# Potting your circuits - How is it done?



## MrNaz (Aug 27, 2009)

I've googled this quite a few times, but I can't find any good information on how to go about potting your circuits. YouTube videos only show it being done on a production line. I've found a few suppliers of potting epoxy here in Australia, but none of them can tell me anything about how to use it or where to get suitable containers to put your electronics into.

So I ask here: How is potting done best? Where can I get good containers for potting my circuits in? Where can I get the potting compound in Australia? Any and all info and tips on potting would be appreciated!


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## wquiles (Aug 27, 2009)

Since you frequent the diving sub-forum, I imagine that you are after a water-tight seal. Is that right? Or is the intent to help remove heat from a circuit?

For potting I have used two part Epoxies, both the "regular" variety, and the Artic Alumina Thermal variety. For some projects I have also used a hot glue gun, but care must be followed since the heat can damage what's being potted.

If being used with electronics, it is important to know if the circuit is susceptible to impedance changes/variation caused by the potting compound - specially important when you have inductors that assume "air" around the core. Finding this information from the less expensive circuits/drivers might be hard, but from products from the Sandwich Shoppe (Wayne) or from TaskLED (George), you would have access to the designer of the circuit, and they should be able to help and clarify which circuits are more or less susceptible to these problems.

Will


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## greenLED (Aug 27, 2009)

I've used either 2-part epoxy or clear RTV silicone. Depending on the type of epoxy you use, it may contract as it cures, which can shear off some components of your circuit.


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## Lyndon (Aug 28, 2009)

Back when I did this as part of my job, we used Master Bond potting epoxy and small circular tubing endcaps from Caplugs to hold the circuit/epoxy while it cured. If you use ordinary epoxy, in addition to the cautions given above, be sure that the epoxy you use is not corrosive to electronics. 3M also makes a hot glue stick that is designed for potting; I think DigiKey carries it. 
Depending on the size of your circuits, you may be able to use silicone cookie pans as potting molds. Now your electronics can have Easter or Christmas themes


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## jtr1962 (Aug 28, 2009)

I use potting boxes like these, potting epoxy like this, and use syringes like these to fill the potting boxes. I clean the syringes with turpentine and reuse them. I found of all the ways to put epoxy in potting boxes, syringes work best. Pouring from a paper cup usually results in the epoxy dripping all over the place. Also, I usually use a small bit of hot melt glue to keep the circuit board attached to the potting box so it doesn't shift around while the epoxy is being poured.


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## TranquillityBase (Aug 28, 2009)

*Gun it! *

*McMaster has quite a few choices, and good information for all their offerings. You should be able to find a similar product, if not the same offerings in Australia.*

This particular compound is low viscosity (almost like thick enamel paint), it will flow into very tiny spaces.


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## wquiles (Aug 28, 2009)

Are the epoxies better than the urethanes for electronic circuits?

Will


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## jtr1962 (Aug 28, 2009)

wquiles said:


> Are the epoxies better than the urethanes for electronic circuits?


You can only use urethanes to coat a circuit board (i.e. conformal coating) as they dry by evaporation. Epoxy hardens by chemical reaction between the hardener and resin, and can therefore be used to fill cavities.


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## Oznog (Aug 29, 2009)

Start over: what you you wish to accomplish here? Why do you want to pot it?

Potting GREATLY reduces the thermal dissipation of the circuit. Flashlight drivers are typically run up near "the edge of the envelope" for max thermal ratings, or even operate beyond mfg ratings.

Potting makes it water resistant, but your circuit must be sealed inside a waterproof housing. Potting may not survive long term immersion, the water can creep up the PVC wire jackets and won't dry out.


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## Lyndon (Aug 30, 2009)

If you're going to make a statement like that, at least qualify it. Still air is an _excellent_ insulator. For potting to reduce thermal dissipation, the potting compound would need a thermal resistance greater than free air. Depending on what you use, this is not necessarily the case. 
Look at this table for example: http://en.wikipedia.org/wiki/Thermal_conductivity



Oznog said:


> Potting GREATLY reduces the thermal dissipation of the circuit.


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## Oznog (Aug 30, 2009)

Lyndon said:


> If you're going to make a statement like that, at least qualify it. Still air is an _excellent_ insulator. For potting to reduce thermal dissipation, the potting compound would need a thermal resistance greater than free air. Depending on what you use, this is not necessarily the case.
> Look at this table for example: http://en.wikipedia.org/wiki/Thermal_conductivity



Free air is never still. Still air is like what you get inside fiberglass. The heat causes convection.

