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I am trying to make a PCB for the first time and am concerned about the sizes of the soldering pads over the actual dimensions that I should realize on the board. That is, with the following diagram:

enter image description here

What size should the top pin's pad be? The dimensions for this pin are given as 3.00 x 1.75 mm. About what size should the associated soldering pad be and what (if any) is the general rule?

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  • \$\begingroup\$ The rule of thumb is "read the datasheet". \$\endgroup\$ Commented Feb 21, 2014 at 5:28
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    \$\begingroup\$ Clearly this is from the datasheet. Some of the datasheets include recommended pads, this one did not. \$\endgroup\$
    – sherrellbc
    Commented Feb 21, 2014 at 5:30
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    \$\begingroup\$ Not necessarily the component datasheet. Some manufacturers have discrete package-specific datasheets. \$\endgroup\$ Commented Feb 21, 2014 at 5:31
  • \$\begingroup\$ I will look into that. \$\endgroup\$
    – sherrellbc
    Commented Feb 21, 2014 at 5:32

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The drawing in the O.P. comes from a datasheet. Some datasheets have a dimensioned drawing for the footprint (land pattern). Here's an example. Notice that the pads (top right corner) a somewhat wider than the legs.

enter image description here
Originally from here. Found this by googling SOT-223.

SOT-223 is a fairly common package. It's likely that your layout software has a standard footprint for it. There's a good chance that it's accurate.

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Depends on how you will be soldering components - I'd add a bit of margin if I intend to hand solder - think of where it would be convenient to access with the soldering iron, leave standard sizes from datasheet for reflow.

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