Solder Paste Flux Composition for Low-Aspect Stencil Printing
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Solution Overview
Problem
The challenge is to achieve improved printability of solder pastes when using metal stencils with minute openings and low aspect ratios, as existing solutions often result in inadequate solder supply to both small and large components due to adhesion issues with the stencil surface.
Innovation Solution
A flux comprising oleyl alcohol, a thixotropic agent, and a solvent, with oleyl alcohol content between 2.0 and 12.0 mass%, is used to enhance the slipperiness of the solder paste, preventing adhesion to the stencil and ensuring consistent solder supply to both small and large components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the metal stencil is increased to secure solder supply to large components, then the amount of solder supplied to large components is improved, but the aspect ratio of the stencil openings is decreased, causing solder paste to adhere to the side surface of the openings and reducing solder supply to small components
Solution Approach 1:
The invention changes the chemical composition parameters of the solder paste by incorporating specific additives (polyethylene glycol with molecular weight 400-4000, and/or carboxylic acid with 1-10 carbon atoms) to modify the paste's flow and release characteristics, enabling effective solder transfer despite the low aspect ratio stencil geometry
Solution Approach 2:
The invention introduces intermediary substances (polyethylene glycol and/or carboxylic acid) that act as mediators between the solder paste and the stencil surface, facilitating controlled adhesion during printing and effective release during the reflow process to ensure proper solder transfer
2Manufacturing precision
If a metal stencil with minute openings is used to accommodate small components, then the printability for small components is improved, but the amount of solder supplied to large components becomes insufficient
Solution Approach 1:
The invention creates a universal solder paste formulation that performs effectively across diverse stencil configurations and component sizes, achieving consistent solder transfer performance for both small components (requiring minute openings) and large components (requiring substantial solder volume)
3Quantity of substance
If the aspect ratio of the metal stencil openings is decreased to increase thickness for large components, then solder supply to large components is improved, but solder paste adhesion to the side surface of openings increases, causing shortage of solder for small components
Solution Approach 1:
The invention converts the potentially harmful effect of increased adhesion (which would normally cause solder paste to stick to the stencil side surface) into a beneficial effect by carefully controlling the adhesion characteristics through additive selection, ensuring sufficient paste retention during printing while enabling complete release and proper transfer during the reflow process
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 improves the printability of solder pastes by reducing adhesion to the stencil, allowing for effective solder distribution across a wide range of component sizes, even with low aspect ratio stencils, thereby enhancing bonding strength and reliability.
Implementation Method 1
the flux including an unsaturated aliphatic alcohol having one unsaturated bond, a thixotropic agent, and a solvent, in which the unsaturated aliphatic alcohol includes oleyl alcohol
Implementation Method 2
a thixotropic agent
Data Source
AI summary
A flux according to the present invention is a flux for soldering, the flux including: an unsaturated aliphatic alcohol having one unsaturated bond, a thixotropic agent, and a solvent, in which the unsaturated aliphatic alcohol includes oleyl alcohol, and a content of the oleyl alcohol is 2.0 mass % or more and 12.0 mass % or less based on the entire flux.