EP0061550A2 - Mit Glas umhüllter scheibenförmiger Thermistor - Google Patents

Mit Glas umhüllter scheibenförmiger Thermistor Download PDF

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Publication number
EP0061550A2
EP0061550A2 EP81304781A EP81304781A EP0061550A2 EP 0061550 A2 EP0061550 A2 EP 0061550A2 EP 81304781 A EP81304781 A EP 81304781A EP 81304781 A EP81304781 A EP 81304781A EP 0061550 A2 EP0061550 A2 EP 0061550A2
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EP
European Patent Office
Prior art keywords
disk
approximately
lead
coated
glass
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Withdrawn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
EP81304781A
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English (en)
French (fr)
Other versions
EP0061550A3 (de
Inventor
Thomas Herbert Lamers
John Michel Zurbuchen
Hardy Wilcox Trolander
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.)
Yellow Springs Instrument Co Inc
Original Assignee
Yellow Springs Instrument Co Inc
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 Yellow Springs Instrument Co Inc filed Critical Yellow Springs Instrument Co Inc
Publication of EP0061550A2 publication Critical patent/EP0061550A2/de
Publication of EP0061550A3 publication Critical patent/EP0061550A3/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/04—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient

Definitions

  • the field of the invention is in the thermistor art and more particularly in the fabrication of highly stable disk thermistors having predetermined resistance characteristics.
  • Thermistors are well known electrical devices that exhibit a wide change in resistance values with changes in temperature. Generally, they are made by sintering mixtures of metallic oxides such as oxides of cobalt, copper, iron, manganese, nickel, and uranium. These mixtures are formed into various shapes, such as beads, disks, probes, rods, and washers. Two very common forms are (1) beads, because they are generally very stable in difficult environments and (2) disk, because they can readily be fabricated and trimmed to provide a predetermined resistance-temperature characteristics, thus interchangeable disk units are readily produced. The bead units are generally fabricated by imbedding lead wires in the bulk thermistor material such as by placing a drop of the thermistor suspension on two lead wires.
  • the entire package is glass coated by applying a drop of glass-liquid suspension over the dried thermistor drop and vitrifying the unit in a high-temperature furnace.
  • the beads thus formed vary not only in size and in compactness of the thermistor material, but also in electrical characteristics.
  • the glass bead structure provides a compact unit that is generally impervious to moisture and other gases and fluids. They will withstand relatively high temperatures, and have firmly anchored leads.
  • a problem with glass coated bead thermistors is that in the present state of the art there is no known method for trimming bead units, or precisely controlling their temperature coefficient of electrical resistivity. Thus, mass production of a quantity of units having even a reasonable percentage of controlled interchangeability is not presently possible.
  • disk units including those with holes through them, i.e., washers, may readily be fabricated under very controlled conditions of uniform size, uniform compacting pressures, uniform firing temperatures, and with a very important feature of being readily cut or trimmed to a specific value of resistance.
  • Contact with the thermistor material is generally made through a sprayed-on glass-silver film. The film does not make a metallurgical bond to the thermistor. The bond is more of a contact or pressure-type bond, wherein the glass forms a porous matrix which fuses to the thermistor. This matrix holds the interstitial silver in contact with the thermistor. Firing the disk cements the silver to the disk of thermistor material.
  • Silver-glass coating on the edge of the disk is removed by grinding, and the disk is further trimmed to produce the desired resistance.
  • Copper lead wires are then soldered to the glass-silver mix that is adhering to the surface of the thermistor material.
  • the assembly is then encased in an epoxy, and a precise unit having predetermined characteristics is provided.
  • the epoxy overcoat is a low stiffness substance incapable of applying significant compressive force to the disk. It is also relatively permeable to gases and water vapor which can cause corrosion of the internal metallic elements.
  • the upper temperature limit of suitable operation of the disk units is generally quite restricted compared to the glass-encased bead units. Generally, units fabricated with conventional solder connections are limited to approximately 150°C by the solder.
  • Pressure contacts units such as typically used in washer types, may be used to approximately 150°C. Units that are lacquer coated instead of epoxy are limited to approximately 100°C. Glass coated bead thermistors will generally operate and remain reasonably stable up to temperatures approaching 300°C, (600°C for short time periods for special bead types). The foregoing temperatures are generally short-term maximum operating temperatures and as such are not indicative of the long-term stability characteristics of the thermistor. It is the imperviousness of the encapsulant to contaminants over a relative lengthy period of time in a relatively moderate temperature and the compression of a conformal glass coating that primarily determines the factor of stability of a thermistor. While the fabrication of embodiments as taught herein does provide a disk thermistor having higher maximum operating temperatures than previous disk thermistors, the primary feature is the greatly improved stability of the disclosed units over the prior art devices.
  • the method of fabrication using a tri-metal contact film, and the thermo-compression bonded leads allows the bulk thermistor material to be both rigidly constrained and protected from ambient contaminants while maintaining the feature of providing controlled electrical characteristics.
