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July 2000

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Subject:
From:
Glynn Shaw <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 10 Jul 2000 08:28:58 -0700
Content-Type:
text/plain
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text/plain (68 lines)
Good morning Ken.

IPC authorizes tear dropping on innerlayers, so we do it automatically on
all inners, with or without a specific design note, providing there is a
note mentioning compliance with IPC...
Tear dropping inners is always better, it hurts nothing from a design
perspective and improves manufacturability. Inners move and shift and
shrink during lamination, so teardrops prevent substandard connections if
the movement is in the direction of the trace feeding the innerlayer pad.
Outers is another story. Since the outer is visible, changes we make would
alter cosmetics. We do not tear drop outers unless specifically authorized
by the customer. Outer layer registration stays where you put it so if you
do a good job of registering the image, for most holes and pad sizes, it
shouldn't be necessary to increase clearances to meet minimum annular ring
requirements. However, drill sizes keep getting smaller and smaller. When
small drills hit a glass bundle, they may be diverted from their vertical
path through the board and exit the bottom of the board in a slightly
different and random direction from where they entered the board.  The
result is nice registration on one side of the board and random
misregistration on the other side of the board. This phenomenon is called
"drill wander". Tear drops will improve reliability on the small holes in
this case.



At 05:14 PM 7/7/00 -0700, you wrote:
>Is tear drop always better? Should I add as a fab note to add tear drop for
>inner and outer layer as and when needed by fab house? or have my design guy
>add it for them?
>
>Any comments will be highly appreciated.
>
>re,
>ken patel
>______________________________________________________
>Ken Patel                       Phone:  (408) 490-6804
>1708 McCarthy Blvd.             Fax:    (408) 490-6859
>Milpitas, CA 95035
>
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