Solder Paste Composition for Low-Void, Easy-Clean Reflow
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Solution Overview
Problem
Existing solder pastes face challenges in preventing separation between flux and solder powder, generating voids, and environmental burden during cleaning, as they often result in thixotropic agent burning and reduced viscosity, which complicates cleaning and storage stability.
Innovation Solution
A solder paste formulation with a flux containing 12-20% polyethylene glycol (PEG) and 5% or less thixotropic agent, along with a rosin content of 15-50%, to maintain PEG's liquid state at high temperatures, prevent burning, and ensure easy cleaning with environmentally friendly liquids, thereby reducing void generation and flux separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the content of thixotropic agent is increased to prevent solder powder and flux separation, then storage stability is improved, but burning occurs during reflow and cleaning becomes difficult
Solution Approach 1:
The patent changes the chemical composition parameters of the thixotropic agent system by specifying PEG content at 12-20 mass% and other thixotropic agent content at 5 mass% or less. This parameter optimization prevents burning during reflow while maintaining adequate storage stability, resolving the contradiction between storage stability and burning prevention.
2Object-generated harmful factors
If the content of thixotropic agent is restricted to prevent burning, then environmental burden during cleaning is reduced, but solder powder and flux may separate due to decreased viscosity
Solution Approach 1:
The patent optimizes the parameter combination of PEG content (12-20 mass%) and other thixotropic agent content (5 mass% or less) to achieve the right balance. This parameter setting maintains sufficient viscosity for storage stability while limiting burning byproducts that increase environmental burden during cleaning.
Solution Approach 2:
The patent uses a composite thixotropic agent system comprising PEG combined with other thixotropic agents (such as metal soaps, waxes, or polymers). This composite approach provides synergistic effects where PEG prevents burning while other agents contribute to viscosity maintenance, resolving the contradiction between reducing environmental burden and preventing separation.
3Temperature
If PEG content is increased to maintain liquid state at high temperature, then burning is prevented, but slump property decreases when content exceeds 7 mass%
Solution Approach 1:
The patent sets PEG content within the specific range of 12-20 mass%, which is higher than the 7 mass% threshold mentioned in prior art. This parameter optimization, combined with controlling other thixotropic agent content at 5 mass% or less, maintains adequate slump property while ensuring PEG remains in liquid state during reflow to prevent burning.
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 formulation effectively prevents flux and solder powder separation, reduces void generation, and allows for easy cleaning with environmentally friendly liquids, enhancing storage stability and reflow performance.
Implementation Method 1
maintain PEG's liquid state at high temperatures, prevent burning
Implementation Method 2
a flux comprising a rosin, an activator, a solvent, and a thixotropic agent
Data Source
AI summary
The present invention relates to a flux including rosin, an active agent, a solvent, a thixotropic agent containing polyethyleneglycol, and a solder powder, wherein the polyethyleneglycol content is 10 to 20% by mass with respect to the total mass of the flux, and the thixotropic agent content excluding the polyethyleneglycol is no greater than 5% by mass with respect to the total mass of the flux.