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Cradles ​

If a DUT doesn't have mounting or tooling holes, a cradle can be used to help locate the DUT within a fixture. Cradles are typically 3D printed from PETG or PLA plastic, or machined from Acetal (Delrin). Below is an example of a 3D printed cradle. 3D Printed Cradle

Common Design Parameters ​

ParameterDescriptionValue
Cradle ThicknessThe thickness of the cradle, measured from the bottom of the fixture to the top of the DUT.10mm
Min Cradle Offset - MachinedThe minimum distance from the bottom of the fixture to the bottom of the DUT.0.1mm
Min Cradle Offset - V-GrooveThe minimum distance from the bottom of the fixture to the bottom of the DUT.0.2mm
Probe Hole DiameterThe diameter of the probe tip clearance hole.probe_tip_diameter + 1mm
Guide Pin Clearance Hole DiameterThe diameter of the clearance hole for the guide pin.guide_pin_diameter + 1mm

Design Tips ​

  • Use either a STEP model of the DUT, or a DXF file of the PCB outline. These can then be used to create an offset path of the DUT.

Offset Path

  • Know the PCBs manufacturing process.
    • If the PCB is machined, a 0.1mm offset can be used
    • If the PCB is V-grooved, a minimum offset of 0.2mm is recommended.
  • The probe hole diameter should be the probe tip diameter + 1mm.
  • If a guide pin is mounted to the Probe Plate, a clearance hole should be added to the cradle to allow the guide pin to pass through.
    • The clearance hole should be the guide pin diameter + 1mm.
  • Chamfer the edges of the cradle to help guide the DUT into place.

Pre-Centering Guides ​

Pre-centering guides are used to help center the DUT within the fixture. They are typically 3D printed from PETG or PLA plastic, or machined from Acetal (Delrin).

Pre-Centering Guides

These will typically only cover a portion of the DUT, and will be mounted to the fixture using a screws. In the example above the guide is mounted using M3 screws from the bottom of the moving plate. Make sure to add a chamfer to the edges of the guide to help guide the DUT into place. This should make it easy to align the DUT so that the guide pins are easily located.