  • a glass coated disk thermistor and the method of fabrication are disclosed.
  • the devices of the invention have the stability and environmental immunity of glass coated bead-type thermistors with the predictability of electrical characterists found only in previous, relatively less stable disk-type thermistors.
  • a glass coated disk thermistor comprising a disk of thermistor material having an upper surface and a lower surface with a film of a mixture of finely divided silver, platinum, and palladium metallurgically bonded to the upper and to the lower surface of said disk.
  • a first wire lead having a silver surface is attached by fusion to the film on the disk's upper surface
  • a second wire lead having a silver surface is attached by fusion to the film on the disk's lower surface.
  • a conformally encapsulating glass coating encapsulates the film coated disk and the wire leads where the leads are attached to the film coated disk.
  • a method of fabricating a stable disk thermistor having a predetermined resistance characteristic comprising the steps of coating the flat surfaces of a disk of pressed thermistor material with a noble metal film containing finely divided silver, sintering the coating to the disk, measuring the resistance of the disk, removing a portion of said coated disk to provide the predetermined resistance, welding leads containing silver to the coated flat surfaces, and fusing a conformal glass coating to the disk and leads.
  • the knowledge of the composition of the bulk material from which to fabricate thermistors is in a well-defined art.
  • the principal materials are a mixture, in precise ratios, of nickel oxide and manganese oxide.
  • the exact ratios of nickel oxide and manganese oxide plus well-known additives such as copper or iron to adjust the bulk resistivity and temperature coefficient to provide a desired type of characteristic are well kriown.
  • the mixture containing the desired amounts of the constituents are typically ball milled and sift milled to accurately control the particle size of the mix.
  • a uniform particle size also provides more uniform control of the coefficient of resistance of the material.
  • an acrylic resin binder as is conventionally used in the art, is added to the sized powder to give the pressed, unfired disk some strength so that it may be easily,handled. After mixing in the resin, the mix is sift dried to break up any large clumps that might be present that might prevent uniform filling of the die. The powdered thermistor material is then compacted under high pressure to provide a mass that will have near theoretical density (generally well over 90%).
  • thermistor pellet is formed.
  • disks of thermistor material may be cut or sliced from a relatively long cylindrical rod or sheet of previously prepared material. Typical sizes and embodiments fabricated as taught herein are approximately .090 inch diameter and .007 inch to .032 inch thick. The portioning of sizes to provide a desired type of electrical characteric is well known in the thermistor fabrication art.
  • a pressed disk 11 of thermistor material after it is ejected from the die is schematically illustrated in elevation in Fig. 1 and in plan in Fig. 2.
  • the physical shape of the thermistor is not critical. Generally, round disks with substantially flat and parallel surfaces are preferred.
  • the invention is just as applicable to disks of square, rectangular or other shape cross sections having two spaced electrical contacting areas.
  • the flat-surfaces 13 and 15 of the disk pellet are coated with an oxidation resistant material, preferably with a paste of finely divided silver, platinum, and palladium in a conventional organic vehicle so that the flat surfaces are covered with a thick film.
  • the ratios of these metals in the mixture are not critical, they do however, tailor the mixture's melting temperature.
  • the use of noble metals permit the firing in an oxidizing atmosphere which is compatible with the thermistor firing.
  • the vehicle aids in the application of the paste. It, the vehicle, is not critical as it will burn away when fired.
  • Typical, suitable, conventional, ratios of metals for typical embodiments, such as being described are silver 54.55%, platinum 9.09%, and palladium 36.36%.
  • An example of a suitable, commercially available well known organic vehicle is Terpineol.
  • Coated disks are fired suspended in alumina powder in a ceramic boat. Generally, a plurality of disks are fired simultaneously. The disks are floated (suspended) in fine aluminum oxide powder in the boat to prevent their sticking to the boat or each other. It has been found desirable to first heat the disks in the alumina powder to approximately 625°C at a rise time of 15°C per minute so that the acrylic resin and the coating vehicle are removed relatively slowly and that no violent out-gassing occurs which could rupture the thermistor. It also prevents the carbonization of the organic materials. The boat, containing the thermistors after the preheat, is then transferred to a sintering furnace where it is preferably held at a temperature of approximately 1200°C for approximately 3 hours.
  • the temperature of the firing may be empirically adjusted to achieve a desired bulk temperature coefficient for a particular ratio of thermistor materials. Typical sintering temperatures range from approximately 800°C to 1500°C with corresponding varying duration times.
  • the boat containing the fired thermistor disks is removed from the furnace, and the thermistors are air-cooled to room temperature at a rate of approximately 200°C per second. This rapid cooling "freezes-in" the desired thermistor grain crystal lattice structure.
  • a fired thermistor disk now appears as illustrated in Fig. 3 with upper contacting film 31 on upper flat surface 13 and lower contacting film 33 on lower flat surface 15. Typical film thicknesses range from approximately .0001 inch to .0005 inch. The thickness is not critical.
