EP0443339A1 - Wärmeübertragungsdruckkopf und sein Herstellungsverfahren - Google Patents

Wärmeübertragungsdruckkopf und sein Herstellungsverfahren Download PDF

Info

Publication number
EP0443339A1
EP0443339A1 EP91100871A EP91100871A EP0443339A1 EP 0443339 A1 EP0443339 A1 EP 0443339A1 EP 91100871 A EP91100871 A EP 91100871A EP 91100871 A EP91100871 A EP 91100871A EP 0443339 A1 EP0443339 A1 EP 0443339A1
Authority
EP
European Patent Office
Prior art keywords
tungsten
copper
electrodes
printing head
electrode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91100871A
Other languages
English (en)
French (fr)
Inventor
Raymon Lane
Vaughn Joseph Schum
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lexmark International Inc
Original Assignee
Lexmark International Inc
International Business Machines Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lexmark International Inc, International Business Machines Corp filed Critical Lexmark International Inc
Publication of EP0443339A1 publication Critical patent/EP0443339A1/de
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/385—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material
    • B41J2/39—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material using multi-stylus heads
    • B41J2/395—Structure of multi-stylus heads

Definitions

  • This invention relates to a resistive ribbon thermal transfer printing head having multiple refractory metal electrodes (also known as "styli") which are electrically energized to locally melt ink in a ribbon.
  • the refractory metals which can be used are tungsten (W), molybdenum (Mo) and tantalum (Ta), most preferably, tungsten.
  • the electrodes are part of a current distributing circuit which are connected via leads and contact pads to copper cable pads also in the circuit. This entire circuit is disposed on a substrate which is in turn adhered to a pliable backing and contained in a rigid casing.
  • the refractory metal most preferably tungsten, is used only to form the electrodes, and the balance of the circuit is predominately copper.
  • One embodiment of the resistive ribbon printer technology used in products today has a print head fabricated from a 25 ⁇ m thick tungsten sheet which is laminated to a substrate or backing sheet for mechanical support during and after etching of the electrodes.
  • Tungsten is at present the material of choice for print head fabrication because it has proved to provide long life without over heating while printing.
  • the tungsten sheet is wet-etched to form the head pattern, and then the etched laminate is molded to silicone rubber to provide a flexible structure.
  • Wet etching is a process that unfortunately undercuts sideways into the material while etching downwards, and this phenomenon limits the extent to which gap width between adjacent electrodes can be narrowed, as is required for higher resolution print heads.
  • narrow gaps i.e. less than about 50 ⁇ m
  • a wet chemical etching process will not suffice.
  • the use of controlled spray etching extends the typical print head electrode dimensions to about 60 ⁇ m wide on 100 ⁇ m centers.
  • a standard printing head made entirely from a sheet of tungsten is approximately 2.5 cm by approximately 5 cm by 25 ⁇ m thick.
  • An object of the present invention is to provide a thermal print head that provides the benefits of the print heads of the type described above comprised entirely of tungsten, while reducing the amount of tungsten used in the assembly of the print head.
  • the thermal print head is not made entirely of tungsten and the tungsten thus eliminated in the print head is replaced with copper, a much less expensive material.
  • R.I.E. reactive ion etching
  • the structure embodied within the scope of the present invention comprises two parts or components, one component formed from a copper-substrate laminate and the other component formed from, a tungsten-substrate laminate.
  • tungsten is used only to form the electrodes or styli, as this is the part of the thermal printing head that is most susceptible to wear as a result of printing.
  • the balance of the circuit of thermal printing head contains a fan-out distribution of the leads that make contact with the cable contact pads present therein.
  • Figure 1 shows the arrangement of the resistive thermal transfer printing head of the present invention in position on an electric typewriter.
  • a rigid casing 1 supports a pliable elastomeric layer (not shown) within the casing.
  • the rigid casing 1 can be any of the natural or synthetic materials available today having the required properties, i.e. impact strength modulus, etc. to satisfactorily encase the rest of the system.
  • the pliable elastomeric layer should be a flexible material which is compressible and resilient and can absorb or diffuse impacts and return to its original shape.
