technical pcb question - reason older board don't use square edge traces?

[ulysses]

hey guys

when you look at older boards like the phase 90 etc they dont have any square edges in the traces.

it looks like they have gone to an effort to make all traces rounded - and look "artsy"

is there a technical reason for this? do rounded edges etch better? do they offer better conductivity?

cheers
ulysses

[Meanderthal]

 They were hand drawn in those days... they had no reason to make them square.

[Hiwatt25]

Angular layouts look so much tidier. 

[grapefruit]

It doesn't generally matter for audio stuff, but by not using right angle bends you can reduce the EMF emissions. For all my CAD PCB designs I use 45 degree corners as a matter of course. It looks a lot nicer than right angles too.

Stew.

[darron]

i do my layout in vectors with round lines. it just gives the shortest path between components quite often.

[The Tone God]

There are other electrical reasons to use 45s but those are side issues for us analog folks. There are issues with the exposure and etching process that can cause breaks in the traces when using 90s rendering the board garbage. To reduce these loses many board houses do not like or will not even except boards with square/90 traces.

Andrew

[R.G.]

You want the real reason?

The older boards were largely laid out with black crepe tape, much like masking tape, in various widths, including quite skinny. It's easer to snake around skinny masking tape than to be continuously cutting corners.

And more reliable. The cut corners were likely to gap apart before the tape masters could be shot to litho film. It's hard to get enough overlap on skinny tapes overlaid on 90 degree or even 45 degree corners.

How do I know this?

I was there.

[The Tone God]

I still have a pile of that tape lying in a drawer somewhere. Thanks for reminding me.

Andrew

[R.G.]

Take it out and BURN IT and bury the ashes.

[The Tone God]

Take it out and BURN IT and bury the ashes.

LOL! I thought about it when I got my first CAD system but actually I keep it around as a reminder of other times and how far we have come along maybe perhaps how far we still need to go.

Andrew

[rockgardenlove]

Hold on...they would use the tape on every PCB?  Or was this just when designing the layout...
hopefully the latter...

[JonFrum]

You want the real reason?

The older boards were largely laid out with black crepe tape, much like masking tape, in various widths, including quite skinny. It's easer to snake around skinny masking tape than to be continuously cutting corners.

And more reliable. The cut corners were likely to gap apart before the tape masters could be shot to litho film. It's hard to get enough overlap on skinny tapes overlaid on 90 degree or even 45 degree corners.

How do I know this?

I was there.

So you knew Pythagoras then?       

[The Tone God]

Hold on...they would use the tape on every PCB?  Or was this just when designing the layout...
hopefully the latter...

Not on the actual PCB. You would use the tape either on the transparency material or some medium to then transfer to the transparency material. The transparency version would be used to photo expose the boards. Sometimes you would need to scale the board larger to tape it and shrink it during the transfer back to correct size.

Andrew

[brett]

It doesn't generally matter for audio stuff, but by not using right angle bends you can reduce the EMF emissions.

If only it were true that it doesn't matter.

I've been given an Epi Junior amp to improve.  One of several flaws in these cool amps was to use traces for the heaters, and then run them close and parallel to the signal path.  So they talk to each other quite a bit.  Now, the heaters don't mind having some music in them, but adding 50/60 Hz hum to the signal isn't cool.

Parallel traces - arggh!

[rockgardenlove]

Hold on...they would use the tape on every PCB?  Or was this just when designing the layout...
hopefully the latter...

Not on the actual PCB. You would use the tape either on the transparency material or some medium to then transfer to the transparency material. The transparency version would be used to photo expose the boards. Sometimes you would need to scale the board larger to tape it and shrink it during the transfer back to correct size.

Andrew

Good!  It all makes sense now.  I was imagining a huge assembly line of people sticking on little tape bits.  That would be a horrible job.

[dxm1]

Tape, pad donuts, transistor/IC footprints... draw it up on graph paper, lay the transparency over it, and start sticking. Seemed like a good idea at the time, but even at 4x, my eyes these days wouldn't hold up. Hmm... I've got a light box around here somewhere...

[mattpocket]

i do my layout in vectors with round lines. it just gives the shortest path between components quite often.

Dont you risk getting shorts from those little squiggly bits in between the traces?

Matt

[darron]

i do my layout in vectors with round lines. it just gives the shortest path between components quite often.

Dont you risk getting shorts from those little squiggly bits in between the traces?

Matt

risk it? i suppose so. now i do them with a solid spacer like this:



but in the image i posted before i carefully hand drew the squiggles in flash and made sure that none of them shorted anything that couldn't be. but for the traces that were allowed to connect i allowed the squiglles to have continuity occasionally so it looks like i stuffed up (:

it's a bit nicer on the eye and doesn't leave large areas to etch. it may have had very minor capacitance issues (not that i noticed) but the ones with the spacer should be fine for our purposes.

[Mark Hammer]

Many older boards will also tend to use not only curved lines (and yes I remember the days of little skinny rolls of black Letraset tape and X-acto knives with great fondness) but to use pudgy traces and pads that almost fill up the entire board, even when the numer of connections is pretty sparse.  My guess is that with more copper protected from the etchant, the etching tank could go further between refills. 

I tend to do the same thing these days for the same reasons.  I'll often completely cover the area surrounding the board I'm going to etch, whether with Sharpie pen or even just masking tape.  Most of the time, the ground trace lies at the perimeter, so I'm essentially just extending the ground plane out a bit.  I can always cut/grind/file the board down to some specific dimensions, but in the meantime, it has taken a bit less time to etch, and saved on etchant.

[pjwhite]

I think another reason for avoiding angles sharper than 45 degrees was to avoid problems with wave soldering.  Solder bridges could form in these angles on the solder side of non-soldermasked boards.  Nowadays though, good soldermasking pretty much eliminates this problem.

I remember tape layouts, too!