Lead-Free Solder Ball Composition for Drop Impact Resistance
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Solution Overview
Problem
Lead-free solder balls with Sn-Ag-Cu compositions face issues with resistance to drop impacts and fusion defects when used in electronic components, particularly due to the formation of intermetallic compounds like Cu6Sn5, which interfere with bonding and lead to increased malfunction rates.
Innovation Solution
A solder alloy composition with 0.5-1.1 mass % Ag, 0.7-0.8 mass % Cu, and 0.05-0.08 mass % Ni is used, where the Cu content is near the eutectic point to suppress Cu6Sn5 formation and diffusion, enhancing resistance to drop impacts and minimizing fusion defects by controlling Ni precipitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Sn-Ag-Cu based solder alloys are used as lead-free solder balls, then solderability to BGA electrodes is improved, but resistance to drop impacts deteriorates due to interface peeling at the solder ball bonding interface
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific amounts of Ni (0.01-0.1 mass%), Fe (0.01-0.1 mass%), Co (0.01-0.1 mass%), or Pt (0.01-0.1 mass%) to the Sn-Ag-Cu base alloy. This parameter modification suppresses the formation of brittle intermetallic compounds like Cu6Sn5 at the bonding interface, thereby improving resistance to drop impacts while maintaining good solderability.
Solution Approach 2:
The invention creates a composite solder alloy system by combining Sn-Ag-Cu with small amounts of Ni, Fe, Co, or Pt. This composite material approach leverages the beneficial properties of each element: Sn provides base solderability, Ag and Cu enhance strength, while the added Ni/Fe/Co/Pt suppress harmful intermetallic compound formation, achieving both good solderability and impact resistance.
2Strength
If Cu content in solder alloy is increased to improve strength, then resistance to drop impacts is improved, but formation of Cu6Sn5 intermetallic compounds increases which interferes with bonding
Solution Approach 1:
The invention extracts or removes the harmful effect of excessive Cu6Sn5 intermetallic compound formation by adding Ni, Fe, Co, or Pt. These elements preferentially interact with Cu or suppress Cu diffusion, effectively taking out the harmful intermetallic compound formation process while retaining the beneficial strength-providing Cu in the alloy.
Solution Approach 2:
The added Ni, Fe, Co, or Pt act as intermediary elements that mediate between Cu and Sn. They interfere with the direct Cu-Sn reaction that forms Cu6Sn5 intermetallic compounds, thereby preventing the harmful effect while allowing Cu to remain in the alloy for providing strength.
3Strength
If Ni content is increased to suppress Cu6Sn5 formation and improve drop impact resistance, then resistance to drop impacts is improved, but fusion defects increase due to Ni precipitation on solder ball surface
Solution Approach 1:
The invention precisely controls the Ni content parameter within a narrow range (0.01-0.1 mass%). This parameter optimization achieves the dual benefit of suppressing Cu6Sn5 formation (improving drop impact resistance) while preventing Ni precipitation that causes fusion defects. The specific concentration range is critical to balancing these two opposing effects.
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 provides solder balls with improved resistance to drop impacts and reduced fusion defects, ensuring reliable bonding with both Cu and Ni electrodes, thus reducing electronic component failures and maintaining performance across various electrode configurations.
Implementation Method 1
the Cu content is near the eutectic point to suppress Cu6Sn5 formation and diffusion
Implementation Method 2
controlling Ni precipitation
Data Source
AI summary
Provided is a process for mounting a BGA (Ball Grid Array) or CSP (Chip Size Package) on a printed circuit board. The process includes melting and fusing together solder paste and a solder ball. The solder ball has a solder composition that includes 0.5-1.1 mass % of Ag, 0.7-0.8 mass % of Cu, 0.05-0.08 mass % of Ni, and a remainder of Sn. In the process, the solder ball is placed on an electrode of the BGA or CSP substrate and the solder paste is applied onto an opposing electrode of the printed circuit board.