Types of Flux

Flux removes the naturally occurring oxide layer that forms on the metal pads of a PCB and allows the solder to bond to the metal. When the flux heats up, the ingredients within the flux gets activated and removes the oxide layer. This allows the molten solder to spread and adhere evenly to the metal pads, also known as wetting.  

What are the types of fluxes?

Water Soluble Flux


  • Highly active and aggressive cleaner that effectively removes oxide and prepares the surface for soldering
  • Barely burns off during soldering process


  • It could be corrosive and could aggressively react with the metal even after soldering
  • Water-soluble resins in the flux leave residue
  • Thorough cleaning is required to remove both corrosive agents and residues that will damage the board

Rosin-Based Flux


  • Fast-acting and easy to clean
  • High compatibility with wide variety of process and soldering
  • Activated/Mildly Activated Rosin flux can be used for heavier oxides


  • Rosin flux that are activated or mildly activated has additives that leaves corrosive residue and needs to be cleaned
  • Residues from rosin flux are sticky and may attract dust and contaminate the PCB
  • Does not function well in harsh conditions

No-Clean Flux


  • Leaves a negligible amount of residue on PCB after soldering
  • Eliminates the need for lengthy machine cleaning process
  • Can be alcohol-based for speedy evaporation and flux spattering reduction


  • Given the low solids and active chemistry, it can be challenging to achieve effective soldering performance
  • While adding active chemistry improves performance, it also increases the amount of residue left on the PCBA.
  • A small amount of residue does not equate to absolutely no residues. PCBAs that are less tolerant of residues will still require cleaning. 

To learn more about which type of flux is best suited for your production, contact our team at sales@tokimeku.com today for a discussion!

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