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How to connect wide net classes with fine pitch parts?

MX21

I'm doing a board design that uses some fine pitch SMD parts.  I have defined 24mil VCC and GND net classes.  This causes problems with routing to the VCC and GND pins on the fine pitch part. 

 

What's the best way to fix it so that I can specify smaller width when connecting to the fine pitch part, but larger width for other portions of the net? 

I'd rather not have to manually change all of the wire widths for those net classes after every autoroute.

 

Thanks,

 

MX21

  • in reply to e14 Contributor

    I was hoping that with version 6 there might be a better way of doing this. 

     

    I had thought about solder bridges.  I've got the SparkFun eagle libraries and noticed they have a normally closed solder bridge, meaning that it is connected by default and you cut the trace to disconnect.  This way, on the prototype I can cut the traces and bring up parts of the board separately, but for quantities I won't have to bridge all of those points.

     

    Thanks

  • On Tue, 21 Feb 2012 19:32:30 +0000, MX21 wrote:

     

    I'm doing a board design that uses some fine pitch SMD parts.  I have

    defined 24mil VCC and GND net classes.  This causes problems with

    routing to the VCC and GND pins on the fine pitch part.

     

    What's the best way to fix it so that I can specify smaller width when

    connecting to the fine pitch part, but larger width for other portions

    of the net? I'd rather not have to manually change all of the wire

    widths for those net classes.

     

    For VCC, I use a solder bridge, with polygon laid over the pads to short

    them out.  Then the net on the "other side" can be fine pitch.  I use a

    few of these scattered around to bring power off of my busses and to the

    actual parts.

     

    For prototyping I leave out the polygon, which lets me power up one

    section of the board at a time, by soldering in the bridge.

     

    For ground, I use thin nets but I pour polygons onto the board after the

    autorouter is done (you can't do this before, because the autorouter

    assumes that the polygon is always connected, even as its cutting it to

    shreds).  If you do this on the top and bottom of a two-layer board, and

    scatter in some vias on the ground net by hand afterwards, you get a

    pretty good "poor man's ground plane".

     

    --

    My liberal friends think I'm a conservative kook.

    My conservative friends think I'm a liberal kook.

    Why am I not happy that they have found common ground?

     

    Tim Wescott, Communications, Control, Circuits & Software

    http://www.wescottdesign.com