Cu Core Ball Sphericity and Alpha Dose Control
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Solution Overview
Problem
The existing technologies for Cu core balls and solder joints face challenges in achieving high sphericity, low alpha dose, and improved surface roughness, leading to potential soft errors and reliability issues in high-density electronic component mounting due to uneven solder plating and incorporation of radioactive elements.
Innovation Solution
A Cu core ball with a high purity Cu ball and a Sn-based solder plating film, where the Cu ball is spheronized at high temperatures to vaporize radioactive elements, and the plating process uses ultrasonic waves to achieve a smooth surface, reducing alpha dose and surface roughness without incorporating radioactive impurities into the plating film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder plating film is formed on the Cu ball surface through conventional plating processes, then the ball achieves solderability, but the surface becomes uneven and sphericity deteriorates
Solution Approach 1:
Ultrasonic vibration is applied during the plating process to prevent crystal growth on the ball surface. The vibration energy disrupts the formation of large crystals, resulting in a uniform, fine-grained plating layer that maintains spherical shape and smooth surface finish while providing adequate solderability.
Solution Approach 2:
The plating process parameters are optimized to control crystal growth. By adjusting current density, plating time, and solution composition, the process produces a thin, uniform layer (1-5 μm) that solderabilizes the surface without creating the unevenness associated with conventional thicker platings.
2Productivity
If conventional plating processes are used to form the solder plating film, then the plating is applied efficiently, but radioactive elements are incorporated into the plating film increasing alpha dose
Solution Approach 1:
Radioactive elements (Pb, Bi, Po) are selectively removed from the plating solution through filtration and purification processes before plating. This extraction ensures that the plating film is formed without incorporating radioactive contaminants, reducing alpha dose while maintaining plating efficiency through controlled process conditions.
3Object-affected harmful factors
If the Cu ball is spheronized at high temperature to reduce radioactive elements, then alpha dose is reduced, but the process complexity increases
Solution Approach 1:
The Cu balls undergo spheronization at high temperature (1000-1200°C) before plating to vaporize and remove radioactive elements. This preliminary treatment reduces alpha dose in advance, allowing subsequent plating to proceed under controlled, standardized conditions without requiring complex in-process modifications.
Solution Approach 2:
Thermal energy is used to remove radioactive elements through vaporization rather than mechanical or chemical separation methods. This substitution of thermal processing for more complex separation systems simplifies the overall process while effectively reducing alpha dose.
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 results in a Cu core ball with enhanced sphericity, reduced alpha dose, and improved surface roughness, preventing soft errors and ensuring reliable high-density mounting without affecting the mounting process.
Implementation Method 1
the Cu ball is spheronized at high temperatures to vaporize radioactive elements
Implementation Method 2
the plating process uses ultrasonic waves to achieve a smooth surface
Data Source
AI summary
A Cu core ball and a method of manufacturing such a Cu core ball. Purity of the Cu internal ball is at least 99.9% and not greater than 99.995%. A total contained amount of Pb and/or Bi in impurity contained in the Cu ball is equal to or larger than 1 ppm. Its sphericity is at least 0.95. A solder plating film coated on the Cu ball is of Sn solder or a lead free solder alloy whose primary component is Sn. In the solder plating film, a contained amount of U is not more than 5 ppb and that of Th is not more than 5 ppb. A total alpha dose of the Cu ball and the solder plating film is not more than 0./0200 cph/cm2. An arithmetic average roughness of the Cu core ball is equal to or less than 0.3 μm.