9018-18076.pdf.pdf - 第64页
7-6 Site Preparation 7 Compressed Air and Vacuum Requirements Connecting Vacuum to the Testhead Figur e 7-31 shows the vacuum port locations on the system. The vacuum manifolds shown are optional. Figure 7-31 V acuum por…
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
• Connecting Vacuum to the Testhead
Vacuum Recommendations and Guidelines
Table 7-14 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.
• If the vacuum manifold is used, a 2-inch vacuum hose should be used. If vacuum ports are
connected individually, a 1-inch vacuum hose must be used.
Table 7-14 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
Connecting Vacuum to the Testhead
Figure 7-31 shows the vacuum port locations on the system. The vacuum manifolds shown are
optional.
Figure 7-31 Vacuum port locations
Large vacuum
manifold
Small vacuum
manifold
Compressed Air and Vacuum Requirements 7
Site Preparation 7-7
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.