# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DbI_MUZgivC
- **Gondola URL:** https://gondola.cc/posts/68267165-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/4caea889b4.jpg
- **Posted:** 2026-07-23T15:30:02.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A silver chloride layer thinner than a human hair is all that stands between your heart’s electric field and an amplifier’s input stage.

Printed ECG electrodes on flex are electrochemistry disguised as manufacturing. The body carries current by moving ions. Silicon carries it by moving electrons. Something has to translate, and that translator is the electrode.

Silver/silver chloride wins because it is non-polarisable. Chloride ions in sweat and interstitial fluid exchange freely with the AgCl layer, so charge crosses the interface as a Faradaic reaction rather than piling up on a capacitive double layer. That gives a stable half-cell potential and minimal baseline wander, which matters when the signal you are chasing is only 0.5 to 5 mV riding beneath mains pickup orders of magnitude larger.

The stack is deceptively simple:

- Substrate: polyimide, PET or TPU, 25 to 125 µm
- Conductor: screen printed silver ink, 8 to 15 µm wet
- Sensing layer: Ag/AgCl blend, typically 80:20 by weight
- Dielectric: printed encapsulant with one open window at the pad
- Optional carbon overprint for corrosion and defibrillation tolerance

Cure temperature dictates substrate choice. Polyimide shrugs off 150 °C. PET distorts near 130 °C, so low-temperature inks with reduced silver loading get used instead, trading sheet resistance for dimensional stability.

Mechanics matter as much as chemistry. Silver is stiff and brittle relative to the polymer beneath it, so cracks nucleate at print edges under repeated flexure. Conductors are placed near the neutral axis, corners are radiused rather than mitred, and dynamic bend radii stay above ten times stack thickness. AAMI EC12 then wants under 100 mV DC offset and under 2 kΩ combined impedance at 10 Hz before anything touches a patient.

Every biosignal begins as a chemical handshake.

#stemantics #flexpcb #printedelectronics #biomedicalengineering #ecg

## Stats

- **Views:** 9,899
- **Likes:** 151
- **Shares:** 0
- **Comments:** 3

## Tags

ecg, biomedicalengineering, flexpcb, stemantics, printedelectronics

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