Metal Ball Alpha Dose Reduction via Impurity Evaporation
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Solution Overview
Problem
High-density mounting of electronic components leads to software errors due to α rays from radioactive impurities in solder alloys and metal balls, which also results in reduced sphericity and increased costs when using high-purity materials.
Innovation Solution
A method of producing metal balls with a low α dose by heating metal materials with reduced U and Th content to evaporate impurities like 210Po, maintaining high sphericity through controlled heating and annealing, and incorporating Pb or Bi to enhance sphericity without increasing α dose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high purity metal material is used to produce metal balls, then alpha dose is reduced, but cost increases and sphericity decreases
Solution Approach 1:
The invention extracts and removes specific radioactive impurities (U, Th, Po) from the metal material through selective purification processes. By targeting and removing only the harmful radioactive elements rather than requiring complete purification to extremely high purity levels, the method achieves low alpha dose (0.0200 cph/cm² or less) while avoiding the excessive costs and sphericity degradation associated with using ultra-high purity metal materials.
2Object-affected harmful factors
If high purity metal material is used to produce metal balls, then alpha dose is reduced, but sphericity decreases
Solution Approach 1:
The invention selectively removes radioactive impurities through targeted purification processes rather than relying on ultra-high purity materials. This extraction approach achieves the required low alpha dose while preserving the sphericity of metal balls, as the purification process does not compromise the spherical shape formation during the ball-making process.
3Productivity
If solder balls are used for high-density mounting, then mounting density increases, but software errors occur due to alpha radiation
Solution Approach 1:
The invention converts the potentially harmful alpha radiation issue into a benefit by identifying and removing the specific radioactive impurities (U, Th, Po) that cause software errors. This allows the continued use of metal balls for high-density mounting applications while eliminating the software error problem, effectively turning a harmful factor into an opportunity for improved reliability.
4Productivity
If metal balls with very small diameter are used for high-density mounting, then mounting density increases, but metal balls are crushed by self-weight
Solution Approach 1:
The invention changes the material parameters of the metal balls by controlling the purity level and specific impurity content (U ≤5 ppb, Th ≤5 ppb). This parameter optimization allows the metal balls to maintain sufficient mechanical strength to support their own weight in high-density mounting configurations while keeping the diameter small enough to achieve high mounting density.
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
The method produces metal balls with an α dose of 0.0200 cph/cm2 or less and sphericity of 0.90 or more, preventing software errors and maintaining high-density mounting capabilities while reducing production costs.
Implementation Method 1
heating the pure metal at a heating temperature which is set to be higher than a boiling point of an impurity to be removed
Implementation Method 2
heating the pure metal at a heating temperature which is set to be higher than a melting point of the pure metal
Data Source
AI summary
Produced is a metal ball which suppresses an emitted α dose. Contained are the steps of melting a pure metal by heating the pure metal at a temperature which is higher than a boiling point of an impurity to be removed, higher than a melting point of the pure metal, and lower than a boiling point of the pure metal, the pure metal containing a U content of 5 ppb or less, a Th content of 5 ppb or less, purity of 99.9% or more and 99.995% or less, and a Pb or Bi content or a total content of Pb and Bi of 1 ppm or more, and the pure metal having the boiling point higher than the boiling point at atmospheric pressure of the impurity to be removed; and sphering the molten pure metal in a ball.