US3857174A - Method of making varistor with passivating coating - Google Patents

Method of making varistor with passivating coating Download PDF

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Publication number
US3857174A
US3857174A US00401334A US40133473A US3857174A US 3857174 A US3857174 A US 3857174A US 00401334 A US00401334 A US 00401334A US 40133473 A US40133473 A US 40133473A US 3857174 A US3857174 A US 3857174A
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US
United States
Prior art keywords
coating
varistor
body portion
metal oxide
reaction product
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.)
Expired - Lifetime
Application number
US00401334A
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English (en)
Inventor
J May
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.)
General Electric Co
Original Assignee
General Electric Co
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 General Electric Co filed Critical General Electric Co
Priority to US00401334A priority Critical patent/US3857174A/en
Priority to CA207,329A priority patent/CA1011884A/en
Priority to IE1769/74A priority patent/IE39769B1/xx
Priority to IT27580/74A priority patent/IT1022209B/it
Priority to SE7412082A priority patent/SE395561B/xx
Priority to DE2445659A priority patent/DE2445659C2/de
Priority to FR7432407A priority patent/FR2246034B1/fr
Priority to US05/509,337 priority patent/US3938069A/en
Priority to JP11004274A priority patent/JPS563644B2/ja
Priority to GB42154/74A priority patent/GB1483811A/en
Application granted granted Critical
Publication of US3857174A publication Critical patent/US3857174A/en
Anticipated expiration legal-status Critical
Expired - Lifetime 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
    • H01C7/10—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 voltage responsive, i.e. varistors
    • H01C7/102—Varistor boundary, e.g. surface layers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49099—Coating resistive material on a base
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49101—Applying terminal

