Potting material recommendations?

[speff]

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

 

speff <spehro@gmail.com> wrote in
news:55818fd7-24e0-4e15-a717-458191986300@googlegroups.com:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see
extreme g forces, vibration and nasty environment. Wide
temperature range too. Electrical characteristics other than good
insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of
papers out there on various solutions. I'm thinking it should have
some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not
too important.

Best regards,
Spehro Pefhany

I know about the only NASA approve potting for HV space circuits, but
it is pretty rigid, not foam. Called "CONAP" it is a polyurethane.
Perhaps it could be made foamlike. Absolutely non-serviceable. Once
attached and cured, good luck. But there are several formulations
too.

This stuff stops a sharp knife thrust at less than 7mm penetration.
I think it could stop a bullet. I know it is not what you are after
though, just wanted to mention it.

Don't know if a foam solution would work against high G forces. You
might actually want a more rigid media.

<http://www.matweb.com/search/datasheettext.aspx?
matguid=adb9a10933574b10b2ff4947551fc710>

 

[George Herold]

On Friday, January 31, 2020 at 9:46:02 AM UTC-5, speff wrote:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Getting shot into space? I wonder if there are any good NASA technical documents?

What's the temperature range?

George H.

 

On Friday, 31 January 2020 14:46:02 UTC, speff wrote:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Any lack of rigidity would allow the various connections to flex, which is seldom good on a pcb, espeically one encountering shock forces. Rigid potting then surrounded by something that can absorb impact forces would be a lot better.


NT

 

[piglet]

On 31/01/2020 2:45 pm, speff wrote:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Some of my products were cast in filled epoxy. We sent out to
encapsulating specialists who made customized steel molds. They did all
the mixing, vacuum and oven cureing etc.

The TCE of the rigid stuff was such that over wide temperature swings
glass diodes (1N4148 etc) would crack so initially we sleeved the diodes
and later brush precoated them either RTV or unfilled, more flexible, epoxy.

Can't recall the details but the resin was made by Ciba-Gigy and the
filler was mineral dust, possibly silica? Colorant dye was added to
customize product lineup. Environmental performance was superb, cannot
speak for vibration but we'd drop them from height onto stone and they'd
survive the shock.

piglet

 

[Clive Arthur]

The standard for high temperature downhole use in extreme vibration
seems to be RTV silicone, degassed under vacuum.

'Heavy' things like power transistors are wired to the PCB with stranded
PTFE wire wrapped, soldered and sleeved onto the legs and then through
strain relief holes on the board, looping back up to solder through a pad.

Pad size is bigger than normal too and more solder. Lots of mounting
holes for the PCB onto a rigid frame which can also form the 'potting
box'. Component orientation can be optimised too if there's an obvious
'preferred' flex direction.

I'm not an encapsulation expert, but I do work with this stuff.

--
Cheers
Clive


On 31/01/2020 14:45, speff wrote:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

 

[Sjouke Burry]

On 31.01.20 15:45, speff wrote:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Silicon (google 2 component silicone )

 

[speff]

On Friday, 31 January 2020 10:31:01 UTC-5, George Herold wrote:

On Friday, January 31, 2020 at 9:46:02 AM UTC-5, speff wrote:
Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Getting shot into space? I wonder if there are any good NASA technical documents?

Hi, George:

Launching isn't all that bad if you don't hit a resonance- not too many g's .. some bad vibration for a short while, even in the cheap seats. After all, meat bags and flimsy rockets can survive it.

What's the temperature range?

George H.

Probably -55 to 125 or 135

Best regards,
Spehro Pefhany

 

[speff]

On Friday, 31 January 2020 11:44:57 UTC-5, tabb...@gmail.com wrote:

On Friday, 31 January 2020 14:46:02 UTC, speff wrote:
Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Any lack of rigidity would allow the various connections to flex, which is seldom good on a pcb, espeically one encountering shock forces. Rigid potting then surrounded by something that can absorb impact forces would be a lot better.


NT

Hi, thanks!

Rigidity often causes issues with temperature changes, even over automotive range. Lots of failures until they started using more flexible compounds.
I'd prefer to avoid having to do a lot of testing on that.

To minimize the deflection I think a small relatively thick board will suffice.
Shock from things like dropping a consumer product on a hard
surface can be quite high.



