Vacuum Interfacing

The Xandex Vacuum Interface is designed for test applications requiring a high degree of parallelism and repeatability. The interface design illustrated below provides 640 pounds of force to compress over 7,000 spring probe pins. Probe card displacement is minimized because compression force is distributed evenly across the face of the probe card instead of at the center and edges, as in traditional mechanical compression strategies. Kinematic docking features integral to the interface provide repeatable docking z height (test head to prober) of <5 µm with reproducable planarity of <4 µm.

A general description of the Xandex vacuum interface is included here, along with links for additional information.

Vacuum Interface Components

The Xandex vacuum interface assembly consists of three main structural and functional components:

Base Plate Assembly

Interface Tower

Probe Modules

For a description of kinematic docking used in the Xandex Vacuum Interface Click Here.

For an operational description of the Vacuum Interface Click Here

For links to more information Click Here.

Base Plate Assembly
The base plate assembly provides a rigid support structure that contains alignment features for installing the PTI on the test head front plane, docking features for docking the test head (and interface) to the prober and mounting features that align the probe block connectors to the test head probe electronics boards.

The base plate also incorporates a pneumatically activated probe card latching ring that retains the probe card in the interface tower during the load/unload operation and prevents the probe card from being released from the PTI in the event that test head power or vacuum fail.

Interface Tower
The interface tower is a circular frame milled from stainless steel that retains and aligns the spring probe block assemblies. The tower incorporates vacuum channels necessary to supply vacuum flow to the probe card side of the interface and seals to maintain vacuum between the interface tower and the probe card. The interface tower is installed and planarized onto the base plate at the factory. Once the base plate/tower assembly is installed onto the test head, planarization of the test head to the prober is achieved by adjustment of the kinematic docking features on the prober.

Probe Modules
Cabled probe modules are installed in the interface tower and provide the electrical connectivity between the test electronics and the probe card. One, two or more separate test sites can be designed into a single module. Probe modules are populated with spring probe transmission line cables to provide signal, power and utility paths between the test head and the probe card. Signal channel ground isolation is accomplished by pairing or surrounding the signal channels with two, three or four individual ground pins, depending on performance requirements.

In configurations with less than a full installation of test sites, blank (unpopulated) modules are installed in the unpopulated sites to maintain PTI vacuum seal integrity.

Probe module tester side connections are designed in pairs and installed into slots machined into the base plate assembly. The interlocking design of each pair of carriers ensures that they are aligned in the PTI base plate so that after the PTI is installed on the test head, probe electronics boards will automatically "blind" mate with the corresponding probe block carriers as the probe electronics boards are installed.

Kinematic Docking
Xandex vacuum interfacing technology utilizes a kinematic docking scheme consisting of three rotating docking ball assemblies installed on the prober head plate. The three docking balls engage three corresponding grooved docking cups integral to the PTI base plate when the test head is docked to the prober.

The docking balls are planarized to the prober chuck top at installation. The test head is positioned for docking over the prober using manipulator controls. Sensors in the PTI base plate docking cups are activated by tuned magnets located at the apex of each docking ball (installed on the prober) indicating that the test head is in position to dock.

At this point the manipulator counter balancing force is removed, allowing the weight of the test head to rest on the three docking balls installed on the prober. This provides precise, planar and highly repeatable kinematic isolation of the test head.


Vacuum Interface Operation Each probe card is mated to a dedicated mounting ring assembly that contains features to align the probe card on the probe card changer, align the probe card to the PTI tower and enable the probe card to be latched into the PTI tower to prevent accidental damage. The probe card/ mounting ring assembly is loaded into the prober and presented to the PTI using the prober's probe card changing mechanism. When the probe card is positioned under the PTI, a latching ring is activated pneumatically to retain the probe card in load position in the PTI as the probe card changer is retracted. Sensors are provided in the PTI tower to sense when the probe card changer is in position to load/unload a probe card and to detect whether or not a probe card is present in the PTI. When the probe card is detected in the PTI and the latching ring sensors indicate a latched condition, the operator initiates the probe card load sequence. A vacuum is initiated and drawn through channels in the face of the PTI tower, pulling the probe card onto the PTI tower vacuum seals and compressing the PTI spring probe pins against the probe card. Fixing the probe card to the interface tower rather than holding it in the prober provides predictable and consistent forces on the probe card and eliminates board deflection caused by docking misalignment common to mechanical latching methods. This results in repeatable Z-location and planarity of probe needles and allows for improved control of "Z-budget" (or "Planarity Window"). Balanced forces on the PTI also ensure a reliable electrical connection between the probe card and the tester.
More Information For a detailed explanation of Xandex vacuum interface and docking technology see the presentation "Enabling X144 Wafer Sort" (PDF 6.25Mb) by Roger Sinsheimer, Xandex Chief Engineer and Ken Karklin, Agilent Technologies R&D Product Manager. Xandex Automated Test Equipment interface design methodology was illustrated in an October 2001 Evaluation Engineering article "ATE Interfacing Outgrows 12" Probe Boards" by Technical Editor Tom Lecklider. Using the Agilent V4400 as an example of a modern high pin count tester that provides a high degree of parallelism, Lecklider examines in detail the interface solution designed by Xandex. Click Here to view an exerpt from the article. For more information on Xandex interface products, contact a Xandex ATE Account manager.