Ink jetting structure having protected connections

An ink jetting structure includes a substrate that has a first surface and a second surface. A heater chip is mounted to the second surface of the substrate, and includes a first set of electrical contacts. A printhead circuit member has a third surface, a fourth surface, and an opening configured to receive the heater chip with the first set of electrical contacts of the heater chip being exposed through the opening. The third surface is mounted to the second surface of the substrate. The fourth surface has a second set of electrical contacts attached by wire bonds to the first set of electrical contacts. The third surface has a third set of electrical contacts electrically coupled to the second set of electrical contacts, and electrically connected to a flexible cable for coupling to corresponding contacts on a printer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink jetting structure, and, more particularly, to an ink jetting structure having protected connections.

2. Description of the Related Art

In jet printheads includes electrical wiring traces and connection points for supplying electrical current to the printhead components, e.g., heater circuits. Corrosion occurs when moisture and ions in fluids attack the wiring traces or connection points, such as wire bonds, solder connections, and tape automated bonding (TAB) circuit bonds over time. Ionic species and moisture present in ink or left over from manufacturing processes migrate through or under various polymeric coatings (e.g., encapsulants, cover coats, solder masks) to reach the wiring traces and bonds where they chemically attack the metal leading to open circuits. Corrosion is accelerated by temperature and voltage. The electrical wiring traces and connection points most susceptible to ink attack are those on the exposed surface of the printhead, which also may be subjected to mechanical forces, such as contact with a printhead wiper blade.

SUMMARY OF THE INVENTION

The terms “first”, “second”, etc., preceding an element name, e.g., first end, second end, etc., are used for identification purposes to distinguish between similar or related elements, results or concepts, and are not intended to necessarily imply order, nor are the terms “first”, “second”, etc., intended to preclude the inclusion of additional similar or related elements, results or concepts, unless otherwise indicated.

The invention, in one form thereof, is directed to an ink jetting structure. A flexible cable has a plurality of conductors. The plurality of conductors has a first end and a second end, with the first end being for coupling to corresponding contacts on a printer. A substrate has a first surface and a second surface spaced from the first surface. The substrate has a second fluid passage extending from the first surface to the second surface. The second fluid passage is in fluid communication with the first fluid passage. An ink jet heater chip is mounted to the second surface of the substrate. The ink jet heater chip is in fluid communication with the second fluid passage of the substrate. The ink jet heater chip includes a first set of electrical contacts. A printhead circuit member has a third surface and a fourth surface spaced from the third surface with embedded conductors being located between the third surface and the fourth surface. The printhead circuit member has an opening configured to receive the ink jet heater chip with the first set of electrical contacts of the ink jet heater chip being exposed through the opening. The third surface is mounted to the second surface of the substrate. The fourth surface has a second set of electrical contacts attached by wire bonds to the first set of electrical contacts of the ink jet heater chip. The third surface has a third set of electrical contacts electrically coupled by the embedded conductors in the printhead circuit member to the second set of electrical contacts. The third set of electrical contacts is electrically connected to the second end of the plurality of conductors of the flexible cable.

The invention, in another form thereof, is directed to an ink jetting structure. The ink jetting structure includes a base having a floor and a plurality of side walls extending outwardly from the floor. The floor has a first fluid passage. A flexible cable has a plurality of conductors. The plurality of conductors has a first end and a second end, the first end being for coupling to corresponding contacts on a printer. A ceramic substrate has a first surface and a second surface spaced from the first surface. The first surface is mounted to the floor of the base. The ceramic substrate has a second plurality of fluid passages extending from the first surface to the second surface. The second plurality of fluid passages is in fluid communication with the first plurality of fluid passages. A plurality of ink jet heater chips is mounted to the second surface of the ceramic substrate. The plurality of ink jet heater chips is in fluid communication with the second plurality of fluid passages of the ceramic substrate, and each of the plurality of ink jet heater chips include a corresponding first set of electrical contacts. A printhead circuit member has a third surface and a fourth surface spaced from the third surface with embedded conductors being located between the third surface and the fourth surface. The printhead circuit member has a plurality of openings configured to receive the plurality of ink jet heater chips with the first set of electrical contacts of the plurality of ink jet heater chips being exposed through the plurality of openings. The third surface is mounted to the second surface of the ceramic substrate. The fourth surface has a second set of electrical contacts attached by wire bonds to the first set of electrical contacts of the plurality of ink jet heater chips. The third surface has a third set of electrical contacts electrically coupled by the embedded conductors in the printhead circuit member to the second set of electrical contacts, and the third set of electrical contacts are electrically connected to the second end of the plurality of conductors of the flexible cable.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and particularly toFIGS. 1-3, there is shown an ink jetting structure10configured in accordance with an embodiment of the present invention. Ink jetting structure10includes a base12, a printer interface board14, a flexible cable16, a substrate18, a plurality of ink jet heater chips20, a printhead circuit member22, and a plurality of nozzle plates24, individually identified as nozzle plates24-1,24-2and24-3. In the present embodiment, ink jetting structure10may be a permanent printhead or a semi-permanent printhead for use in an ink jet printer. Also, ink jetting structure10may be integrated with an ink tank to form an ink jet printhead cartridge.

