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1. Group Assingment

The full group assignment can be found here

For this week assignment we looked at two processes:

For the milling process we used the:

LUNYEE All-Metal 500W CNC Router Machine

Specifications:

  • Working area: 300x180x80mm
  • Machine size: 485x415x374mm
  • Spindle: stnd configuration: 500W 10000 r/min
  • Machine accuracy: +/- 0.1mm
  • Max speed 5000mm/min
  • Max cutting speed 2000mm/min
  • Power supply 48V 500W

This machine is suitable for milling: wood,bamboo,acrylic,plastic, PVC, ABS, PCB, brass and resin.

I general terms, the machine is composed of three axles to displace the milling bit into three directions. In the machine we have two pole terminals (+ and -) that are useful in determining the probe depth. One of the ends is attached to the head of the milling machine and the other other the board. Once the tip of the bit touches the metal plate it will complete a circuit, record the actual depth of the board surface.

Below we can find some safety guidelines:

  • Be aware where the stop button is.
  • Use appropriate goggles when operating the machine.
  • Use appropriate breathing protection given the material you are cutting.
  • If you have long hair tied it back.
  • Do not use gloves as they can get caught in the spindle.
  • Ensure proper ventilation
  • When changing bits disconnect the machine.
  • Make sure clamps are well fastened.
  • Make sure there is no wiring in the cutting area for example remove the probes terminal before cutting.
  • Double check that you have the right cutting area.
  • Stay close by the machine while there is a ongoing cut job.


For engraving in the second process we explored we used the following laser engraver.


ComMarker B4 MOPA 60

Specifications:

  • Laser Source: MOPA-JPT
  • Laser Power: 60W
  • Laser Wavelength: 1064nm
  • Engraving Accuracy: 0.01mm
  • Engraving Speed: 0-15,000 mm/s
  • Frequency 1-4000 KHz
  • Pulse Width: 2-500ns
  • Work Area: 110mm x 200mm dual lenses
  • Primarily designed for engraving metals and plastics
  • Can cut Stainless Steel, Aluminum, Brass, Copper, Silver and Gold.

In this page you can find a blog that describes the advantages that a fiber laser engraver have for PCB engraving. Below you cand find a short summary of this article.

The high precision laser technology of a fiber laser engraver allows to etch, cut and mark the different layers of a printed circuit board. Some specific advantages are:

  • High Precision and Accuracy to achieve fine detail.
  • Efficiency and Speed resulting in faster processing than traditional methods thanks to high speed galvo technology.
  • Versatility: that allows processing several types materials.
  • Auto Focus Technology: Allows adjustments based on material thickness and variations in the material surface.

This is a laser cutter that uses the MOPA technology i.e Master Oscillator Power Amplifier. This technology has a much wider frequency range than q-switch machines and it can also control the pulse width parameter enabling the control of the individual laser pulses.

In the fields of Electronics, Semiconductors, and ITO Precision Machining achieving precise lining is often essential. However, a Q-switched fiber laser struggles with this task due to its fixed pulse width. In contrast, a MOPA fiber laser, with its adjustable pulse width and frequency, effectively delivers smooth edges and precise results. Mopa Fiber laser has a tunable wdith which facilitates small laser spot and tunable energy (source: link)

Steps for engraving a PCB:

    1. Design Circuit Diagram
    1. Input the Circuit Diagram into EZCAD in our case we have a version of Lightburn.
    1. Set Parameters power, speed, and frequency
    1. Preview and adjust position and size
    1. Initiate the laser engraving process.
    1. Check the result.

Safety

These are some complementary safety guidelines to the ones that were described in week 3 as this is very powerful and potentially dangerous machine from the manual:

  • Laser Safety
    • The machines use Class Ⅳ lasers. The lasers are very powerful and can cause eye injuries and burnt kin. It is recommended to wear laser goggles when using the laser engraver.
    • Avoid exposing your skin to Class IV laser beams, especially at close range.
    • Do not touch the laser engraving beam while it is switched on.
  • Material Safety
    • Do not engrave materials with unknown properties.
  • User Safety
    • Use this laser engraving device only in accordance with all applicable local and national laws and regulations.
    • Use this device only in accordance with this instruction manual and engraving software manual.
    • DO NOT leave this device unattended during operation.
    • Cut off all power to the machine and contact either our customer service or repair service if anything seems to be working abnormally
    • Any untrained personnel who might be near the device must be informed the danger of the machine before operation

Some of this are scary that they need to put them.

Generating files in Kicad

One goal for this week was to simulate sending the PCB to a manufacturer for this we had to produce gerber files. Gerber files are a collection of files that are useful in the production of PCB’s. In order to generate the Gerber files we go to the file menu and then choose plots. Thereafter, choose the production settings from our chosen manufacturer.

The following video provides a quick description of the steps needed to take to produce a Gerber file that is formatted for the NextPCB board producer.

Generating Gerber Files in KiCad

At this time I could not find which options to choose in Kicad 9 as the interface has changed so there are two ways to go about this, one is to use the defaults the second one is to use a plugin. We start with the former.

File=>Fabrication Outputs => Gerber

The we get the following menu that you may want to modify if you know the correct settings.


As per the video above we use the defaults and select use protel file name extension. In addition, create a directory were you will output your files as it quickly can become a mess. Then press plot and you can see the files in the specified directory.

And then press generate drill files. This is useful if you have to drill some holes in your PCB e.g. for mounting it.

Thereafter, you will need to generate the zip file with all the files created in order to upload them to NextPCB page that you can see below.



And then you upload the zip file



Here you can see the different options chosen and the price of the boards and shipping resulting from the uploaded files.

The other way to do this is to install a plugging for the manufacturing company using the plugin and content manager in Kicad.


