Patent Publication Number: US-2023143469-A1

Title: Fluid cartridge with vented insert

Description:
TECHNICAL FIELD 
     The disclosure is directed to fluid supply cartridges for fluid ejection devices and in particular to fluid supply cartridges that provide improved dimensional stability for cartridge bodies used for ejecting a variety of fluids. 
     BACKGROUND AND SUMMARY 
     A conventional fluid cartridge body is typically constructed of one or more plastic materials to which a semiconductor ejection head chip is directly attached by means of a die bond adhesive. However, the use of solvent-based fluids in fluid ejection cartridges for inks and other commercial and industrial applications can cause the plastic materials to swell. Swelling of the plastic material of the cartridge body increases mechanical stresses on the silicon of the ejection head chip causing the chip to crack. Additionally, a mismatch of the coefficient of thermal expansion (CTE) between the plastic cartridge body and the ejection head chip causes swelling of the cartridge body during heat curing of the die bond adhesive. The resin material of the cartridge body may swell from about 3 to 5% during the die bond curing step. The swelling of the resin may cause the overall ejection head chip bow in the Y direction to a range of from -5 um to &gt;40 um over a period of 4 weeks. Any imperfection or defects in the ejection head chip generated by deep reactive ion etching (DRIE) or dicing of the ejection head chips from a silicon wafer may provide additional stress concentration areas which can lead to ejection head chip cracking when installed on a plastic cartridge body. 
     Accordingly, there is a need for a dimensionally stable surface for attaching and ejection head chip thereto that has a coefficient of thermal or mechanical expansion similar to that of the ejection head chip. What is also needed is an ejection head chip bonding surface that is chemically stable for use with fluids that cause plastic materials to swell. 
     In view of the foregoing, the disclosure provides a fluid cartridge having a plastic fluid body and a bottom wall having a fluid supply opening therein. A metal insert is adhesively attached to the bottom wall. The metal insert has a fluid supply slot therein corresponding to the fluid supply opening in the bottom wall, a die bond surface adjacent to the fluid supply slot for adhesively attaching an ejection head chip thereto, and a plurality of air vents adjacent to the die bond surface. An ejection head chip is adhesively attached to the die bond surface of the metal insert. 
     In another embodiment, there is provided a method for eliminating mechanical stresses on an ejection head chip. The method includes providing a fluid cartridge having a plastic fluid body and a bottom wall having a fluid supply opening therein. A metal insert is adhesively attached to the bottom wall, wherein the metal insert has a fluid supply slot therein corresponding to the fluid supply opening in the bottom wall, a die bond surface adjacent to the fluid supply slot for adhesively attaching an ejection head chip thereto, and a plurality of air vents adjacent to the die bond surface. An ejection head chip is adhesively attached to the die bond surface of the metal insert. A flexible circuit is electrically connected to the ejection head chip. 
     In some embodiments, the metal insert is a machined, molded, or stamped metal insert. 
     In some embodiments, the metal insert is made of aluminum or stainless steel. In other embodiments, the metal insert is made of an anodized aluminum. 
     In some embodiments, the metal insert has a stamped chip pocket in the die bond surface for adhesively attaching the ejection head chip therein. In other embodiments, the chip pocket includes a racetrack circumscribing the fluid supply slot. 
     In some embodiments, the metal insert includes a deck area between the chip pocket and the air vents for a die bond adhesive that is effective to electrically and chemically insolate a back side of the flexible circuit from the metal insert and from corrosive fluids. 
     In some embodiments, the metal insert has a thickness ranging from about 1.5 to about 4 millimeters. 
     In some embodiments, the cartridge body includes at least two guide pins extending orthogonally from the bottom wall. In other embodiments, the metal insert has apertures therein corresponding to the at least two guide pins for positioning the metal insert on the bottom wall of the cartridge body. 
     In some embodiments, a flexible circuit is electrically connected to the ejection head chip. 
