PCB layout questions

[ebartlet]

I recently built a 2 channel compressor on perf board. I built the first channel. Worked great. Built the second channel which works great. Channel started to oscillate at RF after building channel two one the same board. I fixed this with 33pf caps across the feedback resistors. Now I hear a distorted version of channel two coming across channel one! Not only do I want to fix this one, built I would like to build another one, but with a better layout, as, after testing components, I beleive the layout is the problem. What is recommend for the way power, ground and signals are routed on a PCB?

Thanks

 

[gyraf]

The answer to that question would be the topic for several full books.

The simple answer is - large tracks for power (lowers crosstalk-through-psu). Small tracks for signal (keeps capacitative crosstalk low). Star ground (keeps references clean)

Jakob E.

 

[Leslie West]

[quote author="gyraf"]
The simple answer is - large tracks for power (lowers crosstalk-through-psu). Small tracks for signal (keeps capacitative crosstalk low). Star ground (keeps references clean)
Jakob E.[/quote]

Excuse they for kidnapping this Posting :grin: , but what is a good size for the tracks? I mean signal and Power tracks an a PCB.
And what is a good size for the solder pads?

It would be cool if someone could call the sizes for "home made" PCBs and factory made ones. My Problem is somethimes, that i design to small Pads and have trouble to solder it exactly.

Thanks
Leslie

 

[Leslie West]

 

[gyraf]

Didn't understand your question..?

 

[Leslie West]

[quote author="gyraf"]Didn't understand your question..?[/quote]

Oh sorry. My english is very bad....

My first question is what is a good size to use as a signal tracks an a PCB and what is a good size for a Power Track.
And my 2. is what is a good size of a pad? My pads are sometimes to small to solder it exactly...

Is a signal track with a thickness of 1mm good?

 

[gyraf]

For power tracks, use as wide as possible, up to some 2.5mm. More for high currents. Depends a lot on copper thickness. You can find tables on the internet about current/width.

My defaults are - measured in MILS (1MIL=1/1000 inch) 40MILS~1mm

Tracks:
signal: 20-30 mils
power <50mA: 30-40 mils
power >50mA: 40-60 mils
grounds: all possible width

Pads:
135 mils - transformers, tube sockets
119 mils - bridge rectifiers, trimmers
106 mils - 1n4001-diodes, medium-size caps
90 mils - ic's, resistors, small caps - this is "standard" pad
69 mils - smallest pads when space is crowded

Jakob E.

 

[Leslie West]

Thanks Jakob, Thats what I wanted to know.....

 

[Leslie West]

one more question Jakob....


Are these Pad sizes for "home" made PCBs or Do you use this sizes also when order the PCBs from a factory?

Thanks..

Leslie

 

[gyraf]

Both. I always "homemake" my prototype pcb's before sending them off to manufacturing.

Jakob E.

 

[Leslie West]

[quote author="gyraf"]Both. I always "homemake" my prototype pcb's before sending them off to manufacturing.

Jakob E.[/quote]

Thanks Jakob, so for example a Resistor has always a Pad distance from more than 7,5 mm? In the past i used 5 mm as a distance and had pronlems to solder it good...

My english is very bad, so i hope you understand me....
Thanks for your help Jakob....

Leslie

 

[Leslie West]

Oh I treid it out and for example a NE5534 doesn´t work! The pads are touching each other!
Where is my fault? I am using eagle....

Thanks
Leslie

 

[gyraf]

Sorry - I don't understand your other question?

For IC pads (and some others) yoy need to specify oval pads to get them big enough without touching. I don't know eagle.

Are you asking how close two pads can be? That depends entirely on voltage differences between the two.

If you're asking for pin spacing, then I always use 4modules (1module=1/10inch=2.54mm) - so a resistor is 10.15mm spaced.

But you always need to know physical size of your components before drawing lay-outs anyway. When in doubt, allow for different components - like I do on several capacitors in the G9

For reference, you should take a look at the layout pdf's found at the gyraf/diy pages. The G9 pcb is closest to how I lay out pcb's these days (some of the other projects are very, very old)

Jakob E.

 

[Leslie West]

[quote author="gyraf"]If you're asking for pin spacing, then I always use 4modules (1module=1/10inch=2.54mm) - so a resistor is 10.15mm spaced.[/quote]

Yes, that was my question. Thanks a lot. Now i am on the way.....

I will take a look for the oval pads for my ICs....

Thanks for your patience Jakob.

Leslie...

 

[electronaut]

I found this PCB Design Tutorial a while back and it helped me a lot with the little details.

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

 

[osterchrisi]

Hey guys and girls I'm getting started in doing my very first baby-pcb-layout designs. Could someone plz tell me what size the "standard" pads on the GSSL pcb have? Although the design is super tight and component site is crowded like a free U2 concert ( ) I found those very easy to solder... Are they 90 thou? Or even more?

/edit:
And also the drill holes: Are they 1mm?

 

[Luny Tune]

How about letting ebartlet have his thread concentrated about HIS questions?

Start your own topics, guys!

 

[audiox]

http://www.sg-acoustics.ch/analogue_audio/pcb_design/index.html