Once installed, you can calle it from the menu to verify the options given by the company’s plugin. Therafter, click update price to get a qoutation. You can also press add to cart and this will take you to the compay’s site as before to order the board.




Individual Assignment

Board design and milling/Engraving

The goal for this week was to create a PCB for this purpose I used the board I designed in the electronic design week. Basically the goal of this board is to use it to test an half bridge to us a DC motor. One of the problems that presented was that the board exceeded the dimensions of the board available at the lab. And hence I had to modify the board design to fit these dimensions. I also changed some components and for this use update PCB from schematics tool.

Also, I had to do some modifications as wanted to mount the micro controller on the board as a removable piece and for this there were only pins that alternated from one side to the other.


In order to do this I did a quick fix by modifying the the micro controller footprint from the foot print editor. Note: this is not ideal better to find the right component.



Then, I proceeded to generate some gerber files and used the Png to Gerber online app tool from fab lab Kerala


And produced two files one for cutting and the other one for the traces.


Therafter, in Mods I generated the two corresponding Gcode files. Basically, these files will create the parameters needed for cutting and the paths that the cutting tool will follow.



And thereafter, I imported these files into Candle.

Note here is a website where you can downlaod Candle for Mac: https://bachinmaker.com/?p=73

Mods will produce a Gcode file that will provide the feed and spindle speeds and also the xyz paths that the CNC machine will follow based on the parameter that were input. In the cells one can see what the Gcode is doing in each step. It displays the velocity in the cut case 11000 rpms and 150 mm/s (or 2.5 mm/s). You can see from the file the coordinates in xyz direction that the bit will follow. For the cutting case we had a maximum cutting depth of 1.35 mm and intermediate cutting depths of 0.5 and 1 mm. Note that The board is 1.3 mm.


One can find the specific codes in the following wiki site.

https://github.com/gnea/grbl/wiki

Simmmilarly, for the tracing we had the same values in spindle and feed speeds and a depth of 0.15 mm.


I used Candle to generate a height map to aid the machine to adjust for different heights encountered on the PCB as a result from clamping.


And then I sent the job for tracing. For this we used a 0.4 mm falt end bit. While tracing the board, I broke 2 flat end mill bits.


First, we thought the problem was the feed speed so we reduced it. but later I found out that I had not checked



After this modification we found that no more problems but the job took more than an hour as I did not increase the feed speed (40%) just in case as we had already lost a bit of time.

Below you can find the final board.


Thereafter, I used the ComMarker B4 MOPA 60 laser engraver in order to do the traces i.e. for the second process. I imported an svg file to the Lightburn software which you can see below.


And here you can see the finished board:


I realized that there was a mistakes in the board I designed first, this design is OK for a board with a micro controller that has pull up resistors, if that is the case the case the resistor I placed would have been redundant. I still was not quite sure if this micro controler had this capabilities. So, I modified my board and simplified it a bit and used a pull down resistor. The resulting design can be found below.


I cut the board I produced in the laser engraver with a power setting of 90% with 4 passes. We cutted the produced board with a flat end mill bit of 0.8 mm




On the rush of Friday I forgot to take some pictures of the “naked” last version but found one that had the board only resistors. After I engraved and milled the board I soldered the board.


Soldering

Soldering allows to join two metal surfaces using a filler metal. The metal can be made from alloys including tin-lead, tin-copper etc. In addition to the solder used temperature plays a key role as different solder require different amounts of temperature to melt. The application of heating has to be done carefully to avoid weak joins or damaging the materials that are joint (Wikipedia)

The amount of heat is required depends on the thermal mass of the material

\[ Q = C_{th} \Delta T \] Where Q is the thermal energy transferred, \(C_{th}\) is the thermal mass of the body and the \(\Delta T\) is the change in temperature.

This was the first time I soldered components, it was definetely an experience. Previously, I had watched some videos to prepare myself and on Friday night Mickael show me how to solder in action. Some pointers I got from him was to use a small tip and thread for small components, keep your tip clean. Also show me that after fixing an component that is the first soldering point the next points become easier as the component stops moving. Also using flux might help soldering. Flux is chemical compound that helps prepare metal surfaces for soldering by removing oxides enhancing the flow of solder.



Then I went home with my board and components. On the weekend I was own my own for practice I used a couple of failed boards. Later I tried on my final board. I think I still need to improve but was happy that I was able to attach all the components.



I found the following picture informative on the types of PCB soldering from this blog for future reference (link).


source: circuit specialists
source: circuit specialists


Also some tools that facilitate soldering:

A mat for placing components,

An air extractor to aspire the soldering fumes

And some clamps and magnifying glassess.

Testing

Finally, I decided to test the buttons on the board buttons:

from machine import Pin
import time

buttonA = Pin(8, Pin.IN)
buttonB = Pin(9, Pin.IN)

while True:
    if buttonA.value():
        print("A pressed")
        time.sleep(0.5)
    if buttonB.value():
        print("B pressed")
        time.sleep(0.5)

I also quickly tested a DHT20 sensor, I found this website quite useful as they develop a library for this sensor. The typical libraries are for DHT11 and DHT22.


Key learnings for this week:

  • Using a laser engraver speeded the process a fair bit and is usefull for quick prototyping
  • Soldering skills are key to PCB development and needs a lot of care to avoid damaging components.
  • Now a days is super easy to send board to manufacturers

Evaluation

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

Have you answered these questions?

  • Linked to the group assignment page
  • Documented how you made the toolpath
  • Documented how you made (milled, stuffed, soldered) the board
  • Documented that your board is functional
  • Explained any problems and how you fixed them
  • Uploaded your source code
  • Included a ‘hero shot’ of your board