Solder Paste Flux Composition for Slumping Resistance
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Solution Overview
Problem
Conventional solder pastes face challenges in achieving adequate slumping resistance and reliability, particularly in miniaturized electronic components, due to issues with flux composition and the use of organic acids, leading to solder ball formation and potential short-circuit failures.
Innovation Solution
A solder paste with a flux containing a combination of dibasic acids with specific molecular weights, a monobasic acid, and high-density polyethylenes or polypropylenes, which enhances viscosity and slumping resistance, while maintaining high reliability and soldering ability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-volatile polar substance is added to improve slumping resistance, then slumping resistance is improved, but the substance remains after solder is melted causing contamination
Solution Approach 1:
The patent changes the chemical parameters of the flux by using specific organic acid combinations (dibasic acid with MW 250-600, monobasic acid with MW 150-300) and controlling their content ratios. This chemical composition optimization allows the flux to provide adequate slumping resistance through controlled viscosity while ensuring complete volatilization and decomposition during soldering, eliminating residue contamination without requiring additional anti-contaminant additives.
2Reliability
If amorphous powders are added to improve slumping resistance, then slumping resistance is improved, but flowability and transfer printing characteristics are degraded
Solution Approach 1:
The patent optimizes the chemical composition parameters of the flux by incorporating specific organic acid combinations and controlling their content within defined ranges. This chemical approach modifies the flux viscosity and rheological properties to achieve adequate slumping resistance while preserving good flowability and transfer printing characteristics, avoiding the need to add amorphous powders that would compromise operational ease.
3Reliability
If a dibasic acid with low molecular weight is used as activator, then activation power is improved, but organic acid metal salt deposition occurs on substrate
Solution Approach 1:
The patent changes the molecular weight parameter of the dibasic acid from conventional low MW (≤250) to a higher range (250-600), and optimizes the combination with monobasic acid (MW 150-300). This parameter change maintains strong activation power while improving the solubility and dissolution of the resulting organic acid metal salts in the flux residue, preventing spotted deposition on the substrate. The balanced acid combination ensures both high activation and complete dissolution without requiring additional anti-deposition additives.
4Object-generated harmful factors
If content of dibasic acid is reduced or replaced with monobasic acid to prevent deposition, then deposition is reduced, but activation power is reduced causing soldering failure
Solution Approach 1:
The patent creates a composite activator system combining dibasic acid (MW 250-600) and monobasic acid (MW 150-300) in specific proportions. This composite approach leverages the strong activation power of the dibasic acid while the monobasic acid component enhances the solubility of metal salts in the flux residue. The synergistic combination maintains high activation power sufficient for lead-free soldering while preventing organic acid metal salt deposition, eliminating the need to choose between activation power and deposition prevention.
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 solution effectively improves slumping resistance by suppressing 'shear drop' during heating, ensuring reliable soldering and reducing the risk of solder ball formation, thus enhancing the applicability to miniaturized electronic components without increasing production costs.
Implementation Method 1
the solder paste has a viscosity at 80°C of 400 Pa●s or greater
Implementation Method 2
it has become increasingly difficult to suppress slumping (so-called shear drop) by heating
Data Source
Figure 1~2
AI summary
Disclosed is a solder paste that includes, within a flux, an activator that has: a dibasic acid with a molecular weight of no more than 250, a monobasic acid with a molecular weight in the range of 150 to 300, and a dibasic acid with a molecular weight in the range of 300 to 600; and at least one resin additive that is selected from among the group comprising high-density polyethylenes and polypropylenes. The solder paste has in the range of 4 wt% to 12 wt% resin additive within the flux, and the viscosity of the solder paste at 80°C is at least 400 Pa·s.