i3070series6_Site_Preparation+11-12.3.pdf.pdf - 第50页
7-6 Site Preparation 7 Compressed Air and Vacuum Requirements Compressed Air and Vacuum Primer Ther e ar e two key concepts involv ed in understanding th e compr esse d air and vacuum r equir ements for the i3070. The fi…
Compressed Air and Vacuum Requirements 7
Site Preparation 7-5
Vacuum Requirements
The i3070 uses vacuum (with vacuum-actuated test fixtures) to pull the board
under test down onto test probes. Because of the different sizes of test systems,
test fixtures, and the variety of boards that can be tested, vacuum requirements can
vary significantly.
Keysight recommends that you work with a qualified vendor of vacuum pumps who
can give you advice based on your requirements.
Vacuum Recommendations and Guidelines
Table 7-2 shows the vacuum recommendations for a typical system.
Vacuum Guidelines
Keep these additional guidelines in mind as you design your system:
• Use the largest diameter of pipe practical from the vacuum pump to the
testhead area. This diminishes vacuum loss due to friction in the piping
(especially at bends), and provides a demand reservoir.
• Keysight also recommends that a filter be installed between the vacuum supply
and the testhead to prevent dirt or contaminants from being sucked through
the test fixture into the vacuum supply.
• Pressure meters, flow meter, and filters are optional but recommended.
• A 2-inch vacuum hose should be used.
Table 7-2 Vacuum recommendations for the system
Description Measurement
Recommended Flow Rate of Pump 18.9 l/s at STP (40 SCFM) Use this value as a guideline.
Vacuum specification is dependent on the fixture, not
the testhead. Keysight has found this specification will
pull down most fixtures.
Pressure Performance 50 kPa (7.2 psi)
Vacuum Control Ports available for
controlling external vacuum valves
4 vacuum control ports: switched 24 volts DC,
750 milliamps maximum per port
Vacuum pumps installed for the tester should be installed
outside or vented outside in order to prevent the vacuum
pump from exhausting oil-bearing air or carbon fragments in
areas where there are people.
7-6 Site Preparation
7 Compressed Air and Vacuum Requirements
Compressed Air and Vacuum Primer
There are two key concepts involved in understanding the compressed air and
vacuum requirements for the i3070. The first is pressure and the second is flow rate.
Pressure is the force per unit area that a gas exerts on a surface. If zero is used as a
reference, the measurement of pressure is called “absolute”; if the local
atmospheric pressure is used as a reference, the measurement is called “gage.”
Although atmospheric pressure varies with altitude and weather, gage pressure is
typically used for engineering measurements, so it is used in this manual. A
pressure value below zero gage is considered a vacuum.
Common units for measuring pressure are kilopascals (kPa), pounds per square inch
(psi), and atmospheres (atm).
Flow rate is the quantity of a gas moving through a given area per unit of time. Since
air is compressible, you must know both the speed and pressure of the air when
measuring the flow rate. To reduce confusion, the industry has agreed on a
standard set of conditions for flow rate measurements called “standard
temperature and pressure” (STP). The standard temperature is 0°C (32°F), and the
standard pressure is one atmosphere (101.3 kPa or 14.7 psi).
Common units for measuring flow rate are liters per second (l/s) and cubic feet per
minute (CFM). When using standard conditions, the units are written as “l/s at STP”
or “SCFM” (standard cubic feet per minute).
Compressed Air
The i3070 uses compressed air to activate both the fixture pull-down towers and
the vacuum valves. The system also provides an outlet for supplying air to
accessory equipment such as handlers and air assisted fixtures.
The minimum pressure needed is 480 kPa (70 psi). The system has an internal
regulator to restrict the maximum pressure inside the system to 550 kPa (80 psi).
The flow rate needed is dependent on how often fixtures are changed, but is
generally much less than what is available in most production areas. Additional air
(flow rate) may be needed to supply the outlet for custom fixtures or presses
depending on their requirements.
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.