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
>
> ------------------------------------------------------------------
> ---------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search previous postings at: www.ipc.org > On-Line Resources &
> Databases > E-mail Archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
> information, or contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ------------------------------------------------------------------
> ---------------
>
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
