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I'm currently working on a PCB design that will have to go in a plastic enclosure.

This plastic enclosure will have to endure severe shocks (dropped from 2m to ground) so I'm looking for ways to reduce the mechanical shock transmission to the board to prevent electrical failures.

I've looked at some catalogs of electromechanical components, searching for "rubberised" spacers or similar, but it seems that experienced electrical engineers don't use these kinds of solutions.

What are the best practises/elements to set-up for reducing shock induced stress in a PCB?

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  • \$\begingroup\$ Best practice: Estimate the severity of the shock (g levels) and choose components that are appropriate by some margin. If you need to reduce shock then rubberized spacers can offer some help but, you need to calculate g forces. Mounting components so that g forces are not shearing them from PCB surfaces is a good thing to do. So is rigid encapsulation. \$\endgroup\$
    – Andy aka
    Oct 11, 2019 at 11:39
  • \$\begingroup\$ Elastomer spacers can absorb shock as well as conformal coatings to reduce shear forces of component solder joints. Fragility boundary curve depends on mass of parts for g and v vs t . Bond strengths are variable. g force = ratio drop height to stop height. So increasing stop from 0.1mm to 1mm reduces g /10 for example \$\endgroup\$ Oct 11, 2019 at 11:39
  • \$\begingroup\$ How about epoxy potting? \$\endgroup\$
    – filo
    Oct 11, 2019 at 12:26
  • \$\begingroup\$ Spacers and then mount the PCB on the side of the enclosure which is least likely to hit the ground. \$\endgroup\$
    – Lundin
    Oct 11, 2019 at 12:28
  • \$\begingroup\$ @Lundin: "Dropped" usually implies arbitrary orientations. I'm inclined to close this as "too broad" because the OP has not specified enough about the enclosure material, the total mass of the device vs. the mass of the components on the PCB, how the circuit is powered, etc. \$\endgroup\$
    – Dave Tweed
    Oct 11, 2019 at 12:34

1 Answer 1

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If possible don't mount the board directly to the side walls of the housing. Don't mount the board at 4 corners. Use a minimum number of fasteners to hold the board in place (one center fastener and a few edge slots may suffice). Board mounting holes could be made large to take a standard slotted rubber grommet, the grommet is pressed into the board, it then mounts onto a pin or held in place with a stepped shoulder fastener that doesn't stress or overly compress the grommet. Any board to housing wiring should have a bit of a service loop (for example leave some extra length to prevent stress during movement). Use stranded wire rather than stiff or solid wire. Keep the board assembly lite, specify low mass components, use ceramic caps instead of tantalum or electrolytic (where feasible). If you coat or encapsulate a board be aware of any heat dissipation requirements.

If cost is not a major obstacle consider using a flex PCB material. (Thin polyimide or kapton are nearly indestructible.) Stress due to a deformed housing can be almost entirely eliminated. If designed carefully such a circuit could even eliminate most or all board to housing wiring.

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