Best regards,
Spehro Pefhany

 

[speff]

On Friday, 31 January 2020 10:06:23 UTC-5, DecadentLinux...@decadence.org wrote:

speff <spehro@gmail.com> wrote in
news:55818fd7-24e0-4e15-a717-458191986300@googlegroups.com:

Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see
extreme g forces, vibration and nasty environment. Wide
temperature range too. Electrical characteristics other than good
insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of
papers out there on various solutions. I'm thinking it should have
some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not
too important.

Best regards,
Spehro Pefhany


I know about the only NASA approve potting for HV space circuits, but
it is pretty rigid, not foam. Called "CONAP" it is a polyurethane.
Perhaps it could be made foamlike. Absolutely non-serviceable. Once
attached and cured, good luck. But there are several formulations
too.

Hi,

Thanks, I'll look into that one. Shore D is indeed pretty hard, but
maybe there's a filled version or one using a different hardener.

Best regards,
Spehro Pefhany

This stuff stops a sharp knife thrust at less than 7mm penetration.
I think it could stop a bullet. I know it is not what you are after
though, just wanted to mention it.

Don't know if a foam solution would work against high G forces. You
might actually want a more rigid media.

http://www.matweb.com/search/datasheettext.aspx?
matguid=adb9a10933574b10b2ff4947551fc710

 

[Lasse Langwadt Christense]

fredag den 31. januar 2020 kl. 23.03.09 UTC+1 skrev speff:

On Friday, 31 January 2020 10:31:01 UTC-5, George Herold wrote:
On Friday, January 31, 2020 at 9:46:02 AM UTC-5, speff wrote:
Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Getting shot into space? I wonder if there are any good NASA technical documents?

Hi, George:

Launching isn't all that bad if you don't hit a resonance- not too many g's .. some bad vibration for a short while, even in the cheap seats. After all, meat bags and flimsy rockets can survive it.

and helicopters fly, I've heard them described as a machine that vibrate
so violently that earth repels it

 

[Tom Gardner]

On 31/01/20 22:55, Lasse Langwadt Christensen wrote:

fredag den 31. januar 2020 kl. 23.03.09 UTC+1 skrev speff:
On Friday, 31 January 2020 10:31:01 UTC-5, George Herold wrote:
On Friday, January 31, 2020 at 9:46:02 AM UTC-5, speff wrote:
Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see extreme g forces, vibration and nasty environment. Wide temperature range too. Electrical characteristics other than good insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of papers out there on various solutions. I'm thinking it should have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not too important.

Best regards,
Spehro Pefhany

Getting shot into space? I wonder if there are any good NASA technical documents?

Hi, George:

Launching isn't all that bad if you don't hit a resonance- not too many g's .. some bad vibration for a short while, even in the cheap seats. After all, meat bags and flimsy rockets can survive it.

and helicopters fly, I've heard them described as a machine that vibrate
so violently that earth repels it

They beat the air into submission.

Gliders, OTOH, seduce the air into letting it do what
the pilot wants (on a good day )

 

[whit3rd]

On Friday, January 31, 2020 at 2:06:49 PM UTC-8, speff wrote:

On Friday, 31 January 2020 10:06:23 UTC-5, DecadentLinux...@decadence.org wrote:
speff <spehro@gmail.com> wrote in

I know about the only NASA approve potting for HV space circuits, but
it is pretty rigid, not foam. Called "CONAP" it is a polyurethane.

Thanks, I'll look into that one. Shore D is indeed pretty hard, but
maybe there's a filled version or one using a different hardener.

Hardness isn't so important for acceleration tolerance, but buoyancy might
be. You want the density of the support medium to be similar to the components
and PCB. Even a liquid shape will remain intact through shock, if it's in
a medium that matches it acoustically. I suppose this is a vote for a soft epoxy...

 

Clive Arthur <cliveta@nowaytoday.co.uk> wrote in news:r11pif$7qv$1
@dont-email.me:

The standard for high temperature downhole use in extreme vibration
seems to be RTV silicone, degassed under vacuum.

Most of the RTV silicone potting media I have worked with sheared
pretty easily. Not approved for space so I would not trust it for
high vibe settings.

But hey if that is what you guys used...

If it does not get attacked by the petrols, etc. I would use the
CONAP polyurethane.

I could stab a slab of that stuff with a sharp, stout knife and
barely penetrate. So strong it seems like it would even stop a
bullet.

One shot though. Zero serviceability compared to RTV.

