Today I designed my first PCB ever and I hope this will be the last question I will bother you with… forever.
Designing was quite a fun, however, I am kind of unhappy with the result. Below is the picture obtained after uploading gerber file to the PCB producer:
Those white lines, corresponding to silks layer, make little sense to me. Maybe this is because I am not an electrical engineer? I would prefer that silks would correspond to fab layer, where outlines of individual elements are visible.
So I would like to ask you two things: are such silks normal and if not, how to improve them?
PS. I was playing a little bit and transformed Fab file into SilkS file in text editor. What I got is more pleasing to see, but probably those lines going over copper pads are not OK.
Yes the white lines are the silkscreen and this is meant as a visual guide during placement or debug.
It appears you have turned off the reference designators when you generated the GERBERS. This would have made a bit more sense if you were to look at the PCB.
Two points w.r.t. to your suggestion with the FAB on the SILK
you can’t have silk on pads. A good fab house will clips this, a bad fab house will print on the pad
putting silk under SMT is generally not a good idea as it raises the component and thus causes reflow issues - less of a concern if you are hand soldering.
The part outline aligns quite well with IPC-7351 where there is a general silk for the component body and an indication for pin1.
Your PCB is quite densely populated and that does not leave much room for any sort of silkscreen. You also did not leave any room for mounting holes
Your second screenshot is also not great. Silk screen should never overlap with pads. (DRC in KiCad-nightly can even check for that).
KiCad’s default libraries are mostly geared towards automated assembly, and for that it does not make any sense to put silkscreen underneath footprints. The simple silkscreen lines are mainly to indicate which pads belong to the same footprint. They also have a bit of an overlap in meaning with the courtyard. If those lines start overlapping then assembly becomes more difficult.
But those rules are different from hand assembly.
The link below is for footprint symbols geared more towards hand assembly.
I also agree with Naib.
Tools like InteractiveHtmlBom are a great help with manual assembly.
Right, and not only that, but there should also be some clearance. The silkscreen is rarely without “registration error” and roughness. In your bottom picture U2 and U3 silk lines touch the pads. In real life they will probably cover some of the pads: all the lines may be for example be moved 0.2mm left.
That won’t be very dangerous if you are hand soldering and the components are largish – I can’t tell what’s the size but it looks like they are at least 0804 or larger. The larger the components the better they tolerate certain kinds of problems. But silk lines crossing over pads is no-no.
I do some informal advising of college students who always make their pcb no bigger than necessary. They can build them, BUT troubleshooting is nearly impossible and rework is TRULY impossible.
Make the outline 2x bigger. Add test points, a place to clip a scope Gnd.
The fab layer with ref des under the device are useless on thesilk layer. You need to be able to read those out in the field where all you have is a paper schematic.
College kids learn those lessons when their solar car is dead in the middle of the Australian outback! Lucky you getting all this advice for free!
I get your point - this is normal for SMD PCBs. I just reduced and centered the reference silk text; since all elements are to be soldered by hand. Because I do not intend to learn another plugin just for this project (and possibly another in a few years).
Yes, all the elements are very stuffed and there are no mounting holes - and that is intentional. I’m building a DCC turnout decoder and it needs to be as small as possible.
I have learned that designing a PCB with KiCAD is not such a big deal. Yes, I like it and I will definitely repeat the process if I came across an idea worth designing my own PCB in future. So it depends…
In most cases I do my circuits, even final versions, using prototype PCBs. Just isn’t worth paying PCB manufacture (or shipment from China) for a single item.
It is possible, but the result is that you’re looking at a PCB during design that is not going to be the same like when you are going to order it, and when you get used to looking at that PCB it also becomes easier to forget to tick that box when ordering PCB’s, which may result in silkscreen actually being painted over pads, which is quite a nuisance.
