US-12617694-B2 - Low alpha-ray emission stannous oxide and method of producing the same

Abstract

What is provided is stannous oxide having an α-ray emission amount of 0.002 cph/cm 2 or less after heating in an atmosphere at 100° C. for 6 hours. Tin containing lead as an impurity is dissolved in a sulfuric acid aqueous solution to prepare a tin sulfate aqueous solution, and lead sulfate is precipitated in the aqueous solution and removed. While stirring the tin sulfate aqueous solution from which lead sulfate has been removed, a lead nitrate aqueous solution containing lead having an α-ray emission amount of 10 cph/cm 2 or less is added to cause lead sulfate to be precipitated in the tin sulfate aqueous solution, and simultaneously the tin sulfate aqueous solution is circulated while removing the lead sulfate from the aqueous solution. A neutralizing agent is added to the tin sulfate aqueous solution to collect stannous oxide.

Inventors

• Hirotaka Hirano
• Yoshihiro Yoshida
• Takuma Katase

Assignees

• MITSUBISHI MATERIALS CORPORATION

Dates

Publication Date

20260505

Application Date

20240502

Priority Date

20180730

Claims (4)

1. 1 . A method of producing stannous oxide having a low a-ray emission amount, the method comprising: a step (a) of dissolving tin containing lead as an impurity in a sulfuric acid aqueous solution, to prepare a tin sulfate aqueous solution and performing a first precipitation of lead sulfate in the tin sulfate aqueous solution; a step (b) of filtering the tin sulfate aqueous solution containing the lead sulfate obtained from the step (a) to remove the lead sulfate from the tin sulfate aqueous solution; a step (c) of performing a second precipitation of lead sulfate in the tin sulfate aqueous solution by adding a lead nitrate aqueous solution containing lead having an x-ray emission amount of 10 cph/cm 2 or less to a first tank for over 30 minutes while stirring the tin sulfate aqueous solution, from which lead sulfate has already been removed, obtained from the step (b) at a rotation speed of at least 100 rpm to cause lead sulfate to be precipitated in the tin sulfate aqueous solution, simultaneously circulating the tin sulfate aqueous solution so that a circulation flow rate is at least 1 vol %/min with respect to a total liquid amount in the first tank while filtering the tin sulfate aqueous solution to remove lead sulfate which has been precipitated from the tin sulfate aqueous solution a second time; and a step (d) of adding a neutralizing agent to the tin sulfate aqueous solution obtained from the step (c) to collect stannous oxide.
2. 2 . The method of producing stannous oxide having a low α-ray emission amount according to claim 1 , wherein a concentration of lead nitrate in the lead nitrate aqueous solution in the step (c) is 10 mass % to 30 mass %.
3. 3 . The method of producing stannous oxide having a low α-ray emission amount according to claim 2 , wherein an addition rate of the lead nitrate aqueous solution in the step (c) is 1 mg/sec to 100 mg/sec per 1 L of the tin sulfate aqueous solution.
4. 4 . The method of producing stannous oxide having a low α-ray emission amount according to claim 1 , wherein an addition rate of the lead nitrate aqueous solution in the step (c) is 1 mg/sec to 100 mg/sec per 1 L of the tin sulfate aqueous solution.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This Application is a Divisional of U.S. patent application Ser. No. 17/263,192, filed Jan. 26, 2021, which Application is a U.S. National Phase Application filed under 35 U.S.C. § 371, based on International Patent Application No. PCT/JP2019/027463, filed Jul. 11, 2019, which application claims priority to Japanese Patent Application No. JP 2019-125029, filed Jul. 4, 2019, and Japanese Patent Application No. JP 2018-142078, filed Jul. 30, 2018. The entire contents of these applications are incorporated herein by reference in their entirety. TECHNICAL FIELD The present invention relates to stannous oxide having a low α-ray emission amount, which is suitably used as a material for replenishing tin or a tin alloy plating liquid with a Sn component and has a very small α-ray emission amount, and a method of producing the same. Priority is claimed on Japanese Patent Application No. 2018-142078, filed Jul. 30, 2018, and Japanese Patent Application No. 2019-125029, filed Jul. 4, 2019, the contents of which are incorporated herein by reference. BACKGROUND ART Tin or a tin alloy plating liquid is used, for example, to form a solder bump on a wafer or a circuit board on which a semiconductor integrated circuit chip is mounted, and an electronic component such as the chip is bonded to the wafer or the board by the solder bump. Hitherto, since it is known that lead (Pb) has an effect on the environment, as a solder material for producing such an electronic component, a solder material containing Pb-free tin (Sn) as a primary metal, for example, a solder represented by a Sn—Ag-based alloy such as Sn—Ag and Sn—Ag—Cu is used. However, even with a Pb-free solder material, it is very difficult to completely remove Pb from Sn, which is the primary solder material, and Sn contains a trace amount of Pb as an impurity. In recent years, in semiconductor devices with higher densities and higher capacities, α-rays emitted from 210Po generated from 210Pb, which is an isotope of Pb, cause a soft error. Therefore, there is a demand for tin having a low α-ray emission amount that emits α-rays caused by 210Pb contained as the impurity, as less as possible. Moreover, in the current market, products having an α-ray emission amount of 0.002 cph/cm2 or less are most prevalent, and as an index, it is important that the α-ray emission amount is 0.002 cph/cm2 or less. In addition, with the diversification of the environment in which products are used, there is an increasing demand for 0.001 cph/cm2 or less. In a case where the above-mentioned Sn—Ag-based alloy is subjected to electroplating, when Sn is used as the anode, Ag is substituted and precipitated on the anode surface because Ag is nobler than Sn. In order to avoid this, electroplating is performed using an insoluble anode such as Pt in many cases. However, in order to maintain the concentration of the plating liquid in a constant level, it is necessary to replenish the plating liquid with a Sn component. In general, in a case of replenishing the plating liquid with the Sn component, since monovalent stannous oxide (SnO) is faster in dissolution rate in the plating liquid than metal tin (Sn) or divalent stannic oxide (SnO2) and enables easy production of the replenisher, stannous oxide is suitably used as the material for replenishment with the Sn component. In addition, even regarding stannous oxide for replenishment with such a Sn component, stannous oxide having a reduced α-ray emission amount is required together with tin. In the related art, stannous oxide having a reduced α-ray emission amount and a method of producing the same are disclosed (for example, refer to Patent Document 1 (claims 1 and 3) and Patent Document 2 (claim 1)). Patent Document 1 describes high-purity stannous oxide characterized by an α-ray count of 0.001 cph/cm2 or less and a purity of 99.999% or more excluding stannic oxide (SnO2), and a method of producing high-purity stannous oxide characterized in that electrolysis is performed using Sn which is a raw material as an anode and an electrolytic solution to which a component that forms a complex with monovalent Sn is added as an electrolytic solution, followed by neutralization to produce stannous oxide. Patent Document 2 describes a method of producing a stannous oxide powder for replenishing a Sn alloy plating liquid with a Sn component, which is characterized by including a step of preparing an acidic aqueous solution by dissolving metal Sn having an α-ray emission amount of 0.05 cph/cm2 or less in an acid, a step of preparing stannous hydroxide by neutralizing the acidic aqueous solution, and a step of producing stannous oxide by dehydrating the stannous hydroxide, in which, in the step of preparing the acidic aqueous solution, a Sn lump having an α-ray emission amount of 0.05 cph/cm2 or less is immersed in the acidic aqueous solution after the dissolution. On the other hand, in recent years, a problem has been r