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November 2011

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From:
"Smith, Rick" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Smith, Rick
Date:
Mon, 14 Nov 2011 16:23:19 -0500
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Hi Michael,

When board edges are dimensioned from a datum such as a tooling hole you can figure a +-.005" tolerance from datum to board edge. A soldermask dam between the pad edge and board edge will require about another .010 -.015" (fabricator specific). Check with fabricator for actual number.

So assuming the soldermask pad to board edge clearance is .015" (soldermask) plus .005" (edge clearance tolerance) then .020" is your minimum pad to board edge clearance. 

This number can go up or down a few thousandths depending on your fabricators soldermasking abilities so best to check with them for actual numbers. However, this is a reasonably safe number.

Keep in mind the assembly of the component on these pads - component is unlikely to be placed automatically without routed rails built into the panel design. A scored panel would not be desirable and mouse bites should be placed away from any of these minimum clearance pads.

Regards,
Rick

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kuczynski, Michael (H USA)
Sent: Wednesday, November 09, 2011 3:27 PM
To: [log in to unmask]
Subject: [TN] Tolerances for board and pads

While I go thumb thru my spec's, could anyone provide the following:
 
1) what is the REASONABLE tolerance for a PCB outline for a vendor to
hold? (board I'm working on is 10.85mm x 12mm, with a 4.5mm x 3.9 notch
taken out)
 
2) what REASONABLE tolerance can be held for copper pads to the board
edge?
 
thanks in advance
 
SIEMENS 
Michael Kuczynski     Healthcare Diagnostics Inc. 
Product Eng. II CID   511 Benedict Ave. 
914-524-3118 (Ph)     Tarrytown, NY 10591 
914-524-3322 (Fax)    Mail Stop P25-1-C 
[log in to unmask] 

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