US3736406A - Thermographic print head and method of making same - Google Patents

Thermographic print head and method of making same Download PDF

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Publication number
US3736406A
US3736406A US00264832A US3736406DA US3736406A US 3736406 A US3736406 A US 3736406A US 00264832 A US00264832 A US 00264832A US 3736406D A US3736406D A US 3736406DA US 3736406 A US3736406 A US 3736406A
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United States
Prior art keywords
layer
print head
terminal leads
thermographic
vias
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Expired - Lifetime
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US00264832A
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English (en)
Inventor
J Vossen
Neill J O
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RCA Corp
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RCA Corp
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K1/00—Methods or arrangements for marking the record carrier in digital fashion
    • G06K1/12—Methods or arrangements for marking the record carrier in digital fashion otherwise than by punching
    • G06K1/126—Methods or arrangements for marking the record carrier in digital fashion otherwise than by punching by photographic or thermographic registration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used

Definitions

  • thermographic print head for encoding labels on thermographic paper is made by a method of depositing, on an electrically insulating substrate, first and third layers of electrically conductive material separated by a second layer of insulating material.
  • the first layer comprises a plurality of separated terminal leads
  • the third layer comprises a plurality of separated concentric ring conductors, each of which is connected to selected terminals of the first layer through vias in the separating second layer of electrically insulating material.
  • thermographic print head merit of the novel grap print h ad capaand a method of making same.
  • the novel thermographic print head is particularly useful for encoding labels to be applied to packages, as in a supermarket,
  • a novel thermographic print head comprises a multilayered structure on an electrically insulating substrate.
  • a first layer of electrically conductive material comprises a plurality of separated terminal leads.
  • a second layer of electrically insulating material is disposed over the first layer, and a third layer of electrically conductive material comprises a plurality of separated electrical conductors that contact selected terminals of the first layer through vias formed in the insulating second layer.
  • the first and third layers ofelectrically conductive material comprise molybdenum, and the ratio of the sheet resistivity of the third layer to the first layer is between 2.7 and 10.
  • FIG. 1 is a planar view of an embodiment of the novel thermographic print head
  • FIG. 2 is a planar view of an upper (third) metallic layer comprising a plurality of concentric rings of the thermographic print head shown in FIG. 1;
  • FIG. 3 is a planar view of a lower (first) metallic layer comprising a plurality of separated terminal leads of the thermographic print head shown in FIG. 1;
  • FIGS. 4-11 are enlarged fragmentary portions, in cross section, of the thermographic print head in different stages in the novel method of making it.
  • FIG. 12 is a schematic drawing of the thermographic print head with apparatus for printing a label on thermographic paper.
  • the print head 10 comprises a multilayer structure on a substrate 12 of electrically insulating material, such as a disc of Pyrex glass.
  • a first layer 13 (FIG. 3) on the upper major surface 14 of the substrate 12 comprises a plurality of separated, relatively narrow, elongated, terminal leads 16 and a relatively much larger common terminal lead 18 of electrically conductive material, as shown in FIG. 3.
  • the elongated terminal leads 16 extend in radial directions from a point in common and have terminal connecting portions 17 that are parallel to each other.
  • the common terminal lead 18 has a semicircular area with a terminal connecting portion 20 extending therefrom.
  • a third layer 21 (FIG. 2) of electrically conductive material, comprising a plurality of closely spaced, separated conductors in the form of a plurality of concentric rings 22 around a circular dot 24, is disposed over the first layer 13 of the terminal leads 16 and 18 but is separated therefrom by a thin second layer 28 (FIG. 10) of insulating-material, as will be described in detail hereinafter.
