Fixture Strain and Spring Force Deflection Limits on High Density Assemblies
Fixture spring force and deflection limits enforce maximum micro-strain thresholds to prevent latent BGA pad cratering and ceramic capacitor fracture during testing.
Working Height Deflection
Travel Distance
Operational displacement metrics for spring-loaded pins define the distance a probe travels from its rest position to its point of contact during a test. Working height deflection ensures that the probe is operating within its linear force range to maintain electrical accuracy. This value is calculated by subtracting the height of the probe when it is touching the board from its original uncompressed height.
Probe Compression
The total travel of the probe must be large enough to account for variations in board thickness and fixture tolerances. If the working height deflection is too small, the probe may not make a reliable connection on every board in a production run. Conversely, excessive deflection can lead to the probe bottoming out and damaging the internal spring or the board surface.
Life Cycle
Operating the probe at its recommended working height deflection is the best way to ensure it reaches its full rated lifespan. Most probes are designed to work best when they are compressed to about two-thirds of their maximum possible travel. If the test fixture is set up correctly, the working height deflection will be consistent for every pin and provide a stable test environment.
Regular audits of the fixture alignment are necessary to keep the deflection within the safe and effective range.