Electrode component with electrode layers formed on intermediate layers

Abstract

An electrode component with electrode layers formed on intermediate layers includes a ceramic substrate, two intermediate layers formed on two opposite surfaces of the ceramic substrate, two electrode layers respectively formed on the two intermediate layers, two lead wires respectively connected to the electrode layers, and an insulating layer enclosing the ceramic substrate, the intermediate layers, the electrode layers, and portions of the two lead wires. The intermediate layer formed between the ceramic substrate and the electrode layer replaces the fabrication means for conventional silver electrode layer to provide good binding strength between the ceramic substrate and the electrode layer. Besides same electrical characteristics for original products, the electrode component can get rid of the use of precious silver in screen printed silver electrode and avoid pollution caused by evaporation and thermal dissolution of organic solvent while lowering the ohmic contact resistance between the electrode layer and the ceramic substrate.

Claims

1. An electrode component with intermediate layers, comprising: a ceramic substrate having two opposite surfaces; two intermediate layers respectively formed on the two opposite surfaces of the ceramic substrate, each intermediate layer formed by a metal material selected from one of nickel, vanadium, chromium, aluminum, and zinc or a combination thereof; two electrode layers respectively formed on the two intermediate layers; two pins, each pin having a top portion connected to one of the two electrode layers; and an insulating layer enclosing the ceramic substrate, the two electrode layers, and the top portions of the two pins, wherein the electrode layers are formed by a spray-forming process, and a thickness of each electrode layer is in a range of 5 to 20 m.

2. The electrode component as claimed in claim 1, wherein the intermediate layers are formed by a sputtering process.

3. The electrode component as claimed in claim 1, wherein a thickness of each intermediate layer is in a range of 0.1 to 0.5 m.

4. The electrode component as claimed in claim 2, wherein a thickness of each intermediate layer is in a range of 0.1 to 0.5 m.

5. The electrode component as claimed in claim 3, wherein the electrode layers are formed by a metal material selected from one of zinc, copper, tin, and nickel or a combination thereof.

6. The electrode component as claimed in claim 4, wherein the electrode layers are formed by a metal material selected from one of zinc, copper, tin, and nickel or a combination thereof.

7. An electrode component comprising: a ceramic substrate with two surfaces opposite to each other; two intermediate layers disposed on the two surfaces by a sputtering process with a metal material so that the metal material forms the intermediate layers, the metal material being selected from one of nickel, vanadium, chromium, aluminum, and zinc or a combination of nickel, vanadium, chromium, aluminum, and zinc, wherein a reduced ohmic contact is formed between each intermediate layer and the ceramic substrate; two electrode layers respectively formed on the two intermediate layers by a spray-forming process with another metal material so that the two electrode layers include the another metal material, the another metal material selected from one of zinc, copper, tin, and nickel or a combination of zinc, copper, tin, and nickel; a lead wire connected to each electrode layer; and an insulating layer enclosing the ceramic substrate, the two electrode layers, and top portions of the two lead wires.

8. A method for fabricating an electrode component with two electrode layers formed on two intermediate layers, the method comprising steps of: preparing a ceramic substrate with two surfaces opposite to each other; respectively forming the two intermediate layers on the two surfaces by a sputtering process with a metal material selected from one of nickel, vanadium, chromium, aluminum, and zinc or a combination of nickel, vanadium, chromium, aluminum, and zinc, wherein a reduced ohmic contact is formed between each intermediate layer and the ceramic substrate; respectively forming the two electrode layers on the two intermediate layers by a spray-forming process with a metal material selected from one of zinc, copper, tin, and nickel or a combination of zinc, copper, tin, and nickel; connecting each electrode layer to a lead wire; and enclosing the ceramic substrate, the two electrode layers, and top portions of the two lead wires with an insulating layer.

