CAD PCB software

[Louis Mamakos]

On Mar 30, 2013, at 1:24 PM, Alex Fraser <beatnic at comcast.net> wrote:

> I went to the Cadsoft site and downloaded and installed their Eagle Freeware version PCB design software.
> http://www.cadsoftusa.com/download-eagle/freeware/?language=en
> 
> - It is limited to 4x3.2" which I believe is about 1.3 Altoids in area. 
> - It only does 2 signal layers, which is pretty cool I guess.  
> - The schematic editor only does one sheet.  This sure encourages a modular approach.
> - It is for non commercial use only.  
> 

I've done a board using Eagle, and while there's a learning curve to get proficient, it's really quite capable and effective even within the envelope of the free version.  There are a number of tutorial videos around on the net, and it's usually worth a bit of time to watch them and get a head start on understanding how you're supposed to be using the software.  Personally, it's a huge win that they have Mac version of package they ship along with the WIndoze version.

> I played with it a little last night and figured out how to drop stuff on the drawing and connect them.  The libraries are an education in themselves.  I've done some older Auto Cad  (R14) but I haven't got to the point where I can figure out how to relate the two.  I have gotten Auto Cad files converted to tool movements, G codes to run a mill.   I assume there is a way to program a CNC to drill the holes through the pads, but haven't figured it out yet.  

Make sure you use the right tool to connect nets vs. just drawing them such that they appear to connect to each other :-)  There are tons of libraries around for parts, and they sometime of varying quality..  I usually have my own library that I copy parts into after I've validated that in fact the library parts "work", and have the right signals on the right pins and on the package that I'm using in my design.  

One thing that bit me on my design is that somewhere along the way, an update version of the 0805 SMD footprint got imported with a part, and the pads ended up being too small.  By that, I mean too small for my intended hand-soldering plans, still plenty OK for reflow soldering with paste.  Not fatal, but just a little trickier to hand solder.

Eagle can generate standard Gerber format files for each the layers in the design as well as drill files for the holes.  It's also useful to be deliberate about what stuff you put on what layers, even beyond the top and bottom copper layers.. there are keep-out and restriction layers you can define.  And there are "documentation" layers that can be distinct from the top and bottom silk screen layers.

I'd recommend finding a good gerber previewing package to check the actual output of the board layout to ensure that you're really getting what you think you have.  I actually found a pretty nifty one on the net -- you upload your gerber files, and it will render the design in 3D in a browser window for you to inspect.  There are a bunch of Windows-based gerber previewers as well.

> I haven't played with the auto route feature either, but I'm doing real simple stuff to start off.  

The autorouter sure seems to save a lot of time, even on simple designs.  It can draw the lines straighter than I can, and it also obeys the design rules that you can specify.  I wouldn't hesitate to give it a try.

> 
> Last time I etched a board was with a resist pen and some radio shack chemicals.  Can AMRAD etch?

I'm not sure this is really worth the time, especially if you do a two layer design.  When I did my design, I had these guys:  OSH Park ~ Welcome fabricate the boards.  For $5.00 per square inch of your design, you get 3 copies of the board in a couple of weeks.  They are very high quality, with silkscreen and solder mask on both sides and ENIG gold flash on the exposed pads.  Plated through vias, the whole works.  Highly recommended.  And the come in this very manly purple-colored PCB material.

And if you're doing your own boards, now's a great time to venture into SMD components.  Once you get the hang of it, the assembly time is faster than thru-hole parts, smaller boards, less expensive components.  Don't fear the SMD; even with my aging eyes, doing 0805 and 0603 discrete component assembly with just a magnifying bench light wasn't any big deal.

Here's a couple of photos of the board that I had done.  Small bug in my silk-screen output (relating to comment about documentation vs. silkscreen layers above..)


louie
wa3ymh
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