PCB Layout Designers

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In many cases you just *have* to autoroute some parts of a board. On very complex and dense boards with hundreds or thousands of I/O it can be simply too time consuming to route manually, especially the non- critical traces. And with todays shrinking design cycle times, you can't waste time with lots of manual routing. Autorouting can be an essential and very powerful tool in the hands of someone who knows how to use it selectively.

Dave.

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We generally overwrite the linked datasheet with the latest revision. However if there is a reason to keep multiple datasheets then we can add as many linked documents to a part as we want, labeled appropriately (datasheet-Rev1.pdf etc ). This includes app notes too.

Yes, we do that, and we can also have a selection of footprints for the same device and have it associated with a different ordered part.

It's fantastic having a built up library of components all with linked datasheets, app notes, multiple footprints, purchasing info etc, makes future designs real easy. What's more, basic parametric info is also included with each part, so you can often select a suitable device from the library without even having to view the linked datasheet, and you can sort lists of components by any parameter to make it even easier.

Dave.

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Autorouters don't have strategies, like people can, so start at a huge disadvantage. They often make such a mess of a board that it takes more time to clean it up than it would have taken to do it manually. Not to mention the unbearable ugliness most autorouters create.

We do usually force sensible package sharing at schematic entry (proper halves of a dual opamp, say) when that makes sense. We usually have a rough channel placement or whatever in mind. If we have, say, a bus connector that goes to a 16-pin bus transceiver, we will assign the pins that we know will line up nicely. This is *not* throw-the-schematic-over-the-wall methodology. We'll sometimes meet and plan a layout strategy, and sometimes change the design if it looks like that will help.

If my layout guy has a real problem, he can come to us and we can alter the schematic to help. But on a multilayer board, you don't have the crossover dilemmas that you have on a 2-sided board, so pin/gate swapping isn't as crucial.

John

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How do you handle data sheet revisions? Some, particularly semiconductors, tend to have a number during the life of the part. Do you attach multiple datasheets if there are multiple vendors?

Best regards, Spehro Pefhany

What's a connectivity check? I guess it's checking that all power pins are connected, that there are more than one pins on one net, that no two outputs share the same net, that a net not only has inputs on it, no open inputs... that sort of thing? It's called "electrical rule check" in my CAD.

What's a "ref designator"? The "name" of the Part, such as U22, R4?

Ugh. Who does, anyway?

robert

It's a full check of the pcb connections against the schematic netlist. That's a little more extensive than what you describe.

The "R4" is what we call a "reference designator". Each part can have other attributes, like

type = RES/0805 value = 10K HTI# = 17213 (our stock number) decal = 0805

I guess some people do. Hell, routing is too important to be left to a machine.

John

Ah I see. I was unaware of that because what I use (cheap EAGLE) does it implicitly.

Especially if you're as anal about the aesthetics of the result as I am (and from what I've heard you say, you too).

robert

I even care about the colour of say thru-hole "folien" caps, sometimes you have a choice. Its almost sick when you're prepared to pay a tiny bit more to have the better looking colour, than again some customers do appreciate that :)

SioL

We sell VME boards, where all the parts are in plain sight... no enclosure. So we care a lot about the beauty of the board: colors, placement, lettering, trace flow. It's art.

John

There's true beauty in a nicely laid-out board. I guess that makes us certified geeks.

SioL

messagenews: snipped-for-privacy@kir.physnet.uni-hamburg.de...

have

If for aesthetics or some other reason you want to hide the trackwork then black solder mask is the way to go. Looks more like a finished product than a bare PCB. Very nice when combined with copious amounts of gold flash.

Dave.

Absolutely. I often do mechanical design as well, and the same rules apply. Even when the device in question is eventually buried in some vacuum chamber and (ideally) never sees the light of day again. I think things that look s***ty can't work well: Good looks don't necessarily imply high functionality, but if something turns out to be crap after all -- well, at least it looks good. As long as you never compromise functionality for beauty, I've found this to be a good design strategy. And the mech workshop loves you if you turn in beautiful drawings for beautiful things.

For my latest electronic gadget, see

Part density is very low, but there's an equal amount of stuff (power supplies, 4000B series control logic, relays) on the bottom. Piggy- backed and missing components betray the prototypiness of the thing, as do the almost-non-overlapping mounting screws.

The front panel is CNC milled from red anodized aluminium:

Note the holes for accessing the recessed M5 mounting screws which firmly bolt the device on a UHV flange. The "4mm hex" designation is pretty tacky and cost me a couple Euros extra, but without it the holes had an unmotivated look to them that I didn't like.

--Daniel

AND its much harder to copy your design. Just one of the things that puts the thieves off.

SioL

And depending what you have previously done (like autorouting a class of signals with some impedance restrictions and accordeons generation) will forgot or not to number the ground connections on planes. Which omission will be kept till finishing the board... Pads (2005) is as buggy as any other CAD, maybe you are lucky ?

I'm wandering how you're routing 1000 components (saying you have at least two 1200 balls BGA's on board and every of them with 300 filtering capacitors) and 10-14 layers without autorouting ?

thx, Vasile

What in Johns post gave you the idea of 1200 ball BGAs or 10-14 PCB layers?

robert

Never seen that happen. Every connection on every board is what the schematic says. When we screw up, it's a genuine design error or occasionally an incorrect pinout, plainly visible on the schematic.

We don't prototype; we lay out a board, formally release it as rev A, and have manufacturing build a couple of units to test. Most of the time, we can sell the rev A.

We're using Pads PowerPCB V5, which appears to have no bugs and doesn't crash. Software this good could make a guy stop hating Windows. When Mentor bought PADS and started migrating users, we dropped off the support bandwagon.

As I mentioned, it's an 8-layer board. On this particular board, there are two fpga's and one uP, but no bga's.

See pic in abse.

John

Oops, sorry, that one is 6 layers. We've recently done bga's in six, too.

John

Hi

Don't suppose you have some kind of link to this do you?

Tried a search around the web, found several references, but all seem to be related to something called wcalc.

Tom