...

This page was created by Daniel Puratich to standardize how custom hardware is designed with respect to mounting hole dimensions and mounting patterns during the 2023 competition cycle and is being improved over time.

This document is valid for at least 2023 System Architecture & 2024 System Architecture . This document , and directly refers to Connector Standards as well for implementation. This standard was initially discussed as a part of 2023-02-11 - EE Hardware Mounting Hole Specification in the RFC Forum as a collaboration between WARG’s electrical and mechanical subteamssub-teams.

This document is being revised over time. When creating new board designs, check the recommended specifications below before beginning.

Common Mounting Holes Sizes

For Going forward, all general custom EE flight PCBAs going forward we will follow this the following mechanical mounting hole and pattern specification. These mounting holes can be found in our Altium library:.

Larger is welcome if it is (1) designed with collaboration with the mechanical team and (2) generally intended for a specific application.

For example, https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2694545459/LED+Board+Rev+3?search_id=824a823d-a091-44cd-a839-e67436297d92&additional_analytics=queryHash---e0fa16d9bc21f8c98c92d9fbd02b64297e9353182612e9bd2a87080f9ae2fbc1 uses M4 mounting holes and is intended to share bolts with a mechanical system.

• M3

  • 3.40 mm hole diameter

  • 0.10 mm hole diameter tolerance

  • 6.00 mm annular ring diameter

  • Advised on any PCBA exceeding a board area of 900 mm^2 (this is most boards)

• M2.5

  • Not recommended

• M2

  • 2.40 mm hole diameter

  • 0.10 mm hole diameter tolerance

  • 4.20 mm annular ring diameter

• No Mounting Holes

  • Do this for any smaller boards because running holes smaller than M2 is not really practical as per past conversation .

  • Used on any PCBA with area less than 750mm^2

  • Mounting will be done with double sided sticky tape or Velcro and the board should be designed to facilitate this.

...

• Electrically/Galvanically not connected to the PCBA GND Plane

  • This is because we want our potentially conductive drone frame to be at floating potential in accordance with General System Level Electrical Placement & Routing Guidelines

  • Can be connected to an CGND/ESDGND for ESD purposes though if proper analysis is done.

• Eight vias should be placed evenly in the annular ring around the drill hole

  • Via’s should be plated drills in whichever drill size is used on the board

  • This is done for mechanical stiffness.

  • Altium doesn’t like this, it thinks the vias are shorted to to mounting holes (their net is "No Net") and it keeps complaining about it in DRC. I have to go into design rules → unrouted nets and then set the custom query to “InAnyNet” . Because “No Net” is not actually a net in Altium, use “InAnyNet” to return objects that are actually assigned to a proper net.

• Proper clearance from components

  • Electrical component soldering pads should be at least 1mm away from the annular ring

  • This is done to avoid damaging the components when mechanically securing the board.

    • Board may flex under mechanical load and we do not want to crack components (especially ceramics like big capacitors).

Mounting Hole Pattern

Mounting The mounting hole pattern will be : 30.5x30.5mm for most PCBAs. When measuring the centre-to-centre distance of your mounting holes, you should get 30.5mm for both the X and Y axes.

This means that if you are building a board, try to fit it just in this pattern. If it cannot fit, then expand the board size while keeping the holes within a grid that falls within 30.5x30.5mm pattern. For example, a larger board could have a pattern of 30.5x61mm.

...