Cu Core Ball with Metal Layer for Solder Joint Reliability
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Solution Overview
Problem
Cu balls with high purity suffer from low sphericity and high Vickers hardness, leading to durability issues and bonding defects in electronic components, while those with low sphericity exhibit discoloration and poor wettability, affecting solder joint formation.
Innovation Solution
A Cu core ball with a Cu ball covered by a metal layer containing Ni, Co, Fe, or Pd, and a solder layer, ensuring a sphericity of 0.95 or higher, low Vickers hardness, and suppressed discoloration, maintaining self-alignment 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, but the sphericity of the Cu ball decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the Cu ball by strictly controlling the content of S (sulfur) to 0.003% by mass or less and P (phosphorus) to 0.003% by mass or less, while maintaining Cu purity at 99.997% by mass or higher. This parameter control resolves the contradiction by preventing sulfide formation that would otherwise require higher impurity content to achieve softness, thereby maintaining both low Vickers hardness (20-60 HV) and high sphericity (0.95 or more)
Solution Approach 2:
The invention creates a composite structure by forming a metal layer (containing Ni, Co, Fe, or Pd) on the surface of the high-purity Cu ball. This composite structure allows the core Cu ball to maintain high purity and sphericity while the metal layer provides the necessary softness and low Vickers hardness, resolving the contradiction between purity/shape and strength
2Strength
If the Cu ball contains S to achieve softness, then the Vickers hardness decreases, but the Cu ball forms sulfide or sulfur oxide when heating, causing discoloration and poor wettability
Solution Approach 1:
The invention changes the chemical composition parameter by strictly limiting S content to 0.003% by mass or less, preventing the formation of sulfides and sulfur oxides during heating. This parameter control eliminates discoloration while maintaining appropriate Vickers hardness through the controlled presence of other elements like Fe, Ag, and Ni
Solution Approach 2:
The invention introduces a metal layer containing Ni, Co, Fe, or Pd as an intermediary between the Cu ball and the environment. This layer acts as a protective barrier that prevents direct oxidation and sulfide formation on the Cu surface during heating, thereby preventing discoloration and maintaining good wettability while the core Cu ball maintains its mechanical properties
3Ease of manufacture
If the sphericity of the Cu ball is low, then manufacturing is easier, but the self-alignment property deteriorates and bonding defects occur
Solution Approach 1:
The invention sets the sphericity parameter at 0.95 or more, establishing a minimum threshold that ensures adequate self-alignment property during mounting while allowing manufacturing flexibility within this specification. This parameter setting balances manufacturing ease with reliable self-alignment performance
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 achieves high sphericity and low hardness for the Cu core ball, ensuring reliable self-alignment, improved wettability, and enhanced impact resistance, making it suitable for electronic component mounting with reduced risk of bonding defects and discoloration.
Implementation Method 1
a Cu ball with low alpha rays, which contains Pb and Bi and has a purity which is 99.9% or higher to 99.995% or lower... a Cu ball that has a purity which is 99.9% or higher to 99.995% or lower, has sphericity which is 0.95 or higher and has the Vickers hardness which is 20 HV or higher to 60 HV or lower
Implementation Method 2
The semiconductor package to which the BGA is applied is mounted on a printed circuit board by joining the solder bump melted by the heating to a conductive land of the printed circuit board
Data Source
AI summary
The Cu core ball contains a Cu ball and one or more metal layer for covering a surface of the Cu ball, each layer including one or more element selected from Ni, Co, Fe and Pd. 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 ppm by mass or more to 1.0 ppm by mass or lower, P in an amount of 0 ppm by mass 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% by mass or higher and 99.9995% or lower, sphericity which is 0.95 or higher and a diameter of 1 μm or more to 1000 μm or lower.