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I manage to get the autorouter in Eagle to complete the routing if I use small sizes for the wire and small clearances between wire and pad and wire and wire.

Since I'm making the circuit on a transparency for lazer printers, I'm just curious, what would be the absolute smallest size I could get away with for pads and wires (circuit-board lines) without potentially wrecking the circuit board?

I will be inserting the parts manually (mostly IC's but some LED's and resistors and capacitors) and then soldering them, and the drill I have that I plan to use is 1/16ths of an inch.

My lazer printer can print up to 600 dpi.

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    \$\begingroup\$ Here you are. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 16 '16 at 3:43
  • \$\begingroup\$ 8 mil is possible with care, but it is unlikely that an auto-routed board will be suitable for hand fabrication. If you are going to do that, you really need to route the board by hand with this in mind, given yourself extra copper wherever you can and trying to minimize use of vias, each of which you have to join by hand. Also a 1/16" drill bit is huge in circuit board terms - very little is that large unless it is a power component or a mounting lug. \$\endgroup\$ – Chris Stratton Jul 16 '16 at 21:47
  • \$\begingroup\$ after a while I thought 1/16ths of an inch was too big too. I tried 1/64th on a test board, and the bit broke right away so now im going to use 1/32nd of an inch bit. \$\endgroup\$ – user116345 Jul 17 '16 at 5:21
  • \$\begingroup\$ Bits must be short, stable and board rigid. \$\endgroup\$ – Sunnyskyguy EE75 Feb 2 at 5:37
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With regard to size of tracks, and in terms of the home PCB production equipment itself, I would recommend 0.25mm as the absolute smallest size that you can (reliably) get away with. But I tend to stick to >0.3mm if I can.

Unfortunately this minimum size is dependent upon high quality transparency prints. To achieve 0.25mm I use a 1200DPI printer. You will struggle to do this with a 600DPI printer.
If the printer is your limiting factor, then this will usually be obvious from the printout itself. So you can try some different track sizes and see what the minimum reliable print is. When testing, group a bunch of the tracks together as that will show up the limitations of your printer much more obviously.

Regarding pad sizes, well, this limitation is defined by the part you're designing into your product and not by the capabilities of home PCB production. Look up the datasheet for the part and you should find a recommended footprint for it.

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