Hello all, I am trying to design a PCB from a schematic I’m at the step where I have to assign footprints. What should my considerations be with all of these options? For example, 5x5.3 or 3x5.4? Should I use these default footprints, or would I be better off finding the components on Digikey and finding the specific footprints on SnapEDA?
I hereby certify that I am not simply asking someone else to design a footprint for me.***
This is an auto-generated message that is in place on the “footprints” section of the KiCad.info forum. If I remove it and ask for a footprint to be designed anyway, I understand that I will be subject to forum members telling me to go design my own footprint or referring me to a 3rd party footprint site.
I can’t help in this step because I have never done it but I can suggest one of possibilities you can chose. I am using only my footprints and my symbols and all symbols have already in library associated footprints. So I need not to go through step of assigning footprints.
This way I don’t need to analyse for each project once more and once more what should be the footprint for this or this element. I am simply afraid of my own bugs - for example selecting too small footprint for 22uF capacitor resulting in specifying not existing part.
There are millions of differently sized electronic parts in this world, and in the end you have to fit the parts that you have on the PCB that you made.
Those numbers refer to the diameter and the height of the capacitor. The height will not have an influence on the footprint, but you can see it if you turn on the 3D preview.
KiCad’s own libraries are of a quite high quality, and I use them whenever possible.
There are a bunch of problems with footprint assignment because there are so many different footprints. Small variations in the physical part do require different footprints to fit them on the PCB. Some common problems with footprints:
Small differences in pitch, for example 0.6mm or 0.635mm for soic IC’s.
Some transistors have pins in different locations depending on the suffix.
Connectors have their mating parts defined, but not the footprint on the PCB. There are for example hundreds of footprints just for USB connectors.
Ideally you have all the parts before you order the PCB. Then you can do a test fitting to see whether the footprints fit.
You should use the recommended footprint for the component you use. Always check this with your component data sheet as mistakes happen in all Libraries.
Personally, like @Piotr , I only use footprints from my personal librarys. These are either checked and maybe modified Kicad footprints or personally created footprints.
Ok for example, I’ve got this inductor I want to use. If I’m reading this datasheet pdf correctly, it’s 18.2mm x 18.2mm. But I can’t find anything that size in the default footprints in KiCad (but I am new, so I’d appreciate someone doublechecking me on that). Would I now design my own footprint?
I’ve attached my best first attempt in the form of an image and as the actual footprint if anybody would like a more detailed look.
Very good EXCEPT, you have made a drawing of the inductor instead of the Footprint for the inductor.
You need to create a footprint for the “Typical Land Pattern”. ie. Pads 6mm sq. and F. Courtyard of 19.3mm sq.
Anchor is good. F.Fab is missing.
F.Fab should be the size of the component ie. 18.2 X19.3 mm
F.Courtyard could be 19.3 mm sq. as per land pattern.
F.Silk a little larger than F.Courtyard.
An easy way to remember what layers are needed is to use some other rectangular footprint with two pads in the footprint editor then right mouse click each pad and change the size in Properties and Drag and Move the three outlines until they are the correct length in the correct places.
If anyone cares, I’m setting the footprints with their courtyard touching and I have Silk exactly at courtyard lines (a little wider lines but not little larger (area)).
I care, and many of my footprints are as yours.
I modified my above comment. The courtyard dimensions really rely on the component shape. eg. Transformers, large inductors, some semiconductor packages may have packages larger than the footprints.
I’ve made my first PCB. After bashing my head against a wall trying to design the perfect first PCB, I figured I’d make more progress designing one that I know is bad and getting tips from there. I’ve attached the circuit schematic and the PCB, along with all custom footprints I’ve used so far.
My professor advised me to use the second layer as a ground plane using vias. Have I done that correctly? I’m supposing that running a trace from the Arduino PWM signal directly under my IC isn’t a good idea. I can fix that later, and I’m taking any suggestions.
Sure, but first, how much are you willing to pay us for doing your homework for you?
There are already a bunch of PCB reviews on this forum and proper PCB design is much more than plunking some footprints on a piece of FR4 and drawing some tracks.
Feel free to come back here when you will have any problem with KiCad working differently than you expect or when you know what you want but don’t know how to do it with KiCad.
