@User: There is only one option for the sky130 process, and it comes with five metal layers and two MiM cap layers.

ah thank you! to confirm the redistribution and MiM cap layer is not included in the 5 metal layers so 7 layers total?

Take a look at the stackup diagram, the capacitor layers are included but not redistribution

stackup is here: https://skywater-pdk.readthedocs.io/en/latest/rules/assumptions.html

Awesome, thanks for the help!

@Taylor Marsilio: The redistribution layer is not part of the SkyWater manufacturing process; they farm it out to a 3rd party. The 3rd party manufacturer has changed since the documentation, so the documentation on the redistribution layer is mostly wrong. I need to update and correct. But the bottom line is that we want to cut costs by having one set of masks (3 of them) for the post-processing layers, and not have to change those between shuttle runs. This means that users will effectively be banned from using the redistribution layers on shuttle runs.

@Tim Edwards It's good to know that now, because I was going to do some inductors, and I would have put them on RDL had I not read your comment. It might be worth making sure everyone doing radio stuff knows this.

@Chris Jones: You can try to persuade Tim Ansell otherwise. I was in favor of removing the four bump bonds from the middle of the die and using that space for inductor tests. However, keeping costs down seems to be the overriding factor here. Personally, I don't see it as a huge overhead because the masks for the bump bonds are the eqivalent of a 2um process or something like that and are much cheaper than the SkyWater masks. You can try to lobby Tim Ansell with all the great radio projects you could potentially do. Personally, I would prefer to set aside one of the reticle areas with an experimental inductor. Ultimately, even if we decided to do it in the future, I think there is just not enough time for this shuttle.

@Tim Edwards If on subsequent tape-outs people will not have the automatic option of putting more inductors on the RDL, then I'm not going to push to do it this time to characterise/test them. For next time it would be interesting to quantify the mask cost though - individual users might think it worth paying. Anyway, if RDL inductors are not going to happen then it would be good to announce that in #radio so that people have time to adjust their designs accordingly. Provided there is a >=500um diameter region somewhere with no RDL or bumps above it, the Skywater layers are thick enough to make usable inductors, albeit probably a bit worse than the RDL.

@Tim Edwards Great to know, I’ll keep that in mind for my designs. Thank you