Fundamentals Friday

What is Sheet Resistance?

Did you know that the resistance of a square copper PCB trace is the same regardless of the size?

Dave explains the theory behind this rather counter-intuitive concept called Sheet Resistance, and demonstrates that it is in fact true.

What is the ohms per square of 1oz copper-clad PCB material and how can you use this concept to calculate the resistance of a PCB trace?

Thin Film Precision Resistor Network video HERE

Forum HERE

Podcast: Download

I still have some nuances:

I suppose by saying square means the biggest square you can get? What about a copper sheet with an irrational ratio (i.e. DIN A4)? Or a circular sheet, there are infinite squares… Nice approach though, I missed FF.

Fundamental Fridays are my favorite. Also your 741st video is fast approaching. Do you have any special plans honoring the op amp we grew up with?

No plans.

Another way to “think about it” is let’s say a square is simplified to a resistor with resistance R. Now you double each side, so now you have 4 squares of R – two in parallel, two in series. Analyze that as simple parallel/series resistors and you still have R.

So if you have a 1×1 square of resistance R, a 2×2 or 3×3 or higher array of resistors also produces the same resistance, R.

Exactly. I enjoyed Dave’s comment about squares in the thin film resistor video because it prompted me to pause the vid and think about it – and I came up with the same solution as you, in that I considered it from a series/parallel circuit point of view.

I agree with the previous poster, it’s really easy to comprehend if you just think of a square as being a fixed resistance and stack series “rows” in parallel ladders with each other.

FF are my favorite segment, hands down.