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:
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:
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:
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.
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!

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

Back to PDMS casting Index

3- Plasma bonding

Modding a microwave
Modding a microwave

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

Amount of time: 2 hours.

Total costs: 50 €.

Disclaimer: Modding any devices that plug to the wall socket is very dangerous. If a capacitor is discharged thank to your body, it may result harmful for you. Keep an eye on this.
1. Check the content online, as this or this videos. Many sources of information can be found online. You may find online a better arrangement than the one that we suggest. Although it has worked for us, there is no better understanding than the hands-on experience.
2. Unplug the microwave.
3. Remove the chassis of the microwave.
4. Saw what is necessary for opening a hole that enables the vacuum hose to get into the microwave.
5. Prepare a recipient for the PDMS chip that you want to treat. We drilled a hole into the Borosilicate Glass Narrow Neck Laboratory Bottle and glued a plastic hose adaptor.
6. Connect the hose to both ends: the recipient inside the microwave, and the vacuum pump.
7. Check that the vacuum circuit has no leaks. Plasma needs approximately 1 Pa to pop up. Vacuum pressure is a critical parameter. Make sure there are no leaks within the air circuit.
8. You are ready to proceed to the next step and calibrate the microwave (if it makes sense after all).
Calibrating the microwave
Calibrating the microwave

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

Amount of time: 2 hours.

Total costs: 1 €.
1. CBefore even thinking about treating the PDMS, make sure that the plasma is generated successfully. You just need to test the whole display without PDMS inside the bottle. Calibrating the microwave means knowing how the it works experimentally, so take a pen and a paper.
2. You should make a chart with some parameters as:
3. Sparks will help to generate the plasma inside the bottle. In this regard, you need to place some aluminum foil inside the bottle. Measuring the required amount of aluminum foil is key for the experiment to succeed. We cut pieces of 20 x 20 mm of aluminum foil and use them as our arbitrary building blocks of aluminum foil.
4. First, you need to get some sparks out of the aluminum foil. If you get no sparks, add more aluminum foil, or increase the power. Take notes about how it behaves.
5. Once you get some sparks it is time to generate plasma. Vacuum pressure is key. 1 Pa was recommended. We were limited by the resolution of our manometer. We could only read 755 mmHg as (negative) relative pressure. We have no certainty about the actual value of the pressure.
6. You can use a glass of water to absorb any excess of energy. Note how water affects the experimental arrangement.
7. Once the treatment is done, the borosilicate bottle should not exceed 150 ºC. Test it with an IR thermometer gun.
8. Once you are happy with the experimental outcome, you should proceed to the next step and bake the PDMS.
Baking the PDMS
Baking the PDMS

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

Amount of time: 2 hours.

Total costs: 0 €.
1. This protocol repeats the protocol before, with the exception that now we use the PDMS and the glass and analyze the new results.
2. Although plasma will fill the bottle, you need something to separate the PDMS chip and the aluminum foil. You do not want the PDMS to burn, as it will notoriously change its properties. Glass will prevent the PDMS to burn.
3. Make sure that PDMS and aluminum foil are separated by a glass plate, or any other glass surfaces that you might have at hand.
4. Follow what you have learned in the previous step and bake it.
5. Once the treatment is done, test the hydrophobicity of the PDMS, placing a drop of water on its surface. A treated PDMS chip should be hydrophilic. And a burnt chip will be absolutely hydrophobic
6. You should elaborate another chart with the relevant information about the process, studying the surface tension of the PDMS with respect to a drop of water.
7. Once the surfaces have been treated, they should be joined together immediately, and leave it a few hours to get the desired effect.
8. Two surfaces have joined when the bonding is strong enough to be broken before the surfaces are split up.

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

Team:Madrid-OLM/ProManufacturing

Manufacturing Protocols

Chip

1- Mold making

Laser engraver hacking

Software workflow

Calibration

Cutting

2- PDMS casting

Preparing PDMS

Making a vacuum pump and vacuum chamber

Degassing

Polymerization process: curing time and heating

3- Plasma bonding

Modding a microwave

Calibrating the microwave

Baking the PDMS

4- Closing the microfluidic circuit

Assemblies