JPH02228487A - Production of high purity tin - Google Patents

Abstract

PURPOSE:To simply produce high purity tin having a small alpha-ray count by electrolyzing high purity tin as the anode with an electrolytic soln. contg. highly purified sulfuric acid and hydrochloric acid in a certain ratio. CONSTITUTION:A tin electrolytic soln. contg. 90-240g/l sulfuric acid corresponding to sulfuric acid as a first-class reagent stipulated by JIS and 10-50g/l hydrochloric acid corresponding to hydrochloric acid as a first-class reagent is prepd. Tin of >=99.97wt.% purity as the anode and an SUS sheet, etc., as the cathode are immersed in the electrolytic soln. and tin is deposited on the cathode by electrolysis. The deposited tin is stripped, washed and dried. High purity tin having about <=0.005C/hr.cm<3> alpha-ray count and about <1ppm lead content is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing tin with high purity and low α-ray count, which is useful as brazing material and solder material used mainly in the electronics industry. .

[Prior art and problems to be solved by the invention] In recent years, technology in the electronics field has made remarkable progress.
ICs are trending towards larger capacities, and semiconductor memory development has progressed from 1Mbit to 4Mbit DRAM. In order to improve the performance and reliability of these products, it is inevitable that tin used as brazing material and solder material used in IC assembly etc. should also be highly purified and have low alpha rays.

To obtain high-purity tin, repeated electrolysis or final dry refining such as vacuum distillation or zone refining is performed. However, in the former method, Pb contained in tin,
Impurities such as In remain on the order of several ppm, and high purity of tin can be achieved, but since electrolysis is repeated, it is complicated, poor in productivity, and disadvantageous in terms of cost. In addition, the latter method increases electricity costs, which poses a problem when considering actual operation.

In order to solve this problem, the present inventors have proposed in Japanese Patent Application No. 110436/1983 a method using an electrolytic solution containing a certain amount of highly purified sulfuric acid. However, even in this method, the α-ray count is not sufficiently reduced, and impurities such as PB remain, which poses problems from the viewpoint of high purity.

In view of the above-mentioned problems, the present invention aims to provide a method for manufacturing tin that is highly pure, has an extremely low α-ray count, and is simple and inexpensive.

[Means and effects for solving the problem] The present inventors,
As a result of various studies to achieve the above objective, we decided to conduct 6 electrolysis using an electrolytic solution containing a certain ratio of highly purified sulfuric acid and hydrochloric acid, and arranging highly purified tin as an anode. The present invention was achieved by discovering that the above object can be achieved.

That is, the tin manufacturing method of the present invention conforms to JISK 895
In an electrolytic solution containing 90 to 240 g/J of sulfuric acid that at least meets the standards for the reagent primary sulfuric acid specified in 1 and 10 to 50 g/J of hydrochloric acid that at least meets the standards for the reagent primary hydrochloric acid specified in JIS K8180, Purity is 99.
It is characterized in that electrolysis is carried out using 97% by weight or more of tin as an anode.

In the present invention, sulfuric acid and hydrochloric acid are contained in the electrolytic solution. The sulfuric acid used here is sulfuric acid that at least meets the standards for reagent primary sulfuric acid specified in JIS K8951, and is sulfuric acid that meets the same standards or purified to a higher level. Also,
The hydrochloric acid used here is a hydrochloric acid that at least meets the standards for reagent primary hydrochloric acid specified in JIS K8180, and is a hydrochloric acid that meets the same standards or is purified to a higher level. These sulfuric acids and hydrochloric acids may be either commercially available products or self-purified products as long as they meet at least the above IIs standards.

In the present invention, if either sulfuric acid or hydrochloric acid in the electrolytic solution does not meet the above specifications, the high purity of tin and the reduction in the α-ray count, which are the objectives of the present invention, cannot be achieved.

The sulfuric acid concentration and hydrochloric acid concentration in the electrolytic solution in the present invention are important for further reducing impurities. In particular, the hydrochloric acid concentration affects the lead content, which is an impurity in the pot, and generally, the higher the hydrochloric acid concentration, the more The lead content in the pot is reduced. Also,
Hydrochloric acid concentration is also a factor that influences the electrolysis voltage of the electrolyte.

