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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