Silicon grease damages resistors ?

Petr Fiedler · May 17, 2004

Hello,
some resistors that had been covered by silicon grease fail after some time.
The failure is not due to thermal reasons, it seems that the grease somehow
damages the resistor chemically. Actually the problem appeared at SMD
resistors of 0 ohm (not real resistors so no significat heat dissipation)
so the thermal damage is not the case. Does anyone know if the silicon
grease really can be the cause ? Has anyone met with something similar? We
have sent the failed resistors to an analysis, however right now we do not
know what should we look for. The optical analysis did not show any damage,
chemical analysis is the next step ...

Thanks for help.

Piotr Piatek · May 17, 2004

On Mon, 17 May 2004 13:43:31 +0200, "Petr Fiedler" wrote:

Hello,
some resistors that had been covered by silicon grease fail after some time.
The failure is not due to thermal reasons, it seems that the grease somehow
damages the resistor chemically. Actually the problem appeared at SMD
resistors of 0 ohm (not real resistors so no significat heat dissipation)
so the thermal damage is not the case. Does anyone know if the silicon
grease really can be the cause ?

Perhaps solder flux residue? The silicon could possibly prevent
evaporating of some aggressive flux component. Only a wild guess...

Has anyone met with something similar?

Heavier parts in the consumer electronic products are sometimes glued
to the PCB. I have often encountered traces of corrosion under the
glue layer.

-Piotr

Spehro Pefhany · May 17, 2004

On Mon, 17 May 2004 13:43:31 +0200, the renowned "Petr Fiedler"
<fiedlerp@feec.vutbr.cz> wrote:

Hello,
some resistors that had been covered by silicon grease fail after some time.
The failure is not due to thermal reasons, it seems that the grease somehow
damages the resistor chemically. Actually the problem appeared at SMD
resistors of 0 ohm (not real resistors so no significat heat dissipation)
so the thermal damage is not the case. Does anyone know if the silicon
grease really can be the cause ? Has anyone met with something similar? We
have sent the failed resistors to an analysis, however right now we do not
know what should we look for. The optical analysis did not show any damage,
chemical analysis is the next step ...

Thanks for help.

Maybe the failure has nothing whatsoever to do with the silicone (note
the "e") grease.

If the resistors got contaminated before soldering, OTOH, bad joints
are not unlikely.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Jim Adney · May 18, 2004

On Mon, 17 May 2004 13:43:31 +0200 "Petr Fiedler"
<fiedlerp@feec.vutbr.cz> wrote:

some resistors that had been covered by silicon grease fail after some time.
The failure is not due to thermal reasons, it seems that the grease somehow
damages the resistor chemically. Actually the problem appeared at SMD
resistors of 0 ohm (not real resistors so no significat heat dissipation)
so the thermal damage is not the case. Does anyone know if the silicon
grease really can be the cause ? Has anyone met with something similar? We
have sent the failed resistors to an analysis, however right now we do not
know what should we look for. The optical analysis did not show any damage,
chemical analysis is the next step ...

If you mean that the solder joints at their leads failed, then I'd
suspect some kind of contamination which the silicone kept in place.

If you mean that something about the 0 Ohm resistor itself failed,
then I'm skeptical, because I thought these actually just had a
continuous wire under there. That should be easy for you to determine.

I can't see the silicone itself being the primary cause of either type
of problem.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

Petr Fiedler · May 18, 2004

The board is manufactured by someone else (product of Taiwan). This board is
placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications). Only the 0 ohm
resistors that are covered by the grease fail. Other resistors of the same
kind never fail. Thus I suspect the silicone grease to be the cause. The
hypothesis is that something from the grease gets into the resistor and then
corodes the wire. Friend of mine told me that he had read somewhere
somethink about sulfur geting from the silicone grease into the components,
but he was not sure and he does not remember the source of the information.

Piotr Patek's idea that "the silicon could possibly prevent evaporating of
some aggressive flux component" is another interesting idea.
I hope we fill find the reason soon. The analysis using electron microscopy
is quite expencive and we do not know what should we look for.

Thanks,
Petr

"> If you mean that something about the 0 Ohm resistor itself failed,

then I'm skeptical, because I thought these actually just had a
continuous wire under there. That should be easy for you to determine.

I can't see the silicone itself being the primary cause of either type
of problem.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

Al · May 18, 2004

In article <c8co1f$1fde$1@boco.fee.vutbr.cz>,
"Petr Fiedler" <fiedlerp@feec.vutbr.cz> wrote:

The board is manufactured by someone else (product of Taiwan). This board is
placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications). Only the 0 ohm
resistors that are covered by the grease fail. Other resistors of the same
kind never fail. Thus I suspect the silicone grease to be the cause. The
hypothesis is that something from the grease gets into the resistor and then
corodes the wire. Friend of mine told me that he had read somewhere
somethink about sulfur geting from the silicone grease into the components,
but he was not sure and he does not remember the source of the information.

