WO2017041549A1 - Electrode material and electrode manufacturing method requiring low cost - Google Patents

Abstract

The invention discloses an electrode material and electrode manufacturing method requiring a low cost, and specifically, an electrode material applicable to a varistor. The electrode material comprises an intermediate transitional layer adhered on a surface of a varistor ceramic and an electrical conduction layer adhered on the intermediate transitional layer and connected to a lead. The intermediate transitional layer comprises an electrical conduction metal material including gold, silver, zinc, copper, nickel, aluminium, a silver alloy, a zinc alloy, a copper alloy, a nickel alloy, or an aluminium alloy. The electrical conduction layer comprises a metal or alloy having favorable electrical conductivity. The electrode manufacturing method comprises the following steps: (1) printing a conductive paste on a baseboard, firmly adhering the conductive paste on a surface of the baseboard using a sintering technique; and forming an intermediate transitional layer on the surface of the baseboard; and (2) applying a thermal spray process, using an electric conduction layer having favorable electrical conductivity, on the intermediate transitional layer, wherein the electric conduction layer having the favorable electrical conductivity is a metal or alloy.

Description

Electrode material and low-cost electrode manufacturing method Technical field

The invention relates to a method for manufacturing an electronic component, in particular to a method for manufacturing an electrode, and the method of the invention can be effectively applied to the electrode manufacturing of a varistor, which is of great significance for improving the electrical performance of the varistor.

Background technique

In the manufacturing process of varistor, the manufacture of the electrode is an important process. The usual practice is to apply a paste-like paste on both sides of the sintered wafer-shaped pressure-sensitive ceramic sheet by screen printing. The silver paste is then dried and burned to form a silver electrode with excellent adhesion, conductivity and solderability on the ceramic body. The silver paste contains three main components: one is an organic solvent, has a certain viscosity, and is blended in the slurry to facilitate silk screen processing. After silk screen printing, it is decomposed and volatilized when dried below 400 ° C. The second is silver powder, which accounts for 60-80%. The conductivity and solderability of the electrode are determined by it. The third is glass powder, which accounts for 1-10%. It is mainly composed of low-melting inorganic materials. When the temperature is between 400 °C and 750 °C, the glass powder melts and burns on the surface of the pressure-sensitive ceramic sheet to form good adhesion. Since the process is simple and convenient for mass production, the electrode can be easily fabricated into any shape and size, and thus is widely used in the manufacturing process of the varistor.

Since silver paste has the largest proportion of silver powder, silver is precious metal, and the unit price is high, which leads to high unit price of silver paste. In the raw material cost structure of varistor finished products, silver paste cost accounts for the largest weight. , has a significant impact on the pricing of varistor.

In recent years, the development level of varistor has been continuously improved, and the ability to withstand surge surge has increased from ⁶ kA/cm ² to nearly 9 kA/cm ² . Due to the increase in current density, it is necessary to further reduce the square resistance of the electrode in order to control the heating of the electrode within the requirements. This requires further thickening of the thickness of the silver electrode, which significantly increases the amount of silver paste, which leads to a too high price of the varistor and a poor cost performance of the product. In addition, some advanced processing methods are being introduced into the traditional varistor manufacturing process. Such as laser welding technology, its efficient and precise welding process, strong and reliable solder joints, no need for solder and other solder features, will replace the solder process as the preferred means of connecting leads and electrode processing. Laser welding technology also requires the thickness of the electrode to be sufficiently thick, which will also result in a significant increase in the amount of silver paste. Therefore, there is an urgent need to find an inexpensive alternative material and method to solve this problem.

Since the conductivity of copper is only slightly lower than that of silver, and the price difference is several hundred times, some people use copper powder instead of silver powder to make copper paste, and successfully applied in the ceramic capacitor manufacturing process. However, in the popularization and application of varistor, it has encountered technical problems. When copper powder is heated above 400 °C in air, it will lose its conductivity. Therefore, the infiltration process of copper paste must be carried out in a nitrogen atmosphere furnace. The main component of the pressure-sensitive porcelain, zinc oxide, will be partially lost under such conditions. Oxygen is reduced to zinc, which deteriorates electrical parameters. Therefore, the promotion of copper paste on varistor has stopped here, and progress has been slow for many years, which is difficult to promote and apply.

