JPS6149370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing solder containing small amounts of gas and impurities, which is used for connecting communication equipment, electronic equipment, semiconductors, integrated circuits, etc.

In general, many solders and solder parts are used in the connection process of communication equipment and electronic equipment, but these connections can cause problems in connection reliability, such as a decrease in connection strength and deterioration of electrical and thermal characteristics. Stability is often cited as a problem. Particularly in the precision connections of recent electronic devices, such as small electronic devices such as ICs and LSIs, the above drawbacks affect the lifespan of the entire device, so we need highly reliable connections that eliminate these drawbacks. Increasingly, there is a demand for soldering and soldering methods to obtain the desired results.

The inventor conducted various studies to solve this problem and found the following.

One of the causes of the deterioration of the solder connection surface is considered to be voids generated on the connection surface during soldering. The voids that occur during this connection are thought to be caused by (a) decomposed gas generated from the soldering flux, and (b) gases and nonmetallic inclusions contained in the solder itself. However, while (a) the decomposed gas from the flux can be easily solved by improving the soldering method, the gas contained in the solder itself (b) cannot be removed by improving the soldering method. This is extremely difficult and must be removed during the solder manufacturing process.

However, conventional solder manufacturing methods generally use Sn
After mixing the ingots and Pb ingots in their respective composition ratios, they are melted in the atmosphere with heavy oil or city gas using a cast iron pot at a melting temperature of approximately 400℃ to 500℃, and then stirred to reach the casting temperature. The method used is to cast it into an iron mold at about 250°C to 350°C and rapidly cool it. This method not only does not remove impurities (nonmetallic inclusions) and dissolved gases contained in the metal, but also absorbs gases from the atmosphere due to the high melting temperature. For this reason, solder manufactured using conventional methods contains a large amount of gas and nonmetallic inclusions, which is thought to be a factor in reducing the reliability of connection surfaces using such solder.

Based on the above considerations, the inventors have come to the conclusion that the most effective way to solve the above problems is to subject molten solder to a reduced pressure treatment during solder production.

A conceivable method for this depressurization treatment is to accommodate a ladle containing molten solder in a depressurization chamber, reduce the pressure in the depressurization chamber, and depressurize the molten metal in the ladle. However, since this method uses a closed device, the molten metal is not stirred, and therefore the only way to promote the pressure reduction effect is to rely on high temperature and high vacuum. However, solder has a low melting point, and if the temperature is too high, lead etc. will vaporize, so the maximum temperature is 450°C to 500°C. Further, in order to achieve a high vacuum, it is desirable that the volume of the reduced-pressure processing chamber be small, but in this case, the processing amount cannot be increased. On the other hand, if the volume is increased, not only will the apparatus become expensive, but it will also be difficult to maintain the airtightness of the vacuum processing chamber, which is not economical. As described above, in this method, the molten solder is not stirred and the amount of solder processed at one time is small, so the overall processing time is long, for example, it takes nearly 200 minutes to process 100 kg of solder. In addition, mass production requires increasing the number of devices or repeating the process, and although this method is possible experimentally, it is not practical as a solder manufacturing method in terms of production cost and efficiency.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing solder that enables the production of high-quality solder in large quantities and at low cost, with a low content of gases and impurities that have a harmful effect on connections. It is an object.

The present invention will be explained below.

In the figure, 1 is a molten metal suction pipe for sucking up the molten metal in the ladle A and introducing it to the vacuum treatment tank 3, and 2 is a suction port at the lower end of the molten metal suction pipe 1. 3 is a vacuum treatment tank for reducing the pressure of the molten metal in the ladle A introduced from the molten metal suction pipe 1, and the vacuum treatment tank 3 is installed in the upper part of the vacuum treatment tank 3 by a pressure reduction device (not shown). A pressure reduction port 4 for reducing the pressure is provided.

The ladle, molten metal suction pipe, and decompression treatment tank are made of inexpensive materials such as cast iron, steel, and stainless steel that are less likely to cause mutual diffusion with solder.

