[SI-LIST] Re: Half OT: large PCB at -40C
- From: Jeff Seeger <jseeger@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 30 May 2007 12:54:04 -0400
Augusto Einsfeldt wrote:
> I am involved in a design where a large board (7"x11") may work at -40C most
> of the time while, for 1 to 2 hours, few times a day, goes to +40 and stay
> there for this time.
> My concern is the care I have to take while drawing the board to cope with
> contractions and expansions, and also if there are other concerns like
> snip <
I'd expect your primary issues to be solder joint fatigue and PTH failures.
In general for Hi-Rel product you should be specifying properly both bare
board and assembly, IPC &/or JSTD Class 3. You should probably be talking
with your manufacturing and physical design resources, for their opinions
on specifics.
For the solder, if you have BGA components you should be using an underfill.
Gullwing or Through-Hole are not an issue so long as the joints are formed
properly (driven by specifications above). I've seen a couple of tricks to
help discrete components but these will again depend on those who assemble
and their capabilities.
For the vias, consider building your boards with additional copper plate in
the holes, and be gentle on the aspect ratio with respect to your
fabricators'
capabilities. With these measures FR4 should be fine.
--
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
jseeger "at" appliedcad "dot" com 978 649 9800
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
