Hi all, I have successfully designed and etched a few simple circuits. Now, on to bigger and more complex boards. Problem is...HOW? Can anyone recommend
any literature on how to design boards, IE, correct placement of parts, how to route traces,etc. Once you get to multiple chips, things start getting confusing.
Thanx for any help.

 

It really depends on the frequencies of the signals. Generally, in some datasheets there are recommendations and reference designs. Check the app notes of the chips you'll be using in the design.

 

Hi all, I have successfully designed and etched a few simple circuits. Now, on to bigger and more complex boards. Problem is...HOW? Can anyone recommend
any literature on how to design boards, IE, correct placement of parts, how to route traces,etc. Once you get to multiple chips, things start getting confusing.
Thanx for any help.

It is an real skill in designing boards. You'll spend countless hours on an until 4am, then you'll sleep for 2 hours wake up and resume. It will consume you

Takes years of practical hands on to become half good with it!

 

Here's something to start you off.

I've used a few good books (well, one that comes to mind anyway) but that was very specific to one design package, and in many cases a certain revision of that package!

While most design packages work in their own way, the general flow is similar:

1) Create schematic: essential as this defines the net list, or what connects to what.

2) Import/Create footprints: basically the footprint of each component, the pads where they sit. Also may include some mechanical details when the part needs a simple mounting hole or some complex non-electrical feature

Note you may need to edit the schmatic symbols to get them to work with the footprint. Example: a TO-3 power transistor has two holes to mount the device which also connect to the Collector. The schematic symbol may need (depends on the software) TWO pins for collector so both collector pads can be wired.

3) PCB creation: board size

4) Package placement: all the footprints get assigned a spot. Most packages will show "air wires" which are the connections between pads so you can make the best placement choices. Example: for an adjacent a resistor and cap pair in parallel the air wires will show you if one or the other part should be spun around.

5) Trace Routing: Usually done in several stages beginning with "critical" traces such as power, sensative signals, kelvin connections, etc. Once the critical lines aere places an auto router may be useful to throw down non-critical connections.

6) Design Rule Check (DRC): Very importaint step where the software checks for mistakes such as pads too close, traces too close, etc.

7) Reality Check: a human process where the output is carefully inspected for anything that may break the design. One example is I will print the board 1:1 on paper, then place the components I will ultimately use to insure the footprints are all correct.

Practive makes perfect, and spending some time just looking at other examples is also useful: it always helps to steal ideas from those who did this before you.

 

ErnieM has some great advice.

In addition to the reality check in ErnieM's step 7, I print out a few 1:1 or larger copies and grab different color highlighters. Then I manually highlight all ground connections with one color; power connections with another color. Then continue with inputs, outputs and processing. I've caught unconnected pins and a ground plane area isolated from ground.

 

And to finish off ErnieM's steps:

8) Make PCBs.

9) Find mistakes and repeat steps 1 to 8 to fix mistakes.

 

I manually draw my boards. I don't like these automated routers.
The boards look neater too. Becomes Like an piece of art.
Gifted enceteric people.

The true genius though would make the net list and make use of all these automated functions.

 

I manually draw my boards. I don't like these automated routers.

Do you use the tape method, or do you draw the traces with a sharpie?
Or did you mean you use PC software but not autorouter, like 99.99% of toadys PCB designers do?

 

Do you use the tape method, or do you draw the traces with a sharpie?
Or did you mean you use PC software but not autorouter, like 99.99% of toadys PCB designers do?

Oh I have background in the now defunct graphic arts industry, so I do know about the tape, red ruby and nt knives operating on an light table.

I did the grave yard shift back in 1997 as an scanner operater. (Scitex 720 robotic scanner worth 250K)
Good money. Easy job. Saved up 10K in 6-months.

 

Do you use the tape method, or do you draw the traces with a sharpie?
Or did you mean you use PC software but not autorouter, like 99.99% of toadys PCB designers do?

There is an auto router? I didnt know this. Is that built into the software?

 

Yes, even Eagle has it. It simply tries to connect all the nets, somtimes with not so horrible results, but most of the time it is only useful for checking the placement of your components, then ripping everything up and doing it manually.

 

The last time I used Rubylith it was amber in color.

The autorouter in Orcad PCB Designer is just wonderful. Very fast and thorough, always fun to watch it in real time. It also has a "gloss" function that makes the traces neater.

In spite of both tools being excellent, the last few traces usually needed to be added by hand. Then I would manually tweak trace routing to make it even "nicer."

And to finish off ErnieM's steps:

8) Make PCBs.

9) Find mistakes and repeat steps 1 to 8 to fix mistakes.

It typically requires between 2 and 3 board spins to get the board production ready. If you achieve a number below 2 then you are truly a wizard.

 

In spite of both tools being excellent, the last few traces usually needed to be added by hand. Then I would manually tweak trace routing to make it even "nicer."

That's the problem I have with autorouters. The last two traces are always the most difficult to route. I can do the easy part and so can the autorouter. Why should the autorouter give me the hard part to do.

I always route manually.

It typically requires between 2 and 3 board spins to get the board production ready. If you achieve a number below 2 then you are truly a wizard.

That's ok then you can call me a wizard.

 

Why should the autorouter give me the hard part to do.

Because you're the smart one.

It's also why humans always win over Skynet.

(I would expect a wizard to know all this stuff.)

 

Well they still have not got an perfect algorithm for chess.
Alpha beta pruning.