N_Cook wrote:
Will have to deal with the conductive contamination on the pcb around
the nicad, down to 300K over the polyester of the pcb, soaked in
capilliary-wise?. Removing 4x 74HC as well as the ADC




Conc. aqueous potassium hydroxide (KOH) attacks E glass
(alumino-borosilicate glass fibre) leaving an insoluble white amorphous
deposit of potassium silicates and aluminium hydroxide. This deposit
will be conductive if contaminated with residual KOH as KOH is both
ionic and hygroscopic and will be extremely difficult to remove as it
has probably etched its way below the board surface. After aggressive
cleaning, neutralisation, thorough washing and oven drying, you will
still probably need to grind away the affected PCB surface until the
track to track resistance remains acceptably high after 24 hours
exposure to normal atmospheric humidity, then wash, re-dry and rebuild
the ground away areas with epoxy.

KOH also attacks a number of common plastics to a greater or lesser
degree. Polyester is likely to be moderately affected, Epoxy is
resistant. If you are very lucky, it may simply have made the resist on
the PCB surface conductive and not attacked the underlying fibreglass
significantly.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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