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In article , PhattyMo wrote:
wrote:
On Dec 18, 12:28 am, MarkAren wrote:
Hi All,

Has anyone attempted to use good old fashioned hot melt glue as an
encapsulant for modules ?

Probably needs melting in a pot over a flame (with appropriate care).

A mould could me made out of Plexiglass with appropriate draft
(angles) and high temperature release agent.

A second thought is to use standard two part fiberglass mix, obviously
a lot more rigid, but potting boxes are likely to be needed also.

I guess I could use thin walled pipe to house a long rectifier stack
and associated capacitors.

Both of these options seem significantly less expensive than standard
epoxy potting compound...

Any thoughts ?

Mark

The advantage of hot melt glue is it hardens quickly and even if it
leaks out of your mold, will stop when cool. On the other hand, 2 part
epoxy potting compound when mixed is about as thin as water and will
stay that way for a couple of hours. It will leak from even the
smallest crack or hole.

We use the 2-part epoxy potting compound in custom milled enclosures
for motorcycle control units. The enclosure has two connectors that
have to be sealed in with RTV before the potting compound is added.

This also occurs to me while thinking about our past potting runs. The
hot melt glue will NOT fill all the voids in your unit. Air bubbles
will be trapped and will not be able to get out. The epoxy we use
takes 24 hours to harden at room temp and this allows time for air
bubbles to escape. We have to add more epoxy to each unit for the
first 10-15 minutes as air escapes.

Hope this helps a little.

Paul, KD7HB


One other concern a few people expressed when I was looking for
"alternative" potting compounds- Most epoxies,etc. contract a bit when
they harden/cure. This can (and apparently has,in instances?) "sheared"
components from the PCB's they were soldered to.
The device might work fine,ya pot it,and it works fine..than the epoxy
cures,and it doesn't work anymore because of 'sheared' leads,and cracked
solder joints.
Just something to be aware of.

Some "pro" potting compounds are 2-part RTV rubber. This presumably has
a bit more "give" than a rigid epoxy & is less likely to rip parts off a
board. Another thing to watch out for with two-part materials is that
the ones that aren't designed for potting can get very hot when they
cure. That's one reason you want a very slow curing cycle.

A long time ago I potted a bunch of satellite circuitry in an epoxy
filled with hollow glass microspheres to make it light. The thermal
conductivity was terrible, so you had to be careful to heat sink
anything that might get warm.

Doug White