Composition and preparation of aluminum electrodes for positive temperature coefficient thermistors

Abstract

This invention discloses the composition and preparation of an aluminum electrode for a positive temperature coefficient thermistor, belonging to the field of chemical preparation. The aluminum electrode paste is composed of near-spherical aluminum powder, lead-free environmentally friendly glass powder, organic binder, and protective additives. By optimizing the lead-free glass component, the surface protective film of the aluminum powder is prevented from being eroded, thus preventing oxidation and detachment. The aluminum electrode is formed on a barium titanate ceramic substrate through screen printing and sintering at 580–630℃, achieving good ohmic contact with the substrate. The electrode is firmly attached, oxidation-resistant, does not detach, has a small resistance change rate, and exhibits superior corrosion resistance and weather resistance compared to traditional lead-containing aluminum paste. It is suitable for mid-to-high-end PTC thermistors and applications in energy storage and new energy sectors. This invention solves the problems of easy detachment and poor reliability of existing lead-free aluminum pastes, significantly improving component lifespan and stability.

Description

Technical Field

[0001] An electronic information material prepared by a chemical method, belonging to the field of chemical preparation. Background Technology

[0002] The substrate of a positive temperature coefficient thermistor is a doped barium titanate functional semiconductor ceramic. This ceramic has a negative oxygen layer, requiring the electrode to form an ohmic contact with the ceramic during resistor fabrication. A simple method for checking this is to compare it with an InGa-coated alloy. A resistance equal to or lower than that of the InGa electrode indicates a good ohmic contact; a resistance greater than that of the InGa electrode indicates a poor ohmic contact. To obtain an ohmic contact electrode, electrodes with strong oxygen affinity can be used, such as electroless nickel-plated or zinc-plated electrodes, sintered aluminum electrodes, and aluminum-sprayed electrodes. The inventors used a sintered aluminum electrode in patent ZL200610048681.4.

[0003] Positive temperature coefficient (PTC) thermistors have a wide range of industrial applications. Heating elements are used in air conditioners, mosquito killers, etc. Demagnetizing elements are used in televisions, computers, and mobile phones. Programmable circuit elements are used in programmable circuits and also for motor protection. Due to the application of LED solid-state lighting, energy-saving lamps are rarely produced anymore. Today, with the explosive development of silicon solar photovoltaics, it is a green and inexhaustible energy source. Daily battery power generation requires storage in batteries; currently, lithium batteries have the highest energy density, and the charging and discharging of lithium batteries also relies on PTC thermistors.

[0004] The inventor's patent ZL200610048681.4 primarily uses lead-containing glass, suitable for heating elements. This invention is an improvement and extension of the original invention, enhancing the quality of the aluminum paste through the selection of aluminum powder, improvements to the glass composition, and the addition of protective agents. Currently used lead-free aluminum pastes experience electrode detachment during use after printing and firing. This is ultimately due to the incompatibility between the glass and aluminum powder; the protective film on the aluminum powder surface is no longer effective, allowing the aluminum powder to further oxidize into aluminum oxide and detach. Improvements to the glass composition are needed to extend the lifespan of the aluminum electrodes. Summary of the Invention

[0005] 1. The purpose of this invention is to provide a composition and preparation method of aluminum electrode paste for positive temperature coefficient (PTC) thermistors. The paste comprises 50-75% aluminum powder, 20-35% inorganic binder, and 15-30% organic binder by mass percentage. The aluminum conductive paste is rolled and then screen-printed and sintered onto a barium titanate semiconductor substrate to form an aluminum paste electrode, i.e., a PTC thermistor. The electrode forms a good ohmic contact with the substrate, exhibits good adhesion, a small resistance change rate, no electrode oxidation, and no aluminum film peeling. This invention improves the corrosion resistance and weather resistance of the aluminum electrode based on patent ZL200610048681.4, enabling PTC thermistors to be used in mid-to-high-end products.

