Cheap ckt. potting options

[Mark Hansen]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

 

[mkaras]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

Mark:

First off let me comment that potting a PC board is not an effective
duplication deterrent. One company that I worked for potted some of
their products to seal the circuits for environmental protection.
However whenever there was a field failure the potting would be taken
off the PC board to see what had happened to the device !! So potting
would be somewhat of a bother to the cloner of your product but would
not prevent the copy process.

Secondly please be aware that there are some things to consider when
potting a circuit board. Here is a list of some key areas of
consideration.

1) Some cheap hardware store type epoxy products have fillers in them
that may render the potting conductive. I am aware of both steel and
aluminum filled types.

2) Epoxy products of some types and surface mounted components may not
always be the best mix. The differences in thermal characteristics
between FR4 PC boards and the potting can break small surface mount
component solder connections.

3) There are plenty of epoxy products designed specifcally for
electronics potting so you should not have too much problem finding a
product to use. I would check out some electronics products retailers
such as Newark or McMaster Carr.

4) Partitioning the area to get potted can be very difficult to
implement effectively. In order to make potting practical and have the
material be pourable means that the epoxy is somewhat viscous and it
will run through the smallest hole or crack. If it is the battery area
that you want to leave open then I would pot with a 9V battery harness
protruding above the epoxy surface. In the case of batteries like AA or
AAA then there are some nylon battery holders that you could use to
hold the cells and isolate the area from epoxy fill-in.

5) Even with item 4 above said there can be problems getting complete
fill of the areas under circuit boards if not enough space is left
between the edges of the PC board and the case that it is in. I have
seen the need to angle off the corner(s) of the PC board or provide a
hole through the center of the PC board to allow the epoxy to flow past
and under the board.

6) Two part epoxy can often generate some heat as a result of the
curing process. In addition sometimes ovens are used to hasten the cure
of the epoxy to speed up the manufacturing process. If your PC board
has some sensitive low level analog type circuits it is possible that
the curing heat can cause detrimental shifts in the circuit performance
or destroy any pre-potting calibrations than may have been done.

7) There are some silicon based potting materials available for potting
that have some advantages for surface mounted components.

It is finally my opinion that there are better ways of protecting a
design than potting that are less bothersome than potting. One very
good way is to capture a large part of the product design and
intellectual property into the firmware of a microcontroller on the
product PC board. Select a microcontroller that has a good locking
protection system and you will be much farther toward protecting your
ideas from prying eyes. Even the protections offered by "fuse"
protected FLASH based microcontrollers can be sometimes overcome by
persistent hackers if the product cloner is willing to spend enough
money. So the best way for you to overcome that consideration is to
stay ahead of the cloner by offering changes to the product every so
often that make your product look more attractive to the customer than
an older less capable clone.

Good luck
- mkaras

 

[Harry Dellamano]

Mark:

First off let me comment that potting a PC board is not an effective
duplication deterrent. One company that I worked for potted some of
their products to seal the circuits for environmental protection.
However whenever there was a field failure the potting would be taken
off the PC board to see what had happened to the device !! So potting
would be somewhat of a bother to the cloner of your product but would
not prevent the copy process.

Secondly please be aware that there are some things to consider when
potting a circuit board. Here is a list of some key areas of
consideration.

1) Some cheap hardware store type epoxy products have fillers in them
that may render the potting conductive. I am aware of both steel and
aluminum filled types.

2) Epoxy products of some types and surface mounted components may not
always be the best mix. The differences in thermal characteristics
between FR4 PC boards and the potting can break small surface mount
component solder connections.

3) There are plenty of epoxy products designed specifcally for
electronics potting so you should not have too much problem finding a
product to use. I would check out some electronics products retailers
such as Newark or McMaster Carr.

