JP2925641B2 - Powder solder manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing powder solder.

<Prior Art> Powder solder is mainly kneaded with flux and used as cream solder, and cream solder is mainly used for soldering by a reflow method. Reflow soldering is used for soldering electronic components to a circuit board.A solder paste is printed on a portion of the circuit board where soldering is to be performed by a masking method, and the printed portion is soldered by the adhesive force of the cream solder. The components are temporarily fixed, and then the printed cream solder is melted through a heating furnace to perform soldering.

By the way, recently, as a method for producing metal powder, a cooling liquid is put into a container, and under high-speed rotation of the container, the cooling liquid is formed into a wall shape by a rotational centrifugal force, and the molten metal is formed on a rotating wall surface of the liquid from a nozzle. A method has been proposed in which a continuous flow of the molten metal is injected by a continuous flow, and the continuous flow of the molten metal is divided by a shear force at the time of liquid level contact, and the separated particles are cooled and solidified. The particle size can be adjusted by controlling the difference between the rotation speed of the molten metal and the speed of the continuous flow of the molten metal, the distance between the nozzle and the liquid wall, and the like.

<Problem to be Solved> By the way, the present inventors manufactured a solder powder by this method of manufacturing a metal powder, and performed soldering by a reflow method using a cream solder using the solder powder. The generation of ball solder was remarkable. That is, when the cream solder is heated, the powder solder melts and agglomerates into one lump, and the surface is covered with a flux molten layer. Significant dispersion of small solder poles was observed. This is a very non-spherical shape when the molten solder injected by the continuous flow from the nozzle comes into contact with the centrifugal forming wall during high-speed rotation of the cooling liquid (usually water) and is cut by shearing force. Since the surface tension of the molten solder is small, this non-spherical shape is solidified without being sufficiently sphericalized by the surface tension. Therefore, the shape of the powder solder has a ratio of the vertical axis length to the horizontal axis length (aspect ratio). Ratio), the surface area per unit weight, and therefore the amount of oxide film is large, the oxides cannot be completely dissolved by the flux, and the remaining oxides are dispersed in small particles in the molten layer of the flux. It can be inferred that this is the result.

In the method for producing metal powder by the above-described rotary centrifugal method, a vapor layer is formed around solidifying metal particles moving in a coolant, and the vapor layer acts as a heat insulating layer, Since the solidification of the powder is hindered, the formation of the vapor layer is regarded as an unqualified matter of the coolant. In addition, when a special cooling liquid, for example, a salt melted by heating is used as a cooling liquid for a high melting point metal, the cooling liquid may be heated and used, which is one of the control parameters described above. The purpose is to adjust the clay of the cooling liquid, and is not intended to heat to a temperature at which the solidification of the molten metal particles is prevented in relation to the melting point of the metal.

However, in the present inventors, when manufacturing the solder powder using the method for manufacturing a metal powder by the above-described rotary centrifugal force method, it is necessary to use the above-described cooling liquid conditions which are conventionally improper. I knew that powder solder for cream solder free of solder balls could be obtained.

An object of the present invention is to produce a powder solder for cream solder without generating solder balls by a rotary centrifugal force method.

<Means for Solving the Problems> In the method for producing a powdered solder according to the first invention, a cooling liquid having a vapor pressure higher than water at normal temperature is put into a container, and the liquid is rotated while the container is rotating. The molten solder is formed into a wall shape by centrifugal force, and the molten solder is sprayed from the nozzle onto the above-mentioned wall surface of the cooling liquid, and the molten solder is divided by the shearing force at the time of liquid surface contact, and a vapor layer of the liquid is formed around the divided particles. And forming the separated particles into a sphere under cooling, and the method for producing a powdered solder according to the second aspect of the present invention comprises: placing a cooling liquid in a container; and rotating the container. under,
The liquid is formed into a wall shape by a rotating centrifugal force, the liquid is kept at a temperature of 20 to 60% of the melting point of the solder, and the molten solder is jetted from a nozzle onto the wall surface of the liquid to keep the temperature. The molten solder is divided by a shearing force, and solidified while the spheroidization of the divided powder proceeds in a heat retaining liquid.

<Function> In the first invention, the separated particles generated by the contact with the cooling liquid are surrounded by the vapor layer of the liquid and are difficult to be cooled. The solidification is completed after the spheroidization has sufficiently progressed. Also in the second invention, the same effect as described above is achieved because the temperature of the cooling liquid is high and the divided particles are not easily cooled.

In particular, in the first invention, the space from the nozzle to the rotating wall surface of the cooling liquid is filled with the vapor of the cooling liquid, and oxidation in that space can be prevented. There is no substance, and spheroidization due to surface tension proceeds very remarkably.

In the above second invention, the reason why the heat retaining temperature of the cooling liquid is limited to the temperature of 20 to 60% of the melting point of the solder is that when the temperature is 20% or less, it is difficult to achieve the above-mentioned effect satisfactorily. This is because the particles agglomerate and large aggregates are easily generated.

