Solder Paste Flux Composition for Cohesion and Residue Stability
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Solution Overview
Problem
Solder pastes using dicarboxylic acid and benzotriazole compounds face issues with solder ball formation during reflow soldering due to low cohesiveness, flux residue discoloration, and precipitation over time, which affect electrical reliability.
Innovation Solution
A flux composition containing rosin, a polymer with specific repeating units, a solvent, a thixotropic agent, dicarboxylic acid, and a compound with a benzotriazole skeleton, optimized in terms of weight-average molecular weight, content, and mixing ratios, is used to enhance cohesiveness, suppress residue discoloration, and prevent precipitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a flux containing dicarboxylic acid is used to improve solder alloy powder cohesiveness, then solder ball formation is reduced, but flux residue discoloration (blackening) occurs over time
Solution Approach 1:
The patent introduces a benzotriazole compound as an intermediary substance that mediates between the dicarboxylic acid and the solder alloy powder. This compound prevents direct harmful interactions that cause blackening while allowing the dicarboxylic acid to maintain its cohesiveness-enhancing function. The benzotriazole acts as a protective layer or reactive intermediate that suppresses oxidative discoloration.
Solution Approach 2:
The flux is formulated as a composite material containing multiple active ingredients (dicarboxylic acid, benzotriazole compound, rosin, solvent, and thixotropic agent) in specific proportions. This composite approach allows the beneficial effects of dicarboxylic acid (improved cohesiveness) to be combined with the protective effects of benzotriazole (prevention of blackening), creating a synergistic formulation that addresses multiple issues simultaneously.
2Object-generated harmful factors
If a compound with benzotriazole skeleton is added to suppress flux residue blackening, then discoloration is prevented, but precipitation of the compound occurs over time
Solution Approach 1:
The patent optimizes the concentration parameters of the benzotriazole compound within a specific range (0.1-5% by mass) to prevent precipitation while maintaining effectiveness. By carefully controlling this parameter, the formulation achieves a balance where the compound remains dissolved and stable over time, preventing both blackening and precipitation issues.
Solution Approach 2:
The flux formulation creates different local environments for different components. The benzotriazole compound is positioned in a specific chemical environment created by the solvent and other flux components, which enhances its solubility and stability. This local chemical environment prevents precipitation while allowing the compound to perform its function of preventing blackening.
3Object-affected harmful factors
If lead-free solder with high melting point is used to reduce environmental impact, then environmental safety is improved, but higher soldering temperature is required which increases oxide generation
Solution Approach 1:
The benzotriazole compound serves as an intermediary that protects the solder alloy powder from oxidation during high-temperature reflow soldering. It forms a protective atmosphere or barrier that reduces oxide generation even when lead-free solder requires higher melting temperatures, thus enabling environmental safety without the penalty of excessive oxidation.
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 high cohesiveness of solder alloy powder, prevents flux residue discoloration, and maintains temporal stability, improving the reliability of solder joints.
Implementation Method 1
precipitation of the compound having a benzotriazole skeleton is likely to occur in the flux over time
Implementation Method 2
the cohesiveness of solder alloy powder is evaluated by '4.2 Solder Ball Test' of JIS Z 3284-4:2014
Implementation Method 3
since Bi is a metal element that is easily oxidized, a flux corresponding thereto has been proposed so far
Data Source
AI summary
A flux according to the present invention contains rosin, a polymer (P) having a repeating unit represented by General Formula (p1), a solvent, a thixotropic agent containing polyamide, a specific dicarboxylic acid, and a specific compound having a benzotriazole skeleton. In General Formula (p1), R1 represents a methyl group or a hydrogen atom. R2 represents a hydrocarbon group having 1 or 2 carbon atoms or a hydrogen atom. According to such a flux, the cohesiveness of the solder alloy powder is high during reflow, the blackening of flux residue is suppressed, and the precipitation with time is unlikely to occur, and the favorable temporal stability can be provided.