Frequently Asked Questions - X Probe

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The main difference, for example, is the probe tube on the X75-25 Series is 1.110 [28.19] long vs. 1.000 [25.4] for the 100-25 Series. The added length of the X75 Series is required to form the interconnect housing on the bottom of the probe tube. All other aspects of the probe are the same. The X Probes when used with standard sockets will sit up approximately .085 [2.16] higher than a standard series probe in the same socket. This can be useful in special applications where it’s desirable to have the probe sit up higher in a standard socket.

Pointing accuracy is defined as the maximum radial deviation of a probe tip from the true centerline of a probe’s mounting hole. The total probe-to-target accuracy is dependent upon the “Fixture Offset”, the “Scatter Pattern Offset”, and the “Scatter Pattern Diameter”. When compared to standard probes and sockets, the X Probe’s pointing accuracy is increased because the “Scatter Pattern Offset” is reduced through the elimination of the socket.

The termination pin must not only provide a good electrical path from the probe to the wire termination but also be able to withstand forces during installation, wire wrapping, and many probe insertions and extractions. The termination pin is designed to perform for the life of the fixture under typical test conditions.

A probe can be reinstalled on the same Termination a maximum of 5 times. After this, the probe retention is reduced to the point where the probe is loose on the interconnect pin. The probe retention indents on the probe are the mechanical features that hold the probe to the terminations interconnect pin. Because of the tolerance variability of the mating parts, a probe that is installed onto a different termination than it was originally installed may have lower or higher forces. In the case of low forces, the probe should be replaced with a new one. The probe is designed to be the “wear point” in the system, by replacing the probe; you’ve restored the retention force.

100 separate new X Probes were subsequently installed and then removed from a single termination pin. The retention force of the probe(s) to termination pin was consistent and the interconnect pin showed only light plating wear (viewed at 20X). The termination pin is designed to last the life of the fixture under normal operating conditions. If damaged, however, the pin can be replaced.

The X50 termination pin is designed around a .500 [12.7] long .016 [0.41] square post. The length of the post allows up to four 30 AWG wires to be wrapped to it. Due to its size, a regular style wrap and the installation of shrink tubing on every other post is recommended.

The hole diameter in the Back Plate is too small and the retention bead(s) is being sheared off during installation. These shavings will create shorts between adjacent termination pins. The shavings will “float” and be moved by the vacuum so that the shorts may occur at random making troubleshooting difficult. To prevent the shavings, make sure the hole diameter is within the recommended hole sizes for the termination pin being installed. Please do not assume that drilling AT7000, G10/FR4 or equal with a .038 [.965] carbide circuit board drill will result in a .038 [.965] diameter hole. Quite often, the drills diameter starts .0003 [.0076] undersized and the end hole diameter can be as much as .001 [.0254] undersized. Spot-check hole diameters with the proper Pin Gauge (PG) while drilling to ensure that the hole diameter stays within tolerance.


Yes, the X Probe is compatible with Keysight/Agilent, GenRad, Teradyne and others. Existing fixture kits are able to accommodate X Probes even when additional plates are required. In general, the height of the fixture is increased to maintain the depth of the wiring area to accommodate the personality pins and alignment plate. A taller dress frame is required to accommodate any additional height.

Yes, the X Probe design does not limit the type of fixtures that they can be used on.

Yes, with design considerations standard test probes can be mixed mounted with the X Probe Series. A standard socket would mount in the Probe Plate and clearance holes would be drilled in the Spacer and Back Plates. In a vacuum fixture, a method would have to be designed to maintain the integrity of the vacuum. The best approach is to cut out areas in the plates where the sockets are to be mounted and design inserts with gaskets to accommodate them.

No, the Spacer Plate is an intermediate support plate that when fixed to the Back Plate adds additional strength. On small to medium sized fixtures this can be replaced with fixture standoffs or flanges. Note that the Spacer Plate does help with the alignment of the probe to the termination pin during probe installation.

In large fixtures where the alignment of holes between the three plates is difficult to maintain, it is recommended that the holes in the Spacer Plate be enlarged to accommodate any misalignment, as the size of these holes is not crucial to the X Probe assembly. The holes in the Spacer Plate act as a guide for the X Probe interconnect receptacle onto the interconnect pin. If a relieved hole is desired on the Spacer Plate it is recommended that the oversized hole be on the top surface versus the bottom as this additionally guides the probe.

Yes, the purpose of the .375 [9.525] thick Probe Plate that is shown on our Fixture Layout Examples is to support the probe and guide it to the intended target. The backside or bottom of this plate can be drilled oversized to reduce the top-hole depth.

The height of the probe is controlled by the set height of the termination pin. Note that the set height of conventional fixtures is calculated from the Probe Plate whereas the set height of an X Probe fixture is from the Back Plate

Because the X Probe system relies on accurately drilled and aligned holes, the recommended approach is to remove all of the probes and plates. The new hole locations must be accurately registered from the original reference points so that the probe and termination pin will align during assembly.

Approximately 20 lbs for an average sized fixture. An X Probe fixture requires a Top Plate (Support Plate), Probe Plate, Optional Spacer Plate, and Back Plate while the conventional fixture has a Top Plate and Probe Plate (Socket Mounting Plate).

It depends. The purpose of a Socketless probe is to put a larger probe on closer centers. Meaning, X Probe Socketless Technology was developed for fixtures requiring larger quantities of 75 mil, 50 mil, and 39 mil center probes than 100 mil center probes. The following is a guideline to determine if X Probe Technology should be considered for your fixture.

When comparing the costs of conventional probes to X Probes of like centers (i.e. the 075 to the X75), you will find using X Probes to be more cost advantageous.

  • If a fixture is predominately 100 mil centers, the cost using X Probe would be greater than a conventional 100 mil center probe fixture.
  • If a fixture is predominately 75 mil centers, the cost using X Probe could be equal to or less than a 75 mil center conventional probe fixture.
  • If a fixture is predominately 50 mil centers, the cost using X Probe could be equal to or less than a conventional 50 mil center probe fixture.
  • If a fixture is predominately 39 mil centers, the cost using X Probe should be less than a conventional 39 mil center probe fixture.

But QA does not build fixtures, only a fixture house can determine actual fixture costs/pricing.