  • Each of the rings 22 is connected to the common terminal lead 18 and to a separate one of the terminal leads 16 through vias 30 (FIG. 8) formed in the separating insulating layer 28.
  • the print head 10 is essentially a thin film heater wherein each ring 22 has two terminal leads (l6 and 18) contacting it at points located apart. Because the rings 22 are concentric, the print head 10 is a multilevel metallization structure comprising the two (lower and upper) metallization layers 13 and 21 separated by the insulating layer 28, the latter layer having vias 30 (FIG. 8) etched therethrough for connecting the first and third metallization layers 13 and 21 at desired contact points.
  • the heater ring pattern should have a resistivity high enough so that moderate current densities can be used to heat them, but not so high as to require very high voltages.
  • the insulating second layer 28 and the substrate 12 should have a high enough thermal conductivity so that the rings 22 can be cooled rapidly between printings, but not so high as to require very high voltages.
  • the insulating layer 28 and the substrate 12 should have a high enough thermal conductivity so that the rings 22 can be cooled rapidly between label printings, but not so high as to draw excessive heat from the rings 22 during the printing cycle.
  • the terminal leads 16 and 18 should have a resistivity lower than that of the rings 22, but should not have such a low resistivity as to act as heat sinks during the printing cycle.
  • the insulating layer 28 should be capable of withstanding several times the highest voltage used on the structure, and, the entire structure should be very rugged, scratch resistant, and not show significant parameter shifts with use.
  • the substrate 12 comprising Corning Code 7740 Pyrex glass.
  • the substrate 12 has an excellant chemical resistance, and a moderate thermal expansion (3.3 X l /C), a high resistance to thermal shock, and can be processed at temperatures up to 490C without softening.
  • the thermal conductivity of the substrate 12 is about 0.01 watts/cmK.
  • a practical size for the substrate 12 is a circular disc of about 3 inches in diameter and one-eighth inch in thickness.
  • the first layer 13 of electrically conductive material is disposed on the upper surface 14 of the substrate 12, as shown in FIG. 5.
  • the first layer 13 is a composite layer that comprises a relatively thin lower layer of a metal, such as chromium, titanium, hafnium, tantalum, or alloys thereof, for example, and a relatively much thicker upper layer of molybdenum.
  • the relatively thin layer of the composite first layer 13 is first disposed over the surface 14 of the substrate 12, as by vapor deposition or by sputtering techniques, known in the art. This prevents the relatively thicker, upper layer of molybdenum from recrystallizing because it is necessary to deposit the molybdenum layer on a metallic base.
  • Chromium is preferable to the other metals mentioned supra for the thinner, lower layer because the etchant for molybdenum and chromium can be the same.
  • the thicker upper layer of molybdenum is disposed on the chromium layer by sputtering with an rf induced bias (-150V), as taught, for example, in U. S. Pat. No. 3,640,812, issued to J. L. Vossen, Jr. on Feb. 8, 1972 for Method of Making Electrical Contacts on the Surface of a Semiconductor Device, and incorporated herein by reference.
  • the chromium layer is between 500 and 1,000A thick, and the molybdenum layer is about l0,000A thick.
  • the terminal leads 16 and 18, shown in FIG. 3, are formed by photolithographic techniques, well known in the art.
  • the first (composite) layer 13 is covered with a suitable photoresist, exposed with an image from a photomask to produce the desired terminal lead patterns, and then etched with a suitable etchant to provide the terminal leads 16 and 18, portions of which are shown in FIG. 6.
  • the second layer 28 of electrically insulating material is disposed over the terminal leads l6 and 18 of the first layer 13, as shown in FIG. 7.
  • the second layer 28 has a dielectric strength that is at least 3 or 4 times that required for the maximum working voltage (about 100 volts) of the print head 10, and is extremely rugged and readily etchable.
  • the layer 28 possesses substantially the same thermal conductivity as that of the substrate
  • the second layer 28 is a composite of a relatively thin lower layer of about 5,000A of rf sputtered Pyrex" glass and a relatively much thicker upper layer of a chemically vapor deposited borosilicate glass having a thickness of about 45,000A.
  • the composite second layer 28 ofPyrex" and borosilicate glasses reduces the possibility of the second layer 28 cracking.
