PCBlayout.pdf
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Transcript of PCBlayout.pdf
The EE401 Guide for Laying Out Your Circuit Board for Milling (and some tips for use of Eagle
and layout of all boards in general)
This guide has been created to help ensure that your board is milled with minimal trouble. There are limitations to the PCB milling process. It is suggested that you work through the Eagle tour at http://www.cadsoft.de/.
Use the Eagle 4.xx layout package. Circuit layout done with other packages will be rejected from milling.
Schematic Capture
1. All pins on the package that are to be connected on the PCB must be connected in the schematic. Tip: Use "INVOKE" to place power connections for IC packages on the schematic, if necessary.
2. Use the ERC (electrical rules check) to ensure all connections are made properly.
Printed Circuit Board Layout
1. Design single sided boards only. You will receive a single sided PCB back. Only the bottom side will have copper traces. Doublesided boards may be allowed at the discretion of the course technician.
2. Place parts using a grid size of 0.1 inch. Reduce grid size as needed for final placement of parts and traces.
3. With DB9 connectors and other parts where the pads are not on a simple grid pattern, to connect to the pads use the ROUTE button to first connect from the offgrid pad to the next point on your board.
4. DO NOT use the AutoRouter. The autorouter has caused serious problems with creating a good PCB. If you use the autorouter it is very likely you will get a bad PCB. The only sure way to fix this is to relayout the board without the autorouter.
5. Minimum trace width is 0.04 inch.6. Minimum pad size for jumpers/via's and components is 0.08 inch.7. All holes are drilled with a 40 mil bit: you may use the drill press to open the
holes up further to accommodate component leads.8. Do not run traces between pads separated by 0.1 inch or less spacing. You can
run up to two traces easily out the end of a 0.3 inch wide DIP package. This is to avoid solderbridges when assembling the PCB.
9. Try to keep your inside trace angles greater than 90 degrees as sharp angles tend to collect conductive debris and have other highfrequency effects. Two consecutive 45degree angles redirect the trace 90 degrees. Use 'T' trace intersections if you have to. Avoid 'Y' trace intersections.
10. Place the dimension outline 0.05 inch outside your desired board size. The default PCB panel size is 4x6 inches. If no outline is provided, you are likely to get a rough 4x6 panel with two jig holes in your circuit layout.
Checking Your Board LayoutThis is very important! Do not skip these steps!
1. Turn off all layers but “UNROUTED”. Refresh the screen and make certain there are no unrouted traces.
2. Use the DRC (design rules check) to check clearances on your board. Minimum clearance is 0.013 inch.
3. Save your work.
Other Board Layout Tips1. Have a set of calipers or a ruler on hand for measuring package dimensions and lead
sizes.2. Part specification sheets typically include package information that will aid in
determining pad placement.3. All polarized components (including ICs) should be placed with consistent
orientation.4. Hole sizes should be at least 10 mil larger than the component lead.5. Pads should be at least 15 mil larger than the hole size.6. Place a PCB revision number and name on the top layer.7. Components should be at least 200 mil from the edge of the PCB.8. Traces should be at least 20 mil from the edge of the PCB.