Electronics > Mechanical & Automation Engineering

Epoxy molding, encapsulation, molds and stuff like that!

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DTJ:
I'm working on an ongoing ultrasonic measuring device that's used under water, anything up to 10m or more marine, fresh, brackish or sewer.

To protect the electronics its encapsulated in PU epoxy. We precision locate the PCB and piezo elements in a CNC machined aluminium mold and then just pour the epoxy in.
We then wait 24 hours and then push the units out of the mold using a release pin located in the bottom of the mold

The top of the mold is open so the 'base' of the finished product ends up being what was the exposed opening of the mold.
The mold is coated with a PVA release agent prior to the potting process.


       Pour epoxy in here

                   |
                   |
                  \/

|                                                                     |
|                                                                     |
|     ========= PCB =============      |   <-- mold
|                  | PIEZO ELEMENT|                      |
\__________________________________/



All this works ok but it would be nice to perhaps fully enclose the potted part so we get a nice finish on all the external faces.

It's also a bit messy and labor intensive. Typically we manufacture 10 units at a time.


Is there any resources that cover this sort of process? I was kind of hoping there were documents describing how others do this sort of thing or perhaps others that had done it.

We're going through a model change and I guess I'm wondering if we can be doing this a better way.

DTJ:
I'm also interested in ways people might have to precision position components inside the mold as the ultrasonic tx/rx disks need to be set up at a precise distance from the potting compound surface.

thm_w:

For the height offset:
- pins from the mold rising up to touch the PCB in an appropriate place
- PCB tabs that stick out the side and engage with the mold

In both cases I think this would require additional sealing step after removed from the mold though..

Maybe a plastic cylindrical housing that the PCB sits in, extending down to the mold to set the appropriate height.
We used Al housing but that is not cheap.

Google ultrasonic waterproof sensor, most are either plastic housing, aluminum housing, etc. Some have a step in them, possibly where a PCB sits?


https://www.taiwantrade.com/product/40khz-18-mm-waterproof-ultrasonic-sensor-transducer-1782294.html
https://www.makerfabs.com/water-proof-ultrasonic-ranger-jsn-sr04t.html

DTJ:

--- Quote from: thm_w on December 17, 2021, 10:34:50 pm ---
For the height offset:
- pins from the mold rising up to touch the PCB in an appropriate place
- PCB tabs that stick out the side and engage with the mold

In both cases I think this would require additional sealing step after removed from the mold though..


--- End quote ---

We get around this at the moment by supporting it from above the mold. As you say it means having to seal it after demolding which as an added process is a pain.

An aluminium external housing would be nice, we're fully potting to minimise costs.

Benta:
Please educate me:
what's "PU epoxy"?
I know PU and I know Epoxy, but I've never seen that combination.

Thank You.

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