Pete,
1. How much "leakage current"/resistance are you measuring?
2. What is the voltage level being used by the probes?
3. What is the distance/gap between the probes?
4. What kind/type of flux are you using?
5. Are you "baking" the boards after cleaning and before coating?
There is a source of conductive contamination somewhere.
Have you tried to "peel/remove" the coating from an affected area
then examine/test the area (leakage current and or contamination testing).
If all else fails send some samples to a lab. There are several who specialize
in
locating contamination sources. By the way a RH >50% can create problems with
leakage
currents.
David A. Douthit
Manager
LoCan LLC
Peter Zosimadis wrote:
> Hi David,
>
> Thank you for your response. Answering your questions,
>
> 1. Yes the coating is completely cured.
> 2. No shadow areas.
> 3. Humidity was at standard indoor levels, nothing out of the ordinary.
> Also, we processed boards on different days with similar results.
> 4. We thought of contaminated surface as well. We cleaned the boards, then
> coated them again, same result. Even tried extra thick coating, same
> results.
> 5. Yes, complete coverage over entire board. Used a UV light chamber to
> check distribution of conformal coating.
> 6. Not sure about this one, seems the solder mask is not being effected by
> the UV light.
>
> Any other ideas?
>
> Thanks,
>
> Pete
> ----- Original Message -----
> From: "David Douthit" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, September 25, 2003 1:26 AM
> Subject: Re: [TN] conformal coating help needed
>
> > Pete,
> >
> > 1. Are you sure the coating is completely cured??
> > 2. Does this coating also have a secondary curing agent
> > for "shadow" areas that UV light can not reach?
> > 3. How high was the humidity during application and testing?
> > 4. Are you coating over contaminated surfaces?
> > 5. Is there complete coverage of edges, back sides, beneath, and points?
> > 6. Is the solder mask completely cured and
> > compatible with the coating and coating cure process
> > (intense UV can damage certain materials)?
> >
> > These make good starting places for your answer.
> > I am sure others will add to this list!
> >
> > David A. Douthit
> > Manager
> > LoCan LLC
> >
> > Peter Z wrote:
> >
> > > Hi Everyone,
> > >
> > > Having trouble with conformal coating. Currently using a UV cure
> silicone
> > > based spray on a PCB with gold plating.
> > >
> > > The problem we are experiencing is after the conformal coating is
> applied
> > > and curred (0.002" thick), using simple probes with very little pressure
> on
> > > the probes, we obtain conductivity between certain traces. In other
> words,
> > > the conformal coating is not preventing electrical conduction between
> points.
> > >
> > > Specificially, we are having difficulty coating vias and SMT
> > > resistor/capacitors.
> > >
> > > We tried increasing the thickness of the conformal coating sprayed, but
> no luck.
> > >
> > > Does anyone have any ideas?
> > >
> > > Thanks,
> > >
> > > Pete
> > >
> > > ---------------------------------------------------
> > > Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> > > 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 or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> > > To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> > > Search the archives of previous posts at:
> http://listserv.ipc.org/archives
> > > Please visit IPC web site
> http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information,
> or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> > > -----------------------------------------------------
> >
> > ---------------------------------------------------
> > Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> > 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 or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> > To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> > Search the archives of previous posts at: http://listserv.ipc.org/archives
> > Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
> for additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> > -----------------------------------------------------
> >
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
