Potting PCB for protection
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Tikka308
Jul 29, 2011, 4:26:21 PM7/29/11
to NYCResistor:Microcontrollers
I'm using a PCB in an extended outdoor and semi-abusive environment
and was told that potting the PCB in a "potting" compound (apparently
like an epoxy) is a great way to protect the board. I've found plenty
of info about industrial solutions but am trying to find a DIY home/
small use kit where we can brush or apply it manually to test. Does
anyone have any pointers, products or companies?
Searching on digikey yields things like RTV silicone (http://
search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=473-1138-ND)
- is that "potting"?
and was told that potting the PCB in a "potting" compound (apparently
like an epoxy) is a great way to protect the board. I've found plenty
of info about industrial solutions but am trying to find a DIY home/
small use kit where we can brush or apply it manually to test. Does
anyone have any pointers, products or companies?
Searching on digikey yields things like RTV silicone (http://
search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=473-1138-ND)
- is that "potting"?
Joseph L. Pizzo
Jul 29, 2011, 6:09:39 PM7/29/11
to nycresistormi...@googlegroups.com
What about silicone window caulking?
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Foxx D'Gamma
Jul 29, 2011, 7:37:54 PM7/29/11
to nycresistormi...@googlegroups.com
I have worked on some projects like this before. Potting as its called is pretty much putting your device in an enclosure and pouring in an epoxy medium or the like in order to entirely case in the board and wiring to be nigh' impossible to reverse engineer, repair, but makes it almost indestructible in most cases. Here are some things to take into consideration.
Will it be in direct sunlight? UV Rays can break down some plastics and resins. Epoxy is usually ok for most situations. Silicone Caulk is also a good idea. There are project enclosures you can purchase that can take some decent abuse, like the telephone box on the side of your house (if you have one. Or a FiOS box). Usually I see potting as a copy-protection or anti-mod technique. All of my radio scanners (I am a ham radio guy) have most of the PCB coated in a black/brown/grey epoxy so you cant fiddle with any of circuitry.
Do you want it to be impossible to reverse engineer? Some companies will use a black/brown epoxy, or even epoxy with aluminum 'shavings' in it so you cant see through it, or even X-Ray it.
How weather-proof do you need it? 100% water and humidity tight? Will heat be an issue? Last thing you want is to blow a component and have no way to service the potted PCB.
How often will you need to service the wiring or power supply? There are external connectors for wiring hookup that have INSANE tolerances. Molex makes quite a few that can take psychotic levels of extreme conditions This is a link: http://www.molex.com/molex/products/group?key=sealed_connectors&channel=products I have used a few and I must say if you have a concern about replacing external hookups, sensors, switches, display, keypad/keyboard, even standard connections like serial and USB, this would be an ideal solution.
I have used plain ol' two-part epoxy resin to protect my projects in the past. I wound up using a generic enclosure, ABS Plastic, modified with some external connectors to hook in my power and I/O - then filled it with epoxy. My project was more of a toy, which was intended to take a 40 foot drop onto hard concrete if it had to, or being completely submerged in water. The 5 Minute Epoxy stuff is pretty good for some general tests, and you can get it any almost any hardware store. The caulk route could also be a good choice but it could be fouled by heat generated by the circuit (power supply circuitry tends to give off a bit of heat, especially linear regulators).
Can you give us some more information of what kind of environment you think your gizmo might face? The more details about the project, the more I can help.
Cheers, Beers, and Bunny Ears,
~ Foxx
Will it be in direct sunlight? UV Rays can break down some plastics and resins. Epoxy is usually ok for most situations. Silicone Caulk is also a good idea. There are project enclosures you can purchase that can take some decent abuse, like the telephone box on the side of your house (if you have one. Or a FiOS box). Usually I see potting as a copy-protection or anti-mod technique. All of my radio scanners (I am a ham radio guy) have most of the PCB coated in a black/brown/grey epoxy so you cant fiddle with any of circuitry.
Do you want it to be impossible to reverse engineer? Some companies will use a black/brown epoxy, or even epoxy with aluminum 'shavings' in it so you cant see through it, or even X-Ray it.
How weather-proof do you need it? 100% water and humidity tight? Will heat be an issue? Last thing you want is to blow a component and have no way to service the potted PCB.
How often will you need to service the wiring or power supply? There are external connectors for wiring hookup that have INSANE tolerances. Molex makes quite a few that can take psychotic levels of extreme conditions This is a link: http://www.molex.com/molex/products/group?key=sealed_connectors&channel=products I have used a few and I must say if you have a concern about replacing external hookups, sensors, switches, display, keypad/keyboard, even standard connections like serial and USB, this would be an ideal solution.
I have used plain ol' two-part epoxy resin to protect my projects in the past. I wound up using a generic enclosure, ABS Plastic, modified with some external connectors to hook in my power and I/O - then filled it with epoxy. My project was more of a toy, which was intended to take a 40 foot drop onto hard concrete if it had to, or being completely submerged in water. The 5 Minute Epoxy stuff is pretty good for some general tests, and you can get it any almost any hardware store. The caulk route could also be a good choice but it could be fouled by heat generated by the circuit (power supply circuitry tends to give off a bit of heat, especially linear regulators).
