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January 2002

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Subject:
From:
"<Peter George Duncan>" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 16 Jan 2002 10:28:33 +0800
Content-Type:
text/plain
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text/plain (200 lines)
Two-sided boards aren't so thick - they don't need to be beyond rigidity
requirements -  and don't have the high internal level of resin that MLB's
do, so the unsupported length of plated barrel is relatively short, and
resin recession doesn't occur so much, if at all.

I agree with the observation that the right angled corners between barrel
and pad are a focus for stress fractures, but if there is differential
movement between pad and barrel to cause this fatigue, how much worse or
how much more quickly would it occur if, say, only top and bottom layer
pads were connected to the barrel? (Rhet.) Fewer points across which to
disperse the load.

Peter Duncan




                    Warren_Crow@I
                    -O.COM               To:     [log in to unmask]
                    Sent by:             cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    TechNet              Aero/ST Group)
                    <[log in to unmask]        Subject:     Re: [TN] Remove unused "dead" pads on
                    ORG>                 internal layers


                    01/16/02
                    12:49 AM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum.";
                    Please
                    respond to
                    Warren_Crow






Actually the cracked vias I have witnessed in the inter barrell tend to
start at
the intersection of the copper planes. A corner or stress riser starts the
crack
during thermal shock tests. Don't understand how the extra non- connected
pads
could help barrell, if so then there is no hope for a 2 sided board.







"Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]> on 01/15/2002
07:40:50 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to
      "Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]>








 To:       [log in to unmask]

 cc:       (bcc: Warren Crow/US/I-O INC)



 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

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Com: (478) 926 - 5224
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-----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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