Surface Interaction
Mechanical actions that occur when a test needle slides across a metal pad to remove surface oxides and contaminants. This probe scrub is the result of the horizontal movement caused by the bending of the probe tip as it is pressed down onto the wafer. It ensures a metal-to-metal connection which is required for accurate measurement of electrical signals during the testing phase.
Friction Effect
Interaction between the tip and the aluminum or copper pad creates a visible mark that indicates the quality of the alignment. The length of the probe scrub depends on the angle of the probe and the amount of vertical travel applied by the machine. Engineers analyze the shape of this mark to determine if the contact force is distributed evenly or if the tip is skidding too far.
Shallow Contact
Marks that lack depth might indicate that the probe did not penetrate the oxide layer effectively. Measurement of the scrub length verifies that the mechanical setup is providing enough horizontal motion for a clean connection.
Accumulation Control
Metal particles on the tip can lead to increased contact resistance if the scrubbing is not controlled. Automated cleaning blocks are used to remove these residues from the probes at regular intervals. Monitoring the consistency of the scrub process helps prevent false test failures and extends the life of the probe cards.
