What is the Flux For PCB assembly ?

In PCB Blog

Assembly, as the most important part for electronic product fabrication, flux performs a integral role to assembly, this is why I would like to introduce information for flux now.

  • The function of Flux
    1. Remove the oxide on the surface of part and substrate
    2.Reduce the surface tension of the solder and promote the flow of the solder
    3.To protect the surface of the metal, avoid it to be oxidized under the environment of high temperature.
  • The main ingredients of flux
    1.Rosin: it is refined from the grease of pine tree.
    2.surfactant : Because of the gentle characteristics of rosin, it is not easy to remove the oxide, thus must add surfactant in order to enhance its effect.
    3. Solvent: Dissolve and blend solid state material like rosin and surfactant, general multi-purpose isopropyl alcohol or ethylene glycol.
    4. In addition, there are interface active agent, foaming agent and other ingredients
  • Variety of flux.
    (1) Rosin flux :
    1. R grade : Inactive rosin flux
    2 . RMA : Weak activity rosin flux
    3 . RA : Strong activity of rosin flux
    4 . RSA : Super Strong activity of rosin flux

(2) Synthesis of active flux : This kind of flux is developed by DUPONT company, it’s advantage is can make the residue which caused after soldering can become liquid state, easily for cleaning.
Based on activity, it can be divided into:
SR–No active synthetic flux
SMAR – Weak active synthetic flux
SSAR – Strong active synthetic flux
SAR – Super strong active synthetic flux

Flux For PCB assembly

.Water-soluble flux: The flux of organic acids, performs best help on welding, but must pay attention to the cleaning situation of the base board of welding after washing. If there’s residues, it will cause corrosion of substrate material, military and aerospace industry are banning the use of water-soluble flux process of substrate

. Disposable flux
Rosin kind improved flux: solid content 5-20%, residues will not cause corrosion to the base plate.

Low content of solid flux about PCB assembly: solid content at 5%, disposable flux disposable because its residue in the residues of substrate could not cause corrosion of substrate, but solid content in about 5% of the flux its residue is too much less than the flux with solid content of 5-20%, so if product with high requirements on cleanliness and appearance, you must use the solid content at 5% disposable flux

. VOC-FREE disposable flux :
Does not contain volatile organic solvents of disposable flux, the above all flux contain volatile organic solvent, the solvent flammable (dangerous). Not easy to control (quality) is volatile harmful to human body and the environment (toxic), in order to avoid such problems, so developed the pure water as the solvent of disposable flux.


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