'PCB layout techniques- spacing for ground fill'
I am not an expert at making boards. This is a little OT, but it has (2) pics
on the board so hopefully you'll forgive me.
What is the proper distance that should be used to separate ground fill from
other tracks (different nets) and pads also different nets? The minimum track
width for my board is 10 mil.
It looks like the default for Protel is 4mil. (.004 inches) around holes and
.008 mil from other tracks That seems a little tight.
It also seems a little tight to me, but it's a matter of what your board
house will do. I generally do 12 mil lines and 13 mil clearances (on a
25 mil grid).
On Wed, 24 Nov 1999 22:48:46 EST Jon Petty <AOL.COM> writes: Phxsys3
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I'm regularly working with <100um track and gap and up to 6 layers. The
problem lies with whether your PCB mfgr can reliably produce at these
geometries and keep registration - especially of the soldermask. A solder
splash at this level could need a microscope to be seen - unless you watch
for the glow at power-on :-).
Of course I'm speaking of 3-5V power and signal. If your voltages are higher
eg mains, then you'll have to keep you gaps larger to prevent air breakdown
and arcing from occurring.
John Walshe nmrc.ucc.iewalshej
National Microelectronics Research Centre,
Prospect Row, Cork, Ireland.
Direct Line: + 353 21 904082
Switch: + 353 21 903000
Fax: + 353 21 270271
Home page: http://nmrc.ucc.ie/
William K. Borsum
|At 10:48 PM 11/24/99 EST, you wrote:
>I am not an expert at making boards. This is a little OT, but it has (2) pics
>on the board so hopefully you'll forgive me.
>What is the proper distance that should be used to separate ground fill from
>other tracks (different nets) and pads also different nets? The minimum track
>width for my board is 10 mil.
>It looks like the default for Protel is 4mil. (.004 inches) around holes and
>.008 mil from other tracks That seems a little tight.
For reliability, etc., I generally use 15 mil with a minimum(!) of 10 mil
clearances. 15-20 is preferred! It is very hard, but not impossible for a
PCB house to bugger up this spacing. Even a local house that still uses
silk screen technology for the resist can handle them with NO problem.
Also use 55 mil pads with 35 mil holes for most through hole stuff--this
allows one 15 mil track with 15 mil clearance between holes on 100 mil
Remember to specify GETEK or similar hi temperature material for the PCB.
The slight extra cost is more than covered by the ease of handling the
boards--specially if you are hand soldering parts using a hot air pencil.
They just won't blister and delaminate.
William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<dascor.com> & < borsumhttp://www.dascor.com>San Diego, California, USA
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