4) Partitioning the area to get potted can be very difficult to
implement effectively. In order to make potting practical and have the
material be pourable means that the epoxy is somewhat viscous and it
will run through the smallest hole or crack. If it is the battery area
that you want to leave open then I would pot with a 9V battery harness
protruding above the epoxy surface. In the case of batteries like AA or
AAA then there are some nylon battery holders that you could use to
hold the cells and isolate the area from epoxy fill-in.

5) Even with item 4 above said there can be problems getting complete
fill of the areas under circuit boards if not enough space is left
between the edges of the PC board and the case that it is in. I have
seen the need to angle off the corner(s) of the PC board or provide a
hole through the center of the PC board to allow the epoxy to flow past
and under the board.

6) Two part epoxy can often generate some heat as a result of the
curing process. In addition sometimes ovens are used to hasten the cure
of the epoxy to speed up the manufacturing process. If your PC board
has some sensitive low level analog type circuits it is possible that
the curing heat can cause detrimental shifts in the circuit performance
or destroy any pre-potting calibrations than may have been done.

7) There are some silicon based potting materials available for potting
that have some advantages for surface mounted components.

It is finally my opinion that there are better ways of protecting a
design than potting that are less bothersome than potting. One very
good way is to capture a large part of the product design and
intellectual property into the firmware of a microcontroller on the
product PC board. Select a microcontroller that has a good locking
protection system and you will be much farther toward protecting your
ideas from prying eyes. Even the protections offered by "fuse"
protected FLASH based microcontrollers can be sometimes overcome by
persistent hackers if the product cloner is willing to spend enough
money. So the best way for you to overcome that consideration is to
stay ahead of the cloner by offering changes to the product every so
often that make your product look more attractive to the customer than
an older less capable clone.

Good luck
- mkaras

"Potting is such sweet sorrow" The bard knew in R+J.
Harry

 

[Ancient_Hacker]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

What does the circuit do? There are darn few "new" ideas that can't
be re-engineered or reverse-engineered in a day or two.

Also a quick googling shows that almost anything can be dissolved, even
epoxies.

Your best protection is offering a good product at a competitive price.

 

[default]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

epoxy or polyester resin mixed with very fine sand - less flammable,
stronger, cheaper and better heat conduction than epoxy alone

 

[John Larkin]

"Potting is such sweet sorrow" The bard knew in R+J.
Harry

Ooh, great line.

John

 

[joseph2k]

Mark:

First off let me comment that potting a PC board is not an effective
duplication deterrent. One company that I worked for potted some of
their products to seal the circuits for environmental protection.
However whenever there was a field failure the potting would be taken
off the PC board to see what had happened to the device !! So potting
would be somewhat of a bother to the cloner of your product but would
not prevent the copy process.

Secondly please be aware that there are some things to consider when
potting a circuit board. Here is a list of some key areas of
consideration.

1) Some cheap hardware store type epoxy products have fillers in them
that may render the potting conductive. I am aware of both steel and
aluminum filled types.

2) Epoxy products of some types and surface mounted components may not
always be the best mix. The differences in thermal characteristics
between FR4 PC boards and the potting can break small surface mount
component solder connections.

3) There are plenty of epoxy products designed specifcally for
electronics potting so you should not have too much problem finding a
product to use. I would check out some electronics products retailers
such as Newark or McMaster Carr.

4) Partitioning the area to get potted can be very difficult to
implement effectively. In order to make potting practical and have the
material be pourable means that the epoxy is somewhat viscous and it
will run through the smallest hole or crack. If it is the battery area
that you want to leave open then I would pot with a 9V battery harness
protruding above the epoxy surface. In the case of batteries like AA or
AAA then there are some nylon battery holders that you could use to
hold the cells and isolate the area from epoxy fill-in.

5) Even with item 4 above said there can be problems getting complete
fill of the areas under circuit boards if not enough space is left
between the edges of the PC board and the case that it is in. I have
seen the need to angle off the corner(s) of the PC board or provide a
hole through the center of the PC board to allow the epoxy to flow past
and under the board.

