In olden days 85-86, in air-borne radar systems, only the power supply
boards and a couple of boards with high voltage on them were designated to
be conformal coated with Humiseal, IB-31. Rest of the 10+ boards in the
system, were left bare. The explanation was that the solder mask was
sufficient protection. So, I would expect that this could be one of the
reasons.
The second reason as others have pointed out would be that the solder mask
pealing would be unmanageable, if only traces were masked. Every time the
board sees hot cold cycles (solder, reflow and wash), the traces and the
board would have different heat expansion/absorption coefficients and
imagine what that would do to the thin strips of solder mask, contoured over
uneven surface! The rest of the solder mask over the plain PCB surface is
insurance against this happening.
In addition, the ease of processing. the other reasons above may just be
by-products!
Regards,
Lakshmi
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, February 06, 2003 4:54 PM
Subject: Re: [TN] Soldermask
Good question, Siggi - no answer! (Sorry, I'm feeling facetious this
morning).
I would guess that it's a question of adhesion of the mask to the board. If
only the traces are masked then there would be miles of 'edges' where the
mask ends and the board surface resumes - edges that can be damaged,
delaminated, etc.
Or it may just be tradition, or aesthetics.
Peter
"Zweigart, Siegmund" <[log in to unmask]> 06/02/2003 09:58 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to "Zweigart,
Siegmund"
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Soldermask
I have a simple question but never got an answer.
Why is solder mask on the complete board, not just on the traces?
Because of:
Screen printing
Tradition
??
Any Input?
Siggi
----------------------------------------------------------------------------
-
Kind regards / Mit freundlichen Grüßen
Dr. Siegmund Zweigart
New Technology Manager
Solectron GmbH
Solectronstrasse 2 Fon. ++49 7032 998 194
D - 71083 Herrenberg Fax ++49 7032 998 222
e-mail: [log in to unmask] <mailto:[log in to unmask]>
internet: www.solectron.com <http://www.solectron.com>
----------------------------------------------------------------------------
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----------
From: Martyn Gaudion [SMTP:[log in to unmask]]
Sent: Donnerstag, 6. Februar 2003 14:21
To: [log in to unmask]
Subject: Re: [TN] Here is a Primer on PWB fab
Dear Technetters,
After Jim's question on a PCB fabrication primer, I was
swamped with requests for Polar's introductory
presentation - which goes through the basic steps
involved in building a 6 layer board.. So if you
would like a copy (your customers in the PCB assembly
industry may like to see it )... you can find the
presentation as AP166 in the What's New section
on this page:
www.polarinstruments.com/support/cits/cits_index.html
Kind regards
Martyn Gaudion
www.polarinstruments.com
At 17:54 05/02/2003, you wrote:
>Anyone know of a good primer (for a student intern) on how PWBs
are
built;
>say a web based one from a board show so that she can understand
how PWBs
>are buitl?
>
>One on assembly/soldering would be good too.
>
>Jim
>
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