Print head and method of making same

• US 5,488,394 A
• Filed: 08/08/1994
• Issued: 01/30/1996
• Est. Priority Date: 01/05/1988
• Status: Expired due to Term

• Current Assignee: Max Levy Autograph, Inc. (Coherent Corp.)
• Original Assignee: Max Levy Autograph, Inc. (Coherent Corp.)
• Inventors: Sedberry, Donald C.
• Primary Examiner(s): TRAN, HUAN HUU
• Application Number:
  US08/286,967
• Time in Patent Office: 540 Days
• Field of Search: 346/76 PH, 346/155, 346/139 C, 347/199, 347/141, 347/150
• US Class Current: 346/141
• CPC Class Codes: B41J 2/345 characterised by the arrangement of resistors or conductors
• CPC Class Codes: B41J 2/355 Control circuits for heating-element selection
• CPC Class Codes: H05K 1/0306 Inorganic insulating substrates, e.g. ceramic, glass
• CPC Class Codes: H05K 3/0017 Etching of the substrate by chemical or physical means
• CPC Class Codes: H05K 3/107 by filling grooves in the support with conductive material H05K3/045, H05K3/101, H05K3/1258 and H05K3/465 take precedence
• CPC Class Codes: H05K 3/4644 by building the multilayer layer by layer, i.e. build-up multilayer circuits making via holes in the insulating layers H05K3/0011; special circuit boards as base or core whereon the multilayer is built H05K3/4602

Abstract

A print head is made from an electronic circuit having a pattern of electric conductors embedded in a dielectric substrate. The conductors are formed by depositing a cermet material in grooves in the substrate, and heating the substrate in a kiln so as to make the cermet electrically conductive, and to form a very tight bond between the conductors and the substrate. The resulting circuit is stable, rugged, and capable of withstanding a wide range of adverse environmental conditions. The print head can be used in a thermal or electrostatic printer, or other type of printer using a print head powered by electric circuitry. The rugged, high-density circuit of the present invention can generate a set of very closely-spaced conductors which are then used to produce a high-density image. The invention also includes a multi-layered version of the print head, and permits the production of black and white or color halftone images having very large numbers of grey scale levels, and exceptional resolution.

Claims

1. A print head comprising a plurality of electric conductors, the conductors being formed in grooves in an electrically insulating substrate, the conductors being formed of a cermet material which becomes electrically conductive upon application of heat, the cermet material being firmly bonded to the substrate by firing, wherein the print head is free of organic materials.

2. A print head comprising a plurality of conductors, the conductors being formed in grooves in an electrically insulating substrate, the conductors being formed of a cermet material which becomes electrically conductive upon application of heat, the cermet material being firmly bonded to the substrate by firing, the grooves being formed in a first layer, the print head also including a second layer of insulating material, the second layer having a plurality of grooves filled with cermet material, the grooves in the second layer defining pads for connection of the print head to external electronic components, and means for connecting the conductors in the first layer to the pads in the second layer, wherein the print head is free of organic materials.

3. A print head comprising at least two layers of circuits, each circuit comprising a plurality of lines of conductive cermet material embedded in grooves in an electrically insulating material, the cermet being firmly bonded to the grooves by application of heat, the layers having different areas, wherein at least some of the lines of each layer are exposed to the outside, and wherein the print head is free of organic materials.

4. A print head made by the method comprising the steps of:

a) providing a smooth substrate material, at least the surface of the substrate comprising a dielectric material,

b) applying a layer of material capable of selectively resisting etchants, to the surface of the dielectric,

c) coating the etchant-resistive layer of material with a photoresist,

d) exposing the photoresist to light, the light being directed through a phototool comprising a pattern representing a desired pattern of conductors forming the print head,

e) developing the photoresist to expose the etchant-resistive layer of material in those locations corresponding to elements of the desired pattern of conductors,

f) removing the exposed portions of said etchant-resistive layer of material,

g) etching into the dielectric material, in those locations where the etchant-resistive layer of material has been removed, to form grooves in the dielectric material,

h) removing residual photoresist and etchant-resistive material,

i) filling the grooves with a cermet material capable of bonding to the dielectric substrate upon the application of heat, and

j) firing the substrate to a temperature sufficient to bond the cermet material to the grooves in the dielectric material,

wherein the print head is free of organic materials.

5. The print head of claim 4, wherein step (a) comprises the steps of applying the dielectric material to the substrate, heating the dielectric-coated substrate at a first temperature sufficiently high, and for a time sufficiently long, to drive off impurities in the dielectric, and heating the dielectric-coated substrate at a second temperature, the second temperature being higher than the first temperature, the second temperature being sufficiently high to permit the dielectric material to flow freely.

6. The print head of claim 5, wherein the first temperature is about 400°

-500°

C., and wherein the second temperature is in the range of about 1000°

-1250°

.

7. A print head made by the method comprising the steps of:

a) coating an electrically insulating substrate with a thin layer of material which can resist an etchant,

b) coating the etchant-resistive layer of material with a photoresist,

c) exposing the photoresist to light, the light being directed through a phototool comprising a pattern corresponding to the print head to be made,

d) developing the photoresist to expose the etchant-resistive layer of material in those locations corresponding to elements of the desired print head,

e) removing the exposed portions of said etchant-resistive layer of material,

f) etching into the dielectric material, in those locations where the etchant-resistive layer of material has been removed, to form grooves in the dielectric material,

g) filling the grooves with a cermet material capable of bonding to the dielectric substrate upon the application of heat, and

h) firing the substrate to a temperature sufficient to bond the cermet material to the grooves in the dielectric material,

wherein the print head is free of organic materials.

8. The print head of claim 7, wherein the substrate is prepared by the steps of applying a layer of dielectric material to the substrate, heating the dielectric-coated substrate at a first temperature sufficiently high, and for a time sufficiently long, to drive off impurities in the dielectric, and heating the dielectric-coated substrate at a second temperature, the second temperature being higher than the first temperature, the second temperature being sufficiently high to permit the dielectric material to flow freely.

9. The print head of claim 8, wherein the dielectric-coated substrate is heated at the first temperature for at least two hours, and wherein the substrate is heated at the second temperature for at least about one hour.

10. The print head of claim 9, wherein the first temperature is about 400°

-500°

C., and wherein the second temperature is in the range of about 1000°

-1250°

C.