Interfacial Conduction
Surface topography dictates actual current flow during printed circuit board component placement, because microscopic peaks on copper pads and component leads touch across limited contact points rather than across nominal pad areas. Under normal mechanical clamping forces, micro asperity contact forces electrical current through constricted conducting spots. Oxide films and organic residues inhibit metallic transfer at these microscopic junctions, requiring chemical surface preparation during board fabrication to lower electrical resistance.
Automated optical inspection equipment cannot evaluate subsurface conditions at these interfaces, so manufacturers rely on electrical resistance testing to verify proper mating.
Thermal Dissipation
Heat transfer paths across joined surfaces depend on microscopic gap filling during assembly, because trapped air pockets insulate mating layers. When high power semiconductor devices mount onto printed circuit board heat sinks, micro asperity contact defines the true thermal transfer coefficient across the interface. Filler materials such as thermal paste or phase change pads conform to surface irregularities to displace air, replacing poor conductors with materials possessing higher thermal conductivity values.
Thermal transient testing detects voids and poor surface coupling after reflow soldering operations.
Contact Mechanics
Plastic deformation occurs at microscopic peaks when mating surfaces experience clamping loads during final chassis integration. Hardness differentials between plated copper pads and component terminal finishes dictate whether peaks crush or embed during screw tightening or connector engagement. Permanent electrical stability relies on stable mechanical pressure that prevents fretting corrosion at the interface over operating lifecycles.
Destructive cross section analysis reveals whether excessive clamping pressure flattens asperities beyond elastic recovery limits, risking substrate delamination beneath the pad.