Piotr Patek's idea that "the silicon could possibly prevent evaporating of
some aggressive flux component" is another interesting idea.
I hope we fill find the reason soon. The analysis using electron microscopy
is quite expencive and we do not know what should we look for.

Thanks,
Petr

"> If you mean that something about the 0 Ohm resistor itself failed,
then I'm skeptical, because I thought these actually just had a
continuous wire under there. That should be easy for you to determine.

I can't see the silicone itself being the primary cause of either type
of problem.

OK, you really have to do a competent failure anlysis. You need to
analyze the materials on virgin resistors, virgin silicone grease,
virgin boards and then do the same on the failed ones and compare.

Are these surface mount resistors? or wire wound? or composition? or tin
oxide? Explain please.

Al

--
There's never enough time to do it right the first time.......

Mike Harrison · May 18, 2004

A customer of mine had problems a while ago with resistors changing value over time - this was
thought to be due to sulphur contamination, but I don't think the source of the sulphur was ever
definately identified - I don't think they were using silicone, but the PCB was conformally coated.
I think they eventually changed to using MELF resistors (cylindrical) from 0805's

On Tue, 18 May 2004 12:47:10 GMT, Al <no.spam@here.com> wrote:

In article <c8co1f$1fde$1@boco.fee.vutbr.cz>,
"Petr Fiedler" <fiedlerp@feec.vutbr.cz> wrote:

The board is manufactured by someone else (product of Taiwan). This board is
placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications). Only the 0 ohm
resistors that are covered by the grease fail. Other resistors of the same
kind never fail. Thus I suspect the silicone grease to be the cause. The
hypothesis is that something from the grease gets into the resistor and then
corodes the wire. Friend of mine told me that he had read somewhere
somethink about sulfur geting from the silicone grease into the components,
but he was not sure and he does not remember the source of the information.

Piotr Patek's idea that "the silicon could possibly prevent evaporating of
some aggressive flux component" is another interesting idea.
I hope we fill find the reason soon. The analysis using electron microscopy
is quite expencive and we do not know what should we look for.

Thanks,
Petr

"> If you mean that something about the 0 Ohm resistor itself failed,
then I'm skeptical, because I thought these actually just had a
continuous wire under there. That should be easy for you to determine.

I can't see the silicone itself being the primary cause of either type
of problem.

OK, you really have to do a competent failure anlysis. You need to
analyze the materials on virgin resistors, virgin silicone grease,
virgin boards and then do the same on the failed ones and compare.

Are these surface mount resistors? or wire wound? or composition? or tin
oxide? Explain please.

Al

May 18, 2004

"Petr Fiedler" <fiedlerp@feec.vutbr.cz> wrote:

placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications).

Aha! Silicone sealant (the terminology was confusing, silicone grease
is a different material, and doesn't damage electronics) releases
acetic acid when it cures (hence the vinegar smell). Use an RTV
that's compatable with electronics instead.

http://www.logwell.com/tech/servtips/RTV.html

--
William Smith
ComputerSmiths Consulting, Inc. www.compusmiths.com

Jim Adney · May 19, 2004

On Tue, 18 May 2004 12:20:30 +0200 "Petr Fiedler"
<fiedlerp@feec.vutbr.cz> wrote:

The board is manufactured by someone else (product of Taiwan). This board is
placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications). Only the 0 ohm
resistors that are covered by the grease fail. Other resistors of the same
kind never fail. Thus I suspect the silicone grease to be the cause. The
hypothesis is that something from the grease gets into the resistor and then
corodes the wire. Friend of mine told me that he had read somewhere
somethink about sulfur geting from the silicone grease into the components,
but he was not sure and he does not remember the source of the information.

In exactly what way have the 0 Ohm resistors been failing?

Silicone GREASE should be completely inert, but most kinds of silicone
caulk release acetic acid as they cure, and this will attack most
metals. Are you talking about a silicone compount that hardens, or
does it remain sticky?

The 0 Ohm resistor should just be a simple wire which passes thru a
fake resistor body. The only actual failure that could occur would be
for the wire to corrode away, allowing the connection to go open. If
this is happening, then perhaps the wire used for these "resistors" is
different from that used in the regular resistors. Who makes the 0 Ohm
resistors?

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

Petr Fiedler · May 19, 2004

Oh my god, sorry for confusing you all. It is silicone sealant that hardens
to rubber-like state. It is not silicone grease that remains sticky. The
manufacturer of the silicone calls it silicone putty.The silicone sealant is
claimed to be general purpose but suitable for electronics.

