Can someone/anyone please send me or direct me to a study that concluded
that removing "a land that is not connected electrically to the conductive
pattern on its layer" decreased reliability in any way? How about a study
that concluded a maintained or increased reliability by keeping or adding
non-functional pads? ...I cannot find anything in the IPC specifications
discouraging the removal of non-functional pads.
From practical fabrication experience, removing a non-functional pad does
provide benefits:
1) It is easier to drill through less copper, causing less wear on the bit,
thereby increasing the potential quality of the hole.
2) Most importantly, removing the pads does not change connectivity but does
reduce/eliminate a real potential to short to adjacent connections.
Other effects:
1) Apparently, removing all non-functional pads within the via reduces the
overall capacitance of the via (see
http://www.qsl.net/wb6tpu/si-list/0687.html).
2) For some non-plated holes, if the pads are left on and it is drilled
after etch, the land/pad may be ripped off of the surface if there is not
enough ring to anchor the pad. This only happens on the outer layers.
3) For some applications, a land may be used to anchor the hole connection
to the material (PTFE, flex)
4) Are there other effects? Thermal, impedance, pth reliability?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Hinners Hans M Civ
WRALC/LUGE
Sent: Tuesday, January 15, 2002 8:41 AM
To: [log in to unmask]
Subject: Re: [TN] Remove unused "dead" pads on internal layers
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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