Potting will only transport the heat, it must still be air-cooled. It adds considerable resistance to the thermal path, which is compensated for somewhat by the spreading to additional surface area. However, the added resistance to get to far-off surfaces can easily be more than the dissipation at those far-off surfaces, making the total thermal resistance higher.


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## koala (Aug 30, 2009)

Neutral Cure Silicone go get them at Bunnings. They are soft they dont rip electronics component off the board.


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## KC2IXE (Aug 31, 2009)

[


Oznog said:


> ...snip... It adds considerable resistance to the thermal path, which is compensated for somewhat by the spreading to additional surface area. ...snip....



It's NOT quite that simple. I know when I worked in electronics, potting was one of the more complex problems the mechanical engineers dealt with - what materials, what fillers (to make the materials more/less thermally/electrically conductive OR different mechanical properties)

You would actually be surprised that you can use certain fillers (think things like silver oxide or aluminum powders that can conduct the heat away from the board faster than the still air does. OK, you'll say it's NOT still, but for all intents, it is, the mfgs don't count convective currents as "not still" - you have still air - forced air, and insulated, besides that, in a space as small as a flashlight head, you won't have enough space to get any reasonable amount of convective currents. what you have is some sort of coupling from the item being cooled to the outside of the light, be conductive via say the copper on the lands of the board, or conductive via the air - chip to air to housing.

If you were doing enough of it, I'd say call GE or one of the other potting vendors. I know we used to use something like a dozen different potting compounds - everything from beeswax (from what I understand now banned as a carcinogen) all the way up to filled composites that required a vacuum draw after mixing, then multilayer pours, with draws between each pour, but not enough time to cure, so the layers would become one - heck, how you poured the potting into the mold could actually cause the item to pass/fail


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## BoarHunter (Aug 31, 2009)

Devcon and 3M have a whole range of products for this and guidelines !
Now, I fail to understand the need in the case described. 
Far better and even easier to design a watertight enclosure which anyway is required unless you plan to pot the batteries too ?


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## wquiles (Aug 31, 2009)

Based on the recommendations here, I went to McMaster-Carr and found good information, specially on the Loctite products. I went to the Loctite/Hysol web site, and after looking at various of their data sheets selected their ES1001 two-part epoxy for my particular project. Thanks guys :thumbsup:


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## MisterOblivious (Sep 2, 2009)

jtr1962 said:


> I use potting boxes like these, potting epoxy like this, and use syringes like these to fill the potting boxes. I clean the syringes with turpentine and reuse them. I found of all the ways to put epoxy in potting boxes, syringes work best. Pouring from a paper cup usually results in the epoxy dripping all over the place. Also, I usually use a small bit of hot melt glue to keep the circuit board attached to the potting box so it doesn't shift around while the epoxy is being poured.


 

Just a small tip:
When using a syringe fill the "part" from the bottom up. Placing the tip at the bottom and squeezing slowly keeps air pockets from forming and bubbles to a minimum.


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## wquiles (Sep 5, 2009)

Got my circuit potted:












First tie the wires so that they will point toward the center (they will be inside the Delrin body I made earlier):






Pot the circuit - wait to be cured 24 hours:






Will


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## darkzero (Sep 5, 2009)

Will, curious about the applicator tip on your tube. At work we've been using a Loctite brand adhesive used to hold down BGA ICs which requires baking for 10 mins to cure. Our engineering dept was looking into an alternative that does not require baking to speed up production. The sample he brought me had one of those same mixing applicator tips. 

My concern was the tip after used would basically be a "one time" use since after the epoxy set it would no longer be usable. Is that the case here? Are you able to clean it up somehow so you can reuse it or do you use a new applicator every time/session? In our case the epoxy was a fast cure (5 mins). Your potting epoxy takes 24 hours to cure which would give you plenty of time for clean up, is it possible? Compressed air maybe?


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## nein166 (Sep 5, 2009)

....
[checks watch, makes more popcorn]

[repeat]


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## wquiles (Sep 5, 2009)

darkzero said:


> Will, curious about the applicator tip on your tube. At work we've been using a Loctite brand adhesive used to hold down BGA ICs which requires baking for 10 mins to cure. Our engineering dept was looking into an alternative that does not require baking to speed up production. The sample he brought me had one of those same mixing applicator tips.
> 
> My concern was the tip after used would basically be a "one time" use since after the epoxy set it would no longer be usable. Is that the case here? Are you able to clean it up somehow so you can reuse it or do you use a new applicator every time/session? In our case the epoxy was a fast cure (5 mins). Your potting epoxy takes 24 hours to cure which would give you plenty of time for clean up, is it possible? Compressed air maybe?



