...but it's not a forbidden act in itself. At least not universally; and especially
for 1206 size. In a perfect world all SMT escape routes would be precisely
balanced and accessible after assembly. And in a perfect world, you would
never have an opportunity to work on jobs where a perfect result was not
possible.....
Love Lexington, btw.
-Chris
On Thu, 30 Apr 2009 10:44:33 -0700, Allen Maddox
<[log in to unmask]> wrote:
>Solder-mask is not an insulator, or at least that's not it's purpose or spec'ed
for. The chance of a terminal touching a trace that goes under it is
possible. Most component body are not spec'ed for insulation either. If you
can guarantee no voltage arc from a trace into the body of the component,
then you have that part covered. If you cannot guarantee insulation, don't
take the chance.
Allen Maddox, CID+
Allen Maddox Printed Circuit Board Designs and Services
www.maddoxpcb.com
http://www.linkedin.com/in/trailsitter
________________________________
From: Denis Lefebvre <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, April 30, 2009 1:14:55 PM
Subject: Re: [DC] Traces and vias under components
It can also contribute to "tombstoning"
Denis Lefebvre, CID+
PCB Designer
Finisar Corporation
(408)542-3832
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Brand, Rodney
Sent: Thursday, April 30, 2009 10:06 AM
To: [log in to unmask]
Subject: Re: [DC] Traces and vias under components
With a capacitor the copper in the middle covered with solder mask can
contact the body acting as a fulcrum and causing the part to change
value or fail.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of S.
Roy
Sent: Thursday, April 30, 2009 1:00 PM
To: [log in to unmask]
Subject: Re: [DC] Traces and vias under components
Hello everyone,
Stupid question but...
An Engineer would like to know why it is such a bad idea to run traces
between the pads of the same component, i.e., a 1206 resistor or cap. I
know I shouldn't do it, but I can't put my finger on the spec that
supports my distain for running these traces. Can someone steer me in
the right direction, please? Thanks...
Respectfully,
Steven D. Roy
PCB Designer
Audio Authority Corp.
2048 Mercer Road
Lexington, KY 40511-1071
(859) 233-4599 X-159
[log in to unmask]
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Andy
Kowalewski
Sent: Wednesday, March 18, 2009 6:21 PM
To: [log in to unmask]
Subject: Re: Traces and vias under components
You can almost guarantee that the board they had trouble with had open
vias under the components, and wave soldering filled the vias and made a
little dome on the top side, ready to make short circuits to any metal
bodies.
Properly tenting thye vias would fix that problem.
Cheers...
Andy Kowalewski
0424 432 235
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
wheels
Sent: 2009 03 19 01:44
To: [log in to unmask]
Subject: [DC] Traces and vias under components
Guys,
We have a customer which we are designing a mostly SMT board for that
requires all traces and vias not to be under components. This would also
include any planes being under the components. I guess in the past they
had a board designed by some else that had a shorting problem with
traced and vias under the components. They are insistence that this is
the way it has to be. Has anyone else had experience with this sort of
demands? This is not for space, military, high voltage, high vibration
or a medical application. Can anyone think of anything we could tell
they to change their mind?
Thank you,
wheels
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