Through-holes (TH) and non-plated through-holes (NPTH) have a significant impact on the electrical performance of printed circuit boards (PCBs) in several ways:

1. **Electrical Connectivity**: Through-holes are holes that are drilled, reamed, or milled all the way through the PCB, primarily used for internal layer connections and/or component mounting. NPTHs, on the other hand, are holes that do not participate in the electrical connections of the PCB, meaning they are not plated with conductive material.

2. **Signal Transmission**: The diameter of the holes, the plating on the hole walls, and the distance between holes all affect signal transmission. Larger hole diameters result in less signal loss; thicker plating on the hole walls reduces impedance; closer spacing between holes increases crosstalk.

3. **Signal Integrity**: Reflections and delays in signal transmission are influenced by the depth and shape of the holes, as well as the number and position of holes. Deeper holes minimize signal reflections; more regular hole shapes reduce reflections; more holes and concentrated positions increase signal delay.

4. **Power Distribution**: The thickness of the power plane layer and the density of holes affect power distribution. Thicker power planes improve uniformity of power distribution; higher hole density reduces impedance in power distribution.

5. **Thermal Performance**: The efficiency of heat conduction is influenced by the diameter of the holes and the plating on the hole walls. Larger hole diameters and thicker plating improve heat conduction efficiency.

In conclusion, the impact of through-holes and non-plated through-holes on PCB electrical performance is multifaceted, requiring careful consideration of factors such as hole diameter, hole wall plating, distance between holes, hole depth and shape, number and position of holes, power plane layer thickness, and hole density.