In the present invention, the sulfuric acid concentration in the electrolyte is 90-240
g/J, preferably 120-240 g/J.

If the sulfuric acid concentration is less than 90 g/l, the alpha ray count of tin deposited on the cathode will be high and the sb content in the precipitation pot will be high, and if it exceeds 240 g/l, the tin electrolyte that is the anode will be This is not preferable because the elution of tin becomes intense and the purity of the precipitated tin deteriorates.

Further, the concentration of hydrochloric acid in the electrolytic solution is 10 to 50 g/J, preferably 20 to 30 g/J. When the hydrochloric acid concentration is less than 10 g/J, the allowable amount of lead in the liquid is small. The lead content in the precipitation pot becomes high, and if it exceeds 50 g/i, chlorine gas is generated, which is not preferable.

The water used when diluting the sulfuric acid and hydrochloric acid to create the electrolytic solution is preferably high-purity water that does not contain radioactive substances.

Furthermore, the tin ion concentration in the electrolyte used in the present invention is 1
It is desirable that it is 5 to 50 g/i. If the amount is less than 15 g/J, the tin deposited on the cathode will not be dense, and if the amount is less than 50 g/l
If it exceeds this, the economic efficiency will be poor.

Furthermore, adding 0.5 to 1.0 g/g of gelatin to this electrolytic solution is effective in improving the state of tin deposited on the cathode.

It is desirable that the electrolytic solution containing such components used in the present invention be circulated during electrolysis to prevent uneven concentration within the electrolytic cell.

The tin used as the anode in the present invention has a purity of 99.97.
It is necessary that the amount is at least % by weight. Purity is 99.97
If the amount of tin is less than % by weight, the α-ray count will be high.

In the present invention, electrolysis is carried out using the above-mentioned electrolytic solution and anode. At this time, the anode made of high-purity tin is placed in an isolation box with acid-resistant chemical fibers pasted on both sides. Collect the anode mud. Further, as the cathode, a metal plate such as stainless steel is used, but it is also possible to process and use tin that has been deposited on the cathode once by the manufacturing method of the present invention.

The electrolytic conditions at this time are that the temperature of the electrolytic solution is 15 to 95°C, and the current density is 0.3 to 1. Preferably it is OA/da+2. If the temperature of the electrolytic solution is less than 15° C., the electrical resistance of the electrolytic solution is high, resulting in poor electrolytic efficiency and the effect of the additive is halved. Moreover, if the temperature exceeds 95° C., the electrolyte will be in a boiling state, which is not preferable. moreover,
Even if the electrolytic solution is not particularly heated, electrolysis continues well at temperatures of 15° C. or higher, so from an economic point of view, it is preferable that the temperature of the electrolytic solution be lower.

If the current density during electrolysis is less than 0.3 A/da2, it will not have a negative effect on the tin deposited on the cathode, but the amount obtained per unit time will be small and it will be inefficient.
If it exceeds d2, the anode becomes passivated quickly, which is not preferable.

According to the manufacturing method of the present invention, the purity is 99.998% by weight or more and the α-ray count is 0.005C/hr-a.
i or less, the PB content as an impurity is less than 1 ppm,
Moreover, other impurities such as In, Cu, and Bl.

The content of both A s + S b and Fe
Less than 1 ppm of tin is obtained.

[Function] The electrolytic solution using a certain amount of sulfuric acid and hydrochloric acid is more likely to be the main cause of α-ray emission than the electrolytic solution using a certain amount of sulfuric acid described in the previously filed Japanese Patent Application No. 110438/1982. Radioactive substances such as uranium and thorium, as well as radioactive substances belonging to the decay series such as radium, radon, boronium, bismuth, ascutin, and lead, are further removed from the system, so that the α-ray count becomes 0. .005C/hr
-ci or less, and since it is a mixed solution of sulfuric acid and hydrochloric acid, the permissible amount of lead in the solution is high. It is thought that the amount of ¥ was also less than 1 ppI.

