as have a low material cost thus further reducing per page printing cost. 
     SUMMARY OF THE INVENTION 
     The present invention is a printing system comprising an inkjet printhead responsive to activation signals for ejecting ink onto printing media. The printhead comprises a carrier having an upper surface that defines a recess and a fluid ejecting substrate disposed therein that is configured for establishing electrical and fluidic coupling with the carrier. The fluid ejecting substrate has a generally planar orifice layer disposed opposite the upper surface of carrier. The orifice layer defines a plurality of orifices disposed therein. The printhead has a generally planar contact surface positioned below the orifice layer and an encapsulant that at least partially encapsulates the fluid ejecting substrate and the carrier to form a substantially coplanar surface with the orifice layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one exemplary embodiment of a printing system wherein a printhead is translated across a print media to accomplish printing. 
     FIG. 2 is a schematic representation of a printing system comprising the printhead and a fluid reservoir for replenishing the printhead. 
     FIG. 3 is a bottom perspective view of the preferred printhead of the present invention that includes a carrier and a fluid ejecting substrate mounted in the carrier. 
     FIG.  4 ( a ) is a bottom perspective view of the fluid ejecting substrate shown in FIG. 3 independent of the carrier. 
     FIG.  4 ( b ) is a cross section of the fluid ejecting substrate shown in FIG. 3 where the materials used to form the fluid ejecting substrate are shown. 
     FIG. 5 is a bottom perspective view in isolation of the carrier shown in FIG. 3 configured to receive a fluid ejecting substrate; the carrier receives ink from the fluid reservoir and channels ink to the fluid ejecting substrate. 
     FIG.  6 ( a ) is a perspective view of a carrier with the fluid ejecting substrate inserted therein; the fluid ejecting substrate is electrically and fluidically coupled to the carrier. 
     FIG.  6 ( b ) is a cross section of the carrier shown in FIG.  6 ( a ) where an interconnect formed between the fluid ejecting substrate and carrier is arched. 
     FIG.  7 ( a ) shows a perspective view of a mold configured to inject an encapsulant into selective regions of a countersunk recess formed in an upper surface of the carrier once the fluid ejecting substrate is inserted into the countersunk recess. 
     FIG.  7 ( b ) shows a perspective view of FIG.  7 ( a ) where a portion of the mold has been removed thereby revealing the planar surface formed between the upper surface of the fluid ejecting substrate and the upper surface of the carrier. 
     FIG.  8 ( a ) is a cross-section of FIG. 7 showing the mold, fluid ejecting substrate, and carrier as the encapsulant is injected into the carrier. 
     FIG.  8 ( b ) is a cross section of the present invention where the fluid ejecting substrate is encapsulated within the carrier thereby creating an upper substantially planner surface. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an exemplary embodiment of a printing system  100  that includes a printhead  102  of the present invention. The printing system  100  includes a carriage  101  capable of supporting one or more printhead  102 . The carriage  101  is affixed to a carriage support member  104  which supports the printhead  102  as the printhead  102  is moved though a print zone. Collectively, the carriage  101  and carriage support member  104  are the printhead positioning member  105 . As the printhead  102  is moved though the print zone, print media  106  is simultaneously stepped through the print zone. The printhead  102  receives activation signals from the printing system  100  via interconnect  107  for selectively ejecting ink droplets onto the print media  106  while the printhead  102  is moved through the print zone. Alternatively, the printhead  102  may be stationary and the print media  106  moved relative to the printhead  102  to achieve printing. Whereas printing system  100  shown in FIG. 1 is formatted to print on 8½ by 11 inch print media, those skilled in the art will appreciate that printing system  100  and the printhead  102  are equally well suited to a wide variety of other printing environments, such as large format printing and textile printing to name a few. 
     FIG. 2 shows a schematic representation of a printing system incorporating a preferred embodiment of printhead  102  of the present invention. The printing system includes a fluid reservoir  202  that is fluidically coupled to a printhead  204  wherein ink is ejected from the bottom side (not shown) of printhead  204 . The printhead  204  is connected to the fluid reservoir  202  via a fluid conduit  206 . The fluid conduit  206  is formed of a flexible material that allows ink to continuously flow to the printhead  204  as the printhead  204  is moved across the print media. The printing system shown in FIG. 2 offers the advantage of having a separately replaceable fluid reservoir  202 . Thus, when ink contained in the fluid reservoir  202  is depleted, the fluid reservoir  202  can be replaced without replacing the printhead  204 . Alternatively, the printhead  204  can be replaced independent of the fluid reservoir  202 . 
