|Ask the Experts|
December 10, 2007
Pre clean boards before printing
What is the best solution for cleaning dust and debris from printed circuit boards before screen printing in an automatic SMT line? I currently use paper roll wipes, but upon inspection I still find particles on the boards.
|Expert Panel Responses|
Most companies do not pre-clean their boards before soldering, assuming the boards and clean and fingerprint-free. However, that is often a false assumption, and if your yields are not as high as they should be (95%++) then pre-cleaning might be an option. The fibers you describe often come from cheap wipes made of cheap paper. While they are cost-effective to buy, they leave residues and lint and end up costing more, when rework is included in the equation. You have a couple of different options:
The paper on the left is made from polyester fibers and glue. It is a sample from a very common stencil wiping paper. The fibers are short and fragile, easily breaking in use. Notice how the glue fills up the spaces between the fibers, and coats the fibers with a solvent-soluble residue. All of this is undesirable. On the right is a sample of a high-purity stencil wiping paper. The fibers are long, strong and (although you can't see it on the phone) uncompressible, so they scrub rather than break away into lint. Paper made with these fibers will scrub the bare board or the stencil and leave almost no residues behind. This gives you a much cleaner board, a cleaner stencil, better printing, higher yields and more profit at the end of the day.
You did not describe the environment so I am speculating here based on experience. I believe this is a material handling problem. If you review the packaging coming from your PWB vendor and be sure it is properly sealed and then keep them sealed from dust and dirt you stop the dust and particles before they get there. Then put out on the line only as many are needed to keep the line running. This is all preventative to eliminate the problem rather that fixing it as you go. I hope this is helpful. I realize that you asked about how to clean them not how to stop the problem.
President & CEO - Retired
Bliss Industries, Inc.
Most PCBs are cleaned and then packed in moisture proof packaging. The key here would be to keep them in their original packaging until they are ready for use.
Regional Sales Manager
OK International Inc.
One solution for cleaning is also the use of an ionizer. The ionizer with fan's creating electrostatic charge for discharge your dust. If you have more question you can send me an email.
PROMATION offers a different style of PCB cleaner before screen printing. Our EDR-700 uses an ESD brush, vacuum and ionizer bar to gently sweep and vacuum dust and debris form the top of the PCB prior to printing. The system accepts PCBs from a board loader and then cleans the PCB. SMEMA protocol is used to control line flow between the loader and screen printer. The height of the cleaning brush is adjustable (Z) to allow for varying PCB thickness. The system has a self contained vacuum that provides air suction away from the PCB surface while also capturing debris picked up by the brush. Visit our web site for more information.
President and CEO
There are several different cleaning methods available, depending on the contamination and the location in the SMD line. One solution is called the "sticky roller" approach, where the PCBs are fed underneath a sticky roller and the dirt will be picked up from the PCB onto the sticky roller and then transferred onto another roller not to contaminate the PCB again. Another solution is a brush with an ionized airknife and vacuum on the other side. This solution provides also excellent cleaning results without the cost of the consumerable. If you don't want to "touch" the PCBs, you can also opt for just an ionized airknife with a vacuum system, however your efficiency will be reduced. ASYS can offer a variety of different cleaning systems. Please contact us if you want to learn more.
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