Cu Ball Hardness Control for Solder Joint Reliability
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Solution Overview
Problem
Cu balls manufactured through rapid-cooling methods have low durability due to fine crystal grains, leading to poor impact resistance and sphericity issues, which can result in poor joints during semiconductor chip mounting.
Innovation Solution
Cu balls with Vickers hardness between 20 HV and 60 HV are developed by controlling crystal growth through annealing treatment or slow-cooling processes, ensuring high sphericity and improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid-cooling method is used to manufacture Cu ball, then production rate is improved, but impact resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate and annealing temperature to transform the crystal grain structure. By adjusting these parameters, the Cu ball transitions from fine crystal grains (hard, low impact resistance) to coarse crystal grains (soft, high impact resistance) while maintaining production efficiency
Solution Approach 2:
The patent implements preliminary action by performing annealing treatment after rapid-cooling manufacturing. This preliminary heat treatment modifies the crystal grain structure formed during rapid cooling, transforming hard fine-grained Cu balls into soft coarse-grained Cu balls with improved impact resistance
2Strength
If purity of Cu ball is increased to lower Vickers hardness, then softness is improved, but sphericity deteriorates
Solution Approach 1:
The patent resolves this contradiction by changing the crystal grain size parameter through controlled annealing rather than relying solely on purity adjustment. By optimizing annealing temperature and time, the patent achieves the desired Vickers hardness range (20-60 HV) while preserving high sphericity (0.95 or more)
Solution Approach 2:
The patent applies partial action by using moderate annealing treatment that is sufficient to grow crystal grains and reduce hardness to the target range, but not excessive to the point of deforming the spherical shape. This controlled partial treatment achieves the desired hardness without compromising sphericity
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 enhances impact resistance and maintains appropriate spacing between substrates, ensuring proper self-alignment and preventing poor joints during semiconductor chip mounting.
Implementation Method 1
a method of forming a Cu ball by spherically coagulating Cu metal powder after it is cast into thermal plasma and melted
Implementation Method 2
It is common for the Cu balls formed by such methods to be cooled rapidly to room temperature or cooling gas temperature
Implementation Method 3
controlling crystal growth through annealing treatment or slow-cooling processes
Implementation Method 4
a crystal grain of Cu is formed instantly, so that the Cu ball is formed by a fine crystal grain before the crystal grain grows bigger
Data Source
AI summary
Provided are a Cu ball, a Cu core ball, a solder joint, solder paste and foamed solder, which are superior in the impact resistance to dropping and can inhibit any occurrence of poor joints a junction defect. An electronic component 60 is constructed by joining a solder bump 30 of a semiconductor chip 10 to an electrode 41 of a printed circuit board 40 with solder paste 12, 42. The solder bump 30 is formed by joining an electrode 11 of the semiconductor chip 10 to the Cu ball 20. The Cu ball 20 according to the present invention contains purity which is equal to or higher than 99.9% and equal to or lower than 99.995%, sphericity which is equal to or higher than 0.95, and Vickers hardness which is equal to or higher than 20 HV and equal to or less than 60 HV.