Base12has a floor26-1and a plurality of side walls26-2,26-3,26-4, and26-5that extend outwardly from floor26-1. Referring toFIG. 3, an ink receiving region28is defined by floor26-1and the plurality of side walls26-2,26-3,26-4, and26-5, wherein an ink source is provided. The ink source may be, for example, an ink tank, or a fluid interface coupled by conduits to a remote ink tank. Base12includes a recessed region12-1formed opposite to ink receiving region28, i.e., with floor26-1interposed between recessed region12-1and ink receiving region28. As shown inFIG. 3, floor26-1has a first plurality of fluid passages30, individually identified as fluid passage30-1and fluid passage30-2, for carrying ink received at ink receiving region28.

In the present embodiment, a printer interface board14is mounted to base12, and more particularly, to side wall26-4of base12. Printer interface board14has a plurality of electrical contacts32positioned to engage corresponding contacts34on an ink jet printer36(seeFIG. 3, with ink jet printer36only partially shown).

Flexible cable16has a plurality of conductors38. The plurality of conductors38has a first end38-1and a second end38-2. First end38-1is electrically connected to the plurality of electrical contacts32of printer interface board14to facilitate coupling of first end38-1of the plurality of conductors38of flexible cable16to corresponding contacts34on ink jet printer36. Alternatively, first end38-1of the plurality of conductors38of flexible cable16may be directly electrically connected to corresponding contacts34of ink jet printer36, without the use of printer interface board14.

Substrate18is a planar structure, and is shaped to be received in recessed region12-1of base12. Substrate18may be formed, for example, from a ceramic, a liquid crystal polymer (LCP), or other rigid substrate materials. Substrate18has a surface18-1and a surface18-2spaced from surface18-1. Surface18-1of substrate18is attached to floor26-1of base12, e.g., by an adhesive layer40, such as with an epoxy, or alternatively by a gasket and fastener arrangement. Substrate18has a second plurality of fluid passages42, individually identified as fluid passage42-1and fluid passage42-2, extending from surface18-1to surface18-2. The second plurality of fluid passages42of substrate18are in fluid communication, respectively, with the first plurality of fluid passages30of base12.

In the present embodiment, referring toFIG. 3, the plurality of ink jet heater chips20are individually identified as ink jet heater chip20-1, ink jet heater chip20-2, and ink jet heater chip20-3. The plurality of ink jet heater chips20may be mounted to surface18-2of substrate18, e.g., by an adhesive layer44, such as with an epoxy, before, during, or after attachment of printhead circuit member22to substrate18. The plurality of ink jet heater chips20include electrical heater elements and associated ink ejection chambers (not shown) configured for ejecting ink when a respective heater element is electrically energized, as is known in the art. The plurality of ink jet heater chips20respectively includes a plurality of openings (e.g., openings46-1and46-2shown inFIG. 3) configured to respectively supply ink to the associated nozzle plates24(e.g., nozzle plates24-1and24-2shown inFIG. 3). The plurality of openings of the plurality of ink jet heater chips20are in fluid communication with the second plurality of fluid passages42of substrate18. Each of the plurality of ink jet heater chips20includes a corresponding set of electrical contacts48. In the embodiment shown inFIG. 3, ink jet heater chip20-1includes a set of electrical contacts48-1and ink jet heater chip20-2includes a set of electrical contacts48-2.

As shown in the embodiment ofFIG. 4C, for example, printhead circuit member22may be a multilayer printed circuit board (PCB), with embedded conductors50(trace layer) being formed as an intermediate layer. More particularly, trace layer50is formed on a base layer52and is sealed over by a sealing layer54. Alternatively, printhead circuit member22may be formed as a multilayer tape automated bond (TAB) circuit.

For example, one approach for fabricating printhead circuit member22is to cover the electrical traces on the PCB surface with some kind of conformal coating material (urethane, silicone, etc.), as sealing layer54.

Another approach which may be more robust from a corrosion resistance standpoint is to move the traces to a wiring layer (e.g., trace layer50) internal to the PCB with no exposed wiring traces on either surface of printhead circuit member22, except where it is necessary to make connections to ink jet heater chips20and to flexible cable16that interfaces with ink jet printer36. If some electrical vias or traces must be exposed on a surface of printhead circuit member22for manufacturing reasons, such electrical vias or traces may be kept on the bottom side (e.g., surface22-1) of printhead circuit member22which will be attached to substrate18by adhesive44that can also serve to seal this side of printhead circuit member22against the corrosive effects of ink. Alternatively, a solder mask or conformal coating may be used for protection of the traces prior to attachment.

A third approach is to laminate an ink resistant film, as sealing layer54, over any exposed wiring. These films may be thermoplastics or thermosetting films and may also have an adhesive layer, such as for example, polyimide films with B-staged epoxy, acrylic, or phenolic adhesives. This process would involve lamination through heat and pressure followed by baking for final cure characteristics.

