Flux Composition for Fine-Pitch Solder Paste Printability
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Solution Overview
Problem
Existing solder paste compositions face challenges in achieving good printability and solderability, especially with fine pitch components, and they tend to form voids and solder balls due to adhesion issues with metal masks of varying thicknesses, and the reliability of flux residues is compromised.
Innovation Solution
A flux composition comprising a base resin, an activator, and paraffin wax, which ensures good printability and solderability by optimizing the composition of rosin resin, synthetic resin, carboxylic acids, and halogen-comprising compounds, along with specific ratios and ranges for each component, to prevent voids and solder balls, and enhance the adhesiveness and insulation resistance of flux residues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the particle sizes of solder powders are refined to improve printability on fine pitch patterns, then printability is improved, but the surface area to volume ratio increases making oxidation films difficult to reduce and soldering difficult, causing solder balls and deterioration in storage stability
Solution Approach 1:
The patent changes the chemical composition parameters of the flux by incorporating specific carboxylic acids (formic acid, acetic acid, propionic acid) and halogen-comprising compounds (carbon tetrachloride, chloroform, dichloromethane) in controlled amounts. This chemical parameter adjustment enables effective oxidation film removal from fine solder particles while maintaining printability and preventing solder balls, resolving the contradiction between refined particle size benefits and soldering performance.
2Quantity of substance
If a thick metal mask (150-160 μm) is used to ensure sufficient solder supply for large components, then solder supply is maintained, but the aspect ratio of metal mask openings increases causing adhesion of solder paste composition to the walls and abnormalities in transferred shape
Solution Approach 1:
The patent adjusts the flux composition parameters by incorporating specific ratios of carboxylic acids and halogen-comprising compounds that modify the rheological and adhesion properties of the solder paste. This enables the solder paste to flow more effectively through thick metal mask openings (150-160 μm) without adhering to the walls, maintaining both adequate solder supply and accurate pattern transfer for fine pitch components.
Solution Approach 2:
The patent creates a composite flux system combining multiple carboxylic acids (formic, acetic, propionic) with halogen-comprising compounds and rosin-based resins. This composite composition provides synergistic effects that optimize both the flow characteristics for thick mask penetration and the adhesion properties for precise printing, resolving the contradiction between solder supply quantity and printing precision.
3Manufacturing precision
If paraffin is added to improve flowability and printability of fine pitches, then printability is improved, but the adhesion of solder paste to thick metal mask walls increases causing shape abnormalities
Solution Approach 1:
The patent modifies the flux composition by limiting paraffin content to 5 mass% or less and introducing specific halogen-comprising compounds (carbon tetrachloride, chloroform, dichloromethane) with controlled boiling points and concentrations. This parameter adjustment reduces excessive adhesion to mask walls while maintaining the flowability needed for fine pitch printing, preventing shape abnormalities in the transferred solder paste pattern.
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 reliable printability and solderability across different metal mask thicknesses and opening diameters, preventing voids and solder balls, while maintaining the adhesiveness and insulation resistance of flux residues, even in severe environments.
Implementation Method 1
the surface areas of the particles are too great with respect to their volumes, which makes it very difficult to reduce the oxidation films on the surfaces of the solder powders
Implementation Method 2
(B) an activator which comprises carboxylic acids
Implementation Method 3
the use of a predetermined amounts of a resin having a low glass transition temperature (Tg) and a paraffin wax having a melting point of 60°C or higher, for the purpose of preventing cracking in flux residues and improving adhesiveness of the flux residues after reflowing
Data Source
AI summary
The object of the present invention is to provide a flux composition and a solder paste composition which ensures good printability without impairing solderability (prevention of occurrence of voids and solder balls) and regardless of the metal mask thickness and opening diameter, and also provides reliability of the flux residue (adhesiveness and insulation resistance of the residue). This object has been achieved by the flux composition of the present invention comprising a base resin (A), an activator (B), and a paraffin wax (C), in which the paraffin wax (C) comprising 9% by mass or more and 20% by mass or less of isoparaffin and/or cycloparaffin, and the amount of the paraffin wax (C) is from 0.5% by mass to 20% by mass with reference to the total amount of the flux composition.