Definitions

  • a metal oxlde varlswr Comprising a y [58 Field of Search 29/620, 621, 613, 610; Portion that is Composed essentially of a metal Oxide 338/20, 21, 22, 13; 252/518, 520; 317 234 and a small percentage of a plurality of preselected v 233; 7 0 2 7 2 additives.
  • a passivating coating is applied to the body portion prior to the application of metallic contacts.
  • the passivating coating includes at least some of the UNITED STATES PATENTS preselected additives in order to enhance device stad t 1,483,538 2/1924 Allcutt 338/21 an Insure compa herew'th 3,496,512 2/1970 Matsuoka et al. 29/621 X 7 Claims, 2 Drawing Figures METHOD OF MAKING VARISTOR WITH PASSIVATING COATING BACKGROUND OF THE INVENTION
  • This invention relates to metal oxide varistors and, more particularly, to a passivating coating for improving the stability and electrical characteristics of metal oxide varistors.
  • V and V are the device voltages at given currents I, and 1 respectively.
  • metal oxide varistors At very low voltages and very high voltages metal oxide varistors deviate from the characteristics expressed by equation l and approach linear resistance characteristics. However, for a very broad useful voltage range the response of metal oxide varistors is as expressed by equation (1).
  • the values ofC and a can be varied over wide ranges by changing the varistor formulation and the manufacturing process.
  • Another useful varistor characteristic is the varistor voltage which can be defined as the voltage across the device when a given current is flowing through it. It is common to measure varistor voltage at a current of one milliampere and subsequent reference to varistor voltage shall be for voltage so measured.
  • Still another useful varistor characteristic is the leakage current. This is the dc steady state current through the device when it is exposed to one-half of its varistor voltage. A high leakage current causes wasted power and, if high enough, can cause joule heating of the device, which leads to a higher current. Thus, high leakage current can lead to thermal runaway.
  • the foregoing is, of course, well known in the prior art.
  • Metal oxide varistors are usually manufactured as follows. A plurality of additives is mixed with a powdered metal oxide, commonly zinc oxide. Typically, four to twelve additives are employed, yet together they comprise only a small portion of the end product, for example less than five to ten mole percent. In some instances the additives comprise less than one mole percent.
  • the types and amounts of additives employed vary with the properties sought in the varistor. Copious literature describes metal oxide varistors utilizing various additive combinationsFor example, see US. Pat. No. 3,663,458. A portion of the metal oxide and additive mixture is then pressed into a body of a desired shape and size. The body is then sintered for an appropriate time at a suitable temperature as is well known in the prior art. Sintering causes the necessary reactions among the additives and the metal oxide and fuses the mixture into a coherent pellet. Following sintering metallic contacts are applied and leads are fixed to the contacts. Finally, the device is generally encapsulated.
  • an object of this invention to provide a passivating coating for metal oxide varistors that is fully compatible therewith and improves device stability and reduces leakage current thus providing substantially improved devices.
  • This invention is characterized by a metal oxide varistor comprising a body portion that is composed essentially of a metal oxide and a small percentage of a plurality of preselected additives.
  • the metal oxide and the additives are mixed and then a portion of the mixture is pressed into a body of a desired shape and size.
  • the pressed body is then sintered to form the varistor body in a manner well known in the prior art.
  • a coating is then applied to the body and it is reheated as described below.
  • Metal contacts are applied and wire leads are attached to the contacts. The device is then ready to be encapsulated.
  • a feature of the subject coating is that it is a passivating coating and substantially improves the stability of the device as discussed below.
  • the preselected additives form a major portion of the coating. Thus, compatibility of the coating and the varistor is assured.
  • the preselected additives can be prereacted to form a reaction product which is ground and then mixed with the metal oxide prior to pellet pressing and sintering. It has been found that such a technique provides a varistor with very desirable electrical properties, high stability and of a very uniform composition.
  • the coating can comprise the reaction product.
  • a carrier can be included, as is disclosed below, to enhance the adhesion of the reaction product to the body portion surface.
  • the coating is free of silver and other monovalent ions that tend to diffuse rapidly into the varistor pellet during the step of heating the coating. It is advantageous to prevent such ion diffusion inasmuch as it causes high leakage current and other effects on the varistor properties that are difficult to predict. Furthermore, the coating can be made free of silicon as disclosed below. It has been found that the inclusion of silicon in a varistor pellet coating increases the varistor voltage of the treated device. Thus, when fabricating low voltage varistors, it is preferable that the coating be free of silicon.
  • the coating enhances the contact adhesion.
  • a preferred method of enhancement is to contour the surface of the varistor body.
  • particulate matter can be included in the coating and the step of heating the coating can be carried out, as described below, at a temperature that does not melt the particulate matter.
  • contouring the surface of the pellet can be employed.
  • a coating that shrinks as cured can be employed. The shrinking coat will develop cracks that create a contoured surface effect.
  • a coating for metal oxide varistors that functions as a passivating coating to improve the stability of the device.
  • the coating is fully compatible with the varistor body portion, and, inasmuch as the coating is free of monovalent ions, does not adversely alter the electrical properties of the varistor.
  • the coating can be free of silicon if a low voltage device is being manufactured.
  • the coating enhances the adhesion of the contacts to the varistor body portion, thus preventing device failure due to detached, cracked or torn contacts.
  • FIG. 1 is a sectional view of a preferred metal oxide varistor
  • FIG. 2 is a detailed sectional view of a portion of the varistor depicted in Fig. 1.
  • a metal oxide varistor that includes a sintered body portion 11 composed essentially of a metal oxide and a plurality of preselected additives.
