Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2001-10-31
2003-12-16
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S050000
Reexamination Certificate
active
06663235
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to inkjet printing and, more specifically, to methods and structures for securing a printhead to an inkjet print cartridge, whereby ink is prevented from shorting printhead conductors together.
BACKGROUND OF THE INVENTION
Substantial developments have been made in the field of electronic printing technology. Specifically, a wide variety of highly efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. One such system is a thermal inkjet printer that utilizes ink cartridges. Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle plate. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved across the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
A typical inkjet print cartridge is shown in
FIG. 1
as print cartridge
20
, which includes an ink reservoir
22
for containing liquid ink. The liquid ink is delivered to a printhead
24
that is formed of a flexible polymer tape
30
using Tape Automated Bonding (TAB). Printhead
24
includes a nozzle member
28
comprising offset holes or orifices
26
formed in the flexible polymer tape
30
.
Referring to
FIG. 2
, a back surface of tape
30
includes conductors
42
formed thereon by, for example, using a conventional photolithographic etching and/or plating process. These conductors are terminated by large contact pads
32
(
FIG. 1
) designed to interconnect with a printer. Print cartridge
20
is designed to be installed in a printer so that contact pads
32
, on the front surface of tape
30
, contact printer electrodes providing externally generated energy signals to the printhead. Windows
34
and
36
(
FIG. 1
) extend through tape
30
and are used to facilitate bonding of the ends of the conductors to electrodes on a silicon substrate containing heater resistors.
In the standard print cartridge assembly, the conductors are formed on the back surface of tape
30
(opposite the surface which faces the recording medium). To access these conductors from the front surface of tape
30
, holes (vias) must be formed through the front surface of tape
30
to expose the ends of the conductors. The exposed ends of the conductors are then plated with, for example, gold to form contact pads
32
shown on the front surface of tape
30
. When print cartridge
20
is properly positioned in an inkjet printer, contact pads
32
are pressed against associated contacts on the inkjet printer so as to electrically couple the resistors to a source of electrical current.
Affixed to the back of tape
30
is a silicon substrate
38
containing a plurality of individually energizable thin film resistors. Each resistor is located generally behind a single orifice
26
(
FIG. 1
) and acts as an ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of contact pads
32
(FIG.
1
). Conductors
42
lead from the contact pads
32
to electrodes on substrate
38
. Hole
40
allows ink from an ink reservoir to flow to the front surface of substrate
38
.
The print cartridge structure has a number of drawbacks. For example, conductors that extend out from a flexible circuit and connect to electrodes on a substrate require adequate insulation on the bottom surface of the conductors formed on the bottom surface of the flexible circuit. During the course of printing, cleaning operations need to be done to prevent nozzles from clogging. In addition, spray from the ink ejection is generated. As a result, the ink manages to reach the underside of the flexible circuit, which causes some degree of shorting between conductors. Even at low voltage levels and at fairly low operating speeds, this shorting together of conductors can affect the operation of the printhead. Where higher performance printers and printheads are utilized, which require faster and faster speeds and possibly incorporate active demultiplexing circuitry on the printhead itself, the problem is compounded. Thus, high current power supply voltages and low current control signals that are or will be carried by conductors connected to currently available or future printheads, may result in ink shorting between these conductors which can significantly affect the characteristics of the control signals and may, therefore, cause significant fluctuations in print quality.
Previous solutions to the ink shorts problem have primarily focused on (1) modifying the design on top of the substrate, the layout and geometry of the thin film, thick film and the TAB bond window opening and (2) improving the chemical and mechanical robustness of the adhesive materials and interfaces.
U.S. Pat. No. 5,442,384, entitled “Integrated Nozzle Member and TAB Circuit for Inkjet Printhead,” describes a novel nozzle member for an inkjet print cartridge having a barrier layer, as a separate layer or formed in the nozzle member itself, and including vaporization chambers surrounding each orifice and ink flow channels which provide fluid communication between an ink reservoir and the vaporization chambers. U.S. Pat. No. 5,648,805, entitled “Adhesive Seal for an Inkjet Printhead,” describes a procedure for sealing an integrated nozzle and flexible or tape circuit to a print cartridge, whereby a flexible circuit is adhesively sealed with respect to the print cartridge body by forming an ink seal, circumscribing the substrate, between the back surface of the flexible circuit and the body, thus providing a seal directly between a flexible circuit and an ink reservoir body. U.S. Pat. No. 5,736,998, entitled “Inkjet Cartridge Design for Facilitating the Adhesive Sealing of a Printhead to an Ink Reservoir,” and U.S. Pat. No. 5,852,460, entitled “Inkjet Print Cartridge Design to Decrease Deformation of the Printhead When Adhesively Sealing The Printhead to the Print Cartridge,” describe improved headland designs. However, these designs did not address the problem of ink shorts caused by ink leaking into the conductive leads and conductive traces of the flexible circuit.
On most flexible circuits, these leads are also protected on the back side by a laminated cover layer. For example, U.S. Pat. No. 5,442,386 describes a typical print cartridge assembly including a coating that is laminated to the back side of a tape on which the conductors are formed. The coating comprises a middle layer of polyethylene terephthalate (PET) and two additional outer layers composed of a copolyester film. The three layers are laminated together and provided on a roll. While this coverlayer resolves some of the shortcomings of the prior art methods and print cartridge assemblies, it requires use of a fully-cured and/or multiple-layered coverlayer which increases the cost of production dramatically and complicates the manufacturing process.
Other known print cartridge assemblies have simply relied on use of a single coating, usually consisting of a PET core, coated with a first layer of adhesive on one side and a second layer of adhesive on the other side of the PET core. However, there are a number of disadvantages to this current approach. Current coverlayer adhesives used in the industry are either soluble in ink and polyethylene glycol (PEG) (the latter being used in the printer service station), or will not adhere to adjacent materials used in the cartridge. In view of the solubility of these adhesives to common components in printers, the coverlayers containing such adhesives provide minimal protection to the flexible ci
Erickson David L.
Prasad Ravi
Watts Gary J.
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