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
OpenPGP: http://www.mansfeld-elektronik.de/gnupgkey/mansfeld.asc
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