Team:Madrid-OLM/ProManufacturing

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Manufacturing Protocols

Texto de explicacion/ resumen de la pagina.

Chip

1- Mold making

• Laser engraver hacking

  Laser engraver hacking

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 3 hours.

  Total costs: 100 €.

  The laser usually come with a proprietary software that only allow you to engrave images. As the chips are going to be cuttered as a vector we’ll need to install a new laser firmware (into the laser) to be controlled with other software (into the PC connected to the laser).

  1. Check if your laser could be directly flashable (flash = installing the new firmware) in this link.If the answer is yes, skip to the “software workflow” step. If the answer is no, just continue reading.

  2. When the Arduino UNO and the CNC Shield with the drivers arrive, substitute the old electronics of the laser with the new ones following the tutorial of the previous link. The software that you will need to follow this tutorial will be:

  1. The official Arduino IDE that you could find in their own page.

  2. The open-source laser firmware (GRBL). You could find the version that we have used (v1.1) in our GitHub repository.

  3. TThe program which control the laser and is going to send the designs from the PC (Universal GCode sender). You could find the version that have worked with us in our GitHub repository (same link as the previous step).

  CAUTION: We have uploaded a different version of the laser firmware to the one described in the tutorial. The only connection that you have to do differently is connecting the laser to Z+ pin instead of SpnEn.

  Disclaimer: The programs that we have used in these step are not developed by our group and are hosted in our Github just to keep the version that have worked for us.

• Software workflow

  Software workflow

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 2 hours.

  Total costs: 0 €.

  1. You only need two applications to run your laser engraver:

  • Inkscape (for creating the design and and the.gcode file). A .gcode file stores the required machining orders for the laser to cut the designed geometry.

  • Universal Gcode Sender (send the .gcode file to the Arduino).

  2. In order to create the shape of your microfluidic chip, you need to have a feasible design. There are many open software applications, as:

  • DraftSight (2D): although you could design directly with Inkscape, an specific software for design may result handy at some point of despair.

  • Freecad (3D).

  CAUTION: Alternative versions of a .dxf file will not be imported successfully.

  3. If the design is made in a software different to Inkscape, you should export the file as a .dxf file (R2013). Inkscape can import this sort of files.

  4. Once the design is created and imported into Inkscape, you should place it within the canvas with the required proportions. For NEJE laser engraver, the dimensions of the bed is 38 x 38 mm. You should find how Inkscape work area relates to the effective area of the bed.

  5. Once the dimensions have been corrected and fixed, you should convert the lines to a “path” format, clicking in the “path” tab and selecting “stroke to path”. We have tried to omit this step, and it seems it does not matter skip this step.

  6. Click on “extensions” tab and select “generate laser gcode”, and set the cutting parameters. These parameters should be set experimentally. Speed, laser power, passes vary depending on the specific tape selected, or the surface where you stick the tape. We encourage you to set your desired parameters, based on your specific scenario.

  7. Once the .gcode file has been successfully created, open the Universal Gcode Sender and and set the ports and baud rate (115200 bps).

  8. Now you need to set your “Zero machine coordinates”. From “Machine control” tab, move the X- and the Y- to the coordinates that you want to set as (0,0). And click on “Reset Zero”

  9. Import the file. (File mode tab -> Browse). And finally send it to the laser engraver.

• Calibration

  Calibration

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 2 hours.

  Total costs: 10 €.

  There are three factors that you should consider for calibration purposes:

  1. Choosing the tape: Depending on which depth of channel suits your needs, you should choose one tape or another. Cutting parameters should be established by each user, according to their particular needs.

  ADVICE: We are using brown packing tape. The deep of the tape is 50 microns and the parameters that have fit to us are the following: Travel Speed 200, Laser Speed 50, Laser Power 12000, Power-On Delay 0, Passes 2, and Pass Depth 1.

  2. Calibrating the dimensions of the Inkscape canvas: we highly recommend you to know the correction factors to apply to your design. A good practice should involve (for instance) designing a 10 x 10 mm square in Inkscape and send it to NEJE laser engraver, and measure it afterwards to know exactly how dimensions translate between software and manufacturing hardware.

  3. Getting to know the effective work area of bed of the NEJE laser engraver: if you set the laser over the Zero-machine coordinate, and the, in the “command tab”, you insert the command s01, and M3, you should see how the laser turns on. If you click on X+ or Y+, you should be able to navigate over the edges of the bed, and thus, determine (and engrave) them onto the bed or any other surface that you might consider.

  Disclaimer: The programs that we have used in these step are not developed by our group and are hosted in our Github just to keep the version that have worked for us.

• Cutting

  Cutting

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: Depending on the project

  Total costs: less than 5 €.

