US3903494A - Metal oxide varistor with coating that enhances contact adhesion - Google Patents

Metal oxide varistor with coating that enhances contact adhesion Download PDF

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Publication number
US3903494A
US3903494A US401307A US40130773A US3903494A US 3903494 A US3903494 A US 3903494A US 401307 A US401307 A US 401307A US 40130773 A US40130773 A US 40130773A US 3903494 A US3903494 A US 3903494A
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United States
Prior art keywords
coating
varistor
metal oxide
body portion
reaction product
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Expired - Lifetime
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US401307A
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English (en)
Inventor
John E May
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General Electric Co
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General Electric Co
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Publication date
Application filed by General Electric Co filed Critical General Electric Co
Priority to US401307A priority Critical patent/US3903494A/en
Priority to CA207,348A priority patent/CA1020288A/en
Priority to IE1766/74A priority patent/IE40005B1/xx
Priority to IT27581/74A priority patent/IT1022210B/it
Priority to GB41268/74A priority patent/GB1483812A/en
Priority to DE2445626A priority patent/DE2445626C2/de
Priority to SE7412080A priority patent/SE395560B/xx
Priority to FR7432405A priority patent/FR2246032B1/fr
Priority to JP11004474A priority patent/JPS5623283B2/ja
Application granted granted Critical
Publication of US3903494A publication Critical patent/US3903494A/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

Definitions

  • Appl' 401307 Disclosed is a metal oxide varistor comprising a body portion consisting essentially of a metal oxide and a [52] US. Cl. 338/20; 338/21; 338/238; m l per ntage of a plurality of preselected addi- 1 17/212; 1 17/213; 117/217; 338/327 tives.
  • the body portion defines two major surface [51] Int. Cl. HOlc 7/10; HOlc 7/12 areas n m llic on acts re applied to the two sur- [58] Field of Search... 1 17/212, 213, 217; face areas.
  • V and V are the device voltages at given currents hand 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).
  • C and 01 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. 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 combinations. For example. see U.S. 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.
  • a passivating eoating is sometimes applied to the sintered body. If a coating is applied, the body with the coating is generally reheated.
  • metallic contacts are applied to the body.
  • the contacts can, for example, be applied by techniques such as the application of a silver paste or by metallic flame spraying.
  • 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 invention is that 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.
  • 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.
  • Still another feature of the subject coating is that it is a passivating coating and substantially improves the stability of the devices 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.
  • a full dismission of the method for fabricating a varistor by pre reacting the additives is in my co-pending U.S. patent application Ser. No. 401,13] filed concurrently herewith and entitled Low Voltage Varistor and Process for Making.
  • 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 particulate matter that contours the pellet surface can be grains of the reaction product.
  • 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.
  • FIG. 1 there is shown a metal oxide varistor that includes a sintered body portion Ill 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 i4,
  • conductive coupiers such as solder l7 and 18.
  • FIG. 2 there is shown a portion of the varistor l0 shown in FiG. i. Specifically, a corner of the body portion 11 is shown in HQ. 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 appreciated 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 1'19 and 20 are part of a contact adhesion enhancement system included in the coating l2. 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 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 aforementioned co-pending U.S. 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 ll 1.
  • 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 l and affect the final electrical properties of the device in a manner difficult to predict.
  • 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 20 to the body 11.
  • 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 l35 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 ll are dipped in the coating. The vehicle is then dried at a relatively low temperature. The devices are then heated to a temperature in the range of 600 to l,0O0C 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 11. However, the particulate matter 19 and 20 should not melt so that a body 11 with the coating 12 and the irregular surface depicted in F l6. 2 is provided. Following the heating step, the metal contacts 13 and 14 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 varistor comprising a body portion defining at least two major surface areas, said body portion having a coating thereon, said coating comprising varistor body surface contour means, and wherein said varistor further comprises metallic contacts overlying said coating on at least a portion of said two major surface areas.
  • a varistor according to claim 2 wherein said coating is free of monovalent ions.
  • a varistor according to claim 2 wherein said body portion consists essentially of a metal oxide and a reaction product formed by heating together a plurality of preselected additives, and wherein said particulate matter comprises said reaction product.
  • said coating comprises at least one member of the group consisting of compounds of bismuth, boron, silicon and anti-