9. The method as claimed in claim 8, wherein a thickness of each electrode layer is under 10 m.

10. The method as claimed in claim 8, wherein a thickness of each intermediate layer is in a range of 0.1 to 0.5 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a schematic front view in partial section of an electrode component with electrode layers formed on intermediate layers in accordance with the present invention;

(2) FIG. 1B is a schematic side view in partial section of the electrode component in FIG. 1;

(3) FIG. 2 is a flow diagram of a method for fabricating a varistor;

(4) FIG. 3 is a schematic view of sputtering;

(5) FIG. 4 is a schematic view of a fixture for sputtering with multiple openings in accordance with the present invention;

(6) FIG. 5 is a schematic view of a work piece stand for sputtering;

(7) FIG. 6 is a photomicrograph of an intermediate layer in accordance with the present invention; and

(8) FIG. 7 is a photomicrograph of a conventional silver electrode.

DETAILED DESCRIPTION OF THE INVENTION

(9) With reference to FIGS. 1A and 1B, an electrode component with electrode layers formed on intermediate layers in accordance with the present invention includes a ceramic substrate 1, two intermediate layers 21, two electrode layers 22, two lead wires 3, and an insulating layer 4.

(10) The two intermediate layers 21 are respectively formed on two opposite surfaces of the ceramic substrate 1. The two electrode layers 22 are respectively formed on the two intermediate layers 21. The two lead wires 3 are respectively connected to the two electrode layers 22. The insulating layer 4 encloses the ceramic substrate 1, the intermediate layers 21, the electrode layers 22 and a portion of each lead wire 3.

(11) With reference to FIG. 2, a method for fabricating an electrode component is shown. Given the electrode component as a varistor, the method includes processes of spray granulation, dry press forming and ceramic sintering, which are known as conventional techniques and are not repeated here. After the ceramic substrate 1 is made, a surface treatment process mainly involved with the present invention is applied to the ceramic substrate 1 to form the intermediate layers on the ceramic substrate 1. A process of spray-forming the electrode layers 22 and subsequent processes for pin soldering, insulation packaging, hardening and the like are described in details as follows.

(12) The intermediate layers 21 are formed by a sputtering process to deposit a metal material on the opposite surfaces of the ceramic substrate 1. The metal material used in the sputtering process is selected from one of nickel, vanadium, chromium, aluminum, and zinc or a combination thereof. With reference to FIG. 3, a schematic view of sputtering is shown. As being conventional techniques, the details about the sputtering concepts are not repeated here. With reference to FIG. 4, after cleaned, the ceramic substrate 1 is placed behind a sputtering mask 50. The sputtering mask 50 is built with aluminum material, stainless steel or other high polymer material with high heat resistance, and has multiple openings 52 formed through the sputtering mask 50 for portions of the ceramic substrate 1 to be exposed through the multiple openings 52 as the areas to be sputtered. The form of the areas to be sputtered depends upon the shape of the electrode component to be produced. In the present embodiment, the form of the areas is chosen to be round.

(13) With reference to FIG. 5, multiple sputtering masks 50 and multiple ceramic substrates 1 respectively placed behind the multiple sputtering masks 50 can be placed on a work piece stand in a sputtering chamber. Multiple work piece stands 54 can be simultaneously arranged inside vacuum magnetron sputtering equipment and the sputtering can be started. The vacuum magnetron sputtering equipment may be one-chamber, two-chamber or continuous inline sputtering equipment, and the target may be a planar target or a cylindrical target. Prior to the sputtering, the sputtering power and the sputtering time for each target are configured. The sputtering equipment then starts vacuuming with degree of vacuum in a range of 0.020.08 MPa. Inert gas is further added to the sputtering chamber. The inert gas may be Argon, and has a flow rate in a range of 4550 ml/s. After the sputtering lasts for 10 to 30 minutes, each intermediate layer 21 can be coated by the vacuum magnetron sputtering to have a thickness approximately in a range of 0.10.5 m.

(14) As chemical compatibility between the ceramic substrate 1 and each of nickel, vanadium, chromium, aluminum, and zinc is high, a low-resistance ohmic contact can be formed therebetween with a significantly small sheet resistance (ohm per unit area). Because of the reduced ohmic contact, heat generated by surge current can thus be lessened to prevent the electrode layers 22 from being burned out and damaged by high heat. Also because of no organic silver paste used in the electronic component of the present invention, the electronic component is advantageous in higher solder erosion resistance, such that products having the electronic component of the present invention soldered thereto can avoid solder erosion and therefore prolong life duration of the products.

