Cu Core Ball Alpha Radiation Reduction
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Solution Overview
Problem
Conventional Cu core balls with solder films containing Pb and Bi do not effectively reduce alpha radiation dose, leading to software errors in high-density electronic component mounting, as existing methods fail to form uniform solder films on small Cu balls and introduce radioactive isotopes into the solder film.
Innovation Solution
A Cu core ball with a solder plating film made from a lead-free alloy, primarily Sn, where Pb and Bi form electrically neutral salts in the plating solution, preventing their incorporation into the film, and the Cu ball has a high purity and sphericity to minimize alpha radiation dose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Pb-Sn solder alloy is used to form solder film on Cu ball, then the solder film can be formed, but the alpha radiation dose increases due to radioactive isotopes
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by strictly limiting Pb content to 0.03 wt% or less and Bi content to 0.03 wt% or less, while maintaining Sn as the base metal. This parameter change eliminates radioactive isotopes (210Pb and 210Bi) that cause alpha radiation, thereby preventing software errors in high-density mounting applications
Solution Approach 2:
The invention extracts and removes the harmful radioactive components (Pb and Bi isotopes) from the solder alloy composition. By specifying maximum content limits of 0.03 wt% for both Pb and Bi, the patent effectively takes out the radioactive elements that generate alpha rays, leaving only the essential Sn-based solder material that provides bonding functionality without radiation hazards
2Manufacturing precision
If electrolytic plating is performed on small Cu balls, then solder film can be formed, but uniform film formation is difficult and Pb/Bi are adsorbed into the film
Solution Approach 1:
The invention changes the plating solution composition parameters by adding specific organic additives (sulfonate compounds and carboxylate compounds) that modify the electrolytic plating behavior. These additives change the adsorption characteristics on the Cu ball surface, enabling uniform film formation while preventing Pb and Bi incorporation into the solder layer
Solution Approach 2:
The invention introduces organic additive molecules (sulfonate and carboxylate compounds) as intermediary substances in the plating solution. These intermediaries mediate between the electrolytic plating process and the Cu ball surface, controlling the deposition behavior to achieve uniform film thickness while blocking the incorporation of harmful Pb and Bi isotopes into the solder film
3Object-affected harmful factors
If Cu ball purity is increased to reduce alpha radiation, then radioactive isotope content decreases, but manufacturing difficulty increases
Solution Approach 1:
The invention changes the purity specification parameter from conventional standards to a balanced range: Cu content of 99.9-99.99 wt% and total impurity content of 0.01-0.1 wt%. This parameter optimization achieves sufficiently low alpha radiation doses while maintaining practical manufacturability, avoiding the excessive difficulty of producing ultra-high purity Cu balls
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 solution significantly reduces the alpha radiation dose of the Cu core ball to levels that prevent software errors in high-density mounting, ensuring reliable electronic component connections without radioactive contamination.
Implementation Method 1
as the plating method, an electrolytic plating method such as barrel plating is disclosed
Implementation Method 2
Pb and Bi form electrically neutral salts in the plating solution, preventing their incorporation into the film
Implementation Method 3
the Cu ball has a high purity and sphericity to minimize alpha radiation dose
Data Source
AI summary
A Cu core ball is provided that prevents any soft errors and decreases any connection failure. The Cu core ball includes a solder plating film formed on the surface of a Cu ball that is a Sn solder plating film or is made of a lead-free solder alloy, a principal ingredient of which is Sn. The solder plating film contains U of 5 ppb or less and Th of 5 ppb or less. The Cu ball has a purity of not less than 99.9% Cu and not more than 99.995% Cu. Pb and/or Bi contents therein are at a total of 1 ppm or more. The sphericity thereof is 0.95 or more. The obtained Cu core ball has an α dose of 0.0200 cph/cm2 or less.