Question regarding using epoxy or RTV on PCBs

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

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

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Jim Flanagan wrote in news:45856338$0$11155$ snipped-for-privacy@roadrunner.com:

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

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.

Jim Flanagan wrote in news:45856338$0$11155$ snipped-for-privacy@roadrunner.com:

obsolete

am going

getting

the parts

between the

I need to

corrosive

would guess

regard.

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
.

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

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.

--
Ben Jackson AD7GD

http://www.ben.com/

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!

--
Mark

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.

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.

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**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.

----- 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.

some

is

suggestion

----- 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

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

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):

OrrrrQ-

We use 3M Jet-melt=99 Adhesive: High-Melt 3779 Amber in 5/8" by 2" sticks

- soft point is 325=B0F (163=B0C)

- 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:

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

-- Joe Legris

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.

--

Bye.
   Jasen

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

cut it off with a chisel?

Bye. Jasen

...

Pretty much, yeah. :-) Actually, I usually used the X-acto knife, but now that I think back, ISTR a soldering iron doing the job. ;-)

Cheers! Rich