I am sorry for the mystification. The person that transfered the problem to
me called that stuff "silicone paste" and without significant mental effort
(= stupidity) I accepted it as silicone grease. I did not doublechecked it.
My fault :-(

Thank you for the idea of acetic acid. We will try to check that. Also
thanks for the link (http://www.logwell.com/tech/servtips/RTV.html)

Btw. the resistors are SMD resisitor, the package is 0805 (I am not
completely sure about the package may be it is 1206 i do not have any sample
board now). I am trying to find out who is the manufacturer of the
resistors.

The failure mode of the resistors is such that the resistance increases from
zero to the order of megaohms.

Thanks to all of you for your assistance,
Petr

Spehro Pefhany · May 19, 2004

On Wed, 19 May 2004 11:44:25 +0200, the renowned "Petr Fiedler"
<fiedlerp@feec.vutbr.cz> wrote:

Oh my god, sorry for confusing you all. It is silicone sealant that hardens
to rubber-like state. It is not silicone grease that remains sticky. The
manufacturer of the silicone calls it silicone putty.The silicone sealant is
claimed to be general purpose but suitable for electronics.

I am sorry for the mystification. The person that transfered the problem to
me called that stuff "silicone paste" and without significant mental effort
(= stupidity) I accepted it as silicone grease. I did not doublechecked it.
My fault :-(

Thank you for the idea of acetic acid. We will try to check that. Also
thanks for the link (http://www.logwell.com/tech/servtips/RTV.html)

Btw. the resistors are SMD resisitor, the package is 0805 (I am not
completely sure about the package may be it is 1206 i do not have any sample
board now). I am trying to find out who is the manufacturer of the
resistors.

The failure mode of the resistors is such that the resistance increases from
zero to the order of megaohms.

Thanks to all of you for your assistance,
Petr

Okay, that sounds like the source of your problem. It's not subtle,
you can smell the acetic acid (vinegar) odor quite easily while the
sealant is curing if it is of that type. The acetic acid is corrosive,
of course.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Jim Adney · May 21, 2004

On Wed, 19 May 2004 11:44:25 +0200 "Petr Fiedler"
<fiedlerp@feec.vutbr.cz> wrote:

The failure mode of the resistors is such that the resistance increases from
zero to the order of megaohms.

Is the failure at the solder joints, in the leads, or within the body
of the resistor itself?

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

maxfoo · May 21, 2004

On Wed, 19 May 2004 11:44:25 +0200, "Petr Fiedler" <fiedlerp@feec.vutbr.cz>
wrote:

Btw. the resistors are SMD resisitor, the package is 0805 (I am not
completely sure about the package may be it is 1206 i do not have any sample
board now). I am trying to find out who is the manufacturer of the
resistors.

I've used Dow Corning Ž 3140 RTV to goop MMIC die in Engineering test with no
problem, peels right off and is non-corrosive...

http://www.dowcorning.com/content/etronics/etronicsseal/etronics_aas_1ptov.asp

Remove "HeadFromButt", before replying by email.

Jamie · May 22, 2004

we use a silicone where i work as a water block for marine use in wire.
it has a curing agent that has to be mix as the time of use. the
special oil that is used which comes from germany btw, expands under
heat greatly.
its very possible the encasements of the smt resistors having problems
are not bonding to maintain a seal. this can cause oil from the silicone
to leak into the under layer and thus when heat is applied will cause
pressure internally.. one of the problems we have is the oil leaking
from the silicone..
the oil we use from germany is fine how ever, an alternate oil was
once used and i think it was either Soy oil or peanut base thus caused
a leaching effect . you may want to test a block of silicone and let it
sit in a form after cure for about 2 weeks, then pull it out and examine
the form for oil leaching.

Petr Fiedler wrote:

The board is manufactured by someone else (product of Taiwan). This board is
placed into a box with other electronics and the box is sealed (here in
Europe) using the silicone grease (for marine applications). Only the 0 ohm
resistors that are covered by the grease fail. Other resistors of the same
kind never fail. Thus I suspect the silicone grease to be the cause. The
hypothesis is that something from the grease gets into the resistor and then
corodes the wire. Friend of mine told me that he had read somewhere
somethink about sulfur geting from the silicone grease into the components,
but he was not sure and he does not remember the source of the information.

Piotr Patek's idea that "the silicon could possibly prevent evaporating of
some aggressive flux component" is another interesting idea.
I hope we fill find the reason soon. The analysis using electron microscopy
is quite expencive and we do not know what should we look for.

Thanks,
Petr

"> If you mean that something about the 0 Ohm resistor itself failed,

then I'm skeptical, because I thought these actually just had a
continuous wire under there. That should be easy for you to determine.

I can't see the silicone itself being the primary cause of either type
of problem.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

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