Solder Paste Flux Composition for Aggregate-Free Wettability
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Solution Overview
Problem
Solder pastes with coarse aggregates in the flux lead to non-wetting and heterogeneous solder wettability due to physical hindrance and component precipitation, which is undesirable for fine pitch printing and board surface mounting.
Innovation Solution
A flux composition with a specific range of sorbitol-type thixotropic agents, sorbitol-type additives, and glycol ether-type solvents is used to maintain fluidity and shape retention properties, preventing aggregate precipitation and ensuring homogeneous dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a sorbitol-type thixotropic agent is added to a flux to improve shape retention property, then shape retention property is improved, but coarse aggregates are formed causing non-wetting and heterogeneous solder wettability
Solution Approach 1:
The patent changes the chemical parameters by introducing a specific sorbitol-type additive (sorbitol, monobenzylidene sorbitol, or mono(4-methylbenzylidene)sorbitol) in controlled amounts (0.01 to 1.0 mass%) to modify the molecular interactions in the flux. This parameter change prevents the formation of coarse aggregates while maintaining the thixotropic properties needed for shape retention, thereby resolving the contradiction between shape retention and solder wettability
Solution Approach 2:
The patent creates a composite flux system combining multiple components: sorbitol-type thixotropic agent (0.1 to 5.0 mass%), sorbitol-type additive (0.01 to 1.0 mass%), rosin-type resin (10 to 60 mass%), and other conventional flux components. This composite formulation works synergistically to maintain homogeneous dispersion, prevent aggregate formation, and ensure both shape retention and reliable solder wettability
2Ease of operation
If a flux is designed to have high fluidity for dischargeability, then dischargeability is improved, but shape retention property deteriorates
Solution Approach 1:
The patent utilizes thixotropic properties to create a dynamic viscosity response: the flux exhibits high fluidity under shear stress during dispensing (improving dischargeability) and returns to high viscosity when at rest (maintaining shape retention). The sorbitol-type thixotropic agent and additive combination enhances this dynamic behavior, allowing the flux to adapt its flow characteristics based on applied stress
Solution Approach 2:
The patent optimizes the balance between fluidity and shape retention by precisely controlling the amounts of thixotropic agents and additives. The sorbitol-type additive (0.01 to 1.0 mass%) modifies the molecular network structure to achieve appropriate thixotropic ratio, enabling the flux to have suitable fluidity for dispensing while maintaining shape fidelity after deposition
3Reliability
If the flux components are homogeneously dispersed, then solder wettability is improved, but aggregate precipitation occurs reducing homogeneity
Solution Approach 1:
The sorbitol-type additive acts as an intermediary substance that mediates between the thixotropic agent and other flux components. It prevents direct aggregation of thixotropic agent molecules while maintaining homogeneous dispersion of all flux components. This intermediary role ensures both homogeneous composition and reliable solder wettability without aggregate formation
Solution Approach 2:
The patent controls the concentration parameters of key components to maintain stable homogeneous dispersion. The sorbitol-type additive at 0.01 to 1.0 mass% creates optimal molecular spacing and interactions that prevent precipitation while ensuring uniform distribution of flux components, thereby maintaining both homogeneity and solder wettability
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 achieves homogeneous dispersion and appropriate thixotropy, preventing aggregate formation and ensuring sufficient thixotropy and solder wettability, thereby enhancing the reliability of soldering processes.
Implementation Method 1
In order to impart thixotropy, a thixotropic agent is added to a flux used in a solder paste
Implementation Method 2
a flux containing a specific amount of a sorbitol-type thixotropic agent, a specific amount of a sorbitol-type additive and a glycol ether-type solvent
Data Source
AI summary
It is an object of the present invention to provide a flux containing flux components homogeneously dispersed without precipitation of aggregates in addition to having an appropriate balance between fluidity and shape retention property, and a solder paste. A flux comprising 0.5 to 3.5 mass % of a sorbitol-type thixotropic agent selected from the group consisting of dibenzylidene sorbitol, bis(4-methylbenzylidene)sorbitol and a combination thereof, and 2 to 350 mass ppm of a sorbitol-type additive selected from the group consisting of sorbitol, monobenzylidene sorbitol, mono(4-methylbenzylidene)sorbitol and a combination thereof, and a glycol ether-type solvent.