JPS5848601A - Production of sintered parts - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy of products in the stage of producing Mo sintered products as electrodes for semiconductors by using fine powder of specific grain sizes for raw material Mo. CONSTITUTION:In the stage of producing glass-molded diodes, etc., Mo having a cofft. of thermal expansion similar to that of glass and silicon is used as metallic electrodes. Here, in order to produce said electrodes as sintered parts having high flatness and dimesnional accuracy such as electrodes for lead-mount type diodes by molding and sintering the powder of Mo, the Mo is used as fine granular powder of 20-200mu grain sizes and <=45 deg. angle of repose by a spray granulating method. The Mo powder is molded with an org. binder and is calcined to allow the org. binder to scatter; thereafter, the moldings are sintered at 1,700-1,900 deg.C, whereby the sintered products as electrodes are produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a sintered part, and more particularly to a method of manufacturing a sintered part with a dimension of 111 degrees.

Silicon rectifier diodes are widely used as elements for power supply*a circuits or control circuits of consumer electrical equipment. A lead-mounted diode is an element that has a relatively small capacitance in practical use. On the inner surface,
Usually, one plane part of the cylindrical metal electrodes of the same diameter is joined by pressure welding or brazing, and a lead wire is attached to the other plane part by pressure welding, etc., and the wafer and This is an element in which the entire electrode is hermetically sealed with a glass mold or resin mold.

In these devices, especially glass-molded diodes, heat generated due to the semiconductor resistance of the device during operation tends to accumulate inside the device. Therefore,
The metal electrode has the role of leading the heat accumulated inside the wafer to the outside, but due to the difference in heat and tensile coefficient between the element and the metal electrode, the internal stress of the element decreases. This caused thermal expansion failure.

Therefore, with the main purpose of reducing this internal stress, we developed molybdenum (Sl 7), whose thermal expansion coefficient is close to that of silicon and glass.
．． 6 x 10-' K-” (40C) Te MO for K
5,28lO-' having a coefficient of linear expansion of -1 (0 to 100IZ') was developed as an electrode material.

In order to stabilize the characteristics of the element, the molybdenum electrode used in this lead-mounted diode is designed to have a uniform potential and current density over the entire flat area of the element during operation. In addition, it is necessary that the bonding surface of the electrode with the element be a smooth surface with excellent flatness and dimensional accuracy. Also, from a manufacturing standpoint, for example, when attaching a lead hole to a flat surface of an electrode by pressure welding or the like using an automatic welding machine, the length of the electrode should have a high sense of direction in order to prevent welding defects at these connections. Dimensional accuracy is required. For example, diameter 1.5 used in lead-mounted diodes with a current capacity of 1 ampere class.
In the case of a cylindrical molybdenum electrode with a length of 111% and 2.0-
Generally flatness of 5 μI or less in the flat part and diameter ±0
．． 05■, length accuracy (kl~0.005mm dimensional accuracy is required).

Conventionally, such a molybdenum electric wire 4 is manufactured by forming and sintering molybdenum powder (usually by a powder metallurgy method), then forging and wire-drawing the obtained sintered body ingot, and cutting the resulting product. A method was used to obtain a product with a desired shape. According to this method, because of the processing such as forging and wire drawing after sintering, it is possible to obtain a product that has a dense structure close to the theoretical density and has a high dimension '1IItL. However, the processing operations and equipment after sintering are complicated, resulting in high costs and other manufacturing difficulties.

Therefore, a method has been developed to overcome these manufacturing difficulties and obtain a product that is dense and has high dimensional accuracy at the sintering stage.

For example, efforts have been made to use molybdenum powder as a raw material with a fine and uniform particle size. Conventional molybdenum powder usually has an average particle size of 3 to 10μ.
With this particle size, the resulting sintered body can be densified to some extent, but the surface shape is unstable and the flatness and dimensions of the product are unstable. There were variations in accuracy. Therefore, high flatness, such as the electrode for the 1 ampere class lead mount type diode mentioned above,
The problem is that it is difficult to obtain products that require high-dimensional MU.

Therefore, attempts have been made to obtain a dense sintered product with a stable surface shape by using even finer molybdenum powder. However, when powder with an average particle size of 10 μm or less is used, the density of the sintered body becomes even higher, but it is not always possible to maintain sufficient flatness and dimensional accuracy due to filling variations during molding. Therefore, it was not possible to obtain a sintered product with the following characteristics.

As a result of intensive research to develop a manufacturing method for sintered parts that require high knitting flatness and high dimensions, such as the electrodes for glued-mounted diodes mentioned above, the present inventor discovered that the fluidity of the powder during molding was (Angle of repose) greatly affects the above properties, and if molybdenum powder is granulated prior to molding, filling variations during molding will be reduced, and therefore a dense and stably oriented structure will be created. The present inventors have discovered that a sintered product with high flatness and high dimensional accuracy can be obtained, and have completed the present invention.

An object of the present invention is to provide a method for manufacturing sintered parts with high product dimensional accuracy.

That is, a method of manufacturing a \XMe\ sintered part of the present invention is characterized by molding and sintering molybdenum powder having an angle of repose of 45 degrees or less.

