Typical "Packaged Part" Test Fixture
The Cassini ATE Systems use an aluminum Test Fixture to interface the Testhead and Tester Interface Module resources. The Fixture is designed to provide shielding as well as a convenient place to mount components and protect the custom RF and DC wiring for the DUT. In a production environment, the Fixture excels at providing a robust, quickly changed, repeatable method of customizing the ATE system for different DUTs while minimizing cost and maximizing system activity.
To mount a Fixture to Cassini's Test Head, align the fixture with the mounting holes and push the Test Head handles inwards to secure the Fixture. The Fixture is properly connected when the green "Release Fixture" button illuminates. To remove the fixture, push the green "Release Fixture" button at the base of the Test Head Manipulator, pull the Test Head handles outward and lift the Fixture off the test head. The "Release Fixture" button will blink when it is pressed for more than 6 seconds to prevent solenoid wear. If the system is powered down, you can pull the manual Fixture release pin along the side of the Testhead.
RF Test Fixture and DUT Interface Layers
The Test Fixture consists of a stiff precision bottom plate that mates with a Cassini Test Head. The Test Fixture clamping mechanism is designed with spring reliefs to guard against accidentally over torquing the interface. RF and DC cabling is user configurable and software programmable to form a unique custom designed hard dock solution. The Fixture uses standard, easily attainable RI Kits, or "RIK" parts. The DUT Interface Board (DIB) and backing plate stiffener are custom designed for each device. All the needed parts are all available from stock that can be ordered via our website: www.roos.com. RI also provides DUT board and Fixture design that is licensed for customers own use. We will cover Test Fixture in greater detail later in the seminar.
RF DUT Interface Board
A thin DUT Interface Board, typically 8 mm and only two layers, is used to minimize RF parasitic interference. The picture shows the traces on the bottom side of a typical RF DUT Interface Board for a transceiver chip designed for the RI 20 RF Test Fixture (RIK0074A). The DUT and socket are located on the shielded top side. The pads for the DC pogo pins are around the periphery and the 12 RF launches. The dielectric of the traces and "vias" that are used to pass the signal to the socket side are tuned for 50 ohms. The close physical proximity of the decoupling to the actual part is intended to get the best possible measurement fidelity. The dark areas are solder mask areas to allow DC signal traces to pass through the shielded pedestal and the DUT boards RF gasket material.
Test Fixture Top Plate
The Test Fixture Top Plate is shown with the DUT Interface Board removed. You can see the populated DC spring pogos coming through the cutout channel from the inside carrier board and the 12 RF SMA sparkplug launches. The RF launches are solid coax end launch connectors (no spring contact) to provide the best blind mate RF transition that is good for up to 12 GHz operation. The DUT Interface Board is placed inverted on the fixture top plate. There are two alignment pins and matching holes to insure proper orientation, these two are at 90 degree angles to each other (pins not installed here).
Typical Dual Site DUT Interface Board
This is an example of a typical Dual Site DUT board for the RI 20 RF Test Fixture (RIK0074A). For each device, a custom pedestal mounts to this side of the DUT board and contacts the board at the four corners (see the dark mask points). The pedestal supports the Test Socket for each device with RF gasket material at the perimeter, outlined by the dark mask lines between the mask corner, with cut outs for the RF traces to pass through. All DC connections should have a dielectric mask on the DUT board at the pedestal interface crossing to insure proper isolation of the trace. The Pedestal acts as a shield to guard against unwanted signals coupling onto the exposed traces.
DUT Interface Board installed on the Test Fixture Top Plate
The quickly changeable RF DUT Interface Board (DIB) is held in place by a DUT Interface Clamp and, in the case of the RI 12 RF Top Plate, 16 screws. The DIB has small angled cuts by each RF launch to provide alignment. The board material itself helps create a good RF connection by acting as a spring to absorb any pressure created by the DUT. DIBs are calibrated with an available serial IC that can be attached to the board to provide fool-proof operation during production. The DIB's top ground plane and the aluminum Test Fixture produce an effective shield against RF noise commonly found in production floor environments. A test socket is then placed on top of the DUT Interface board without the need for special (and costly) alterations.
RI Custom Test Fixture Carrier Board Feature Expansion
RI offers a variety of reusable Fixture modules that are placed inside the Test Fixture or on the Top Plate Carrier Board to allow easy customization and expansion of the base ATE system's features for specific devices or family of device pinouts. These modules include: dual single-pull double-throw (SPDT) RF switches, single ended/differential adapters, delay lines, programmable attenuators, digital control lines and other signal conditioning modules. They will be discussed in detail later in the seminar and are available for purchase as RI Kits from our web site: www.roos.com.
Here is an example of a high performance 6 GHz dual SPDT RF switch module. These can be combined to expand the basic four full S-Parameter measurement ports of Cassini to more than 32 ports.