Recipe for making polyimide wings

Date: Jul 22 2002

Description: Recipe for making light-weight polyimide wings with polyester face sheet. Each wing should weigh about 0.2 mg and has an inertia of about 11 mg-mm^2 about the flapping axis. This is in contrast to a mass of 0.5 mg and an inertia of 20 mg-mm^2 for the last recipe.

The wing is made by bonding 3.1 mil ID x 0.5 mil thick poly tubes onto a 2 micron polyester film. The process is much simpler than the last recipe and yields a wing within about 20 minutes instead of about 1.5 hours (including etching) for the last wing recipe.

Step 1: Preparing the wing pattern using polyimide tubes (takes about 3 minutes / wing)

  1. Use 3.1 mil ID x 0.5 mil thick micron poly tubes from HV Tech. (labelled as 0.0031'' ID x 0.0005'' thick ). Cut them into 3 pieces of the desired lengths using the ruler made for the purpose. (The ruler is just a straight laser cut line on steel shim with markings to mark off the correct lengths). If the ruler has four segments marked off, then use the first three starting with the longest segment.
  2. Lay down the tubes in the slots of the wing mold. This is a 100 micron steel shim with slots etched in it where the tubes can fit. Do not put a tube in the farthest slot.
  3. Cut out a small square of X8. Press down the sheet onto the tubes (after exposing the adhesive surface). When the X8 is lifted off, the tubes should come off with it held in the correct relative positions.
Step 2: Preparing a polyimide film (2 mins for each batch)
  1. Prepare a 12.5 micron SS for spin coating. Its not necessary to use X4 to hold the shim onto the glass slide because the smoothness of the face-sheet is not so critical. Its sufficient to moisten a glass slide and then flatten a 12.5 micron steel shim onto it. Squeeze the water out from beneath the shim which generates a good bond. A strip of sticky tape on the sides might be a good idea.
  2. Spin coat PI 2525 on it with the following settings:
    spin 1: 10 seconds at 1 oclock, spin 2: 50 seconds at 4 oclock
    This gives a 4-5 micron poly film. (Again, the thickness is not too critical).
Step 3: Preparing the polyester film (2 mins for each batch)
  1. Cut out a 5 cm x 5 cm piece of X0.
  2. Remove the protective film and gently transfer the 2 micron film onto the gelpak by "unrolling" the gelpack onto the polyester film roll.
Step 4: Bonding the poly tubes onto the polyester film (< 1 min for each wing)
  1. Place the poly tubes on the wet spincoated polyimide film and leave it on there for a few seconds. You should notice a meniscus form around the tubes. If a meniscus is not observed then gently press the tube onto the polyimide.
  2. Now place this assembly (with the tubes containing wet polyimide) on the 2 micron polyester film. Again press down slightly.
Step 5: Curing (15 minutes for each batch)
  1. Place the whole assembly in the oven at 200C for 15 minutes.
Step 6: Post Processing (2 mins for each wing)
  1. After the tubes are bonded onto the film, gently remove the X8 from the tubes and remove the polyester film from the X0 gelpak.
  2. Using a scalpel, trim the film so it does not extend beyond the tubes.