# What do you use for potting electronics?



## js-lots (Dec 30, 2009)

I have done numerous google searches through cpf and cannot find alot of information regarding potting circuit boards etc. I have also sent out a couple of pm's to no avail. Could someone please recommend a good fairly inexpensive potting epoxy for the occasional modder like myself. I am looking for something that does not require an additional mechanism to dispense it. I am looking to encase a couple of circuit boards in a couple of heatsinks. Thanks in advance.


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## lucca brassi (Dec 31, 2009)

use google with :

http://www.google.com/search?hl=sl&q=polyurethane+potting+compound&btnG=Iskanje&lr=


for potting you must prepaire electronics in right mould which is thermocondustive ( metal) and without unnecessary openings and holes to avoid leaking compound out .


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## datiLED (Dec 31, 2009)

I use Devcon 2 Ton epoxy, mixed with a heavy dose of aluminum oxide powder. The 30 minute working time of the epoxy gives plenty of time to get the epoxy in place, and let it self-level. It creates a solid, smooth looking surface. Be sure to test and doublecheck everything before potting. There are no second chances.


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## js-lots (Dec 31, 2009)

lucca brassi said:


> use google with :
> 
> http://www.google.com/search?hl=sl&q=polyurethane+potting+compound&btnG=Iskanje&lr=
> 
> ...



thanks for your help, I didn't google polyurethane yet, only epoxy potting compound. I keep seeing a 3m product called dp270 but it requires an additional dispensing mechanism. hopefully I can find something that doesnt require an addition of some metallic powder. Something that is ready to go


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## nailbender (Jan 1, 2010)

Go to Digikey and run a search on potting compounds they have several from M&G , some are heat conductive some are not, they have different specs. Some are two part. 
Some are high priced and then they have some for about 30 bucks. 
They also have silicones in RTV format and such.

DatiLED is probably the cheapest route and works good

Dave


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## js-lots (Jan 2, 2010)

nailbender, thanks alot!


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## Icarus (Jan 2, 2010)

datiLED said:


> I use Devcon 2 Ton epoxy, mixed with a heavy dose of aluminum oxide powder. The 30 minute working time of the epoxy gives plenty of time to get the epoxy in place, and let it self-level. It creates a solid, smooth looking surface. Be sure to test and doublecheck everything before potting. There are no second chances.


 
+1 ... as can be seen here.


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## darkzero (Jan 2, 2010)

datiLED said:


> I use Devcon 2 Ton epoxy, mixed with a heavy dose of aluminum oxide powder. The 30 minute working time of the epoxy gives plenty of time to get the epoxy in place, and let it self-level. It creates a solid, smooth looking surface. Be sure to test and doublecheck everything before potting. There are no second chances.


 


Icarus said:


> +1 ... as can be seen here.


 
++1

I also have been using the same mix ever since the Shoppe started selling small quantaties of it back in 2003/2004. To add, if you refer to the datasheet for Devcon 2 Ton epoxy, it also states that one of it's intened uses are for potting electronic components & assemblies, has good impact resistance, & cures without shrinking. This mix is also much easier to remove compared to the industrial type black potting. All my builds can pretty much be disassembled if one knows how to do so.

I also use a similar mix as an alternative for thermal epoxy. _All_ my builds listed in My Archive are built using these mixes. I don't remember the last time I bought AATA.


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## js-lots (Jan 2, 2010)

thanks darkzero, that is exactly what I am looking for. Do you think I could use it without the addition of the powder? Do you do anything different for making a thermal epoxy? I will try to trackdown the two ton epoxy. thanks again


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## jrpnutt (Jan 5, 2013)

Take a look at this video http://www.youtube.com/watch?v=DeKoMUWLv2Y

This shows great alternative to traditional potting. The process uses a highly thermally conductive vibration damped visco elastic material designed to provide mechanical support of an electronics assembly, while reducing the thermal rise of electronic components within that assembly..

More info - http://ultimatesolutions-inc.com


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## CTS (Jan 10, 2013)

There are different reasons for potting and differing materials for each application. Sometimes there are multiple needs. 

Keep in mind, most potting compounds are thermal insulators. Their primary use is for vibration/impact abatement or hermetic sealing. In the one photo above it appears that the potting is being used structurally. If the primary goal would be as a component adhesive I would suggest there are better approaches. That is, unless there is absolutely no reason ever you need to access the componentry. 

If your goal is thermal management, I would suggest examining your approach. Many drivers have individual components projecting at different heights from their boards. If your goal is to use a potting compound to heat sink them all in one shot you are likely doing more detriment than good. 

Thermally conductive potting compounds are much better at moving heat than ordinary potting compounds. But that's a statement that requires some context. And that requires understanding how heat moves. There are two basic thermal paths in the devices we're discussing- conductance and emittance. Conductance is the energy of excited electrons moving through a mass. Emittance is that energy radiating from that mass as electromagnetic energy- radiant heat. An un-potted driver is relying on emittance to dissipate heat. That might work to a certain degree if the components were exposed to a steady flow of cooling air, but that doesn't exist inside a flashlight. So we need something that's efficiently conductive to get that heat to a point where it can be emitted. As you can imagine, emittance is significantly less efficient than conductance. 

All materials conduct heat at varying rates. That transfer is expressed in how many watts of energy are transferred for a given area. You will see this commonly stated at watts per square meter in degrees Kelvin (W/m K). Copper conducts at about 400 W/m K, aluminum at about 200. Arctic Silver 5 conducts at about 10. There's simply no substitute for how heat energy transfers via an atomic bond. If you took two blocks of copper, polished them to a sub-micron finish and pressed the two together with a binder of micron-sized copper powder in between, they won't conduct the same as a solid block. But there is a way to minimize the effect.

Thermal conductance exists in two forms- in-plane and through-plane. Without getting too deep into this, in-plane is substantially more efficient. This is the very reason every driver manufacturer and every seller of thermal compounds instructs to use the absolute thinnest amount of product for affixing or sinking. Even an extra thousandth or two of thickness has a substantial impact upon performance. The reason for this is that is that the closer two surfaces are, the less through-plane effect they are subjected to. Imagine a highly excited electron moving rapidly. That electron is looking to give that energy to a molecule that has less energy. Since they're atomically bonded to the adjoining molecules, it's an efficient process. When you expend that energy into a material that conducts at a slower rate, the transfer slows to the maximum that second material is capable of conducting at. If you can minimize that material's thickness between two highly conductive materials, the kinetic energy of those excited molecules can "jump the gap", so to speak. The thinner the gap, the more kinetic energy is transferred. This effect diminishes logarithmically as thickness increases. In a very short thickness, the effect is lost and now you're conducting at the rate that material is capable of. Really good thermal potting compounds conduct at about 2 W/m K.

If you're looking to control heat in a driver, the absolute best way to do that is to sink each heat-sensitive component individually. I have a cheap driver I'm working with now. The coil is 0.080" taller than the diode and 0.100 taller than the IC. All it takes is a 1" piece of 1/4" x 1/8" copper square cleanly filed to fit each step. With this filler bonded to the two components, the driver now has a three-point contact with the heat sink. When making heat sinks, there's no such thing as too smooth. I work the surfaces on a glass sheet moving from 400 grit down to 2000. It makes a difference.


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