6) Two part epoxy can often generate some heat as a result of the
curing process. In addition sometimes ovens are used to hasten the cure
of the epoxy to speed up the manufacturing process. If your PC board
has some sensitive low level analog type circuits it is possible that
the curing heat can cause detrimental shifts in the circuit performance
or destroy any pre-potting calibrations than may have been done.

7) There are some silicon based potting materials available for potting
that have some advantages for surface mounted components.

It is finally my opinion that there are better ways of protecting a
design than potting that are less bothersome than potting. One very
good way is to capture a large part of the product design and
intellectual property into the firmware of a microcontroller on the
product PC board. Select a microcontroller that has a good locking
protection system and you will be much farther toward protecting your
ideas from prying eyes. Even the protections offered by "fuse"
protected FLASH based microcontrollers can be sometimes overcome by
persistent hackers if the product cloner is willing to spend enough
money. So the best way for you to overcome that consideration is to
stay ahead of the cloner by offering changes to the product every so
often that make your product look more attractive to the customer than
an older less capable clone.

Good luck
- mkaras

For runs in the hundreds and above all good advice, i think OP was talking
one dozen or two.

 

[Ross Herbert]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

In addition to the sound advice from mkaras I would add that using any
hard epoxy to pot components which generate heat will definitely
result in early failure of the device.

Way back in the dim dark ages when Evinrude/Johnson started making
solid state ignition systems they used hard epoxy to encapsulate them.
A service agent gave me a few dud ones to look at and see if I could
find out their main failure mode. I had to import a gallon of exotic
epoxy solvent from the US at great expense and after a couple of weeks
I finally removed enough epoxy to get down to the board level.
Inspection showed that components which ran hot would try to expand.
Naturally, the epoxy resisted, being hard against both the underside
of the pcb and the top of the component, and so the through-hole
component leads expanded the other way and either ripped the solder
pads off the board or produced dry solder joints.

If potting components which are going to expand I use a primary layer
of soft silicon rubber prior to encapsulation in the hard epoxy
potting compound. This gives some leeway for expansion.

 

[Robert Baer]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

$pend all you can; no matter what you do, it is impossible to prevent
duplication.

 

[Robert Baer]

epoxy or polyester resin mixed with very fine sand - less flammable,
stronger, cheaper and better heat conduction than epoxy alone

Adding sand only makes it slightly more difficult to "bust into".
And sand is a good insulator; there is no such thing as "thermally
conductive" epoxy *unless* a conductive additive like fine particles of
metal (silver, copper, aluminum, etd) or carbon was used--and that makes
it electrically conductive.

 

[John Popelish]

And sand is a good insulator; there is no such thing as "thermally
conductive" epoxy *unless* a conductive additive like fine particles of
metal (silver, copper, aluminum, etd) or carbon was used--and that makes
it electrically conductive.

Though metals are good, cheap thermal conductors, alumina
(aluminum oxide) is much better than sand, and the purer,
the better.

 

[RST Engineering \(jw\)]

Yes, but did he have to quote two hundred redundant lines to do it?

Jim

 

[RST Engineering \(jw\)]

Expandable caulk from Home Depot. $2.99 the tube for about 1 m^3 potting.

Jim

 

[[email protected]]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

Pretty much all of the low-cost potting epoxies will turn into a gell
state when heated to between 80-150 degrees, then they can then be
readily peeled off. Two-part araldite permanently changes composition
at around 100 degrees.

As others have mentioned, it can be a pain in the arse to properly pot
the device, and then you have to worry about thermal expansion issues.

A good technique for providing environmental protection and some degree
of protection against hackers is to use a hard conformal coating. There
are many varieties around, Dymax sell a very hard black conformal
coating that is very difficult to remove. Advice: put some electrical
tape around the edge of the board, put a plob of coating on top, let it
settle nicely, shine a UV light at it (or buy a two-part agent), then
peel off the tape. You can also buy hard spray on coatings, that work
well (not silicone or acrylic).

