Topmetal-S sensor tiled plane

PCB

We use KiCad and python script to generate schematic, footprint, and PCB layout with minimal manual intervention.

Procedure:

Schematic

1. Draw a Topmetal-S schematic symbol and save in a SCH library TMSch.lib. TMSch.lib is symlink-ed to every project. When modifying the library, open the original ```.lib''' file directly instead of opening the symlinks.
2. run GenSch.py to generate desired schematic for the TMS array with correct net connectivity. Here we save the generated file as array.sch, which is a 2nd-level hierarchical schematic under Phi10cmBonding.sch.
3. Open Phi10cmBonding.sch and generate a netlist.

PCB

1. Run KiPcbFp.py to generate a footprint TMS1mm.kicad_mod and save it under TMPcb.pretty which is a footprint library. One may need to modify ~/.config/kicad/fp-lib-table in order for KiCad to find the library: (lib (name Topmetal)(type KiCad)(uri ${KIPRJMOD}/TMPcb.pretty)(options "")(descr "Topmetal bonding footprints")). An alternative is to save a local fp-lib-table file in the project directory.
2. Use pcbnew manually to setup a PCB `template' with appropriate layer structure, via and track classes etc. Here we call the template template.kicad_pcb.
3. Draw trace connections within a single footprint using a copy of the template PCB. Save the single chip SCH and PCB as TMS1mm1chip.{sch,kicad_pcb}. It is preferable to place TMS1mm module's center at the very center in the unit cell. It will be used as a reference (local origin).
4. Make a copy of the template PCB and load the netlist into it. This step will bring all footprints into the PCB.
5. Run GenPcb.py which references the netlist-loaded PCB and TMS1mm1chip.pcb, and generates the correctly laid out array.
6. Remember to press `b' in pcbnew to (re-)fill zones.

Software

KiCad

Pull source from https://github.com/KiCad/kicad-source-mirror and compile.

KiCadScript in Hardware/PCB/KiCadScript/

Run scripts in Pcbnew's python shell:

import os, sys, runpy
scriptPath = os.environ['KIPRJMOD'] + "/../KiCadScript"
sys.path.append(scriptPath)
sys.argv = ['', '-h']
fileGlobals = runpy.run_path(scriptPath + "/GenSch2ExDAC.py", run_name="__main__")

Compile C source code to be used in python

cd KiAuto/hexlib/
python setup.py build
cd build
ln -s lib.freebsd-11.0-STABLE-amd64-2.7/hexlib.so .

KiCad schematic sheets and netnames

KiCad schematic sheets are organized hierarchically. Sheet paths are named as /58F9164E/58F91649 with the numbers being timestamps in hex format. Netnames local to a sheet start with a leading /. Global netnames do not have leading /.

PCB design and manufacturing

Manufacturer capabilities

Sunstone capabilities

	Sunstone preferred	Sunstone capable
minimum drill size	0.008"	0.005"
minimum trace width	0.004" 1 oz Cu	0.003"
trace clearance	0.004" 1 oz Cu	0.003"
through-hole pad dia	0.018" larger than finished hole dia	0.016" larger

Finished hole dia = drill dia - 4mil

Typical board thickness in inch

0.062, 0.093, 0.125, 0.0886(14-layer), 0.0756 (16-layer)

1oz copper thickness is 34um (1.34mil)

Typical drill sizes diameter in inch

0.008, 0.014, 0.020, 0.025, 0.029, 0.033, 0.035, 0.040, 0.043, 0.046, 0.052, 0.061,
0.067, 0.079, 0.088, 0.093, 0.100, 0.110, 0.125, 0.141, 0.150, 0.167, 0.192, 0.251

For boards thicker than 100mil, usually drill size cannot be smaller than board thickness / 10 (aspect ratio).

Via

A recommendation: make the drill size diameter the same as the width of the trace, and the pad size roughly twice the diameter.

Impedance

width/clearance 6mil/6mil and 4mil/4mil on surface layers, 4mil/7mil and 4mil/10mil inner layers are commonly used for Zo=50Ohm, Zdiff=100Ohm.