     An unexpected advantage of embodiments of the disclosure is the flatness of the ejection head chip after curing the die bond adhesive when using a metal insert between the ejection head chip and the bottom wall of the cartridge body. Without the metal insert, the ejection head chip may bow during curing of the die bond adhesive causing inaccurate placement of fluid droplets ejected from the ejection head. Another advantage of the disclosed embodiments is that a wider variety of fluids may be used with the fluid cartridge and ejection head without causing ejection head chip cracking due to swelling of the resin of the plastic cartridge body. 
    
    
     
       BRIEF DESCTRIPION OF THE DRAWINGS 
         FIG.  1    is an exploded, perspective bottom view of a fluid cartridge according to the disclosure. 
         FIG.  2    is a plan bottom view of a portion of the fluid cartridge showing details of a bottom wall of the fluid cartridge of  FIG.  1   . 
         FIG.  3    is a partial perspective view of the fluid cartridge of  FIG.  1    and metal insert therefor. 
         FIG.  4    is a plan view of top side of the metal insert for the fluid cartridge of  FIG.  1    according to an embodiment of the disclosure. 
         FIG.  5    is a plan view, not to scale, of a fluid ejection chip for the fluid cartridge of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
     With reference the figures,  FIG.  1    is an exploded, bottom view of a fluid cartridge  10  according to an embodiment of the disclosure. The fluid cartridge  10  includes a plastic cartridge body  12  made from a polymeric thermoplastic resin such as polyethylene, polypropylene, polyamide, polystyrene, and the like. As shown in  FIGS.  2 - 3   , a bottom wall  14  of the cartridge body  12  contains a fluid supply opening  16  therein for providing fluid from the cartridge body  12  to an ejection head chip  18  that is electrically attached to a flexible circuit  20 . A fluid filter  22  is provided in the cartridge body  12  on a filter tower structure to filter the fluid flowing to the ejection head chip  18 . 
     According to an embodiment of the disclosure, a metal insert  24  is attached by means of a first adhesive  26  to the bottom wall  14  of the cartridge body  12 . A second adhesive  28  is used to bond the flexible circuit  20  to the metal insert  24  while also insulating the metal insert from lead beams on the flexible circuit  20 . The metal insert  24  has an overall thickness ranging from about 1.5 to about 4 mm in thickness and will typically have a thickness ranging from about 1.75 to about 2.5 mm. The length L of the metal insert  24  may range from about 18 to about 25 mm and the width W of the metal insert  24  may range from about 12 to about 14 mm. A particularly suitable metal insert  24  is a machined, molded, or stamped metal insert formed from a metal selected from aluminum and stainless steel. The aluminum may be an anodized aluminum or the metal insert may include an inert coating to prevent flocculation of solids from fluids ejected by the ejection head chip  18 . 
     The bottom wall  14  of the cartridge body  12  also includes at least two guide pins  30 A and  30 B for guiding the metal insert  24  into place on the bottom wall  14  of the cartridge body  12 . As shown in  FIG.  4   , the metal insert  24  includes apertures  32 A and  32 B therein corresponding to the guide pin locations on the bottom wall  14  of the cartridge body  12  to enable easy placement of the metal insert  24  on the bottom wall  14  of the cartridge body  12  as shown in  FIGS.  1  and  3   . 
     Another feature of the bottom wall  14  of the cartridge body  12  is the planarization pads  34 A- 34 C that provide a substantially planar surface for the attachment of the metal insert  24  to the bottom wall  14  of the cartridge body  12 . The planarization pads  34 A- 34 C may be raised pads molded into the bottom wall  14  of the cartridge body  12  or machined to provide a planar surface to which the metal insert  24  is adhesively attached. 
     The first adhesive  26  used to attach the metal insert  24  to the bottom wall  14  of the cartridge body  12 , may be a heat curable epoxy adhesive that is compatible with the resin used to make the cartridge body  12 . In order to enhance adhesion between the metal insert  24  and the bottom wall  14 , the underside  36  of the metal insert  24  may be cleaned and treated with water, isopropyl alcohol, or silane. The underside  36  may also be blasted with a high pressure stream of air or aluminum oxide to enhance adhesion. Likewise, the bottom wall  14  of the cartridge body may be coated with an adhesion enhancing coating such as a silane coating. 
