What is a PCB fan hole?

PCB fan hole: A term in PCB design that refers to an action, commonly understood as pulling wires to drill holes.

Requirements for PCB Fan Holes in PCB Design

1. The main function of via is to connect the signal layer by layer. When using via in design, signals must be connected at different layers, and not only one layer, which can cause STUB. Excluding heat dissipation holes.

2. The number of through holes used in the same design should not be too many, generally not more than 3. The conventional through-hole sizes are 8/16, 10/22, and 12/24. In special cases, 8/14, 10/20, and 10/18 through-holes can be selected. HDI designs generally use 4/10, 4/8 laser holes. Generally, it is preferred to choose the type with a larger through-hole diameter, which can improve the qualification rate of production and reduce production costs. In principle, a 12/24 type through-hole design should be selected for the 2-layer board.

3. The selection of through-holes must consider the plate thickness and aperture ratio. For designs with thicker plates, larger through-hole types must be selected. For special copper thickness design requirements, priority should be given to selecting through holes with larger apertures. If conditions do not permit, timely communication with the plate factory should be made regarding their production capacity requirements.

4. The selection of through-hole types and design quantities should consider their current carrying capacity. To ensure design margin, space will be processed twice the calculated quantity and can be selected based on specific design requirements.

5. When fanout through holes, the spacing should be considered, and it is required that one signal line can pass between the two holes to prevent the holes from damaging the integrity of the ground and power supply. It is recommended to have a center distance of at least 1mm (39.37mil) between the two through holes.

6. Priority should be given to the outer side of the IC fan out, and multiple rows should be adjusted as much as possible to fan out near the pins through the signal holes of the power supply. The left and right through holes should be kept on the same horizontal line to facilitate inner layer wiring.

7. The capacitor fanout should ensure that its loop to the power supply pin is minimized. Avoid drilling through holes on the plate to prevent welding defects and increase production costs. It is necessary to drill holes in the tray, and the holes should be drilled at the edge of the pins, not at the center position.

8. The edge of the board must be drilled with a GND through-hole along the position where the board frame is retracted. The distance between the through-hole and the through-hole should be around 50-200 mils.

9. When the BGA device is fanout, the through hole should be drilled at the diagonal center of two pads and fanout in all directions. The cross channel in the middle is prohibited from drilling through holes to ensure the current carrying capacity of its power channel.

10. When fanning out BGA devices, it is possible to consider pulling out the front two rows of holes for a certain distance. The pulled out through holes should be aligned with the through holes in the middle of BGA as much as possible to facilitate the inner layer output of BGA device signals.

11. Generally, the number of output lines per layer can be estimated based on the spacing between BGA devices, and the required design board layers can be planned. Generally, for channels with a spacing of more than 1mm, two signal wires can be laid in one channel, and for channels with a spacing of less than 1mm, one signal can be laid in one channel. 0.4mm spacing can generally only be used for HDI design.

12. For devices larger than 0805 packaging, it is recommended to use cross connection processing. Large area copper plated through-hole solder pads generally adopt cross connection treatment, especially for GND network through-hole pins of multi-layer boards, to prevent excessive heat dissipation during welding and poor welding.

13. When designing multi-layer boards, avoid situations where there is no copper on a large area, in order to prevent the presence of copper in multiple layers within a certain area. The density difference on the board is too large, and thermal expansion and contraction during temperature changes can cause bending of the board, especially for larger areas.

14. After the PCB design is completed, the copper skin on the board must be repaired with copper treatment to eliminate the sharp corners of the copper skin. The presence of isolated copper on the PCB must be checked and strictly prohibited.

15. When switching layers of differential signals, GND vias must be added near the layer changing vias to ensure a short reflux path.

16. In the middle of the two vias of the differential signal, all layers remain clear and other signals are prohibited from passing through.

17. The differential signal output method should maintain coupling and symmetry, and minimize the uncoupling length as much as possible.

18. When the BGA device is fanout, in order to facilitate the placement of the filtering capacitor, the power and ground holes can be combined. Generally, two pins are allowed to share one through hole, and multiple pins are not allowed to share one through hole. During design, efforts should be made to avoid hole closure to ensure the current carrying capacity of the power supply and ground.

19. It is recommended to drill at least one ground through-hole on each ground pad of the high-speed connector, and the through-hole should be as close as possible to the pad.

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