[PCB_FORUM] Re: Removing unused pad rings on inner layers DURING design...

  • From: Kevin McCowan <kmccowan@xxxxxxxxxxxxxx>
  • To: icu-pcb-forum@xxxxxxxxxxxxx
  • Date: Fri, 01 Apr 2005 09:44:52 -0500

I've been following this thread and it is very interesting.
My only issue, and I have done this before, is what happens
when you need to add a pad back and there is no longer
any room for it? The pads are needed to keep this situation
from arising. I also was using the Mentor (veribest) tool at
the time, but I cannot say it was easy by any stretch of
the imagination. Maybe they have added a way to do it that
wasn't there when I used the tool. (It's been 2 years.)
When I did it the tool had a feature to remove unused
pads after it was routed, but before creating gerbers.
It is possible to set up the rules to plan for the eventual
removal of the pads, but is it a good idea?

Kevin McCowan
Sr. PCB Designer
TSI Telsys

Musetti, Carl wrote:
Really Good idea!

I'm sure most of you are aware of this but when you talk about
making a pad size the size of the drill you need to consider
that pad size as the actual drill bit size not finished drill + the
standard manufacturing tolerances. Then you would apply that minimum
clearance to that pad shape.

My 2 cents

Carl

-----Original Message-----
From: MAILER-DAEMON@xxxxxxxxxxxxx [mailto:MAILER-DAEMON@xxxxxxxxxxxxx]
Sent: Thursday, March 31, 2005 5:06 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Removing unused pad rings on inner layers
DURING design...


OK, so what if you defined the via "pad" to be the hole size. Then
each via you routed to on a certain layer, where you really wanted a
full size "pad", you could add a circular filled shape at the via site.
It's still manual, but a lot less work than messing with multiple via
padstacks. And ... I'm guessing that if you were proficient in skill, a program
could be written to add the little circular shapes wherever a via had a
connection made.


-----Original Message-----
From: David Greig [mailto:david@xxxxxxxxxxxxxx] Sent: Thursday, March 31, 2005 3:08 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Removing unused pad rings on inner layers
DURING design...


Julian

So long as there is a pad defined the size of the drill then the
clearance
will be as if drill to copper. Even works without any pad, or at least
used
to. One trick for no pad power pins is to make sure there is a spacing
rule
for the power, give it the priority over everything else and also give
it
your desired drill to copper.



Best Regards
David Greig
______________________________
GigaDyne Ltd
Buchan House
Carnegie Campus
Dunfermline KY11 8PL
United Kingdom
t: +44 (0)1383 624 975
http://www.gigadyne.co.uk
______________________________


-----Original Message-----
From: MAILER-DAEMON@xxxxxxxxxxxxx [mailto:MAILER-DAEMON@xxxxxxxxxxxxx] Sent: 2005-March-31 20:26
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Removing unused pad rings on inner layers
DURING
design...



David,

So you are saying that the padstack should be using "drill to copper" by
default (no pads); If there is a connection on a particular inner layer,
a
pre defined pad size should be used Instead. I like that.

Thanks,
Julian


-----Original Message-----
From: David Greig [mailto:david@xxxxxxxxxxxxxx]
Sent: Thursday, March 31, 2005 11:14 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Removing unused pad rings on inner layers
DURING
design...

Hi Austin,

There does not seem to be any way of doing this. I too prefer to err
towards
drill to copper clearances rather than have unused pads.
Certainly for power planes under area array devices this significantly
reduces the colander effect, and so long as one is aware of CAF this is
preferable.
Designing without non-functional pads is highly preferable for the very
reason that some 3D solver translators still include them even if the
padstack is optional.
If only normal routing would choose an appropriate padstack in the same
way
as blind/buried. Padstack editor unfortunately does not allow a
blind/buried
definition if both top and bottom pads are defined. There is no easy
workaround.

If Cadence are listening, please remove some of the formal hard coded
rules
and allow drilled vias with selective internal pads to be used in the
same
way as blind/buried.
A drill to copper clearance rule set would also be nice...


Best Regards
David Greig
______________________________
GigaDyne Ltd
Buchan House
Carnegie Campus
Dunfermline KY11 8PL
United Kingdom
t: +44 (0)1383 624 975
http://www.gigadyne.co.uk
______________________________


-----Original Message-----
From: Austin Franklin [mailto:austin@xxxxxxxxxxxx]
Sent: 2005-March-31 18:29
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Removing unused pad rings on inner layers DURING
design...

Hi,

Is there a way to not have inner layer pad rings show up unless a trace
is
connected to it on that specific layer?  I know that the pad rings can
be
removed by the fabricator, but I want to remove them during design to
allow
for more clearance for routing between vias.  How I've handled this in
another tool is to set-up custom padstacks that have pad rings only on
the
two outer layers, and the one internal layer.  It worked fine, but
obviously
required more work when picking vias.

Regards,

Austin


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