[SI-LIST] Re: PCB STACKUP
- From: "Robert Sefton" <rsefton@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 22 Jan 2004 09:40:33 -0800
> Perry Qu wrote:
> >
> > Can someone comment on the impact of assymetrical stackup on PCB
yield ?
> >
>
> For rigid boards you are setting the stage for warpage,
> otherwise known as bow and twist. In some cases it can
> be accomodated but always at a price.
>
> The need for flatness with today's devices is considerable.
> Industry standards for "flat" are tight when all aspects
> are in alignment, and yet the assembly community will still
> have coplanarity challenges with boards that meet standards.
>
> This is not so much a board fab yield issue as it is a next
> level assembly producability concern.
>
> Flexible boards have a different set of issues.
This is a timely topic with all of the recent PDS discussions. To reduce
the mounted inductance of bypass caps it's advantageous to cram all of
the pwr/gnd pairs toward the outside of the stack. It's tough to do this
and keep the stackup balanced without a big increase in layers. I did a
big (12"x13") board last year with the stackup below. 16 layers, 0.091"
thick after plating. I left it to the board vendor to balance it as best
he could. The only adjustment he made was to use 0.5oz copper for the
bottom two gnd planes. No copper pours on routing layers or anything
like that. The board had BGAs top and bottom and we had no coplanarity
problems at all. I'd be very interested to hear what you can and cannot
get away with in a stackup without causing coplanarity problems. What
adjustments can be made to balance an asymmetric stackup?
top (0.5oz)
gnd (1oz)
pwr (1oz, split)
pwr (1oz, split)
gnd (1oz)
sig (0.5oz)
sig (0.5oz)
gnd (1oz)
gnd (1oz)
sig (0.5oz)
sig (0.5oz)
gnd (0.5oz)
sig (0.5oz)
sig (0.5oz)
gnd (0.5oz)
bottom (0.5oz)
Robert
------------------------------------------------------------------
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.org
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:
