This article describes how to clean gel flux residue from a circuit board after hand soldering a quad flat pack component. The process involves full immersion cleaning, which means fully submersing the board into solvent while brushing in order to dislodge and dissolve as much of the flux residue as possible.
Start by putting on some “powder free latex gloves” to protect your hands. Also make sure that you are wearing safety glasses and that your work area is reasonably well ventilated.
Place the board on the bench. No solvents are used at this stage. I call this step “dry wiping”. Get a small brush, such as a horse hair or small parts cleaning brush and simply run the brush along each edge to remove the bulk of the flux residue.
Wipe the brush on a tissue to get the flux residue off of the brush. The objective is just to remove the bulk of the flux residue before the full immersion cleaning process.
Next, place your circuit board into a plastic container with some methylated spirits (or “metho”).
The plastic container can be a lunch box, a food container or an empty ice cream container. Choose the size of the container depending on how big your circuit boards are and how many you want to put in to wash or soak at one time.
Ensure that there is enough metho in the container to fully immerse the board, including the components.
Then simply brush around the edge of the chip where the flux residue is. Continue to brush around until it looks like most of the flux residue has come off.
Take the board out of the metho to get an idea of how you are going.
Blow off the metho with compressed air (a nozzle, moisture separator, air hose and air compressor). The compressed air also helps to dislodge the residue, especially some of the residue sitting behind the chip legs.
At this stage you will be able to see how much of the flux residue is left on the board. Put the board back into the metho and do some more brushing.
Take the board out again and blow off the metho and residue with the compressed air. Again, you will be able to see how much residue is left. The residue will look like a think sticky film. Put the board back in and give it another go.
Keep going until you are satisfied that you have removed as much of the flux residue as possible. You don’t have to worry is there is a little bit of flux residue left on the board because the gel flux used is “no-clean” type, which is inert and non-corrosive.
That completes this article. We covered how to clean gel flux residue from a circuit board, including “dry brushing”, full immersion cleaning, using compressed air to blow off solvent and dislodge residue, and inspection.