JPH064886B2 - Cream solder manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing cream solder.

[Conventional technology]

Conventionally, in order to produce cream solder (mixed product of solder particles and flux), molten solder is made to flow out from pores, and an inert gas jet is made to act on it to cause it to scatter and granulate. While flying in an inert gas, this is cooled and solidified to obtain a solder particle, and this solder particle is mixed with a flux.

In this method of manufacturing cream solder, the granulated molten solder is cooled and solidified by contact with the inert gas, and the slow cooling rate reduces the flight time of the granular molten solder in the inert gas. Therefore, there is a disadvantage that a large-sized inert gas tank is required, the manufacturing apparatus becomes large-scale, and the manufacturing speed is slow.

By the way, the present inventors have advanced the practical application of the rotary water spraying method as a method for producing metal particles, and have investigated Fe-based, Cu
Significant results have been obtained for Al-based and Al-based alloys.

In this rotary water spray method, a cooling liquid is put in a rotating drum, the rotating drum is rotated to form the above cooling liquid in layers by centrifugal force, and a molten metal is continuously injected into this cooling liquid layer by a nozzle, and this injection is performed. The continuous flow is divided by shearing by the rotating cooling liquid surface, and cooling is performed while the divided particles settle in the cooling liquid.
This is a method of solidifying to obtain metal particles, and since it is cooled with a liquid, there are advantages that cooling and solidification can be performed at high speed, the manufacturing speed is high, and the apparatus can be made compact.

In the solidification process of the fragmentation of the jet continuous flow in this rotary water atomization method, the form when the jet continuous flow of molten metal is divided in contact with the rotating cooling liquid layer is amorphous, and this amorphous fluid is the surface It is cooled and solidified while being spheroidized by the tension.

[Problems to be Solved by the Invention]

However, when solder granules are manufactured by the rotary water spray method, depending on the cooling liquid used, soldering with cream solder using the solder causes soldering defects such as poor wetting.

However, even if the manufactured solder granules are once washed with water and then mixed with flux, it is difficult to completely wash them with water, and soldering of electronic parts to circuit boards where soldering failure rate is a problem in the order of ppm It is a problem to use it for attachment.

An object of the present invention is to produce a cream solder which allows easy production of a cream solder which enables defect-free soldering by mixing the solder granules obtained by the rotary water spray method with the flux as they are without washing them. To provide a method.

[Means for Solving the Problems]

The manufacturing method of the cream solder of the present invention, as a cooling liquid in the rotating drum, put the fluid paraffin, the rotating drum is rotated to form the above cooling liquid in layers by centrifugal force, the molten solder from the nozzle this cooling liquid. The solder particles are sprayed onto the layer to obtain the solder particles, and the solder particles are mixed with the flux without cleaning.

〔Example〕

 The present invention will be described below with reference to the drawings.

FIG. 1 shows an apparatus used in the rotary water spray method. In FIG. 1, reference numeral 1 is a drum, which has an edge plate 2 at its upper end, and is rotated at high speed by a motor 3 via a belt 4.
Reference numeral 5 denotes a nozzle, which continuously ejects molten metal under pressure by gas pressure.

When producing, for example, a metal powder by the rotary water spray method, first, a cooling medium is put in the drum and the drum is rotated at a high speed. Thus, when the cooling medium receives a centrifugal force according to the specific gravity, the peripheral speed, etc. and the centrifugal force becomes considerably larger than the gravity acting on the cooling medium, as shown in FIG. Are formed in layers using the edge plate 2 as a weir. The molten metal is then jetted in a continuous stream from the nozzle toward the layer of cooling medium. Therefore, the layer surface is traveling at the peripheral speed accompanying the high speed rotation of the drum, and since this speed is higher than the flow velocity of the continuous flow of the molten metal, a shear force acts on the molten metal flow, and this shear force is When it reaches a certain value, the molten metal is fragmented (fragmented), and the fragmented particles are cooled and solidified while being spheroidized while being spheroidized by the interfacial tension acting on the interface between the molten metal of the fragmented particles and the cooling liquid. To be done. The shear force acting on the molten metal flow reaches the above-mentioned constant value when the contact amount of the molten metal with respect to the cooling medium reaches a constant value. Done.

