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I am learning Cadsoft Eagle and have noticed that the pads for SMT devices are on the 'top'/'bottom' display layer, whereas the pads for THT components are on the 'pads' layer. Why is this?

I have enlarged the pads for the SMT device so that I don't commit Seppuku with my iron during hand production. Looking at the soldermask 'stop' layer, it appears that all is well, as the SMT pads are not covered. I just want to check that this difference between SMT/THT pads is correct before making my first batch of coffee coasters.

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  • \$\begingroup\$ Your image host is redirecting that URL to a full webpage, which the image upload utility was never meant to handle. That being said, I also am having issues uploading images this morning (it was working last night) \$\endgroup\$ – Adam Lawrence Mar 4 '13 at 12:57
  • \$\begingroup\$ It does not work for direct upload from my computer either . . . meta.electronics.stackexchange.com/questions/2725/… \$\endgroup\$ – learnvst Mar 4 '13 at 13:08
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The features in the PADS layer goes on all layers of the PCB (with actually some additional modifications when you're using more than 2 layers, such as having a smaller copper ring in the inner layers instead of the large pad). SMD components, though, exist only on one side of the PCB. So their pads go on TOP or BOTTOM depending on which side the component is on.

As an aside, be careful when enlarging pads. Go with lengthening the pads and not widening them, since that could reduce the space available between adjacent pads and make soldering it harder, even if it still clears the rules for the fabricator. Also, it become counterproductive to leave more than one or two millimeters beyond how far the IC pin is expected to go. The extra exposed copper makes soldering by hand slightly more tricky.

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