[Examples] The present invention will be specifically described below based on Examples and Comparative Examples.

Examples 1 to 6 Containing sulfuric acid and hydrochloric acid and tin of the specifications shown in Table 1,
The concentrations of sulfuric acid and hydrochloric acid are shown in Table 1, and the tin concentration is 20.
Electrolysis was carried out using an electrolytic solution of g/. During this electrolysis, 10XloX of tin with a purity of 99.97% by weight was
L, 5cm cast as an anode, l0XIOX
A stainless steel plate of O.20 was used as a cathode. The electrolytic conditions were a current density of 0.4 A/dm2 and an electrolytic temperature at room temperature.

The electrolytic solution described above was prepared in Example 1 by adding hydrochloric acid to a tin sulfate solution, and in Examples 2 to 6, sulfuric acid was added to a tin chloride solution. In addition, gelatin was added to the above electrolyte before applying electricity.
g/i was added, and the amount was constantly lowered by 0.5 g/day for 7 m while the current was being applied. The anode was placed in an isolation box with acid-resistant chemical fibers pasted on both sides to recover the anode mud, and the cathode was finished with Sand Vapor No. 2000 to improve peelability.

After electrolysis, the tin deposited on the cathode was peeled off, washed with water, and dried.
At the same time as measuring alpha ray counts using an alpha ray measuring device, a quantitative analysis of the lead content in the pot was conducted.

The results are shown in Table 1.

Comparative Examples 1 to 2 In place of the electrolytic solution containing sulfuric acid and hydrochloric acid used in Examples 1 to 6, an electrolytic solution containing a tin sulfate solution with the concentration shown in Table 1 was used, and the other conditions were as in Example 1. Electrolysis was carried out in the same manner as in steps 6 to 6.

After electrolysis, the tin deposited on the cathode was peeled off, washed with water, and dried.
At the same time as measuring alpha ray counts using an alpha ray measuring device, a quantitative analysis of the lead content in the pot was conducted.

The results are shown in Table 1.

As shown in Table 1, in Examples 1 to 6, in which electrolysis was performed using an electrolytic solution containing sulfuric acid and hydrochloric acid, the alpha ray count of precipitated tin was 0.005 C/hr-cIi or less, and the The lead content was also less than 1 ppa+. In addition, regardless of the method of preparing the electrolyte, the electrolytic voltage will drop, and the α
It can be seen that tin with low line count and lead content can be obtained.

On the other hand, in Comparative Examples 1 and 2 in which electrolysis was performed using an electrolytic solution containing only sulfuric acid, the alpha ray count of precipitated tin was 0.
006 to 0.008 C/hr-crj, the lead content in the pot is 20 to 30 ppn+, and the alpha ray count and lead content in the pot are higher than those in Examples 1 to 6. Further, it can be seen that the electrolytic voltage is also higher compared to Examples 1 to 6.

[Effects of the Invention] As explained above, the production method of the present invention uses an electrolytic solution containing a certain proportion of highly purified sulfuric acid and hydrochloric acid, and uses highly purified tin as an anode for electrolysis. The alpha ray count of precipitated lead is less than 0.005C/hr-7, and the lead concentration is less than 1 ppa+, which is higher than that of conventional tin.
Low line count and high purity can be obtained efficiently.

By using the tin obtained in this way as a brazing material or solder material when assembling large-capacity semiconductor memories, it is possible to reduce soft errors in semiconductor memories and improve the reliability of electronic devices. It is.

Patent applicant: Mitsui Metal Mining Co., Ltd.

Claims (1)

[Claims] 1. Sulfuric acid 90-240g/J and JIS that at least meet the standards for reagent primary sulfuric acid specified in JISK8951
It is characterized by carrying out electrolysis using tin with a purity of 99.97% by weight or more as an anode in an electrolytic solution containing 10 to 50 g/l of hydrochloric acid that at least meets the standards for the reagent primary hydrochloric acid specified in K8180. A method for producing tin.