  • a substrate (also not specifically shown in FIG. 1) is bonded adhesively or fixed by any other convenient means to the elastomeric layer. Both are contained within the casing after the printing head has been assembled.
  • the substrate can be made of any material which is strong enough to support the current distributing circuit having electrodes 2 secured to it.
  • the substrate is substantially inert, and can withstand the temperatures, pressures and reactive gases present in the reaction chamber without substantial degradation.
  • a particularly suitable material for example is the polyimide bearing the trademark Kapton.
  • the temperature of the process to make the print head as described hereinafter should be less than about 125 o C during the etching process.
  • FIG. 2 is a simplified depiction of an etched copper-substrate laminate which forms a part of the current distributing circuit.
  • substrate 11 supports copper cable pads 12, 12' and 12", the copper contact pads 13, 13' and 13" each of which is connected by respective copper leads 14, 14' and 14" to the corresponding cable pads noted.
  • Figure 3 is a simplified depiction of the tungsten-containing component of the printing head which contains the tungsten electrode tips 15, 15' and 15" and contact pads 16, 16' and 16" which are connected the "fan-out" leads 17, 17' and 17.” These components are also all disposed on substrate 11.
  • the electrodes, leads, contact pads and cable pads forming a layer in the laminar printing head structure are collectively referred to as the electric current distributing circuit, as these elements provide the means for the operation of the printing head.
  • the electric current distributing circuit in operation comprises a combination of the elements disclosed in Figs. 2 and 3.
  • the plurality of tungsten electrode tips 15 are disposed at one edge of said substrate, each said electrode tip being connected to a tungsten contact pad 16 by means of a tungsten lead 17.
  • the plurality of tungsten contact pads 16 of FIG. 3 are secured in contact with a plurality of corresponding copper contact pads 13 depicted in FIG. 2.
  • the R.I.E. process which is used to make the electrodes 15 depicted in FIG. 3 requires that a copper film be deposited on the tungsten sheet from which the electrodes will be formed.
  • bonding to tungsten is normally very difficult. This is due to the formation of a native oxide on the tungsten surface.
  • a very important part of the R.I.E. process as described hereinafter is getting the copper film (also called "mask") used, to adhere to the tungsten.
  • a very careful etching of the tungsten is needed prior to depositing the copper mask. Good adhesion is necessary so that the mask material can withstand the R.I.E. etching process.
  • the tungsten sheet from which the electrodes are to be formed using the R.I.E. process has a copper film on it both before and after the R.I.E. process.
  • the copper film remaining on the tungsten can be put to good use, in that it, by virtue of the efficient etching treatment has formed a strong bond to the tungsten sheet surface.
  • Solder or conducting epoxy can be adhered to the part containing the tungsten.
  • the electrode section is made out of tungsten and the remainder of the head out of copper.
  • FIG. 4 is a perspective view depicting copper contact pad 13 and tungsten pad 16 having copper film 20 bonded thereto.
  • the copper underside 20 of tungsten contact connecting pad can be either tinned with solder or it can be wet with conducting epoxy 21 at the area shown in FIG. 7.
  • the two sections can now be bonded together by securing copper contact pad 13 with tungsten contact pad 16 using epoxy or solder 21.
  • the contact area is far enough away from the electrode tips that no heat from the tip will affect it.
  • the bond between 13, 16 through material 21 is electrically conducting.
  • the resultant part i.e., substrate and conducting circuit is molded into a plastic holder with silicone rubber.
  • the head package is formed having much less tungsten material, the tungsten having been replaced by copper.
  • each of the copper cable pads 13 being connected to a corresponding copper contact pad by means of a copper lead 14.
  • contact pads 13 can be modified to also serve as the cable pad, thereby eliminating the need for lead 14.
  • the tungsten metal used in the system in the instant invention is a rolled sheet material having a thickness between 15 and 50 ⁇ m preferably 25 ⁇ m, and the thickness variation should not generally exceed about 2 ⁇ m after the rolling process.
  • the substrate of the laminated samples has to be heat sunk efficiently so as to protect the adhesive from excessive heating leading to loss of adhesion properties during etching.
  • thermal transfer printing head Using the method hereinafter described, an improved thermal transfer printing head is obtained.