     Once the metal insert  24  is adhesively attached to the bottom wall  14  of the cartridge body, the ejection head chip  18  may be adhesively attached to the metal insert  24  using a die bond adhesive. A conventional ejection head chip  18  is illustrated in  FIG.  5    and includes a silicon semiconductor substrate  40  that includes a flow feature layer  42  made from a photoresist material having fluid channels  44  and fluid chambers  46  photoimaged therein. A fluid supply via  48  is etched through the semiconductor substrate  40  and imaged in the flow feature layer  42  and provides fluid to the fluid channels  44  and fluid chambers  46 . Each of the fluid chambers  46  includes a fluid ejection device  50  that may be selected from a resistor heater or a piezoelectric device for ejecting fluid from the fluid chambers  46  through associated nozzle holes  52  in a nozzle plate  54  attached to the flow feature layer  42 . Because a fluid supply via  48  in the ejection head chip  18  must be precisely aligned with a fluid supply slot  56  in the metal insert  24  in order to provide fluid to fluid ejectors  50  on the fluid ejection chip  18 , a chip pocket  58  is provided in the metal insert  24  ( FIG.  3   ) and the ejection head chip  18  is adhesive attached to the metal insert  24  in the chip pocket  58 . The chip pocket  58  is a recessed area in the metal insert  24  that provides a somewhat confined area for the die bond adhesive. The fluid supply slot  56  in the metal insert  24  has a length ranging from about 14.8 mm to about 15.6 mm and a width ranging from about 1.5 to about 2.0 mm. 
     The flexible circuit  20 , which is used to connect fluid ejectors  50  on the ejection head chip  18  with a control activation device for the fluid ejectors  50 , surrounds the ejection head chip  18  and is fastened to the metal insert  24  using the second adhesive  28 , also known as a preform pressure sensitive adhesive. The flexible circuit  20  includes a plurality of beams which extend therefrom and electrically connect with bond pads (not shown) on the semiconductor substrate  40  of the ejection head chip  18 . After the ejection head chip  18  is placed within the chip pocket  42  and the flexible circuit  20  is attached to the ejection head chip  18 , an ultraviolet (UV) photosensitive adhesive is applied along the sides of the ejection head chip  18 , over the beams, as an encapsulant and protectant to prevent shorting by the metal insert  24  and corrosion from fluid ejected by the ejection head chip  18 . A light source is applied to the UV adhesive to cure the same. However, a portion of the UV adhesive which flows around and behind the beams is not exposed to the applied UV light source, and therefore is not cured thereby. 
     Once the fluid cartridge  10  is fully assembled, the fluid cartridge  10  is placed within an oven and the die bond adhesive is cured at an elevated temperature to permanently affix the ejection head chip  18  to the metal insert  24 . During the curing process, the adhesive may produce gas which forms gas bubbles in the adhesive. Some of the gas may remain entrapped within the adhesive as residual gas bubbles after the curing process is finished. Such gas bubbles, because of the void left in the adhesive, may affect the bond strength between the ejection head chip  18  and the metal insert  24 . Moreover, other gas bubbles may expand at the elevated cure temperature and/or join with adjacent gas bubbles to form passageways or channels within the adhesive. Such a phenomenon, known as “die bond channeling,” may result in channels which extend from the fluid supply slot  56  within the metal insert  24  to the ambient environment, thereby allowing fluid to leak from the fluid cartridge assembly to the ambient environment. Alternatively, in the case of a multi-fluid cartridge assembly, the channels formed in the adhesive may allow cross-contamination between the different fluids within the cartridge body  12 . 
     Additionally, the uncured UV or thermally cured epoxy adhesive is subsequently cured and/or volatilized by the heating process used to cure the die bond adhesive. During the heat curing process, the UV and/or thermally cured epoxy adhesive may also produce gas. Because the UV and/or thermally cured epoxy adhesive placed over the beams on each side of the ejection head chip  18  has previously been cured, and the flexible circuit  20  is affixed to the metal insert  24  and surrounds the ejection head chip  18 , gas which is produced during the heat curing process may expand (because of the increased temperature) and flow through the die bond adhesive and UV adhesive toward and into the fluid supply slot  56  within the metal insert  24  creating channels for leaking of fluid from the fluid supply cartridge out to the ambient environment. 
