Flux Residues on a assembled PCB

What Is The Flux?

Flux is a very celebrated name in the electrical industry. It is a chemical used in Automatic PCB assembly and soldering. Electric technicians use it to solidify electrical connections through some other type of soldering process.

Flux does leave some yellow residues during application on the boards. Those residues can damage your PCB board as it slowly eats up the components. It is crucial to clean the residues to avoid inhabitation of the printed wiring on the PCB and obscuring other components.

Flux comes in different types. They are classified into three categories based on the flux activity. They include:

1.Rosin flux

2.No-clean flux

3.Water-soluble flux

In Figure 1, the residues are either a result of the formulation of the flux or due to poor process conditions. Many no clean materials rely on the correct pre-heat temperature helping to minimize the residues left on the board. Wave contact time may also affect the residues left on the board. Discussion with the flux supplier should provide the correct process parameters.

Figure 1: The flux residues here could have been caused by the formulation of the flux or by poor process conditions.

Why We Need to Clean Flux From PCB?

Flux residues tend to build on the soldering components on the PCB. The PCB can be a bit delicate, and the following are reasons why you need to clean the flux off the circuit board:

1.Improve the Reliability of PCB

2.Prevent Corrosion On the PCB

3.Improving the Aesthetic Appearance of the PCB

4.Avoid Adhesion Problems with Conformal Coating

5.Prevent Dendritic Growth From Ion Contamination

Three Ways to Remove Flux from PCB

1.Use A Clean Toothbrush

What you'll need:

*A clean toothbrush

*A dry rag

*Isopropyl alcohol, or acetone

How to do it:

a.Dip the clean toothbrush in a solution of isopropyl alcohol or acetone. Flip your hand twice or thrice as you hold the wet toothbrush to flick away the excess solvent solution.

b.Gently scrub the flux on the PCB with the wetted toothbrush. The isopropyl alcohol or acetone will dissolve the flux. However, you should take care not to apply too much pressure as this may break the soldered points. Repeat this step if necessary until all the flux is removed.

c.Once all the flux is removed, wipe down the now clean area with a dry rag. Clean the toothbrush in distilled water. Allow the printed circuit board some time to dry out and then blow any remaining flux dust with canned air.

2.Use an acid brush

This is probably the cheapest dedicated PCB flux cleaner. The procedure is also simple and straightforward- I bet you'll like this one. Let's see how this works.

What you'll need:

*An acid brush

*A liquid dispenser (a pump bottle or a wash bottle can do)

*A solvent (isopropyl alcohol, or any other that is above 90%proof)

*A paper wipe

Another great advantage of isopropyl alcohol is that it's cheap and readily available and evaporates rapidly. Compared to any other PCB flux cleaner, isopropyl alcohol contains far much lesser chemicals. Nevertheless, you should check to ensure the isopropyl alcohol isn't going to damage any of the components you're working with. This is not to mention that you should have latex gloves on and in a well-ventilated area.

How to do it:

a.Cut the acid brush to angle the bristles to leave s shorter and a longer side. The shorter side should ideally be scrubbing, while the longer side should remove flux from hard to reach places.

b.Wet the brush in the solvent solution and gently scrub the flux residue off the board. You may also wet the flux area directly.

c.Wipe off the cleaned area to dry the excess solvent. Isopropyl alcohol will evaporate in seconds, so you do not have to stress over-drying the board. Your PCB is now clean and free of flux.

3.Use a Poly Clens

Poly Clens in a product specifically designed for cleaning flux off PCBs. Your neatly soldered circuit boards deserve a better clean up job. The flux should not dilute the correctly done job. Luckily, one of the PCB DIYers agrees totally. He shared a method he learned online. Believe me, after trying it too, you'll be in for a surprise.

What you'll need:

*A container big enough to immerse your soldered PCB

*Poly Clens solution

How to do it:

a.Put a sufficient amount of Poly Clens solution in the container.

b.Submerge the assembled board into the solution as you stir it gently for around 30 seconds.

c.Rinse the circuit board with distilled water once the flux is removed.

d.Dry the PCB with a heat gun.

Essentially, this is the simplest method as you do not have to scrub a thing with a brush. The Poly Clens solution will do all the work for you.

Conclusion

Cleaning flux off your PCBs is as crucial as finishing the soldering job itself. Although one may whine about how unpleasant cleaning feels, the three cleaning methods shared in this guide are more than enough to give your PCB a sparkling finish. Just don't let the PCB look messy over a job you could do in under two minutes and without breaking a sweat. Or you could just cooperate with reliable like PCBA Store to help deal with such works.