A, PCB vias: generally refers to a hole in a printed circuit board, for fixing the connector mounting or interconnecting wiring layer . For the multilayer PCB, PCB vias can usually be divided into: through holes , buried vias , blind holes categories. In the design of the PCB through hole, should avoid the use of blind and buried vias, since the requirement is not satisfied testability.
Second, the mechanical properties of the through hole:
(1), through-hole diameter: hole diameter must be more than the diameter of the connector pin, and leave a certain margin. The minimum diameter of the through hole alignment can be achieved by the defined drilling and plating techniques. Hole diameter, the smaller the space occupied by the circuit board, the smaller the parasitic capacitance, good high frequency performance, but also the greater cost consuming.
(2), via pads: Electrical bond pads plated through hole printed circuit board with the inner surface (or inside) the traces.
Third, the capacitive through holes: each through hole has a parasitic capacitance to ground , the rising edge of the through hole of the parasitic capacitance will slow down or degraded digital signal is not conducive to high frequency signals, which is the parasitic capacitance of the main through-hole Negative Effects. In general, the through-holes affect the parasitic capacitance is very small, negligible. Hole diameter, the smaller the parasitic capacitance .
Fourth, the through-hole inductance: each through hole has a parasitic series inductance , vias reduce the effectiveness of the parasitic inductance of the power supply bypass capacitor, will cause the entire power supply filtering effect is deteriorated. For digital circuits, the parasitic inductance of the through hole larger than the influence of parasitic capacitance, thus to avoid the use of a high frequency circuit through hole.