In the above description, the term "spherical" refers to those having a ratio of the vertical axis length to the horizontal axis length (aspect ratio) of 1.5 or less, and includes a polyhedral spindle shape.

<Description of Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

The drawings show a manufacturing apparatus used in the present invention.

In the figure, reference numeral 1 denotes a container, which is open at the top, and provided with a horizontal wall 11 at the opening. Reference numeral 2 denotes a rotating shaft for rotating the container 1 at a high speed, 3 denotes a chamber, and 4 denotes a nozzle. 5 is a heater for keeping warm. Numeral 6 denotes a cooling liquid placed in the container 1, which is formed into a wall shape by centrifugal force under high-speed rotation of the container 1. The nozzle 4 is provided with a heater. A predetermined amount of solder is put into the nozzle 4, the solder is melted by the heater, and the molten solder is jetted toward the wall surface of the cooling liquid 6 by the gas pressure 7 in a continuous flow. The rotation speed of the wall surface of the cooling liquid 6 is set to be higher than the injection speed of the molten solder. Therefore, when the continuous flow of the molten solder contacts the rotating wall surface of the cooling liquid, a shear force acts on the continuous flow, It is divided into granules. When all of the molten solder in the nozzle 4 has been ejected, the solder is put into the nozzle again, and the above operation is performed again. The amount of solder used in this one operation is significantly smaller than the amount of the cooling liquid, and the rise in temperature of the cooling liquid due to the injection of the molten solder into the cooling liquid can be ignored.

Hereinafter, embodiments of each invention will be described. In any of the embodiments, 63Sn-37Pb was used for the solder, the melting temperature of the solder was 200 to 300 ° C., the injection pressure of the molten solder was 1 to 5 kg / cm ^2, and the rotation speed of the cooling liquid (in Peripheral speed) 5
It was 900-14000 cm / sec.

Example of First Invention 2-propanol having a boiling point of 25 ° C. was used as a cooling liquid. When the molten solder injected from the nozzle came into contact with 2-propanol, 2-propanol was vaporized, and the inside of the chamber was filled with the gas phase of 2-propanol. When the continuous flow of the molten solder from the nozzle comes in contact with 2-propanol, the continuous flow is divided by a shear force,
Since the divided granules are surrounded by the vapor layer of 2-propanol, the cooling of the divided granules is removed, and the spheroidization of the divided granules is sufficiently advanced. The particle size of the obtained solder powder was 1 to 100 μm, and the average was 1.1 when the aspect ratio was measured by extraction inspection. The oxygen content of the solder powder was about 100 PPm / g.

Example of the Second Invention Methylhydroabietate (boiling point: about 360 ° C.) kept at 100 ° C. was used as a cooling liquid. The difference between the temperature of the cooling liquid and the temperature of the molten solder is as small as about 70 ° C. as compared with the case of a normal cooling liquid temperature of 30 ° C., and the cooling of the separated molten solder particles can be guaranteed. As in the case, the spheroidization of the solder particles was sufficiently promoted. Also in this case, the aspect ratio of the solder particles was 1.1 on average. However, the oxygen content was about 100 PPm per 0.3 g, which was higher than in the case of the first invention.

Comparative Example Dipropylene glycol at room temperature was used as a cooling liquid.
Other conditions were the same as those in the above example. All of the obtained solder powders were in the form of flakes, and the oxygen content was about 250 PPm per 0.3 g.

Using the powder solder obtained in the above examples and comparative examples,
Create cream solder with flux content of 10% by weight,
When the presence or absence of generation of ball solder was tested, when the first invention product and the second invention product were used, generation of ball solder was not observed, but generation of ball solder was remarkable in the comparative example product. . The flux used was 60% by weight of WW rosin, 4% by weight of caster wax, 1% by weight of cyclohexylamine HBr, and the balance of butyl carbitol.

<Effects of the Invention> As described above, according to the method for producing a powder solder according to the present invention, powder solder that can eliminate the occurrence of ball solder even when used for cream solder can be produced by a rotary centrifugal method, It becomes possible to produce powder solder for high quality cream solder.

[Brief description of the drawings]

The drawing is an explanatory view showing an apparatus for manufacturing a powder solder used in the present invention. 1 ... container, 4 ... nozzle, 6 ... cooling liquid.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 35/40

Claims (2)

(57) [Claims] 1. A cooling liquid having a vapor pressure higher than that of water at room temperature is put into a container, and the liquid is formed into a wall shape by rotating centrifugal force while rotating the container, and the molten solder is cooled from a nozzle. Injecting the liquid onto the wall surface, cutting the molten solder by the shearing force at the time of liquid surface contact, forming a vapor layer of the liquid around the separated particles, and spheroidizing the separated particles under cooling. A method for producing a powdered solder, comprising: 2. A cooling liquid is placed in a container, and the liquid is formed into a wall shape by rotating centrifugal force while rotating the container.
The liquid is kept at a temperature of 20 to 60% of the melting point of the solder, and the molten solder is jetted from a nozzle onto the wall surface of the above-mentioned liquid for keeping the liquid. A method for producing a powder solder, comprising solidifying a powder while making the powder spheroidized.