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label: PCB manufacture,PCB Fabricator,PCB clean

Soldering is an integral step in printed circuit board manufacturing, but residual soldering flux is a source of contamination that must be removed by manufacturers.  Ultrasonic cleaning is widely used as a final step in removing flux contamination.  Its removal must be undertaken with care because flux residues in the ultrasonic cleaning solution must be disposed in a safe manner.

A point of clarification here:  We are discussing PCB manufacturing, not cleaning PCBs in PDAs due to exposure to dirt, water and other contaminants during use.  For suggestions on that topic see our post on refurbishing PDAs with an ultrasonic cleaner.

Most PCB ultrasonic cleaning formulations are water based and biodegradable.  Fluxes and solder pastes, however, may or may not be soluble in water.  If not, they require special solutions based on the flux formulation.

Two cleaning solution concentrates that can be used to remove water-soluble fluxes are the mildly alkaline elma tec clean A1 and neutral elma clean 260 d&s, the latter of which may be effective in removing some fluxes that are not water soluble. Rather than our presenting a shopping list of solutions to remove fluxes please contact our scientists for recommendations based on your specific requirements.

Ultrasonic Cleaners for PCB Fabricators

There are a number of ultrasonic cleaners on the market that are ideal for PCB fabricators. The process is rather straightforward and can be summarized thusly for water-based solutions:

?Select an ultrasonic cleaner with a “Sweep” function to prevent potentially damaging harmonic vibrations.
?Follow cleaning solution manufacturers’ instructions concerning diluting the concentrate, the correct cleaning temperature and estimates of cleaning time.
?Fill the ultrasonic cleaning tank with water then adding the correct amount of cleaning solution formulation.  
?Turn on the unit without a load to mix and degas the solution.  Degassing removes air trapped in the liquid, which slows down the cleaning process.  Some units are equipped with a degassing mode to speed the process.
?Place the boards in a basket or rack in such a way that they do not contact each other.  When ready lower them into the solution and activate the Sweep function.
?At the end of the cycle remove and inspect.  When satisfied rinse the boards with de-ionized water to thoroughly remove cleaning solution residues and allow them to dry.  Large capacity fabricators may elect to employ electric dryers for this process.
Solder Flux Disposal

As suggested above, cleaning solutions may be biodegradable and safely disposed of in sanitary sewers according to local regulations.  Flux residues are another matter.  These must be isolated from the cleaning bath and disposed of in a proper manner.  Suitably equipped ultrasonic cleaners are essential in this aspect. Equipment design also helps you to extend the life of the cleaning solution by removing contaminants that build up in the solution during the cleaning process.

Soldering flux contaminants that rise to the surface can be skimmed off using weirs that direct them to a collection container for storage and later disposal.  Industrial ultrasonic cleaner tanks can be equipped with diverter valves allowing operators to direct floating contaminants or those that settle to the bottom of the tank to filtration systems, returning treated solution to the cleaning bath.  Tanks fabricated with sloping bottoms facilitate collection of settled fluxes for routing to the filtration system.   Check our post for more information on skimmers and filters for ultrasonic cleaners.

Eventually, however, PCB cleaning time will increase as the solution loses its effectiveness in removing solder flux.  It must be replaced.  Drain the tank and dispose of the spent solution according to local regulations.  Take this time to thoroughly rinse the tank with fresh water to remove contaminants that remain on the bottom.  Fill the tank with fresh solution and proceed as above.

*A Note on Solvent-Based PCB Cleaning Solutions

Solvent-based cleaning solutions for water insoluble fluxes may require special precautions.  For example, non-flammable solvent-based solutions can be used very effectively on water-insoluble fluxes.  BUT: if you use these in filter-equipped tanks be certain that the filtering system is compatible with the formulation.  AND: if you use flammable solvents you must use an explosion-proof ultrasonic cleaner.

We hope this post is helpful. Contact the ultrasonic cleaning professionals at Tovatech to discuss PCB cleaning equipment, solutions and solution maintenance options tailored to your production requirements