First, the suction port 2 at the lower end of the molten metal suction pipe 1 is immersed to a relatively deep position in the molten metal in the ladle A, and when the pressure is reduced from the depressurization port 4 using the decompression device, the molten metal suction pipe was the only communication port with the outside air. Since the suction port 2 of 1 is blocked by molten metal, the pressure in the vacuum treatment tank 3 is reduced.
Therefore, the molten metal in the ladle A rises in the molten metal suction pipe 1 to a height equal to the difference between the atmospheric pressure inside the vacuum treatment tank 3 and the atmospheric pressure outside the vacuum treatment tank 3, and the molten metal is introduced into the vacuum treatment tank 3. be done. (This height is L _1. )
Next, the molten metal suction pipe 1 is raised so that the suction port 2 at the lower end of the molten metal suction pipe 1 comes to a relatively shallow position of the molten metal in the ladle A. Since the height from the upper surface of the molten metal in the ladle A to the upper limit of the molten metal that has risen through the molten metal suction pipe 1 is always the same, the upper limit of the molten metal that has reached the inside of the vacuum treatment tank 3 is the height of the molten metal that has risen up the molten metal suction pipe 1.
down to. (This height is assumed to be _L2 .) If the length of the part of the molten metal suction pipe 1 exposed from the molten metal in the ladle A is h1 in the case of Fig. ₁ and _h2 in the case of Fig. 2, then
Compared to the state shown in Fig. 1, in the case of the state shown in Fig. 2, the amount of molten metal in the state shown in Fig. 1 existing above the L ₂ level and the suction pipe with a length of (h ₂ - h ₁ ) The amount of molten metal returned to ladle A is the same as the amount of molten metal in ladle A. Similarly, when the apparatus is moved up and down so as to alternately repeat the state shown in FIG. 1 and the state shown in FIG.
The molten metal moves between the ladle A and the ladle A by repeating suction and discharge. Since the molten metal introduced into the decompression treatment tank 3 is subjected to depressurization treatment, the entire molten metal in the ladle A is sequentially depressurized in this way.

After repeating the vertical movement until the molten solder is sufficiently depressurized, the depressurization in the depressurizing tank 3 is released, the decompressing tank 3 is raised, and the suction pipe 1 is removed from the ladle A. The vacuum-treated molten solder in pot A is poured into a mold and rapidly cooled.

Note that instead of moving the decompression treatment tank 3 up and down, the ladle A
Alternatively, both may be moved up and down.

The outline of the process of the solder manufacturing method of the present invention described above is shown in FIG. 3.

Next, to describe an example, 100kg of Sn60 and Pb40 was melted at 300°C, and the vacuum treatment tank 3 was moved up and down for 10 minutes while heating a cast iron ladle to maintain this temperature. The vacuum treatment was repeated. The vacuum treatment tank 3 and the suction tube 2 were made of stainless steel, and the degree of vacuum in the vacuum treatment tank 3 was set to 5×10 ⁻¹ torr. Next, Sn-Pb solder was obtained by casting into a mold at a casting temperature of about 240°C to 300°C and cooling at a cooling rate of 50°C/min.

Manufactured by applying reduced pressure treatment as described above.
Communication equipment is manufactured using Sn60/Pb40 solder (hereinafter referred to as the former) and the conventional method that does not undergo depressurization treatment.
Comparing the properties of Sn60/Pb40 solder (hereinafter referred to as the latter) manufactured using raw materials that have been carefully examined for use in electronic devices, the following results were obtained.

(1) When the amount of residual gas in the solder was measured using Lansley's gas content measuring device, the latter solder
It was confirmed that the former contained only about 0.4 cc of gas per 100 g, whereas the former contained only about 0.4 cc of gas, indicating that the contained gas had been significantly removed.

(2) The content of metal impurities such as zinc and cadmium in the former is reduced to less than half of the latter, and the content of arsenic, cadmium, etc.
A slight decrease in non-metallic impurities such as sulfur was also observed. Metal impurities deteriorate the fluidity of solder, but these include Sn,
Since its vapor pressure is higher than that of Pb, it was reduced by depressurization treatment.

(3) When melting solder on a test piece with copper vapor-deposited on the top surface of a glass slide plate and examining the state of void generation in the area where the solder diffused from the back side of the glass plate, it was found that the number of voids was significantly greater in the former than in the latter. It was confirmed that the number is decreasing.

(4) The meniscograph method was used to measure the wetting speed of the solder to the copper plate by melting the solder at 240°C and immersing a copper plate coated with activated rosin flux in the solder. It was confirmed that the wetting speed was approximately 20% faster.

(5) We punched out a disc of solder, placed it on a slide glass plate, heated it to 240℃, and compared the changes in the shape of each solder by visual observation, and found that the melting start time of the former was much faster than the latter. was confirmed.

(6) Similarly, when a disc-shaped solder was punched out and heated and the spread area of the solder was compared, it was confirmed that the former was about 15 to 20% larger than the latter.

