Classifications

• • 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
  • H01C7/1006—Thick film varistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
  • H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
  • H01C17/065—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thick film techniques, e.g. serigraphy
  • H01C17/06506—Precursor compositions therefor, e.g. pastes, inks, glass frits
  • H01C17/06513—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component
  • H01C17/06533—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component composed of oxides
  • H01C17/06546—Oxides of zinc or cadmium
• • 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

Definitions

• the invention relates to a method for producing thick film varistors with zinc oxide as the main component, in which the varistor materials and an organic binder are applied as varistor paste to an insulating substrate and are converted into a thick film varistor by sintering the varistor paste.
• the current flowing through the varistor, V the applied voltage, C a constant and the exponent n denote the so-called steepness of the varistor.
• the numerical value of the slope n should be as high as possible, since this exponent indicates the degree of deviation of the varistor from an ohmic characteristic.
• the known varistors are generally designed as discrete components, which are produced by pressing and sintering the pulverized varistor materials. From US Pat. No. 3,725,836 it is also already known to produce varistors in thick-film technology and to integrate them directly into thick-film circuits. To produce these known thick-film varistors belonging to the group of ZnO varistors, the varistor materials are mixed with glass frit and an organic binder, applied as a screen-printable varistor paste to an insulating substrate and sintered to form the varistor. The electrodes required for contacting the varistor can then also be applied to the surface of the varistor using thick-film technology. The steep he i tn thick film of the varistors produced in this manner is in the order 4-8 and is therefore for the most applications too low.
• DE-A-2 446 708 describes the production of varistor material without glass components, which has the greatest possible steepness.
• the material dealt with in this published publication relates to the classic manufacture of varistor components, which amounts to a powder pressing technique.
• This manufacturing method involves a discrete varistor, which e.g. is soldered into a plastic circuit board.
• the invention has for its object to provide a method for producing thick film varistors with improved values of the slope n.
• the invention is a thick film varistor that can be integrated with resistors and conductor tracks, the structures of which are e.g. applied by screen printing.
• glass frit is always used as an inorganic binder in conductor pastes, resistance pastes and the known varistor pastes.
• the pastes mentioned are sintered, the glass frit forms a solid glass matrix, which ensures the cohesion of the other solids and the bond to the substrate.
• varistor paste which contains 87.5 to 98.0% by weight of zinc oxide, based on the solids content.
• a varistor paste which contains bismuth oxide, tricobalt tetroxide and manganese dioxide is advantageously used.
• the addition of these oxides to the zinc oxide favors the crystal formation in the manufacture of the thick film varistor and thus leads to a further improvement in the electrical properties.
• a varistor paste which relates to the solids content contains.
• Thick film varistors produced with such a varistor paste are particularly suitable for higher operating voltages. These operating voltages are, for example, in the range of 200 volts per millimeter of active varistor material.
• a varistor paste which relates to the solids content contains.
• Thick film varistors produced with such a varistor paste are particularly suitable for lower operating voltages. These operating voltages are, for example, in the range of 30 V / mm active varistor material.
• the response voltage of the thick-film varistor can also be influenced by the choice of temperature.
• the peak temperature during sintering of the varistor paste is preferably maintained for a period of between 5 and 20 minutes.
• a further advantage of the crystal formation and thus a further improvement of the electrical properties can be achieved in that the thick film varistor is cooled after the sintering at a temperature gradient between 2 and 8 ° C / min.
• the varistor paste is preferably applied to the insulating substrate in such a way that the thick-film varistor has a thickness between 100 and 200 ⁇ m after sintering. With such thick film varistor thicknesses, particularly favorable electrical properties are achieved.
• a varistor paste that could be screen-printed was first produced from the varistor materials.
• the powdery solids were weighed in as follows:
• the solids were wet-mixed and ground in ball mills for 18 hours, then freed of water by filter suction and then dried in a drying oven at a temperature of 150 ° C. for 24 hours.
• the maximum particle size distribution of the powder mixture after this treatment was 1 ⁇ m.
• an organic binder 75 g of an organic binder were mixed into a batch of 100 g of the powder mixture thus prepared and homogenized on a roller mill.
• Other known organic binders such as e.g. a solution of nitrocellulose in butyl carbitol acetate are equally suitable.
• the viscosity and flow behavior of the varistor paste produced in this way was adjusted so that it could be processed using the screen printing process.
• the finished varistor paste was then screen printed onto an insulating substrate made of A1 2 0 3 ceramic at the locations provided for the varistors.
• the approx. 150 ⁇ m thick layer of varistor paste was then dried in a drying oven at a temperature of approx. 60 ° C.
• the varistor properties were formed. Sintering was carried out in an oxidizing atmosphere at a temperature between 1 100 and 1 200 ° C, the peak temperature being held for 10 minutes. The temperature increase during heating was about 10 ° C per minute, while a temperature drop of 7 ° C per minute was observed during cooling.
• the thick-film varistors produced according to the procedure described above are particularly suitable for operating voltages in the Suitable range of 200 volts per millimeter of active varistor material.
• the powdered varistor materials were first weighed out as follows:
• the powdery varistor materials were then processed in the manner described in Example 1 to form a screen-printable varistor paste and screen-printed onto an insulating substrate made of A1 2 0 3 - Ceramic printed.
• the approx. 150 ⁇ m thick layer of varistor paste was then dried at a temperature of approx. 60 ° C.
• the subsequent sintering was carried out at a temperature between 1 100 and 1 200 ° C, the peak temperature being held for 10 minutes.
• the temperature increase during heating was about 10 ° C per minute, while when cooling down to a temperature of approx. 1000 ° C a temperature drop of 3 ° C per minute and below 1000 ° C a temperature drop of 6 to 7 ° C per minute Minute was observed.
• the varistor electrodes and the other elements of the thick-film circuit can be produced in a known manner.
• the fully contacted thick film varistors again had excellent electrical properties compared to the known glass thick film varistors.
• the thick-film varistors produced according to the procedure described above are particularly suitable for operating voltages in the range of 30 volts per millimeter of active varistor material.
• thick-film circuits with integrated thick-film varistors can be produced.
• thick film varistors as discrete components.
• a large number of varistor elements are applied and sintered on an insulating substrate using the screen printing process.
• conductor tracks for contacting the varistor elements are applied using screen printing technology, dried and sintered.
• the substrate is then perforated in a known manner, for example with the aid of a laser, and separated into individual elements. These individual elements can then be soldered into printed circuits or layer circuits as so-called varistor chips.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Thermistors And Varistors (AREA)

Applications Claiming Priority (2)

Publications (2)

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• 1977
  • 1977-08-05 DE DE2735484A patent/DE2735484C2/de not_active Expired
• 1978
  • 1978-06-19 EP EP78100192A patent/EP0000864B1/de not_active Expired
  • 1978-06-22 US US05/917,857 patent/US4186367A/en not_active Expired - Lifetime
  • 1978-08-02 CA CA000308575A patent/CA1117223A/en not_active Expired
  • 1978-08-02 JP JP53094452A patent/JPS5928962B2/ja not_active Expired
  • 1978-08-04 IT IT26492/78A patent/IT1097664B/it active

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