  • One embodiment of the thermal transfer printing head possesses up to 10 electrodes/mm, preferably 10 electrodes/mm, with a relatively large footprint (i.e., the end cross-sectional view of the electrode showing the width and height area).
  • the benefit of this embodiment is that the larger footprint reduces the contact resistance, with the net result that the electrode runs cooler and thus has an extended life.
  • the width of the footprint is between about 80 ⁇ m and 90 ⁇ m, preferably 88 ⁇ m, the height as noted above is 15 ⁇ m to 50 ⁇ m, preferably 25 ⁇ m, and the electrodes with said footprint are located on 100 ⁇ m centers.
  • another effective embodiment comprises a smaller footprint with the electrodes packaged closer together, i.e., at up to about 50 electrodes/mm.
  • a higher number of electrodes/mm is possible, but it must be kept in mind that as the number of electrodes/mm increases, the thickness of the tungsten must decrease proportionally. Good results have been obtained using 40 electrodes/mm printheads; for example, the 40 electrodes/mm printhead has 160,000 dots/cm2 printing capability.
  • the width of the footprint is between about 13 ⁇ and 21 ⁇ , preferably 16 ⁇ m
  • the height is between about 13 ⁇ m to 25 ⁇ m, preferably 25 ⁇ m
  • the electrodes with said footprint are located on 25 ⁇ m centers.
  • 10 electrodes/mm can be raised up to 40 electrodes/mm, for example by reducing the gap width and electrode width to have a 25 ⁇ m center to center distance.
  • a R.I.E. system is used in forming the complete print head structure described above.
  • the R.I.E. process used in the present invention is a plasma process wherein reactive gases are used with ion bombardment to cause chemical reactions at the surface of the material being etched.
  • an anisotropic etching process is required.
  • a problem associated with the R.I.E. process is "loading." This means that increasing the amount of material to be etched has the effect of reducing the etch rate.
  • the present invention reduces the amount of tungsten to be etched.
  • the reduction allows the R.I.E. of 10 times the number of print heads.
  • a practical advantage of the instant invention is the reduction in cost of the print head.
  • the copper-substrate laminate is much less expensive than the tungsten substrate laminate.
  • a copper film is deposited on the surface of the tungsten sheet.
  • the copper acts as a mask for the R.I.E. of the tungsten.
  • tungsten samples are first etched in a cleaning solution (such as sodium hypochlorite, Chlorox), for a minute to remove the surface oxide, followed by a rinse in deionized water for about another minute. Then the surface is prepared for vacuum deposition by giving a light etch for 30 seconds in a solution of equal parts of NH4OH, H2O2 and deionized water.
  • a cleaning solution such as sodium hypochlorite, Chlorox
  • Prolonged R.I.E. runs i.e.greater than one hour which are required in accordance with the present invention because the process embodies etching thick tungsten films.
  • the prolonged run necessitates the use of metal masks for delineating the pattern, since a photoresist cannot withstand exposures in excess of about 1 hour.
  • copper is used as the masking material.
  • the next step in the sequence is to sputter etch the copper film forming the mask for the R.I.E. step.
  • a 500 o A thick film of titanium or chromium was first sputtered on to the tungsten sheet as an adhesion promoter.
  • the thickness of this copper mask ranges between about 1 and 4 ⁇ m which range has proved to be sufficient thickness to withstand the R.I.E. processing times in excess of 1 hour.
  • the copper film thus applied is thereafter delineated into the required print head pattern by the use of photolithography and wet chemical etching.
  • the resist usually remains on the copper masking pattern prior to R.I.E. etching.
  • Printing heads falling within the scope of the instant invention are conveniently prepared in a parallel plate R.I.E. machine operating at about 13.6 MHz.
  • the machine comprises a chamber and a pumping section.
  • the chamber and the electrodes are conveniently made of aluminum.
  • the cathode in the chamber is water-cooled and the temperature can be vary between 20 o C and 80 o C (as measured by the water temperature at the outlet).
  • the pumping system consists of a turbo molecular pump and a mechanical roughing pump.
  • the system pressure is regulated by a automatic throttle valve.
  • the chamber is pumped via a 11 cm2 diameter port in the center of the cathode electrode, and this effects the uniformity of the etch rate.
  • the pumping capabilities of this system permit operation at about 10mtorr pressure with a flow rate at of about 100cmin for the reactive gas mixtures.
