Try baking the affected boards for at least 30 min at 150C. I suspect you 
are getting some water absorption in the solder mask filler and if this is 
the case the bake will eliminate the white. If you don't have an oven for 
baking try using a heat gun directly to the white spots, that could work 
as well.

Regards,

Bob Metcalf
Atotech Western Regional Manager

Cell 714-334-7667
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From:   prashant chopra <[log in to unmask]>
To:     <[log in to unmask]>
Date:   07/10/2013 08:07 AM
Subject:        [TN] Black solder mask having white patch -- need advice
Sent by:        TechNet <[log in to unmask]>



Hi Everyone,
 
We are using a black soldermask for one of our PWA. After the assembly and 
aqueous wash cleaning, we see a white patch on the bottom side. This patch 
is in small area and the top side is all clean. Again this is not 
happening on all the PWAs. I have attached a picture above for reference.
 
I need expert advice on what can be the issues either from the PWB 
fabricator end or during the assembly process which can cause this? We are 
using the black solder mask for first time and we do not have such issue 
with either green or grey solder mask.
 
Thanks in advance for your help.
 
rgds
Prashant

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