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
US401307A 1973-09-27 1973-09-27 Metal oxide varistor with coating that enhances contact adhesion Expired - Lifetime US3903494A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US401307A US3903494A (en) 1973-09-27 1973-09-27 Metal oxide varistor with coating that enhances contact adhesion
CA207,348A CA1020288A (en) 1973-09-27 1974-08-19 Metal oxide varistor with coating that enhances contact adhesion
IE1766/74A IE40005B1 (en) 1973-09-27 1974-08-26 Improvements in varistors
GB41268/74A GB1483812A (en) 1973-09-27 1974-09-23 Varistors
IT27581/74A IT1022210B (it) 1973-09-27 1974-09-23 Varistore ad ossido metallico con rivestimento che migliora l atesione di contatto
DE2445626A DE2445626C2 (de) 1973-09-27 1974-09-25 Varistor
SE7412080A SE395560B (sv) 1973-09-27 1974-09-25 Varistor
FR7432405A FR2246032B1 (enrdf_load_stackoverflow) 1973-09-27 1974-09-26
JP11004474A JPS5623283B2 (enrdf_load_stackoverflow) 1973-09-27 1974-09-26

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US401307A US3903494A (en) 1973-09-27 1973-09-27 Metal oxide varistor with coating that enhances contact adhesion

Publications (1)

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US3903494A true US3903494A (en) 1975-09-02

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US401307A Expired - Lifetime US3903494A (en) 1973-09-27 1973-09-27 Metal oxide varistor with coating that enhances contact adhesion

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US (1) US3903494A (enrdf_load_stackoverflow)
JP (1) JPS5623283B2 (enrdf_load_stackoverflow)
CA (1) CA1020288A (enrdf_load_stackoverflow)
DE (1) DE2445626C2 (enrdf_load_stackoverflow)
FR (1) FR2246032B1 (enrdf_load_stackoverflow)
GB (1) GB1483812A (enrdf_load_stackoverflow)
IE (1) IE40005B1 (enrdf_load_stackoverflow)
IT (1) IT1022210B (enrdf_load_stackoverflow)
SE (1) SE395560B (enrdf_load_stackoverflow)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4198443A (en) * 1978-05-26 1980-04-15 General Electric Company Sinterless zinc oxide varistor devices
US4371860A (en) * 1979-06-18 1983-02-01 General Electric Company Solderable varistor
US4460623A (en) * 1981-11-02 1984-07-17 General Electric Company Method of varistor capacitance reduction by boron diffusion
US4538347A (en) * 1984-06-18 1985-09-03 Gte Laboratories Incorporated Method for making a varistor package
US6279811B1 (en) * 2000-05-12 2001-08-28 Mcgraw-Edison Company Solder application technique
US6735068B1 (en) 2001-03-29 2004-05-11 Mcgraw-Edison Company Electrical apparatus employing one or more housing segments
US20080012127A1 (en) * 2006-06-28 2008-01-17 Inpaq Technology Co., Ltd. Insulation structure for multilayer passive elements and fabrication method thereof
US20090027153A1 (en) * 2007-07-25 2009-01-29 Thinking Electronic Industrial Co., Ltd. Metal oxide varistor with heat protection
US20090302992A1 (en) * 2005-08-05 2009-12-10 Kiwa Spol. S R.O. Overvoltage Protection with Status Signalling
US20100231346A1 (en) * 2009-03-13 2010-09-16 Shinko Electric Industries Co., Ltd. 3-electrode surge protective device
US20100328016A1 (en) * 2009-06-24 2010-12-30 Robert Wang Safe surge absorber module
US20120105191A1 (en) * 2009-06-24 2012-05-03 Robert Wang Explosion-roof and flameproof ejection type safety surge-absorbing module
US20130038976A1 (en) * 2011-03-07 2013-02-14 James P. Hagerty Thermally-protected varistor

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3069294A (en) * 1954-06-03 1962-12-18 Corning Glass Works Electrical metal oxide resistor having a glass enamel coating
US3496512A (en) * 1966-05-16 1970-02-17 Matsushita Electric Ind Co Ltd Non-linear resistors
US3512057A (en) * 1968-03-21 1970-05-12 Teledyne Systems Corp Semiconductor device with barrier impervious to fast ions and method of making

