[SI-LIST] Half OT: large PCB at -40C
- From: "Augusto Einsfeldt" <aee@xxxxxxxxxxxx>
- To: "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 29 May 2007 10:48:33 -0300
Hello,
I need some advice, if possible, since I have not found much info on
this subject anywhere else.
I am involved in a design where a large board (7"x11") may work at -40C m=
ost
of the time while, for 1 to 2 hours, few times a day, goes to +40 and sta=
y
there for this time.
My concern is the care I have to take while drawing the board to cope wit=
h
contractions and expansions, and also if there are other concerns like "I=
have to split the board (small size single units) to avoid problems... Or=
use a different PCB material instead of regular FR4"...
I have done designs to work at -40C continuously but with very small PCB.=
The PCB will be a four layer FR4, 2 ounce thick cooper, 10 mils tracks, h=
olding a PQ208 FPGA,
three DC-DC converters, 8 IDC connectors and few other components like AD=
Cs,
memory, LDOs and a lot of 0805 capacitors and resistors.
The MTBF is a concern and split the board in 2 or 3 will reduce it, so I'=
d
like to avoid splitting if possible.
I am thinking to use near 20 mounting holes for screws to help improve
mechanical strength since case and PCB may have different expansion rates=
.
Maybe there are another list where to ask for directions but I was unable=
to
find.
Thanks in advance for any advice.
-Augusto
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