Nickel Ball Alpha Dose Reduction via Controlled Impurities
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Solution Overview
Problem
Existing Ni balls used in solder joints for high-density semiconductor packaging do not adequately address the issue of alpha radiation, leading to software errors, and their high purity increases production costs without necessary reductions in alpha dose, while low sphericity affects bump formation and mounting reliability.
Innovation Solution
Ni balls with a purity of 99.9% to 99.995% and impurity elements like Pb or Bi at 1 ppm or more are produced to achieve a low alpha dose of 0.0200 cph/cm² or less, enhancing sphericity to 0.90 or more, and are coated with solder plating to further reduce alpha radiation and ensure reliable solder joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Ni balls with high purity (99.99% or higher) are used, then the alpha dose is reduced, but the production cost increases
Solution Approach 1:
The invention changes the purity parameter from conventional high purity (99.99% or higher) to a specific range (99.9% to 99.995%) and controls impurity elements (Pb: 0.0003% or less, Bi: 0.0003% or less) to achieve alpha dose of 0.0200 cph/cm² or less. This optimized parameter range reduces production cost while maintaining low alpha radiation.
Solution Approach 2:
The invention applies local quality control by specifically limiting certain impurity elements (Pb and Bi) while allowing other impurities within acceptable ranges. This targeted approach reduces alpha radiation from specific radioactive isotopes without requiring complete purification of all elements, thereby lowering production costs.
2Object-affected harmful factors
If Ni balls with low impurity content are used, then the alpha dose is reduced, but the sphericity deteriorates
Solution Approach 1:
The invention optimizes the impurity content parameters within a specific range (total impurities: 0.005% to 0.01%, with controlled Pb and Bi content) rather than minimizing all impurities. This parameter optimization maintains sphericity of 0.90 or more while achieving low alpha dose through controlled impurity composition.
3Productivity
If high-density packing is implemented, then the miniaturization is achieved, but software errors occur due to alpha radiation entering memory cells
Solution Approach 1:
The invention converts the harmful effect of alpha radiation into a benefit by using controlled impurity elements that, when present in specific amounts, actually reduce the alpha dose through nuclear absorption effects. The Pb and Bi impurities at controlled levels absorb alpha radiation, protecting memory cells while allowing high-density packing.
Solution Approach 2:
The invention changes the impurity composition parameters to achieve a balance where controlled amounts of Pb and Bi (0.0003% or less each) reduce alpha radiation damage to memory cells, enabling high-density packing without software errors.
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 approach results in Ni balls and Ni core balls with reduced alpha radiation, improved sphericity, and cost-effective production, preventing software errors and ensuring consistent bump formation and mounting reliability in high-density packaging.
Implementation Method 1
an α-ray dose radiated thereof is 0.0200 cph/cm 2 or less
Implementation Method 2
the α-ray radiates with α decay of radioactive isotopes such as U, Th, 210
Data Source
Figure 1~2
Figure 3
AI summary
To provide a Ni ball having a low α dose and high sphericity even when it contains impurity elements other than Ni in certain amounts. The Ni ball contains an element U, a content thereof being 5 ppb or less, and an element Th, a content thereof being 5 ppb or less, wherein a purity of the Ni ball is 99.9% or more but 99.995% or less, an α dose thereof is 0.0200 cph/cm2 or less, a content of either Pb or Bi, or a total content of both Pb and Bi is 1 ppm or more, and a sphericity thereof is 0.90 or more, in order to prevent any software errors and reduce connection failure.