Design your credit card in a vector graphics format. I used Inkscape. You can take your existing designs. Convert it into paths. Convert lines into 2D objects (squares, circles etc.). Basically, make sure that everything is a 2D shape with no strokes. No need to design the channels etc. at this stage.

Import the SVGs into your CAD software. I used FreeCAD. Extrude everything by a defined length. I also made a quick macro to refer the extrusion length to a spreadsheet value. That way it is more parametric and you can easily update it. This value is the depth of your visible features (text/logo/QR code).

• For the printed only version: Join (union) all those features. Design a prism (thick paper card) and
  subtract those features. The card needs to be thicker than the features! Features should leave empty pockets on the card.
• For the PDMS version: Join (union) all those features. Design a prism (thick paper card), add some rims/walls* and
  add those features on the surface. The card needs to be thicker than the features! Features should extrude on the surface of the card.
* this piece will be a mold for the PDMS. It should be a container to contain the viscous PDMS until it cures. That's why we need the walls.

Design the channels in a way that it goes through as many edges of letters as possible. Avoid dead ends as much as possible.

• For the printed only version:
  • Single piece version:I ended up using large thicker channels for my printing setup. Otherwise, cleaning single prints was impossible. I had to go in with needles to flush the inside, which required some tiny holes on the side.
  • 2 pieces version: Thinner channels were ok.
• For the PDMS version: I used thin tiny channels and it looked much better that way.

I 3D printed the pieces as usual.

• For the printed only version:
  • Single piece: You have to remove all the uncured resin from the devices. I had to dive in with needles (required some holes on the side) and IPA.
  • 2 pieces version: Usual cleaning and curing.
• For the PDMS version: Extra curing with UVC lamp. You need to find your settings for your lamp. I had a cheap aquarium lamp and needed ~1 h. Use aluminium foils to reflect light around the object.

• For the printed only version:
  • Single piece: Screw your blunt needles gently. These connectors are brittle. Attach the tubings to a syringe and remove all the air and then connect to the device.
  • 2 pieces version: First bond the 2 pieces together with either glue or epoxy resin (like I did). Use tiny amounts and press the pieces together.
• For the PDMS version:
  1. Treat the molds with PTFE spray to prevent PDMS from binding to the mold. I rubbed the PTFE with gloves (safety!!!) all over the mold and let it dry. I removed the excess PTFE gently with a paper towel.
  2. Pour degased PDMS mix (10:1 (curing agent)). I used a shaker for this but people also mix it for ~5 mins by hand. Degas before pouring on the molds (I used a vacuum chamber).
  3. Degas again but make sure that it doesn't spill over. Watch while bubbles come out.
  4. Leave it at ~60-80°C for 24h
  5. Remove the PDMS from the mold (I used a flat blank piece as the second piece).
  6. Puncture the holes for inlets and outlets.
  7. Bond these piece with plasma activated surfaces. I used high setting for 2 minutes then immediately placed the activated surfaces on top of eachother. Then I left the pieces on a hot surface (~150°C for ~1 h).
  8. Prepare a syringe+needle+tubing+pin assembly filled with water and another one with and additional fluorescent dye.
  9. Always remove all the air from the tubings before connecting with the device.

In all cases, always flush the devices with water and get rid of the air bubbles as much as possible. Then switch to the syringe with the dye and slowly push the dyed liquid through the card. Place the PDMS card on a UV light source to see the glow in the dark.