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Mark245 12th May 2009 07:15 PM

PCB Routing
 
Hey everyone,
I am trying to route all the traces for my amplifier in FreePCB for a single sided board. I have run into a problem because it seems pretty tough to route all of these traces for 50 parts without overlapping some of them. Do you have any reccommendations for getting around this problem? One thing I know I could do is run a few jumpers to prevent the overlap. But this seems to contradict the purpose for using PCB in the first place. Any thoughts?

Thanks
Mark

Mr Evil 12th May 2009 07:28 PM

Try to use the components themselves as jumpers. Larger, axial-leaded components are better for this.

Steerpike 12th May 2009 10:00 PM

Nothing wrong with using jumpers or wire bridges!
Particularly on circuits where otherwise long pcb traces might cause oscillations, noise pickup etc.

jackinnj 13th May 2009 02:08 AM

Layout the parts "a la schematic" first -- so you can see where you're going. I mean REALLY put the parts down on a piece of paper so you have a tactile feel of what you're gonna be doing.

If you're doing regular analog, you have to set your mind to two tasks -- your "0" net, i.e. GND , and V+, V- should be thought of as on the bottom of the board -- the other simultaneous (2nd) task is to mentally view horizontal traces on one plane, and vertical traces on the other -- this is how auto-routing systems work on their first pass.

If you have to "jumper" just think of a resistor with zero-ohm impedance. Unless you are going to move current at a couple of tens of Megahertz, the impedance jump and it's SWR are almost irrelevant (as Groucho said).

Mark245 13th May 2009 08:25 PM

Thanks for the replies. So I what part should I use for the ends of the jumpers? Can I just use a pad and then solder the wire to it? Thanks again I am kind of new to pcb layout.

mark

Dave 13th May 2009 08:39 PM

2 Layer Board
 
You could go with a 2 layer board, the prices at www.pcbcart.com are very good.

Steerpike 13th May 2009 11:32 PM

Quote:

Originally posted by Mark245
So I what part should I use for the ends of the jumpers? Can I just use a pad and then solder the wire to it?

Just use exactly the same pads as for your 1/4 watt resistors.

Treat the jumpers like any other components - resistors, capacitors, diodes - except you can space them much closer together, and they can be any length you want.
If you dont need close spacing, just use a 'resistor, value=0 ' in your layout.

I always save all the resistor / capacitor lead cut-offs when making boards - to use as jumpers.

Mark245 14th May 2009 12:41 AM

Ok that sounds good. Thanks everyone for the help!

Mark245 14th May 2009 05:21 PM

Actually I have one more question. I can't seem to find a footprint for the TO-126 package. Has anyone else had this problem? I am using FreePCB and the footprint is not there and I cant find it on the internet. I guess I could just use TO-220 package and switch the pins around in Capture because the transistor pins are opposite for TO-220 and TO-126. I am trying to use the MJE340/350 in my amplifier design. Any suggestion will be appreciated.

Mark

jackinnj 15th May 2009 11:56 AM

Quote:

Originally posted by Mark245
Actually I have one more question. I can't seem to find a footprint for the TO-126 package. Has anyone else had this problem? I am using FreePCB and the footprint is not there and I cant find it on the internet. I guess I could just use TO-220 package and switch the pins around in Capture because the transistor pins are opposite for TO-220 and TO-126. I am trying to use the MJE340/350 in my amplifier design. Any suggestion will be appreciated.

Mark


If you go to the On-Semi website they have a section devoted to footprints of their devices -- International did the same thing as On-Semi -- didn't have the mechanical drawing or pinout on the PDF.


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