What Are Circuit Board Mounts?
The circuit board mounts are exactly what their name suggests - mounts that are meant to secure PCBs to the car. This document is a recap of the methods used to mount circuit boards onto the car in MSXIV. This is not an exhaustive list nor instruction manual, and if a better method can be found or thought of, it should be evaluated. This document is not gospel.
All information on this page was compiled (and inferred and observed) from the following sources:
Board Vibration Mounting - Electrical - Confluence (atlassian.net)
Circuit Board Mounts Design Decisions - Mechanical - Confluence (atlassian.net)
A step-by step description of the MSXIV board mount design process may be found in Circuit Board Mounts Design Decisions - Mechanical - Confluence (atlassian.net)
Additionally, more guidelines for designing for high vibration loads may be read and found here:
motor - How to mount electronics on a vehicle chassis safely - Electrical Engineering Stack Exchange
How Best to Protect PCB Mounted Components from Vibration (humiseal.com)
(2) How to protect a circuit board in high vibration environment : AskElectronics (reddit.com)
motor - How to mount electronics on a vehicle chassis safely - Electrical Engineering Stack Exchange
Importing Circuit Boards into Solidworks
To import a circuit board into solidworks, the established method is Altium Codesigner, a plugin for solidworks which allows the synchronization of circuit boards between Altium and Solidworks.
For further information, see Designing Board Mounts - Mechanical - Confluence (atlassian.net)
The Purpose of Board Mounts
Our car will be experiencing very violent vibration. Constant mechanical stress can can break connections on boards and lead to a loss of functionality. This can be catastrophic.
Mounting Techniques
1st Mounting Technique: PCB Mounting Feet
This is a very common way to create a standoff between the PCB and the base it is attached to.
By preventing direct contact, it provides additional protection against base vibrations.
The picture above shows an example of the PCB foot. It is a 90 degree piece of plastic with a tapped hole to screw in the PCB and secure it to a base such as a wooden board. A few notes about the PCB feet:
Very cheap option.
You are able to buy these feet and screws in packs of 40+ for a relatively low cost
Easy to implement.
All that is needed is to tap a hole in the PCB corners and attach the feet/PCB configuration to a central base
Able to resist torsion.
The more of these feet we screw along the corners/edges of the PCB, the more rigid the PCB becomes and is better able to resist torsion
Board Fragility.
Any puncture along the board’s edges or corner increases the risk of crack propagation throughout the board.
It is recommended to avoid puncturing a hole right against the edge/corner of a PCB
As shown above, it is better to leave some space between the screw (S) and any corner/edge.
As illustrated in the first picture the PCB will have to be mounted to a base. It is recommended that the base be wooden. Wood is lighter than metal, cheaper than metal, and is a viscoelastic material. This means it can better dissipate energy such as mechanical vibration.
2nd Mounting Technique: Epoxy
The second method is more simplistic. It involves smearing clear epoxy resin onto the mounting base and gluing the PCBs onto it. A few notes about this method:
Cheap
I believe we still have some left over clear epoxy resin in the bay
It is permanent
Once the epoxy goes on and is hardened, it is hard to change the location of the PCB or make alterations
Not very effective
The lack of elevation from the base in addition to the potential for vibration resonance makes this a risky solution
Resin can be used in addition to another mounting strategy but should not replace it all together
MSXIV decided to work with the first option, with all the bosses placed on a permanent base
Possibly use polyerthane poron in between base of mount and base of box → some vibration protection → 1/8” thick foam
In future, have boards have bottom clearance of ~8mm diameter host
Stackup, from top to bottom:
PCB
3D Printed Board Mount with Heat Set Inserts
Epoxy
1/8” Polyurethane Foam Strip/Sheet
Epoxy
Enclosure Bottom (Fiberglass plate)
motor - How to mount electronics on a vehicle chassis safely - Electrical Engineering Stack Exchange
Designing a Board Mount
Board mounts are best designed slightly larger than the footprint of the board, with a method of mechanically aligning the board to the screw holes for ease of manufacturing.
Boards should be mounted on standoffs with heat-set inserts. The standoffs should be just taller than that required by the length of the heat-set inserts to preserve stability.
Ask elec if there is a standard screw for board mount, if not, we may have to decide ourselves
It never hurts to add a bit of supporting material to the sides of the standoff
Size the hole to be slightly larger in diameter than the tip of the heat-set insert for alignment
Holes for heat-set inserts should be 2-3mm deeper than the length of the heat-set insert to make a channel for the displaced plastic to flow into so it doesn’t rise up through the center of the heat-set and block the hole
When 3D printing board mounts, or other large, flat objects, it is best to have rounded corners >=5mm in radius to disperse stresses from nozzle motion. This reduces the likelihood of parts peeling off the base
Boards should be supported from beneath in areas which will undergo high stress, e.g. by connectors, which will undergo stress when being inserted. The electrical team should be consulted on location of supports.