JPH04290201A - Voltage dependent nonlinear resistor and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the cost of a voltage dependent nonlinear resistor wherein a silver electrode had been made by applying expensive silver paste on a ceramic substrate and baking it in the past. CONSTITUTION:An electrode, which has a total thickness of 5mum or more required for the uniform current dispersion of the current, is made by applying base metal such as copper, etc., on the following silver layer after making the silver layer, which has a thickness of 3mum or less required for the ohmic connection with a substrate, on the ceramic substrate. Or, by baking the foil of bake metal while pushing it against the silver paste after applying the silver paste, the base metal foil is bonded onto the silver layer by the heat during baking.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage nonlinear resistor (hereinafter referred to as a varistor) having electrodes on both sides of a sintered body mainly composed of zinc oxide, and a method for manufacturing the same.

0002

[Prior Art] Zinc oxide varistors are intended to protect industrial and consumer equipment from malfunctioning and destruction of electronic circuits caused by momentary abnormal high voltages, that is, surge voltages.
This is a so-called surge absorption element. Zinc oxide varistor is
Ohmic electrical connections and soldering of lead wires, etc. on both sides of the ceramic body obtained by molding and sintering powder made from a mixture of zinc oxide and various additives. An electrode is formed for the purpose of connection. As shown in FIG. 2, the electrode 2 deposited on the varistor substrate 1 is usually coated with silver paste.
The silver electrode is formed by firing and requires a thickness of 5 to 15 μm. Silver electrodes have good adhesion to ceramics,
Although it is optimal for ohmic connection, when the thickness of the silver electrode becomes thinner than 5 μm, its sheet resistance increases, making it impossible to disperse the surge current from the lead wire over the entire surface of the silver electrode, and the current flows through the lead wire. There were cases where problems occurred that were concentrated in a small area directly under the surge, leading to current breakdown below the original surge withstand capacity.

0003

[Problems to be Solved by the Invention] As mentioned above, it is essential for the silver electrode to have a thickness of 5 to 15 μm in order to function as a varistor, but silver is relatively expensive, and such a thick silver electrode is This increases the cost of varistors, which poses a problem in providing a highly reliable varistor at a low price.

SUMMARY OF THE INVENTION An object of the present invention is to provide a varistor and a method for manufacturing the same that solve these problems and reduce the cost of electrodes provided for ohmic connection to a ceramic body and connection of lead wires, etc. be.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the varistor of the present invention has a ceramic substrate made of a material containing silver as a main component on the surface of a ceramic substrate containing zinc oxide as a main component. It is assumed that an electrode made of a base metal material is attached to the farther side. And it is effective that the base metal is copper. In addition, the manufacturing method for such varistors involves molding raw material powder whose main component is zinc oxide.
a step of sintering to form a ceramic substrate; a step of applying a paste containing a conductive material containing silver as a main component to the surface of the ceramic substrate and firing it to form a first conductive layer having a thickness of 3 μm or less; The method includes a step of coating and firing a paste containing a base metal as a conductive substance to form a second conductive layer on the first conductive layer so as to have a total thickness of 5 μm or more. Alternatively, a process of forming and sintering a raw material powder mainly composed of zinc oxide to form a ceramic substrate, applying a paste containing a conductive material mainly composed of silver to the surface of the ceramic substrate, and firing it to a thickness of 3 μm. The method includes a step of forming a conductive layer having the following thickness, and a step of adhering a foil made of a conductive base metal onto the conductive layer to form an electrode having a thickness of 5 μm or more made of the conductive layer and the foil.

[0006]

[Function] For ohmic connection with the ceramic body of the varistor, it is sufficient to form a layer with a thickness of 3 μm or less made of a noble metal such as silver, and a second conductive layer made of a base metal to be laminated on top of it. By adhering the foil to a thickness sufficient to distribute the current over the entire surface of the electrode, the cost of the electrode can be reduced without sacrificing the inherent surge resistance.

[0007]

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which silver paste is applied to both sides of a varistor substrate 1 by a transfer method, and 750
℃ to form a silver layer 2 of about 2 μm, then apply copper paste and bake at 650 ℃ to form a copper layer 3 of about 4 μm.
was formed. The silver paste used has a gr unit price of 30 yen or more, while the copper paste has a unit price of 10 yen or less, so the material cost for electrode formation is 1/2 that of the conventional case of only a silver layer.
It becomes below. Copper has good adhesion with silver and can be soldered, but to improve solderability, copper layer 3
It is advisable to further electroplate copper on top of this. In another example, after applying silver paste, a copper foil with a thickness of 10 μm is placed on top of the silver paste and heated to 750° C. while applying pressure. As a result, the silver paste is fired to form a silver layer with a thickness of 3 μm or less, and the copper foil is bonded on top of it by the heat during firing.
A two-layer electrode is obtained.

Although silver paste was used in the above embodiments to form the silver layer in contact with the varistor substrate, other pastes such as silver palladium paste may also be used. In addition to layering a copper layer or copper foil on top of the silver layer, nickel,
Layers such as aluminum or foil may be applied.

[0009]

[Effects of the Invention] According to the present invention, a conductive layer mainly composed of silver and having a thickness of 3 μm or less is brought into contact with the ceramic body of the varistor to ensure ohmic connection. By laminating conductive layers or conductive foils using base metals, it was possible to form electrodes with low sheet resistance in which current is distributed over the entire surface at low cost. Furthermore, since the silver layer is formed from a paste whose main component is silver, the thickness is thin, making it possible to use the transfer method known for character printing without using the conventionally required screen printing, improving work efficiency. It also has the effect of

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a varistor according to an embodiment of the present invention.

[Figure 2]
Cross-sectional view of a conventional varistor

[Explanation of symbols]

1 Varistor board 2 Silver layer 3 Copper layer

Claims (4)

[Claims] 1. A voltage non-conductor characterized in that an electrode is deposited on the surface of a ceramic substrate whose main component is zinc oxide, the ceramic side of which is made of a material whose main component is silver, and the side farther from the ceramic is made of a base metal material. Straight resistor. 2. A voltage nonlinear resistor according to claim 1, wherein the base metal is copper. [Claim 3] Molding raw material powder mainly composed of zinc oxide,
a step of sintering to form a ceramic substrate; a step of applying a paste containing a conductive material containing silver as a main component to the surface of the ceramic substrate and firing it to form a first conductive layer having a thickness of 3 μm or less; 2. The method according to claim 1, further comprising the step of applying a paste containing a base metal as a conductive material and firing it to form a second conductive layer on the first conductive layer so as to have a total thickness of 5 μm or more. 2. The method for manufacturing a voltage nonlinear resistor according to 2. Claim 4: Molding raw material powder containing zinc oxide as a main component,
A process of sintering to form a ceramic substrate, a process of applying a paste containing a conductive material mainly composed of silver to the surface of the ceramic substrate and firing it to form a conductive layer with a thickness of 3 μm or less, and a process of forming a conductive layer with a thickness of 3 μm or less. A foil made of a base metal of
3. The method of manufacturing a voltage non-linear resistor according to claim 1, further comprising the step of forming the above electrodes.