PCB Design

I've found "Printed Circuit Board Design Techniques for EMC Compliance" and the other book by Mark Montose to be very helpful. I am a pretty inexperienced EE who doesn't have a mentor to work with. These two books have taught me a great deal. Don't worry about the EMC part, they are a great references for general PCB concerns.

DON'T SPLIT THE GROUND PLANES!

John

The target audience is threefold, roughly in order of decreasing priority:

- EEs starting out in PCB design right out of school, with no prior knowledge

- Hobbyists advanced enough to be making PCBs, rather than just proto-boards. (I figure with the growing availability of cheap and fast ICs, there's some hobbyists who need to know good practices)

- people who make simple, slow circuit, noise not an issue, PCBs for a living, but perhaps want to move to doing some digital stuff, high speed stuff, low noise stuff...

Keep the ideas coming

Thanks,

Chris

What is the target audience?

Best regards, Spehro Pefhany

oops. sorry.

John

They're basically text books, in that realm $100/book isn't unusual. Most eng students budget $500/term or more for books. Perhaps we are being gouged, but it's not like these are bestsellers, so it might just be a supply/demand thing.

Chris

Because you're using cheap software and cheap board houses? Much PCB design software still has a 4 digit price tag, and I imagine that there's some that's still 5. Similarly, go get some price quotes for 8 or 12 layer boards and then start complaining about book prices...

Seriously, if you can't afford books, there is plenty of free PCB layout information available on the Internet. Nevertheless, there are books that are easily worth more than the asking price in that they can save you a lot more time than that many hour's wages would pay...

Why is it that PCB design books cost more than the design software and your first 3 orders from a PCB house combined? All of them are $90+

Midrange price for technical books. But design software often costs many thousands.

Best regards, Spehro Pefhany

Hello John,

Psssst. Don't spill the beans. After all, the more people adhere to split grounds the more work there will be for people like us ;-)

Regards, Joerg

I read in sci.electronics.design that martin griffith wrote (in ) about 'PCB Design', on Tue, 12 Apr 2005:

This does look paradoxical, but that is because both statements are

1. Keep 'ground' as low impedance as possible. Everywhere;

2. Keep analogue currents out of digital areas of the board, and keep digital currents out of analogue areas.

Statement 1 leads to 'Don't split the ground plane.'

Statement 2 requires you to LOOK where currents are going to flow, and remember they flow IN LOOPS on the board. I was going to try to show in ASCII art what that implies, but it's too difficult.

Imagine that you have the device in the centre of a square board. with the Aground pin towards the 'west' and the Dground pin towards the east. They are connected together, but around the device is a continuous ground plane. Then ALL digital currents must flow substantially westwards to the Dground, and all analogue currents must flow substantially eastwards to the Aground.

Keep the sectors roughly from NW to NE and SW to SE for power management and other stuff that isn't sensitive signals. If you get it right, there should be very little analogue or digital current flowing in the strip of ground plane perpendicular to the bridge between the Aground and Dground pins.

But there may well be a lot of 'trash' current there, which would cause mischief elsewhere if you split the ground plane along the length of that strip.

slightly OT, look at the many data sheets of ADC's and DAC's and they ALL specify having seperate Digital and Analog grounds joined at one point only.

Every time this topic is brought up here, All the SED gurus say "DONT SPLIT THE GOUND PLANES"

martin

"Wales is a big welsh-shaped rain collection device"

Hello Chris,

That's the point. They might sell a few thousand total, if that. So it can't be produced at the same cost as an Agatha Christie thriller in paperback.

Regards, Joerg

Hello Chris,

I'd do a hands-on seminar instead, no dry teaching from the pulpit. Get a cheap but good CAD program such as Eagle. That has schematic and layout nicely integrated and there are freeware and educational versions.

Then show the audience the actual work, explaining what you do and why. Of course, the auditorium needs to be equipped with a good projector (and a spare bulb...) and ideally with WLAN so the students can also follow on their own laptops.

Regards, Joerg

look at the El Cheapo 5 day PCB merchants, Olimex, ExpressPCB etc, it might give you a different angle, Like "what you can get for 25 ? $ £" options

martin

"Wales is a big welsh-shaped rain collection device"

I'm not claiming to make anyone an experienced designer here. This is going to be a small, free, seminar offered by a non-profit group to local EEs. The first thing out of my mouth is probably something along the lines of "This does not qualify you to design anything, for that you need experience, but it does cover the basic issues so you can keep them in mind."

So if you were going to "educate them properly" what topics would you go over? Hands on may be difficult given our resources, but I can still include plenty of worked examples of good vs bad practices and why things are done one way or the other.

Chris

So here I am, stuck trying to organize a mini-course on eye surgery for those with no prior experience.

Can anyone give some advice on what can go into a 3-4h session on the basics of operating on the human eye? The format will be primarily lecture as we don't have the resources (or the time) to do anything with actual eyeballs.

(In other words, either take the time to educate them properly, or don't educate them at all and hire someone who is already educated. The world already has quite enough marginals layouts already without you making people think they can do a layout after a four hour lecture.)

BTW, don't split ground planes. :)

Get pre-sensitized board stock, watch your exposure time and light source (I used sunlight the time I did one) and watch your etch times and etchant concentration, and agitate.

You can drill before or after etching, and you can simulate plated- through holes with a piece of #30 wire. If you absolutely need real plated-through holes, send it out.

If you do double-sided, be sure to give yourself register marks OFF the main board real estate. I laid a little board out decades ago, by hand with tape and peel-off stickers and an X-acto knife and all that crap, at 2X, and had the print shop print it 6-up while maintaining registration,for a surprisingly reasonable amount of money.

For huge ground/power planes, consider using some kind of lattice, and don't forget the thermal relief!

Good Luck! Rich

Confucius say: Woman who fly upside-down....