Question regarding using epoxy or RTV on PCBs

[Jim Flanagan]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

 

[Roger Hamlett]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

Very much so.
Non acidic RTV's are sold by aquarium shops, and for electronic
encapsulation. The former is usually the 'easier' source if only a small
quantity is required. 'Normal' RTV's give off acetic acid, and are not
suitable for use on a PCB. Look for GE 142, Rutland 76R, and similar
products. As an alternative, consider a low melting point hot-melt glue.

Best Wishes

 

[[email protected]]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

http://www.barnhillbolt.com/specs/loctiteTAKPAKtds.pdf

 

[default]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

Cured Silicone RTV is great for bonding heavy components to PCBs and
is an excellent corona resistant compound. In theory the acetic acid
may be corrosive, but I never see any evidence of it even with bare
copper and silver.

Another alternative is hot melt adhesive - if heat and/or flame is
unlikely

 

[Jim Yanik]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

Hot glue works well as long as the unit does not operate in a hot
environment,like a car's interior on a sunny day.

 

[D from BC]

I just use whatever clear silicone is at the hardware store. I
do smell the acetic acid in silicone.
Did you know you can make copper bright and shiney in vinegar?
Vinegar has acetic acid..
So I wasn't worried too much about home silicone containing some
"Alien" acid that would eat through the floor.
If there are corrosives in the RTV..the reactivity I believe is
limited and reduces to nothing after cure. Some microscopic
copper loss can be tolerated.
I don't like the RTV slow cure time and the hot glue suggestion
below from another poster is something I use frequently.

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

Hot glue works well as long as the unit does not operate in a
hot
environment,like a car's interior on a sunny day.

--
Jim Yanik
jyanik
at
kua.net
..

 

[Michael A. Terrell]

I just use whatever clear silicone is at the hardware store. I
do smell the acetic acid in silicone.
Did you know you can make copper bright and shiney in vinegar?
Vinegar has acetic acid..
So I wasn't worried too much about home silicone containing some
"Alien" acid that would eat through the floor.
If there are corrosives in the RTV..the reactivity I believe is
limited and reduces to nothing after cure. Some microscopic
copper loss can be tolerated.

I have seen copper traces with opens from the wrong RTV.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ben Jackson]

To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb.

At work we use Loctite 444 with the matching accelerant. It works very
well, but the accelerant does smell very strongly of potpourri! It will
run a bit, so if you need to control where it goes (keep it off of pins
or pads) use a toothpick or something to transfer it.

If you just need to insulate an area, kapton tape works very well.

I just did something very similar to what you describe on a board I got
out of a prototype box. The original rework was secured with something
like double-stick tape and some small circular bits of tape (for wires)
that were *very* strong. I'd like to find out what those are.

 

[Eeyore]

Very much so.
Non acidic RTV's are sold by aquarium shops, and for electronic
encapsulation. The former is usually the 'easier' source if only a small
quantity is required. 'Normal' RTV's give off acetic acid, and are not
suitable for use on a PCB. Look for GE 142, Rutland 76R, and similar
products. As an alternative, consider a low melting point hot-melt glue.

I've found hot melt glue to be suitable only as a very temporary measure.

Graham

 

[Eeyore]

I have seen copper traces with opens from the wrong RTV.

I've seen a copper trace completely dissolved as a result of extended use in a
night club where it got exposed to an acid environmemt from hot sweaty people !
Cigarette smoke possibly also played a part.

Humidity's a bitch !


Graham

 

[qrk]

Hot glue works well as long as the unit does not operate in a
hot
environment,like a car's interior on a sunny day.
I just use whatever clear silicone is at the hardware store. I
do smell the acetic acid in silicone.
Did you know you can make copper bright and shiney in vinegar?
Vinegar has acetic acid..
So I wasn't worried too much about home silicone containing some
"Alien" acid that would eat through the floor.
If there are corrosives in the RTV..the reactivity I believe is
limited and reduces to nothing after cure. Some microscopic
copper loss can be tolerated.
I don't like the RTV slow cure time and the hot glue suggestion
below from another poster is something I use frequently.

I've seen silicon glue w/ acetic acid eat aluminum coating on mirrors.
It took a couple weeks to show up. That was an expensive mistake!

 

[budgie]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.

There are (at least) two distinct groups of silicone adhesives/sealants in
widespread use. They are usually labelled accordingly as "neutral cure" or
"acid cure". As others have pointed out, acid cure types are a potential
corrosion problem, and should be avoided. Make sure the type you use is neutral
cure.

 

[Robert Baer]

Hello..
I am trying to repair a circuit board which has a couple of obsolete
components. These parts are unavailable and it appears that I am going
to have to resort to 'cludging' an alternate part in order to getting
the pcb back up and running. To do this, I will need to bond the parts
to the pcb in some fashion, using some insulation material between the
component and the pcb. My desire is to use clear RTV in case I need to
possibly remove the part at a later date.

The question is, how safe is using RTV on pcbs? Is there some corrosive
properties that possibly take place later down the road? I would guess
that some formulations of RTV are better than others in this regard.
Your ideas and suggestions would be appreciated.
Thanks -
Jim
Largo, Fl USA

You want to use GE Silicone II which does not generate acetic acid.
It is available in clear and white; most hardware stores carry it.