In addition, methods such as vacuum evaporation, sputtering, and electroplating have been continuously explored, but factors such as efficiency, electrode thickness, shape and size control, adhesion, and environmental protection are not satisfactory, and there has been no successful application.

There is also a mature technology called thermal spraying technology, which uses a method such as arc to heat a metal material such as copper to a partially melted state, and then blows it into a high-speed moving small particle by a high-pressure airflow, and deposits a coating on the surface of the workpiece to form a coating. High process efficiency, material saving, masking technology can be used to easily set the shape and size of the coating. The thickness of the coating can reach 0.1mm or more and the thickness can be easily controlled. It has been widely used in the surface treatment of metal processing. application.

When the surface of the workpiece is a metal substrate, the adhesion of the thermal spray coating is quite strong, and even some of the worn precision workpieces can be thickened and then put back into the wear-resistant use. However, when applied to ceramic surfaces, the situation is very different. Theoretically, there is no binding force between the thermal spray coating and the ceramic surface. Even in the test, even the pressure-sensitive ceramic sheets are cleaned very cleanly, and even the surface of the ceramics is sanded by sand blasting. Pretreatment, the resulting thermal spray electrode adhesion is also very poor. The coating is peeled off by gently pulling the lead wire welded on it. Even if it is barely made into a varistor finished product, it will have no practical value because it cannot be reliably subjected to the tensile test and the vibration test. Therefore, thermal spray technology cannot be directly applied to the electrode fabrication of varistor.

Summary of the invention

The object of the present invention is to overcome the problems in the prior art that the improvement of electrode resistance, cost control, adhesion improvement, electrode thickening and the like are difficult to be simultaneously improved, and a low-cost electrode manufacturing method is provided. In many aspects, the performance of the electrode is improved, and the side resistance, thickness, adhesion, and manufacturing cost of the electrode are partially or simultaneously effectively improved.

In order to achieve the above object, the present invention provides the following technical solutions:

A varistor electrode material comprising an intermediate transition layer attached to a surface of a pressure sensitive ceramic sheet, and a conductive layer attached to the intermediate transition layer, and a lead wire is connected to the conductive layer. The intermediate transition layer contains gold, silver, zinc, copper, nickel, aluminum, a silver alloy, a zinc alloy, a copper alloy, a nickel alloy or an aluminum alloy as a conductive material, and the conductive layer is a metal or alloy having good electrical conductivity, such as metallic copper. , nickel, zinc, tin, or copper alloy, nickel alloy, zinc alloy, tin alloy, and the like.

Further, the intermediate transition layer has a thickness of 2 to 100 μm.

Further, the intermediate transition layer is a glass glaze phase, wherein the glass glaze accounts for 1 to 15%, and the metal material accounts for 85 to 99% (by weight). The composition of the intermediate transition layer mainly contains a metal conductive material, and then contains a certain amount of glass glaze composition, the glass glaze acts as a bond strengthening structure, and the metal material mainly acts as a conductive material, and the two form a composite material/structure, both It has good adhesion and sufficient conductivity.

Further, the intermediate transition layer is formed by infiltration. In particular, the conductive paste is coated on the substrate, and the metal/alloy intermediate transition layer is formed by the infiltration process. Since the transition layer is a stable bond of the glass glaze into the interior of the pressure-sensitive ceramic sheet, the adhesion is very prominent. The conductive layer is thicker and has better stability, and can withstand the high temperature effect of laser welding when connecting the leads, and can also reduce the square resistance and disperse the current flowing through the electrode to ensure the electrode material. reliability.

Further, the conductive layer is copper, nickel, zinc, tin, a copper alloy, a nickel alloy, a zinc alloy or a tin alloy. The conductive layer is made of a common conductive metal material, and has the characteristics of good electrical conductivity and low preparation cost.

Further, the conductive layer has a thickness of 10 to 100 μm. The conductive layer has a thick thickness, a low electrical resistance, and is well connected to the electrode lead. It is preferably 20 to 30 μm. It satisfies the requirements of the electrode resistance and heat generation of the varistor, and the production cost is low.