  • the backs of the samples to be treated are directly affixed to the R.I.E. electrode by one of two methods: either a thermal grease used for vacuum coupling, or double sided masking tape. It was found that the samples that were thermally coupled with the double side adhesive tape consistently had a more uniform etched rate both across the sample and from sample-to-sample on a densely populated cathode. A variation of about 1 to 2 ⁇ m is measured for a total etching time of about 75 minutes and this is close to the variation in the surface finish of the tungsten sheet.
  • the gas mixtures used in the chamber in the R.I.E. process comprise a number of different halogen based gases such as CF4, NF3, SF6 alone and in combination, and also with the addition of various inhibitors (CHCl3, CHF3, CH4).
  • CF4, NF3, SF6 alone and in combination
  • various inhibitors CHCl3, CHF3, CH4
  • the mixture of SF6 and CHCl3 was found to be most effective and is therefore preferred.
  • a higher etch rate is achieved at higher pressures.
  • the higher pressures usually lead to under-cutting, and the upper limit is generally thought to be about 25 mtorr to avoid any potential problems in etching thick films such as encountered in the present invention.
  • the gas flow rate is linked to the total loading of the tungsten being etched in the system, i.e. the etch rate will decrease if there is an insufficient amount of gas available for the exposed tungsten surface area.
  • increasing the gas flow allows an increase in the amount of tungsten being etched at a fixed rate.
  • tungsten-copper thermal printing head was made using the R.I.E. system wherein the prepared tungsten sample was contacted with 90% SF6 and 10% CHCl3.
  • the fragile electrodes of the head were potted with silicone rubber solution whereupon the electrode tips are then mechanically dressed to fit the curved platen of the printer.
  • the gas mixture of SF6 and CHCl3 was selected and used to R.I.E. the tungsten because of its etch rate of the tungsten.
  • This gas mixture has an etch rate of 20 ⁇ m/hr in region between the electrodes, while only etching the sidewalls of the electrodes less than 2 ⁇ m/hr. These rates are achieved at a power level of 1w/cm2.
  • CHCl3 as an inhibitor gas gives excellent side wall protection to the narrow electrodes during the R.I.E. step, the measured amount of under cut is only 1 ⁇ m per wall.
  • Other inhibitor gases that have acceptable etch rates have produced greater than 2 ⁇ m of undercut.
  • straight walls is meant that the top width of the electrode is ⁇ 2 ⁇ m narrower than the bottom width of the electrode when the electrode height is 25 ⁇ m. If the height of the electrode is ⁇ 25 ⁇ m the difference in the width of the top and bottom is proportionately reduced.
  • a possible problem with using CHCl3 for the extended etch times associated with the present invention is that while in the plasma phase it reacts with copper forming a film, which can dislodge from the copper surface. During the R.I.E. step, this film has frequently flaked off and deposited between the electrodes, stopping any further etching of the tungsten below the flaked film. To control this problem it has been found experimentally that a photo resist film thick enough to withstand both the sputter etch step and the R.I.E. step will protect the copper surface from the CHCl3.
  • the photo resist mentioned above must be thin enough to resolve the 12 ⁇ m gap between the electrodes, but thick enough to withstand the two subsequent etch steps and passivate the copper mask during the R.I.E. etching of the tungsten. Keeping the copper mask thin minimizes the length of time the photo resist is exposed to the sputter etch process.
  • a copper thickness between about 0.5 and 2.0 ⁇ m is thick enough to survive the R.I.E. step.
  • the optimum photo resist thickness that survived both the etching steps is >2.0 ⁇ m, i.e. about 2.25-2.50 ⁇ m. At this thickness the 12 ⁇ m gap in the photoresist that is required between the electrodes is still defined.
  • the electrodes After the R.I.E. step, it is important to protect the electrodes, which are very fragile by means providing mechanical stability to the electrodes.
  • This protection is achieved by potting the entire electrode area in a thin mixture of a cleaner such as Dow Corning 1200 prime coat and 732 RTV.
  • the mixture has to be thin enough so as to wick into the narrow gaps between the electrodes.
  • An added benefit of using this mixture is that is has the needed good high temperature properties. For example it can be heated to 400 o C without breaking down.
  • This high temperature stability of the potting solution keeps the electrodes from being damaged by the heat generated during the printing process.
  • the potting also allows the mechanical dressing of the print head to the shape of the curved platen and optimization of the fit of each electrode foot print.

