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Discoloration and Stains after washing EN plated Aluminum plates

2004

Hello,

I have a washing process were Electroless Nickel Plated Aluminium plates with a size of 78mm(length) X 69mm (width) X3mm (thickness) are washed in a cleaning system using soft water and DI water at an elevated temp of 70degC. The plates are finally dryed by means of a hot air blower at 110degC.

The EN plated Al plates are required to be plated because soldering is carried out on these Al plates. The solder paste used has flux.

The plates are washed in order to remove ALL traces of flux residues from the assembly. When washing the plates (after soldering), the EN plated Aluminium plates have spots of discoloration, like black/brown/sepia spots. This problem does not happen always. The water used (soft water and DI water for final rinse at <5uS) becomes contaminated with flux but it is changed regularly. We have noted this discoloration even with clean water, i.e. not with contaminated water (with flux) only.

Does this discoloration have something to do with the EN plating? Maybe Phosphorus% content? Nickel plating quality? Quality of washing water? Water temperatures?

And something else which we notice is that the EN plated plates are sometimes bright (like a mirror) and on other occasions matte or semi matt after EN plating. It seems that when they are bright, this problem of discoloration does not happen.

YOUR help is greatly appreciated.

Regards,

CLAUDE D'AMATO
ELECTRONICS - ZEJTUN, MALTA, EUROPE