Hi Graham,
I've worked in the industry selling EnSolv, Lenium, and now ENTRON solvents, which are all based on stabilized NPB.
These solvents do not always clean the no lead pastes. The problem is that the pastes are becoming more like adhesives, rather than what we know as solder pastes from the past.
The optimal time for cleaning in a vapor degreaser with ENSOLV IONIC, should be 30 seconds in hot vapor over the boil sump, followed by an immersion in the clean sump of about 3 minutes, followed by a spray off of about 20 seconds back over the dirty tank. However, if you have a difficult to remove paste, change to this process. Lower the basket over the boil sump, spray the parts for 45 seconds, then immerse on the clean side for about 3 minutes, then bring up to dwell in between the primary coils and the freeboard coils, and finally bring them out.
You also may want to test your paste to see if it is even soluble in ENSOLV. Get a small beaker, scoop our some of the hot solvent from the vapor degreaser, drop some paste in the beaker, and swirl it around. If it doesn't readily dissolve, then its just not going to work. Change paste or use another chemistry for cleaning first (Such As CitraFlor EG3) as a prewash before putting into the vapor degreaser.
Contact me for more information at rperkins@chemlogic.us or at 512-426-5728. Rick Perkins, Chemical Logic
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