TECHNET Archives

May 2009

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Mon, 11 May 2009 09:45:02 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (234 lines)
It has always been my sense that some solder masks will absorb moisture.
I guess my original point should be modified to say that solder mask is
not conformal coating. The function of solder mask is to prevent solder
shorts between traces not seal the circuitry. I think Denny is correct.
Oxidation protection is accomplished by a surface protection applied to
copper from the fabrication process and oxidation protection from the
solder mask chemistry but is not particularly a moisture barrier.

Then again there may be some solder masks that are impermeable to water.
I would wonder what happens when an impermeable solder mask is applied
to a board that has absorbed moisture. At assembly I expect the mask
would blister due to the pressure of the escaping water vapor.

Paul Reid

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
Sent: Monday, May 11, 2009 9:06 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Mask

Well, I disagree to a point.? Many printed circuit?formulations contain
benzotriazole as a copper "adhesion promoter" and that functions as an
antitarnish also.? I am not saying solder mask contains benzotriazole,
but I wouldn't be surprised.? Used to be, solder mask only had to adhere
to traces through high temp excursions of soldering.? Now, you also have
to adhere through tough plating cycles like ENIG.? Copper antitarnish is
applied from water base solutions, so I don't see how that can be a
moisture barrier. I think it is wrong to equate oxidation protection and
moisture barrier. 

Denny Fritz

-----Original Message-----
From: Victor Hernandez <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, 11 May 2009 8:31 am
Subject: Re: [TN] Solder Mask



If solder mask protect exposed copper from oxidation then it must be a
moisture barrier.



Inert protective coatings serve a variety of purposes. They:

Protect the copper traces from oxidation. You must passivate every
exposed piece of metal that you can't protectively coat. Examples of
structures requiring passivation include solder pads and edge-connector
fingers. 
Protect the substrate from humidity. Most substrate materials readily
absorb water vapor from the air. In epoxy-glass materials, the water
vapor can enter microscopic interstitial voids between the glass fibers
and the epoxy matrix, traveling great distances into the interior of the
substrate. The water reduces the dielectric strength of the substrate
and greatly increases its dielectric loss. 
Increase insulation resistance between traces. The inevitable
accumulation of dirt and water degrades the insulation resistance
between exposed metallic contacts on the surface of a board. In
high-voltage circuits, it can cause arcing. An insulating coating
covering the traces prevents conduction from one trace, through the
dirt, to the next trace. 
Decrease spurious shorts between traces. During the reflow-soldering
process, any water trapped within the solder paste explodes into steam,
spewing tiny solder balls all over your board. If you cover the traces,
the solder balls are less likely to short anything out. 
Control movement of solder during soldering. During reflow soldering, a
via placed too close to a solder pad tempts the solder paste to slide
over to the via and disappear down the hole. A thin line of solder mask
drawn between the solder pad and the via acts as a solder dam,
preventing the solder from moving to the via.

Victor,



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Friday, May 08, 2009 4:45 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Mask

Nice one Joe

Victor here is a link describing the effect of solder mask on trace
impedance :

http://www.sigcon.com/Pubs/edn/PassivationandSold
erMask.htm


As Joe alludes it is indeed a dielectric with a typical dielectric
constant value of 3.3. You will find in RF designs that often the boards
are specified without solder mask for this very reason.

Have a great weekend,

John



John Burke
(408) 515 4992


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad
Sent: Friday, May 08, 2009 1:11 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Mask

Victor
 
How/why do you conclude that solder mask is not a dielectric? 
 
Cheers,
Joe 
 
 
In a message dated 5/8/2009 12:37:48 P.M. Pacific Daylight Time,
[log in to unmask] writes:

Fellow  TechNetters:



Besides being a moisture barrier and solder  dam what else is the
function of solder mask.   It is not a  dielectric.



Victor,


---------------------------------------------------
Technet  Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100  ext.2815
-----------------------------------------------------

**************A Good Credit Score is 700 or Above. See yours in just 2
easy steps! 
(http://pr.atwola.com/promoclk/100126575x1221322931x1201367171/aol?redir
=htt
p://www.freecreditreport.com/pm/default.aspx?sc=668072&hmpgID=115&bcd
=May5509AvgfooterNO115)

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100
ext.2815
------------------------------
-----------------------


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2