  • the rf sputtered Pyrex glass over the terminal leads 16 and 18 provides a uniform surface upon which the chemically vapor deposited borosilicate glass can nucleate.
  • the preferred composition of the borosilicate glass layer of the second composite layer 28 consists of between 15-20 mol% B 0 and 85-80 mol% SiO
  • the second layer 28 is covered with a photoresist, exposed through a suitable photomask, and etched by photolithographic means well known in the art to provide a plurality of vias 30 therein that extend to, and expose, the terminals 16 and 18, as shown in FIG. 8.
  • a portion of the second layer 28 is also etched away to expose the parallel terminal connecting portions 17 of the terminal leads l6 and the terminal connecting portion 20 of the common terminal lead 18 so that electrical connections can be made thereto for electrically energizing the print head 10.
  • the third layer 21 of electrically conductive material such as molybdenum, is sputtered with an rf induced bias (-200V), in accordance with the aforementioned U. S. Pat. No. 3,640,812, onto the second layer 28, covering all surfaces of the second layer 28 and contacting the terminal leads 16 and 18 of the first layer 13 through the vias 30, as shown in FIG. 9.
  • the third layer 21 is deposited to a thickness of about 3,500A.
  • the third layer 21 is sputter deposited onto the second layer 28 in the manner described in the aforementioned patent because such a deposition method enables the sputtered metal to extend into the vias 30 and to make good electrical contact with the terminals 16 and 18.
  • the third layer 21 is covered with a suitable photoresist, exposed through a photomask for forming the desired heater ring pattern, and etched by photolithographic means well known in the art to form the concentric pattern of heater rings 22, a fragment of which is shown in cross section in FIG. 10.
  • Each ring 22 is connected to both the common terminal lead 18 and to a separate one of the smaller terminal leads 16. Also, the two connections to each ring 22 are spaced 180 apart with respect to the circular dot 24.
  • Molybdenum is the preferred metal for the rings 22. More conductive metals either do not stick well to glass or are subject to electromigration. In addition, oxides stick well to molybdenum.
  • the only possible disadvantage of using molybdenum in the print head 10 involves oxidation. Molybdenum oxidizes in air completely at 500C, and the oxide completely vaporizes at 650C. However, since the oxidation temperature is approximately twice the operating temperature (about 250C) of the print head 10, the aforementioned disadvantage is felt to be inconsequential.
  • the properties of the heater rings 22 largely dictate the properties of the other materials used in the print head 10.
  • the heater rings 22 are 0.01 inch wide and are separated by 0.001 inch on the print head 10.
  • the optimum range of sheet resistivities for the heater rings 22 has been determined as between 0.5 and 0.75 ohm/- square. This range limits the highest operating voltage (voltage on the outer ring 22) to about between and volts.
  • the resistivity can be controlled. Under these sputtering conditions, the resistivity of the molybdenum is approximately 24 X 10 ohm cm.
  • the range of thickness of the rings 22 as required for the desired sheet resistivity of the layer 21 is between 2800A and 4600A. This is a relatively broad range and easy to con- X A/cm This value is considerably below that at which electromigration becomes a problem with molybdenum.
  • the stresses in sputter-deposited molybdenum are relatively low (approximately 10 dynes/cm and are compressive under the aforementioned method of deposition. This is not always true for other deposition methods.
  • any poor connection between the first and third layers 13 and 21, through the vias 30, can result in hot spots and eventual opens in the print head 10. This is avoided by making the first layer 13 approximately 10,000A thick. Also, the rings 22 must cross about 2024 steps over this structure without cracking, notching, or thinning. In addition, there are about 88 vias 30 in the print head 10, and each via height is between 4.5 and 5.0 pm. The walls of these vias 30 must be uniformly coated. To insure perfect edge coverage, a delicate balance exists between the sputtered deposition rate and the rf bias, as described in the aforementioned patent and also in the Journal of Vacuum Science and Technology, Vol. 8, page S12 (1971). The rf bias voltage is chosen to maximize small angle re-sputtering to insure side-wall coverage, and the deposition rate is held down to about 37A/minute.
