week_04

Electronics production

Objectives



Assignments



Characterize the design rules for PCB production process


For this week’s group assignment, I had to characterize the specification of my PCB production process on our small CNC milling machine (Roland SRM-20).


Roland SRM 20


The machine in my lab is Roland SRM-20, The Machine Specs are as follows:

  • Work Envelope: - X axial: 200mm, Y axial: 150mm, Z axial: 50mm;
  • Speed: - ~8000 RPM;
  • Default collet size: - ~6mm;
  • ...
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    G-code


    I have learned the tool that help to convert monochrome PNG file into G-code, and also I have learned the software of NX UG. The main requirement is that there should either black or white parts of on the picture. The white parts will be stay, and the black parts will be cut out by the mill. Therefore, it is important to keep the distance between significant enough so that the endmill can go between two white parts.
    ① Choose select PNG file. I loaded my picture of my mill traces.
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    ② Choose the output format, as roland mill. Then I clicked on the third labeled option mill traces 1/64.
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    ③ Then, I go to the box that is label as Roland SRM-20 milling machine. This boxes label as X, Y, Z axial are very important. So, some of the setting selected for the PCB traces are:

  • Origin: X axial =10, Y axial=10, Z axial=0.
  • Z Jog: 3mm (means that the machine will lift the tool 3mm while not cutting).
  • Cut Depth: 0.1mm.
  • Offset-overlap: 50%.
  • number of offsets: -1.
  • ...
    ④ I go to click on calculate. This option calculated my toolpath for the machine to raster my trace.
    ...
    ⑤ Finally, The machine is ready now just click send and the machine will start to cut.

    Sacrificial layer


    What you put on top of the machine in order not to break the tool. It is located on top of the work plate to protect the tool. Also, the Sacrificial layer needs to be level, otherwise when you are cutting your circuit it won't cut the deepness to the same level. So, I milling the sacrificial layer with a 6mm endmill to ensure the plane level.

    ...

    Result


    This is the result of the test:

    Individual assignment


    I choose the model of Brian with consist of Attiny45 microcontroller from Atmel, nowadays from Microchip.The model of Brain needed materials are:

    1x ATtiny45 or ATtiny85
    2x 1kΩ resistors
    2x 499Ω resistors
    2x 49Ω resistors
    2x 3.3v zener diodes
    1x red LED
    1x green LED
    1x 100nF capacitor
    1x 2x3 pin header

    The schematic and PCB board are:

    ...

    G-code


    ① Used Fab Modules. First, I download the traces image from Website. Then I imported the traces image, the image is in PNG format, with only black and white lines.
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    ② I Choose the output format, as roland mill. Then, I choose the process, which is milling the traces.
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    ③ I choose the machine’s model I’m using for milling, which is SRM-20. I also need to zero point of the endmill by adjusting the values of the X axial and Y axial. The toolpath was generated for an offset of 4, which is the number of times the endmill will be milling the copper around the trace.. I finally press calculate to generate the toolpath and save the toolpath code.
    ...
    ④ Then, I will import the outline image to Fab Modules. I repeat the process as above but this time I choose the outline process instead of the traces process.
    ...

    Milling


    ① I fix the PCB to the milling machine plate use double side tape. I need to make sure that tape layer is smooth with no wrinkles. The surface of the material must be parallel to the x and y-axis of the machine.
    ...
    ...
    ② I used a 0.4mm endmill to engrave the traces on the material surface and a 0.8mm endmill to cut through the material.
    ...
    ③ First, I need measure the workpiece coordinate system, that is setting the origin of X axial, Y axial and Z axial(the method of try cutting).
    ...
    ...
    ...
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    ④ Click on Cut to output the file to the miller. You are all set.

    ⑤ Remove the material from the material bed slowly with a palette knife. Then remove the double-sided tape on the back of the material. Then, clean the copper face of the board with alcohol to retrieve traces of grease.

    Soldering


    ① Wet the sponge for cleaning the tip of the heater.
    ...
    ② Cut the a piece of solder from the roll to work better with it. My solder should not be thick particularly for this project, because it is a small component.
    ...
    ③ Start with soldering the components from starting from the middle of the board (ATtiny45), then I go to the next near to the board’s exterior. I must note the components that installed in the correct orientation:
    A. The zener diodes are marked, both in the drawing and on the packages, with a line on the cathode side.
    B. The LED cathodes on the PCB drawing are marked with dots and thicker lines. Package marking conventions differ between LED manufacturers, but there is usually a green or black line visible on the cathode side of the epoxy lens. Some LEDs have an extra copper marker on their cathode pad on the bottom. Some print a small arrow on the bottom, which corresponds to the schematic symbol: the arrow points towards the cathode. If in doubt, you can use a multimeter in the diode check mode; the LED will glow slightly when the red probe is on the anode and the black probe is on the cathode (this is also useful for determining color).
    C. The ATtiny45 marks pin 1 with a dot laser-etched into the corner of the package. Pin 1 is marked in the drawing with a dot as well.

    ④ Final Product

    Programing ISP (Windows)


    I followed the routine on Brian’s page.
    ① Install the Atmel GNU Toolchain.
    Download the Atmel AVR Toolchain for Windows from Atmel's site and run the installer.

    ② Install GNU Make.
    Download Gnu Make and launch the installer. Accept the default location for the installation.
    ...
    ③ Install abrdude.
    Unzip the archive, and copy the archive inside to C:\Program Files.

    ④ Update my PATH.
    Now we need to tell Windows where to locate all of the tools you've just installed when you type their names on the command line. Go to the Start menu and open the Control Panel, then go to System. From the left pane, choose "Advanced System Settings". Under the Advanced tab, click the "Environment Variables" button.
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    The three values to add are:
    C:\Program Files\avr8-gnu-toolchain\bin
    D:\Program Files (x86)\GnuWin32\bin
    C:\Program Files\avrdude
    ...
    ...
    ⑤ Install Drivers for my Programmer
    Download Zadig and launch it. Plug in your programmer, and select the "USBtinySPI" device in the list. (If it doesn't show up, go to the Options menu and click "List All Devices". The driver you want to install (to the right of the green arrow) is either libusb-win32 or libusb0. Click the "Install Driver" button. You should only have to do this once.

    ⑥ Sanity Check
    Everything is now installed. Let's check that it all works.Go to the start menu and search for "Git Bash" and start it. When you see instructions telling you to open your terminal in other tutorials, this is the terminal window you should use. Check to make sure that the commands we installed work okay.

    contact Me


    Address: No.10, Kehua street, Wuhou District, Chengdu, Sichuan Province, China
    TEL: (028) 85406538 (+86)18981085882
    E-mail: linzihao@scuspark.com
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