JP2998623B2 - Method for producing low alpha ray lead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing lead for semiconductor materials in which the count number (.alpha. Dose) of radioactive .alpha.

[0002]

2. Description of the Related Art Lead is used not only as a solder material for assembling circuits of electronic equipment, but also for its alloy as a brazing material for die bonding of various LSIs and bonding of device members. It is also used as a glass component as a sealing material for packages. By the way, in these electronic devices, a soft error has become a problem with the high integration of the semiconductor element. This is because α-rays emitted from the element packaging material are the main cause. There is a demand for low α lead with as little α dose as possible.

[0003] As a method of obtaining such a lead having a small α dose, a method of electrolyzing a sulfamic acid solution as an electrolytic solution (Japanese Patent Publication No. 62-47955) or a method of separating the weight of lead ore to a source of α rays is used. A method of removing host rocks and gangues and subjecting them to alkali reduction in an oxygen atmosphere (Japanese Patent Laid-Open No. 1-132725) and the like are conventionally known.

[0004]

According to the former electrolytic refining method, metallic lead having a much smaller α dose can be obtained as compared with a normal electrolytic method using hydrofluoric acid as an electrolytic bath. It is greatly affected by the alpha dose of lead metal. If the α dose of the lead metal used for electrolysis is high, there is a limit to the reduction of α by the present electrolysis method. Conventionally, lead ingots are conventionally roasted and converted to lead oxide, mainly of galena, and reduced by melting or
Alternatively, it is obtained by air reduction at the same time as oxidation. However, in these smelting methods, the yield of crude lead is low, and it is difficult to obtain lead with low α dose at low cost.

[0005] In the latter alkali reduction method, host rocks and gangues, which are sources of α-rays, are removed by weight separation, and lead ore is used as coarsely dispersed as possible. The α dose varies greatly depending on the place of production, and the influence of the place of production is large, so that it is difficult to maintain stable quality. In addition, the smelting method after the beneficiation follows the above-mentioned general reduction method, and therefore, there is a problem that the yield of crude lead is low and the production cost increases. Furthermore, there is a limit to the reduction of α, and the α dose of the obtained crude lead is about 0.01 to 0.05 immediately after electrolysis.
Although it is about CPH / cm ² , there is a problem that after 1 to 2 years, the α dose becomes about 10 times the above value.

The present invention solves the above-mentioned problems in the conventional low α lead, and provides a lead for semiconductor materials which has a significantly lower α dose than conventional products and which maintains a low α dose over time. It is an object of the present invention to provide a method for producing with high yield.

[0007]

According to the present invention, there is provided the following method for producing low-alpha dose lead for semiconductor materials according to claims 1 and 2. (1) Lead sulfide is heated and melted in a non-oxidizing atmosphere together with aluminum and flux having an α dose of 1 CPH / cm ² or less, and the lead is desulfurized and reduced. By electrolytically refining sulfamic acid containing no isotope as an electrolytic solution, it is possible to produce lead for semiconductor materials having a quality of 4 nines or more and a radioactive α particle count of 0.05 CPH / cm ² or less. Characteristic method for producing low α-ray lead. (2) Using sodium chloride having an α dose of 1 CPH / cm ² or less as a flux and a lead concentration of 30 to 150 g /
^{2. The} method according to claim 1, wherein the electrolytic purification is carried out at a sulfamic acid concentration of 30 to 150 g / l and a cathode current density of 0.5 to 2.0 Amp / dm2.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (I) Smelting Step In the manufacturing method of the present invention, in the smelting step of obtaining lead metal from raw material ore (sulfide ore), roasting reduction in which conventional lead sulfide is roasted and converted into lead oxide and then reduced. Unlike the alkaline reducing agent using sodium carbonate alone as a reducing agent or the method described above, lead sulfide is heated and melted together with aluminum and flux, and directly reduced and desulfurized without oxidizing and roasting to obtain a lead metal. Lead sulfide (lead sulfide) as a raw material may contain a small amount of copper or zinc.

