Hi Robert,
Are you allowed to add non-functional copper or ground planes on the layers
that have
minimum circuitry ? If you are, it will help to balance the build-up
and you will have a flatter board.
Your board shop should be able to help you with these issues also.
Good Luck,
Andre Demers - C.I.D.
Summit Technologies Ottawa Inc.
329 March Road, Suite 203
Kanata, Ontario
Canada K2K 2E1
Phone :(613) 599-3881
Fax :(613) 599-7889
Pager :(613) 368-0506
Email :[log in to unmask]
-----Original Message-----
From: Harter, Robert [mailto:[log in to unmask]]
Sent: September 30, 2004 10:34 AM
To: [log in to unmask]
Subject: [DC] Layer Stack Up Questions
Hi All,
I have questions about a board I am working on now and how best to keep
it as flat as possible. This board is part of a surface mount RF
pre-selector module that is long and narrow and unfortunately cannot be
changed since its shape was pre-determined by the amount of area left on
our customer's PCB.
Top Core is 25mil 6010 although any of the other materials will work as
long the Dk is close to 10.2. There are currently 2 other cores which
are 5mil FR-4 using 5mils of pre-preg for bonding. All edges of the
board will have plated half vias that serve as both mechanical fastening
and signal connections. I think another problem is that from top to
bottom the copper isn't balanced. This board has both RF and mixed
signal control circuitry onboard so a majority of the copper is on the
top layer with a solid ground plane layer directly below it. The other
4 signal layers have a minimum of copper on them and are used for
routing.
We have had this board built 4 times already strictly for proto-type and
theory proving, however this go round is for customer delivery and it's
warped in both the x and y directions. The shape and size of this board
add another twist (no pun intended) to this build, its dimension are
1.24 in. x 2.70 in. The finished stack height is 51mils and I can't add
much more to that for added stiffening so I'm hoping that someone can't
help me engineer what I have better.
Thanks,
Bob Harter, Jr.
PCB Designer
Paratek Microwave, Inc.
6935 G Oakland Mills Rd.
Columbia, MD 21045
PH# (443)259-0140 x278
CP# (443)739-8407
WWW.PARATEK.COM <http://www.paratek.com/>
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