and I want the surface to be as flat as possible. That’s why I’m asking about vias and how much extra copper they create (if any) on a particular layer of copper they are connect to. I’m guessing that it wouldn’t “double up” the layer? i.e. Copper layer + extra via layer on top? So there’s only ONE layer of copper for each copper layer right?
My layering would be:
-solder mask (everything covered (including vias) except the 0.1 connectors);
-copper
-Fiber Glass
-copper
-solder mask (everything covered, maybe put a hatched grounding plane… is that a good idea?)
Vias are made by adding a copper layer to the inside of the hole? How do they insure that it’s connected to the copper layer it’s supposed to be connected to. I’m just wondering about that side of the manufacturing process. Would I need to use the soldermask to flatten things out by cutting holes around the vias?
If anyone can give me some keywords/terms I should know when reading the kicad manuals I would appreciate. So far, I’ve been told to read up on the “footprint editor”. Any advice on touchpad would be appreciated also.
Making footprints with odd geometries can be tricky, but is doable. In your case, you might be better off making a PNG and then importing that to the copper layer.
Here is a series of videos about making footprints manually in the module (footprint) editor:
And here is a video about importing a bitmap and using that:
The second video is about importing it to the silkscreen layer but it also shows how you can change the layer to the top or bottom copper. You might have better luck with this since you’re trying such a complex pattern.
Through hole plated holes (including vias) are plated, a common thickness is about 0.5OZ (17um). The way they ensure this doesn’t affect the outer layer is that they plate the whole of that too!
So a typical stack up I use for work uses laminate with 0.5oz copper on the outer layers then after drilling and plating the outer layer will be 1oz. This means the outer layer is smooth and has good connection. For most low cost PCB fabs I’ve not had to specify this kind of detail they just do it.
So for your cap-touch design you shouldn’t need to do anything special with vias to get a smooth finish. Keeping them small will help keep the surface from feeling bumpy.
Hi @riqi, did you end up making the PCB for the touchpad?
I’m following your path exactly, and planned to use Kicad to create a touchpad for the MPR121 using the PCB design in the application note AN4600 from Freescale Semiconductor on the MPR121.
If you’ve already made the PCB design in Kicad, could you share it with me? It would save me a lot of time… Thanks.
Its not a hard footprint to make, You would create a square pad of the size you need, rotate it 45 degrees, then keep on adding them to the final pattern shape, you would then number the pads according to the rows / columns, e.g. every pad for column 1 is pin 1, this way when your laying it out the rats nest and unconnected count will show how you need to wire it up.
Thanks.