Can you give us some more information of what kind of environment you think your gizmo might face? The more details about the project, the more I can help.
Cheers, Beers, and Bunny Ears,
~ Foxx
TerryKing
Jul 29, 2011, 8:54:32 PM7/29/11
to NYCResistor:Microcontrollers
Two-Part Epoxy is good. Check for a locaL Marine supplier and get
West Epoxy in quarts / gallons. There are also good fillers and
thickeners if you want to "only coat circuit boards" against moisture.
Most Silicone products and caulks cure from moisture in the air and
will only cure about 1/8" in a day and 1/2 inch in a week.. so not
good for a bulk pour.
Regards, Terry King
...In The Woods In Vermont
te...@yourduino.com
On Jul 29, 7:37 pm, "Foxx D'Gamma" <foxx...@gmail.com> wrote:
> I have worked on some projects like this before. Potting as its called is
> pretty much putting your device in an enclosure and pouring in an epoxy
> medium or the like in order to entirely case in the board and wiring to be
> nigh' impossible to reverse engineer, repair, but makes it almost
> indestructible in most cases. Here are some things to take into
> consideration.
>
> Will it be in direct sunlight? UV Rays can break down some plastics and
> resins. Epoxy is usually ok for most situations. Silicone Caulk is also a
> good idea. There are project enclosures you can purchase that can take some
> decent abuse, like the telephone box on the side of your house (if you have
> one. Or a FiOS box). Usually I see potting as a copy-protection or anti-mod
> technique. All of my radio scanners (I am a ham radio guy) have most of the
> PCB coated in a black/brown/grey epoxy so you cant fiddle with any of
> circuitry.
>
> Do you want it to be impossible to reverse engineer? Some companies will use
> a black/brown epoxy, or even epoxy with aluminum 'shavings' in it so you
> cant see through it, or even X-Ray it.
>
> How weather-proof do you need it? 100% water and humidity tight? Will heat
> be an issue? Last thing you want is to blow a component and have no way to
> service the potted PCB.
>
> How often will you need to service the wiring or power supply? There are
> external connectors for wiring hookup that have INSANE tolerances. Molex
> makes quite a few that can take psychotic levels of extreme conditions This
> is a link:http://www.molex.com/molex/products/group?key=sealed_connectors&chann...
West Epoxy in quarts / gallons. There are also good fillers and
thickeners if you want to "only coat circuit boards" against moisture.
Most Silicone products and caulks cure from moisture in the air and
will only cure about 1/8" in a day and 1/2 inch in a week.. so not
good for a bulk pour.
Regards, Terry King
...In The Woods In Vermont
te...@yourduino.com
On Jul 29, 7:37 pm, "Foxx D'Gamma" <foxx...@gmail.com> wrote:
> I have worked on some projects like this before. Potting as its called is
> pretty much putting your device in an enclosure and pouring in an epoxy
> medium or the like in order to entirely case in the board and wiring to be
> nigh' impossible to reverse engineer, repair, but makes it almost
> indestructible in most cases. Here are some things to take into
> consideration.
>
> Will it be in direct sunlight? UV Rays can break down some plastics and
> resins. Epoxy is usually ok for most situations. Silicone Caulk is also a
> good idea. There are project enclosures you can purchase that can take some
> decent abuse, like the telephone box on the side of your house (if you have
> one. Or a FiOS box). Usually I see potting as a copy-protection or anti-mod
> technique. All of my radio scanners (I am a ham radio guy) have most of the
> PCB coated in a black/brown/grey epoxy so you cant fiddle with any of
> circuitry.
>
> Do you want it to be impossible to reverse engineer? Some companies will use
> a black/brown epoxy, or even epoxy with aluminum 'shavings' in it so you
> cant see through it, or even X-Ray it.
>
> How weather-proof do you need it? 100% water and humidity tight? Will heat
> be an issue? Last thing you want is to blow a component and have no way to
> service the potted PCB.
>
> How often will you need to service the wiring or power supply? There are
> external connectors for wiring hookup that have INSANE tolerances. Molex
> makes quite a few that can take psychotic levels of extreme conditions This
> I have used a few and I must say if you have a concern about replacing
> external hookups, sensors, switches, display, keypad/keyboard, even standard
> connections like serial and USB, this would be an ideal solution.
>
> I have used plain ol' two-part epoxy resin to protect my projects in the
> past. I wound up using a generic enclosure, ABS Plastic, modified with some
> external connectors to hook in my power and I/O - then filled it with epoxy.
> My project was more of a toy, which was intended to take a 40 foot drop onto
> hard concrete if it had to, or being completely submerged in water. The 5
> Minute Epoxy stuff is pretty good for some general tests, and you can get it
> any almost any hardware store. The caulk route could also be a good choice
> but it could be fouled by heat generated by the circuit (power supply
> circuitry tends to give off a bit of heat, especially linear regulators).
