What are the differences between liquid flux and paste flux?

1. Physical Form and Composition Differences

Liquid Flux

Transparent or translucent liquid primarily composed of rosin, activators (such as organic acids or halides), solvents (e.g., alcohol, acetone), and antioxidants.

Characteristics: High fluidity, volatile nature; requires sealed storage to prevent solvent evaporation and performance degradation.

Paste Flux

A paste containing resin (providing tackiness), activators (removing oxides), solvents, and thixotropic agents (regulating flow).

Fitech's eco-friendly resin series utilizes high-purity resins and low-halogen activators, resulting in minimal residue and excellent insulation properties, making it ideal for precision electronic soldering applications.

2. Application Scenarios and Process Compatibility

Liquid Flux

Suitable for: Wave soldering, manual soldering, flame brazing (e.g., copper and copper alloys, stainless steel welding).

Typical Applications: Manual rework of electronic components, pre-treatment for pipe welding.

Paste Flux

Suitable Scenarios: Reflow soldering, BGA chip packaging, high-density PCB soldering (e.g., 0201-sized components).

Compatibility Case: Fitech's low-temperature vacuum series flux, when paired with low-temperature solder paste, enables gradient vacuum reflow soldering of magnesium-aluminum alloys with solder joint porosity <5%, meeting precision process requirements.

3. Operational Convenience and Residue Management

Liquid Flux

Advantages: Uniform coating, suitable for large-area soldering.

Disadvantages: Residues may contain corrosive components, requiring cleaning.

Residue Management: Water-soluble types can be cleaned with water or alcohol; no-clean types require prior confirmation of non-corrosiveness.

Paste Flux

Advantages: Precise placement, minimizes solder splatter; no-clean residues form transparent films with minimal component impact.

Performance Benefits: Fitech's no-clean insulating series residues meet ISO 11442 standards with insulation resistance >10⁸Ω, eliminating additional cleaning steps and boosting production efficiency.

4. Cost and Efficiency Comparison

Liquid Flux

Single-batch cost: Lower cost when used with 63/37 solder wire, suitable for small-batch production scenarios.

Efficiency performance: Manual soldering offers flexibility, but automated production lines require additional coating equipment, potentially increasing initial investment.

Paste Flux

Single-batch cost: Higher initial investment, but delivers more stable solder joint yield in mass production, reducing long-term rework costs.

Efficiency data: Fitech solder paste achieves a solder joint rejection rate <0.1% in mass production—60% lower than conventional products. Production speed for orders of thousands increases fivefold, significantly boosting large-scale manufacturing efficiency.

5. Special Application Scenarios

Liquid Flux

High-Temperature Soldering: Boric acid-based formulations suit flame brazing, forming protective films during welding to minimize oxidation and ensure quality.

Paste Flux

Precision Soldering: Highly reactive types accommodate difficult-to-solder materials like stainless steel, meeting exacting connection requirements.

Special Application Scenarios: Fitech's automotive electronics series flux, paired with high-reliability solder paste, meets AEC-Q200 standards and 5G communication high-frequency PCB requirements, catering to demanding industrial environments.

Summary and Recommendations

Selecting Liquid Flux

Suitable Scenarios: Manual soldering, wave soldering, flame brazing.

Core Advantages: Low cost, flexible operation, suitable for small-batch or non-precision welding needs.

Precautions: Residue must be promptly cleaned to prevent corrosive components from affecting component lifespan.

Selecting Paste Flux

Suitable Scenarios: Reflow soldering, BGA packaging, precision component welding.

Core Advantages: Precise positioning, minimal residue, suitable for automated production lines and precision processes.

Precautions: Require refrigerated storage to maintain performance; no-clean types necessitate prior insulation verification.

Recommendations:

Standard SMT Applications: Fitech Standard Paste Series;

High-Reliability / Special Materials: Fitech Water-Soluble Flux Paste.