DD140598A1 - Ceramic electrical resistance and method of making same - Google Patents

Abstract

The invention relates to a ceramic electrical Resistor based on an n-type ceramic material of barium titanate. BaTiC> 3 or zinc oxide ZnO with barrier-free Contacts and a method of making the same. The task of Invention is such a resistor and a method to find its manufacture, the resistance with respect to its contact materials is constructed so that certain Contact properties even with relatively strong electrical Loading can be achieved and the method of application the contacts ensures a high degree of automation. The Task is-by a contact system of at least three layers solved. The lowest layer is a chromium layer (0.01 to 0.5 μm), on a copper layer (0.1 b.is 1,5 μτη.) And as a conclusion a silver layer (1 to 50 pm) applied. The chrome and the copper layer according to the invention by vapor deposition or Sputtering applied in a vacuum. The silver layer is called Silver paste applied and baked.

Description

Dr, Dieter Bühling

Reinhard Müller ·

Günter Jander P 654

Rolf Peteriaann IPK: H 01 C, 7/02

Konrad Voigt '· 20.10 * 78

Title of the invention

Ceramic electrical resistance and method for its production

Field of application of the invention

The invention relates to a ceramic electrical resistance made of an n-type ceramic material, based on barium titanate BaTiOo or zinc oxide ZnO, with barrier-free contacts: and a method for its preparation.

Characteristic of the known technical solutions

It is known, such components in particular PTC, with. an indium or indium gallium layer by steaming or rubbing au contact. Although this barrier-free contacts can be made, but have too low adhesion, too low heat resistance and poor solderability (acid and bottles

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in "'Proof of the Electronic Comp Symposium", 1956, pp. 41-56)

Although burnt-in pure silver layers * have a high adhesive strength, good solubility, and a high heat resistance, but lead to barrier layers during firing. The combination of indium or indium gallium layers with silver pastes (DE-AS 14 90 713 and DE-OS 16, 65 880). leads to useful contacts. The cost of rubbing the indium or indium gallium layer is due to the material and labor costs relatively high. In addition, the adhesive strength of the system and the stability of the PTC thermistor greatly depend on the individual factors influencing the uniform coating and the baking temperature of the silver paste.

Another proposal has been to deposit a base metal, such as aluminum or zinc, adjacent to the ceramic, by vapor deposition and to secure a layer of silver to this layer by baking (GB-PS 911 741).

This proposal places high demands on the application of the metal layer and on the stoving of the silver layer in order to prevent oxidation and breakdown, which leads to damage to the ceramic.

However, it has been found that this method can not produce low-resistance contacts. For example, Z ₆ B, PTC thermistors, which had been contacted with high-vacuum vapor-deposited aluminum, showed approx. Orders of magnitude! higher resistance values than PTC thermistors contacted by galling indium gallium.

It is also known, the ceramic body having a first layer ^su. Provided, consisting of boric acid, boron trioxide or boric acid ester thermally decomposed. Then a silver paste is baked CDE-OS 20 3.1 480) "

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Thereby it is also not possible to reduce the contact resistance to such an extent that practically only the distance of the half-body is effective.

To eliminate the Spanriungsabhängigkeit of the PTC thermistor has been proposed to apply a metal for contacting, which is able to reduce the contained in the ceramic tetravalent metal oxide of ferroelektris hen base material (DE-OS 14 15 406). However, the eligible base metals can be heavily armored with the usual for ceramic components with silver electrodes method and provide high-impedance contacts, For this reason, it is proposed in DE-OS 14 §o 268 to reduce the surface to be contacted to solderable metals, such as B. to use copper. However, this method is expensive, prone to failure and the applied metal layers have too low adhesion. It is also known to produce a barrier layer by free contact by first rubbing a metal which diffuses into the semiconductor body, with the same or a higher valence state than that of the cation of the semiconductor body to be displaced. On this coating a SiIberßchebrasse is baked (DE-AS 1 123 019). This method has the disadvantages already described above.

It is known from thin-film technology that chromium layers are used to improve the adhesion and, in order to reduce the sheet resistance, apply alternating or simultaneously copper layers with simultaneous substrate heating (DE-OS 1 771 765).

This proposal can not be applied to PTC thermistors and low-resistance ZnO varistors because the series resistance caused by this contact is too high to achieve low-resistance, low-aging devices.

- 4 - ZO ^ £ l. .p 654 Aim of the invention

It is an object of the invention to produce an Iceramic electrical resistance with adhesive, barrier-free and low-resistance contacts and thereby eliminate the shortcoming of the previous solutions,

Explanation of the essence of the invention

The object of the invention is a ceramic electrical resistance and a method for its manufacture. : Lung to find _s wherein the ceramic electrical resistor is constituted in terms of its contact materials so that the formulated in the aim of the invention properties of the contact, even with relatively large electric load erreicht'werden, and wherein the method of applying the contacts extensive automation guaranteed.

The object is achieved by a constructed of at least three layers contact. The bottom layer is a chromium layer in a thickness of 0.01 , at, to 0.5 / Um. On top of that there is a copper layer in a thickness of 0.1 μm to 1.5 μm. The topmost layer of the contact consists essentially of silver and has a layer thickness of 1 / μm to 50 μm.