  • the body 11 can be manufactured by methods well known in the prior art or by an improved technique to be discussed below.
  • Surrounding the body portion is a passivating coating 12 and, overlying the coating on two major surface areas of the body, are two metallic contacts 13 and 14.
  • Two wire leads l5 and 16 are coupled to the contacts 13 and 14, respectively, by conductive couplers such as solder l7 and 18.
  • FIG. 2 there is shown a portion of the varistor 10 shown in FIG. 1. Specifically, a corner of the body portion 11 is shown in FIG. 2.
  • the passivating coating 12 is more clearly visible. It is seen to consist of a coating material with particulate matter embedded therein. It will be appreci ated that some of the grains 19 of the particulate matter project beyond the surface of the coating 12 while other grains, such as the grains 20, are completely encapsulated by the coating. The grains 19 and 20 are part of a contact adhesion enhancement system included in the coating 12. It will be appreciated that the surface of the coating 12 is substantially roughened or contoured as compared to what it would be were the contouring particles 19 and 20 absent.
  • the coating 12 preferably comprises at least some of the preselected additives.
  • an effective passivating coating can be provided utilizing the reaction product" that is discussed in my aforementinoed co-pending US. application entitled Low Voltage Varistor and Process for Making, filed concurrently herewith.
  • the reaction product described therein is formed by thoroughly mixing the preselected additives in the absence of the metal oxide and then prereacting the additives.
  • the additives can be heated and cooled and thus fused into a solid body. This body is then ground to form the reaction product.
  • the metal oxide is mixed with the reaction product and pressed and sintered in the conventional manner.
  • a varistor with excellent electrical characteristics can be fabricated from 98 mole percent zinc oxide, 0.5 mole percent bismuth oxide, 0.5 mole percent cobalt oxide, 0.5 mole percent manganese oxide, and 0.5 mole percent titanium oxide.
  • the oxides of bismuth, cobalt, manganese and titanium are thoroughly mixed in equal molar amounts, then heated and cooled to form a crystalline solid body.
  • the crystalline solid body is ground to form the reaction product.
  • Zinc oxide and the reaction product are thoroughly mixed and a portion of the mixture is pressed and sintered to form the varistor body 11.
  • effective passivating coatings can be produced from any of the following base materials:
  • the sixth formula can be used in medium or high voltage varistors, but it may be desired to avoid the sixth formula, which includes silicon, in the manufacture of low voltage varistors inasmuch as silicon increases the voltage rating of a varistor.
  • each of the above formulations is free of silver and other monovalent ions that would tend to diffuse rapidly through the varistor body 11 during the coating heating step to be described subsequently. Such a diffusion of monovalent ions could adversely affect the stability of the varistor l0 and affect the final electrical properties of the device in a manner difficult to predict.
  • it is beneficial to omit silver and other monovalent ions from the varistor fomulation for reasons more fully discussed in a co-pending US. application Serial No. 401,323 entitled Silver Free Varistor Passivating Coating, filed by S. 1. Gabrail concurrently herewith and assigned to the same assignee as this application.
  • the compounds of bismuth, boron, antimony, and silicon, where included, are carriers and serve to ultimately enhance the adhesion of the particulate matter 19 and to the body lll.
  • any of the above formulas is selected and mixed with a vehicle to facilitate handling.
  • a vehicle that has been found effective for the above formulations is composed of 135 grams of n-butyl acetate, 20 grams of ethyl cellulose and 15 grams of butyl carbitol.
  • the coating which when mixed with the vehicle is fluid, is poured over the sintered bodies 11 or the bodies 11 are dipped in the coating.
  • the vehicle is then dried at a relatively low temprerature.
  • the devices are then heated to a temperature in the range of 600 to 1,000C for a preselected time.
  • the temperature and time selected should insure that the carrier is fused and thus enhances the adhesion of the particulate matter 19 and 20 to the body l1.
  • the particulate matter 19 and 20 should not melt so that a body 11 with the coating 12 and the irregular surface depicted in FIG. 2 is provided.
  • the metal contacts 13 and 114 are applied by conventional techniques such as the application of silver paste or flame spraying. As mentioned previously, the contacts 13 and 14 will closely conform to the irregular surface of the body 11 and thus adhere tightly thereto.
  • the carrier can be utilized with different particulate matter.
  • suitable particulate matter is grains of aluminum oxide.
  • a method for manufacturing a varistor comprising the steps of:
  • said coating comprising a small quantity of the reaction product
  • a method according to claim 2 wherein said step of heating said body portion with said coating thereon comprises heating to a temperature sufficient to fuse said carrier means but insufficient to melt said reaction product.
  • said carrier means comprises a compound of at least one member of the group consisting of bismuth, boron, antimony, and silicon.
  • additives comprise the oxides of bismuth, cobalt, manganese and titanium, and wherein said metal oxide is zinc oxide.
  • a method according to claim 3 further comprising the step of applying metallic contacts to said body portion with said coating thereon.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
US00401334A 1973-09-27 1973-09-27 Method of making varistor with passivating coating Expired - Lifetime US3857174A (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
US00401334A US3857174A (en) 1973-09-27 1973-09-27 Method of making varistor with passivating coating
CA207,329A CA1011884A (en) 1973-09-27 1974-08-19 Metal oxide varistor with metallic contacts on passivating coating
IE1769/74A IE39769B1 (en) 1973-09-27 1974-08-26 Improvements in varistors
IT27580/74A IT1022209B (it) 1973-09-27 1974-09-23 Varistore ad ossido metallico conrivestimento passivante
SE7412082A SE395561B (sv) 1973-09-27 1974-09-25 Metalloxidvaristor, samt sett att framstella varistorn
DE2445659A DE2445659C2 (de) 1973-09-27 1974-09-25 Metalloxid-Varistor
FR7432407A FR2246034B1 (enrdf_load_stackoverflow) 1973-09-27 1974-09-26
US05/509,337 US3938069A (en) 1973-09-27 1974-09-26 Metal oxide varistor with passivating coating
JP11004274A JPS563644B2 (enrdf_load_stackoverflow) 1973-09-27 1974-09-26
GB42154/74A GB1483811A (en) 1973-09-27 1974-09-27 Varistors

