JP2754030B2 - Manufacturing method of high purity tin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing tin having high purity and low α-ray count, which is useful mainly as a brazing material or a solder material used in the electronics industry.

[Problems to be Solved by Conventional Techniques and Inventions] In recent years, the technological progress in the electronics field has been remarkable, and ICs have been moving toward larger capacities, and the development of semiconductor memories from 1 Mbit to 4 Mbit DRAMs has been progressing. Was.
In order to obtain high performance and high reliability, it is inevitable that the brazing material used for IC assembly and the like and the tin used as a solder material also need to have high purity and low α ray.

In order to obtain high-purity tin, electrolysis is repeated, or dry purification such as vacuum distillation or zone purification is performed for finishing. However, in the former method, Pb, I contained in tin
Impurities such as n are only on the order of a few ppm, so that high purity of tin cannot be achieved, and since the electrolysis is repeated, it is complicated, poor in productivity and disadvantageous in cost. In addition, the latter method has a problem in that electric power costs are increased and actual operation is considered.

In order to solve this problem, the present inventors have proposed in Japanese Patent Application No. 63-110436 a method using an electrolytic solution containing a fixed amount of sulfuric acid having a high degree of purification. But,
Even in this method, the reduction of the α-ray count is not enough,
In addition, impurities such as Pb remain, and there is a problem from the viewpoint of high purity.

In view of the above problems, an object of the present invention is to provide a simple and inexpensive method for producing tin, which has a high purity, an extremely small α-ray count, and is inexpensive.

[Means and Actions for Solving the Problems] The present inventors have conducted various studies in order to achieve the above object, and as a result, using an electrolytic solution containing sulfuric acid and hydrochloric acid with a high degree of purification at a fixed ratio, The inventors have found that the above object can be achieved by arranging high-purity tin as an anode and performing electrolysis, and arrived at the present invention.

That is, the method for producing tin of the present invention is based on JIS K 8951
In an electrolyte containing 90 to 240 g / sulfuric acid that meets at least the standard of reagent primary sulfuric acid specified in JIS K10 and 10 to 50 g / hydrochloric acid that meets at least the standard of reagent primary hydrochloric acid specified in JIS K8180, the purity is Electrolysis is performed using tin of 99.97% by weight or more as an anode.

In the present invention, the electrolytic solution contains sulfuric acid and hydrochloric acid. The sulfuric acid used here is a sulfuric acid which conforms at least to the reagent primary sulfuric acid standard specified in JIS K 8951, and is a sulfuric acid purified to the same standard or higher. Also,
The hydrochloric acid used here is a hydrochloric acid that conforms at least to the standard for reagent primary hydrochloric acid specified in JIS K 8180, and is hydrochloric acid of the same standard or purified to a higher level. These sulfuric acid and hydrochloric acid may be either commercial products or self-purified products as long as they satisfy at least the above JIS standards.

In the present invention, when either sulfuric acid or hydrochloric acid in the electrolytic solution does not satisfy the above-mentioned standard, the purifying of tin and the reduction of α-ray count, which are the objects of the present invention, cannot be achieved.

The sulfuric acid concentration and the hydrochloric acid concentration in the electrolytic solution in the present invention are important for further reducing impurities, and in particular, the hydrochloric acid concentration affects the lead content, which is an impurity in tin. The lead content in tin decreases. Further, the hydrochloric acid concentration is also a factor that determines the electrolysis voltage of the electrolytic solution.

In the present invention, the sulfuric acid concentration in the electrolytic solution is 90 to 240 g /
, Preferably 120 to 240 g /. Sulfuric acid concentration is 90g /
If less than, the α-ray count of the deposited tin on the cathode is high,
If the Sb content in the deposited tin increases and exceeds 240 g /, the elution of tin as an anode into the electrolytic solution becomes severe and the purity of the deposited tin deteriorates, which is not preferable.

The hydrochloric acid concentration in the electrolyte is 10 to 50 g /, preferably
20-30 g /. If the concentration of hydrochloric acid is less than 10 g /, the lead content in the deposited tin becomes high because the lead tolerance in the liquid is small,
If it exceeds 50 g /, chlorine gas is generated, which is not preferable.

The water used for preparing the electrolytic solution by diluting the sulfuric acid and hydrochloric acid is preferably high-purity water containing no radioactive substance.

Further, the tin ion concentration in the electrolytic solution used in the present invention is
It is desirably 15 to 50 g /. If it is less than 15 g /, the tin deposited on the cathode will not be dense, and if it exceeds 50 g /, the economic efficiency will be poor.

Further, when 0.5 to 1.0 g / gelatin is added to this electrolytic solution, it is effective in improving the state of deposition 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 in order to prevent concentration unevenness in the electrolytic cell.

Tin used as the anode in the present invention must have a purity of 99.97% by weight or more. Purity 99.97% by weight
In the case of less than tin, the α-ray count increases.

In the present invention, the electrolysis is performed using the above-described electrolyte solution and the anode.At that time, the anode made of high-purity tin is charged into an isolation box having acid-resistant chemical fibers attached to both sides, Collect the anode mud. Further, a metal plate such as stainless steel is used as the cathode, but it is also possible to process and use tin once deposited on the cathode by the production method of the present invention.

