Week 08: Electronic PCB Production

Assignment

Group Assignment

Characterize the design rules for your in-house PCB production process: document feeds, speeds, plunge rate, depth of cut (traces and outline) and tooling.
Document the workflow for sending a PCB to a boardhouse
Document your work to the group work page and reflect on your individual page what you learned

Individual Assignment

Make and test a microcontroller development board that you designed

Learning Outcomes

Described the process of tool-path generation, milling, stuffing, de-bugging and programming
Demonstrate correct workflows and identify areas for improvement if required

Hero Shot

Process Documentation

This is the schematic I created for the lamp with PIR sensor which is the basis for my PCB schematic

Once we have the kicad file of our board we must export it as a pdf. I exported the file from kicad.

I went to file, then Print and a box pops up. I made sure to include my Copper Layer as well as the edge Cuts and then clicked on Print.

The exporter processes the file into a pdf format

In Pdf format all the different parts of the PCB such as the traces, holes, and outline are all bunched together. So from here we must separate the files into their respective layers and create PNG files – from there we take those PNG files and slice them in modsproject.org which is an online PCB slicing software.

When the Pcb is cut, different layers will need to be cut with a different end mill and therefore in a different order. We use software such as Illustrator or Inkscape to create the layers in different files.

As you can see from the screenshot I created several layers on the right. I have an outline layer, a hole layer, a Copper/Traces Layer and a background, a copper (traces) layer, an outline layer, a background and Layer 1. Initially we select all and all the paths go into Layer 1. Step by step we highlight the holes and put them into the holes layer and then the outline, traces and create a background too. So by the end, Layer 1 will be empty and the other layers will have their relevant paths in them.

If we start with holes for example, we find a hole and right click to 'select similar' which highlights all the other holes – we then move to layer.

Once all the layers are ready, we want to export each layer to a PNG file to slice.

First we select the holes layer and make sure the background is white and the holes are in black and we export as a PNG.

Then we create a black background and a white body for the Outline PNG.

Finally we create a Png file from the Traces layer with traces in white and background in black

Slicing Process

Now we are ready for slicing and go to modsproject.org, then right click and click on 'programs'

Then click on 'open programs'

Then we choose our specific machine which is an Roland SRM-20

This takes us to the Slice page

First, we click on 'Select PNG file' and select our chosen file, in my case, 'Traces' from the folder.

The page should look similar to this:

Next we click on 'Mill Traces' so the slicer knows that we will be milling the copper traces

Our 'Mill Raster 2D' setting should have a Cut Depth of 0.15mm and Max Depth of 0.15mm instead of the outline or holes setting of 0.696mm for cut depth and 1.82879mm.

Then we alter the speed setting to 2, and X,Y,Z co-ordinates to 0. Finally we activate the auto-save feature.

This is how it should look

and then we click on Calculate to generate the RML file (sliced file)

This is how the RML should look

Then we send the three files that we have done for Traces, Outline, and Holes to the SRM-20 PCB Mill and save them to Downloads.

We work on the traces first, then holes and finally the outline. The workflow is intuitive as the traces will have very shallow engraving, then deeper holes will be made and finally an outline will be cut out. We could not do it in another order as any other layer after outline might move around a lot.

We look for the drill bit that we need. It will be 1/64th mm size for the traces and 1/32th for the holes and outline.

PCB Milling Process

Roland SRM-20 in action milling my chip

Final Results

How it looked when finished

Removing the Endmill to put back in its box

Downloadable Files

Individual Assignment - Make and test a microcontroller development board that you designed

This was my first time soldering a board, testing and looking at it closely. 80% of the issue was not having the right magnifying equipment and 20% of the difficulty was identifying what to do.

Firstly I'd like to say that soldering is for me an immensely relaxing and enjoyable process.

We have our soldering iron which we turn up to a temperature of around 400c

In the second image notice the yellow pad and curly metallic looking material below the soldering iron….we rub the tip of the iron into that metallic looking material to clean it and then press it on to the wetted sponge to make sure the iron is clean and clear.

In the picture below can be seen the solder that we use. It is called Rozin solder and is hollow 60% tin and 40% lead. Inside the hollow is flux which is a chemical that helps strip an oxidative layer from the solder so that it can be more malleable and easily attach to the PCB.

I also like to have some actual flux nearby just in case although I tend not to use it

Finally, the incredibly useful desoldering strip which can be seen in the image below. It is very useful if one has applied too much solder and created a short, or one needs to clean up the PCB. I used it a lot!

Another worthy mention is the mini extraction unit which helps to gently suck out all the noxious fumes that are released when soldering. It can be seen to the left of the picture with a shot of me soldering

After I completed the soldering Adai sat with me and showed me how to test the PCB with the multimeter. It was my first time doing so and I found it quite hard to see the board perfectly. The explanation was very helpful though I am personally in the 'I feel like I've landed on an alien planet' stage. I am hoping to get much more exposure to this.

The final chip

Now I have the final chip I need to flash it for the first time using a bootloader.

Just as I wrote this I realised that I broke off the connector that I needed for this bootloading operation. I have been carrying it around with me for over a week.

I'm quite peeved as I was looking forward to finally being able to do this. If you look closely at the image you can see at the top that broken 4-pin connector and the space missing on the chip

So it turns out that for my final project I will need one or two other connectors on my PCB for a dimmer control, potentiometer control, and enlarging the board before soldering all the components back onto the chip. I will be working on it this weekend and hope to have figured it out - I think i can do it although it takes me a while to process the information and apply it.