 

[Robert Baer]

Cured Silicone RTV is great for bonding heavy components to PCBs and
is an excellent corona resistant compound. In theory the acetic acid
may be corrosive, but I never see any evidence of it even with bare
copper and silver.

Another alternative is hot melt adhesive - if heat and/or flame is
unlikely

**NO** "theory"; acetic acid generated by the "standard" or "normal"
variety of RTV can and has caused severe corrosion - and can continue
for years after "curing".
Absolutely use the GE Silicone II and get the lower cost versions
available at Lowes, Home Depot, etc and not the expensive version
availble at electronic outlets.

 

[Robert Baer]

I just use whatever clear silicone is at the hardware store. I
do smell the acetic acid in silicone.
Did you know you can make copper bright and shiney in vinegar?
Vinegar has acetic acid..
So I wasn't worried too much about home silicone containing some
"Alien" acid that would eat through the floor.
If there are corrosives in the RTV..the reactivity I believe is
limited and reduces to nothing after cure. Some microscopic
copper loss can be tolerated.
I don't like the RTV slow cure time and the hot glue suggestion
below from another poster is something I use frequently.

----- SNIPped ------
"After cure" is a mistake!!!
The stuff is always curing, even months after application!
That is why it is vital to use the Silicone II which does not
generate acetic acid.
Acetic acid will attack everything; the resulting corrosion will be
impossible to stop and the circuit will not last or be repairable
afterwards.

 

[D from BC]

I just use whatever clear silicone is at the hardware store. I
do smell the acetic acid in silicone.
Did you know you can make copper bright and shiney in vinegar?
Vinegar has acetic acid..
So I wasn't worried too much about home silicone containing some
"Alien" acid that would eat through the floor.
If there are corrosives in the RTV..the reactivity I believe is
limited and reduces to nothing after cure. Some microscopic
copper loss can be tolerated.
I don't like the RTV slow cure time and the hot glue suggestion
below from another poster is something I use frequently.

----- SNIPped ------
"After cure" is a mistake!!!
The stuff is always curing, even months after application!
That is why it is vital to use the Silicone II which does not
generate acetic acid.
Acetic acid will attack everything; the resulting corrosion
will be
impossible to stop and the circuit will not last or be
repairable
afterwards.

------------
I tried sniffing my washroom silicone caulking and don't smell
anything..When I applied it, my eyes were burning from the acid
release.
Of course the last molecule of acetic acid will take a long time
to wiggle out.
But I agree with other postings...The safer cheaper hardware
store available silicone is the GE II Silicone. I've used this
before but forgot that it didn't irritate my eyes.
And I had a heck of a time removing the silicone when I burnt
out some components ... (Not the silicone at fault..voltage
spike.)
D

 

[Rich Grise]

"After cure" is a mistake!!!
The stuff is always curing, even months after application!
That is why it is vital to use the Silicone II which does not
generate acetic acid.
Acetic acid will attack everything; the resulting corrosion will be
impossible to stop and the circuit will not last or be repairable
afterwards.

I know there must be something RTV-like that's non-corrosive, because
I saw a lot of it used to fasten down components in military stuff,
back in the 1970's.

It makes it a real bitch to replace the component, by the way. ;-)

Cheers!
Rich

 

[J.A. Legris]

Hot glue works well as long as the unit does not operate in a hot
environment,like a car's interior on a sunny day.

No problem for the *professional* hot-melt glue and 3-M makes it for
just this purpose. Expensive, but works great.

Product brochure here (.pdf):
http://multimedia.mmm.com/mws/mediawebserver.dyn?6666660Zjcf6lVs6EVs666WkNCOrrrrQ-

We use 3M Jet-melt™ Adhesive: High-Melt 3779 Amber in 5/8" by 2"
sticks
- soft point is 325°F (163°C)
- good electrical properties with high heat resistance for potting,
wire staking.
- UL 94 V-O
- minimum order is 11 lbs (!) s unless you find a distributor

You'll also have to buy a 3-M's fancy temp controlled glue gun:
http://www.etoolsrus.com/browse.cfm/4,2.html

Warning: Don't get this stuff on your skin when it's hot - very hot!!

 

[jasen]

**NO** "theory"; acetic acid generated by the "standard" or "normal"
variety of RTV can and has caused severe corrosion - and can continue
for years after "curing".
Absolutely use the GE Silicone II and get the lower cost versions
available at Lowes, Home Depot, etc and not the expensive version
availble at electronic outlets.

some of those cheap neutral cure silicones contain chemicals that will attack
polycarbonate and/or other plastics, I know it was a GE silicone I used when
I was doing polycarbonate roofs, I think GE owns the polycarbonate roofing
material factory too.

 

[jasen]

I know there must be something RTV-like that's non-corrosive, because
I saw a lot of it used to fasten down components in military stuff,
back in the 1970's.

dow corning has a number of electronics targeted milspec silicones....

It makes it a real bitch to replace the component, by the way. ;-)

cut it off with a chisel?

Bye.
Jasen