In addition, or alone, you can also use a solvent that will dissolve
the part numbers of your components. I haven't tried it so I can't tell
you what would do the job. Its pretty hard to tell an opamp is an
opamp, especially if its in a funny case like a PLCC.

/andrew

 

[neon]

Your potting idea is bad. it is just like a lock it is meant to keep honest people from getting into it. A di-honets guy that will not stop him just makes it harder that is all. My solution to the circuit that i want it keep secret was simply to add do nothing circuits that send them into visciuos circle.And it worked.

 

[Homer J Simpson]

In addition, or alone, you can also use a solvent that will dissolve
the part numbers of your components.

You could also hotstamp an obliterating label over the top of each part
before assembly. But most competent techs can probe around and make a good
guess at the functions.

You should read Don Lancaster on patents and protections. He makes valid
points.


--
++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Required crap appended to avoid restrictions imposed by brain +
+ damaged idiots.
+
+ Server Response: '441 Posting Failed (Rejected by POST filter)', +
+ Port: 119, Secure(SSL): No, Server Error: 441,
+
+ Error Number: 0x800CCCA9
+
++++++++++++++++++++++++++++++++++++++++++++++++++++

 

[Ken Smith]

You could also hotstamp an obliterating label over the top of each part
before assembly. But most competent techs can probe around and make a good
guess at the functions.

If your quantity is large enough, you can get the ships custom marked with
your companies part number. This can save a bit of time.

If you really want to cause trouble for those copying the circuit, have
the parts numbered with something that misleads. An op-amp with a logic
gate's number is an example.

 

[Macgyver]

I am manufacturing a small run of devices which I would like to
protect from duplication. They consist of a 50x50mm PCB in a hand-held
plastic case with batteries. I plan to partition the case and pour in
a self-curing potting agent

Dedicated two-part potting epoxy is relatively expensive. Can anyone
suggest a few hardware variety alternatives, in order of preference?

Thank you,

Mark Hansen

As with all the other comments a multi-stage approach is going to give
you the best protection, but it still will never be perfect (more like
disuading the average curious hacker and making the more determined
reverse engineer's job more difficult). Shaving the top layer off of
the chips with a file to remove the marking works well, along with
using microchip protection like blowing internal fuses, software
protection, etc).
Also a two-part polyester potting compound with a shore A hardness of
about 95 seems to be a good balance between being too rigid
(encapsulation self-disassembles when you hit it with a hammer, no give
for thermal expansion, etc) or too soft (can easily be removed with a
craft knife).
A dark coloured hard conformal coating may be the best idea (I have
never tried this thou), especially if it is difficult to remove with
heat or chemicals.

In the end thou, if it is a simple product with a potentialy large
market, then you will not be able to protect it from the determined who
see a buck to be made.

 

[Robert Baer]

Pretty much all of the low-cost potting epoxies will turn into a gell
state when heated to between 80-150 degrees, then they can then be
readily peeled off. Two-part araldite permanently changes composition
at around 100 degrees.

As others have mentioned, it can be a pain in the arse to properly pot
the device, and then you have to worry about thermal expansion issues.

A good technique for providing environmental protection and some degree
of protection against hackers is to use a hard conformal coating. There
are many varieties around, Dymax sell a very hard black conformal
coating that is very difficult to remove. Advice: put some electrical
tape around the edge of the board, put a plob of coating on top, let it
settle nicely, shine a UV light at it (or buy a two-part agent), then
peel off the tape. You can also buy hard spray on coatings, that work
well (not silicone or acrylic).

In addition, or alone, you can also use a solvent that will dissolve
the part numbers of your components. I haven't tried it so I can't tell
you what would do the job. Its pretty hard to tell an opamp is an
opamp, especially if its in a funny case like a PLCC.

/andrew

No wonder why i keep burning my fingers!

 

[Rich Grise]

Though metals are good, cheap thermal conductors, alumina
(aluminum oxide) is much better than sand, and the purer,
the better.

I imagine they don't recommend powdered beryllia. ;-)

Cheers!
Rich