Why the PCB copper foil’s thickness called ounce of (OZ)?

1. PCB copper the ounce (OZ) itself is a unit weight. 
2. PCB copper The conversion formula of oz and (g) is as follows: 1OZ ≈ 28.35 g.
3. PCB copper In the PCB industry, 1OZ means the thickness of a uniform tile of copper that weighs 1OZ on an area of 1 square foot (FT2).
4. PCB copper It represents the average thickness of copper foil in terms of weight per unit area. In terms of formula, that is, 1OZ=28.35g/ FT2.
5. PCB copper Specifically, it can also be said that the thickness of the conversion method is as follows:

the density of copper ρ = 8.9g/cm3

1cm = 10mm;

1mm = 1000 μm

1mil ≈ 25.4um

1 FT2 ≈ 929.0304 cm2

1mil ≈ 25.4um

Based on the mass formula m = ρ × V (volume) = ρ × S (area) × t (thickness), Knowing that the weight of copper foil divided by the density and area of copper is the thickness of copper foil!

 So,

1OZ=t*929.0304cm2*8.9g/cm3=28.35g/cm2,

Then: t=2 8.35 / 929.0304 / 8.9cm ≈ 0.0034287cm=34.287um ≈ 34.287 / 25.4mil ≈ 1.35mil

And then the thickness of 1OZ copper foil is about 35um or 1.35 mils. 

pcb Copper thick 1 OZ (0.035mm)

pcb Copper thick 1.5OZ (0.05mm)

pcb Copper thick 2 OZ (0.07mm)