0
\$\begingroup\$

I have a 4 pin RGB LED with a common anode. I'm trying to make my first PCB and I am creating the footprint for the LED now.

I don't have a datasheet for the LEDs unfortunately.

I have a ruler DigiKey sent me and it seems like the pins fit snugly in the 0.6mm hole. I think the space between the pins is roughly the same as the pin width.

I think that gives me a pitch of 1.2mm. I was considering a 1.0mm pad with a 0.6mm hole. That'd give me only 0.4mm around the pin for soldering and paltry 0.2mm between the pads. This seems like a lot of extra work for the small benefit of being able to settle the LED all the way down on the board and solder the pins on the back of the holes.

Another option I considered is spreading the pads out using roughly the entire 10mm of space under the LED. With a 0.1mil pitch, the LED would stick out further from the board but soldering would be somewhat easier because I could have larger annular rings.

Should I spread the pads out on my THT LED and how do you go about making decisions like that?

\$\endgroup\$
  • 2
    \$\begingroup\$ No datasheet = no purchase =-D \$\endgroup\$ – Tyler Nov 28 '18 at 16:51
  • 2
    \$\begingroup\$ It is common pratice to spread the leads on such parts - look at the TO-92 transistor footprints for example. \$\endgroup\$ – Peter Bennett Nov 28 '18 at 16:54
  • \$\begingroup\$ @Tyler, heh! Yeah, I wish I had known that when I bought them. :) \$\endgroup\$ – D. Patrick Nov 28 '18 at 16:55
  • 1
    \$\begingroup\$ I'd use 0.7mm for the holes, so the LEDs will still fit despite manufacturing tolerances. The extra space will be filled with solder anyway. \$\endgroup\$ – Simon Richter Nov 30 '18 at 14:53
  • \$\begingroup\$ @SimonRichter thanks! I started thinking about my soldering abilities (or lack there of) and decided I needed larger pads and more margin. I made the holes bigger too because the manufacturer wanted +- 0.08mm. Thank you very much for the comment! \$\endgroup\$ – D. Patrick Dec 1 '18 at 0:19
1
\$\begingroup\$

Most professionals here will tell you not to buy a product without a datasheet, and that's good advice. On the other hand, most "generic" products are similar to properly documented products (perhaps with greatly relaxed performance). In this case, I think it's similar to the Kingbright part shown here:

enter image description here

You can make measurements (with calipers and/or micrometer preferably) to confirm or disprove that hypothesis. So let's say this is the actual part.

I would say this is a bit close, but possible, depending on design rules, the below is 2mm x 0.8mm pads which results in 10 mil spaces (0.254mm) and 0.1mm annular ring, which is probably okay.

enter image description here

Whatever you do, you should not push the LEDs all the way down to the board, as that will stress the epoxy and may result in failures. The Kingbright LED has a leadframe feature that will stop it from being pushed all the way down, but you can also use a spacer or a jig.

\$\endgroup\$
  • \$\begingroup\$ Is that what the flat spots on the pins are for? As a "don't go past here" guide? \$\endgroup\$ – D. Patrick Nov 28 '18 at 17:21
  • 1
    \$\begingroup\$ @D.Patrick I am not sure that is the intention. Some of the features are required by the progressive die and later stamping out of the lead frames. It's a reasonable distance in any case. \$\endgroup\$ – Spehro Pefhany Nov 28 '18 at 18:05

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.