Q15: Which to Use – Rosin Flux or Water Soluble? What are the major differences between rosin based fluxes and water soluble fluxes? Assuming we have up-to-date equipment and cleaning systems to handle either process, under what circumstances should we use one process over the other?

Rosin based fluxes use natural rosin as the activator to clean the metals so that the liquid alloy can coalesce and wet to the solder pad. ROL0 (Rosin Low activation) is generally used in no clean applications.

Water soluble flux. There are basically two types

Water washable
Water soluble.

Water washable – flux may contain rosin and in addition a surfactant to remove the flux residue after reflow.

Water soluble generally uses organic acid activators as the flux and every component in the flux system should be soluble in water and therefore clean with only water. These types of paste are generally high activation flux.

Why use one or the other ?

It depends on what you are making. If you need high reliability for a long term then it is a good idea to use a water soluble paste as it has high activation flux and after cleaning there will be no residue or contamination left on the board.

If you are conformaly coating the board you should either use a cleaning process after soldering, chemical or water, or test the compatibility of any no clean flux used with the conformal coating. At HumiSeal we can provide a compatibility test service for no clean flux residues.

Monday, 15th February 2010