Today, nearly 70% of all printed circuit boards (PCBs) are assembled with no clean fluxes & pastes. A No Clean process was chosen to reduce the cost per assembly, decrease cycle time and reduce material handling defects by eliminating the cleaning process. It also avoids the increasing costs of floor space, equipment, chemicals, water and electricity that are all required to run the cleaning process.
Many assemblers may clean no clean flux residues to improve the cosmetic appearance of the boards. They just clean the boards they want to clean, not always the boards they perhaps need to clean.
But there are several reasons to remove no clean flux residues from PCAs:
Perhaps most importantly, when cleaning is required by contract or Procurement as agreed between User and Manufacturer or when the IPC J-STD-001 is cited.
According to IPC-A-610 and/or J-STD-001, any residues mustn’t interfere with visual inspection. If there is anything left that is obscuring solder joints, for example, then it must be cleaned off, either by hand or by using one of the automated cleaning machines available. If you leave the no clean residue on the board, that interfere with visual inspection, it would be a defect for class 2 and 3 products.
Another reason for cleaning is that no clean residues present on circuit boards can interfere with signal transmission in most instances.
Assemblers may clean no clean flux residues to remove solder balls and/or to prevent corrosion in PCBs exposed to extreme environments.
Also, no clean fluxes can inhibit proper adhesion of conformal coatings. No clean flux residues can absorb moisture in process. In any further curing processes, the release of any moisture can cause the coating to be separated from the board and incomplete conformal adhesion can occur. This can allow corrosive materials, carbon dust build-up, or moisture to penetrate under the assembly and cause corrosion, signal transmission problems, and component failure.
Flux residues left behind by no clean fluxes & pastes are more difficult to remove from PCBs than other fluxes. Since they are formulated not to be cleaned, the residues from no clean products can be left on the board in unwanted areas with detrimental effects on the PCB. They’re not necessarily designed to come off.
creates a cleaning challenge if you need to clean off a residue that was not
designed to be removed.
Many electronics assemblers are still struggling with the process of adequately and effectively removing no clean flux materials.
Want to know more about cleaning PCB’s and PCA’s? ETECH has a training course about cleaning PCB’s and PCA’s. In this Cleaning of PCB’s and PCA’s training, you will learn more about the reason for cleaning (Pro’s & Con’s), how clean is “Clean”? and what about No-clean flux? Do we need to clean No-clean flux?