Imidazole Flux Composition for Void-Suppressed Solder Paste
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Solution Overview
Problem
Conventional methods of improving flux activity in solder pastes, such as adding organic acids or halogen compounds, are insufficient in suppressing the generation of voids during soldering.
Innovation Solution
A flux for solder pastes containing 25% to 35% by mass of an imidazole compound, along with rosin, a solvent, and optional additives like block organic acids and thixotropic agents, which maintains tackiness and effectively suppresses void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the activity of the flux is increased by adding highly active components such as activators, then the solderability of the solder paste is improved, but the viscosity of the solder paste increases and the preservation stability degrades
Solution Approach 1:
The patent changes the chemical composition parameters of the flux by incorporating specific imidazole compounds (2-ethylimidazole, 2-methylimidazole, or imidazole) within defined concentration ranges (2-10%, 1-5%, or 0.5-2% by mass respectively). This parameter optimization enables sufficient flux activity for good solderability while maintaining preservation stability during storage.
2Reliability
If conventional methods are used to improve flux activity by adding organic acid or halogen compound, then the solderability is enhanced, but the generation of voids during soldering is not sufficiently suppressed
Solution Approach 1:
The patent replaces conventional organic acid or halogen compound activators with imidazole compounds, changing the chemical nature of the flux. This substitution maintains effective solderability while significantly suppressing void generation during the soldering process, as confirmed by comparative examples in the patent.
3Object-generated harmful factors
If the content of imidazole compound is increased to suppress voids, then the generation of voids is reduced, but the tackiness of the solder paste may be impaired
Solution Approach 1:
The patent optimizes the concentration parameters of imidazole compounds within specific ranges (2-10%, 1-5%, or 0.5-2% by mass depending on the specific compound) to achieve the right balance. This parameter control ensures sufficient void suppression while maintaining adequate tackiness for proper component mounting.
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 with a high imidazole content enhances oxide removal and prevents void generation during soldering, maintaining the solder paste's tackiness and stability.
Implementation Method 1
fluxes used for soldering have efficacy of chemically removing a metal oxide present between a solder and the metallic surface of an object to be joined
Implementation Method 2
enabling the movement of a metal element in the boundary between the solder and the object
Implementation Method 3
the substrate is heated in a heating furnace called a reflow furnace to melt the solder
Implementation Method 4
the formation of an intermetallic compound between the solder and the metallic surface of the object to be joined
Data Source
AI summary
Provided are: a flux that is for a solder paste and that can inhibit occurrence of voids; and a solder paste using the flux. This flux for a solder paste contains rosin, an imidazole compound, and a solvent, wherein the contained amount of the imidazole compound is 25-35 mass %. The flux also contains 0-20 mass % of a block organic acid and 0-3 mass % of an activator.