  • the heater rings 22 may be left bare, but since they are very closely spaced, dust particles can gather between them and cause them to are over and burn.
  • a fourth layer 34 in the form of a cap layer of rf sputtered Pyrex is deposited through a mechanical mask over the heater rings 22.
  • the fourth layer 34 is about 6,000A in thickness.
  • the ratio of the heater rings sheet resistivity to the terminal leads sheet resistivity must lie between 2.7 and 10. If this ratio islarger (i.e., the terminal leads 16 and 18 are more conductive), the terminal leads l6 and 18 heat sink the heater rings 22 during printing. This, then, necessitates overdriving the rings 22, to carry out the printing function, producing several detrimental side effects as follows:
  • the overheating extracts resinous material from the thermographic paper on which the labels are printed, and the extracted material polymerizes on the print head 10, eventually causing arcing between the rings 22 and ruining the print head 10.
  • the terminal leads 16 and 18 are not conductive enough, they get hot enough to print.
  • the safe range for the sheet resistivity of the terminal leads l6 and 18 is between 0.075 and 0.1 85 ohms/per square.
  • thermo graphic print head 10 is shown schematically with apparatus for printing labels on a web of thermographic paper 36.
  • the web of thermographic paper 36 is unwound from a feed roll 38, mounted for rotation about a fixed spindle-40, and wound up on a take-up roll 42, mounted on a power-driven spindle 44 for rotation therewith.
  • the print head 10 is mounted parallel to, and slightly spaced from, one major surface of the thermographic paper 36.
  • a resilient mat 46 having a cross-sectional diameter substantially equal to the overall diameter of the ring pattern of the print head 10,-is disposed boh adjacent to the ring pattern of the print head 10 and adjacent the opposite major surface of the thermographic paper 36, as shown in FIG. 12.
  • the mat 46 is adapted to be moved reciprocally, perpendicularly to the print head 10, in the directions indicated by the doubleheaded arrow 48, to periodically press the thermographic paper 36 against the print head 10 for printinglabels on the thermographic paper 36.
  • Electrodes such as a lead 50 connected to the terminal connecting portion 20 of the common terminal lead 18 and a plurality of leads 52 (only one being shown in FIG. 12), each connected to a different one of the terminal connecting portions 17 of the terminal leads 16, are connected to a suitable source of electrical energy (about volts or less) through suitable energizing and switching means (not shown).
  • the rings 22 can be selectively energized in accordance with a predetermined code, to heat selected rings 22.
  • the thermographic paper 36 is thermally affected by the selected heated rings 22 and provides a coded, printed label thereon.
  • the mat 46 presses the thermographic paper 36 against the print head 10 every time the print head 10 is energized for printing acoded label.
  • the printing temperature is approximately 250C, and the heater rings 22 are cycled over a 225C range once per second in operation. This implies that all of the parameters in the manufacture of the print head 10 must be well controlled, since a single defect in the involved method will render the print head 10 inoperative.
  • thermographic print head comprising:
  • a third layer of electrically conductive material comprising a plurality of separated conductors disposed over said second layer, each of said conductors extending to, and contacting, two of said terminal leads through said vias.
  • thermographic print head as described in claim 2, wherein each of said second and fourth layers comprises sputtered glass having a melting point in excess of 490C and a thermal expansion of about 3.3 X 10 /C, and
  • said second layer is a composite of a bottom layer of said sputtered glass and a top layer of chemically vapor-deposited borosilicate glass.
  • thermographic print head as described in claim 1, wherein 7 8 said plurality of conductors comprises a plurality of posed over said rings.
  • thermographic print head as described in claim said plurality of terminal leads comprises a relatively 1, wherein large common terminal lead and a plurality of relathe ratio of the sheet resistivity of said third layer to tively much narrower elongated terminal leads, that said first layer is between 2.7 and 10. each of said rings being connected to said common 7.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Electronic Switches (AREA)
US00264832A 1972-06-21 1972-06-21 Thermographic print head and method of making same Expired - Lifetime US3736406A (en)