An electrode manufacturing method comprising the following steps:

(1) A conductive paste is printed on a substrate, and a conductive paste is attached to the surface of the substrate by a sintering process to form an intermediate transition layer on the surface of the substrate. Preferably, the substrate is a pressure sensitive ceramic sheet.

(2) Thermally spraying a conductive layer having good electrical conductivity on the intermediate transition layer. Preferably, the conductive layer having good electrical conductivity is a metal or an alloy. Preferably, the metal refers to one of copper, nickel, zinc, and tin, and the alloy is a copper alloy, a nickel alloy, a zinc alloy, a tin alloy, or the like. That is, the material of the conductive layer is selected from the group consisting of metal copper, copper alloy, nickel, nickel alloy, zinc, zinc alloy, tin, tin alloy, and the like.

The invention first applies the conductive paste to the substrate by printing, and then applies a metal or metal alloy-based electrode transition layer on the pressure-sensitive ceramic sheet by a sintering process, which is good with the pressure-sensitive ceramic body. Adhesion, and good adhesion to the thermal spray coating, as an intermediate transition layer, and then thermally spray a layer of copper or other metal or metal alloy with good electrical conductivity and excellent weldability to make low cost. An electrode with low square resistance, good adhesion and good solderability. Moreover, the electrode obtained in this way can still provide good adhesion when the thickness is thicker, can meet the requirements of advanced technologies such as laser welding, and has the advantages that it is difficult to achieve in all other ways or in combination.

Further, the conductive paste is a slurry mainly composed of a conductive metal powder commonly used in the electronic component processing industry. Generally, the content of the conductive metal powder in the conductive paste is 40% or more, preferably 60% to 90% by weight. Conductive metal powder as the main raw material component, plus an appropriate amount of organic solvent and glass powder, the conductive paste prepared by the conductive paste has good printing and coating performance, and after melting, the molten glass glaze can penetrate into the ceramic body to a certain depth, Good adhesion characteristics. The printing paste may be a silver paste commonly used in the prior art, or may be a slurry which is appropriately adjusted according to actual production needs by those skilled in the art, as long as the conductive paste can be formed into an intermediate transition layer and a thermal spray electrode. The substrate has good adhesion ability.

Further, the metal or metal alloy paste used as the intermediate transition layer for screen printing must be subjected to infiltration treatment in air at a temperature range of 400 ° C to 750 ° C, wherein the metal powder is not easily oxidized. For example, silver powder, nickel-copper alloy powder, or the like can be selected.

Further, the thickness of the intermediate transition layer is 2 to 30 μm. Since it only serves to improve the adhesion, the thickness of the coating layer can be greatly reduced, and the electrical conductivity of the metal powder can be not necessarily as high, even if it is still used. Silver paste is used as the transition layer. The thickness of the silver layer can be reduced by 60-80% compared with the pure silver electrode, which is still more cost-effective than the electrode made of pure silver paste. Of course, the choice of nickel-copper paste as a transition layer will reduce the cost.

Further, a conductive paste is screen printed. The screen printing has a simple process and is easy to mass-produce, and the electrode can be conveniently fabricated into any shape and size, and can meet the production requirements of the processing transition layer of the present invention.

Further, the metal or alloy material of the conductive layer has a thermal expansion coefficient equivalent to that of the transition layer, and the difference in thermal expansion coefficient between the two is controlled within 50%, preferably 20%. It is best to select the material with the same thermal expansion coefficient, but in order to ensure the easy implementation of the processing technology, the cost of the material is controlled at a lower level, so it is allowed to use the material with the difference in thermal expansion coefficient, but try to control the difference between the two in a smaller range. Inside.

Further, in the step (1), the conductive paste is screen-printed, and a layer of a metal or a metal alloy-based electrode transition layer is coated on the pressure-sensitive ceramic sheet by a sintering process.

Further, the electrode method is a method of manufacturing a pressure sensitive electrode.

