Solder Paste Flux Composition for High-Temperature Sag Resistance
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Solution Overview
Problem
Existing solder pastes face challenges in suppressing heating sagging during reflow, especially on large substrates, as the preheating temperature needs to be increased, but existing fluxes fail to adequately prevent sagging at temperatures above 180°C.
Innovation Solution
A flux comprising rosin, a solvent, a thixotropic agent with specific polyamide compounds, and an activator, where the polyamide is a condensate of aliphatic carboxylic acids and amines, providing an endothermic peak temperature range of 120°C to 200°C, is used to enhance thermal stability and prevent sagging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the preheating temperature is increased to suppress temperature variations on large substrates, then temperature uniformity is improved, but heating sagging worsens
Solution Approach 1:
The patent applies parameter changes by selecting a polyamide with a specific endothermic peak temperature range (120°C to 200°C) to modify the thermal behavior of the flux. This parameter selection allows the flux to maintain appropriate viscosity at elevated preheating temperatures (180°C to 190°C) while preventing sagging, thus resolving the contradiction between temperature uniformity and heating sagging.
Solution Approach 2:
The patent uses a composite thixotropic agent system comprising both a compound of formula (1) and a polyamide. This composite material approach combines the thixotropic properties of the compound with the controlled endothermic behavior of the polyamide to achieve stable paste characteristics across the preheating temperature range, preventing sagging while maintaining temperature uniformity on large substrates.
2Temperature
If the preheating temperature is set to 180°C to 190°C for large substrates, then temperature variations are suppressed, but heating sagging cannot be sufficiently suppressed
Solution Approach 1:
The patent changes the thermal parameter of the flux by incorporating a polyamide with an endothermic peak between 120°C and 200°C. This parameter change enables the flux to undergo a controlled endothermic process during preheating, absorbing excess heat and maintaining paste stability even at elevated temperatures of 180°C to 190°C, thus preventing both sagging and composition instability.
Solution Approach 2:
The patent implements beforehand cushioning by using the polyamide's endothermic peak to pre-absorb thermal energy before the main heating process. This prior cushioning effect prevents the solder paste from overheating and becoming unstable during preheating, maintaining composition stability and preventing sagging even when preheating temperatures are increased for large substrates.
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 effectively suppresses heating sagging during reflow, even at elevated preheating temperatures, ensuring reliable soldering on large substrates by maintaining the integrity of the solder paste.
Implementation Method 1
the temperature of the endothermic peak of the polyamide by differential scanning calorimetry is 120° C. or higher and 200° C. or lower
Data Source
AI summary
The present invention uses a flux containing a rosin, a solvent, a thixo agent, and an activator. The thixo agent contains a polyamide and a compound represented by general formula (1). The polyamide is a condensate between an amine and at least one selected from aliphatic carboxylic acids and hydroxy group-containing aliphatic carboxylic acids, and has an endothermic peak at a temperature of 120-200° C. In the general formula, R11 represents a hydrocarbon group having 11-30 carbon atoms. R0a represents a hydrogen atom or a hydrocarbon group having 12-31 carbon atoms. R0b represents an n-valent hydrocarbon group having 4-12 carbon atoms. R21 represents an alkylene group having 2-6 carbon atoms. R0c represents a single bond or an alkylene group having 2-6 carbon atoms. n represents 1 or 2. When n represents 1, m represents an integer of 1-3. When n represents 2, m represents 1.