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July 2001

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From:
"Busko, Wolfgang" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 27 Jul 2001 11:51:44 +0200
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Hi Daan,

just looked at our data. We use openings with 1.27 (50mil) diameter for
0,3mm finished hole size vias. The boards are 233mmx 160mm. Sounds a bit
large ? I thought that we aimed at 1-1,1mm. But thatīs our newest design I
opened.

The explanation from our CAD guys is that this has been checked with our
favorite boardhouses to meet their tolerance specs and to be on the safe
side of life.
This is not based on any IPC or other document, just our practice to prevent
problems. 
I canīt tell you wich diameter will do with no problems but usually the
boardhouse is gonna give us a call if something within our data calls for
problems and ask if they are allowed to change it to meet their
requirements.
For new jobs we usually intergrate those new dimensions in our CAD if there
is no problem with other technical requirements.
Your spacing doesnīt allow for much tolerance and you have to consider that
you have to drill a bit larger to get 0,3mm finished diameter.
If your boardhouse didnīt give you a call although they expected trouble I
would place their name on a different supplier list.

Best to you 
Wolfgang

  

-----Ursprüngliche Nachricht-----
Von: d. terstegge [mailto:[log in to unmask]]
Gesendet am: Freitag, 27. Juli 2001 10:37
An: [log in to unmask]
Betreff: [TN] Clearance area around holes

Hi Technet,

Here's a question for the bare board experts out there:

One of our pcb-suppliers had rejects on a complete batch of our boards
because the clearance between the via's and the surrounding copperplane was
so small that it resulted in short circuits.
The holes were designed 0.3 mm (finished hole size) and the openings in the
copperplane were 0.6 mm, leaving only a small clearance area. The board
measures about 20*15 cm.
What do you think, is a board like this manufacturable for a decent board
shop, or is it really that difficult?  Could you give me a typical value for
the minimum clearance around the finished-hole that board vendors need ?   

Best regards,

Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

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