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US26483272A 1972-06-21 1972-06-21

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US (1) US3736406A (de)
JP (1) JPS5340456B2 (de)
AU (1) AU476058B2 (de)
CA (1) CA990341A (de)
CH (1) CH567305A5 (de)
DE (1) DE2331536C3 (de)
FR (1) FR2190057A5 (de)
GB (1) GB1389387A (de)
IT (1) IT986440B (de)
NL (1) NL7308317A (de)
SE (1) SE392840B (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4327283A (en) * 1979-09-24 1982-04-27 Rca Corporation Workpiece with machine-readable marking recessed therein and method of making same
US4391535A (en) * 1981-08-10 1983-07-05 Intermec Corporation Method and apparatus for controlling the area of a thermal print medium that is exposed by a thermal printer
US4446362A (en) * 1979-05-21 1984-05-01 Rca Corporation Workpiece with abraded machine-readable marking therein and method of making
US4568818A (en) * 1981-03-24 1986-02-04 Shigeru Ikemoto Heat cutter for plastic wrapping films using film resistors
US5414245A (en) * 1992-08-03 1995-05-09 Hewlett-Packard Corporation Thermal-ink heater array using rectifying material

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57138961A (en) * 1981-02-23 1982-08-27 Fujitsu Ltd Crossover formation for thermal head
DE20205708U1 (de) * 2002-04-12 2003-08-21 Heidemanns, Peter, 47839 Krefeld Vorrichtung zum taktweisen Transport von Musterkollektionen bei deren Kennzeichnung

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3483356A (en) * 1968-06-27 1969-12-09 Sprague Electric Co Thermal printing head
US3495070A (en) * 1967-05-29 1970-02-10 Murray H Zissen Thermal printing apparatus
US3578946A (en) * 1969-10-27 1971-05-18 Ncr Co Thermal print head wafer and method of making the same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3495070A (en) * 1967-05-29 1970-02-10 Murray H Zissen Thermal printing apparatus
US3483356A (en) * 1968-06-27 1969-12-09 Sprague Electric Co Thermal printing head
US3578946A (en) * 1969-10-27 1971-05-18 Ncr Co Thermal print head wafer and method of making the same

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4446362A (en) * 1979-05-21 1984-05-01 Rca Corporation Workpiece with abraded machine-readable marking therein and method of making
US4327283A (en) * 1979-09-24 1982-04-27 Rca Corporation Workpiece with machine-readable marking recessed therein and method of making same
US4568818A (en) * 1981-03-24 1986-02-04 Shigeru Ikemoto Heat cutter for plastic wrapping films using film resistors
US4391535A (en) * 1981-08-10 1983-07-05 Intermec Corporation Method and apparatus for controlling the area of a thermal print medium that is exposed by a thermal printer
US5414245A (en) * 1992-08-03 1995-05-09 Hewlett-Packard Corporation Thermal-ink heater array using rectifying material
US5609910A (en) * 1992-08-03 1997-03-11 Hewlett-Packard Company Method for forming thermal-ink heater array using rectifying material

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Publication number Publication date
SE392840B (sv) 1977-04-25
CH567305A5 (de) 1975-09-30
FR2190057A5 (de) 1974-01-25
DE2331536C3 (de) 1981-02-12
CA990341A (en) 1976-06-01
AU476058B2 (en) 1976-09-09
JPS5340456B2 (de) 1978-10-27
AU5698773A (en) 1974-12-19
NL7308317A (de) 1973-12-27
DE2331536A1 (de) 1974-01-17
IT986440B (it) 1975-01-30
JPS4958841A (de) 1974-06-07
GB1389387A (en) 1975-04-03
DE2331536B2 (de) 1980-05-22

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