(15) After the intermediate layers 21 are formed, the process of spray-forming the electrode layers 22 can be started. The electrode layers 22 are respectively sprayed on the intermediate layers 21. The electrode layers 22 can be formed by a metal material selected from one of zinc, copper, tin, and nickel or a combination thereof. The two electrode layers 22 are simultaneously formed by electric arc spray or flame spray. The work piece stands pass through continuous spray chambers in a tunnel, and the process of spray-forming the electrode layers 22 can be done in approximately 2 to 10 seconds depending on parameter setting at each station.

(16) The process of spray-forming the electrode layers has the following steps.

(17) Step 1: Place the treated ceramic substrate 1 on a work piece stand into a continuous arc spray machine or a flame spray machine.

(18) Step 2: Apply continuous spraying equipment with multiple spray nozzles for multiple processes at different spray stations to directly spray a surface of each intermediate layer 21. Each spray nozzle sprays one metal or an alloy of a desired metal material.

(19) Step 3: Set up spray voltage in a range of 2035V, spray current in a range of 100200 A, spray air pressure at 0.5 Mpa, spray time in a range of 25 seconds, and spray thickness in a range of 510 m for each spray station.

(20) After the electrode layers 22 are formed, the two electrode layers 22 are soldered to the two respective lead wires 3. The ceramic substrate 1, the intermediate layers 21, the electrode layers 22, and the lead wires 3 are enclosed by the insulation layer 4, which may be formed by epoxy, to form the electrode component with the lead wires 3 partially exposed. Electrical characteristics of the electrode component are further tested.

(21) The electrode component in accordance with the present invention may be applied to one of metal oxide varistor (MOV), gas sensitive resistor, PTC (Positive temperature coefficient) thermistor, NTC (Negative temperature coefficient) thermistor, piezoelectric ceramic, and ceramic capacitor. The shape of the electrode component may be square, round, oval, tubular, cylindrical or pyramidal. Given a MOV as an example, a surge withstand capability (Imax) of the electronic component in the MOV against combination wave increases about 50%. The following table shows comparison between the varistors using conventional silver electrode and the varistors using the electrode component of the present invention.

(22) TABLE-US-00001 No. of combo. wave (6 KV/3 KA) Material of Film Varistor Imax (KA, withstood before electrode thickness voltage 8/20 s) failure Printed Ag 8.6 495.6 4.5 34 Printed Ag 15.4 472.3 6 65 Sputtered Ni; 6.5 490.0 6 60 sprayed Zn Sputtered Cr; 5.8 491.9 6 120 sprayed Cu Sputtered Ni; 7.2 484.6 6.5 124 Sprayed Sn

(23) As shown in the second and third rows of the above table, to withstand the impact of large transient energy, conventional varistor adopts the means of printed silver electrode to form a thicker electrode layer (Ag) for current density distribution. If the requirement of surge withstand capability (Imax) is 6 KV, the thickness of the silver electrode layer is normally 16 m and more.

(24) As for the fourth to sixth rows of the above table, a total thickness of the electrode layer 22 and the sputtered intermediate layer 21 of the electrode component in the present invention for lowering ohmic contact resistance and electrode erosion caused by solder is under 10 m. When the conventional silver electrode as shown in FIG. 7 is compared with the intermediate layer 21 of the present invention as shown in FIG. 6, the single-layer screen printed silver electrode has a loose structure with lots of large cavities formed therein while the sputtered intermediate layer 22 of the present invention has a more compact structure with smaller cavities. Furthermore, as indicated in the third and fourth rows of the above table, under the same surge withstand capability (6 KA), a total thickness of the sputtered Ni for the intermediate layer 21 and the sprayed Zn for the electrode layer 22 is just 6.5 m. In contrast to the thickness of the conventional screen printed silver electrode, which is 15.4 m, the total thickness of the present invention is greatly reduced. As far as the number of combination wave (6 KV/3 KA) testing the varistors at 90 degrees phase angle and withstood by the varistors for 60 seconds before failure of the varistors is concerned, the number is from 35 to 65 for the varistors using the conventional silver electrode while the number is 100 to 120 for the varistors using the electrode component of the present invention, which almost doubles that for the varistors using the conventional silver electrode.

(25) Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.