     FIG. 3 shows a bottom perspective view of printhead  204  previously shown in FIG.  2 . The printhead  204  has been oriented such that the bottom portion of the printhead  204  from which ink is ejected is visible. The printhead  204  includes a carrier  300  and a fluid ejecting substrate  304 . The fluid ejecting substrate  304  is formed of a semiconductor material and has a plurality of orifices  306  defined in an orifice layer. Ink is ejected through the orifices  306  and onto a print media to accomplish printing. Additionally, the fluid ejecting substrate  304  is electrically coupled to the carrier  300  via electrical interconnect  308  which supplies excitation signals to the fluid ejecting substrate  304 . The electrical interconnect  308  electrically connects electrical connectors  307  formed in the carrier  300  to electrical contacts  309  formed on the fluid ejecting substrate  304 . In the present invention, electrical interconnect  308  is formed of gold wire however, other electrical conductors such as copper, aluminum, or silver to name a few, may also be used. 
     When the printhead  204  is inserted into the carriage  101  of printing system  100 , the electrical contact pads  310  contact adjacent electrical contact pads formed within the carriage  101  thereby forming an electrical connection between the printing system  100  and printhead  204 . Electrical interconnects  308  and a portion of fluid ejecting substrate  304  are encapsulated with an encapsulant  312 . The encapsulant  312 , as will be discussed in greater detail shortly, is configured to prevent ink from contaminating the electrical interconnect  308 . 
     FIG.  4 ( a ) is a perspective view of fluid ejecting substrate  304  shown in FIG. 3 independent of carrier  300 . The fluid ejecting substrate  304  has a first planar surface  400 , a second planar surface  402  and a bottom surface  403 . The first planar surface  400  has a plurality of orifices  306  defined in an orifice layer  401 . The second planar surface  402 , commonly referred to as a contact surface, has eight electrical contacts  309  although more or less electrical contacts  309  may be formed on second planar surface  402  depending on the particulars of the printhead. For example, the number of electrical contacts  309  tend to vary with the number of orifices  306 , number of signal lines, and multiplexing scheme of the printing system. The electrical contacts  309  are formed of an electrically conductive material such as aluminum or gold. The bottom surface  403  of the fluid ejecting substrate  304  contains a fluid channel  405 . Fluid from fluid channel  405  is channeled to the heater resistors (not shown) and selectively ejected through orifices  306  formed in the orifice layer  401 . 
     FIG.  4 ( b ) shows a greatly enlarged cross section of a preferred embodiment of fluid ejecting substrate  304  shown in FIG.  4 ( a ). The fluid ejecting substrate  304  further comprises an ink chamber  410  and heater resistors  412 . Ink received from carrier  300  flows into the fluid channel  405  of the fluid ejecting substrate  304 . The ink is then channeled into an ink chamber  410  where the ink resides on top of heater resistors  412  located at the base  413  of the ink chamber  410 . The heater resistors  412  receive excitation signals through electrical interconnects  308  (not shown) and subsequently eject ink through the orifice(s)  306 . 
     The fluid ejecting substrate  304  of FIG.  4 ( b ) is made of several materials that are sequentially layered to form a high quality, reliable printhead. Each layer has a predetermined thickness and a unique function. First, a semiconductor substrate  415  is provided that is approximately 0.6 mm thick. Next, a 1.2 μm thick oxide layer  414  is formed on top of the semiconductor substrate  415  to insulate the semiconductor substrate  415  from the forthcoming metal layers. The metal layers, formed on top of the oxide layer  414  consist of Aluminum (Al)  418  and Tantalum Aluminum (TaAl)  420  respectively. The metal layers are used to form the heater resistors  412  formed of a resistive material such as tantalum aluminum  420  and signal lines made of aluminum  418 . In the preferred embodiment, the combined thickness of the metal layers is 1.2 μm. Next, a 0.4 μm thick passivation layer  422  is formed on top of the metal layers. The passivation layer  422  prevents ink, being channeled to heater resistors  412 , from attacking the metal layers. An additional layer of protection, commonly referred to as a cavitation layer  424 , is formed on top of the passivation layer  422 . The cavitation layer  424  is made of Ta and ranges in thickness between 0.1 um and 0.8 um. An orifice layer  401  is then formed on top of the Ta layer  424 . The orifice layer  401  is typically 40 μm thick although a lesser or thicker orifice layer may be used. 
