[PCB_FORUM] Re: How-to? [Impedance]

Hi William,
 
Add an area constraint around the bga and set the width to the size you need.
 
Here's an example:
Area constraint = Net_Physical_Constraint = BGA_AREA
Create new Net_Physical_Constraint = 5_mil_width
 
Then under the assignment table set no_type in the BGA_AREA to 5_mil_width 
constraint.
 
When you route into the bga it will automatically change to 5 mils then change 
back
to 5.68 when you exit the bga area. Assuming you have the default width set to 
5.68 for
the 50 ohm nets.
 
Regards,
Stephen Feehan
Siemens Network Convergence
 
 
________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of William Billereau
Sent: Thursday, July 27, 2006 1:19 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] How-to? [Impedance]


Hello All.
 
We are actually fighting with impedances!
all:all:50 ohm:5%
 
Allegro routes with an autocalculated line width of 5.68mils.
This is not possible to route inside the BGA which has an area with minimum 
line width set to 5 mils.
small lenght routed with 5mils have impedance DRCs.
 
I try to route them without the area using neck mode. The neck mode off the 
line is still 5mils. It does not switch again to 5.68mils...
but it is not even a solution because the neck has also DRCs.. grrrrr.
 
How do you generally proceed in such cases?
 
Thanks in advance!
 
    William.
 
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