Further, when the conductive layer is thermally sprayed, copper, copper alloy, zinc, zinc alloy, tin, tin alloy is used as the spray material, and pure copper is preferred as the spray material. Copper has high electrical conductivity, good solderability and low cost. Of course, a copper alloy material or other metals such as zinc, tin or alloys thereof may be selected. In the test, silver paste was used as the transition layer, and other conductive materials (especially pure copper) were used to thermally spray the coating of 0.02-0.05 mm thick. The obtained electrode adhesion was the same as that of the pure silver electrode, and the electrode solderability was good. Strong adhesion. When the surge impact density is increased to 12KA/cm ² , although the pressure-sensitive porcelain body has been overloaded at this time, the heat generation of the electrode is still within the required range, indicating that the coating at this thickness has sufficient square resistance. Low, fully in line with design requirements. When spraying with zinc or other metal materials, the same requirements can be achieved by increasing the thickness of the coating.

Compared with the prior art, the beneficial effects of the invention: compared with the conventional screen printing silver electrode process, although the operation method of the method of the invention is complicated, the overall cost is still saved due to the saving of a large amount of expensive silver materials. To reduce by more than 25%, it is very competitive, and more valuable is the varistor electrode made by this process, which is pure in the processing of the subsequent process, or the electrical properties and anti-aging properties of the finished product. The physical properties of the silver electrode achieve high quality and low price expectations, and also contribute to a bottleneck difficulty for the continuous improvement of the performance of the varistor and the use of advanced laser welding processes.

BRIEF DESCRIPTION OF THE DRAWINGS:

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the tensile breaking test of the electrode obtained by the present invention.

Marked in the figure: 1-pressure-sensitive porcelain, 2-intermediate transition layer, 3-sprayed layer, 4-solder, 5-lead, 6-weight.

Detailed ways

The invention provides an idea to firstly print a conductive paste by screen printing, and apply a layer of metal or metal alloy electrode transition layer on the pressure sensitive ceramic sheet by a sintering process, which is good with the pressure sensitive ceramic body. The adhesion, and the good adhesion of the thermal spray coating, as an intermediate transition layer, and then thermal spraying a layer of copper or other metal or metal alloy with good electrical conductivity and excellent weldability, resulting in low cost , low square resistance, good adhesion, good solderability of the electrode.

In this solution, the metal or metal alloy slurry used as the intermediate transition layer for screen printing must have the infiltration treatment in the air at a temperature range of 400 ° C to 750 ° C, wherein the metal powder is not easily oxidized. characteristic. For example, silver powder, nickel-copper alloy powder, etc. may be selected; of course, copper powder slurry may be used for brushing and infiltration, and when copper slurry is used for infiltration, it is preferable to use a suitable reducing atmosphere as a shielding gas to prevent copper slurry from being used. The copper powder is oxidized, similar to other oxidizable metal materials. Since it only serves to improve the adhesion, the thickness of the coating can be greatly reduced, and the electrical conductivity of the metal powder can be as high as required, even if the silver paste is used as the transition layer, the thickness of the silver layer. It can be 60-80% thinner than pure silver electrode, still more cost-effective than the electrode made of pure silver paste. Of course, the choice of nickel-copper paste as a transition layer will reduce the cost.

The hot spray coating is preferred as a pure copper material, which has high electrical conductivity, good solderability and low cost. Of course, a copper alloy material or other metals such as zinc, tin or alloys thereof may be selected. In the test, the silver paste was used as the transition layer, and the coating of 0.02-0.05 mm thick was thermally sprayed with pure copper material. The electrode adhesion was the same as that of the pure silver electrode. The electrode solderability was good, the lead adhesion was firm, and the surge density was increased. When the temperature is up to 12KA/cm ² , although the pressure-sensitive porcelain body has been overloaded, the heat of the electrode is still within the required range, indicating that the coating at this thickness has a sufficiently low square resistance, which fully meets the design requirements. It is. When spraying with zinc or other metal materials, the same requirements can be achieved by increasing the thickness of the coating.

Compared with the traditional screen printing silver electrode process, although the operation method of the process of the invention is more complicated, the overall cost is still reduced by more than 25% due to the saving of a large amount of expensive silver materials, which is very competitive and more valuable. The varistor electrode made by the process achieves the physical properties of the pure silver electrode in both the processing of the subsequent process and the electrical properties and anti-aging properties of the finished product, realizing the expectation of being inexpensive. It also solves a bottleneck difficulty for the continuous improvement of the performance of varistor.

The present invention will be further described in detail below in conjunction with the test examples and specific embodiments. However, the scope of the above-mentioned subject matter of the present invention should not be construed as being limited to the following embodiments, and the technology implemented based on the present invention is within the scope of the present invention. The percentages not specifically stated in the present invention are all percentage by weight.