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US00401334A US3857174A (en) 1973-09-27 1973-09-27 Method of making varistor with passivating coating

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US05/509,337 Division US3938069A (en) 1973-09-27 1974-09-26 Metal oxide varistor with passivating coating

Publications (1)

Publication Number Publication Date
US3857174A true US3857174A (en) 1974-12-31

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ID=23587321

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US00401334A Expired - Lifetime US3857174A (en) 1973-09-27 1973-09-27 Method of making varistor with passivating coating

Country Status (9)

Country Link
US (1) US3857174A (enrdf_load_stackoverflow)
JP (1) JPS563644B2 (enrdf_load_stackoverflow)
CA (1) CA1011884A (enrdf_load_stackoverflow)
DE (1) DE2445659C2 (enrdf_load_stackoverflow)
FR (1) FR2246034B1 (enrdf_load_stackoverflow)
GB (1) GB1483811A (enrdf_load_stackoverflow)
IE (1) IE39769B1 (enrdf_load_stackoverflow)
IT (1) IT1022209B (enrdf_load_stackoverflow)
SE (1) SE395561B (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4031498A (en) * 1974-10-26 1977-06-21 Kabushiki Kaisha Meidensha Non-linear voltage-dependent resistor
US4097834A (en) * 1976-04-12 1978-06-27 Motorola, Inc. Non-linear resistors
US4148135A (en) * 1978-03-10 1979-04-10 General Electric Company Method of treating metal oxide varistors to reduce power loss
US4186367A (en) * 1977-08-05 1980-01-29 Siemens Aktiengesellschaft Thick film varistor and method of producing same
US5455554A (en) * 1993-09-27 1995-10-03 Cooper Industries, Inc. Insulating coating
WO2001003148A3 (de) * 1999-07-06 2001-07-19 Epcos Ag Vielschichtvaristor niedriger kapazität

