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.
Push Finger Design
Actuator Alignment
Test fixture components used in automated testing systems provide the mechanical force needed to seat a board against probe pins. A push finger design specifies the geometry and placement of the actuators that contact the PCB surface to ensure uniform pressure without damaging components. These fingers are usually made of non-conductive and non-abrasive materials like Delrin or nylon to prevent scratching the board.
Contact Force
The main job of the fingers is to overcome the combined spring force of all the test probes in the fixture. A push finger design must distribute this load across the board to prevent it from bending or cracking during the test cycle. If the fingers are placed incorrectly, they can apply too much stress to specific solder joints or fragile components.
Fixture Reliability
High-volume production requires the fingers to be durable enough to withstand hundreds of thousands of cycles without wear or deformation. Engineers use mechanical simulations to determine the best locations for the push finger design based on the layout of the board and the position of the test points. The design also includes features to guide the board into the correct position and to hold it steady while the probes are engaged.
Properly designed push fingers ensure a reliable electrical connection and protect the board from mechanical damage throughout the testing process.