The method of reducing a metal oxide at a high temperature using aluminum is generally known as a thermite method, but the present invention uses it for desulfurization of lead sulfide. By using this method, lead sulfide as a raw material can be directly reduced by aluminum, and metallic lead can be recovered with a high yield. In order to obtain low α-ray lead, it is necessary to use aluminum having a small amount of α-ray source.
CPH / cm ² or less is used. In the analysis of gold and silver, a method of directly reducing lead oxide with iron powder (iron nail method) is known. However, in the method of reducing and desulfurizing lead sulfide using iron powder instead of aluminum, 1300 ° C. However, there is a disadvantage that a relatively high temperature is required and the recovery yield of crude lead is significantly low.

The flux used with aluminum is
It absorbs impurities in aluminum sulfide and ore generated by desulfurization to form slag and moderates excessive reaction heat generated in the thermite reaction due to the addition of aluminum. The flux is sodium borate (Na ₂ B ₄ O ₇ ) or calcium chloride (CaCl ₂ ) can be used. In addition, it has a low melting point and α
Sodium chloride is the best commercial product for low doses.

When sodium chloride is added to lead sulfide of a raw material ore together with aluminum and heated and melted in a non-oxidizing atmosphere, lead sulfide is desulfurized and reduced by aluminum according to the following formula to obtain crude lead. Aluminum sulfide generated by desulfurization is absorbed by sodium chloride to form slag. PbS + NaCl + 2 / 3Al → Pb + 1/3 (Al 2 S 3 · 2NaCl)

It is preferable that the amounts of the respective raw materials are used slightly in excess of the equivalent ratio in the above reaction formula. Specifically, lead sulfide 1
It is appropriate to use 10 to 30 parts by weight of aluminum and 20 to 50 parts by weight of sodium chloride with respect to 00 parts by weight. These raw materials are charged into a melting furnace or crucible, and are heated and melted in a non-oxidizing atmosphere at a temperature of 700 to 1200 ° C. By this reaction, lead metal accumulates at the bottom of the melting furnace or crucible, and slag of sodium sulfide is deposited thereon. This slag of sodium sulfide also absorbs other impurity elements in the raw material lead sulfide and silica in the ore, and is removed from the lead metal.

The recovery rate of metallic lead in the above smelting method is as follows:
As shown in the examples described later, it is 90% or more, and a remarkably high recovery rate is achieved as compared with the recovery rate of the conventional smelting method. In addition, in the above-mentioned smelting method, by using aluminum and sodium chloride with a low α dose, lead having an α dose of 0.02 CPH / cm ² or less and an extremely low α dose can be obtained.

(II) Electrolytic Refining Step The lead metal with a low α dose obtained in the smelting step is electrorefined to obtain a high-quality ultra-low α dose purified metal lead. Electrolytic refining, the lead metal obtained in the smelting process as an anode,
Sulfamic acid containing substantially no radioisotope is used as the electrolyte. The following ranges are suitable for the liquid composition and the electrolysis conditions. Electrolyte composition: lead concentration 30 to 150 g / l, sulfamic acid concentration 30 to 150 g / l, liquid temperature: 15 to 50 ° C. cathode current density: 0.5 to 2.0 Amp / dm ²

As the electrolytic solution, sulfamic acid containing substantially no radioisotope is used, and commercially available sulfamic acid may be used. It is not preferable to use silicic hydrofluoric acid, which is commonly used in general lead electrolytic refining, for the electrolytic solution instead of sulfamic acid. Since commercially available silicic hydrofluoric acid has a high thorium content, the α dose of purified lead is higher than that of crude lead.

The lead concentration in the electrolyte is suitably from 30 to 150 g / l. If the lead concentration is lower than this range, elements other than lead are also precipitated, which become impurities and lower the quality. On the other hand, when the lead concentration exceeds the above range, the electrolytic efficiency decreases.
The concentration of sulfamic acid in the electrolytic solution is also 30 to 150 g /
l is appropriate. If the sulfamic acid concentration is lower than this, dissolution of lead does not proceed smoothly, and if the concentration exceeds the above range, precipitation of sulfamine occurs, which is not preferable.

The temperature of the electrolytic solution is suitably from 15 to 50 ° C. If it is less than 15, the electric resistance of the electrolytic solution becomes large, so that the electrolytic efficiency is lowered. The current density of the cathode is 0.5 to 2.0
Amp / dm ² is appropriate. If the current density is lower than this, the electrolysis time will be prolonged, and if the current density is higher than the above range, elements other than lead will precipitate and cause impurity contamination.

