Two reasons:

1.  Mother boards commonly have 5 or more tooling holes because there
are multiple sockets on the board.  Pushing a daughter card into the
sockets causes a substantial amount of deflection if the area around the
socket is not supported.

2.  A router bit develops a substantial "push" on a board mounted on a
tooling plate.  Adding more tooling holes increases the resistance of
the board to movement from the forces imparted by the router bit; which
allows better accuracy with the final finished dimension.  Of course,
this trick can only gain a small amount of tolerance.

As you already know, from a practical standpoint, 2 tooling holes is
generally sufficient for depanel (assuming reasonable tolerances).

Regards,
Ryan Grant

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Smith, Richard
Sent: Friday, February 02, 2007 8:54 AM
To: [log in to unmask]
Subject: [TN] Tooling Hole Quantity

Folks,
 
Can you think of any (legitimate) reasons why more than 3 tooling holes
would be necessary on a PWB? 
 
Thanks Much!
 
Rick
 

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