​Independent Vacuum

Typical testing environments require a means of holding the Device Under Test (D.U.T.) during the measurement. One of the ways to secure the D.U.T. is a vacuum through seventeen holes beneath the D.U.T. in the Chuck or platform. The vacuum will pull the device to stable position and keep it there during the measurement. Some measurement efforts require that the device be re-measured if the alignment of the probe and the device is altered.

In some situations several devices must be evaluated in a comparative or a successive manner. When one device is through being measured, another device must take its place. Vacuum to all the remaining devices must be separately or independently controlled. (Rotating the D.U.T. is the next step.)

​Tester Height/Size

Typical test systems have the Device Under Test (D.U.T.) height above the bench at a height too high for normal microscope use while standing, or much less sitting down. These test systems have very large dimensions that take a lot of clean room space. These test systems usually necessitate vision systems because the microscope is too far away for the user to use. A better solution would be a test system that allows the user to see most or all of the device while seated and the remainder of the device while standing. Measurements without an expensive vision system or using up more valuable clean room space could be made for devices.

​Rotation of Devices

When testing Circuit Boards, Wafers, Packaged devices, connectorized devices, or Fixtured devices, there is usually the problem of getting probes to more than one set of contact pads. Most test systems will have the user moving the device from the preset area by releasing the vacuum (and all the alignment efforts) and re-measuring. Rotating the Chuck with the devices is better. The devices stay aligned with their own vacuum and the probes stay aligned without being affected. Faster results and fewer errors are made because measurements are made once.

​Ganged Independent Movement Probe Positioners

Positioner movement to get the probe contacts to the devices is made of fine and coarse movements. Typical test systems have the positioner coarse movement range of 3 inches and a fine movement of 1 inch. This is good for devices with pads that are close together. When the device (or devices) are far apart the test data is taken in parts and summed together introducing errors. Having all Probes reach the entire area in ganged (more than one at a time) or independently, means that any size device can be measured with the same high accuracy of a small device. (A large 355.6mm chuck.)

​Heavy Loads

Testing devices with Probes means that the positioner will be supporting the weight of the probe and a coaxial cable to the test system. Keeping the wafer from any harm is important. If the probe were to accidentally be bumped down by a microscope or by a user, the wafer and probe would certainly be damaged. Having the Z-axis of the Positioner  mechanically captured to  keep this from happening is best. Sometimes a user needs something a bit different in the measurement effort. The weight of these set-ups can be enormous when compared to the weight normally seen by a positioner. A gantry style test system is better.

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A gantry style test system has the advantages of carrying enormous weight easily. This allows accurate placement under severe conditions.

​Probe Replacement Repeatability

A common source of calibration and measurement error is to place the probes on the contact pads (of the device under test) inconsistently. The analogy of this type of error is of connector mate and de-mate repeatability. (Connectors have difficulty with consistent electrical performance versus frequency with varying torque, dirty contacts, worn contacts, damaged threads, poor plating, loose parts, et-cetera.) One degree of variation on GaAs coplanar microstrip at 60 GHz is demonstrated when only a 0.2 mil change in probe placement is made.

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