What is Causing White Residue on my PCBs?

White residues are the bane of the electronics industry. The white residues themselves usually (but not always) are salts, which are the “activators” in the fluxes. When these salts meet heat or other chemicals, white residues can result. These residues can corrode delicate circuits. There are dozens of different possible sources — the boards, the solvent and fluxes, the people, the processes, the way the fluxes and solder paste are stored, and even the weather. It is very hard to determine precisely what might be causing the problem.

Since the industry switched primarily to lead-free soldering materials, problems with white residues have skyrocketed. These materials use different ingredients, operate at higher temperatures and respond to solvents differently than the older products. MicroCare has introduced new cleaners specifically to help deal with these high-temperature issues.

But lead-free isn’t the only source of residues. For example, if somebody uses the wrong flux, white residues can result. If cleaning is not performed properly, white residues can result. Even improperly cured substrates can manifest white residues after reflow. So determining the true root cause can be tricky.

All too often, people blame the solvent because it’s the last chemical to touch the board even when the true cause is some other process or change. The good news is that you can be absolutely sure that the source of the problem is NOT contamination in the MicroCare solvent itself. All MicroCare cleaners are filtered to 0.2 microns. This means they are factory-pure. And — unlike some cleaning companies — we never use reclaimed (recycled) materials in our cleaning solvents.

The number one cause of complaints about PCB cleaning are white residues on the board. These usually are salt crystals, residues of imperfect cleaning.
The number one cause of complaints about PCB cleaning are white residues on the board. These usually are salt crystals, residues of imperfect cleaning.

So, what is causing the residues?

There are three likely places to look: the contamination, the solvent, and then the process.

First, look for a change in what you’re trying to clean. For example, have you just switched to lead-free? Or, did a spool of RMA solder get slipped into a “no clean” process? These material changes can cause unexpected residues and cleaning problems.

Next, look for a mismatch between the solvent and the contamination. If the residues are an even, smooth layer of white film across a large area this usually indicates you have the wrong solvent for that flux. For example, the Heavy-Duty Flux Remover – SuprClean™ generally will leave white residues on “no-clean” fluxes. As another example, once in a great while the ingredients in the Alcohol- Enhanced Flux Remover – ProClean™ also will react with “no clean ” fluxes and produce white residues. Change the solvent and the problem goes away.

Lastly, check the cleaning process. When people report white residue problems, it often is a process problem. Look for streaks or spots of white residues. These are the indicators of improper cleaning technique. If your people are using the TriggerGrip™ circuit board cleaning system, check and see if they are using it correctly. Remember the four-step cleaning process: Wet, Scrub, Rinse and Dry. 

To select a solvent, use this very simplified progression from the mildest cleaners to the strongest:

Alcohol-Enhanced Flux Remover – ProClean™ → No-Clean Flux Remover – VeriClean™ → Lead-Free Flux Remover – PowerClean™

If all the other possibilities have been eliminated, contact MicroCare for more personalized assistance.