Low Alpha-Ray Bismuth Production via Electrolysis and Ion Exchange
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Solution Overview
Problem
Current methods fail to effectively reduce alpha-ray emissions from bismuth to the desired levels for modern semiconductor devices, which are prone to soft errors due to high alpha-ray exposure from materials used in semiconductor production.
Innovation Solution
A method involving the use of a nitric acid solution for electrolysis of bismuth, followed by passing the bismuth nitrate solution through an ion-exchange resin to eliminate polonium, and then recovering bismuth through electrowinning, which reduces alpha-ray emissions to 0.003 cph/cm2 or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional refining methods are used to reduce alpha rays from bismuth, then the alpha dose can be reduced to some extent, but the reduction is insufficient for modern semiconductor device requirements
Solution Approach 1:
The patent extracts and removes polonium-210, the primary source of alpha-ray emissions, from bismuth through selective electrochemical methods. The process uses controlled electrolysis to separate Po-210 from Bi at different stages, achieving alpha dose reduction to 0.003 cph/cm² or less, which meets modern semiconductor device requirements.
Solution Approach 2:
The patent changes multiple parameters including electrolyte composition (nitric acid concentration), electrochemical potential conditions, and processing stages to optimize the separation of polonium from bismuth. By controlling the electrochemical environment, the method achieves selective removal of Po-210 while maintaining high bismuth purity.
2Object-affected harmful factors
If a complicated multi-step process is used to reduce alpha rays from tin, then the alpha dose can be reduced, but the process complexity increases and industrial efficiency decreases
Solution Approach 1:
The patent combines multiple refining operations into an integrated electrochemical process. By merging the dissolution, purification, and metal recovery steps into a coordinated electrochemical sequence, the method reduces process complexity while achieving the required alpha dose reduction for industrial application.
Solution Approach 2:
The patent performs preliminary removal of polonium-210 during the dissolution stage and continues removal through subsequent electrochemical steps. This preliminary and continuous action approach eliminates the need for separate, complex post-refining treatments, simplifying the overall process while ensuring low alpha-ray emissions.
3Manufacturing precision
If high purity raw materials are used without regard to cost, then high purity bismuth can be obtained, but the cost increases significantly
Solution Approach 1:
The patent employs self-purification through electrochemical methods where the bismuth refining process itself removes impurities including polonium-210. The electrochemical potential differences naturally drive the separation, eliminating the need for expensive external purification agents or multiple high-cost refining passes, thus achieving cost-effective high purity bismuth production.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces alpha-ray emissions in bismuth, making it suitable for use in semiconductor devices, thereby minimizing soft errors caused by alpha rays in high-density, low-voltage semiconductor devices.
Implementation Method 1
the raw material bismuth is melted in a nitric acid solution via electrolysis to eliminate elements having an electric potential nobler than bismuth
Implementation Method 2
the bismuth nitrate solution is passed through a column filled with ion-exchange resin to eliminate polonium contained in the solution by an ion-exchange resin
Implementation Method 3
bismuth is recovered by means of electrowinning from the solution that was passed through the ion-exchange resin
Data Source
AI summary
Provided is low alpha-ray emitting bismuth having an alpha dose of 0.003 cph/cm2 or less. Additionally provided is a method of producing low alpha-ray emitting bismuth, wherein bismuth having an alpha dose of 0.5 cph/cm2 or less is used as a raw material, the raw material bismuth is melted in a nitric acid solution via electrolysis to prepare a bismuth nitrate solution having a bismuth concentration of 5 to 50 g/L and a pH of 0.0 to 0.4, the bismuth nitrate solution is passed through a column filled with ion-exchange resin to eliminate polonium contained in the solution by an ion-exchange resin, and bismuth is recovered by means of electrowinning from the solution that was passed through the ion-exchange resin. Recent semiconductor devices are of high density and high capacity, and therefore are subject to increased risk of soft errors caused by the effects of alpha rays emitted from materials in the vicinity of semiconductor chips. In particular, there is a strong demand for higher purification of solder materials used near semiconductor devices, and there is a demand for low alpha-ray emitting materials. Therefore, the present invention aims to elucidate the phenomenon of alpha ray generation from bismuth, and to provide a low alpha-ray emitting, high-purity bismuth that can be applied to the required materials and a production method thereof, as well as to provide an alloy of low alpha-ray emitting bismuth and tin and a production method thereof.