Ounce is a unit of weight. Why is it used to indicate thickness in PCB?

The first thing to note is that an ounce (OZ) is itself a unit of weight.

The conversion formula of ounce and gram (g) is: 1OZ ≈28.35g.

In the PCB industry, 1OZ means the thickness of copper that weighs 1OZ evenly spread over an area of 1 square foot (FT2).

It is the weight per unit area to express the average thickness of copper foil.

This is expressed by the formula, 1OZ=28.35g/ FT2 (FT2 is square feet, 1 square foot =0.09290304 square meters).

Specifically, the conversion method between it and length, also known as thickness, is as follows:

First, we know that the density constant of copper and the relevant unit conversion formula are as follows:

The density ρ of copper =8.9g/cm3

1 cm (cm) =10 mm (mm)

1 mm (mm) =1000 micron (um)

1 mil material 25.4 um

1 FT2≈929.0304cm2

1 mil material 25.4 um

According to the mass calculation formula m = ρ×V (volume) = ρ×S (area) ×t (thickness), know the weight of copper foil divided by the density and area of copper foil thickness!

As previously known, 1OZ=t×929.0304cm2×8.9g/ cm3=28.35g

Therefore, t=28.35÷929.0304÷8.9cm≈0.0034287cm=34.287um≈34.287÷25.4mil≈1.35mil

The thickness of 1OZ copper foil is 35um or 1.35mil.

Copper thickness 1.OZ(0.035mm) Copper thickness 1.5OZ(0.05mm) Copper thickness 2.OZ(0.07mm)