Will,

Yes, these are designed to be a one-use only mixing/applicator tips. But given its 24h cure time, and the fact that this particular potting epoxy that I selected is very thin (picked up on purpose to make sure of covering every nut/cranny), it should be possible to clean them up and re-use:
http://m3coupe.com/Diving/HYSOL_ES1001.pdf

Compressed air could be very messy. I wonder if we can submerge in the right solvent?


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## QtrHorse (Sep 6, 2009)

darkzero said:


> Will, curious about the applicator tip on your tube. At work we've been using a Loctite brand adhesive used to hold down BGA ICs which requires baking for 10 mins to cure. Our engineering dept was looking into an alternative that does not require baking to speed up production. The sample he brought me had one of those same mixing applicator tips.
> 
> My concern was the tip after used would basically be a "one time" use since after the epoxy set it would no longer be usable. Is that the case here? Are you able to clean it up somehow so you can reuse it or do you use a new applicator every time/session? In our case the epoxy was a fast cure (5 mins). Your potting epoxy takes 24 hours to cure which would give you plenty of time for clean up, is it possible? Compressed air maybe?


 
As Will stated, they are a one time use. It is really bad when you are using a 5 minute cure two part epoxy.

The company I work for sells a few different types of two part epoxies that use the same type of gun applicator and tip that Will used. The tips are a low cost item. We sell them for around $00.50 each for that smaller version.


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## Mick (Sep 6, 2009)

I hope you read this Will.


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## TranquillityBase (Sep 6, 2009)

darkzero said:


> Will, curious about the applicator tip on your tube. At work we've been using a Loctite brand adhesive used to hold down BGA ICs which requires baking for 10 mins to cure. Our engineering dept was looking into an alternative that does not require baking to speed up production. The sample he brought me had one of those same mixing applicator tips.
> 
> My concern was the tip after used would basically be a "one time" use since after the epoxy set it would no longer be usable. Is that the case here? Are you able to clean it up somehow so you can reuse it or do you use a new applicator every time/session? In our case the epoxy was a fast cure (5 mins). Your potting epoxy takes 24 hours to cure which would give you plenty of time for clean up, is it possible? Compressed air maybe?


Not worth the time and trouble, the tips are relatively inexpensive.


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## wquiles (Sep 6, 2009)

Mick said:


> I hope you read this Will.



Absolutely. This is why I contacted the designer of the hipCC (George, from TaskLED), before I even started. Once he gave me the OK to pot the circuit for my specific application, then I ordered the supplies and potted the circuit 

Will


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## darkzero (Sep 6, 2009)

Come to think of it, trying to clean one up is too troublesome. I was thinking of the applicator tips for work use. I already have a mix that I use for potting that I'm very happy with.

At work we may get a new contact which would require at least 14 techs & each one would need to produce 8 units a day. Although the tips are inexpensive I don't see them as being practical for use on my repair line. That's more supplies I'd have to inventory too. 112 tips at $30 -$50 a day at the least plus a lot of waste doesn't sound too good. We will definitely have to find another solution. Thanks


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## gadget_lover (Sep 6, 2009)

The "proper" assembly line procedure is to make up units through-out the day, then pot them when you have enough to use up all the potting compound in one batch. While those are setting you proceed with the batch that was potted previously. 

Of course, the epoxy company really wants you to use up a whole tube in one shot so they can sell more.

Daniel


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## darkzero (Sep 6, 2009)

gadget_lover said:


> The proper assembly line procedure is to make up units throught the day, then pot them when you have enough to use up all the potting compound in noe batch. While those are setting you proceed with the batch that was potted previously.
> 
> Daniel


 
Our line is a repair line rather than an assembly line. We once tried the method of passing each unit to a different tech that each performed a specific repair. Our line was too small to run efficient this way so we changed to having each tech complete the entire repair process for a single unit.

In our case, after BGA repair the system board must be pre tested before applying epoxy to the BGA IC. Each system board is coded & can not be mixed with a different unit, it will not function. Perhaps the method may work if we do get the contract & need to expand the line but even with 14 techs it still may not work out.


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## 1wrx7 (Sep 7, 2009)

The static mixers are meant for one time use... depending on the gel time of the material. I build adhesive dispensing equipment for a living. I think we have about 30 different types of mixers in stock. For our high production equipment we program a purge feature into it, so after X amount of time the machine runs and clears the mixed material out of the mixer into a bucket. It's funny when people don't change the mixer and then pop the rupture discs when the pressure gets too high It only takes seconds to develop several thousands of PSI when the mixer is cured. I bet the time it takes to clean up the mess costs a lot more than changing the mixer.

We've built a lot of machines for potting applications... but I'm not sure if we've built anything for a flashlight manufacturer. I know we've built some to pot light bulbs though.


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