PCB Notes

PCB Thickness

Copper thickness is commonly expressed in oz, for example 1 oz Cu. This is shorthand for the height of copper if spread over a square foot surface.

To calculate the height for 1 oz Cu, we need a few conversions:

• $ 1\ \mathrm{oz} = 0.0625\ \mathrm{lbs}$
• $\mathrm{Cu}\ \mathrm{density} = 8.96 \frac{\mathrm{g}}{\mathrm{cm}^3} $
• $ 1\ \mathrm{g} \approx 0.00220462\ \mathrm{lbs} $
• $ 1\ \mathrm{cm} \approx 0.393701\ \mathrm{in} $

This implies:

• $\mathrm{Cu}\ \mathrm{density} = \frac{8.96 \cdot 0.00220462\ \mathrm{lbs}}{(0.393701^3)\ \mathrm{in}^3} \approx 0.324 \frac{\mathrm{lbs}}{\mathrm{in}^3} $
• $ h\ \mathrm{in} = \frac{1\ \mathrm{oz}}{ 1\ \mathrm{ft}^2 } = \frac{0.0625\ \mathrm{lbs}}{ 144\ \mathrm{in}^2 } \approx .00134 $

Or, in general,

$$ z\ \mathrm{oz}\ \mathrm{Cu} \rightarrow z \cdot 1.34\ \mathrm{mil} $$

Where $1\ \mathrm{mil} = \frac{1}{1000}\ \mathrm{in}$.

Decoupling Capacitors

• Either one 100nF or two, one of 0.1uF and another of 10uF
• Place as close to the chip as possible
• Place the decoupling capacitor across the power supply (3.3v or 5v)

(src)

SMD Sizes

2018-02-03