     FIG. 5 shows a perspective view of carrier  300  having an upper surface  500  and a countersunk recess  502  therein. The countersunk recess  502  is sized to accommodate the fluid ejecting substrate  304 . In a preferred embodiment, the countersunk recess  502  has a recess bevel depth indicated by reference character “d 1 ”. Recess bevel depth dl extends from upper surface  500  to inner lower surface  512  of carrier  300 . The counter sunk recess  502  contains electrical connectors  307  which receives excitation signals (not shown) from the printing system. The electrical connector  307  resides above the inner lower surface  512  by an electrical connector height designated by reference character “h 4 ”. The number of electrical connectors  307  typically correspond to the number of electrical contacts  309  on fluid ejecting substrate  304 . The carrier  300  also contains an aperture  506  that is coupled to fluid reservoir  202  shown in FIG.  2 . Ink flowing in aperture  506  inters a channel  510  on top of which fluid channel  405  of fluid ejecting substrate  304  resides. In a preferred embodiment of the present invention, carrier  300  is formed of molded plastic, however, other materials could be used to form the carrier  300  including ceramic, metal, and carbon composites. 
     FIG.  6 ( a ) shows carrier  300  having fluid ejecting substrate  304  inserted into the countersunk recess  502 . The second planar surface height designated by reference character “h 3 ” shown in FIG.  4 ( b ) is chosen such that when the fluid ejecting substrate  304  is inserted into the carrier  300 , second planar surface height h 2  and electrical connector height designated by reference character “h 4 ” align. Additionally, bevel height h 2  is chosen such that first planar surface  400  of fluid ejecting substrate  304  and upper surface  500  of carrier  300  align as well. Alternatively, first planar surface  400  of fluid ejecting substrate  304  may extend above upper surface  500  of carrier  300 . Next, the fluid ejecting substrate  304  is electrically coupled to the carrier  300  via electrical interconnect  308 . The electrical interconnect  308  is formed below the first planar surface  400  of the fluid ejecting substrate  304  and upper surface  500  of carrier  300 . 
     FIG.  6 ( b ) shows an enlarged cross section of one electrical interconnect  308  formed between the fluid ejecting substrate  304  and carrier  300 . The electrical interconnect  308  is wire bonded to the electrical connector  307  and electrical contact  309  such that the electrical interconnect  308  is arched at a radius indicated by reference character “R” shown in FIG.  6 ( b ). Positioning the electrical interconnect  308  as such is a common practice in the semiconductor industry. Forming an arch with the electrical interconnect tends to relieves stress which may otherwise lead to an electrical failure. The radius  602  is typically 100 μm and is less than the film stack height indicated by reference character h 1  shown in FIG.  4 ( b ) which typically equals 41 μm. 
     To ensure that the arched electrical interconnect  308  does not extend beyond the first planar surface  400  of the fluid ejecting substrate  304 , a bevel height indicated by reference character “h 2 ” shown in FIG.  6 ( b ) is increased. Increasing bevel height h 2  effectively lowers the electrical interconnect  308  relative to first planar surface  400 . Perhaps most significantly, the value of bevel height h 2 , which is typically 150 μm, can be chosen such that first planer surface  400  extends beyond the upper surface  500  of the carrier  300  while the arch of the electrical interconnect  308  resides below the upper surface  500  of carrier  300 . Alternatively, the value of bevel height h 2  may be chosen such that first planar surface  400  and upper surface  500  reside in the same plane while the arch of the electrical interconnect  308  resides below the upper surface  500 . Although in an embodiment of the present invention, a wire bond was used, a TAB circuit, which typically has a thickness greater than height h 1  may be used as well. 
