For high frequency testing, IDI's patented Coaxial
Spring Probe provides electrical performance up to 3 GigaHertz
(with shielding plunger) and 500 MegaHertz (without shielding plunger).
Coaxial Probes have the option of being double-ended (compliant on both
ends) or single-ended (compliant on one end), and most have an option
for a flanged contact barrel. Many single-ended coaxial probes 
come with
a pre-attached coaxial cable and are terminated with an optional SMA
or SMB connector (other connector options are also available. Other coaxial
probe designs include: coaxial probe with a built-in SMB connector and
non-rotating shielding plunger. Most coaxial probe assemblies have signal
conductors that are often replaceable with a standard probe (consult
factory for probe replacement options). Other options include smooth-faced
or serrated shielding plungers.
Coaxial probes with a flanged barrel can be mounted via two fixture plates.
The two fixture plates are mounted above and below the flange and bolted
together at the fixture corners for retention as seen in the figure above.
Caution should be used in this fixturing arrangement when using a pre-attached
SMA connector or other large 
connector
on the end of the coaxial cable. The diameter of the SMA connector is
larger in diameter than the contact barrel of the coaxial probe. This
makes it impossible for the coaxial probe with connector to slip through
the bottom fixture plate.
An alternative to the two-plate method is a press
fit mount into one plate, whether the coax probe is flanged or
unflanged. Again, with single ended probes, a cable may be threaded
through a plate or plated through hole. For double ended probes,
proper orientation needs to be confirmed before mounting the probes
in place. Tooling may be needed to aid in the mounting process.
For all probes, care must be taken to hold a tight tolerance on
the mounting hole to ensure the amount of holding force needed.
Once again, the size of connector may need consideration before
using this method of fixturing. Proper positioning of unflanged
coaxial probes and hole tolerancing are left to the discretion
of the customer.
A different method for fixturing coaxial probes is to simply epoxy the
contact barrel to the fixture substrate. This method can be used for
virtually all IDI coaxial probes.
This
method may make the probes more complicated for replacement. But it is
uncommon for whole coaxial probe assemblies to be replaced because the
signal conductor of the assembly is often replaceable.
Similar to the epoxy method, solder can also be used for fixturing coaxial
probes. Using a temperature-controlled application, solder instead of
epoxy can be used to hold the contact barrel to the fixture substrate.
This method can also be used for virtually all IDI coaxial probes and
may offer better electrical conductivity than epoxy. Coaxial probes such
as the 100304 and 100305 series can be surface mounted using the signal
pin tail for positioning in a mounting hole. However, like the epoxy
method, entire probe assemblies may be more difficult to replace. Care
is needed in the soldering technique to avoid damage due to prolonged
and excessive heating. Other standard soldering techniques should also
apply.
These methods are offered based on previously observed applications.
These or other methods of fixturing coaxial probes should be chosen by
the customer based on specific applications and experiences. The footprint
of test pad/via, signal test pad and ground test pad should be laid out
similar to the footprint illustrated in the figure below. The test pad
for the ground is only required for coaxial probe applications using
the shielding plungers. Consult factory for alternate tip styles and
other probe options.
