Author Topic: PCB design Questions  (Read 7652 times)

The Rocket From The Tombs

PCB design Questions
« on: June 16, 2012, 12:50:14 PM »
So, the pcb I'm designing, the original artwork doesn't exactly fit the copper board I have, so I'll need to make some modifications to the artwork but, I'm not sure about what factors make a good artwork, for example I know that you should never have 90deg. angles, and I've also heard it's better to have thicker traces. So, are there any other rules or tips involving the traces for making an efficient board? thanks

defaced

Re: PCB design Questions
« Reply #1 on: June 16, 2012, 12:57:09 PM »
This is a very broad topic that could span pages to cover fully and is very dependent on the circuit and what etching capabilities you have at your disposal.  It'd be best to modify the layout to the best of your abilities, then as for someone to look it over for you.  What project are you working on? 
-Mike

frequencycentral

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Re: PCB design Questions
« Reply #2 on: June 16, 2012, 12:59:15 PM »
Why should you not have 90o angles? Do the electrons bunch up in the corners?
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The Rocket From The Tombs

Re: PCB design Questions
« Reply #3 on: June 16, 2012, 01:05:23 PM »
@defaced my method of etching is the toner transfer one and I'm building a gcb-95 wah wah.
@frequencycentral I'm not really sure but, the guide I read seemed pretty adamant about not having those angles. Here's a link to the guide:
http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

Colonel Angus

Re: PCB design Questions
« Reply #4 on: June 16, 2012, 01:16:52 PM »
Why should you not have 90o angles? Do the electrons bunch up in the corners?

I think I found an appropriate signature!
Why should you not have 90o angles? Do the electrons bunch up in the corners?

davent

Re: PCB design Questions
« Reply #5 on: June 16, 2012, 01:31:11 PM »
Why should you not have 90o angles? Do the electrons bunch up in the corners?

This is copied from PCB Design Tutorial by David L. Jones.
Quote
ˇ  Tracks should only have angles of 45 degrees. Avoid the use of right angles, and under no
circumstances use an angle greater than 90 degrees. This is important to give a professional and neat
appearance to your board. PCB packages will have a mode to enforce 45 degree movements, make use
of it. There should never be a need to turn it off. Contrary to popular belief, sharp right angle corners on
tracks donít produce measurable EMI or other problems. The reasons to avoid right angles are much
simpler - it just doesnít look good, and it may have some manufacturing implications.

ˇ  Forget nice rounded track corners, they are harder and slower to place and have no real advantage.
Stick to 45 degree increments. Rounded track bends belong to the pre-CAD taped artwork era.  

http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

I always thought it was because there was a greater chance of a trace lifting from the board at the sharp bend then if it was a gentler bend but seems it's aesthetics.

dave
« Last Edit: June 16, 2012, 02:27:57 PM by davent »
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frequencycentral

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Re: PCB design Questions
« Reply #6 on: June 16, 2012, 01:31:29 PM »
Why should you not have 90o angles? Do the electrons bunch up in the corners?

I think I found an appropriate signature!

I believe Small Bear now stock logarithmic electrons, which corner like they're on rails.
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Colonel Angus

Re: PCB design Questions
« Reply #7 on: June 16, 2012, 01:54:43 PM »
Just to be clear, no flame intended. Just the mental picture of an electron zooming along all "doh-de-doh, I'm an electron" and then crashing into a traffic jam as it rounds the bend on a sharp turn... it maded me lolz.

Thanks for the link on that PDF, it looks thick with information. Someday I'll do PCB layout, i need to learn to etch more reliably first.
Why should you not have 90o angles? Do the electrons bunch up in the corners?

.Mike

Re: PCB design Questions
« Reply #8 on: June 16, 2012, 02:02:39 PM »
Contrary to popular belief, sharp right angle corners on
tracks donít produce measurable EMI or other problems. The reasons to avoid right angles are much
simpler - it just doesnít look good, and it may have some manufacturing implications.

Interesting. This paper [pdf] disagrees, although I think it is more in the realm of high-speed digital stuff:

Quote
To conclude, it appears that bends and corners on PCB traces have a definite effect on EMC and emissions but it depends on the traces that are routed next to them. If there are long traces that have a potential to radiate and are routed right next to bends then there is more likely an opportunity to have an EMC problem.

