JP2007237269A - Dross prevention method of molten solder, and flow soldering apparatus or melting furnace for producing solder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective solution since prevention of dross generated from a molten solder in a melting furnace or a flow soldering apparatus is an important problem. <P>SOLUTION: In a dross prevention method of a molten solder, a large number of ceramic members fabricated into a generally spherical shape are floated on the liquid surface of the molten solder so as to cover the entire surface or parts of the liquid surface. According to this dross prevention method, in the melting furnace, for example, when the ceramic members are floated on the entire liquid surface of the molten solder to cover the entire surface, the generation of dross is reduced to an amount (5-10% of the conventional amount) compared to a case when the ceramic members are not floated thereon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for suppressing dross, which is an oxide of molten solder, and a flow soldering apparatus for applying molten solder to a surface to be soldered on a circuit board to perform soldering or a melting furnace for manufacturing molten solder.

In the melting furnace and flow soldering apparatus, suppression of dross generated from molten solder is a very important problem.
For example, in a melting furnace for producing molten solder, the production efficiency of the molten solder is reduced by the amount removed by dross, so that generation of dross is not preferable.
In addition, when the amount of dross generated is large even in the flow soldering apparatus, the amount of molten solder consumed increases, and the dross may adhere to the surface to be soldered of the circuit board and reduce the soldering quality. Yes (see Patent Document 1 [0006] to [0008]). On the other hand, in the flow soldering device, when soldering circuit boards with exposed copper parts, electronic component leads, etc., copper may elute from these copper products and the copper concentration of the molten solder may increase. In contrast to such an increase in the copper concentration of the molten solder, there is a positive aspect that moderate dross takes out copper and suppresses the increase in copper concentration (see Patent Document 2 [0008]).
JP 2002-361406 A JP 2005-294624 A

  As described above, suppression of dross generated from molten solder is an extremely important problem in melting furnaces and flow soldering equipment, but no effective solution has been found so far, and the industry still has dross. Suppression is an important issue.

A dross of molten solder in which a large number of ceramic bodies formed into a spherical shape or a substantially spherical shape are floated on the liquid surface of the molten solder and the entire surface thereof is covered or a part of the liquid surface is covered. Provide a suppression method.

  According to a second aspect of the present invention, there is provided the method for suppressing dross of molten solder according to the first aspect, wherein the ceramic body has a surface polished after firing.

Further, as described in claim 3, to provide at least a surface formed by a black or nearly black claims 1 or 2 fused solder method dross suppression description of the ceramic body.

Further, as described in claim 4, a flow soldering apparatus comprising: a solder tank in which molten solder is placed; and an ejection member that ejects molten solder in the solder tank above the liquid surface, Provided is a flow soldering apparatus in which a large number of ceramic bodies formed in a spherical shape or a substantially spherical shape are floated on a liquid surface of molten solder so as to cover the entire liquid surface or a part of the liquid surface.

  According to a fifth aspect of the present invention, there is provided the flow soldering apparatus according to the fourth aspect, wherein the ceramic body has a surface polished after firing.

Further, as described in claim 6, there is provided the flow soldering apparatus according to claim 4 or 5, wherein at least the surface of the ceramic body is black or substantially black.

Further, as described in claim 7, the liquid surface of the molten solder in the furnace body floats a large number of ceramic bodies formed in a spherical shape or a substantially spherical shape to cover the entire liquid surface or a part of the liquid surface. A melting furnace for manufacturing solder is provided.

  Further, as described in claim 8, the ceramic body provides a melting furnace for manufacturing solder according to claim 7, wherein the surface of the ceramic body is polished after firing.

The solder melting furnace according to claim 7 or 8, wherein at least the surface of the ceramic body is black or substantially black as described in claim 9.

If a ceramic body formed and fired into a spherical shape or a substantially spherical shape is floated on the surface of the molten solder so as to cover the entire surface, the amount of dross generated is larger than when the ceramic body is not floated (the conventional amount of 5). To 10%).