If the angle of repose of the molybdenum powder exceeds 45°, the filling of the powder into the molded product will not be stable, resulting in variations in dimensional accuracy and flatness. The angle of repose is usually measured by a method called an interpolation angle method or a multiple free deposition method. This is an orifle, such as a funnel.
In this method, the powder is gently dropped onto a plate and the inclination angle of the cone of the powder deposited in a cone is determined. Further, the molybdenum powder is preferably granulated into a granulated powder having a particle size of 20 to 200 μm. As a granulation method, spray granulation is preferable. The granulation method for keratin is to spray molybdenum powder into a slurry with an organic binder and dry it rapidly with hot air. It has particularly good liquidity. Further, the raw material for the granulated powder is preferably fine molybdenum powder with an average particle size of about 3 to 10 μm. Next, if necessary, the obtained granulated powder is sieved to a final particle size of 20.
A granulated powder of ~200 μm is obtained. In addition, considering the filling state, the particle size is preferably in the range of 30 to 150 μm.

The thus obtained granulated powder is molded to obtain a molded body of a desired shape. It is preferable that the density (green density) of the molded product obtained by this molding is 6.5 to 7.59. This is because if the density is less than 6.59/cm", the resulting sintered body will not be sufficiently dense, the strength of the compact will be insufficient, the dimensions will vary, and it will break during handling. If it exceeds 7.59/lx, gas will escape from the compact during calcination or sintering, and the density of the sintered compact will decrease.

Next, the obtained molded body is calcined to scatter the organic binder contained in the molded body. Calcination is performed in a reducing atmosphere to prevent oxidation of the surface of the molded product.

It is usually preferable to carry out the reaction in a hydrogen atmosphere. The calcination temperature and time may be %400 to 500C and about 60 minutes.

The thus calcined molded body is sintered. Furnace sintering is preferred as the sintering method. Sintering is usually carried out in a reducing atmosphere.
Preferably, this is carried out in a hydrogen atmosphere. Maku sintering temperature is
It is preferable to carry out the process at a temperature range of 1700 to 1900 C or higher. This is because if the temperature is below 1700C, the desired densification of the sintered body cannot be achieved sufficiently.

The sintering time varies depending on the sintering method, sintering temperature, etc., but is usually 3 to 7 hours.

According to the method of the present invention, a molybdenum powder with good fluidity and an angle of repose of 45° or less is used, and a uniform and fine molybdenum powder with a particle size of 3 to 10 μm is used as a starting material, and this powder is molded. Prior to this, granulation is performed to obtain a particle size of 20~
Since it is a granulated powder of 200 μm, filling variations during molding are reduced, and a sintered product containing dense and stable orientation, high flatness, and high dimensions n degrees can be obtained. In addition, it can be said that it is an industrially advantageous method because it is low cost because processing operations and equipment such as forging, wire drawing, and cutting after sintering can be omitted. Small molybdenum sintered parts used for electrodes or substrates for semiconductor devices such as silicon controlled rectifiers (thyristors),
'Excellent as a manufacturing method for products that require a small amount of filler powder during molding. It is also useful as a method for manufacturing molybdenum sintered products used as contact materials or X-ray targets.

Example Using an uninvented method, the sintered diameter was 1.5 wm and the length was 2.
．． A 0 wam cylindrical sintered part was manufactured.

Molybdenum powder with an average particle size of 3 μm is kneaded with polyvinyl alcohol (13% concentration), and the molybdenum content is about 70%.
Spray granulation was carried out using a solution (specific gravity 2.7 f/an"). Spray granulation was carried out at a spray rate of 3 no/hour. The obtained granulated powder was sieved and granulated. O granulated powder with a diameter of 20 to 200 μm was obtained.

The granulated powder thus obtained was filled into a press mold, the angle of repose and the filling weight were examined, and the molded product was molded using the press mold at a pressure of 2 tOQ/ex', and the resulting molded body was heated at room temperature in a hydrogen atmosphere furnace. The molded body was calcined for 8 hours from 1000C to 1000C to scatter the organic binder, and then this molded body was sintered in a urea atmosphere at 1800G for 15 hours by furnace sintering.

As a comparative example, molybdenum powder with particles of vk 3 to 10 μm was used, without being granulated, and molded and sintered under the same conditions as the method of the present invention to obtain sintered parts of the same shape. The filling weight and the angle of repose of the molybdenum powder during molding were measured, and the results are shown in the table.

The sintering accuracy, dimensional accuracy, and flatness of the 10 molybdenum small sintered parts according to the present invention and the 10 comparative examples thus obtained were measured. Results are shown in Table ○ As is clear from the above results, the small molybdenum sintered parts according to the present invention have less variation in filling weight and higher product dimensional accuracy than conventional examples.

Claims (1)

[Claims] 1. A method for manufacturing a sintered part, which comprises molding and sintering molybdenum powder having a repose angle of 45° or less. 2. Molybdenum powder is granulated into grains i20-20
92. The method of manufacturing a sintered part according to claim 91, wherein the powder is 0μ. 5. Claim # where the molybdenum powder has a particle size of 30 to 150μ! 2. A method for manufacturing a sintered part according to item 2. 4. The granulation is performed by spray granulation according to Claim 1
2. Method for manufacturing sintered parts described in Section 1. 5. The method for manufacturing a sintered part according to claim 1, wherein the sintered part is an electrode for a semiconductor element.