Probably non-existent since the thickness of insulation layer isn't controlled. Surprisingly, silicone rubber has a dielectric constant between 2 and 4 [1], wh

Probably non-existent since the thickness of insulation layer isn't controlled. Surprisingly, silicone rubber has a dielectric constant between 2 and 4 [1], which is pretty close to FR-4's 4.4. So maybe it isn't impossible? [1]https://res.mdpi.com/d_attachment/polymers/polymers-09-00533/article_deploy/polymers-09-00533-v2.pdf https://res.mdpi.com/d_attachment/polymers/polymers-09-00533...