DIY flexible circuit boards

Materials needed:

First, cut out a piece of copper clad Kapton at least .5" larger than the circuit board tracing that is to be etched. Prepare squirt bottles of acetone and 99% isopropyl. I recommend performing the next few steps by the sink. It is also helpful to wear gloves at this point.

In the sink, cover the copper side of the Kapton with isopropyl and let dry. Then cover with acetone and let dry.

After the Kapton is dry, rinse with water. Then take sandpaper, preferably fine grit (I’m using 2000) and sand the copper side in a circular manner. Make sure to not use too much force as to crinkle the Kapton.

When done, rinse the Kapton with water.

With a wet sponge on the abrasive side, scrub the copper side of the Kapton with a small amount of kitchen metal cleaner (like Easy-Off) in a circular motion before rinsing.

Let dry. The copper after this process should have a brighter sheen to it.

Print the circuit board tracing on magazine stock paper with a laser printer on the high print quality setting and cut out the excess. (I use a Samsung printer and whatever magazine ad is glossy and just thick enough to feed in the printer. Brother toner supposedly does not transfer well by lamination.)

Lay the stock paper face down on the Kapton and secure the sides with Kapton tape. Make sure to smooth the stock paper of wrinkles during this process.

After the sides are secured down, run it into a laminator at a setting of approximately 250 degrees. Repeat this process 30 times or until there is a noticable embossment of the tracing appearing on the stock paper. Make sure to rotate the Kapton 90 degrees after every 5 feedings or so to keep the Kapton flat.

Let it sit in water for 30 minutes or so until the stock paper lifts away from the Kapton.

Carefully remove the pieces of tape and slowly peel off the stock paper. Discard the pieces of tape and stock paper.

With a soft bristled toothbrush, gently clean up the tracing of stock paper remnants.

Rinse with water and let dry. The tracing will oxidize (this is normal). Check for broken or hairline connections. Repair traces by carefully retracing with a permanent extra fine tip marker and remove connections with a hobby knife. The boards made in this post have 6mil spacing as Kapton etches much better than rigid FR4 PCB.

Carefully pour Copper Chloride in Aqueous Hydrochloric Acid Solution into a glass pan. Using tongs, completely submerge the Kapton into the acid bath. It is very important to have good ventilation and air circulation during this process. Do not breathe this stuff in and clean up any splashes or condensed residue with baking soda as it will corrode surfaces.

Seal the glass pan with cling wrap and wait patiently. The estimated time is 30 minutes to several hours depending on the acid concentration, oxygen, and amount of copper to etch. Be sure to check the progress every 30 minutes.

As you can see here, the copper around the tracing has dissolved into the bath, exposing the Kapton. (I use an aquarium bubbler to increase oxygen.)

This is the result we want.

Using tongs, fetch the Kapton out of the acid bath, rinse with water and lay them out to dry on paper towels. Store the bath for future reuse.

Once completely dry, the circuit boards (these are prototype Light Square and Sewpads for Fyber Labs) are ready to be populated. :)

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