Example 1

The silver paste was applied to the surface of the pressure-sensitive ceramic sheet by a screen printing process, the diameter of the ceramic sheet was 14 mm, the diameter of the silver paste coating was 11.3 mm, and the electrode area was about 1 cm ² . The coated pressure-sensitive ceramic sheet was fired at 630 ° C to obtain a ceramic sheet having an electrode transition layer having a surface of 5 μm adhered thereto. Then, a copper layer having a thickness of 30 μm was sprayed on the transition layer by a thermal spraying process. The corresponding pins are soldered and then encapsulated with epoxy resin to form a finished varistor component.

The electrode material of the varistor prepared in this embodiment has an intermediate transition layer having a thickness of 5 μm adhered to the surface of the pressure-sensitive ceramic sheet, and the main component thereof is silver, which is obtained by infiltration of silver paste at 630 ° C; A 30 μm conductive layer is attached to the intermediate transition layer, and the material is realized by a thermal spraying process, and leads (pins) are connected to the conductive layer. The intermediate transition layer formed by the infiltrated silver paste is formed by the glass glaze penetrating into the interior of the pressure-sensitive ceramic sheet to form a stable bond, and the tensile strength is outstanding, and the adhesion is excellent. The conductive layer realized by thermal spraying has good adhesion to the intermediate transition layer, can apply a thick conductive layer, and has high processing speed and good stability. When the thicker conductive layer is connected to the lead, it can withstand the high temperature of laser welding while reducing the square resistance and dispersing the current flowing therethrough.

Preferably, the silver paste used in brushing the silver paste has a solid content of about 70%, wherein the conductive silver powder accounts for more than 60%, and contains an appropriate amount of glass glaze to achieve effective adhesion of the slurry during the infiltration process. On the ceramic substrate.

Examples 2 to 6

The pressure-sensitive electronic component was prepared by the same process scheme as in Example 1. The slurry, the infiltration temperature, the thickness of the transition layer, the material of the spray coating, and the thickness of the spray were selected in the preparation process.

Table 1

The infiltration temperature can be controlled within 600-650 ° C, adjusted according to the content ratio of the metal powder and the glass glaze in the coated conductive paste and the solid content of the conductive paste to ensure that the glass glaze is fully melted during the infiltration process. Penetration into the ceramic matrix results in an intermediate transition layer having sufficient adhesion.

The spray thickness can be further increased to 100 μm or even higher. Because the conductive paste used in the invention is applied to the ceramic substrate, not only the adhesion to the ceramic substrate is good, but also the sprayed conductive layer metal material in the spraying process. The affinity of the material is good, so the thickness of the conductive layer sprayed can be further broken. When the thickness of the metal material of the conductive layer is increased, those skilled in the art can not only complete the soldering of the lead by brazing, but also weld the lead wire by laser welding.

In general, silver, copper, gold, and aluminum have the best electrical conductivity, and the material resistivity can be as low as 10 ^-8 Ωm, but the cost of gold is too high, while aluminum is very easy to oxidize, and the temperature and time required for infiltration Precise control. Therefore, in combination with the case where the conductive paste is used in the subsequent infiltration process, a material which can be stabilized at the infiltration temperature, such as silver, copper, nickel-copper alloy (such as Monel 400), is more preferable. When copper is used as the conductive metal in the conductive paste, it is preferable to design a corresponding protective gas during the infiltration to prevent oxidation of the high temperature state of the copper during the infiltration process.

test

The varistors prepared in Examples 1 to 6 were tested to test the peak current impact strength and the tensile failure test, respectively. The specific test methods and criteria are as follows:

1. Peak surge impact strength:

The impact current waveform selects 8/20μs standard lightning waveform, and the number of samples in each group is 13 pieces, and one of them exceeds the standard and is judged as unqualified. The unqualified judgment criteria are: varistor voltage change rate ≥10% before and after impact or any mechanical damage in the appearance of the component. There are two main factors affecting this index. When the pressure-sensitive porcelain body can not withstand the impact, the grain boundary layer encounters damage, which shows that the varistor voltage change rate is ≥10%; when the electrode resistance is too large, the impact The current causes the electrode to heat up too much, causing the encapsulating layer epoxy to crack and form mechanical damage.

