Caveats for Multi Layer Boards?

Profile available? Make a daughter card and pin hole row to attach it with. Or use a std SIMM socket or the like as your connection mode. Or make a parallel attached daughtercard that stands over the board on pegs.

Then, all you have to adjust are node locations and add vias, etc to accept the interconnections. Shove everything over and route to an edge and use a ribbon flat cable.

1. Layers are expensive.

1. I can't say for sure, but two ground planes are usually unnecessary, and often worse.

2. Inner-layer traces are a fact of life nowadays. Check your design and layout carefully before you order boards. Have somebody else check it, too.

1. Lately we use copper pours for ground and power, not planes. The difference is that you can route traces inside or around or between pours, but you can't on planes. That can be useful, used carefully.

John

(!!) Why two ground planes? If you need separate grounds, can't you *split* the ground plane (use a pour)?

What sort of design is it (analog, digital, power)? How "fast" (or "clean")? etc. What packaging technology(ies)?

I much prefer cutting down layers at the expense of moving signal layers to internal layers -- just don't make any mistakes! :>

(you can always turn the crank one more time to fix those screwups)

If you can squeeze back *down* to 4 layers, go for it. Above *6*? Costs go up really quick. Consider enlarging the board (if possible) instead of making it "thicker".

Good Luck!

Unless you have worked out how to embed chips inside the board, even buried traces are accessible to the "exacto knife" at both ends. You may have to bend up the relevant lead on the package tp break the connection to the buried trace, but it's always do-able, though often not that easy.

And I've certainly worked with circuits where it was a very good idea to have a ground plane - or a least a ground or power pour - directly under traces carrying fast signals, and on both sides of buried traces. Extra layers do cost money, but so do the logic chips that are fast enough to need them, and providing a sub-optimal electromagnetic environemnt can throw away the money you spent on the faster chips in the first place.

-- Bill Sloman, Nijmegen

I was able to get the last couple traces to route without adding a signal layer. Regarding the ground planes what I meant to say is there is a copper pour for ground that is divided by into two areas one for analog and one for digital as opposes to two actual ground planes.

Thanks much to all who contributed to my post.

Best, Ed Vogel