Abstract:
An electrical connection is encapsulated by dispensing an encapsulant on a first side of the electrical connection only, and directing the encapsulant to a second side of the electrical connection from the first side, where the second side generally faces opposite the first side.

Description:
BACKGROUND 
   Fluid-ejection devices, such as print heads, usually include a carrier and a fluid-ejecting substrate (or print die), e.g., formed from silicon or the like using semiconductor processing methods, such as photolithography or the like. Conventionally, electrical interconnections are made using a flexible circuit that has metal leads that are coupled to bond pads located on the fluid-ejecting substrate. The metal leads and bond pads are usually encapsulated for protection. Encapsulation is usually accomplished by dispensing an encapsulant (or adhesive) to the bottom of the flexible circuit, curing the encapsulant, turning flexible circuit over, dispensing encapsulant on the top of the flexible circuit and over the bond pads, and curing the encapsulant. Subsequently, the fluid-ejecting substrate and the flexible circuit are adhered to the carrier. However, this produces stresses on the fluid-ejecting substrate where the flexible circuit is attached that could damage the fluid-ejecting substrate. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of an embodiment of a fluid-ejection device, according to an embodiment of the invention. 
       FIG. 2  is a top view of a portion of the fluid-ejection device of  FIG. 1 , according to another embodiment of the invention. 
       FIG. 3  is a cross-sectional view of another embodiment of a fluid-ejection device, according to another embodiment of the invention. 
       FIG. 4  is a top view of a portion of the fluid-ejection device of  FIG. 3 , according to another embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice disclosed subject matter, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the claimed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the claimed subject matter is defined only by the appended claims and equivalents thereof. 
     FIG. 1  is a cross-sectional view of a fluid-ejection device  100 , such as a print head, according to an embodiment. Fluid-ejection device  100  includes a carrier  110  that may be fabricated from plastic, ceramic, silicon, or the like. A fluid-ejecting substrate  120  (e.g., a print-head die or substrate) is adhered to carrier  110 . For one embodiment, fluid-ejecting substrate  120  includes orifices (or nozzles)  122  and resistors  124 . Resistors  124  are selectively energized to rapidly heat a fluid, e.g., a marking fluid, such as ink, channeled thereto, causing the fluid to be expelled through orifices  122  in the form of droplets. Note that fluid-ejection device  100  is inverted with respect to its normal operating orientation so that orifices  122  are directed upward. Hereinafter, for purposes of discussing  FIG. 1 , terms, such as “up” and “down,” “upper” and “lower,” etc., will used and are taken to be relative to  FIG. 1 . Note, however, for one embodiment, fluid-ejection device  100  is oriented as is shown in  FIG. 1  during manufacturing. 
   A spacer  130 , e.g., a polymer layer (or film), is also adhered to an upper surface of carrier  110 . Spacer  130  is substantially co-planer with fluid-ejecting substrate  120  and is located laterally of fluid-ejecting substrate  120 . A portion  132  of an end of spacer  130  is located at a lateral distance S 1 , e.g. about 125 to about 250 microns, from fluid-ejecting substrate  120  to form a channel  134  between end portion  132  and a side of fluid-ejecting substrate  120 . For one embodiment, a thickness of end portion  132  can vary, e.g. about 100 to about 500 microns. A portion  136  of the end of spacer  130  is recessed relative to end portion  132  so that end portion  136  is located at a lateral distance S 2 &gt;lateral distance S 1  from fluid-ejecting substrate  120  to form a channel expansion  138  between end portion  136  and the side of fluid-ejecting substrate  120 . Note that channel  134  opens into channel expansion  138 . 
   A flexible circuit  140  is adhered to spacer  130 , as shown in  FIG. 1 . For one embodiment, flexible circuit  140  is configured as a flying-lead assembly and includes electrical leads  142  formed in a film  144  and that extend from an end of film  144 . Specifically, for one embodiment, a lower portion of film  144  is adhered to an upper surface spacer  130 , e.g., by heat staking. For one embodiment, film  144  may be a polymer, such as polyimide, polyester, polyethylene naphthalate (PEN), etc. For another embodiment, a thickness of spacer  130  is selected so that when flexible circuit  140  is adhered thereto, a lower surface  143  of lead  142  is substantially flush with an upper surface  148  of fluid-ejecting substrate  120  at which orifices  122  terminate and so that lead  142  aligns with a contact  150  in fluid-ejecting substrate  120 . Note that contact (or bond pad)  150  is electrically connected to one or more of the resistors  124 . 