I like 45 degree angles. No scientific reason, I just like the way they look. :)

Mike
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davent

Re: PCB design Questions
« Reply #9 on: June 16, 2012, 02:05:41 PM »
Just to be clear, no flame intended. Just the mental picture of an electron zooming along all "doh-de-doh, I'm an electron" and then crashing into a traffic jam as it rounds the bend on a sharp turn... it maded me lolz.

Thanks for the link on that PDF, it looks thick with information. Someday I'll do PCB layout, i need to learn to etch more reliably first.

PCB etching is a snap, it's trying to do toner transfers that's the killer. Look into presensitized photo boards, couldn't be easier and the results are superb!

dave
"If you always do what you always did- you always get what you always got." - Unknown
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Colonel Angus

Re: PCB design Questions
« Reply #10 on: June 16, 2012, 02:21:50 PM »
Funny that! I had a breeze with the toner transfer. Where I work we get this garbage rag full of ads that is masquerading a Whiskey journal. I used the Dell laser printer to print on the magazine paper, got some good looking transfers. My problem has been Sodium Persulfate, specifically keeping at a high enough temp that you don't pass out on the couch Whiskey drunk waiting for it (just an anecdote, that never happened, I swear). After talking to my multi-talented art teacher friend I am less scared of Ferric, so I'll try that next.
Why should you not have 90o angles? Do the electrons bunch up in the corners?

Jdansti

Re: PCB design Questions
« Reply #11 on: June 16, 2012, 02:31:50 PM »
Maybe a little off topic, but has anyone tried removing the toner from just the pads using a Dremel polishing bit with polishing rouge on it instead of soaking the entire PCB in solvent?  Would the toner close to the pad cook and make a mess when you solder?
R.G. Keene: EXPECT there to be errors, and defeat them...

davent

Re: PCB design Questions
« Reply #12 on: June 16, 2012, 02:34:27 PM »
I, and many others go with the easily obtained and cheap, Hydrogen Peroxide/Muriatic Acid mix for etching.

http://www.opencircuits.com/Chemical_Etchants
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Colonel Angus

Re: PCB design Questions
« Reply #13 on: June 16, 2012, 02:51:40 PM »
I clean the toner off with nail polish remover and a green 3m scrubby. I'm sure a Dremel would work, since I got mine I use it for everything - on that note check smallbear, they sell a toothbrushing attachment. Make sure to pick up some logarithmic electrons while you are there.

Muriatic/Peroxide sounds pretty no fail, and pretty cheap to boot. Will it etch aluminum?
Why should you not have 90o angles? Do the electrons bunch up in the corners?

.Mike

Re: PCB design Questions
« Reply #14 on: June 16, 2012, 02:55:26 PM »
Muriatic/Peroxide sounds pretty no fail, and pretty cheap to boot. Will it etch aluminum?

Yes, however...

Using Home Depot acid (32%, I think) and regular H2O2 (3%), it is a very, very slow reaction.

A couple of days ago, I bought some 40% H2O2 ("Clarioxide") from a beauty supply shop, and diluted it down to 10% (3:1).

It etched much, much faster.

Mike
If you're not doing it for yourself, it's not DIY. ;)

My effects site: Just one more build... | My website: America's Debate.

CodeMonk

Re: PCB design Questions
« Reply #15 on: June 16, 2012, 03:01:14 PM »
Muriatic/Peroxide sounds pretty no fail, and pretty cheap to boot. Will it etch aluminum?

Yes, however...

Using Home Depot acid (32%, I think) and regular H2O2 (3%), it is a very, very slow reaction.

A couple of days ago, I bought some 40% H2O2 ("Clarioxide") from a beauty supply shop, and diluted it down to 10% (3:1).

It etched much, much faster.

Mike

14.something %
At least at my local Home Depot.
Like $10 for 2 one gallon jugs.

And I have never had issues with 90 degree bends, but I can see where possible trace lifting might be an issue.
But in some cases, there is no other way.

