# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DZQhE2lyG8V
- **Gondola URL:** https://gondola.cc/posts/66312613-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/7c253c5c57.jpg
- **Posted:** 2026-06-06T20:37:11.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Drill a via through a multilayer board and you create a problem most people never notice: a copper-plated barrel punching straight through a solid power or ground plane it was never meant to touch. The fix is the antipad, a deliberate ring of absent copper etched into the plane around the hole.

At its simplest the antipad is just clearance. The plated barrel needs an air-and-dielectric gap from the surrounding pour or you short signal straight to plane. But the moment you care about anything above a few hundred MHz, that void stops being a manufacturing afterthought and becomes a tuning parameter.

A signal via sandwiched between reference planes is, electrically, a short coaxial line. The barrel is the inner conductor; the antipad edge is the outer shield. That geometry sets the via’s characteristic impedance:

	•	Z is proportional to (60/sqrt of er) x ln(b/a)
	•	a = barrel/pad radius
	•	b = antipad radius
	•	er = dielectric constant of the laminate

Widen the antipad and you pull the plane edge away, cutting parasitic capacitance and raising impedance. Tighten it and capacitance climbs, impedance drops. On a 50 or 100 ohm differential link, that single dimension decides whether the via stays invisible or becomes a reflection point.

Antipads carry hidden costs too. Every void is a break in the return-current path, so high-speed return currents must detour around it, which is why stitching ground vias hug signal vias on well-designed boards. Oversize them and neighboring antipads merge into a slot that starves the plane of copper and drives up loop inductance.

In high-speed design, the copper you remove ends up mattering as much as the copper you keep.

#stemantics #pcbdesign #signalintegrity #electronicsengineering #hardwaredesign

## Stats

- **Views:** 4,241
- **Likes:** 369
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- **Comments:** 1

## Tags

hardwaredesign, electronicsengineering, signalintegrity, pcbdesign, stemantics

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