Not surprised. All you will have done is to hydrolyse the rosin, making 
it slightly hygroscopic, and release the activators to do their worst. I 
suggest you ask your transformer supplier to do a proper removal of his 
residues. Probaly scraping is worse than doing nothing, as you will 
expose the joint to the contaminants.

Brian

Kevin Glidden wrote:
> Anyone have data as to what can happen if you remove (should actually say
> ATTEMPT to remove) rosin flux residues with DI water?
>  
> Long story short, we buy a transformer that the mfr told me is soldered with
> rosin, medium activity flux.  Their cleaning process is  "scrape flux
> residues with a knife"....enough said about that...  We solder with organic
> high activity and clean with DI water.  Guess what - return from field with
> fire on the pcb...burned out a trace through the PCB under the power pin of
> the transformer.  Since learning of the above info, I am inclined to think
> maybe the rosin residue could have trapped water or OR flux / flux residues
> and created a nice little corrosion spot.
>  
> Anyone have opinions or experience on what can happen if you try to clean
> the "no clean" with just water?
>  
>  
> 
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