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE635491C (de) * 1933-07-25 1936-09-18 Aeg Aus leitfaehigen Stoffen und Bindemitteln zusammengesetzter Widerstand fuer UEberspannungsableiter
NL39212C (enrdf_load_stackoverflow) * 1933-07-26
DE688073C (de) * 1934-10-27 1940-02-12 Ellinger & Geissler Fabrik Ele Verfahren zur Herstellung von metallischen End- oder Zwischenkontakten auf kohlenstoff-haltigen Halbleiterschichten fuer feste und veraenderliche Widerstaende
US2501322A (en) * 1946-11-07 1950-03-21 Westinghouse Electric Corp Moisture-resistant lightning arrester valve block
DE1046154B (de) * 1956-03-29 1958-12-11 Siemens Ag Elektrischer Schichtwiderstand mit zur Kontaktierung dienender Metallschicht
CA831691A (en) * 1967-10-09 1970-01-06 Matsuoka Michio Non-linear resistors of bulk type

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3069294A (en) * 1954-06-03 1962-12-18 Corning Glass Works Electrical metal oxide resistor having a glass enamel coating
US3496512A (en) * 1966-05-16 1970-02-17 Matsushita Electric Ind Co Ltd Non-linear resistors
US3512057A (en) * 1968-03-21 1970-05-12 Teledyne Systems Corp Semiconductor device with barrier impervious to fast ions and method of making

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4198443A (en) * 1978-05-26 1980-04-15 General Electric Company Sinterless zinc oxide varistor devices
US4371860A (en) * 1979-06-18 1983-02-01 General Electric Company Solderable varistor
US4460623A (en) * 1981-11-02 1984-07-17 General Electric Company Method of varistor capacitance reduction by boron diffusion
US4538347A (en) * 1984-06-18 1985-09-03 Gte Laboratories Incorporated Method for making a varistor package
US6279811B1 (en) * 2000-05-12 2001-08-28 Mcgraw-Edison Company Solder application technique
US6575355B1 (en) 2000-05-12 2003-06-10 Mcgraw-Edison Company Solder application technique
US6840432B1 (en) 2000-05-12 2005-01-11 Mcgraw-Edison Company Solder application technique
US6735068B1 (en) 2001-03-29 2004-05-11 Mcgraw-Edison Company Electrical apparatus employing one or more housing segments
US20090302992A1 (en) * 2005-08-05 2009-12-10 Kiwa Spol. S R.O. Overvoltage Protection with Status Signalling
US7839257B2 (en) * 2005-08-05 2010-11-23 Kiwa Spol. S.R.O. Overvoltage protection with status signalling
US20080012127A1 (en) * 2006-06-28 2008-01-17 Inpaq Technology Co., Ltd. Insulation structure for multilayer passive elements and fabrication method thereof
US20090027153A1 (en) * 2007-07-25 2009-01-29 Thinking Electronic Industrial Co., Ltd. Metal oxide varistor with heat protection
US7741946B2 (en) * 2007-07-25 2010-06-22 Thinking Electronics Industrial Co., Ltd. Metal oxide varistor with heat protection
US20100231346A1 (en) * 2009-03-13 2010-09-16 Shinko Electric Industries Co., Ltd. 3-electrode surge protective device
US8217750B2 (en) * 2009-03-13 2012-07-10 Shinko Electric Industries Co., Ltd. 3-electrode surge protective device
US20100328016A1 (en) * 2009-06-24 2010-12-30 Robert Wang Safe surge absorber module
US20120105191A1 (en) * 2009-06-24 2012-05-03 Robert Wang Explosion-roof and flameproof ejection type safety surge-absorbing module
US8836464B2 (en) * 2009-06-24 2014-09-16 Ceramate Technical Co., Ltd. Explosion-proof and flameproof ejection type safety surge-absorbing module
US20130038976A1 (en) * 2011-03-07 2013-02-14 James P. Hagerty Thermally-protected varistor
US9165702B2 (en) * 2011-03-07 2015-10-20 James P. Hagerty Thermally-protected varistor

Also Published As

Publication number Publication date
DE2445626A1 (de) 1975-04-03
JPS5623283B2 (enrdf_load_stackoverflow) 1981-05-30
GB1483812A (en) 1977-08-24
CA1020288A (en) 1977-11-01
SE7412080L (enrdf_load_stackoverflow) 1975-04-01
IE40005L (en) 1975-03-27
SE395560B (sv) 1977-08-15
IE40005B1 (en) 1979-02-14
IT1022210B (it) 1978-03-20
FR2246032B1 (enrdf_load_stackoverflow) 1983-04-15
DE2445626C2 (de) 1986-09-18
FR2246032A1 (enrdf_load_stackoverflow) 1975-04-25
JPS5076590A (enrdf_load_stackoverflow) 1975-06-23

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