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March 2003

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Subject:
From:
Phil Nutting <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 31 Mar 2003 12:22:00 -0500
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Peter,

To the best of my knowledge all boards designed by our CAD group use the same "standards" and in this case 0.015 is the spacing.

The problems only show up on this one engineers boards and it doesn't seem to matter what the board layout or circuit application is.

The Fab house is always the same.

Sigh!

Thanks, Phil

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, March 27, 2003 6:52 PM
To: TechNet E-Mail Forum.; Phil Nutting
Cc: [log in to unmask]
Subject: Re: [TN] PTH clearance between pad and gnd plane



Hi, Phil,

OUr (CLass 3) boards were designed using IPC-2222 guidelines and our
pad-to-copper fill area clearance is 0.015". So far we have not experienced
any shorts with this clearance, so you should be OK.

Do your shorts occur in the same places each time? Is the problem with one
product from this engineer of yours or a number of them? Are the problems
on every board of the type or just some? Are there any features in his
design that don't appear in other designs because design rules haven't been
followed - e.g. specified registration tolerances, drill positional
tolerances, hole:pad diameter ratios, etc.

Sounds like you may have either or both of two things - over-tight
tolerances from your designer, or poor process control from your fab house.
Do you use the same fab house for all your products?

I had something of an issue with our technical director a couple of years
ago when I received a number of "comments" from our fab houses that our
tolerances were very tight. I discovered that the r.m.s. manufacturing
tolerance allowance had not been included in the pad:hole diameter ratio,
making it virtually impossible for the fabs to achieve my annular ring
requirements. Director's excuse was that as they didn't know what tolerance
any given fab house could work to, they didn't specify one at all in the
mistaken belief that they were doing the right thing. Maybe you have a
similar sort of a problem?

Good luck
Peter



Phil Nutting <[log in to unmask]> 27/03/2003 10:38 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Phil Nutting
                                                                                                                              
              To:  [log in to unmask]                                                                                            
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)                                                        
              Subject: [TN] PTH clearance between pad and gnd plane                                                           
                                                                                                                              
                                                                                                                              
                                                                                                                              





Good morning,

We sometimes have a problem with PTH leads shorting to the ground plane.
The curious thing is we use the same design and assembly methods for all
our boards, but the problems only show up on one engineer's product.

What is the "recommended" clearance between a pad and the adjacent ground
plane?  Ours look to be 0.015".

TIA

Phil Nutting

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