*******************************************************
Todays forums are sponsored by Ian Martin Limited
Engineering/Technical Placement Specialists
www.ianmartin.com
*******************************************************


Jeff,

I agree with everything John states below.  It is well written and good advice.
Also consider the smallest drill to board thickness, a.k.a. aspect ratio, that will 
change the price of building your design at the board house.  A related issue is the 
count of different sized holes made by your design.

Cheers!
Drew


----- Original Message ----- 
From: "John Haddy" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Wednesday, October 03, 2001 5:01 PM
Subject: Re: [PEDA] Annular Ring question, via question


> Jeff:
> 
> First step for a question like this should be your board house. They
> should be able to tell you right off the bat whether there will be
> any impact on their yield (read: cost to you) with the lower annular
> ring.
> 
> Another alternative would be to drop your trace widths and clearances.
> 9/9 is very generous - most board shops will do at least 8/8 with no
> cost penalty, while 6/6 is also not unusual for high performance shops
> without yields suffering (bleeding edge at 4/4 and below is another
> story...).
> 
> As an example, one of my local (ordinary quality) board shops has a standard
> set of design rules (i.e. high yield expectations) that include:
> 0.15mm (0.006") track width
> 0.15mm (0.006") tack spacing
> 0.25mm (0.010") annular ring
> 
> With this shop, I regularly do 0.175mm (0.007") annular rings (by mutual
> agreement), and with a consequent yield impact (i.e. I'm happy to pay
> the extra cost).
> 
> If you do drop your annular ring below the board shop's accepted standard,
> then you should restrict the use of these pads/vias to only the locations
> necessary. The more instances of "exceptions to rules" that exist on the
> board, the higher statistical probability of a board failing in mfr.
> 
> Remember that the principal reason for min. annular ring specifications
> is to guard against drill breakout. There are alternative design techniques
> that can allow you to shrink the annular ring, by allowing controlled
> breakouts (usually on interior layers) without sacrificing board
> performance. For example, teardropping to a pad provides a guard against
> breakout on the side of the connection. (If you use this or other
> techniques you'll need to give your board shop explicit permission to
> allow breakouts)
> 
> Hope this helps,
> 
> John Haddy
> 
> 
> > -----Original Message-----
> > From: Jeff Adolphs [mailto:[EMAIL PROTECTED]]
> > Sent: Thursday, 4 October 2001 6:15 AM
> > To: Protel EDA Forum (E-mail)
> > Subject: [PEDA] Annular Ring question, via question
> >
> >
> > Cheers Protel Group!
> > 1. Since I am using a small via to make routing SMT easier. Small via
> > having a 10 mil dia. annular ring (pad of 31_21). Am I free to reduce
> > the annular ring on other parts without any harm. Specificly, reducing a
> > Pad of 75 with a drill of 43, to a Pad of 61 with a drill of 43? A pad
> > of 61_43 would make a connector much easier to route.
> > Board info:  So far I'm trying to keep the PCB at space 9 mil minimum,
> > trace of 9 mil minimum.
> >
> > 2. Will I save money by using a Via of 31_21 only when necessary and
> > using a Via of 50_28 everywhere else.
> >
> > Thanks in advance!
> > Jeff Adolphs
> > Lake Shore Cryotronics, Inc
> > Westerville, Ohio, USA
> >
> 

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to