     FIG.  7 ( a ) shows a mold  700  being used to dispose the encapsulant  312  in selected areas of carrier  300 . The encapsulant  312  is supplied to mold  700  in liquid form through inlet  704 . Additionally, a groove  702  is formed in mold  700 , thereby preventing the orifice layer  401  beneath mold  700  from being damaged when mold  700  is brought in contact with the carrier  300 . FIG.  7 ( b ) shows a perspective view of FIG.  7 ( a ) where a portion of mold  700  has been removed thereby revealing the planar surface formed between first planar surface  400  of fluid ejecting substrate  304  and upper surface  500  of carrier  300 . The encapsulant  312  is selectively disposed into two areas of carrier  300 . First, the encapsulant  312  is disposed in seams  706  created adjacent to the fluid ejecting substrate  304  and the countersunk recess  502  following the insertion of the fluid ejecting substrate  304 . Second, the encapsulant  312  is disposed in an interconnect region  708  of the fluid ejecting substrate  304 . 
     FIG.  8 ( a ) shows a cross section of FIG.  7 ( a ) where mold  700  is put in contact with carrier  300 . The encapsulant  312  is injected into the carrier  300  through channels  800  or alternatively, the encapsulant  312  is drawn into carrier  300  through channels  800  via capillary action. While the encapsulant  312  is dispensed onto the carrier  300  through mold  700 , the encapsulant  312  is isolated from the orifice layer  401 . Shielding the encapsulant  312  from the orifice layer  401  is important because the encapsulant  312 , if exposed to the orifice layer  401 , will permanently clog the orifices  306  formed therein. Once the encapsulant  312  has been dispensed, the encapsulant  312  dries at ambient temperature or is externally heated to accelerate the drying/curing process. Additionally, ultraviolet light may be used to cure the encapsulant as well. In a preferred embodiment of the present invention, the curing of the encapsulant  312  is accelerated by heating coils  802  formed within mold  700 . 
     FIG.  8 ( b ) shows a preferred embodiment of the present invention where the encapsulant  312  has been injected into the carrier  300  and mold  700  has been removed. The encapsulant  312  further planarizes the upper surface  500  of the carrier  300  and prevents ink on the orifice layer of the fluid ejecting substrate from reaching the electrical interconnect  308 . Consequently, damage to the electrical interconnect  308  by the ink is eliminated. Furthermore, since the electrical interconnect  308  is formed below the first planar surface of the fluid ejecting substrate  304  prior to the formation of the encapsulant  312 , the encapsulant bead prevalent in conventional printheads is eliminated. By eliminating the encapsulant bead, the printhead  204  of the present invention is operated in close proximity of the print media. In one embodiment, the encapsulant  312  allows the printhead positioning member  105  to position the orifice layer within 0.5 millimeters of the print media. Consequently, trajectory errors and parasitic effects inherent to the printing environment are minimized thereby improving print quality. 
     Previous attempts have been made to improve the reliability of printheads. For example, U.S. Pat. No. 4,873,622 to Komuro, et al., entitled “Liquid Jet Recording Head” describes a pressure transfer molding technique used to form a recording head. The recording head contains a discharge element having a membrane disposed thereon from which ink is ejected onto a print media. The discharge element is electrically coupled to a metal frame. The electrical connection is made on top of the discharge element and an epoxy is molded around the electrical connection and recording head. The membrane is recessed within the molded epoxy. 
     In the present invention, makes use of a stepped die so that the electrical connection is formed sufficiently below the orifice layer so that the encapsulant can be formed in the same plane as the orifice layer. The encapsulant of the present invention is in plane with the orifice layer in contrast to the Komuro reference where the membrane is recessed within the molded epoxy and therefore, the printhead of the present invention allows the orifice layer to be positioned closer to print media than the membrane of Komuro. Positioning the orifice layer closer to the print media allows trajectory error to be reduced. In addition, the printhead of the present invention provides a planar printhead surface that is readily cleaned in contrast to Komuro that has a recording head structure with a recess that tends to trap ink residue and debris and is harder to clean using conventional wiping technology.

Technology Classification (CPC): 1