A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich structure of conductive and insulating layers: each of the conductive layers is designed with an artwork pattern of traces, planes and other features (similar to wires on a flat surface) etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate.
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Producing our own electronics allows us to customise it to meet product requirements and the footprint for the product. It also improves reliability while improving product integration and ability to prototype with faster iterations.
I will be using the StepCraft CNC Machine to mill out my PCBs.
The first step is to prepare the raw test file which can be downloaded here. The numbers shown are in inches with the smallest width being 0.001" (aprox. 0.025mm). We will need to turn the png image into a ns file which is the machine readable gcode format. This can be done by importing the image into the mod website via the following steps:
It should look something like this:
With reference to the image above:
Before milling, it is good practice to perform simuation check to ensure everything runs accordingly. For this, ncviewer can be used. The steps are as follow:
After running the simulation, the next step is to prepare the CNC machine. In general, there are 2 types of drill bits; flat and angled. The flat is used primarily for milling out the outline whereas the angled is used mainly to mill out the traces of the PCB. It is also important to note that milling out the traces should come before milling out the outline.
Flat | Angled |
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With some double sided tape and a pen knife, we can secure the copper board onto the sacrificial board. We can then secure the drill bit onto the machine using a wrench and we can then set up the UCCNC software used by StepCraft. After initialisation is completed, the required g-code file is loaded into the software. The next step is to set the drill position to the desired position (indicated by the yellow dot on the screen). The X and Y positions are set by moving the drill to the desired starting point followed by clicking the X and Y zero buttons. For the Z-direction, the touch sensor probe is used. The diagnostic tab is first activated to check if the probe is connected and operating properly before the calibration in the z-direction is carried out. Once everything is set, the drill is switch on and the milling operation is started by clicking on the "Cycle Start" button twice.
Going from right to left, the air-gap and the trace were both visible and well defined from 0.02 inches to 0.016 inches. For 0.015 inch, the trace was nicely cut but the air-gap is completely missing. The limit of the CNC machine using 0.4 mm flat end drill bit is hence 0.016 inches or 0.4064 mm, which is the same as the diameter of the drilling bit.
With the skills learned and picked up from the group assignment, we will now proceed with making 2 boards (FTDI and UPDI) so as to allow an in-circuit programmer to interact with a computer to be programmed. The trace and outline used can be found here:
Important to note that mill outline is selected in step 2 for the FTDI/UPDI outline. The cleaning up and preparation process of the PCB for soldering will be explored further in Electronics Design. For now, we will first cover on the soldering. Soldering on the PCB is done using Surface-mount Technology (SMT) where the components are attached and connected to the surface. Having a soldering station with a micoscope will help significantly with the soldering process. To solder SMT components, it is advisable to first lay some solder on one tab of the PCB which will be attached first to one of the legs. After you have finished soldering both the FTDI and UPDI board, it should look something like this: