Compressed Air and Vacuum Requirements 7
Site Preparation 7-7
Vacuum
The system doesn’t use vacuum directly. Rather, the vacuum is used by the fixture
to pull a device under test (DUT) onto the probes. The system provides valves,
plumbing and control to assist in supplying vacuum to the customer’s fixture.
The pressure requirements for vacuum come from the need to compress the probes,
fixture springs and seals. Since most commercial vacuum systems operate around
50 kPa (7.5 psi), vacuum fixtures are limited in their ability to handle DUTs with high
probe densities. If the sum of the probe, spring and seal forces divided by the area
of the DUT is above 48 kPa (7 psi) the fixture will not be able to properly pull the
DUT onto the probes.
The flow requirements for vacuum come from fixture leaks, number of fixture cycles
per minute, the size of the DUT and the need to quickly evacuate the fixture to make
a good seal around the DUT. Due to the variability of these factors, it is difficult to
provide an exact flow rate recommendation. Keysight has found that a flow rate of
19 l/s (40 SCFM) will pull down most fixtures.
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