Landscapes

  • Electronic Switches (AREA)
EP91100871A 1990-02-21 1991-01-24 Wärmeübertragungsdruckkopf und sein Herstellungsverfahren Withdrawn EP0443339A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US48257890A 1990-02-21 1990-02-21
US482578 1990-02-21

Publications (1)

Publication Number Publication Date
EP0443339A1 true EP0443339A1 (de) 1991-08-28

Family

ID=23916614

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91100871A Withdrawn EP0443339A1 (de) 1990-02-21 1991-01-24 Wärmeübertragungsdruckkopf und sein Herstellungsverfahren

Country Status (2)

Country Link
EP (1) EP0443339A1 (de)
JP (1) JPH04216070A (de)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0067953A2 (de) * 1981-06-22 1982-12-29 International Business Machines Corporation Elektrothermischer Drucker
US4415403A (en) * 1978-11-20 1983-11-15 Dynamics Research Corporation Method of fabricating an electrostatic print head
US4546364A (en) * 1982-10-29 1985-10-08 Fuji Xerox Co., Ltd. Head for electrostatic recording
US4689638A (en) * 1984-03-26 1987-08-25 Fujitsu Limited Thermal recording head and process for manufacturing wiring substrate therefor
EP0274062A2 (de) * 1987-01-07 1988-07-13 Lexmark International, Inc. Druckknopf mit Elektroden

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5711046B2 (de) * 1975-02-20 1982-03-02
JPS61181658A (ja) * 1985-02-07 1986-08-14 Oki Electric Ind Co Ltd サ−マルヘツド
JPS6294354A (ja) * 1985-10-21 1987-04-30 Seiko Epson Corp 記録ヘツド
JPS63299343A (ja) * 1987-05-29 1988-12-06 Matsushita Electric Ind Co Ltd エッチング方法
JPH0223618A (ja) * 1988-07-12 1990-01-25 Seiko Epson Corp 半導体装置の製造方法
JPH0380317A (ja) * 1989-06-13 1991-04-05 Matsushita Electric Ind Co Ltd リセットパルス信号出力回路

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4415403A (en) * 1978-11-20 1983-11-15 Dynamics Research Corporation Method of fabricating an electrostatic print head
EP0067953A2 (de) * 1981-06-22 1982-12-29 International Business Machines Corporation Elektrothermischer Drucker
US4546364A (en) * 1982-10-29 1985-10-08 Fuji Xerox Co., Ltd. Head for electrostatic recording
US4689638A (en) * 1984-03-26 1987-08-25 Fujitsu Limited Thermal recording head and process for manufacturing wiring substrate therefor
EP0274062A2 (de) * 1987-01-07 1988-07-13 Lexmark International, Inc. Druckknopf mit Elektroden

Also Published As

Publication number Publication date
JPH04216070A (ja) 1992-08-06

Similar Documents

Publication Publication Date Title
EP0321075B1 (de) Integrierter Tintenspritzdruckkopf und Verfahren zu dessen Herstellung
US6061077A (en) Thermal head
JPS6046030B2 (ja) プリントヘツドの製造方法
US6929349B2 (en) Thin film ink jet printhead adhesion enhancement
EP0443339A1 (de) Wärmeübertragungsdruckkopf und sein Herstellungsverfahren
US5077564A (en) Arcuate edge thermal print head
KR100206622B1 (ko) 서멀헤드에 있어서의 공통전극 패턴에 대한 보조전극층의 형성방법
KR20010062345A (ko) 인쇄 유체 분사 프린트헤드
EP0335660B1 (de) Wärmebeständiges, isolierendes Substrat, thermischer Druckkopf und thermografischer Apparat
JP2684675B2 (ja) 印字記録ヘッド
JPWO1996041722A1 (ja) サーマルヘッドにおける共通電極パターンに対する補助電極層の形成方法
JP2004154969A (ja) サーマルヘッド及びその製造方法
JP3616809B2 (ja) サーマルヘッドおよびその製造方法
JP3231951B2 (ja) サーマルヘッドおよびその製造方法
US5070343A (en) Printing head for resistive ribbon type printing apparatus
KR920009367B1 (ko) 박막 써멀 헤드 및 그 보호막 제작방법
JP3461245B2 (ja) インクジェット記録ヘッドの発熱体基板
JPH04305466A (ja) サーマルヘッドおよびその製造方法
JPH02158350A (ja) サーマルヘッド
JPH0557936A (ja) サーマルヘツドおよびその製造方法
JPH0466706B2 (de)
JPH04211958A (ja) インクジェットヘッド、該インクジェットヘッド用基体、インクジェット装置およびインクジェットヘッド用基体の製造方法
JPH03227660A (ja) サーマルヘッドおよびその製造方法
JPH04239655A (ja) サーマルヘッド及びその製造方法
JP2004090254A (ja) 端面型サーマルヘッド及びその製造方法

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): DE FR GB

RAP1 Party data changed (applicant data changed or rights of an application transferred)

Owner name: LEXMARK INTERNATIONAL, INC.

17P Request for examination filed

Effective date: 19911106

111Z Information provided on other rights and legal means of execution

Free format text: DE FR GB

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN WITHDRAWN

18W Application withdrawn

Withdrawal date: 19921029