Best Flux for Soldering

Flux is essential for successful soldering. It removes oxides from metal surfaces, prevents new oxidation during heating, and helps solder flow smoothly. Choosing the right flux improves joint quality and reliability.

How Flux Works

During soldering, heat causes metal surfaces to oxidize rapidly. Oxidized surfaces repel solder, preventing proper bonding. Flux chemically cleans surfaces and creates a protective barrier, allowing solder to wet and flow correctly.

Types of Flux

Rosin Flux (R, RMA, RA)

Derived from pine tree resin, rosin flux is the traditional choice for electronics.

R (Rosin): Mildest activity, minimal residue. Best for clean surfaces and simple joints.

RMA (Rosin Mildly Activated): Moderate activity, suitable for most electronics work. The most common type for hand soldering.

RA (Rosin Activated): Strongest rosin type, for difficult-to-solder surfaces. Requires thorough cleaning.

Pros: Safe for electronics, established track record, available everywhere.

Cons: Leaves sticky residue, may require cleaning.

No-Clean Flux

Formulated to leave minimal, non-corrosive residue that doesn't require removal.

Pros: Saves cleaning time and cost, residue won't cause problems, widely used in manufacturing.

Cons: Residue may affect cosmetics or coating adhesion.

Best for: Production environments, repairs where cleaning is impractical.

Water-Soluble Flux

Highly active flux that cleans easily with water.

Pros: Very effective on difficult surfaces, easy cleanup with just water.

Cons: Must be cleaned—residue is corrosive. Not suitable for situations where cleaning is impossible.

Best for: Industrial applications with proper wash facilities.

Top Flux Brands

Kester

Industry standard for professional soldering. Their 951 no-clean flux and 44 rosin core solder are widely respected.

Recommended: Kester 951 liquid flux, Kester 186 flux pen.

MG Chemicals

Excellent value with professional quality. Good range of flux types.

Recommended: 835 rosin flux paste, 8341 no-clean flux.

Chip Quik

Specialty products for difficult soldering tasks, especially SMD rework.

Recommended: SMD291 flux, no-clean flux paste.

Amtech

Popular among hobbyists and repair technicians for its effectiveness.

Recommended: NC-559-ASM for general use.

Flux Forms

Liquid: Applied with brush or dropper. Good for coverage on larger areas.

Paste: Thick consistency, stays where applied. Excellent for SMD work.

Flux Pen: Convenient for touch-up and precision application.

Cored Solder: Flux inside the solder wire—convenient for hand soldering.

Choosing the Right Flux

Application	Recommended Type
General electronics	RMA or no-clean
SMD rework	No-clean paste
Through-hole	Rosin core solder
Difficult metals	Water-soluble
Production assembly	No-clean

Application Tips

1. Apply flux before heating, not after
2. Use only enough flux to wet the joint area
3. Clean residue when required by your flux type
4. Store flux properly to prevent drying or contamination
5. Never use plumbing flux on electronics—it's corrosive

Conclusion

For most electronics work, a quality no-clean flux or RMA rosin flux works well. Kester and MG Chemicals are reliable choices. Match your flux type to your cleaning capabilities and application requirements.