  Needless to say, since dross is an oxide of molten solder, generation of dross can be suppressed by covering the liquid surface with a lid that fits the upper surface opening of the furnace body and solder bath described later and shutting off the air. However, in the case of a spherical ceramic body, there is inevitably a gap between adjacent ones, so even if it is floated and spread over the liquid surface, air is not shut off. You should not think that dross can be suppressed even if the body floats on the surface of the molten solder.

  However, as a result of actually observing the generation of dross by floating a substantially spherical ceramic body on the surface of the molten solder, an unexpected result of drastic suppression was obtained. The exact mechanism is not clear at this stage, but it is estimated that the air heated by the heat of the molten solder rises and cool new air (air that oxidizes the molten solder) flows from the surroundings Then, in the present invention, the phenomenon occurring on the liquid surface of the molten solder occurs above the ceramic body floating on the liquid surface, and as a result, new air that becomes an oxidation factor reaches the gap between the ceramic body and the ceramic body. It is thought that there is no.

  Therefore, the coverage of the molten solder liquid surface by the ceramic body can be freely set by the number of ceramic bodies to be floated. Of course, the larger the cover ratio covering the liquid surface, the smaller the amount of dross generated. Therefore, when focusing on dross suppression, it is sufficient to cover the entire liquid surface of the molten solder with a ceramic body. On the other hand, if it is desired to suppress the increase in copper concentration by generating appropriate dross, the number of ceramic bodies is sufficient. It is sufficient to reduce the amount of the liquid level so that a part of the liquid level is exposed to the outside. Since the amount of dross generated varies greatly depending on the conditions such as the temperature of the molten solder, the optimal coverage by the ceramic body is the number of ceramic bodies while observing the state of dross generation according to the situation at each site. It may be obtained by increasing or decreasing.

As described above, the present invention is to suppress dross by floating a spherical or substantially spherical ceramic body on the liquid surface of the molten solder.
(A) As a characteristic of ceramic, it has corrosion resistance against molten solder.
(B) As a characteristic of the ceramic, the molten solder does not easily wet, that is, has a property that it is difficult to adhere.
(C) Because more than half of the height comes out above the liquid level and dross due to the specific gravity with the molten solder, it can be easily scooped up and easily separated from the dross and molten solder.
(D) Due to the spherical shape or the substantially spherical shape , the state of sticking between adjacent ones in a state of floating on the liquid surface is constant and stable, and sticks depending on the respective directions in the state of floating like non-spherical bodies. There is no instability that varies.
(E) There are no protrusions or corners that are easily chipped due to being spherical or substantially spherical , and therefore there is little risk of chipping during use even if the material is ceramic.
Therefore, the spherical or substantially spherical ceramic body is optimal as a dross suppression material for molten solder in shape and material.

The inventions of the second, fifth, and eighth aspects are such that the surface of the ceramic body is polished after firing, and by doing so, it becomes difficult for the molten solder to be further wetted. Further, if at least the surface of the ceramic body is made black or substantially black as in claims 3, 6 and 9, the collection of ceramic bodies exhibits a visual effect such as a dark background, and the metallic color Easily understand the occurrence of molten solder and dross. Incidentally, the "substantially black" in the ceramic body, including those classified into almost black lines on social norms and achieve the visual effect.

  Embodiments of the present invention will be described below with reference to FIGS. 1 is a front view of a ceramic body, FIG. 2 is a longitudinal sectional view of a melting furnace for producing solder, and FIG. 3 is a longitudinal sectional view showing an outline of a flow soldering apparatus.

[Ceramic body]
FIG. 1 is a front view of a ceramic body 1 to be used. This ceramic body 1 is a ceramic having excellent heat resistance such as silica-based, lithia-based, and alumina-based, and is formed by firing an appropriate raw material into a spherical shape. The ceramic constituting the ceramic body 1 includes heat resistant glass.

The diameter of the ceramic body 1 should just be at least 5 mm or more, Preferably a diameter of 10 mm-50 mm is good. If the diameter of the ceramic body 1 is smaller than 5 mm, it is not easy to separate the ceramic body 1 and the dross, and it may be difficult to repeatedly use the ceramic body 1 or to regenerate the dross.
The spherical shape of the ceramic body 1 is preferably as accurate as possible. However, if the ceramic body 1 rolls even if there is some distortion, a necessary effect is exhibited.

