Solder Paste Flux Composition for Low-Void Lead-Free Joints
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Solution Overview
Problem
Solder joints formed using lead-free solder pastes with mixed metal particles often contain voids due to volatile flux components, leading to increased electric resistance and heat generation, as the gas bubbles are not effectively removed during solidification.
Innovation Solution
A solder paste with a flux comprising a fatty acid and an aliphatic primary amine as main components, where the fatty acid has a boiling point above the reflow temperature and the aliphatic primary amine has a lower boiling point, reducing void formation by minimizing gas retention in the molten Sn metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder paste composed of a mixture of different metal particles (Sn and Cu) with different melting points is used, then the solder joint portion can maintain its joined state during reheating due to IMC layer formation, but voids easily occur within the solder joint portion due to gas bubbles remaining in the molten Sn metal
Solution Approach 1:
The patent changes the chemical composition parameters of the flux by specifying a fatty acid to aliphatic amine molar ratio between 1:0.5 and 1:1.5, and controlling the flux content between 3-15 mass%. This optimization of chemical parameters reduces gas generation and improves gas release characteristics, thereby reducing void formation while maintaining the reliability benefit of IMC layer formation.
Solution Approach 2:
The patent uses a composite flux system comprising multiple components: fatty acid (30-70 mass%), aliphatic amine (10-40 mass%), and additional additives (5-20 mass%). This composite formulation creates synergistic effects where the fatty acid provides lubrication and the aliphatic amine enhances gas release, collectively reducing void formation while maintaining solder joint reliability.
2Ease of manufacture
If volatile flux components are used to facilitate soldering, then the flux can effectively clean and promote bonding, but gas bubbles are generated that remain in the molten metal forming voids
Solution Approach 1:
The patent converts the harmful effect of volatile flux components into a beneficial outcome by selecting specific fatty acids and aliphatic amines that volatilize at controlled rates. The aliphatic amine component specifically promotes gas bubble coalescence and rise to the surface, transforming the harmful gas generation into a beneficial gas release mechanism that reduces void formation.
Solution Approach 2:
The patent optimizes the boiling point parameters of flux components by selecting fatty acids with boiling points above the soldering temperature and aliphatic amines with moderate volatility. This parameter control ensures that flux components volatilize at appropriate rates during heating, allowing gas bubbles to escape before solidification while maintaining effective soldering action.
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 use of this flux in solder paste significantly reduces voids in solder joints, enhancing the contact area and reducing electric resistance and heat generation, thereby improving the reliability of the soldered structure.
Implementation Method 1
when a solder paste such as the one mentioned above is heated, a volatile component such as a flux is volatilized to generate gas
Data Source
AI summary
Provided is a flux for solder paste including an organic component as a main component, which is composed of a fatty acid and an aliphatic primary amine.