Printhead circuit member22has a plurality of openings56, individually identified as opening56-1, opening56-2and opening56-3, configured to receive the plurality of ink jet heater chips20, respectively. Any gap between printhead circuit member22and ink jet heater chips20may be filled with a sealant, such as an epoxy. The set of electrical contacts48of the plurality of ink jet heater chips20are exposed through the plurality of openings56at surface22-2of printhead circuit member22.

The surface22-1of printhead circuit member22is mounted to the surface18-2of substrate18, e.g., by adhesive layer44. The surface22-2of printhead circuit member22has an outer set of electrical contacts58, individually identified inFIG. 4Aas the set of electrical contacts58-1, the set of electrical contacts58-2, and the set of electrical contacts58-3.

The outer set of electrical contacts58of printhead circuit member22is connected, e.g., attached by wire bonds, to the set of electrical contacts48of the plurality of ink jet heater chips20. As shown inFIG. 3, for example, the set of electrical contacts58-1of printhead circuit member22are connected by wire bonding to the set of electrical contacts48-1of ink jet heater chip20-1, and the set of electrical contacts58-2of printhead circuit member22are connected by wire bonding to the set of electrical contacts48-2of ink jet heater chip20-2. An encapsulant59is located to hermetically seal around the set of electrical contacts48of plurality of ink jet heater chips20and the set of electrical contacts58of printhead circuit member22.

As shown inFIG. 4C, the surface22-1of printhead circuit member22has a set of electrical contacts60electrically coupled by embedded conductors50and internal leads62in printhead circuit member22to the set of electrical contacts58of printhead circuit member22. The set of electrical contacts60(seeFIGS. 4B and 4C) is electrically connected to the second end38-2of the plurality of conductors38of said flexible cable16(seeFIG. 3).

In the embodiment ofFIG. 3, a portion22-3of the printhead circuit member22having the set of electrical contacts60cantilevers past substrate18and extends across a proximal end64of one of the plurality of side walls, e.g., side wall26-4, of base12. As shown inFIG. 3, the second end38-2of the plurality of conductors38of flexible cable16is interposed between the proximal end64of side wall26-4and the surface22-1of printhead circuit member22. An encapsulant66is located to hermetically seal around the second end38-2of the plurality of conductors38of flexible cable16and the set of electrical contacts60of printhead circuit member22.

The embodiment ofFIG. 5is similar to the embodiment ofFIG. 3, except that printhead circuit member22having the set of electrical contacts60does not cantilever past substrate18and does not extend across side wall26-4of base12. Rather, in the embodiment ofFIG. 5, a void68, e.g., a relief area, is located between substrate18and printhead circuit member22for accommodating the second end38-2of the plurality of conductors38of flexible cable16(connected to the set of electrical contacts60of surface22-1of printhead circuit member22) between the surface18-2of substrate18and the surface22-1of printhead circuit member22. Encapsulant66is located to hermetically seal around void68.

Thus, in the embodiment ofFIG. 5, the second end38-2of the plurality of conductors38of flexible cable16is interposed between the surface18-2of substrate18and surface22-1of printhead circuit member22. Also, encapsulant66hermetically seals around second end38-2of the plurality of conductors38of flexible cable16and the set of electrical contacts60of printhead circuit member22.

In at least one embodiment, printhead circuit member22and flexible cable16are assembled as a subassembly, with second end38-2of the plurality of conductors38of flexible cable16being connected to the set of electrical contacts60located at the surface22-1of printhead circuit member22, prior to mounting to substrate18. The subassembly including printhead circuit member22and flexible cable16may then be attached as a unit to substrate18, i.e., with the surface22-1of printhead circuit member22being mounted to the surface18-2of substrate18by adhesive layer44.

In another embodiment, printhead circuit member22and the plurality of ink jet heater chips20may be assembled as a subassembly, with second end38-2of the plurality of conductors38of flexible cable16being connected to the set of electrical contacts60located at the surface22-1of printhead circuit member22, prior to mounting to substrate18. The subassembly including printhead circuit member22, the plurality of ink jet heater chips20, and flexible cable16may then be attached as a unit to substrate18, i.e., with the surface22-1of printhead circuit member22being mounted to the surface18-2of substrate18by adhesive layer44.

In the embodiments ofFIGS. 3 and 5, optional through holes70in printhead circuit member22may be used with corresponding through holes in the flexible cable16for automatic alignment using a fixture with through pins. Alternatively, alignment may be accomplished optically with no through holes. If through holes are used, after alignment the through holes may be filled with encapsulant to prevent ink access to the circuit and solder connections.

In the embodiments ofFIGS. 3 and 5, the connection point of flexible cable16to printhead circuit member22at surface22-1advantageously is not at a surface (i.e., surface22-2) that is exposed to ink or exposed to the mechanical force applied to printhead circuit member22by a printhead wiper during printhead maintenance, e.g., printhead wiping, thereby providing protection against corrosion, and permits more clear external surface area of the external surface22-2that may be used for a capping seal and for paper gap/clearance, i.e., the connections of flexible cable16to the set of electrical contacts60located at the surface22-1of printhead circuit member22are not exposed and do not protrude into the paper path of ink jet printer36.