The electrolysis conditions at this time are preferably such that the temperature of the electrolytic solution is 15 to 95 ° C. and the current density is 0.3 to 1.0 A / dm ² . If the temperature of the electrolytic solution is lower than 15 ° C., the electric resistance of the electrolytic solution is high, so that the electrolytic efficiency is deteriorated and the effect of the additive is reduced by half. Also 95
If the temperature exceeds ℃, the electrolyte will be in a boiling state, which is not preferable. Further, if the temperature is 15 ° C. or more without particularly heating the electrolytic solution, the electrolysis continues favorably. Therefore, it is preferable that the temperature of the electrolytic solution is lower in terms of economy.

Although current density during electrolysis in the case of less than 0.3 A / dm ² is not bad influence on the tin to be deposited on the cathode, obtaining the amount per unit time is less inefficient, if it exceeds 1.0A / dm ² is It is not preferable because passivation of the anode is quickly caused.

According to the production method of the present invention, the purity is 99.998% by weight.
Above, the α-ray count is 0.005 C / hrcm ² or less, the content of Pb as an impurity is less than 1 ppm, and the content of any of the other impurities In, Cu, Bi, As, Sb, Fe Less than 1 ppm of tin is obtained.

[Effect] An electrolyte using a certain amount of sulfuric acid and hydrochloric acid is a main cause of α-ray emission than an electrolyte using a certain amount of sulfuric acid described in Japanese Patent Application No. 63-110436 previously filed. Uranium,
Radioactive substances such as thorium and radium, radon, polonium, bismuth, astatine, lead and other radioactive substances belonging to the decay series are further removed from the system, so that the α-ray count is 0.005 C / hr.・ Below cm ²
Further, it is considered that the allowable amount of lead in the liquid was high because of the mixed liquid of sulfuric acid and hydrochloric acid, and therefore, the content of Pb, which is an impurity in the deposited tin, was also less than 1 ppm.

[Examples] Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples.

Examples 1 to 6 contain sulfuric acid, hydrochloric acid and tin of the specifications shown in Table 1, the concentrations of sulfuric acid and hydrochloric acid are those shown in Table 1, and the tin concentration is
Electrolysis was carried out by circulating through about 5 electrolytic layers at a rate of about 55 ml / min using an electrolytic solution of 20 g / min. At the time of this electrolysis, 99.97% by weight of tin was cast into 10 × 10 × 1.5cm tin to form an anode,
A 10 × 10 × 0.2 cm stainless plate was used as the cathode. Electrolysis was carried out at a current density of 0.4 A / dm ² and at room temperature.

The electrolytic solution described above was prepared by adding hydrochloric acid to the tin sulfate solution in Example 1, and in Examples 2 to 6, sulfuric acid was added to the tin chloride solution. Also, gelatin should be added to the above electrolyte before energizing.
1 g / addition was conducted, and 0.5 g / day was constantly dropped during energization. Also,
The anode was placed in an isolation box with acid-resistant chemical fibers stuck on both sides to collect the anode mud, and the cathode was finished with sandpaper No. 2000 to improve the peeling state.

After the electrolysis, the tin deposited on the cathode was peeled off, washed with water and dried, and the α-ray count was measured with an α-ray measuring device, and at the same time, the lead content in tin was quantitatively analyzed. Table 1 shows the results.

Comparative Examples 1 and 2 Instead of the electrolyte solution containing sulfuric acid and hydrochloric acid used in Examples 1 to 6, an electrolyte solution containing a tin sulfate solution having a concentration shown in Table 1 was used. Electrolysis was carried out in the same manner as in Nos. 6 to 6.

After the electrolysis, the tin deposited on the cathode was peeled off, washed with water and dried, and the α-ray count was measured with an α-ray measuring device, and at the same time, the lead content in tin was quantitatively analyzed. Table 1 shows the results.

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 α ray count of the deposited tin was 0.005 C / hr · cm ² or less, The lead content in it was also less than 1 ppm. In addition, it can be seen that regardless of the method of preparing the electrolytic solution, the electrolytic voltage drops, and tin having a small α-ray count and lead content in tin 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 α-ray count of the deposited tin was 0.3.
006 to 0.008 C / hr · cm ² , the lead content in tin is 20 to 30 ppm, and the α ray count and the lead content in tin show higher values than those in Examples 1 to 6. Also, it can be seen that the electrolysis voltage is higher than in Examples 1 to 6.

[Effects of the Invention] As described above, according to the production method of the present invention in which an electrolytic solution containing sulfuric acid and hydrochloric acid having a high degree of purification at a fixed ratio is used, and high-purity tin is arranged as an anode to perform electrolysis.
When the α-ray count of the precipitated lead is 0.005 C / hr · cm ² or less and the lead concentration is less than 1 ppm, the α-ray count is lower than that of conventional tin, and a highly pure product can be obtained efficiently.

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

Claims (1)

(57) [Claims] (1) 90-240 g / sulfuric acid, which meets at least the standard of primary sulfuric acid of reagent specified in JIS K 8951, and JIS K
In an electrolyte containing 10 to 50 g / hydrochloric acid, which meets at least the specification of reagent primary hydrochloric acid specified in 8180, purity is 9
A method for producing tin, characterized in that electrolysis is carried out by using 9.97% by weight or more of tin as an anode.