If it is from hard water, it can be restored by using a solution of pure water with a chelating agent in it, such as EDTA.

This should "dissolve" the residue, if it is salts from hard water. Then rinsing with ultra pure water should 'do the trick'.

First of all what is on the PCB's ? Calcium?

I believe Calcium is dissolved in Sulphuric Acid.

If it is hard water stains, I would try a solution that will suspend the mineral deposits. The Axarel sounds like a flux remover and as a result it is drying to fast on the board to remove the hard water deposits.

We have recoved bare boards using sapoinified DI water with our Aquastorm 200 removing tap water residues and recovered solderability as well as removing the contamination. Please contact me for details because all saponifiers do not work.

I am not an expert when it comes to cleaning but I do know a little bit about chemistry as one of my companies, Florida Cirtech blends chemicals for the Printed Circuit Fabrication industry.

In the Fab industry we use a basic solution with a chelating agent which should solubilize this residue. I think you might be able to wash the circuit boards off with a solution like this and then rinse with DI water. I suggest checking with an expert like Kyzen as they might have a solution that can solve your problem.

It is highly recommended using De-ionized water for rinse cycles as well as for mixing/diluting the water-based cleaning agents for the wash cycles.

There are several reasons why you could be observing the film:

* Most Axarel products are insoluble in water, and therefore it is nearly impossible to rinse the Axareal off the board surface with water, especially if the rinse water is used at ambient temperature. Hot rinse water may able to resolve the technical issue, but there is no guarantee.

* Second reason could be hard water used for rinsing purposes.

* Third reason maybe the partially removed flux residues.

You could send Zestron few parts that exhibit this appearance for analytical investigation and our engineers could advise you whether this is related to your current cleaning agent's rinsability or the hard water used or the cleaning performance issue.