Interconnect Contact
Junction where a microvia makes a physical and electrical connection to the landing pad on the layer below is the foundation of high-density routing. Quality of the target pad interface determines the overall reliability of the vertical interconnect structure in a multilayer board. A strong bond at this point is necessary to withstand the mechanical stresses of thermal expansion and contraction.
Any contamination or oxidation on the surface of the pad before the via is plated can lead to a weak or intermittent connection.
Electrical Performance
Functionality of the via depends on a clean metal-to-metal contact over the entire area of the junction. If the laser ablation process leaves a thin film of resin on the pad, the resulting resistance will be high and may fluctuate over time. This instability can cause signal degradation or localized heating when carrying high currents.
Microsectioning is used to verify that the copper plating is fully integrated with the pad and that there are no visible gaps or inclusions. Reliable interfaces show a seamless transition between the two metal layers under a microscope.
Mechanical Stress
Failure often begins at the corner of this interface where the stress is most concentrated. Proper pad sizing and plating thickness help to distribute these forces and prevent the via from pulling away during assembly.
