During the PCB assembly process, contamination is inevitable. Flux residues, adhesives, dust and other debris can remain on the board and underneath components. To rid the board of this contamination, there are several choices available for PCB cleaning. Among these are DI-water (for water-soluble fluxes) and engineered PCB cleaning chemistries.
Printed circuit board design and manufacturing is becoming more intricate boasting increasingly complex board designs, lower standoff heights and stacked components. Additionally, the industry has seen an increased use of lead-free solder pastes which requires higher soldering temperatures.
So, is cleaning with DI-water good enough? That depends on the level of reliability needed for your PCBs, and only you can make that determination.
While many PCB cleaning processes rely on cleaning water-soluble fluxes (also known as organic acid or OA fluxes) with DI-water only, recent studies suggest that the ability for water to clean PCBs has reached its physical limitations, favoring the use of a chemically assisted cleaning process.
The increased use of water-soluble, lead-free solder requires more flux activators and higher soldering temperatures. This often results in more burnt-in fluxes and produces water-insoluble contamination. DI-water alone has a limited to no ability to solubilize non-ionic residues on the board’s surface.
In terms of board design, we’ve seen a shift to more densely packed components which further limits the effectiveness of pure DI-water. Due to its high surface tension of over 70 dynes/cm, water cannot effectively penetrate underneath low standoff components. Chemistry assisted cleaning processes, however, can reduce the surface tension to 30 dynes/cm and below, allowing the spaces under low-standoff components to be reached and cleaned.
If you have cleaning machinery capable of using engineered cleaning chemistry, an additional advantage of chemistry is that often processes can operate at lower temperatures and with a wider process window. Having this flexibility may lead to operational savings for years to come. Management will love it!
Perhaps it’s time to examine your process to determine if there’s a better solution to address your unique cleaning needs. The use of an engineered PCB cleaning solution can ensure flux residues and other contaminants are fully removed from the assemblies. If you have questions, don’t go it alone. Get some help. Think about aligning yourself with a partner that can aid you in determining a better cleaning process.