Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.8 Electronic industry 909
cleaning because manual applications are not based on precisely defined cleaning processes.
This can also result in fluctuations of the printing result.
(3) Manual cleaning must be completed with the utmost care. Such care costs time and
money, thus making it very expensive. The investments for a cleaning machine can be recovered
within a very short period, independent of the number of substrates that are to be
cleaned.
Example: A worker requires 1 hour per day for stencil cleaning. On the basis of
$40.00/h and 220 workdays, a small machine ($8,700) can be a worthwhile investment
within a year.
Some users clean misprinted assemblies manually. This can prove to be very labor and
cost intensive when larger quantities are involved. The cleaning results and their
reproducibility will be rather inconsistent. Manual cleaning of PCBs with vias and blind
holes with a brush or cloth can mean that solder beads are actually rubbed into the holes.
Such holes can only be satisfactorily freed by ultrasonic or other mechanical means. It is imperative
that the via are free of solder particles, otherwise the consequential damage can be
very expensive.
14.8.3.5 Cleaning equipment for stencil cleaning applications
As previously mentioned, it may well prove to be an economical proposition to invest in a
specially designed cleaning machine if this can be justified by the number of substrates that
have to be cleaned. In general, PCB assemblers use the following different types of cleaning
equipment for stencil and misprint cleaning:
• Spray in air,
• Spray under immersion, and
• Ultrasonic.
Spray in air cleaning equipment
Spray in-air machines consist of either a
single or multiple reservoirs containing
wash and rinse fluids (detergents, solvents,
saponifiers, water, etc.). The stencils are
placed in a separate chamber, and the
wash/rinse fluids are then pumped from the
reservoirs into the stencil chamber, and delivered
onto the stencil via low pressure
(