PCB *style* question

[Paul Perry (Frostwave)]

www.waldherr.com
this is the only pcb prog that was simple enough for me!
(it isn't the one I use for my commercial work, but I have an engineer do that).

[ErikMiller]

Chapter 17 (Circuit Board Layout Techniques) of Opamps For Everyone might also be worth a read...

Oh yes. Starting with 17.4.4 "Unexpected PCB Passive Components."

He lays it all down, so to speak.

Good scientific explanations for practices that I've learned empirically.

[R.G.]

What drives me nuts is the two different methods in laying out pcb pads for off-board connections. Some commercial and DIY pcb's have pads on the pcb for almost all the off board connections: all pots and their lugs, and jack tips, for example. Other commercial and DIY pcb's have the minimum number of pads, and you jumper to most of the off board components. Obviously, a pad per connection eats up a lot of board space. especially since most of the pads are usually on one end of the board.

But is one quieter or more efficient than the other? It be nice if there was a simple tutorial on the layout of that alone.

Simple tutorial on that alone
Neither is particularly quieter or more efficient. In "PCB Layout for Musical Effects" I point out that the PCB is really a substitute for hand wiring; any wires that can be put on the board have no chance to be mis-wired. I also introduce the "cost basis" for each design decision. There's a cost of everything you do on a PCB. Deciding to put all the wiring to external controls and such saves you PCB complexity and gives you a (marginally) smaller board but it costs you more every time you assemble a finished product. Putting every possible thing on the PCB costs you some board space and some comlexity, but it saves you time spent cutting and stripping wires and making wiring mistakes every time you make one. So you have to make a decision - save time and PCB space once when doing layout, but pay time and errors when assembling, or spend time and PCB layout once when doing layout, but save time and errors when assembling. The tradeoff is pretty clear if you're making zillions - spend the time and effort once. I deliberately force the PCB to absorb the controls wiring complexity in all my layouts to save the user time and errors in building. Other people may not value assembly time as much as I do.

As for trace width/style. The two styles are "minimum etch" and "minimum copper". Minimum etch is how most boards used to be made in the 1958-1964 era. The great problem with it is thermal wicking - it's hard to get the pad area hot enough to solder right, and that exacerbates any soldering skill problems that beginners might have. It also encourages beginners to get out a huge and hot gun and melt the traces off the board. Hand soldering minimum etch boards is hell.

Minimum copper is much easier to solder for beginners if the traces are not too small. I use 25 mil traces for all the signal traces and for power/ground in effects. In larger power users, you should go to 35 or 50 mil traces for power/ground.

My personal thinking is that mimimum copper is a bad idea. I hate working on boards that use this in spite of being very familiar with it.

Bigger pads and traces are more resistant to lifting. For all transistor/RC circuits, you can use big pads, like 085-100 or so for all the pads. However, this severely limits the number of traces that can run under one resistor or cap between the pads. If you have IC's on the board, you automatically bought 100mil spacing with 060-070 mil spacing for the pads, so you might as well go with that for all parts.

My personal defaults, tested by beginners like the people here for almost a decade now are 070 pads, 025 to 030 traces. Off-board pads are 100 to 120.

By the way, a lot of this gets touched in "PCB Layout for Musical Effects".

[RDV]

I've been getting mini-boards for a few years now and a love them.

Are you talking about double sided pad per hole perf, or those surfboard things for the surface mount stuff?

Regards

RDV

[Fret Wire]

Thanks for the detailed explanation RG. I think it's time to check out your book.

[Peter Snowberg]

I've been getting mini-boards for a few years now and a love them.

Are you talking about double sided pad per hole perf, or those surfboard things for the surface mount stuff?

Regards

RDV

Check out http://www.expresspcb.com/ExpressPCBHtm/SpecsMiniboard.htm

You get 3 double sided boards with plated throughs for $67 in California (incl. tax).

For me, it's more than worth it because the quality of a real PCB is head and shoulders above a home etch and you don't get plated throughs with a home etch or the ability to use feature sizes of .007"

Take care,
-Peter

[Paul Perry (Frostwave)]

Minimum etch is how most boards used to be made in the 1958-1964 era. The great problem with it is thermal wicking - it's hard to get the pad area hot enough to solder right, and that exacerbates any soldering skill problems that beginners might have.

One way around this 'heatsinking' effect is to have a little clear circle around the outside edge of the pad, with small traces across the circle (like a crosshair target circle).

[R.G.]

... one way around the heatsinking...

Yep, that works, and is standard practice for ground plane-style boards.

I shy away from that for all my simple boards for public consumption because in a world of beginners who have trouble with what a pad is and how big to make holes, putting an inverse ring around a pad is a big hump to get over. It works, it's for the technically advanced.