Resin Flux Solder Paste Composition for Delayed Curing Joints
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Solution Overview
Problem
Existing solder pastes using thermosetting resins struggle to form reliable solder joints with high-melting-point solders like SAC solder due to premature curing of the epoxy resin, which inhibits the formation of a suitable solder joint and resin reinforcing portion, especially under high-temperature conditions required for heat-resistant applications.
Innovation Solution
A resin flux solder paste composition containing a mixture of biphenyl aralkyl, naphthalene, and dicyclopentadiene type epoxy resins, along with a curing agent comprising biphenyl aralkyl phenol resin and phenol novolac resin with an allyl group, which delays curing until the solder reaches its melting point, ensuring the resin reacts and solidifies after the solder is melted, thereby forming a strong and heat-resistant joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thermosetting resin is used in the flux to reinforce the solder connection, then the strength of the solder joint is improved, but the resin cures prematurely before the solder melts, preventing proper joint formation
Solution Approach 1:
The patent changes the chemical composition parameters of the flux by incorporating specific resin systems (epoxy, phenolic, polyester, or carboxylic acid resins) with controlled molecular weights and functional groups. This allows the resin to remain stable at soldering temperatures while still providing reinforcement, resolving the contradiction between strength improvement and reliable joint formation.
Solution Approach 2:
The patent creates a composite flux material combining multiple resin types (e.g., epoxy with phenolic, or polyester with carboxylic acid) to achieve synergistic effects. This composite approach allows the flux to provide both reinforcement for joint strength and controlled curing behavior for reliable joint formation, simultaneously addressing both requirements.
2Temperature
If a high-melting-point solder like SAC solder is used to improve heat resistance, then the heat resistance is improved, but the epoxy resin in the flux cures before the solder reaches its melting point
Solution Approach 1:
The patent adjusts the resin composition parameters to include high-temperature stable resins such as phenolic resins, polyesters, or carboxylic acid resins, which maintain their stability at the high temperatures required for SAC solder processing. This allows the use of high-melting-point solders while preventing premature resin curing, thus improving heat resistance without sacrificing processability.
Solution Approach 2:
The patent introduces specific resin intermediaries that mediate between the high-temperature soldering process and the flux's curing behavior. These resin intermediaries remain stable during the high-temperature soldering process and only cure after the solder has properly formed, enabling the use of high-melting-point solders while maintaining ease of manufacture.
3Strength
If the resin cures before solder melting to provide reinforcement, then the structural strength is improved, but the solder joint formation is inhibited
Solution Approach 1:
The patent precisely controls the resin's chemical parameters including molecular weight, functional group density, and crosslinking characteristics. This precise parameter control ensures the resin maintains appropriate viscosity and reactivity throughout the soldering process, providing structural strength without interfering with the precise formation of the solder joint.
Solution Approach 2:
The patent designs the resin to perform preliminary reinforcement actions during the soldering process without completing full curing before solder melting. The resin begins to provide structural support while remaining sufficiently reactive to allow complete joint formation, achieving both structural strength and manufacturing precision.
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 proposed solder paste achieves high heat resistance with a glass transition temperature of 80°C or higher, enabling reliable connections and mechanical strength for electronic components under severe heat cycle conditions, overcoming the limitations of premature curing and low-melting-point solders.
Implementation Method 1
the flux contains at least an epoxy resin, a curing agent, a curing accelerator, and an activator
Implementation Method 2
By heating solder paste containing a thermosetting resin in a flux, the resin contained in the flux and the solder are separated from each other in a step of melting and connecting the solder
Data Source
AI summary
A resin flux solder paste includes a solder powder, and a flux, in which the flux contains at least an epoxy resin, a curing agent, a curing accelerator, and an activator, the epoxy resin contains 10% to 90% by weight of one or more of a biphenyl aralkyl type epoxy resin, a naphthalene type epoxy resin, and a dicyclopentadiene type epoxy resin, having an epoxy equivalent of 200 to 400, with respect to a total amount of the epoxy resin, and the curing agent contains 30% to 95% by weight of a biphenyl aralkyl phenol resin having a hydroxyl group equivalent of 150 to 350 with respect to a total amount of the curing agent, and 5% to 70% by weight of a phenol novolac resin having an allyl group having a hydroxyl group equivalent of 100 to 200 with respect to the total amount of the curing agent.