3
\$\begingroup\$

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?

\$\endgroup\$
  • \$\begingroup\$ The rule of thumb is "read the datasheet". \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 21 '14 at 5:28
  • 1
    \$\begingroup\$ Clearly this is from the datasheet. Some of the datasheets include recommended pads, this one did not. \$\endgroup\$ – sherrellbc Feb 21 '14 at 5:30
  • 2
    \$\begingroup\$ Not necessarily the component datasheet. Some manufacturers have discrete package-specific datasheets. \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 21 '14 at 5:31
  • \$\begingroup\$ I will look into that. \$\endgroup\$ – sherrellbc Feb 21 '14 at 5:32
3
\$\begingroup\$

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.

\$\endgroup\$
2
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.