     FIG. 2  is a top view of a portion of  FIG. 1  illustrating leads  142  of flexible circuit  140  overlying upper surface  148  of fluid-ejecting substrate  120 . Note that each of leads  142  respectively corresponds to a contact  150 .  FIG. 2  also shows an upper (or inlet) portion of channel  134 . 
   For one embodiment, after adhering flexible circuit  140  to spacer  130 , the ends of leads  142  are bonded to their respective contacts  150  of fluid-ejecting substrate  120  to form an electrical connection between flexible circuit  140  and fluid-ejecting substrate  120 . Alternatively, the ends of leads  142  may be bonded to their respective contacts  150  before adhering flexible circuit  140  to spacer  130 . For one embodiment, a conventional TAB bonder may be used to press the ends of leads  142  into contacts  150 , as is known in the art. Note that connecting leads  142  to contacts  150  electrically connects resistors  124  to a controller, such as a printer controller, for selectively activating resistors  124 . 
   After forming the electrical connection between flexible circuit  140  and fluid-ejecting substrate  120 , the electrical connection is encapsulated using an encapsulant  160 . Encapsulant  160  is dispensed, e.g., using a needle dispense, on portions of the electrical connection accessible from substantially one direction, above, and is wicked (or carried by capillary action) to portions of the electrical connection that are substantially inaccessible from above. More specifically, encapsulant  160  ( FIGS. 1 and 2 ) is dispensed on an upper surface  145  of film  144 , on upper portions of leads  142 , and on upper surface  148  of fluid-ejecting substrate  120 . Encapsulant  160  flows downward through interstices  162  between successively adjacent leads  142  ( FIG. 2 ), around leads  142 , and through channel  134  ( FIG. 1 ). 
   For one embodiment, capillary action drives the flow of encapsulant  160 . Specifically, forces between molecules of encapsulant  160  and surfaces of leads  142  that bound interstices  162  cause encapsulant  160  to wet these surfaces and produces the capillary action that draws adhesive  160  through interstices  162 . Similarly, forces between molecules of encapsulant  160  and bounding surfaces of channel  134  (end portion  132  and the side of fluid-ejecting substrate  120 ) produce the capillary action that draws encapsulant  160  through channel  134 . However, when encapsulant  160  reaches channel expansion  138 , the surface tension of encapsulant  160  acts to prevent encapsulant  160  on end portion  132  from flowing past channel expansion  138 , thus stopping the flow of encapsulant  160 , as shown in  FIG. 1 . Therefore, channel expansion  138  functions as a capillary stop. 
   When encapsulant  160  stops flowing, it completely encapsulates the electrical connection between flexible circuit  140  and fluid-ejecting substrate  120 . This means that the electrical connection can be completely encapsulated by dispensing encapsulant  160  onto portions of the electrical connection that are accessible from substantially above by wicking encapsulant  160  to portions of the electrical connection that are substantially inaccessible from above, such as by using channel  134 . This enables fluid-ejecting substrate  120  to be adhered to carrier  110  before encapsulation rather than after, as is done conventionally. Adhering fluid-ejecting substrate  120  to carrier  110  before encapsulation rather than after acts to reduce stresses on the electrical connection that are transferred to fluid-ejecting substrate  120 . These stresses can result in premature failure of fluid-ejecting substrate  120  in that the stresses act to pull apart layers that form fluid-ejecting substrate  120 . 
