I am new to the forum and new to Kicad and consider myself a beginner in making my own circuit boards.Please excuse me if I say something stupid. I am designing a PCB with SMD LEDs for my Star trek next generation Mk7 tricorder prop. I made the schematic and did a board layout with Pcbnew. When I was assigning footprints to the SMD LEds I picked I discovered there were no footprints for my specific SMD LEd (I picked these from digikey). I noticed digikey had “generic” footprints for 1206,0603,and 0805 SMD LEDs so I assigned those to my LEds . I guess I assumed that the footprints for the different sized LEds would be standardized.However, when I was reviewing my design I checked the datasheets on the SMD LEDs and saw that the solder pad size and spacing was different from the generic footprint I had assigned .
So I have been watching tutorials on making footprints.I can make the solder pads and get the spacing, but I am a bit confused about the outline around the footprint. Am I supposed to make an outline showing the outline of the part on the f.fab layer ? None of the footprints of SMD LEDs I have found seem to do this. I also read that I should draw an outline on the f.silk layer,but this will have to be a little bigger than the actual led because the there will be no silkscreen where the solder mask is applied. Is this correct?
Again I apologize if this seems obvious.I tried a search and couldnt find any answers to my questions and I am not asking anyone to design anything for me-just offer some guidance.If there are tutorials you could point me to that would be great too.
Only the copper pads and mask openings are mandatory. I recommend following KiCad’s library conventions or some other convention and add silk, fab and courtyards layers. Fab layer should have the simple (possibly simplified) but 1:1 outline of the physical component. The silk layer is possibly printed on the board and should help you when you “read” the physical board before and/or after the components have been assembled there, so use your common sense. Full outline is often too much there (historically it has been used as a map for assembly, but nowadays the fab layer should be used for that).
If you get the ready made footprint from some other source than KiCad’s library, it may follow or not follow some convention.
Thank you. if I use the place pad function in the footprint editor will that generate the copper and mask openings automatically ? I havent seen a step in any of the tutorials where you have to make the mask openings.
I was really surprised that there seems to be no standardization of solder sizes and spacing for smd LEds.
thanks again for the fast response.
See also What is the meaning of the layers in pcb_new and in the footprint editor? (KiCad 5 and earlier) and https://kicad.org/libraries/klc/#_footprint_guidelines. And of course you can look at the footprints in the KiCad library to see examples.
Maybe Tutorial: How to make a footprint in KiCad 5.1.x? is useful.
By default SMD pads have copper and mask opening. Look at the pad properties dialog carefully.
They are of different sizes. 1206 etc. are not necessarily exact sizes when the LEDs are described. Even if the outline is exact, the pads may differ in size. Height matters, too. Therefore the ideal footprint for some LED may be different than a standard footprint. What is good enough for you depends on the assembly process etc.
Thanks again for all of your help.
This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.