Solder Paste Flux Composition for High-Temperature Reflow Sag Control
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Solution Overview
Problem
Existing solder pastes face challenges in suppressing heating sagging during reflow, especially on large substrates, as the fluxes disclosed in prior art are ineffective at preheating temperatures above 180°C.
Innovation Solution
A flux comprising rosin, a solvent, a thixotropic agent with specific polyamide properties, and an activator, where the polyamide is a condensate of aliphatic carboxylic acids and amines, providing a high endothermic ratio to control temperature variations 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 invention changes the chemical composition parameters of the flux by specifying a polyamide with particular structural characteristics (condensate of aliphatic carboxylic acid with 11-20 carbon atoms and aliphatic amine with 3-10 carbon atoms) and specific thermal properties (endothermic ratio ≥90% in 50-190°C range). This parameter change enables the flux to maintain appropriate viscosity at elevated preheating temperatures (180-190°C), thereby suppressing heating sagging while allowing temperature uniformity to be improved.
Solution Approach 2:
The invention utilizes the phase transition behavior of the specially designed polyamide, which exhibits endothermic absorption in a specific temperature range (50-190°C) covering 90% or more of its total endothermic amount. This phase transition characteristic allows the flux to absorb heat during preheating, maintaining stable viscosity and preventing sagging even when preheating temperature is increased for large substrate uniformity.
2Temperature
If the preheating temperature is increased 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 invention modifies the compositional parameters of the flux by defining specific ranges for polyamide structure (aliphatic carboxylic acid with 11-20 carbon atoms, aliphatic amine with 3-10 carbon atoms) and thermal properties (endothermic ratio ≥90%). These parameter changes enable the flux to maintain compositional stability and appropriate viscosity at 180-190°C preheating temperatures, simultaneously achieving temperature variation suppression and solder paste stability.
Solution Approach 2:
The invention creates a composite flux formulation combining rosin (30-50 mass%), solvent (40-60 mass%), thixotropic agent (1-20 mass%), activator (0.1-5 mass%), and the specifically designed polyamide (0.5-20 mass%). This composite material approach leverages the synergistic effects of各 components, particularly the specially designed polyamide, to achieve both temperature variation suppression and solder paste stability at elevated preheating temperatures.
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 processes on large substrates by maintaining fluidity and preventing void generation.
Implementation Method 1
regarding an endothermic amount calculated from a peak area of a differential scanning calorific curve obtained by differential scanning calorimetry, in the PA2, a ratio of an endothermic amount in a range of 50° C. or higher and 190° C. or lower is 90% or more with respect to a total endothermic amount in a range of 50° C. or higher and 200° C. or lower
Data Source
AI summary
The present invention employs a flux which contains rosin, a solvent, a thixotropic agent and an activator. The thixotropic agent contains a polyamide (PA2). The PA2 is a condensation product of an aliphatic carboxylic acid, a hydroxy group-containing aliphatic carboxylic acid and an aliphatic amine having from 3 to 10 carbon atoms; and the aliphatic carboxylic acid includes an aliphatic dicarboxylic acid having from 11 to 20 carbon atoms. With respect to the endothermic amount calculated from the peak area of the differential scanning calorimetry curve of PA2 as obtained by differential scanning calorimetry measurement, the ratio of the endothermic amount within the range of from 50° C. to 190° C. to the total endothermic amount within the range of from 50° C. to 200° C. is 90% or more.