[0006] 2. Technical Solution (1) Aluminum powder: Purchase commercially available spherical aluminum powder with a particle size ≤8μm and a purity of 99.85%, accounting for 50-75% of the slurry composition; (2) Components and preparation of inorganic binder glass powder: The following components are present: TiO2 0.3-1.5%, K2CO3 0.2-1.5%, Ba(OH)2 0.5-3.0%, (NH4)2HPO4 1.0-3.0%, Al2O3 0.1-1.0%, SiO2 2-8%, Bi2O3 8-16%, H3BO3 20-35%, ZnO 40-50%, TeO2 0.5-3.0%, Ti2O3 0.2-1.2%, FeO 0.1-2.0%, NiO 0.1-1.0%, Cu2O 0.1-1.0%, totaling 100%. These components are mixed in a porcelain crucible, melted at 1100-1200℃, and then water-quenched and crushed to obtain glass powder. (3) Composition and preparation of organic adhesives: One or two of ethyl cellulose, cellulose acetate, and polyacrylic acid resin, in a content of 3-8%; terpineol 40-60%; diethylene glycol monobutyl ether 10-15%; benzyl alcohol 5-10%; butyl carbitol acetate 8-15%; Span 85 0.5-3.0%; silicone oil 2.0-5.0%. Total content 100%. Heating and melting yields the adhesive. (4) Additives: Mg, B, Zn, P, Sb, Te; (5) Aluminum paste preparation: The composition consists of 50-75% aluminum powder, 12-32% glass powder, 15-30% organic binder, and one or two additives at a content of 0.1-4.0%, with a single additive content of 0.1-3.0%. The total amount is 100%. The aluminum paste is rolled and printed onto both sides of a barium titanate substrate for a positive temperature coefficient thermistor. The substrate is then baked at 580-630℃ to obtain the resistor. After cooling to room temperature, the resistance is measured, which is the resistance value of the component. The aluminum electrode is ground off, and InGa is coated. After a short time, the resistance is measured again. The resistance is compared with that of the aluminum electrode. If the resistance is the same or the aluminum electrode resistance is lower than that of the InGa electrode, the ohmic contact is good. If the aluminum electrode resistance is higher than that of the InGa electrode, the ohmic contact is poor. Generally, a 5% higher resistance between the aluminum electrode and the InGa electrode is permissible. Other aging tests are conducted using known aging test methods.

[0007] 3. Advantages and positive effects compared to known technologies (1) The present invention prepares environmentally friendly lead-free glass. The glass does not corrode the protective film of aluminum powder, ensuring that the electrode of the component will not fall off due to further oxidation of aluminum powder caused by damage to the protective film, thus greatly extending the life and reliability of the component. (2) Select appropriate additives. Aluminum is a base metal and is prone to component reaction in the calcination range of 580-630℃. Adding corresponding additives can regulate the reaction process of aluminum and maintain the original state of the substrate. (3) The thermistor prepared by the present invention is superior to the resistor made by patent ZL200610048681.4; (4) The aluminum paste of the present invention can be used for energy storage.

[0008] IV. Implementation Methods 1. Example 1 (1) Aluminum powder, commercially available, spherical, particle size 6.0 μm, purity 99.85%; (2) Preparation of organic adhesive: 6.0% ethyl cellulose, 50% terpineol, 16% diethylene glycol monobutyl ether, 10% diethylene glycol monobutyl ether, 14% butyl carbitol acetate, 2.0% Span 85, 2.0% silicone oil, total 100%, hot melt to obtain adhesive; (3) Glass powder preparation: The following ingredients are present in a mixture: TiO2 0.5%, K2CO3 1.0%, Ba(OH)2 1.5%, (NH4)2HPO4 1.0%, Al2O3 0.5%, SiO2 7.0%, Bi2O3 8.0%, H3BO3 28%, ZnO 43%, TeO2 5.5%, Ti2O3 1.0%, FeO 0.5%, NiO 2.0%, Cu2O 0.5%, totaling 100%. The mixture is thoroughly mixed, placed in a porcelain crucible, melted at 1150℃, and then water-quenched and crushed to obtain glass powder. (4) Commercially available additives: Commercially available boron powder; (5) Slurry preparation: The composition includes 62% aluminum powder, 19% organic binder, 17% inorganic binder glass, and 2.0% boron powder. The mixture is thoroughly mixed and rolled to obtain a uniform aluminum paste. The paste is printed onto a thermistor substrate and dried. It is then sintered at 620℃, cooled to room temperature, and a positive temperature coefficient thermistor is obtained. The resistance value is measured. Both aluminum electrodes are ground off, and an InGa alloy is coated. After cooling, the resistance value is measured again. The resistance of the aluminum electrode is slightly higher than that of the InGa electrode, indicating that the electrical performance is acceptable. Electrical aging and damp heat aging tests are performed according to known methods, and the results are satisfactory.