I tried etching aluminum once with that solution.
I probably had the ratios for aluminum wrong though (Recommendations?).
I etched it in a plastic container, which melted from the heat.
« Last Edit: June 16, 2012, 03:05:38 PM by CodeMonk »

.Mike

Re: PCB design Questions
« Reply #16 on: June 16, 2012, 03:17:05 PM »
14.something %
At least at my local Home Depot.
Like $10 for 2 one gallon jugs.

Really? The only stuff they sell here is SKU 346289. It's 31.45%.

I was using it 1:1 w/ 3% peroxide for enclosures. I don't like the face-down-in-the-acid method, since it is too hard to monitor and seems to get out of control. I do use it to get the reaction going, but then I switch to a dip-and-toothbrush type method.

Mike
If you're not doing it for yourself, it's not DIY. ;)

My effects site: Just one more build... | My website: America's Debate.

CodeMonk

Re: PCB design Questions
« Reply #17 on: June 16, 2012, 03:22:23 PM »
14.something %
At least at my local Home Depot.
Like $10 for 2 one gallon jugs.

Really? The only stuff they sell here is SKU 346289. It's 31.45%.

I was using it 1:1 w/ 3% peroxide for enclosures. I don't like the face-down-in-the-acid method, since it is too hard to monitor and seems to get out of control. I do use it to get the reaction going, but then I switch to a dip-and-toothbrush type method.

Mike

This is all they have here, at least the one closest to me:
http://www.homedepot.com/webapp/catalog/servlet/Search?storeId=10051&langId=-1&catalogId=10053&keyword=Muratic%20Acid&Ns=None&Ntpr=1&Ntpc=1&selectedCatgry=SEARCH+ALL

I look around more next trip.
What section was your in?

davent

Re: PCB design Questions
« Reply #18 on: June 16, 2012, 03:32:17 PM »
So, the pcb I'm designing, the original artwork doesn't exactly fit the copper board I have, so I'll need to make some modifications to the artwork but, I'm not sure about what factors make a good artwork, for example I know that you should never have 90deg. angles, and I've also heard it's better to have thicker traces. So, are there any other rules or tips involving the traces for making an efficient board? thanks

Back to the beginning and assuming self made pcb's a few of my (aesthetic) guidelines when laying out a board... i like the look of the 45ļ bends so use those but i also like the curved traces but they're a big hassle to do with the software i use.

Make the traces as wide as possible but always less wide then the pad it connects to, keeps the solder on the pad when you solder up, makes for a nicer looking, distinct solder joint and uses less solder. The less copper to etch off the board the quicker the etch is done.

No matter the size or shape of the pad, (or needed final drilled hole size) the pad-hole size is 20 or 25mil, once etched the resulting small dimple in the middle of the pad helps the drill bit self-center in that pad when you go to do the tedious drilling task. Eliminates the need to center punch.

Try to have pads for off-board components around the perimeter of the board, again makes for a neater final appearance, maybe easier assembly,  so not really a primary concern just something to keep in mind.

dave
"If you always do what you always did- you always get what you always got." - Unknown
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R.G.

Re: PCB design Questions
« Reply #19 on: June 16, 2012, 03:38:22 PM »
As generalities:
- for audio and low ultrasonics, thicker traces up to about 0.030"/ 1mm are better than tiny (0.008" / 0.25mm) are better. In the range from 0.020"/0.5mm to 0.030"/1mm there's not much to choose from other than routing convenience.
- for etching reasons, corners sharper than 90 degrees are not preferred. If you must do an angle sharper than 90, chamfer the inside with a separate trace to avoid undercutting
- for aesthetics, 45 degrees is nice and easy to route; a 90 can frequently be done as two 45s, but don't kill yourself doing it
- for RF, give it up and let a skilled RF layout guy do it; there is a book on RF practice entitled "the handbook of black magic"; no, I'm not making that up
- for fast logic, see above; the edges of fast logic signals contain harmonics well up into the 100's of MHZ or low GHZ, and they can radiate out if you look at them. This is where the "don't do sharp corners" comes from. In fact, for high RF or fast logic, don't even do single traces; do controlled impedance strip line

Don't sweat the small stuff for audio and effects. There is a neato book targeted directly at laying out pedal effect circuits that I remember someone writing...  :icon_biggrin:
Lots and lots of the practicalities are in there.
R.G.

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