  • the disks each now have an ohmic resistance value between their parallel surfaces that at a specific temperature such as 25°C is a function of the disk material and the thickness and cross-sectional area of the disk.
  • the relative temperature- resistance characteristic has substantially already been determined by the choice of materials and the foregoing steps.
  • the coated thermistor material is cut to a size yielding the desired resistance.
  • thermistor material is removed from the edge of a disk of thermistor material. Obviously, only increases in the resistances of the disks as formed can be made. This is conventionally done as illustrated in simplified schematic form in Fig. 4.
  • the coated disk 41 is passed back and forth across the face of a rotating grinding stone 43, grinding a flat 45 on the edge of the disk 41.
  • the electrical resistance of the disk is monitored as material is being removed by conventional resistance measuring apparatus 47. Electrical contact is schematically shown as made with the disk through pressure contacting tabs 49 and 51. When the desired resistance is achieved, grinding is stopped and the disk is removed from the grinding fixture. This step is generally termed "trimming the thermistor.” Additional information on this well known step is contained in U. S. patent No. 2,970,411 to patentee Trolander.
  • the disk now has the general appearance as illustrated in Fig. 5.
  • the electrical characteristics of the thermistor are now established and further steps must not significantly alter the resistance level or temperature coefficient of the device.
  • Wire leads that will bond with the conductive coating on the surfaces of the disk are required for making electrical contact with the device.
  • Silver or silver-clad wire leads are preferred.
  • a suitable wire lead has been found to be approximately .006 inch diameter copper wire with a 100 microinch silver coating.
  • the end regions of the leads are prepared for attachment by cleaning and removing any insulation in the region of attachment and preferably flattening them slightly, so that an area of contact rather than a line contact is originally made, and placing then on the coated surfaces of the disk.
  • the amount of flattening is not critical. Generally, a flat approximately equal to or slightly greater than the radius of the wire is suitable.
  • the flattened length should preferably be slightly longer than the desired contact length with the conducting coating, but not so long as to extend beyond the glass coating in the final assembly. Flattening is not a requirement. Round wire may be used directly, as some flattening will occur normally in the bonding process.
  • the coated, fired, and trimmed thermistor disk 41 with prepared wire leads 61 and 63 are positioned between the anvils 65 and 67 of a thermal-compression bonding fixture and heat and pressure are applied. Generally, the leads are bonded to the central portion of the surfaces of the disk. If desired, the bonding may be located close to the edge. It is not critical.
  • thermo-compression welding temperature should be at least 460°C as this is the temperature at which silver oxide surface contaminants decompose to silver (metal) and oxygen (gas).
  • the bonded wire to coating conducting area was over a contact length of approximately .050 inch and a width of approximately .003 inch. In equivalent metric dimensions, this is approximately equivalent to a pressure of 140 kilograms per square centimeter.
  • the thermal-compression bonding technique provides a metallurgical weld of the wire to the film and avoids excessive heating of the thermistor material. It is to be noted that the step of trimming of the disk to a desired resistance value may take place after attaching the lead wires rather than before attaching them if desired.
  • the disk and the wire leads where attached to the disk and in the general area of the disk, are coated with a conventional low melting temperature glass frit mixed in a liquid binder.
  • a disk is held by the lead wires and is dipped in the liquid. This is a convenient means of coating this assembly.
  • the preferred glass frit has a melting temperature of approximately 500°C and a coefficient of thermal expansion closely matched to the disk and the leads.
  • the frit paste is air dried to remove.the binder.
  • a suitable low-temperature glass frit is Owens-Illinois type SG-67.
  • a suitable binder is water or Terpineol.
  • the dipped coating should be a "heavy" dipped coat with a thickness surrounding the disk that is at least the thickness of the disk.
  • the glass frit is fused to the disk and wire leads in a furnace at a temperature at approximately 500-600°C for 1 to 2 minutes. A shrinkage of approximately 20% of the glass coating is typical. The time is kept relatively short to minimize the chance of a shift in the resistance or coefficient of resistance of the disk.
  • a typical finished glass coated disk thermistor has the general appearance illustrated in Fig. 7.
  • the glass coating 75 provides a conformal glass coat completely encasing the thermistor disk and a portion of the wire leads 61 and 63 providing support and anchorage to the leads.
  • a suitable conformal glass coat may be obtained by the conventional dipping of the disk and lead wires in molten glass held at a temperature of approximately 600°C to approximately 700°C for approximately 3 to 10 seconds.
  • Conventional flame sprayed glass may also be used to form the conformal glass coat.
  • the stability of the glass coated disk thermistors fabricated as taught herein is approximately the same as that of conventional glass bead-type thermistors in the temperature range up to approximately 200°C.
  • the maximum high temperature limit for trimmed disk thermistors is also appreciably extended.
  • the average stability data from four early embodiments of the invention, each having a resistance of approximately 1200 ohms at 40°C, is as follows:
EP81304781A 1980-10-14 1981-10-14 Mit Glas umhüllter scheibenförmiger Thermistor Withdrawn EP0061550A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US19699180A 1980-10-14 1980-10-14
US196991 1980-10-14

