RU2287869C1 - Method for producing enhanced-voltage porous niobium bulk anode - Google Patents

Abstract

FIELD: production of niobium oxide-semiconductor capacitors such as enhanced-voltage ones.

SUBSTANCE: proposed method for manufacturing porous niobium bulk anode involves compression of anode pellets from hydration treated niobium powder, sintering of niobium anode pellets, molding of sintered anodes, and additional molding of anodes in hot electrolyte; anodes are to be molded in two stages; first stage lasting 1 h involves use of phosphoric acid aqueous solution at normal room temperature and second stage lasting 4 h , use of phosphoric acid aqueous solution mixed up with deionized water and ethylene glycol at room temperature of 8 °C.

EFFECT: enhanced operating voltage of niobium anodes produced in this way.

5 cl, 1 tbl

Description

The invention relates to the manufacture of electronic products, specifically to the production of capacitors, and more specifically to niobium capacitors, mainly niobium oxide semiconductor capacitors, namely niobium oxide semiconductor capacitors of increased nominal voltage.

It is difficult to obtain niobium capacitors with a nominal voltage above 25 V, for example 32 V, and a nominal voltage of 40 V is generally problematic due to the unattainability of the required molding voltage with conventional electrochemical oxidation or molding technology. Molding electrolytes with different concentrations of aqueous solutions of phosphoric acid are usually used, in which valve metals, including niobium, practically do not dissolve. The mechanism of the formation of metal oxide and the problems that arise during this are described in the book by L. N. Zakheim “Electrolytic Capacitors”, Gosenergoizdat, M-L., 1963, and are as follows. When the valve metal is turned on anode, an electrolytic cell is created in which a double layer appears at the metal-electrolyte interface, consisting of positive metal ions and negative oxygen ions from the electrolyte side. Since the metal of the anode does not dissolve in the electrolyte, metal and oxygen ions accumulate in the double layer until the charges create a potential sufficient for the appearance of a simple chemical reaction - the formation of metal oxide. Another possible reaction - the discharge of oxygen ions and oxygen evolution at the oxide layer-electrolyte interface - takes place only during breakdown of the oxide layer and does not occur at the stage of the normal molding process, when the initial electrons in the oxide layer do not appear, since almost all oxygen ions are consumed on oxide formation, reacting with valve metal ions. As the thickness of the oxide layer increases, when the voltage drop across the electrolytic cell grows and its distribution is achieved so that the discharge of oxygen ions at the oxide-electrolyte interface becomes possible, the molding slows down and the released electrons enter the oxide layer and lead to the first breakdown stage . A sharp increase in voltage, ending with a spark breakdown, occurs due to such a sufficiently large oxide thickness at which gas interlayers are formed, where the discharge and breakdown of the oxide layer occur. Frequent sparking over the entire surface of the oxide layer gives a thermal effect that causes crystallization of the oxide, which leads to a sharp deterioration in its electrical characteristics, such as insulation resistance and dielectric loss tangent (tan δ). Due to this, the molding voltage should always be less than the sparking voltage of the molding electrolyte.

A known method of producing a niobium volume-porous anode used in the manufacture of the capacitor K53-4 EVA.673 547.010СБ, where the molding of the anodes is carried out in a molding electrolyte, which is a 5% aqueous solution of phosphoric acid, at molding voltages of 40-85 V, 60 -85 V, 80-95 V for operating voltages of 6.3 V, 16 V and 20 V, respectively, the minimum duration of the molding cycle is 1.0-2.5 hours, the molding current set at 10-15 mA / g niobium, after which the anodes are washed first with hot running deionized water (tamper round 50-60 ° C) for 20 minutes in the washing bath, and then in the washing and drying unit (water temperature 70 ± 10 ° C, water flow not less than 2 l / min, drying temperature 150 ± 10 ° C) in two positions for 15-20 minutes.

In this method, it is impossible to manufacture niobium anodes for capacitors with an increased operating voltage, namely 40 V, due to the fact that the required increased magnitude of the molding voltage of niobium anodes is not achieved due to the occurrence of a sparking process in the molding electrolyte.

Closest to the claimed method according to the technical nature (prototype) is the method described in patent GB 1165510, class. H 01 G 9/05, publ. 10/01/1969, according to which a dielectric on an anode made of valve metal powder, an oxide-semiconductor capacitor is formed into two successively deposited layers by electrochemical oxidation, the first of which, the main one, is obtained in an electrolyte from a 0.02% aqueous solution of phosphoric acid and the second, on top of the first layer, additional, in particular in an electrolyte consisting of a 0.005% solution of phosphoric acid in a water-ethylene glycol mixture (ethylene glycol-water 50:50), which has a reduced ionic mobility awn that provides enhanced in the capacitor dielectric strength as a whole.

The disadvantage of the prototype is that this method, despite the increase in the strength of the dielectric oxide layer due to the use of a molding electrolyte with reduced ionic mobility, does not eliminate the sparking of the electrolyte and, therefore, does not provide niobium anodes, and therefore niobium capacitors, and an increased operating voltage , in particular 40 V.

The objective of the invention is to obtain a niobium volume-porous anode of high nominal voltage, in particular 40 V.

