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PCB module is about the size of a nickel and has an ARM processor and a sensor chip or two, plus a connector with 5 or 6 wires.

Module must be firmly attached to device because device will be vibrating. Environment of device may vary: hot/cold, wet/dry, wind/dust.

Cannot modify the target device in any way.

All I can think of is epoxy the bottom (non-circuit side) of PCB to device, which will be metal or plastic, possibly painted. Specifically, coat entire bottom of PCB with epoxy and stick to device.

Surface of device is flat. Device surface may be larger or smaller than module diameter, but always big enough for epoxy to work.

If surface of device is conductive, then standoffs would be epoxied between PCB and device surface.

I cannot think of another method to attach module.

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  • $\begingroup$ Is it desirable to force the module to vibrate with the device, or would a small amount of damping, e.g. as provided by a neutral-cure silicone adhesive, be helpful? $\endgroup$ Sep 27 '16 at 15:19
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If you can't modify the surface you are attaching to then it sounds like an adhesive is your only practical option.

The best adhesive for the task will depend a lot on the target surface. Epoxy is among the strongest classes of engineering adhesives but it can be sensitive to application conditions and surface preparation. It also tends not to be great at filling large gaps.

One attractive alternative is construction type grab/gap filling adhesives. These tend to be reasonably tolerant of adverse conditions and adhere well to a wide variety of surfaces. Their high viscosity also means that they give immediate adhesion and combined with the fact that they are often air curing means that they are quite convenient to use.

Obviously if you glue something to a painted surface the bond strength will be limited by the adhesion of the paint to the underlying surface. Similarly, some types of plastic are very resistant to adhesion (especially things like polypropylene) and may require specialist adhesives and/or surface preparation.

There are also double sided and foam backed tapes which can be good for this sort of application.

As with most adhesive applications you really want to select the best product for the specific circumstances of the job so you would probably do well to talk directly to a specialist adhesive manufacturer or dealer as there are thousands of specialist products available.

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Depending on temp, and inertial effects, you may consider solder. Fatigue limit of epoxy is not always reliable. Wire connection to the board should not be solder, embrittlement of the conductor should be considered.

Lastly, have you considered, with the above mentioned, using Bluetooth instead of wired connectors.

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One technique that might work is to use velcro and 3M Very High Bond Tape (sticky on both sides) to adhere the velcro strips to the circuit board and the vibrating member. This will give you the advantage of having the board easily removable. Try an experiment with this and see if you can shake the board loose, VHB tape is Very sticky, so much so that 3M classifies it as a mechanical fastener , not just plain old tape ;-)

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