   For another embodiment, a film  170 , e.g., a polymer film, such as a polyester film (e.g., MYLAR LBT), may be located atop encapsulant  160  ( FIGS. 1 and 2 ) before curing. Film  170  helps retain some of encapsulant  160  on top of leads  142 . For one embodiment, encapsulant  160  is a paste, such as an epoxy. For another embodiment, thixotropes, such as fumed silica particles (e.g., about 0.1 to about 1.0 micron particles), alumina particles (e.g., about 1.0 to about 50 micron particles), etc., are added to the paste to enhance wicking. For another embodiment, encapsulant  160  is a paste at about 20° C. to about 25° C., and when heated to about 65° C. to about 145° C., it wicks to desired locations. For some embodiments, a silane coupling agent is added to encapsulant  160  to enhance wicking. 
   For another embodiment, encapsulant  160  is dry and disposed on a film, such as film  170 , and the film is positioned as shown in  FIG. 1  for film  170 . The film is heated to about 165° C., causing it to liquefy and flow (or wick) over upper surface  145  of film  144 , on upper portions of leads  142 , and on upper surface  148  of fluid-ejecting substrate  120  and to wick through interstices  162  ( FIG. 2 ) and through channel  134 , as described above. 
   For some embodiments, the surfaces contacted by encapsulant  160  in  FIG. 1 , i.e., upper surface  145  of film  144 , leads  142 , upper surface  148  of fluid-ejecting substrate  120 , and the bounding surfaces of channel  134 , are treated before dispensing encapsulant  160  thereon to improve wetting and adhesion. For one embodiment, the treatment is a plasma treatment (or plasma etch) or a chemical etch that acts to polarize and roughen the surfaces. For another embodiment, a laser is used to roughen the surfaces by cutting grooves into the surfaces. 
   For other embodiments, the flow of encapsulant  160  to the underside of leads  142 , i.e., through interstices  162  and channel  134 , may involve using a vacuum to draw encapsulant  160  to the underside of leads  142  or pressurized air to push encapsulant  160  to the underside of leads  142 . For one embodiment, the assembly of  FIG. 1  may be centrifuged for forcing the encapsulant  160  to the underside of leads  142 . For some embodiments, encapsulant  160  is forced to the underside of leads  142  from the top using a needle dispense. For one embodiment, encapsulant  160  is forced through the needle using a syringe. 
     FIGS. 3 and 4  are respectively cross-sectional and top views of a fluid-ejection device  300 , according to another embodiment. Elements in  FIGS. 3 and 4  that are similar to elements in  FIGS. 1 and 2  use the same reference numbers as in  FIGS. 1 and 2  and are as described above. In  FIGS. 3 and 4 , a flexible circuit  240  is adhered to an upper surface of spacer  130 , e.g., by an adhesive, such an epoxy. Flexible circuit  240  includes contacts (or bond pads)  242  that are exposed at an upper surface  244  of a film  246 , as shown in  FIGS. 3 and 4 . For one embodiment, film  244  may be a polymer, such as polyimide, polyester, polyethylene naphthalate (PEN), etc. Conductive traces  248  are disposed in film  246  and are respectively electrically connected to contacts  242 . Contacts  242  are respectively electrically connected to contacts  150  of fluid-ejecting substrate  120  using wire bonds  250 , as is known in the art, to form an electrical connection between flexible circuit  240  and fluid-ejecting substrate  120 . 
   Encapsulation of the electrical connection between flexible circuit  240  and fluid-ejecting substrate  120 , e.g., wire bonds  250 , contacts  242 , and contacts  150  using encapsulant  160  is generally as described above in conjunction with  FIGS. 1 and 2 . That is, encapsulant  160  is dispensed from above and wicks downward through interstices  262  between successively adjacent bond wires  250  ( FIG. 4 ), around bond wires  250 , and through channel  134  ( FIG. 3 ). Wicking stops when encapsulant  160  encounters channel expansion  138 . For one embodiment, film  170  retains some of encapsulant  160  on top of bond wires  250 . For other embodiments, the surfaces contacted by encapsulant  160  in  FIG. 3  are treated before dispensing encapsulant  160  thereon to improve wetting and adhesion, as described above. 
   CONCLUSION 
   Although specific embodiments have been illustrated and described herein it is manifestly intended that the scope of the claimed subject matter be limited only by the following claims and equivalents thereof.