When selecting a cleaning process - any cleaning process - the chemistry should be selected first. Justification and reasoning for this are explained in an article by Richard Clouthier, "SMT Stencil Cleaning: A Decision That Could Impact Production."

Another excellent source of information is the IPC-7625, "Stencil and Misprinted Board Cleaning Handbook." These and several other related articles may be found at: http://www.smartsonic.com/article.html.

When selecting a stencil cleaning chemistry, some important selection criteria should include the following:

How long has the chemical been in use?

Cleaning chemicals come and go. One that works well on your current flux may not work well on others. When it comes time to change to a new flux, and everyone does sooner or later, will the chemical support the change? Or, will a different chemical be required?

A different chemical means "change" and change can cost money in the form of different equipment, different waste management, and time. If a chemistry has been in use for 10 - 20 years, it is more likely to continue to support future requirements.

If a chemical was recently introduced, it is probably because the manufacturer's previous products could not meet current requirements.

Is the chemical environmentally compatible?

Solvents are commonly considered undesirable do to their environmental impact. VOCs (volatile organic compounds) are highly regulated is states such as California, New Jersey, Illinois, etc. and will only become more regulated in other areas do to their contribution to air pollution.

Be sure to get written documentation from the manufacturer regarding VOC and solvent content of the product as disclosure of these items are not mandatory on the MSDS and, therefore, disclosure is often skirted by the manufacturer.

If a product is VOC free, it will definitely be printed on the label. Many so called "aqueous chemistries" are simply solvents suspended or mixed with water to give the appearance of an aqueous product.

Once the proper cleaning chemical is identified, how to apply the chemical and which machine to use is explained in the articles referenced above.

Ultrasonic stencil cleaners are still the industry standard for cleaning paste from apertures in stencils, but what is changing is the chemistry used to do so.

We have been very successful in winning evaluations at CM’s and OEM’s when we present one of Simple Green’s latest products, mixed with D.I. water at a specific ratio. It is extremely effective, safe on stencils, safe for people, is biodegradeable, has no VOC’s and is all around planet friendly.

It reduces waste stream and material costs significantly, is heavy loading and has no flammable fumes.

The Sawa 5000GUS removes solder balls from stencil apertures after normal wipe cleaning. A powerful hand held ultrasonic cleaning head (W4.61xD4.61xH3.94 in) is manually applied over apertures with any suitable solvent of choice.

During application of the cleaning head, a large 32 x 32 tray containing a foam pad lightly soaked with solvent is held underneath the stencil to capture solder balls dislodged by the cleaning head.