This problem is solved in the proposed method for manufacturing a niobium volume-porous anode during the formation of the oxide layer by electrochemical oxidation to obtain a technical result, which consists in preventing the sparking of the forming electrolyte when the required magnitude of the increased molding voltage is achieved.

To achieve this technical result, the proposed method uses a molding electrolyte with reduced ion mobility, which consists of an aqueous solution of phosphoric (orthophosphoric) acid with a significant addition of ethylene glycol as a co-solvent, and molding is carried out at a reduced room temperature, as a result, the magnitude of the sparking voltage of the molding electrolyte.

The present invention is implemented in serial production at OJSC Elecond, Sarapul.

The technological process for manufacturing volume-porous anodes of an increased operating voltage of 32–40 V contains typical operations, such as pressing anode tablets from prepared hydrogenated niobium powder, sintering niobium anode tablets, electrochemical processing (molding) of anodes in a hot electrolyte (after forming the sintered anodes and measuring electrical parameters of molded anodes), and differs in the operation of forming anodes, which includes the following steps and modes.

1. Pre-treatment of the anodes before molding to improve the subsequent impregnation with molding electrolyte, when the anodes are kept for 30 minutes in an electrolyte from a 0.01% aqueous solution of phosphoric acid (resistivity under normal conditions, that is, at normal room temperature, (NU ) 1500-1800 Ohm · cm) at a temperature of 60 ± 5 ° С.

2. The molding of the anodes, consisting of two stages (the transition to the second stage is carried out without washing), in the modes:

- Stage 1. Molding electrolyte - 5% aqueous phosphoric acid solution (resistivity in NU 36-40 Ohm · cm); molding temperature - normal room temperature; molding current per batch of anodes at the rate of 30 mA / g niobium; molding voltage 35-40 V; molding cycle duration of at least 1 hour;

- 2 stage. Molding electrolyte - a solution of orthophosphoric acid in a mixture of deionized water and ethylene glycol (ethylene glycol - 50-60 l, deionized water - 30-40 l, orthophosphoric acid - 1.5-1.7 l; resistivity in NU 400-600 Ohm · cm ); molding temperature - lowered room temperature equal to 8 ± 3 ° С; molding voltage 120-200 V; molding current per batch of anodes at a rate of 50-60 mA / g niobium until the molding voltage reaches 120 V and 10 mA / g niobium when the molding voltage is more than 120 V; molding cycle duration of at least 4 hours.

3. Anode washing: first with hot running deionized water (temperature 50-60 ° С) for 20 minutes in the washing bath, and then in the washing and drying unit (water temperature 70 ± 10 ° С, water flow rate at least 2 l / min , drying temperature 150 ± 10 ° С) in two positions for 15-20 minutes.

Data on the electrical characteristics (capacitance, tan δ, leakage current) of anodes made by the present method for niobium oxide semiconductor capacitors with an operating voltage of 40 V and the capacitors themselves are shown in the table and are indicated in connection with the technological operation after which the measurement was performed.

The data are presented for a large number of batches of capacitors, the batch volume is 150-300 pieces, one of the representatives of each dimension of the entire nominal scale with an operating voltage of 40 V, which is implemented by the proposed method.

Nominal (overall) capacitor, V × μF Technological operation Electrical characteristics of the anode Capacitance, microfarad tg δ, max.% Leakage current max. ΜA one 2 3 four 5 40 × 22 ± 20% (IV) Anode forming fifteen 75 Shaping anodes fifteen fifty Capacitor Acceptance Test 17.8-26.0 eighteen 45 40 × 15 ± 20% (III) Anode forming 6 fifty Shaping anodes 6 35 Capacitor Acceptance Test 12.2-17.8 13.5 eighteen 40 × 6.8 ± 20% (II) Anode forming 6 fifty Shaping anodes 6 35 Capacitor Acceptance Test 5.5-8.0 13.5 eighteen 40 × 3.3 ± 20% (I) Anode forming four twenty Shaping anodes four fifteen Capacitor Acceptance Test 2.7-3.9 9 9

Claims (5)

1. A method of manufacturing a niobium volume-porous anode of increased operating voltage, which consists in pressing anode tablets from prepared hydrogenated niobium powder, sintering niobium anode tablets, molding sintered anodes, forming anodes in a hot electrolyte, characterized in that the forming of the anodes is carried out in two stages and in the first stage, which lasts at least 1 h, a molding electrolyte is used, consisting of an aqueous solution of phosphoric acid, at normal room temperature, and in the second, the last lasts at least 4 hours, - a molding electrolyte, consisting of a solution of phosphoric acid in a mixture of deionized water and ethylene glycol, at a temperature of 8 ° C. 2. The method according to claim 1, characterized in that in the first stage of forming an aqueous solution of phosphoric acid is 5% and has a specific resistance measured under normal conditions, 36-40 Ohm · cm 3. The method according to claim 1, characterized in that in the first molding step, the molding voltage is set to 35-40 V, and the molding current is calculated at a rate of 30 mA / g niobium. 4. The method according to claim 1, characterized in that in the second molding step, the molding electrolyte has a resistivity measured under normal conditions of 400-600 Ohm · cm. 5. The method according to claim 4, characterized in that the molding voltage is 120-200 V, and the molding current is set at a rate of 50-60 mA / g of niobium to achieve a molding voltage of 120 V and 10 mA / g of niobium with a molding voltage of more than 120 AT.