Meaning
Microscopic flattening of metallic asperities occurs when two conductive surfaces are pressed together. Since surfaces are never perfectly smooth, a-spot deformation represents the actual area of electrical contact rather than the apparent physical area. The process depends heavily on the hardness of the plating material.
Mechanical Load
Pressure increases cause the contact area to grow through plastic flow of the metal until the supporting area can withstand the applied normal force. During this phase, a-spot deformation lowers the constriction resistance by providing a wider path for electrons while simultaneously breaking through brittle surface contaminants. Higher loads typically yield more stable electrical performance because the increased surface area reduces the current density at each individual spot and limits the heat generated by the interface.
Resistance Stability
Long term reliability depends on maintaining the pressure that created the contact spots. If the force drops due to stress relaxation or material creep, a-spot deformation decreases and the contact resistance rises. Vibration can also shift the points of contact and cause intermittent signal loss.
Connection Life
Cycling the connector multiple times can wear down the asperities. This wear eventually leads to base metal exposure and a-spot deformation becomes impossible to maintain. The assembly fails when the spots cannot maintain low resistance.
