Reduce flux

Change pastes, although insufficient heating may leave excessive residues.

Is this on one board or all products? No Clean or water soluble? Do you profile accurately or "guesstimate" your settings?

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If you are, in fact, running a No-Clean solder paste:

Different no-clean solder pastes will leave different types of (benign) residues. If your paste has been qualified from a Bellcore/SIR/Electromigration standpoint, any residues remaining will NOT ever cause problems in the field...EVER!

Some typical areas that flux residues pool up: 1.) Around chip components. 2.) Around fine pitch IC Leads.. 3.) The DPAK Heatsink area... etc..

Flux residues will also look... 1.) brown and gummy. 2.) flakey 3.) or gummy transparent..

Again it depends on the solder paste.

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