 

piglet <erichpwagner@hotmail.com> wrote in
news:r11r85$ii7$1@dont-email.me:

On 31/01/2020 2:45 pm, speff wrote:
Hi, folks:-

Non-negotiable have to pot a circuit because it's going to see
extreme g forces, vibration and nasty environment. Wide
temperature range too. Electrical characteristics other than good
insulation are not too critical.

Looking at syntactic foam materials, and there are a bunch of
papers out there on various solutions. I'm thinking it should
have some damping characteristics, and not be too rigid.

Any tried and true high performance recommendations? Cost is not
too important.

Best regards,
Spehro Pefhany


Some of my products were cast in filled epoxy. We sent out to
encapsulating specialists who made customized steel molds. They
did all the mixing, vacuum and oven cureing etc.

The TCE of the rigid stuff was such that over wide temperature
swings glass diodes (1N4148 etc) would crack so initially we
sleeved the diodes and later brush precoated them either RTV or
unfilled, more flexible, epoxy.

Can't recall the details but the resin was made by Ciba-Gigy and
the filler was mineral dust, possibly silica? Colorant dye was
added to customize product lineup. Environmental performance was
superb, cannot speak for vibration but we'd drop them from height
onto stone and they'd survive the shock.

piglet

Conformal coat with the UV cure stuff. It is thick and soft, and
then pot over that. It looks clear-ish but lights up under UV for
inspection of coating completion. That is what the mil boys use.
Weather seal! Double protection! Stops those danged tin whiskers too
(a little bit)(on RoHs crap).

Hey, I know! Make a thin potting case for the softer stuff (RTV)
and another case that goes into for a cladding of the tougher stuff.
You could even used harder epoxies for the tougher layer. That would
even make the interior 'package' removeable and serviceable, whereas
epoxy or urethane potting usually makes servicing very difficult.
Your final enclosure would be the potting shell for the outer layer.

 

Lasse Langwadt Christensen <langwadt@fonz.dk> wrote in
news:8d0aa8a6-9af5-4064-bffe-65fb9a281994@googlegroups.com:

and helicopters fly, I've heard them described as a machine that
vibrate so violently that earth repels it

I saw that video.

The early whirlys

https://www.youtube.com/watch?v=JlbxE4vuk5g

 

whit3rd <whit3rd@gmail.com> wrote in
news:f470b903-e5ce-48e0-8d05-8ce85037b143@googlegroups.com:

On Friday, January 31, 2020 at 2:06:49 PM UTC-8, speff wrote:
On Friday, 31 January 2020 10:06:23 UTC-5,
DecadentLinux...@decadence.org wrote:
speff <spehro@gmail.com> wrote in

I know about the only NASA approve potting for HV space
circuits, but it is pretty rigid, not foam. Called "CONAP" it
is a polyurethane.

Thanks, I'll look into that one. Shore D is indeed pretty hard,
but maybe there's a filled version or one using a different
hardener.

Hardness isn't so important for acceleration tolerance, but
buoyancy might be. You want the density of the support medium to
be similar to the components and PCB. Even a liquid shape will
remain intact through shock, if it's in a medium that matches it
acoustically. I suppose this is a vote for a soft epoxy...

Soft durometer epoxies with good surface adhesion sounds great. The
RTVs suggested usually shear quite easily.

I suggested a polyurethane and said the word 'rigid', but I meant
as rubbery things go, not like solid, firm epoxies or such.

 

Rigid compounds can shear AND components off the board when it cures

We use flexible compounds for that reason

Cheers

Klaus

 

klaus.kragelund@gmail.com wrote in news:34dda629-318e-40ec-8404-
0f8fa1efc92e@googlegroups.com:

Rigid compounds can shear AND components off the board when it
cures

We use flexible compounds for that reason

Cheers

Klaus

When I said 'rigid' about CONAP polyurethane, I maent compared to
RTV. A more rigid RUBBERY compound.

Not like HARD (better term than rigid for what you want to convey)
epoxies such as StyCast, etc.

It is rigid inasmuch as it is a dense 'rubbery' like medium. It
gives under thermal cycling and stresses nothing when curing or after
cure.
StyCast, a hard curing epoxy, would break SMD diodes and though
hole too.

They had a thermal version that was blue, and we gave it better
thermal performance by adding small silica dust to it at mix time.
It was not as hard, but was still able to shear parts from their
mounts.

So referring to the polymer types, the term 'rigid' usually means
'more firm', but NOT 'rigid' like when describing the cured feel of
an epoxy.