Get supplies needed for etching flexible PCB. Copper clad Kapton/polyimide can be bought on eBay relatively easily. Sheet or roll will work fine. Sewpads only require single sided.

Our hand etching post on medium explains the chemicals required and we recommend glass containers. There are specialized etching containers available.

Download the required Sewpad layouts from Github - https://github.com/FyberLabs/FlexModule/tree/master/sewpads

Diptrace (free download) can print them in 'Mirror' for toner transfer.

Follow our steps on hand etching - https://medium.com/@cinlin/diy-flexible-circuit-boards-58c3794ed0cb

Tin the Sewpad with MG Chemical Liquid Tin

Solder the Flex Modules on to the Sewpads as needed -

Drill holes through Sewpad for 5-8mm snap buttons. Place 'male' snap through the drill hole and solder to pad. Sew 'female' snap to mounting fabric. OR:

Sew Sewpad by hand or machine on to mounting fabric. Use stainless steel thread or silicone covered wire to stitch directly into pad and solder thread/wire to pad.

Optionally coat the sewpad with conformal coating to protect the electronics better from water and ESD.
Silicone Conformal Coating Spray
or
Silicone Conformal Coating Brush On