Peter,
Thank you for the nice categorical breakdown of RTV.
It is certainly an area that has been taken for granted because "we always
do it that way". I'll certainly be more aware of intended applications and
be more selective.
One question that I have is whether or not the corrosive properties still
exist after cure or does the corrosive nature take place only during the
vulcanizing process.
Bill Kasprzak
Moog Inc., Systems Group, Process Engineer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Peter Swanson
Sent: Monday, December 20, 2004 1:03 PM
To: [log in to unmask]
Subject: Re: [TN] RTV potting materials
There are a number of different types of RTV silicone cure mechanisms, all
of which give off a by-product upon curing:
1) Acetoxy - by-product of cure is acetic acid, not normally used in the
electronics environment because of corrosivity. Quick cure, and the stuff
you normally get to seal your shower at home.
2) Amine - cyclohexylamine (a building or construction grade product)
3) Oxime - methylethylketoxime
4) Alkoxy - commonly a mixture of methanol and ethanol
These two are used in electronics, can be called "neutral" cure. The oxime
types, like the Dow Corning product mentioned, can react with copper - check
this.
5) Acetone - acetone
This latter one is a newer variety, and seems to offer a lot of promise,
because the very small amounts of acetone given off are non-corrosive, non
toxic, not very smelly and they cure pretty quick.
Peter
--
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Peter Swanson [log in to unmask]
INTERTRONICS http://www.intertronics.co.uk
Tel: +44 1865 842842 Oxfordshire, England
INTERTRONICS is dedicated to providing quality material,
consumable and equipment solutions to the high
technology, high performance assembly industries,
incorporating outstanding levels of technical support
and customer service.
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: 20 December 2004 16:25
To: [log in to unmask]
Subject: Re: [TN] RTV potting materials
Dave,
We currently use Dow Corning 737 Neutral cure RTV for bonding many large
components, capacitors, inductors, etc., to circuit boards and chassis
parts.
The acetal cure of many RTVs stinks, but more importantly is the fact that
it creates acetic acid as it cures which can etch bare copper...
that could be bad. The neutral cure stuff has little of no discernable
odor.
I'm sure GE makes a competitive product.
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roach, David
Sent: Monday, December 20, 2004 11:15 AM
To: [log in to unmask]
Subject: Re: [TN] RTV potting materials
We currently use an alcohol-based RTV silicone (Dow 3145) to adhere some
tall through-hole capacitors to the PCB to improve vibration resistance.
Is
anyone aware of any water-based RTV silicones that are PCB firendly that
would work as well and not have the odor while curing?
Dave Roach
Trane Controls
St. Paul, Minnesota
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