Acidic (low-pH) rosin flux has been an industry standard for PCB manufacturing for many years. To clean PCBs of this flux residue alkaline PCB cleaning agents were a natural choice and were found throughout the PCB cleaning industry. These cleaning agents were able to react with and saponify the flux, removing it and leaving the PCBs clean.
These alkaline PCB cleaning agents are excellent at removing acidic contamination from the board such as halide and carboxylic activators that make up the bulk of rosin, but they can also be corrosive. For this reason, ensuring thorough rinsing becomes a critical step after cleaning. Also, alkaline cleaning agents could adversely affect metals like copper and aluminum as well as finishes such as anodized aluminum, iridite finish, and others.
Corrosion inhibition packages were introduced to protect these sensitive metals and finishes on PCBs. These inhibition packages are essentially chemical additives that help mask the effects of alkaline cleaners on those sensitive metals.
Another concern with alkaline cleaning agents is that the high pH levels of the spent cleaning solution also might require a wastewater neutralization step through dilution or acidification to balance out the strong bases. Without this step, the disposal of the spent cleaning solution might not meet local environmental and disposal regulations.
To overcome the above-mentioned concerns, pH neutral PCB cleaning chemistries were developed using molecular technologies that do not rely on the traditional acid-base interaction. These pH PCB neutral cleaning agents allow for effective cleaning of a wide variety of contaminants including newer synthetic resins. The pH neutrality of these chemicals in combination with inhibition packages help protect sensitive metals. Because the pH neutral PCB cleaning agents are neither acidic nor basic, the spent cleaning agent does not need to be neutralized at the end of the cleaning process before being disposed of.
Both Alkaline PCB cleaning products and pH neutral PCB cleaning products are still in use today. What’s the right choice for you? Depending on what you’re cleaning, the level of PCB reliability you require, and your cleaning process, both have their place and can be very effective. If you’re looking for a definitive answer to that question, it may make sense to reach out to an industry partner or cleaning agent provider for some recommendations – don’t go it alone.