Hi Amol!
We deal with multiple customers here. We request drawings specify
either tolerances, or a verbal description of the area e.g. "mating
surfaces of connectors". We have some instances where the drawing has a
cross-hatched area and a drawing note that says to mask approximately
where shown.
We have had problems where drawings only specify a dimensioned keep-out
area, and the general tolerance for the drawing is something small - so
it says to mask something like .25" +- .005" - not my idea of a good
time. When we get drawings like that we submit change requests to
loosen the tolerance for the keep-out area.
Always fun.
regards,
Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215
>>> [log in to unmask] 02/05/07 10:06AM >>>
Dear all,
Since we are on the topic of conformal coating, I wanted to get a feel
for how conformal coating masking requirements are being requested by
the customer and being handled by the manufacturers. The customer
drawing usually states the type of CC to be used and the keep-out areas
for the coating (usually location Ids on the board). When one is masking
on the keep-out areas, what tolerances are being used around the
keep-out areas?.......IPC 610 D only states that there should be no CC
on keep-out areas, and therefore by logical deduction, also assumes that
all areas except the keep-out areas are to be covered by coating.
Obviously, there are practical limitations to this requirement. For
example, a test via is a keep-out area, but the trace running from the
via is not. Is everybody out there JUST masking the via, and then doing
manual touch up on the extra keep-out area if any, afterwards? If one
goes too close, the coating flows on the keep-out area, and if one
leaves some space, you are violating IPC specs! .,..........I am
thinking along the lines of asking customers to specify a tolerance for
the keep-out areas as some of them are very particular about this
issue.
Requesting your thoughts, current best practices etc
Regards,
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael
Sent: Friday, February 02, 2007 6:27 PM
To: [log in to unmask]
Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
Hi Steve: Well let's think about this again. Some food for
thought......
* I assume your are using the HT500 tape. Have you tried a
different tape? In addition to the HT500 we also use Shercon's
"Conformal Coat" tape. It has a different backing and adhesive.
* Possible compatibility issue with the soldermask? Have you
tried
the HT tape on a different soldermask and a different lot of boards
with
the same soldermask?
* Possible flux or wash residue or moisture interactions? Are the
boards washed and thoroughly dried prior to CC?
* Are you absolutely sure that the masking tape was on the board
for only an hour?
* Could the tape been applied to a hot board? Locking in the
adhesive?
* Since the initial problem have you built some up "by the book".
Same problem?
Have a Good Weekend
Mike Barmuta
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, February 02, 2007 12:19 PM
To: [log in to unmask]
Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
Hi Michael!
Believe it or not, it is adhesive. When we go to remove the residue,
it's real gummy and sticky...just like the tape adhesive. Take a look
at
this picture:
http://stevezeva.homestead.com/files/Tape_Adhesive.jpg
It's a piece of the tape that I've taken and carefully scrapped at on
the sticky (adhesive) side until I've gotten to the carrier part of
the
tape, and the carrier part of the tape is actually clear...it's the
adhesive that's tan. I looked at the MSDS and the tape is actually a
polyethyleneterephthalate film, and the adhesive is listed as a rubber
adhesive.
Like I said, I've never had this problem before.I used Humiseal tape
over at LaBarge while I was there, and switched our conformal coat
area
over to the tape since I've been here at OAI. I've just now started
seeing the problem.
The tape doesn't stay on the board for more than 1-hour after spraying
before we remove it. The one weird thing that I am seeing is that I
only
see the residues at places like in my first picture where we've masked
over PTH locations where the tape is completely on the PCB soldermask.
I
don't see the residues on places where the tape is over the tin/lead
board finish, or metal (like the connector sheilds on press-fit
connectors.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael
Sent: Friday, February 02, 2007 12:34 PM
To: [log in to unmask]
Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
Steve: I would agree with Doug. By the appearance and color of the
residue it looks like the tape itself.
We are also using Humiseal's tape, in both strip and dot form. We have
not seen any issues with adhesive residue. One thing we monitor
closely
is how long the tape is on the board after application. After
application we wait for two hours then remove the tape. Longer times
can
cause release problems with the tape.
Hi Kenny: We used to use a liquid latex maskant but found it messy and
cumbersome to use. Have you considered preformed masking aids or tape?
Or is the design such that they won't work?
Check with Chemtronics they had a peelable latex product, Chemmask HV.
The rheology of the formulation was very good, preventing it from
flowing or spreading out after application.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, February 02, 2007 9:31 AM
To: [log in to unmask]
Subject: [TN] Humiseal Masking Tape Residues...
Hi All!
I have a conformal coat masking problem too along with KennyB. We're
getting residues from the Humiseal tape we're using when we remove the
tape.
We're coating the boards with 1B31, and we don't bake the boards with
the tape on. We take the tape off right after we spray the board.
Check
out:
http://stevezeva.homestead.com/files/Tape_Residues.jpg
I've not had this problem with Humiseal tape before. Our customer is
rejecting the boards and it is quite time consuming to remove these
residues.
I've got a call into Humiseal to see if they can help. Do any of you
use
any other tape for masking that doesn't leave residues?
Have a great Friday!
-Steve Gregory-
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