In a message dated 14/04/99  11:32:55PM,  [log in to unmask] writes:

> Has anyone heard of rosin based fluxes causing corrosion?
>
>  It is on a connector with solder cup connections and the flux used is
>  a RA flux.  The pins and the solder is showing signs of corrosion.
>  Could this be caused or accelerated by the flux?
>
>  Any help is appreciated.

.....
Yes, RA fluxes can cause corrosion. However, for interest/comparitive peace
of mind and a check on possible implications for already assembled/issued
products, you may immediately want to see if what you have got is actually
corrosion rather than just some degradation of the rosin residues themselves.
RA tend to be high solids so the amount of post solder rosin can be high with
good visibility.
A simple first line check would be
If it is just something like a rosin bloom which will typically be a matte
offwhite yellowy finish, warming to over 70-80C (use hot air blower or touch
with an iron) will melt the rosin which will revert to its normal hard amber
state. If it doesn't then its most likely corrosion.
Any other colour - especially blue/green hue  or black - should be regarded
as evidence of corrosion.

"RA"  is not a precise term. On its widest intepretation it can include any
resin containing flux which is more active than RMA. In other words there is
no top limit to the amount of active chemicals which have been added to the
resin to increase its effectiveness. I agree that this is being less than
generous to your supplier but you may want to check out what you have
actually got, especially if your move to an RA was prompted by soldering
difficulties in the first place. Naturally you will have selected the most
effective one.
As a general rule RA fluxes are ususally removed post soldering in all but
low cost domestic/consumer products. The relatively high ionic content  in
RAs means that you will need a highly polar process, simple solvents will
probably generate white residues.


Mike Fenner

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