Solder Paste Flux Composition for Wettability and Washability
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Solution Overview
Problem
Fluxes containing organic sulfonic acid activators face issues with washability and transferability due to the formation of Sn salts, which deteriorate solubility and thixotropy, affecting the wettability and usability in soldering processes.
Innovation Solution
A flux composition with a specific ratio of organic sulfonic acid activator, high-molecular-weight nonionic surfactant, and low-molecular-weight nonionic surfactant, along with a co-activator and solvent, is used to enhance washability and transferability without compromising wettability, featuring a combination of nonionic surfactants with different mass-average molecular weights and the exclusion of cationic surfactants and amines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of organic sulfonic acid activator is increased to improve wettability, then the oxide film removing capability and wettability of molten solder are enhanced, but the washability deteriorates due to formation of Sn salts with poor water solubility
Solution Approach 1:
The patent applies parameter changes by carefully controlling the content of organic sulfonic acid activator within 1-10 wt% and combining it with specific ratios of nonionic surfactants (10-40 wt% high-molecular-weight and 5-75 wt% low-molecular-weight). This optimized parameter combination maintains effective oxide film removal and wettability while the nonionic surfactants prevent excessive Sn salt formation and improve water solubility of residues, thereby resolving the contradiction between wettability and washability
Solution Approach 2:
The patent creates a composite flux system combining organic sulfonic acid activator with nonionic surfactants (specifically polyethylene glycol and polypropylene glycol or their adducts). This composite material approach allows the flux to simultaneously achieve strong oxide film removal capability from the sulfonic acid while the nonionic surfactant components ensure good washability and transferability by modulating the solubility and rheological properties of the flux residue
2Productivity
If nonionic surfactants are added to improve transferability, then the amount of flux transferred to circuit boards is increased, but the washability may deteriorate if inappropriate surfactants are used
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the molecular weight parameters of nonionic surfactants - using high-molecular-weight surfactants (Mw > 1200) for transferability and low-molecular-weight surfactants (Mw ≤ 1200) for washability. The specific content ratios (10-40 wt% high-Mw and 5-75 wt% low-Mw) are optimized to ensure sufficient flux transfer to circuit boards while maintaining excellent washability through appropriate solubility characteristics
3Reliability
If organic sulfonic acid activator is used to remove Ni oxide films, then the oxide film removing capability is enhanced, but the formation of Sn salts deteriorates the solubility in water
Solution Approach 1:
The patent creates a composite system where organic sulfonic acid activator (providing strong oxide film removal capability) is combined with nonionic surfactants. The nonionic surfactant component, particularly polyethylene glycol and polypropylene glycol or their adducts, acts as a solubility enhancer that complexes with Sn salts formed during soldering, significantly improving their water solubility and enabling effective washability while preserving the excellent oxide film removal properties of the sulfonic acid
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 flux composition ensures excellent wettability, washability, and transferability, effectively removing Ni oxide films and maintaining the benefits of organic sulfonic acid activators, as demonstrated by comprehensive evaluation results.
Implementation Method 1
The flux chemically removes metal oxides that are present on the surface of solder and metal oxides present on the metallic surface of a subject of soldering
Implementation Method 2
A flux composition with a specific ratio of organic sulfonic acid activator, high-molecular-weight nonionic surfactant, and low-molecular-weight nonionic surfactant
Implementation Method 3
fluxes composed of an organic sulfonic acid activator and a solvent such as water have low thixotropy and thus have a problem in that it is not possible to increase the amount of the flux that is transferred to circuit boards
Data Source
AI summary
A flux containing 1 to 10 wt % of an organic sulfonic acid activator, 10 to 40 wt % of a high-molecular-weight nonionic surfactant that is a nonionic surfactant having a mass-average molecular weight Mw of more than 1200 and 5 to 75 wt % of a low-molecular-weight nonionic surfactant that is a nonionic surfactant having a mass-average molecular weight Mw of 1200 or less, in which the content of the low-molecular-weight nonionic surfactant is equal to or larger than the content of the organic sulfonic acid activator. This flux contains no cationic surfactant or contains more than 0 wt % and 5 wt % or less of the cationic surfactant. A solder paste containing this flux and a Sn-based solder metal.