(III) α dose and quality of purified lead The purified lead obtained by the above-mentioned production method has a quality of 4 nines or more and a count of radioactive α particles of 0.05 CPH.
/ cm ² or less. The α dose of purified lead obtained by the conventional manufacturing method is limited to about 0.1 CPH / cm ^2. Therefore, according to the above manufacturing method, the α dose is less than half of that of the conventional product, and is low for a long time. An extremely low α dose of purified lead that maintains the α dose can be obtained.

[0019]

Examples and Comparative Examples Examples of the present invention are shown below together with comparative examples. Example 1 500 g of raw lead ore (galena) having the grades shown in Table 1
Sodium chloride (purity 97%, α dose 0.3CPH / cm ² )
50g and aluminum powder (99% purity, α dose 0.1CP
H / cm ² ) 75 g were mixed in a graphite crucible, and the crucible was charged into a heating furnace under a nitrogen atmosphere, heated to 200 ° C. to remove moisture and oxygen, and further heated at 1000 ° C. for 2 hours. To melt the raw material. After slow cooling, the slag and the metal were separated to obtain a lead metal. Table 2 shows the α-ray dose, quality, and recovery of crude lead along with the type and amount of the alkali metal salt. Using this lead metal as an anode, lead was refined according to the electrolytic solution composition and electrolytic conditions shown in Table 2 to obtain purified metallic lead. Table 2 also shows the quality, α dose and yield of this purified lead.

Example 2 A lead metal was obtained in the same manner as in Example 1 except that 200 g of sodium carbonate (Na ₂ Co ₃ : 98% purity) was used instead of sodium chloride. Using this lead metal as an anode, lead purification was carried out according to the electrolytic solution composition and electrolytic conditions shown in Table 2 to obtain purified metallic lead. The results are summarized in Table 2.

Comparative Example 1 (Oxidative Desulfurization) In place of aluminum and sodium chloride in Example 1, 200 g of sodium carbonate and 100 g of sodium chloride were used.
The lead metal was obtained by heating to a temperature of 800 to 1000 ° C. for 6 hours while blowing air. Using this lead metal as the anode, Table 2
In accordance with the electrolytic solution composition and the electrolytic conditions shown in Table 1, lead purification was performed to obtain purified metal lead. The results are summarized in Table 2.

Comparative Example 2 ( Iron nailing method) The raw material was heated and melted under the same conditions as in Example 1 except that iron powder was used as a reducing agent, and lead sulfide was used together with sodium carbonate and sodium borate. Was. Using this lead metal as an anode, lead purification was carried out according to the electrolytic solution composition and electrolytic conditions shown in Table 2 to obtain purified metallic lead. The results are summarized in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

As shown in the results in Table 2, the α dose of the purified lead of this example is 0.005 to 0.01 CPH / cm ² immediately after the electrolysis, and this becomes slightly higher after two years, but is increased to 0.1 CPH / cm ² . 03-0.
It is about 05. On the other hand, the α dose of the purified lead of the comparative example is 0.03 to 0.05 CPH / cm ² immediately after electrolysis, but is 0.1 to 0.15 CPH / cm ² after 2 years. More than twice.

[0026]

According to the present invention, purified lead having an α dose of 0.05 CPH / cm ² or less, which was conventionally difficult to produce, can be obtained in high yield. The refined lead obtained by the present invention is of high quality and has an extremely low α-dose, and is suitable for semiconductor materials because it maintains this low α-dose for a long period of time, and is advantageous in preventing soft errors in memories in semiconductor devices. is there.

Claims (2)

(57) [Claims] 1. Crude lead obtained by desulfurizing and reducing lead sulfide by heating and melting lead sulfide together with aluminum and a flux having an α dose of 1 CPH / cm ² or less in a non-oxidizing atmosphere is used as an anode. Electrolytically refining sulfamic acid containing no radioisotope as an electrolytic solution to produce lead for semiconductor materials having a quality of 4 nines or more and a count of radioactive α particles of 0.05 CPH / cm ² or less. A method for producing low α-ray lead, comprising: ^2. A sodium chloride having an α dose of 1 CPH / cm ² or less as a flux, and a lead concentration of 30 to 1 in an electrolytic solution.
50 g / l, the production method according to claim 1, sulfamic acid concentration 30 to 150 g / l, the cathode current density 0.5~2.0Amp / dm ² to electrorefining.