Leo
A little late but, our experience shows that UV curables have high ionics,
perhaps/probably from the photo-initiators; however, they are certainly
conductive in their uncured state as our SIR measurements showed.
It is fair to say that uncured water based materials will be equally
undesirable, but perhaps less so as they use deionised water? :-)
Certainly experience to-date indicates that they are far easier to implement
into volume production than UV's.
Regards Graham Naisbitt
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> -----Original Message-----
> From: Leo Roos [mailto:[log in to unmask]]
> Sent: 05 April 2002 16:04
> To: TechNet E-Mail Forum.; Graham Naisbitt
> Subject: Re: Re: [TN] Conformal Coating Shadow Curing Problems
>
>
> Mark:
>
> I think Graham is off base. Normally if you talk about an aqueous
> developable materials they contain acid groups and might be considered to
> have some degree of ionic nature. If Graham is talking about
> impurities then
> all materials used in the electronic industry are :ionic" in nature. For
> information, unless the waterborne systems use non-ionic surfactants, you
> may be jumping from the frying pan into the fire since, if you consider a
> surfactant a soap, they frequently are based on quaternary ammonium slats
> (ionic) or acid based also ionic.
> Sincerely,
>
> Leo Roos, Ph.D.
> ----- Original Message -----
> From: "Graham Naisbitt" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, April 05, 2002 4:00 AM
> Subject: Re: [TN] Conformal Coating Shadow Curing Problems
>
>
> > Mark
> >
> > The supplier is correct in what they have advised. By their very nature,
> UV
> > curable materials are ionic in their uncured state and you don't need me
> to
> > tell you that this is not a good thing.
> >
> > You have gone on to explain all the cautionary points that are important
> > with this technology, but I am not clear as to what you are asking the
> > Techies to do.
> >
> > I imagine that your original environmental testing was
> conducted on parts
> > that were fully cured, perhaps not on true production
> equipment? This has
> > been a common problem in my experience, and is why, for the benefit of
> > others, always ensure that the coating for such tests, is
> produced on the
> > intended production equipment.
> >
> > You ask about other materials. I suggest / recommend, that you
> take a look
> > at the new water based coatings that are now MIL Spec. qualified and UL
> > approved - we have them.
> >
> > Regards Graham Naisbitt
> >
> > [log in to unmask] <mailto:[log in to unmask]>
> >
> > Concoat ANNOUNCE their acquisition of the former Multicore
> SPCID business.
> >
> > MUST II Solderability Testing Systems -
> > CM Cleanliness Testing Systems -
> > Auto-SIR Reliability Testing Systems -
> > SoldaPro & NEW SoldaPro Wizard Thermal Profilers
> >
> > For more information please visit our new web site:
> www.concoatsystems.com
> > <http://www.concoatsystems.com>
> >
> > Concoat Limited
> > Alasan House, Albany Park
> > Camberley GU16 7PH - UK
> >
> > www.concoat.co.uk <http://www.concoat.co.uk>
> >
> > Phone: +44 1276 691100
> > Fax: +44 1276 691227
> > Mobile: +44 79 6858 2121
> >
> >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]]On Behalf Of Mark E. Schumacher
> > > Sent: 04 April 2002 19:12
> > > To: [log in to unmask]
> > > Subject: [TN] Conformal Coating Shadow Curing Problems
> > >
> > >
> > > Problem -
> > > We are using Dymax 984-LVUF, one part, UV cure, acrylic/urethane,
> > > conformal
> > > coating. This product is not a shadow cure product, and has been
> verified
> > > to be in the fluid state under SMD components such as capacitors and
> > > resistors, even for BRDs which are a year old. Dymax indicates
> > > that this is
> > > bad on 3 counts:
> > > a) Uncured 984 is corrosive.
> > > b) Uncured 984 acts as a solvent for coating that is
> cured, causing
> > > loss of bonding strength.
> > > c) Uncured 984 acts as a solvent for FR-4 PCB epoxy.
> > > This UV cure product can be cured using heat but the cure times and
> > > temperatures, 110C for 1 hour, are not practical.
> > >
> > > We have not seen any Warranty issues using this conformal
> coating, but
> we
> > > have only been using it for about 2 years, and do not know
> what the long
> > > term effects are for the uncured product.
> > >
> > > The current Dymax coating, and application (or
> misapplication), has been
> > > qualified for all our environmental tests.
> > >
> > > It is noted that before Dymax was used, Crown used a 2-part
> shadow cure
> > > product, Loctite 394. Our SCS spraying machine, model SCS-4398, has a
> > > single line, and coating material would have to be premixed.
> This would
> > > result in clogged lines and spray head within several hours, in
> > > addition to
> > > allot of scrapped coating material.
> > >
> > > Note that we have demonstrated that silicone type conformal
> coatings are
> > > not desirable as they do not provide adequate resistance to sulfur
> > > atmosphere.
> > >
> > > Questions:
> > > 1) Do I need to be concerned about uncured Dymax in shadowed areas?
> > > 2) When going to a shadow cure product, such as the Dymax 984
> Sure Cure,
> > > what issues do I need to be concerned about?
> > > 3) Do I need to be concerned with Coefficient of Linear thermal
> Expansion
> > > and possible damage to SMD parts? (Now that the material between SMD
> parts
> > > and PCB will be cured / hard) Are there guidelines for CTE to
> follow for
> > > this application?
> > > 4) Do you have any recommendations regarding specific
> conformal coating
> > > products other than Dymax?
> > > 5) What type of conformal coating system is the industry using? Are
> these
> > > shadow cure or non-shadow cure? If using shadow cure, how is it
> > > being mixed
> > > and sprayed? Are there shadow cure products that are easier to use (do
> not
> > > clog lines and head) than the Loctite products?
> > >
> > > Mark
> > >
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