Publications (2)

Publication Number Publication Date
EP0061550A2 true EP0061550A2 (de) 1982-10-06
EP0061550A3 EP0061550A3 (de) 1983-10-05

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EP81304781A Withdrawn EP0061550A3 (de) 1980-10-14 1981-10-14 Mit Glas umhüllter scheibenförmiger Thermistor

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EP (1) EP0061550A3 (de)
JP (1) JPS5799703A (de)
CA (1) CA1175954A (de)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111361A1 (de) * 1982-12-07 1984-06-20 Philips Patentverwaltung GmbH Symmetrischer Temperatursensor
EP0171877A1 (de) * 1984-08-02 1986-02-19 Stc Plc Verfahren zum Kontaktieren eines Thermistors an Anschlusselemente
US5142267A (en) * 1989-05-30 1992-08-25 Siemens Aktiengesellschaft Level sensor which has high signal gain and can be used for fluids particularly chemically corrosive fluids
AT398636B (de) * 1989-05-30 1995-01-25 Siemens Matsushita Components Niveaufühler mit hohem signalhub für flüssigkeiten, insbesondere chemisch aggressive flüssigkeiten
CN105890794A (zh) * 2016-06-02 2016-08-24 句容市博远电子有限公司 一种传感器包封灌封一体化装置及其操作方法
CN106092364A (zh) * 2016-05-26 2016-11-09 句容市博远电子有限公司 Ntc温度传感器插片生产装置及方法
CN114291783A (zh) * 2021-12-31 2022-04-08 深圳市信为科技发展有限公司 具有微细多引线的压力传感器及其制备方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB685229A (en) * 1949-06-28 1952-12-31 Western Electric Co Methods of making thin film resistors
GB770175A (en) * 1955-03-22 1957-03-20 Welwyn Electrical Lab Ltd Improvements in or relating to electrical resistors
GB1257148A (de) * 1970-08-18 1971-12-15

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB685229A (en) * 1949-06-28 1952-12-31 Western Electric Co Methods of making thin film resistors
GB770175A (en) * 1955-03-22 1957-03-20 Welwyn Electrical Lab Ltd Improvements in or relating to electrical resistors
GB1257148A (de) * 1970-08-18 1971-12-15

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111361A1 (de) * 1982-12-07 1984-06-20 Philips Patentverwaltung GmbH Symmetrischer Temperatursensor
US4533898A (en) * 1982-12-07 1985-08-06 U.S. Philips Corporation Symmetrical temperature sensor
EP0171877A1 (de) * 1984-08-02 1986-02-19 Stc Plc Verfahren zum Kontaktieren eines Thermistors an Anschlusselemente
US5142267A (en) * 1989-05-30 1992-08-25 Siemens Aktiengesellschaft Level sensor which has high signal gain and can be used for fluids particularly chemically corrosive fluids
EP0400167B1 (de) * 1989-05-30 1994-10-26 Siemens Aktiengesellschaft Niveaufühler mit hohem Signalhub für Flüssigkeiten, insbesondere chemisch aggressive Flüssigkeiten
AT398636B (de) * 1989-05-30 1995-01-25 Siemens Matsushita Components Niveaufühler mit hohem signalhub für flüssigkeiten, insbesondere chemisch aggressive flüssigkeiten
CN106092364A (zh) * 2016-05-26 2016-11-09 句容市博远电子有限公司 Ntc温度传感器插片生产装置及方法
CN106092364B (zh) * 2016-05-26 2019-05-17 句容市博远电子有限公司 Ntc温度传感器插片生产装置及方法
CN105890794A (zh) * 2016-06-02 2016-08-24 句容市博远电子有限公司 一种传感器包封灌封一体化装置及其操作方法
CN114291783A (zh) * 2021-12-31 2022-04-08 深圳市信为科技发展有限公司 具有微细多引线的压力传感器及其制备方法

Also Published As

Publication number Publication date
CA1175954A (en) 1984-10-09
EP0061550A3 (de) 1983-10-05
JPS5799703A (en) 1982-06-21

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Inventor name: TROLANDER, HARDY WILCOX