[0009] 2. Example 2 (1) Aluminum powder: Same as in Example 1; (2) The preparation of the organic adhesive is the same as in Example 1; (3) Glass preparation is the same as in Example 1; (4) Additives: Commercially available antimony powder; (5) Aluminum paste preparation: 2.0% antimony powder, the remainder is the same as in Example 1, totaling 100%. Processing and sintering tests are the same as in Example 1. The resistance of the aluminum electrode is almost the same as that of the InGa electrode, and the electrical performance is qualified. Electrical aging and damp heat aging tests were performed according to known methods, and the results were qualified.

[0010] 3. Example 3 (1) Aluminum powder: Same as in Example 1; (2) The preparation of the organic adhesive is the same as in Example 1; (3) The glass powder preparation is the same as in Example 1; (4) Additives: Commercially available tellurium powder; (5) Aluminum paste preparation: 2.0% tellurium powder, the remainder is the same as in Example 1, totaling 100%. Other aspects are the same as in Example 1. After sintering, the resistance of the aluminum electrode is 2.5% lower than that of the InGa electrode, and the electrical performance is qualified. Electrical aging and damp heat aging tests were performed according to known methods, and the results were qualified.

[0011] In addition to being used in ZL200610048681.4, the product of this invention is also used in energy storage devices and is a material for new energy components.

Claims

1. The composition and fabrication of an aluminum electrode for a positive temperature coefficient thermistor, characterized in that, Aluminum electrode paste formulation: by mass percentage, 50–75% aluminum powder, 12–32% inorganic binder (glass powder), 15–30% organic binder, and 0.1–4.0% additives, wherein the additives are one or two of Mg, B, Zn, P, Sb, and Te, with the content of a single additive being 0.1–3.0%, and the total amount of all components being 100%. The aluminum powder is spherical with a particle size ≤ 8 μm and a purity ≥ 99.85%. The inorganic binder glass powder comprises, by mass percentage: TiO2 0.3–1.5%, K2CO3 0.2–1.5%, Ba(OH)2 0.5–3.0%, (NH4)2HPO4 1.0–3.0%, Al2O3 0.1–1.0%, SiO2 2–8%, Bi2O3 8–16%, H3BO3 20–35%, ZnO 40–50%, TeO2 0.5–3.0%, Ti2O3 0.2–1.2%, FeO 0.1–2.0%, NiO 0.1–1.0%, and Cu2O 0.1–1.0%, totaling 100%. The organic binder comprises, by weight percentage: 3–8% of one or two of ethyl cellulose, cellulose acetate, and polyacrylic acid resin; 40–60% of terpineol; 10–15% of diethylene glycol monobutyl ether; 5–10% of benzyl alcohol; 8–15% of butyl carbitol acetate; 0.5–3.0% of Span 85; and 2.0–5.0% of silicone oil, for a total of 100%.

2. The aluminum electrode composition and preparation of a positive temperature coefficient thermistor according to claim 1, characterized in that, The aluminum electrode paste of claim 1 is screen-printed onto both sides of a barium titanate semiconductor substrate, dried, sintered at 580–630°C, and cooled to form an aluminum electrode; the aluminum electrode forms a good ohmic contact with the substrate, and the resistance of the aluminum electrode deviates from that of the InGa alloy electrode by ≤5%.