In circuit boards, through-holes and non-metallic vias serve distinct purposes and differ in several key aspects:

1. **Functionality**: Through-holes are primarily used to connect conductive traces on different layers of the circuit board, facilitating internal interconnections or serving as mounting holes for components. Non-metallic vias, on the other hand, are mainly used to secure component leads to the circuit board, ensuring stable positioning of the components.

2. **Process**: Through-holes are holes that go through the entire thickness of the circuit board, making them easier and less costly to manufacture. Non-metallic vias are formed within the inner layers of the PCB and do not extend to the surface, typically created using a via-forming process before lamination.

3. **Location**: Through-holes are located on the top and bottom surfaces of the PCB and have a certain depth, allowing them to connect surface traces with underlying inner layer traces. Non-metallic vias are situated within the inner layers of the PCB and do not protrude to the surface.

4. **Solder Mask Requirement**: Through-holes do not require a solder mask, as they are essential for connecting conductive traces between different layers. Non-metallic vias, however, need to be covered with a solder mask to maintain good electrical isolation between component leads and other elements on the circuit board.

5. **Cost**: Due to their simpler manufacturing process and lower cost, through-holes are used in most PCBs. Non-metallic vias are relatively more expensive to produce and are typically employed only when securing component leads or achieving specific electrical connections is necessary.

In summary, through-holes and non-metallic vias each have their specific applications and advantages in circuit board design. Understanding the differences between them can help optimize circuit board layouts, enhancing both performance and reliability.