In a refinement of the invention, it is expedient for barium titanate-based resistors with positive temperature coefficients of resistance, for contact a chromium layer in a thickness of 0.2 to 0.3 μm and a copper layer in a thickness of 0.8 to 1.0 μm. to use.

The material chromium can be replaced according to the invention by chromium / nickel, nickel or iron / Uickel. The chromium layer according to the invention prevents the formation of barrier layers, serves as a diffusion barrier and increases the adhesion of the overlying layers of copper and silver

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the copper interlayer reduces the resistance of the device and improves the adhesion between the chromium and silver layers. The silver layer guarantees a good solubility, a good electrical resistance and mechanical © as well as climatic stability of the contacts ·

According to the invention, the chromium and copper layers are applied to the surface to be contacted by vapor deposition or sputtering in a vacuum. Subsequently, the silver layer is applied as silver paste and baked.

It is also expedient, after the vapor deposition or sputtering of the chromium and copper layer in a vacuum, to apply a tin coating.

According to the invention, the layer thicknesses of the individual layers of the contact can be varied only within the stated limits.

embodiment

The invention will be described below with reference to an embodiment.

The accompanying drawing shows the ceramic electrical resistance 1 with its Kontaktbelegungera invention in cross section.

The contact system according to the invention is applied according to the properties to be achieved in certain thicknesses for the individual layers. In this case, chromium 2 and copper 3 were used as the first two layers. These two materials are significantly cheaper than indium and gallium, and guarantee lower resistance to transfer than e.g. Aluminum and zinc. With chrome and silver layers without a copper layer, it is not possible to achieve the required low-resistance components with low aging and high adhesive strength.

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The optimum thickness of the chromium layer 2 has been 0.25 to 0.30 / do. The copper layer 3 is optimally applied in a thickness "in the range of 0.8 to -1 μm,

It is possible to achieve the same contactor characteristics when the chromium layer 2 is replaced by a chromium / nickel layer, a nickel layer or an iron / nickel layer. Chrome or. Chromium / nickel layers alone as contact layers are not applicable because of their high resistivity. The aspired data can not be realized in this way. The mere combination of a chrome and a silver layer also shows no satisfactory results.

The cleaned ceramic bodies 1 are coated on the surfaces to be contacted under high vacuum at a pressure of 1 to 2 mPa with vapor deposition rates of 60 to 250 nm / s, first with chromium 2 and then with copper 3. Subsequently, e.g. applied with the rolling process, the silver paste 4, at. Temperatures between 450 to 65O ° C is baked.

Hitherto, due to the relatively high specific levels of the materials in question, high vacuum vapor deposition has been discarded as the contacting method for this type of component.

The following advantages are achieved by the ceramic electrical resistor 1 according to the invention and the method for its production:

- Increasing the stability of the PTC thermistors by non-barrier contacting of the η-conductive ceramic body

- Increasing the adhesion of the contacts

- extensive automation of the contact procedure

- Reduction of material and manufacturing costs - Reduction of contact resistance.

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The technical improvement achieved by the invention in cable ladders is shown in the following table:

parameter In Ga State of the art Cr thickness 0.15-0.5 / um Ag 0.15 / 0.7 0.25 / 0.5 0.3 1.0 33 al 66 40 42 33 Resistance at room temperature (R ₀₀ ) in ohm ^dO 150 82,000 500 b. 800 420 540 Adhesion strength in N / cm2 -5 -7.5 +4 to + M -6 to + ^: + 11 + 3 -5 -2 Aging R ₂₀ in % after 70Oh at 18O ⁰ C at 220 V. c according to the proposal of the invention Cr / Cu 0.15 / 0.5 • 55 I- + 24 y

Claims (5)

~ 8- 209 261 P654 Invention claim 1. Ceramic electrical resistance, consisting of a η conductive material, based on barium titanate or zinc oxide, with at least one barrier-free, low-resistance and well-adhering contact, characterized in that a contact is composed of a layer system of at least three layers, in which the lowermost layer as a chromium layer (2) <in a layer thickness of 0.01 to 0.5 / μm and the intermediate layer as a copper layer (3), in a layer thickness of 0.1 / μm to 1 5 / In order to apply and the uppermost layer consists essentially of silver (4) and is present in a layer thickness of 1 / lim to 50 / um. 2. Ceramic electrical resistance according to item 1, characterized in that at a Y / iderstand (1) based on barium titanate with positive temperature coefficient of resistance, the chromium layer (2) in a thickness of 0.2, by up to 0.3 / Around and the copper layer (3) in a thickness of 0.8 , by up to 1.0, applied to « 3. Ceramic electrical resistance according to item 1 and 2, characterized in that in the three-layer system of contact chromium is replaced by chromium / nickel, winding or FeWi » 4. A method for producing a ceramic electrical resistance according to item 1 ,. characterized in that on the surface to be contacted, the chromium (2) .- and the copper layer (3) are applied by vapor deposition or sputtering im.Vakuum and that then a silver paste * is applied and baked. 5. The method according to item 4, characterized in that on the surface to be contacted, the chromium (2) - and copper layer (3) are applied by vapor deposition or sputtering and tinning the copper layer (3) »preferably in the immersion bath, is made. For this // page drawing