>
> Can you give us some more information of what kind of environment you think
> your gizmo might face? The more details about the project, the more I can
> help.
>
> Cheers, Beers, and Bunny Ears,
> ~ Foxx
>
> external hookups, sensors, switches, display, keypad/keyboard, even standard
> connections like serial and USB, this would be an ideal solution.
>
> I have used plain ol' two-part epoxy resin to protect my projects in the
> past. I wound up using a generic enclosure, ABS Plastic, modified with some
> external connectors to hook in my power and I/O - then filled it with epoxy.
> My project was more of a toy, which was intended to take a 40 foot drop onto
> hard concrete if it had to, or being completely submerged in water. The 5
> Minute Epoxy stuff is pretty good for some general tests, and you can get it
> any almost any hardware store. The caulk route could also be a good choice
> but it could be fouled by heat generated by the circuit (power supply
> circuitry tends to give off a bit of heat, especially linear regulators).
>
> Can you give us some more information of what kind of environment you think
> your gizmo might face? The more details about the project, the more I can
> help.
>
> Cheers, Beers, and Bunny Ears,
> ~ Foxx
>
> On Fri, Jul 29, 2011 at 6:09 PM, Joseph L. Pizzo <jlp0...@gmail.com> wrote:
>
>
>
>
>
>
>
> > What about silicone window caulking?
>
>
>
>
>
>
>
>
> > What about silicone window caulking?
>
E l
Jul 31, 2011, 6:19:02 AM7/31/11
to nycresistormi...@googlegroups.com
This might work - give it 3 coats, letting it dry between coats:
Rolan
Jul 31, 2011, 7:11:28 AM7/31/11
to NYCResistor:Microcontrollers
Have you considered putting it into a rugged tupperware container
along with a few bags of silica gel?
~Rolan
along with a few bags of silica gel?
~Rolan
w1jp
Jul 31, 2011, 12:26:09 PM7/31/11
to NYCResistor:Microcontrollers
Potting is a great idea; however, there are some gotchas.
One thing that I haven't seen discussed here is the thermal
properties. How much heat does this PCB generate? (a good guess is the
power IN (e.g., 5V*500mA=2.5W) vs. power out (whatever this board is
doing). While most electronics use a thermal epoxy (an epoxy with
added elements to increase the thermal conductance), the thermal
conductance and dielectric strength of typical consumer epoxies is
hard to find. In undergrad my advisor's specialty was composite
conductance, static, and lightning protection. I spent way too much
time trying to track down this information. Unfortunately, I didn't
keep it—alas...
Anyway–you are going to want to use an epoxy that is specifically
formulated for thermal conductance or you may end up running your
board hot. Take the component with the highest heat generation and run
the thermal calc (W/(m•ºC)). When doing this, keep in mind the thermal
environment this unit is being placed in and allow for surface
heating. The epoxy must conduct more heat than that part can generate
or you are going to get a steady increase in die temp resulting in out
of tolerance thermal specs. Don't use silicone as the thermal
conductance is much worse (guesstimate 10x) and 100x worse than
thermal epoxies.
Another thing to think about is cable strain relief (just as you would
with a normal enclosure). My suggestion is to knot your cables and
slip a piece of straw or tubing over them. After the epoxy has cured,
fill the tube with silicone (keeping the cable in the middle of the
hole).
There are a whole mess of other environmental concerns as well;
however, I'll just start with this.
Net: Use a thermal epoxy and make sure that the environment supports
convective cooling (i.e., it can breath).
73,
Jon
w1jp
One thing that I haven't seen discussed here is the thermal
properties. How much heat does this PCB generate? (a good guess is the
power IN (e.g., 5V*500mA=2.5W) vs. power out (whatever this board is
doing). While most electronics use a thermal epoxy (an epoxy with
added elements to increase the thermal conductance), the thermal
conductance and dielectric strength of typical consumer epoxies is
hard to find. In undergrad my advisor's specialty was composite
conductance, static, and lightning protection. I spent way too much
time trying to track down this information. Unfortunately, I didn't
keep it—alas...
Anyway–you are going to want to use an epoxy that is specifically
formulated for thermal conductance or you may end up running your
board hot. Take the component with the highest heat generation and run
the thermal calc (W/(m•ºC)). When doing this, keep in mind the thermal
environment this unit is being placed in and allow for surface
heating. The epoxy must conduct more heat than that part can generate
or you are going to get a steady increase in die temp resulting in out
of tolerance thermal specs. Don't use silicone as the thermal
conductance is much worse (guesstimate 10x) and 100x worse than
thermal epoxies.
Another thing to think about is cable strain relief (just as you would
with a normal enclosure). My suggestion is to knot your cables and
slip a piece of straw or tubing over them. After the epoxy has cured,
fill the tube with silicone (keeping the cable in the middle of the
hole).
There are a whole mess of other environmental concerns as well;
however, I'll just start with this.
Net: Use a thermal epoxy and make sure that the environment supports
convective cooling (i.e., it can breath).
73,
Jon
w1jp
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