X Probe Termination Set Heights

An X Probe Termination pin set height is a critical factor in the performance and life of the X Probe. When set too low, the X Probe is under-stroked, reducing the contact force and the probe's ability to penetrate surface contaminants. When set too high, the X Probe is over-stroked, resulting in decreased spring life or possible tip or UUT/PCB damage due to bottoming. To calculate the proper set height, follow these steps:

STEP 1

Make a cross-sectional sketch of the fixture in the actuated (2/3 stroke) position. Diagram A is typical of many vacuum fixtures.

STEP 2

Dimension the thickness of the items that stack up on the top surface of the probe mounting plate. Add these dimensions to get a final distance (H) from the top of the plate to the contact surface of the UUT. Subtract the average lead length from this dimension if contacting component leads.

  • (A) is the distance from the UUT to the top of the Back Plate.
  • (C) is the X Probe tube length (see Table A).
  • (P) is the distance from the X Probe tip to the top of the X Probe tube (see Table A). Remember this dimension is with the X Probe compressed to its recommended working stroke.
  • (A) = (H) + .375 [9.53] (Probe Plate) + .563 [14.29] (optional Spacer Plate). Use actual plate thickness or standoff lengths as per your design.
  • Proper set height = (A) - (C) - (P)
  • Example for X39-25 Series

    H = Spacer + Support Plate + Board Stop
    = .062 [1.58] + .196 [4.98] + .125 [3.18] = .383 [9.73]
    P = .105 [2.67] (from table)
    Set Height = (A) - (C) - (P)
    = 1.321 [33.55] - 1.178 [29.92] - .105 [2.67] = .038 [.97]

    To mix X Probe Series within a fixture, calculate the proper set height for each series used in the fixture. Thicker mounting plates allow the greatest set height range, but hole straightness may suffer. For dual level testing, a .400 [10.16] stroke X Probe is mounted using the same termination pin at the same set height, as a standard .250 [6.35] stroke X Probe. As a result, .250 [6.35] and .400 [10.16] stroke X Probes can be interchanged freely from one termination pin to another as test needs dictate.

    Key Probe Dimensions for Calculating Set Heights

    Series

    Probe Tube
    Length C

    Recommend
    Extension P

    X31-25

    1.210 [30.73]

    .133 [3.38]

    X31-40

    1.210 [30.73]

    .133 [3.38]

    X31-40-D *

    1.210 [30.73]

    .283 [7.19]

    X39-25

    1.178 [29.92]

    .105 [2.67]

    X39-40

    1.178 [29.92]

    .120 [3.05]

    X39-40-D *

    1.178 [29.92]

    .270 [6.86]

    X50-25

    1.110 [28.19]

    .133 [3.38]

    X50-40

    1.110 [28.19]

    .133 [3.38]

    X50-40-D *

    1.110 [28.19]

    .283 [7.19]

    X75-25

    1.100 [27.94]

    .143 [3.63]

    X75-40

    1.100 [27.94]

    .143 [3.63]

    X75-40-D *

    1.100 [27.94]

    .293 [7.44]

    * See Decreased Stroke Probes for more information
    ** To account for irregularities at the hole ends, a margin of at least .020 [0.51] is recommended between the press ring and the closest plate surface.