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April 2015

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Subject:
From:
Wayne Thayer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wayne Thayer <[log in to unmask]>
Date:
Thu, 23 Apr 2015 14:39:36 +0000
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Thanks for the contribution Mathias. Good points. I agree it is best to get
them into the CAD system.

Wayne

-----Original Message-----
From: Matthias Mansfeld [mailto:[log in to unmask]] 
Sent: Thursday, April 23, 2015 10:24 AM
To: TechNet E-Mail Forum; Wayne Thayer
Subject: Re: [TN] Teardrops (Cu trace expansion) on thin traces - needed for
OSP?

On 23 Apr 2015 at 13:51, Wayne Thayer wrote:

[...]
> Most fabricators only ask for permission to put in the teardrops. I 
> haven't used one which required us to put them in. Be careful doing 
> this because sometimes the clearance check misses some problems this 
> can cause (or whoever does this forgets to run the clearance check 
> when they're done. For example, if you pour all around traces and then 
> put in teardrops/snowmen, you'll get a lot of clearance errors/shorts 
> where the extra metal gets added.

And the fabricator can never know net/signal specific spacing requirements
like increased spacings, high voltage spacing class pairs etc. because he
does never know what the board does. He can only assume a mostly
insufficient "basic" clearance >> teardropping by board fabricator is an
absolute no go for most power electronics (frequency inverter, motor control
etc.).

> More sophisticated CAD systems can
> auto-place the teardrops, and that helps with the error checking when 
> done. But I haven't seen a CAD system that inherently supports 
> teardrops. By this I mean that when teardrops get placed, they do it 
> by adding extra traces or pads, which it is then up to you to manage 
> when you start doing the inevitable revisions.

My CAD system can do this and will make automatic/interactive DRC also
against the above mentioned spacing class pairs during routing and before
post process. Any teardropping which is made afterwards from CAM software
with dumb gerber data is in my eyes especially for power electronics
directly from hell.....

Regards
Matthias

--
Matthias Mansfeld Elektronik * Printed Circuit Board Design and Assembly
Neithardtstr. 3, D-85540 Haar, GERMANY
Phone: +49-89-4620 0937, Fax: +49-89-4620 0938
Internet: http://www.mansfeld-elektronik.de
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