Methinks it's an Old Husband's tale, unless your pcb vendor in question
produces uncured boards. If the unused pads are free to move about, so is
everything else (though perhaps a little less freely if they're anchored to
other features).
I can understand the argument when it comes to drilling holes. The extra
copper might well hasten the degradation of a drill's sharpness, and blunt
drills cause copper smear which could connect one layer to another layer
when you don't want it to. "If the pads ain't there to start with, there
ain't nought to smear." BUT I think that's penny-pinching by the fab houses
and not in the best interest of boards, particularly class 3 boards, where
the extra support offered by the unused pads is valuable. If nice sharp
drills are used, at the right speed and feed, you should get nice clean
holes, no?
Rgds
Peter
"Roger M. Stoops"
<rstoops@SPECTRAPRECISI To: [log in to unmask]
ONDAY.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: TechNet Aero/ST Group)
<[log in to unmask]> Subject: Re: [TN] Remove unused "dead" pads on
internal layers
01/17/02 03:10 AM
Please respond to
"TechNet E-Mail
Forum."; Please respond
to rstoops
I have been following this thread with interest. When I asked a pcb vendor
about having non-functional pads in the inner layers, they said it was not
a good idea, that the unattached pads/lands would move around, or "float,"
and cause potential mfg problems, such as shorts to other copper.
Question: Is there any truth to this statement, or is this just an old
husband's tale?
TIA,
Roger M. Stoops, C.I.D., PCB Designer
[log in to unmask]
Trimble
Engineering and Construction Division
5475 Kellenburger Rd.
Dayton, OH 45424-1099 USA
Ph: +01 937.233.8921 or +01 937.233.4574 ext 288
Fax: +01 937.233.7511
"<Peter
George To: [log in to unmask]
Duncan>" cc:
Sent by: Subject: Re: [TN] Remove
unused "dead" pads on internal layers
TechNet
<[log in to unmask]
ORG>
01/15/02
09:09 PM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
peter.duncan
Hi,
Actually these "unused" pads are replicates of the hole "rules" created for
the surface layers. Most routing packages, or routers, seem to do this by
default for each layer to save manual replication where traces, etc are to
be connected. (At least PADS, Alegro and Mentor do). On the grounds that
it's always easier to destroy than to build, it's easier to delete pad data
than to create it, so it's put in by default as there's a good chance it
will be needed.
I still say you should consider hole barrel strength/support issues before
just deleting them - e.g. they can constrain the "resin recession" and hole
wall pull-away that have been recent threads on this forum. Think of the
"unused" pads as 'wall ties' holding the copper at frequent intervals to
the hole wall. Copper bulging or pull-away in the event of recession or
whatever is reduced.
Peter Duncan
Hinners Hans M Civ
WRALC/LUGE To: [log in to unmask]
<Hans.Hinners@ROBI cc: (bcc: DUNCAN
Peter/Asst Prin Engr/ST
NS.AF.MIL> Aero/ST Group)
Sent by: TechNet Subject: Re: [TN] Remove
unused "dead" pads on
<[log in to unmask]> internal layers
01/15/02 09:40 PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to Hinners
Hans M Civ
WRALC/LUGE
Hi Patrick,
As others have said, I don't think the class of board matters for "unused"
pads. It all depends on what your procurement documentation states, are
you
building to drawing or is there a clause that says process improvements
that
do not affect functionality are permissible.
"Are they really unused pads?"
They may be electrically nonfunctioning but they are there for a reason -
better lamination quality (avoiding low pressure areas or excessive prepreg
flow), better hole wall quality, better plating quality (esp. for any
isolated traces), reduced loading of your etch solution or better thermal
loading during assembly.
Hans
Integrity First - Service Before Self - Excellence in All We Do
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
226 Cochran Street
Robins AFB GA 31098-1622
mailto:[log in to unmask]
Com: (478) 926 - 5224
Fax: (478) 926 - 4911
DSN Prefix: 468
-----Original Message-----
From: Patrick Lam [mailto:[log in to unmask]]
Sent: Friday, January 11, 2002 5:12 PM
To: [log in to unmask]
Subject: [TN] Remove unused "dead" pads on internal layers
Hi TechNetters,
For class 3 boards, is it acceptable to have unused pads removed on
interanal
layers.
Thanks,
Pat
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