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.
Spring Probe Pre-Load
Initial Tension
Initial mechanical tension in a test pin ensures that the internal spring is already partially compressed before the probe makes contact with the board. Spring probe pre-load provides a consistent starting force that improves the repeatability of measurements across thousands of test cycles. This feature helps the probe overcome the initial resistance to movement and ensures it stays seated in the fixture.
Force Curve
The amount of force the probe applies increases linearly as it is compressed further during the test. A specific spring probe pre-load is chosen so that the probe is already at a useful force level the moment it touches the test point. This design prevents the probe from bouncing or sliding when it first hits the pad, which could cause damage or a poor connection.
Test Consistency
Consistent pre-load across all probes in a fixture ensures that the board is supported evenly and that no single area is subjected to a sudden spike in force. Manufacturers measure the spring probe pre-load during the assembly of the fixture to verify that all pins meet the specification. If the pre-load is too high, the board may be difficult to seat correctly, while a pre-load that is too low can lead to unreliable test results.
Maintaining these settings is a requirement for high-precision automated test equipment.