# 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

SMD mm inch
2920 7.4 x 5.1 0.29 x 0.20
2725 6.9 x 6.3 0.27 x 0.25
2512 6.3 x 3.2 0.25 x 0.125
2010 5.0 x 2.5 0.20 x 0.10
1825 4.5 x 6.4 0.18 x 0.25
1812 4.6 x 3.0 0.18 x 0.125
1806 4.5 x 1.6 0.18 x 0.06
1210 3.2 x 2.5 0.125 x 0.10
1206 3.0 x 1.5 0.12 x 0.06
1008 2.5 x 2.0 0.10 x 0.08
0805 2.0 x 1.3 0.08 x 0.05
0603 1.5 x 0.8 0.06 x 0.03
0402 1.0 x 0.5 0.04 x 0.02
0201 0.6 x 0.3 0.02 x 0.01
01005 0.4 x 0.2 0.016 x 0.008
Package Pitch (mm)
SOIC 1.27
TSOP 0.5
SSOP 0.635
QSOP 0.635
VSOP 0.4, 0.5, 0.65
LQFP 1.4
PLCC 1.27