Probably you dissolved the rosin, but then dried it back on the board. After cleaning, rinse with clean isopropanol, or wipe with a clean cloth soaked in isopropanol.
Point is it won't be clean after it has dissolved resin into itself. FLow fresh alcy onto the board, and even warm flowing water under the sink tap.
You use enough alcohol to wet the brush, and after cleaning, the alcohol has to be discarded.
Use the driest - least moisture - one you have, the 70% will have a lot of water, and that can cause the problem you have.
Good you solved it...
After soldering, I use a watch size screw driver to pry off clumps of flux, then a fiber glass brush...finally an old tooth brush and a small quantity, about 2 ml of iso alcohol.
Inspection using eye loupe...
Then if any residue is left, do the tooth brush thing again.
Throw away the spoiled alcohol, it is contaminated.
This works most times...
Use the driest - least moisture - one you have, the 70% will have a lot of water, and that can cause the problem you have.
Good you solved it...
After soldering, I use a watch size screw driver to pry off clumps of flux, then a fiber glass brush...finally an old tooth brush and a small quantity, about 2 ml of iso alcohol.
Inspection using eye loupe...
Then if any residue is left, do the tooth brush thing again.
Throw away the spoiled alcohol, it is contaminated.
This works most times...
A microfibre cloth dipped in alcohol also works well. Use the dry part of the cloth after the initial scrub to wipe off the residue.
If you brush on a conformal coating then the board will look super glossy and shiny. Although it is meant to be sprayed on I always spray some into a small container and pour and then brush.
https://cpc.farnell.com/electrolube/cpl200h/clear-protective-lacquer-cpl-200ml/dp/SACPL200H
https://cpc.farnell.com/electrolube/cpl200h/clear-protective-lacquer-cpl-200ml/dp/SACPL200H