Air Gap Corrections in Clamped Stripline in Plane Permittivity Extraction
Air gap corrections eliminate systematic two to six percent dielectric underestimation in clamped stripline tests, preventing finished board impedance failures.
Fixture Pressure
Mechanical Force
Load applied to a circuit board by a testing or assembly jig ensures that the electrical probes make solid contact with the pads. Maintaining the correct fixture pressure is necessary to overcome the surface tension of oxide layers without damaging the delicate copper features. Too little force leads to false failures during electrical testing due to high contact resistance.
The total load is distributed across the entire board surface to prevent bending.
Contact Reliability
Spring loaded pins within the test fixture require a specific amount of compression to reach their rated resistance levels. Consistent fixture pressure across all probe points prevents intermittent connections that would otherwise delay the production line. Technicians adjust the pneumatic or mechanical actuators to match the requirements of the specific board layout.
Measurements of the individual pin forces are performed regularly to ensure the test system remains within calibration.
Substrate Stress
Physical deformation of the laminate under the weight of the test heads can cause microcracks in the solder joints or the internal copper layers. Monitoring the fixture pressure prevents the application of excessive stress that would compromise the long term reliability of the assembly. Protective bumpers or support pillars are often used to limit the board deflection during the test cycle.
Proper calibration of the clamping force ensures that the inspection process does not introduce new defects into the finished product. Excessive force can also lead to pad cratering where the copper pad is ripped away from the dielectric material.