[PCB_FORUM] Re: mysterious via shifting

Hi Patrick,

You are probably on the trail... I placed the vias in the BGA footprint in 
mm (0.8mm). The shift is likely derived from the rounding to mils in the 
tool which may have occurred when I experimented with the "Fanout By Pick" 
command. I never ran fanout on the BGA, my experiment was on a bypass cap 
for another IC. I also tried to add another decimal point to the database 
but Allegro would only allow 2 for mils.

Oh the woes of unit conversion!

I was curious if anyone else had similar experience... I opted NOT to use 
the "Fanout By Pick" command in the master copy and the 0.8mm BGA is 
holding up so far.

Thanks for the input.




"westfeldt" <westfeldt_nbcd@xxxxxxxxx> 
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[PCB_FORUM] Re: mysterious via shifting






I'm not sure when Allegro decides it has an unconnect, but if you fanned 
out, copying at 31.5 mils, 5 copies gets you a .02mil error.  I don't 
really see how this is the mechanism for your problem, but you do have a 
tiny error in your 31.5mils spacing, should be 31.496.
 
Patrick Westfeldt, Jr. 
720-406-0887 
 

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Ed Caldwell
Sent: Friday, May 19, 2006 6:11 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] mysterious via shifting


Anyone experience a mysterious shifting of vias in Allegro 15.2 s126 
(v15-2-51EU) (12/14/2005) i86... ? 

The design is in mils to 2 decimal places. The vias are in a 0.8 mm BGA 
(spaced at 31.50 mils apart). Somehow the group of vias within the 
rectangle pictured below shifted by 0.10 mils sometime during my edits - 
cause unknown... 



It is important to note that I did not change the database resolution - it 
has remained (mils to two decimal places). The only thing I changed was 
the routing grid which I switched between 25 mils, 5 mils and 0.1 mils as 
I was working in different areas of the layout and I was not working in 
the area where the vias shifted. 

Puzzl_Ed 

Ed Caldwell 
Electronic Design Services, LLC 
Canton, GA - USA

JPEG image

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