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IE47121B1 (en) * 1977-07-29 1983-12-28 Gen Electric Stabilized varistor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1483538A (en) * 1919-05-06 1924-02-12 Westinghouse Electric & Mfg Co Lightning arrester
US3496512A (en) * 1966-05-16 1970-02-17 Matsushita Electric Ind Co Ltd Non-linear resistors
US3663458A (en) * 1967-10-09 1972-05-16 Matsushita Electric Ind Co Ltd Nonlinear resistors of bulk type
US3768058A (en) * 1971-07-22 1973-10-23 Gen Electric Metal oxide varistor with laterally spaced electrodes

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE471978C (de) * 1919-06-01 1929-02-20 Rudolf Schnabel Verfahren zur Herstellung keramischer elektrischer Widerstaende
DE733726C (de) * 1937-09-12 1943-04-01 Siemens Ag Verfahren zur Herstellung von metallisierten Isolierstoffolien
DE941300C (de) * 1943-05-01 1956-04-05 Siemens Ag Verfahren zur Erzielung groesserer Flaechenleitfaehigkeit an Kontaktstellen von metallischen Schichtwiderstaenden
US2501322A (en) * 1946-11-07 1950-03-21 Westinghouse Electric Corp Moisture-resistant lightning arrester valve block
DE1066654B (enrdf_load_stackoverflow) * 1955-09-30 1959-10-08
GB1037822A (en) * 1961-12-15 1966-08-03 Ass Elect Ind Improvements relating to non-linear electrical resistance elements
US3217281A (en) * 1962-05-28 1965-11-09 Corning Glass Works Electrical resistor
NL6901538A (enrdf_load_stackoverflow) * 1969-01-31 1970-08-04
DE2026011C3 (de) * 1970-05-22 1980-06-26 Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka (Japan) Spannungsabhängiger Widerstand
JPS5240038B2 (enrdf_load_stackoverflow) * 1972-12-29 1977-10-08

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1483538A (en) * 1919-05-06 1924-02-12 Westinghouse Electric & Mfg Co Lightning arrester
US3496512A (en) * 1966-05-16 1970-02-17 Matsushita Electric Ind Co Ltd Non-linear resistors
US3663458A (en) * 1967-10-09 1972-05-16 Matsushita Electric Ind Co Ltd Nonlinear resistors of bulk type
US3768058A (en) * 1971-07-22 1973-10-23 Gen Electric Metal oxide varistor with laterally spaced electrodes

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4031498A (en) * 1974-10-26 1977-06-21 Kabushiki Kaisha Meidensha Non-linear voltage-dependent resistor
US4097834A (en) * 1976-04-12 1978-06-27 Motorola, Inc. Non-linear resistors
US4186367A (en) * 1977-08-05 1980-01-29 Siemens Aktiengesellschaft Thick film varistor and method of producing same
US4148135A (en) * 1978-03-10 1979-04-10 General Electric Company Method of treating metal oxide varistors to reduce power loss
US5455554A (en) * 1993-09-27 1995-10-03 Cooper Industries, Inc. Insulating coating
WO2001003148A3 (de) * 1999-07-06 2001-07-19 Epcos Ag Vielschichtvaristor niedriger kapazität
US6608547B1 (en) 1999-07-06 2003-08-19 Epcos Ag Low capacity multilayer varistor

Also Published As

Publication number Publication date
SE395561B (sv) 1977-08-15
JPS5076588A (enrdf_load_stackoverflow) 1975-06-23
IE39769L (en) 1975-03-27
GB1483811A (en) 1977-08-24
CA1011884A (en) 1977-06-07
SE7412082L (enrdf_load_stackoverflow) 1975-04-01
DE2445659C2 (de) 1982-09-09
DE2445659A1 (de) 1975-04-03
IE39769B1 (en) 1978-12-20
JPS563644B2 (enrdf_load_stackoverflow) 1981-01-26
FR2246034B1 (enrdf_load_stackoverflow) 1981-08-21
FR2246034A1 (enrdf_load_stackoverflow) 1975-04-25
IT1022209B (it) 1978-03-20

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