  Although cutting is a pretty straight forward process, please, take this advises into consideration:

  1. Mind your eyes: Please, do not hesitate to use the safety glasses devoted to look to the laser.

  2. Use your final polymerization surface to support your tape: we have used an acetate sheet that fits in our final polymerization chamber. Ensure your surface are horizontal and without bubbles between the tape and itself. Lifting off the table from the surface in which it has been cuttered may cause the deformation of the original pattern.

  3. Chlorine content in many tapes: As many tapes contain a remarkable amount of chlorine, we advise you to cut in a ventilated place and to avoid inhaling this.

  4. Enjoy not always you get the results that you are planning. Take the time to set your arrangement and enjoy this process!

Back to Mold making Index

2- PDMS casting

• Preparing PDMS

  Preparing PDMS

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 1 hour.

  Total costs: 120 €.

  1. Working with PDMS require tidiness and cleanliness. It is mandatory to have a clear work space and dedicated hardware, as pipettes and recipients specifically devoted to mix. You will need gloves and cover your clothes (if you barely do care).

  2. Mixing PDMS with the curing agent require that you follow the following weight ratio: 10:1 (PDMS/curing agent).

  ADVICE: Note that for many purposes, you may want to vary this proportion. Adding more curing agent will affect the final outcome, as it might be stiffer. Depending on your purpouse you shold adjust this proportion experimentally.

  3. Mix it with the stirrer. Many air bubbles will appear as a result of this. You want to bring them out for the PDMS chip not to be porous.

  4. Pour the mix into a recipient that fits into a vacuum chamber

• Vacuum pump and chamber

  Making a vacuum pump and vacuum chamber

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 3 hour.

  Total costs: 20 €.

  1. First you need to modify the compressor into a vacuum pump. To achieve it, we recommend consulting the following video

  ADVICE: The time spended in the degassing process depend on the strength of your vacuum. For fast degassing (and also for making larger vacuum chambers) consider to spend a little more in a better vacuum pump. The ones from air conditioner systems works well for almost any purpose and fits well for the next plasma treatment steps.

  2. Once you have converted the compressor into a functional vacuum pump, you can create a vacuum chamber. Please, take into account that the vacuum chamber should be able to accommodate the recipient where the PDMS, the curing agent and the army of air bubbles are.

  3. You might want to provide your vacuum chamber with a venting valve for pressurizing the chamber alternatively, as we explain in the following point.

  4. You should seal every possible leakage with PTFE tape. Air leaks are not desirable, and your duty is to avoid them.

• Degassing

  Degassing

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 30 minutes

  Total costs: 0 €.

  1. Degassing involves extracting the air embedded in the mix of PDMS and the curing agent. First you need to place the recipient which holds the mixture of PDMS and bubbles inside the vacuum chamber.

  2. Turn on the pump. The vacuum pressure provided by the pump is more than enough for our purposes. Leave it for 20 seconds and you will see the bubbles migrating towards the surface.

  3. Once a significant amount of bubbles has moved towards the surface, let the airflow inside the vacuum chamber. Many bubbles will burst, and thus the air will be successfully extracted.

  4. Repeat the process enough times to remove all the trapped bubbles.

  5. Once the PDMS is homogeneous, you can pour the mixture into the polymerization chamber, where you are planning the PDMS to cure.

  CAUTION: If you do not want to trap air bubbles when pouring the mixture , do not rise the recipient. Pour it as close as possible from the bottom of the polymerization chamber.

• Polymerization process

  Polymerization process: curing time and heating

  Bill Of Materials: You could see a complete BoM here (upload the bill).

  Amount of time: 1 hour.

  Total costs: 0 €.

  1. This is the final step of the whole process. Once the PDMS is ready to cure, you may want to have the material ready in an hour, or maybe you can leave it curing overnight.

  2. If you place the mixture inside a drying oven (65ºC), your PDMS will be cured in just half and an hour.

  ADVICE: The relation between time and temperature varies, but it seems to be linear. Although this relation seems to vary from one commercial brand to another. 24 hours of polymerization should be enough at room temperature, but sometimes it is not enough. Test it experimentally with a small PDMS quantity.

  3. Elaborate a chart with the parameters that suit your needs better.

  CAUTION: When heating, you should take into account the materials of the polymerization chamber. Mind the temperature, as an excess of heat may melt the materials of the polymerization chamber.

Back to PDMS casting Index

3- Plasma bonding

• Modding a microwave
• Calibrating the microwave
• Baking the PDMS

Back to Plasma bonding Index

4- Closing the microfluidic circuit

• Choosing the pump, the tubing and the connectors
• Troubleshooting the leaks

Back to Closing circuits Index

Assemblies