  The ceramic body 1 is substantially black, and is polished and finished after firing. The degree of polishing may be such that the surface is glossy, but the adhesion prevention effect of the molten solder 2 can be enhanced as the degree of polishing is increased to approach the mirror surface state.

[Smelting furnace for solder production]
Next, the case where the molten solder 2 is manufactured will be described with reference to FIG.
FIG. 2 is a cross-sectional view showing a melting furnace 3 for manufacturing the molten solder 2. As shown in the figure, the melting furnace 3 for solder manufacture includes a heat-resistant furnace body 4 and its furnace body 4. It is comprised by the stirring means 5 provided in the upper part. The main material of the furnace body 4 is stainless steel at present. However, since there is a risk of corrosion with the lead-free solder, it is preferable that the furnace body 4 is formed of a ceramic having excellent heat resistance similar to the ceramic body 1.

  On the other hand, the stirring means 5 is such that the electric motor 5b is fixed to the fixed support frame 5a, and the stirring member 5c is rotated by the electric motor 5b. The stirring member 5c is also used to enhance the corrosion resistance. It is good to form with the ceramic excellent in heat resistance similar to the ceramic body 1.

  Then, a molten metal such as tin, silver, copper, or the like, which is a raw material for solder, is charged into the furnace body 4 at a predetermined rate, and the furnace body 4 is heated with a heat source (not shown). In this state, a sufficient number of ceramic bodies 1 are placed in the furnace body 4 to cover all of the liquid level, and the molten solder 2 is stirred by the stirring means 5. After the stirring is completed, only the ceramic body 1 is scooped up with a scooping tool having a small hole (perforated handle pattern), and the molten solder 2 is extracted from a discharge port (not shown) provided at the bottom of the furnace body 4.

[Verification test]
A ceramic body 1 of alumina ceramic (Al ₂ O ₃ + SiO ₂ baked at 1200 ° C. to 1300 ° C.) having a spherical shape of about 15 mm in diameter is floated on the entire liquid surface of the furnace body 4 having a diameter of about 1 m, and the stirring means 5 is left as it is. The molten solder 2 was manufactured by stirring the above. As a result, the amount of dross generated drastically decreased to 5 to 10% compared to the conventional case in which the ceramic body 1 was not used. In addition, the fuel efficiency is greatly improved by the heat retaining effect of the ceramic body 1.
The ceramic body 1 floating on the liquid surface of the molten solder 2 was separated and recovered from the molten solder 2 with a scooping tool having a small hole and repeatedly used.

[Flow soldering equipment]
Next, a soldering method by the flow soldering apparatus 10 will be described with reference to FIG.
FIG. 3 is a longitudinal sectional view showing an outline of the flow soldering apparatus 10. As shown in FIG. 3, the flow soldering apparatus 10 includes a heat-resistant solder bath 11 and an ejection member provided inside the solder bath 11. 12 and a conveyor 14 that conveys a circuit board 13 that is an object to be soldered.

  The ejection member 12 includes a pressure feeding chamber 12a for sucking the molten solder 2, an ejection nozzle 12b for ejecting the molten solder 2 above the liquid surface of the molten solder 2 at the upper end of the pressure feeding chamber 12a, and a pressure feeding chamber 12a. And a rotating blade 12c for sucking the molten solder 2 and ejecting the molten solder 2 from the ejection nozzle 12b, and an electric motor 12d for rotating the rotating blade 12c.

  The molten solder 2 in the solder bath 11 of the flow soldering apparatus 10 is maintained at 250 ° C. to 350 ° C. by a heater (not shown), and is sucked into the pressure feeding chamber 12a by the rotation of the rotary blade 12c and ejected nozzle 12b. And then returns to the solder tank 11 along the outer surface of the ejection nozzle 12b. Then, the circuit board 13 is moved so as to be in contact with the top of the molten solder 2 blown from the ejection nozzle 12b, so that the molten solder 2 is applied to the surface to be soldered of the circuit board 13. In the figure, reference numeral 13 a denotes an electronic component provided on the circuit board 13.

