The units of this equation resolve to ohms ω.
Copper sheet resistance ohms per square.
The unit mω 1 means mω per square shaped sample as for the same material the sheet resistance is always the same for a square sized sample with the same thickness regardless of its dimension.
If two squares of the material the same size as above are laid end to end and electrodes attached as shown below the resistance is the addition of these two squares or 2 ohms.
This concept was developed in the thin film circuitry industry to design traces with the same resistance by dividing each trace into squares.
Resistance of a thin film resistor of length l.
The sheet resistance of 1 oz copper is 0 5 mohm sq the sheet resistance of conductive ink at 70um thickness is 12 mohm sq bad.
Sheet resistance r s is commonly defined as the resistivity ρ of a material divided by its thickness t.
That for a given material and a given thickness the resistance from an electrode across one side to the opposite side is a constant the same for small square and large squares an intrinsic property of that material.
The ipc spec for copper bulk resistivity at 20ºc is 1 72µω cm.
Ohms per square is a core concept.
When electrodes are attached as shown and the ohm meter measures 1 ohm we can state that this material has a surface resisitivty of 1 ohm per square.
So you can measure length and width in microns centimeters mils etc and then determine the number of squares by dividing length by width.
As such the units ω ohms per square are commonly used.
This is the origin of the very simple rule of thumb that.
For a square so the unit can be thought of as loosely ohms aspect ratio.
A 3 unit long by 1 unit wide aspect ratio 3 sheet made of material.
However it actually represents the resistance between opposite sides of a square of a material rather than bulk resistance.
Square is a legitimate unit why bad.
The sheet resistance of 1 oz.
If the sheet resistivity of the thin film resistor is 50 ohms square we are looking at a 300 ohm resistor.
The sheet resistance of the electroless copper deposits from different plating solutions against plating time.
Sheet resistivity or simply sheet resistance is given in ohms per square.
Note that squares have no units.
To calculate ohms cm using a four point probe one needs to know the thickness of the wafer if it is a homogeneous wafer or the thickness of the top layer that s being measured to be able to.
The reason for the name ohms per square is that a square sheet with sheet resistance 10 ohm square has an actual resistance of 10 ohm regardless of the size of the square.
For example 1oz copper foil has a weight of one ounce per square foot.
