Kester83-1097-2331 Organic Water Soluble Liquid Flux Pen for Lead-Bearing and Lead Free Alloy, 0.33 fl. oz.

Makes work on PC boards easier and cleaner. When doing a repair on a printed circuit board, often the rosin core solder doesn't seem to wet out well on the traces. A quick wipe with this pen on the trace makes the solder flow out as well as it does on the component lead or wire. Minimal additional residue to clean off. Wish I had tried this decades ago!

Works amazing. I build fpv drones for a living and this is the absolute best flux you can use. Very clean

Used it for soldering some tiny surface mount components. Worked like a charm, very little residue.

Great product, worked well for me for reworking

I bought mine after finding it on the Kester "Solderability of metals" flyer on their website.Using this flux allowed me to solder nickel plated wiring, which normal rosin core solder wouldn't touch.I also found that it works wonderfully to solder other metals that would normally be difficult or impossible to solder.