In the method for producing a cream solder of the present invention, a solder granule is obtained by the above-mentioned rotary water spraying method using a fluid paraffin as a cooling liquid, and the flux is applied to the solder granule without cleaning the solder granule. To produce cream solder, and the injection speed of the molten solder from the nozzle is usually 6 to 8 and preferably 7 m with a nozzle diameter of 0.5 mm.
/ S, the injection temperature is usually 120 ~ 200 ℃,
The cooling liquid peripheral speed is set to 30 to 60 m / s, and the particle size of the obtained solder particles is usually 20 to 80 μm. Examples of the present invention will be described in comparison with comparative examples. The lead alloy used is 55.8 wt% Bi-44.2 wt% Pb.

Example 1 Liquid paraffin was used as the cooling liquid. This cooling liquid was put into a rotating drum having an inner diameter of 500 mm, and the drum was rotated so that the peripheral speed of the inner surface of the cooling layer formed by centrifugal force was 40 m / sec. Under such rotation, the above Bi-Pb alloy was sprayed onto the coolant surface at a spraying temperature of 200 ° C. and a spraying speed of 7 m / sec from a graphite nozzle having a diameter of 0.5 mm. The obtained granules were almost spherical as shown in FIG. 2 (240 times micrograph), and the particle size was about 30 μm.

Comparative Example 1 The procedure of Example 1 was repeated except that water was used as the cooling liquid. The obtained granules were flaky as shown in Fig. 3A (240 times photograph).

Comparative Example 2 The procedure of Example 1 was repeated except that a 1% aqueous solution of polyethylene glycol 4000 was used as the cooling liquid. The obtained granules are the third
It was in the form of flakes as shown in Fig. B (240 times magnification photograph).

Comparative Example 3 The procedure of Example 1 was repeated except that a 2% aqueous solution of polyethylene glycol 2000 was used as the cooling liquid. The obtained granules are the third
It was in the form of flakes as shown in FIG. C (240 times photograph).

With respect to the example product and the comparative example product obtained as described above, cream solder was prepared by mixing 90 parts by weight of solder particles and 10 parts by weight of flux (rosin-based) without cleaning the solder particles ( Viscosity is 250,000-300,000 cps).

When a soldering test was performed using each cream solder, no poor wetting was observed with the cream solder of the example product, but 40 to 6 with the cream solder of the comparative example product.
Insufficient wetting was recognized at a defect occurrence rate of 0%.

〔The invention's effect〕

In the method for producing the cream solder of the present invention, the solder granules are obtained by the rotary water spraying method using the fluid paraffin as the cooling liquid, and the solder granules are sufficiently spherical, and the surface is oxidized by comparison with flakes. The amount of oxide is small. In addition, the paraffin used as the cooling liquid is established as a flux fluidity adjusting agent, does not adversely affect soldering, and even if the solder granules adhere to the paraffins, the solder granules The cream solder in which the and the flux are mixed does not cause a soldering defect.

Therefore, according to the present invention, a reliable cream solder can be easily manufactured by mixing the solder granules obtained by the rotary water spray method with the flux as they are without washing them with water.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a rotary water spraying device used in the present invention, and FIG. 2 is an enlarged photograph (240 times) showing a particle structure of a lead alloy produced by the present invention, FIGS. 3A and 3B. In addition, FIG. 3C is an enlarged photograph (240 times) showing the particle structure of the lead alloy in the comparative example. In the figure, 1 is a drum and 5 is a nozzle.

Claims (1)

[Claims] 1. A fluid paraffin is put in a rotating drum as a cooling liquid, the rotating drum is rotated to form the cooling liquid into a layer by centrifugal force, and molten solder is sprayed from the nozzle onto the cooling liquid layer. A method for producing cream solder, comprising obtaining a solder granule and mixing the solder granule with a flux without cleaning.