  Accordingly, in the present invention, the circuit board 13 is soldered in a state where a large number of ceramic bodies 1 are floated on the liquid surface of the molten solder 2 in the solder bath 11. The amount of the ceramic body 1 illustrated as an embodiment is such that there is room for the molten solder 2 to flow into the liquid surface along the outer surface of the ejection nozzle 12b. In addition, when it is desired to increase the amount of dross generated for the purpose of adjusting the copper concentration as described above, the number of ceramic bodies 1 may be reduced to increase the exposed area of the liquid surface.

[Verification test]
A ceramic body 1 made of alumina ceramic (Al ₂ O ₃ + SiO ₂ baked at 1200 ° C. to 1300 ° C.) having a spherical shape with a diameter of about 15 mm is floated on the liquid surface of the solder bath 11 to the same extent as in FIG. The circuit board 13 was soldered continuously. As a result, the amount of dross generated drastically decreased to 50% or less compared to the conventional case where the ceramic body 1 is not used. In addition, the fuel efficiency is greatly improved by the heat retaining effect of the ceramic body 1.

The embodiments of the present invention have been described above, but the present invention is of course not limited to the above embodiments. For example, in the embodiment, the ceramic body 1 is floated in a single layer, but a multilayer structure in which two or three layers are stacked may be used. Thereby, dross can be further suppressed and the heat retaining property is also improved.
In the embodiment, the color of the ceramic body 1 is substantially black. However, other colors may be used.
Moreover, although the surface of the ceramic body 1 was grind | polished in embodiment, a temporary effect is acquired even with the unpolished ceramic body 1. FIG. Further, it is possible to make the molten solder 2 hardly wet by applying a glaze to the surface of the ceramic body 1.
Further, the melting furnace 3 and the flow soldering apparatus 10 shown in the embodiment are merely examples, and it is needless to say that the present invention is not limited to the illustrated configuration.
Further, the present invention relates to a method for suppressing dross of molten solder, but can also be applied as a method of suppressing dross of molten lead or other molten metal. In that case, molten lead or other molten metal enters the furnace body 4 of the melting furnace 3 of FIG. 2, and the ceramic body 1 floats on the liquid surface.
Also, as an application of the present invention, the ceramic body 1 can be formed in a plate shape and floated on the liquid surface to suppress dross.

It is a front view of a ceramic body. It is a longitudinal cross-sectional view of the melting furnace for solder manufacture. It is a longitudinal cross-sectional view which shows the outline of a flow soldering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ceramic body 2 ... Molten solder 3 ... Melting furnace for solder manufacture 4 ... Furnace main body 10 ... Flow soldering apparatus 11 ... Solder tank 12 ... Ejection member

Claims (9)

  A method for suppressing dross of molten solder, characterized in that a large number of ceramic bodies formed into a substantially spherical shape are floated on the liquid surface of the molten solder so as to cover the entire surface or a part of the liquid surface.   The method for suppressing dross of molten solder according to claim 1, wherein the ceramic body has a surface polished after firing.   3. The method for suppressing dross of molten solder according to claim 1, wherein at least the surface of the ceramic body is substantially black. A flow soldering apparatus comprising: a solder tank for containing molten solder; and an ejection member for ejecting molten solder in the solder tank above the liquid surface,
A flow soldering apparatus, wherein a large number of ceramic bodies formed in a substantially spherical shape are floated on a liquid surface of the molten solder so as to cover the entire liquid surface or a part of the liquid surface.   The flow soldering apparatus according to claim 4, wherein the ceramic body has a surface polished after firing.   6. The flow soldering apparatus according to claim 4, wherein at least a surface of the ceramic body is substantially black.   For solder manufacturing, characterized in that a large number of ceramic bodies formed in a substantially spherical shape are floated on the liquid surface of the molten solder in the furnace body to cover the entire liquid surface or a part of the liquid surface. melting furnace.   8. The melting furnace for manufacturing solder according to claim 7, wherein the ceramic body has a surface polished after firing.   9. The melting furnace for manufacturing solder according to claim 7, wherein at least the surface of the ceramic body is substantially black.

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