Cu Core Ball Solder Joint Reliability
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Solution Overview
Problem
Cu balls with high sphericity and low hardness are needed to prevent discoloration and ensure proper self-alignment and impact resistance in electronic components, while maintaining wettability and avoiding sulfide or sulfur oxide formation, which can lead to bonding defects and short-circuits in high-density mounting structures.
Innovation Solution
A Cu core ball with a Cu ball covered by a solder layer containing Ag, Cu, and Sn, and optionally a metal layer of Ni, Co, or Pd, where the Cu ball includes Fe, Ag, or Ni impurities to achieve high sphericity and low hardness, suppressing discoloration and enhancing wettability and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the purity of the Cu ball is increased to achieve softness (low Vickers hardness), then the Vickers hardness decreases and impact resistance improves, but the sphericity of the Cu ball decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the Cu ball by precisely controlling the content of impurity elements (Pb: 0.003-0.03 mass%, Bi: 0.003-0.03 mass%, Fe: 0.003-0.03 mass%, Ni: 0.003-0.03 mass%, and other impurities: 0.003-0.03 mass%) to achieve the optimal balance between softness and sphericity, resolving the contradiction between these two properties
Solution Approach 2:
The invention creates a composite structure by covering the Cu ball with a metal layer containing specific elements (Sn: 0.1-5.0 mass%, Ni: 0.1-5.0 mass%, and other elements: 0.01-1.0 mass%), which modifies the surface properties while maintaining the core Cu ball's mechanical properties, thus resolving the contradiction between softness and sphericity
2Shape
If the content of S in the Cu ball is increased to achieve high sphericity, then the sphericity improves and self-alignment property is maintained, but the Cu ball becomes easy to discolor due to sulfide or sulfur oxide formation
Solution Approach 1:
The invention changes the chemical composition parameter by strictly limiting the S content to 0.003 mass% or less in the Cu ball, preventing sulfide and sulfur oxide formation that cause discoloration, while maintaining high sphericity through controlled impurity elements that act as crystal cores
Solution Approach 2:
The invention introduces a metal layer as an intermediary between the Cu ball and the external environment, containing elements like Sn and Ni that prevent direct oxidation and sulfide formation on the Cu ball surface, thus preventing discoloration while maintaining the Cu ball's high 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 maintains high sphericity and low hardness of the Cu core ball, ensuring proper self-alignment and impact resistance, while preventing discoloration and sulfide formation, thus preventing bonding defects and improving the reliability of solder joints in electronic components.
Implementation Method 1
the crystal grains grow up largely when there is a small amount of impurity elements since the impurity elements function as a crystal core in the Cu ball, so that the Vickers hardness of the Cu ball decreases
Implementation Method 2
a Cu ball containing at least a predetermined amount of S forms a sulfide or a sulfur oxide when heating the ball so that it is easy to discolor. The discoloration of the Cu ball may cause the wettability thereof to deteriorate
Data Source
AI summary
The Cu core ball contains a Cu ball and a solder layer for covering a surface of the Cu ball. The Cu ball contains at least one element selected from Fe, Ag, and Ni in a total amount of 5.0 or more to 50.0 ppm by mass or lower, S in an amount of 0 or more to 1.0 ppm by mass or lower, P in an amount of 0 or more to less than 3.0 ppm by mass, and remainder of Cu and inevitable impurities. The Cu ball contains purity which is 99.995% or higher and 99.9995% by mass or lower, and sphericity which is 0.95 or higher. The solder layer includes Ag in an amount of more than 0 to 4.0% by mass or less, Cu in an amount of more than 0 to 3.0% by mass or less, and remainder of Sn.