Agree. If it is aircraft, you may consider thermal impact as well (many of PWA use ground as heat sink in old days and conduction only - not much convection cooling used for electronics in high altitude. Not sure what is nowadays).
--------------------------
Sent using BlackBerry
----- Original Message -----
From: Upton, Shawn [mailto:[log in to unmask]]
Sent: Tuesday, January 11, 2011 01:28 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Trace Widths Entering SMT
Ah, well that is something different--if it predates, and must be
followed, well, you're stuck most likely, unless if you want it to be
your neck if you attempt otherwise.
If you want to have fun with him, ask how far away the necking down of a
trace is--for instance, let's say you wanted a 50mil trace to the pad,
how far away do you have to neck down to 20mil? IOW, how long is the
minimum 20mil trace length from the pad supposed to be?
The rule doesn't make sense to me, but I only deal with low volume
stuff. I did have one board house tell me that I didn't need thermal
reliefs on a rather large SMT pad! [It was a small, low volume board
though.] I haven't run into a problem with assembly houses and "too
thick" traces, other than if I need to have a board reworked once we got
it back (blew something up in the lab, let's say). Then those thermal
reliefs matter--but a 50mil wide trace is hardly that much of a
conductor of heat...
Shawn Upton, KB1CKT
Test Engineer
Allegro MicroSystems, Inc
[log in to unmask]
603.626.2429/fax: 603.641.5336
-----Original Message-----
From: Cote, Clint (GE Intelligent Platforms, US)
[mailto:[log in to unmask]]
Sent: Tuesday, January 11, 2011 1:21 PM
To: Upton, Shawn; TechNet E-Mail Forum
Subject: RE: [TN] Trace Widths Entering SMT
Yes, standard FR4 multi-layer with soldermask. I asked the Engineer and
he isn't sure because the requirement pre-dates him. But, he is adamant
that the requirement must be met.
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