[SI-LIST] Re: Need advice on basic 6-layer stackup - board warpage
- From: "Sol Tatlow" <Sol.Tatlow@xxxxxxxxxxxxxxx>
- To: <GrahamDavies@xxxxxxxx>, "steve weir" <weirsi@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 25 Apr 2005 09:03:51 +0200
Hi Graham,
"By Cu imbalance ..."
Steve is absolutely right to advise against non-symmetrical board
stacks,
and here's an example why:
A few years ago, a company came to us, unhappy with their layout house
that had designed them a 14 layer board covered in expensive FPGAs. The
layout house had come up with a SUPERB stackup, where all 6 pwr and gnd
planes where in the top half of the board ... no joke!
The PCB manufacturer had obviously not thought about it, and
manufactured
it as requested. Even the non-populated boards 'looked' ok - warpage was
acceptable, apparently. But the ASSEMBLED boards - that was a different
matter altogether: they were as straight as a banana. And worse still,
not a single board functioned. Cue customer changes layout house, to us.
But, this is an example of an *extreme*. Your board with only one 'off'
plane, and with this being closest to the centre of the board, is, *in
my
experience*, unlikely to be a big problem. Of course, you'd like to be
SURE,
and this is why I thought I'd comment on your mail and Steve's reply:
although you definitely should ask your PCB fabricator, as Steve
suggests,
you should perhaps ask your populator as well. They will be able to give
you a different slant on it, as they see lots of different types of
boards
(not just yours) at the END stage, and the type of soldering also plays
its
part in achieving an acceptable assembled PCB (wave soldering heats one
side far more than the other, while reflow and vapour phase soldering
offer
more uniform temperatures). PLUS, any products that will be sold in
Europe
after July 2006 will be faced with lead-free soldering, where soldering
temperatures are significantly higher, so any problems will then worsen.
Regards,
____________________________________
Sol Tatlow, M.Eng. (Oxon)
ProDesign Electronic & CAD Layout GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062-808-302
Fax: +49 (0) 8062-808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________=20
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