     Accordingly, the metal insert  24  is configured with at least one air vent, and preferably, a plurality of air vents adjacent to the chip pocket  58  to enable air to escape from the die bond adhesive and/or UV adhesive during the curing process. With reference again to  FIG.  4   , the metal insert  24  includes a plurality of grooves  60  and  62  adjacent to the chip pocket  58  that provide air flow communication from the chip pocket  58  to the ambient atmosphere. Grooves  60  define one or more longitudinal grooves (extending substantially parallel to a longitudinal direction of chip pocket  58  along longitudinal axis  64 ), and grooves  62  define a plurality of lateral grooves extending between chip pocket  56  and longitudinal grooves  60 . Longitudinal grooves  60  extend to edges  66  and  68  disposed adjacent to the ambient environment. The combination of longitudinal grooves  60  and  72 , lateral grooves  62  that are in flow communication with the ambient atmosphere at edges  66  and  68  of the metal insert  24  provide the plurality of air vents for the insert  24 . Exemplary air flow through the grooves  60 ,  62  and  72  from the chip pocket  58  to edges  66  and  68  are represented by arrows  80  and  82 . 
     The grooves have dimensions corresponding to the dimensions represented by the reference letters W1, S and L1. The dimension W1 is preferably between 0.15 and 0.75 mm, and more preferably between 0.2 and 0.3 mm. The dimension S is preferably between 0.75 and 2.5 mm, and more preferably between 1 and 2 mm. The dimension L1 is preferably between 1.0 and 4.0 mm, and more preferably between 1.5 and 2.5 mm. Further, grooves  60  and  62  have a depth (substantially perpendicular to the drawing in  FIG.  4   ) which is preferably between 0.1 and 0.5 mm, and more preferably between 0.25 and 0.35 mm. A raised racetrack  70  having a height ranging from about 0.04 to about 0.1 mm and a width ranging from about 0.15 mm to about 0.5 mm circumscribes the fluid supply slot  56  to prevent a die bond adhesive applied in the chip pocket from  58  from flowing into the fluid supply slot  56 . An internal longitudinal groove  72  having the width W1 is provided between the chip pocket  58  and the raised structures  74  to provide a raised landing area relative to the chip pocket  58  for the die bond and/or UV adhesive to coat the back side of the lead beams on the flexible circuit  20  and to prevent short circuiting between the flexible circuit  20  and the metal insert  24 . 
     During the heat curing process for the die bond adhesive and/or the UV adhesive, any gas generated will flow from the lateral grooves  62  to the longitudinal grooves  60  and  72  and out to the ambient atmosphere at the edges  66  and  68  of the metal insert rather than flowing inward toward the fluid supply slot  56 . Accordingly, air channels in the adhesive are avoided by use of the metal insert  24  containing the grooves  60 ,  62 , and  72 . 
     An advantage of having the ejection head chip  18  bonded to the metal insert  24  rather than to the plastic cartridge body  12  is that the metal insert  24  provides a mechanically stable surface for the ejection head chip  18  so that any swelling or distortion of the plastic cartridge body  12  is isolated from the ejection head chip  18 . Accordingly, a wider variety of fluids may be ejected with a fluid cartridge  10  have the metal insert  24  as described above, including organic fluids that may cause the resin of the cartridge body  12  to swell. In some embodiments, when using a metal insert  24 , the metal insert  24  may also provide a heat sink for cooling the ejection head chip  18  during fluid ejection. 
     While the foregoing embodiments are directed specifically to metal inserts, other dimensionally stable materials, such as ceramic and carbon fiber reinforced polymers may be used as an insert. Such alternative materials may also be formed with vents as described above to prevent air channels from forming in the bonding adhesives during heat curing cycles. 
     It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items 
     For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values 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 following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. 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. 
     While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or can be presently unforeseen can arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they can be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.