(7) Cold-roll the solder to a plate thickness of 0.5 mm, punch it into a JIS No. 13B test piece with a gage distance of 50 mm, and test it using an Instron type tensile tester at a temperature of 25°C and a tensile speed of 20.
As a result of performing a tensile test at mm/min, the elongation rate of the former was 165%, and the elongation rate of the latter was 50%, which was more than three times the elongation property.

Further, the cold rolling limit value was about 0.05 mm in the latter case, but 0.01 mm or less in the former case, and it was recognized that the solder according to the present invention could be easily processed into ultra-thin plates and ultra-fine wires.

In the above embodiment, the degree of vacuum was set at 5×10 ⁻¹ torr, but it would be better if the vacuum was even higher. Furthermore, if the cooling rate is 10°C/min or higher, there is no particular difference in effectiveness.

Further, a heating device (for example, using a nichrome wire) may be provided on the outer periphery of the molten metal suction pipe 1 to prevent the temperature of the molten metal moving between the depressurization treatment tank 3 and the ladle A from decreasing during the depressurization treatment. .

As described above, according to the present invention, the molten solder is subjected to a reduced pressure treatment in the reduced pressure treatment tank 3 and is constantly stirred as it moves between the reduced pressure treatment tank 3 and the ladle A. For this reason, the efficiency of vacuum processing is extremely high; as mentioned above, in the closed method in which a ladle is housed in a vacuum processing chamber, it takes nearly 200 minutes to process 100 kg of solder, but with the present invention it can be processed in just 10 minutes. In addition, it is versatile because a normal ladle can be used, and the entire molten metal in the ladle can be depressurized in a short time using a decompression treatment tank equipped with a molten metal suction pipe, reducing pressure in terms of production costs and efficiency. The present invention is extremely practical as a method for producing treated solder. In addition, as mentioned above, high vacuum and high temperature are normally required for depressurization treatment of molten metal, but solder is a low melting point alloy, and in particular, in the case of solder containing Pb, due to the characteristics of Pb's vapor pressure, At high temperatures, Pb
However, in the method of the present invention, the temperature of the molten metal is less than Sn60/Pb40.
Even in this case, a temperature of about 300°C is sufficient. In addition, the closed method requires a high degree of vacuum of about 10 ^-3 torr, but in the present invention, the degree of vacuum is 10 -3 torr or less.
10 ^-1 torr is sufficient and requires a simple decompression device. Furthermore, since the present invention does not require high temperature or high vacuum, it is easy to manufacture the vacuum treatment tank and molten metal suction pipe used in the present invention.

As explained above, according to the present invention, high-quality solder with a low content of gases, impurities, etc. that have a harmful effect on connection parts can be efficiently produced in large quantities at low cost.

Therefore, if the solder thus obtained is used, reliability will be dramatically improved even in precision connections of small electronic devices and the like. In addition, it has good wettability and spreading rate, and the melting start time is accelerated, which improves work efficiency.

Also, as with general metals, Sn and Pb metals have subtle differences in impurity composition depending on the production area or refining method (dry or wet). 4 types up to 99.90, Pb
Bullion metals are classified into five types with main components ranging from 99.95 to 99.99, but by applying the above-mentioned depressurization treatment, the solder becomes uniform and highly purified, so no matter which type of metal you use. However, it becomes possible to stably process materials such as ultra-thin plates or ultra-fine wires.

Therefore, the method according to the present invention is industrially extremely effective.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams showing the method of the present invention, Figure 3
The figure is a diagram schematically showing the process of the method of the present invention. 1... Molten metal suction pipe, 2... Suction port, 3... Decompression treatment tank, 4... Decompression port, A... Ladle.

Claims (1)

[Scope of Claims] 1. A molten metal suction pipe provided in a vacuum processing tank for processing molten solder under reduced pressure is immersed in the molten solder contained in a ladle, and the pressure in the vacuum processing tank is reduced to remove the molten metal into the vacuum processing tank. The molten solder is introduced from the suction pipe, and the molten metal in the ladle is moved to the vacuum processing tank via the molten metal suction pipe by the relative vertical movement between the vacuum processing tank and the ladle, and then returned to the ladle. 1. A method for manufacturing solder, which comprises repeating the operation of returning the solder to a vacuum to apply a pressure reduction treatment to the entire molten metal in the ladle, and then removing the molten solder from the ladle and solidifying it. 2. The method of manufacturing solder according to claim 1, wherein the molten metal suction pipe is heated by a heating device in order to maintain the molten metal moving in the molten metal suction pipe at a predetermined temperature.