By definition, a vacuum is a volume of space that contains fewer atoms than a similar
volume under normal atmospheric pressure. Vacuum is measured in units of torr, which
is equivalent to the pressure exerted by a one-millimeter thick layer of mercury under a
gravity field of one Earth normal gravity. Zero torr is a total vacuum, defined as a
volume containing no atoms whatsoever, and 760 torr is standard sea level atmospheric
pressure. The DP-HF machine has chosen to display the vacuum level in inches of
mercury (inHg) as a standard unit. 1 torr is equivalent to 29.91 inHg.
To create a vacuum, a volume must first be completely sealed. Vacuum pumps can
then remove atoms to create a vacuum in that volume. There are several types of
vacuum pumps, with each type having its own specific method of removing atoms. A
positive displacement pump seals off a volume of air and forces that air out of the
vacuum chamber. This type of pump is most effective for rough vacuums, and usually
has a lowest achievable pressure of around 28 inHg.
Circuit Automation has introduced the concept for a Vacuum Chamber for printed circuit
board manufacturing. A vacuum chamber is designed as an integral part of soldermask
application process. Due to the shrinking feature sizes in PCB manufacturing, increased
track height, reduced spaces between traces, soldermask via plugging, and the
requirement for increased coating thickness for ENIG applications, air entrapment has
become a major manufacturing issue. Traditional mixing of two part epoxy soldermask
inks and application techniques has entrained and entrapped air into the mask. The
entrapped air causes problems and defects upon further processing either by the
vacuum in the exposure process or by creating “volcanoes” in the final baking process.
This vacuum pump works on the claw principle.
The components are dimensioned such, that on the one hand there is never contact
between the two claws or between a claw and the cylinder, on the other hand the gaps
are small enough to keep the clearance loss between the chambers low.
In order to avoid the suction of solids, the vacuum pump is equipped with a screen in
the suction connection. To avoid reverse rotation after switching off, the vacuum pump
is equipped with a non-return valve. The vacuum pump compresses the inlet gas
absolutely oil-free. A lubrication of the pump chamber is neither necessary nor allowed.
Manuals and Documentation