I discussed this in a bit of detail in an earlier article on tooling holes, primarily because some prominent resources do not distinguish between mounting holes and tooling holes. Mounting holes can be non-plated, although this is only a desirable practice with plastic screws or standoffs used in the design.Mounting holes should be sized to accommodate some standard-size fastener.Because floating bits of metal can be sources of EMI, the mounting holes should be connected to some ground net (earth (PE), signal ground (SGND), a grounded enclosure, etc.).Mounting holes should generally be plated as this allows mounting with metal screws.There are a few points that everyone agrees on when it comes to PCB mounting holes: How to Design PCB Mounting HolesĪs the name implies, PCB mounting holes are used to secure your circuit board to an enclosure. If you understand how power and ground are defined on the input to your PCB, it will be easier to design a mounting strategy that properly accounts for ground. Like most design rules that are framed this way, the real answer is more complicated and involves many aspects of a design, ranging from input power to the structure of your grounding system. One person will claim they always ground their mounting holes to an enclosure, while another person will claim it should never be done as it will ruin the design. This is a fun question, and the answer is typically framed as an "always/never" situation. Should mounting be grounded in the design, and if so, how should they be grounded? Should they always be connected to chassis, only to an internal ground, or somewhere else? One question that often arises in this instance is the grounding and PCB mounting holes. These PCB mounting holes generally have the pad exposed beneath solder mask so that, if needed, the mounting point can be connected electrically back to one of your nets. In order to provide a secure mount without damaging the surface of the PCB with a screw, it's typical to simply place plated through holes in the corners.
Whenever you place your board into an enclosure, it will need to mount to that enclosure somehow.
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