In this test, we designed three surge current strength, are representative of the current state ① standard level 6KA / cm ^2; ② representative of the current level of the advanced 8.5KA / cm ^2; ③ destructive purposes 12KA / cm ^2.

2, tensile damage test:

In order to more accurately and accurately detect the adhesion of the electrode, the varistor sample used a semi-finished product before epoxy encapsulation. The diameter of the tinned copper wire was 0.8 mm, and a tensile force of 10 Newton was applied to the lead for 10 seconds. The electrode could not be torn. Or fall off.

The test results of Examples 1 to 6 are as follows:

Table 2

Comparing Example 1 with Example 2, it can be seen that when the thickness of the intermediate transition layer is reduced to 1.5 μm, the tensile test is unacceptable and has no practical value.

Comparing Example 1 with Example 3, it can be seen that when the thickness of the sprayed copper layer is reduced to 15 μm, the product conforming to the national standard impact strength can be produced, but the impact resistance of the most advanced ceramic technology cannot be matched.

Comparing Example 1 and Example 4, it can be seen that when the sprayed layer is made of a zinc material having a thickness of 30 μm, it can meet the requirements of the electrode of the current state of the art ceramic technology, but there is no greater margin.

Comparing Example 1 and Example 5, it can be seen that when the intermediate transition layer is made of nickel-copper alloy and the sprayed layer is made of 30 μm thick copper material, it can meet the requirements of the current state-of-the-art ceramic technology for the electrode, but the margin is not as good as that of the embodiment 1. .

Comparing Example 1 and Example 6, it can be seen that when the intermediate transition layer is made of nickel-copper alloy and the copper material of the sprayed layer is only 15 μm, only products meeting the national standard impact strength can be produced.

Claims (13)

A varistor comprising an intermediate transition layer attached to a surface of a pressure sensitive ceramic sheet, and a conductive layer attached to the intermediate transition layer, the lead being connected to the conductive layer; The intermediate transition layer contains gold, silver, zinc, copper, nickel, aluminum, a silver alloy, a zinc alloy, a copper alloy, a nickel alloy or an aluminum alloy as a conductive metal material; The conductive layer is a metal or alloy having good electrical conductivity. The electrode material according to claim 1, wherein the intermediate transition layer is a glass glaze phase, wherein the glass glaze accounts for 1 to 15%, and the metal material accounts for 85 to 99% by weight. The electrode material according to claim 1, wherein said intermediate transition layer is formed by infiltration of a conductive paste. The electrode material according to claim 1, wherein the intermediate transition layer has a thickness of from 2 to 100 μm. The electrode material according to claim 1, wherein the conductive layer is copper, nickel, zinc, tin, a copper alloy, a nickel alloy, a zinc alloy or a tin alloy. The electrode material according to claim 1, wherein the conductive layer has a thickness of 10 to 100 μm. An electrode manufacturing method comprising the following steps: (1) printing a conductive paste on a substrate, and adhering the conductive paste to the surface of the substrate by a sintering process to form an intermediate transition layer on the surface of the substrate; (2) thermally spraying a conductive layer having good electrical conductivity on the intermediate transition layer; The conductive layer having good electrical conductivity is a metal or an alloy. The electrode manufacturing method according to claim 4, wherein the conductive layer is metallic copper, copper alloy, nickel, nickel alloy, zinc, zinc alloy, tin or tin alloy. The electrode manufacturing method according to claim 4, wherein the conductive paste forming the intermediate transition layer contains a metal powder, and the metal powder is silver powder or nickel-copper alloy powder. The electrode manufacturing method according to claim 4, wherein the intermediate transition layer has a thickness of 2 to 30 μm. The electrode manufacturing method according to claim 4, wherein the conductive paste is screen printed. The electrode manufacturing method according to claim 4, wherein the step (1) is an electrode transition layer mainly coated with a metal or a metal alloy on the pressure-sensitive ceramic sheet by a screen printing conductive paste. . The electrode manufacturing method according to claim 4, wherein a copper, a copper alloy, a zinc alloy, a zinc alloy, a tin alloy, and a tin alloy are used as the spray material for thermally spraying the conductive layer.

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