Pete,
I'd have to disagree. I think Daan's board barely meets Level C
(reduced producibility) standards according to IPC-2221, Section 9.0.
Daan requires a 0.3mm (12 mil) diameter finished hole. Add to that
** at least ** 0.2mm (8 mils) of fabrication allowance. That leaves
0.1mm (4 mils) left - that's 0.05mm (2 mils) of clearance between
the barrel and the surrounding copper that needs to be etched in a
production environment. That would be very tough to do under highly
controlled experimental conditions!
In my humble opinion, that board was bound from the start to be a
problem once it got to production.
Michael Hiteshew
Lockheed Martin NE&SS Marine Systems
410-682-1259
-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: Sunday, July 29, 2001 8:50 PM
To: [log in to unmask]
Subject: Re: [TN] Clearance area around holes
Daan,
The sizes you quote are not especially small, nor is the difference between
them. I'm not totally clear from your description what you are meaning,
but, (converting to my old-fashioned language), do you have 12 mil diameter
holes going through 24 mils diameter exclusion zones in the copper planes?
Unless your Fab House's registration accuracy is very bad, you will have a
nominal 6 mils all-round clearance and in practice, shouldn't have less
than 3 to 4 mils clearance. Is this OK electrically if your small
clearances are, for example, at layers with high power? It should not be a
difficult job for a decent Fab House to make this board for you, though.
Pete Duncan
----------------------------------------------------------------------------
---
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
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
