[SI-LIST] Re: Flooded Vias vs Thermal Relief
- From: Hal Murray <hmurray@xxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 20 Mar 2010 02:41:34 -0700
> OK, let's start with the low hanging fruit and move up. We certainly don't
> want things to be difficult for you while checking, so leave the thermals on
> for your check and then change them when you are done. The best of both
> worlds right? As you said, it's only a mouse click.
It's much more than just a mouse click. It's also remembering to do that
mouse click at the right time.
Can you put that mouse click in the script/whatever that makes your gerbers?
If you have to do it by hand, do you have a checklist? (and somebody
watching over your shoulder when you run through it)
Otherwise, you are likely to forget when you are in a rush to get a revised
board out with just a quick/simple fix...
---------
> I was just wondering if there were ever signal integrity problems with
> spokes
How close together can you get vias? If your wheels are too close together,
there won't be room enough for the rims of the wheels to get between them.
The tool will trim out any chunks of copper that don't meet the minimum line
widths. Do that enough and you get a hole in your plane.
It should be obvious if you visually inspect the gerbers. (But if it's a big
board, you may not look carefully enough.)
As somebody else suggested, check under BGAs. (and around connectors)
BGAs have a regular pattern. The router may drop in vias on a different
pattern that doesn't work well in dense areas.
Many years ago, back before I even recognized the term SI, I remember a
widely distributed memo from a senior engineer. He had just tracked down a
SI problem. The memo was simple, but strongly worded, good material for
BSing about over lunch.
This was back in the days of DIPs but edge rates were getting interesting.
If you used conservative design rules, ones the board factory liked, the
clearance holes on a row of DIP pins would overlap and turn into a slit in
your planes. The above event involved a signal crossing one of those slits.
I think everybody got the message. I still remember it after 25 years.
--
These are my opinions, not necessarily my employer's. I hate spam.
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