Meaning
Electrical property measuring the opposition to the flow of electric current offered by the vertical interconnect access structure in a circuit. Via resistance depends on the conductivity of the plating material and the thickness of the barrel walls. High values of this property cause localized heating and voltage drops in the power delivery network.
Manufacturing Variation
The consistency of the plating process determines the uniformity of the wall thickness across the entire production lot. Incomplete plating or the presence of voids inside the barrel increases the via resistance and creates potential failure points. Inspection through cross-sectioning or electrical testing verifies that the structures meet the design specifications.
Excessive Signal
Excessive resistance in a high speed signal path alters the characteristic impedance and causes reflections that distort the data waveform. While a single via might have a small impact, the cumulative effect of a via resistance in a complex routing path can degrade the eye diagram. Designers use multiple vias in parallel to reduce the total resistance and improve the reliability of the connection.
Heat Management
Heat generated by the power loss in the interconnect must be dissipated through the surrounding dielectric and copper planes. Calculating the expected temperature rise requires an accurate model of the via resistance under peak load conditions. Standard design tables provide the maximum current ratings for various via sizes to prevent the delamination of the board.
