coefficient of thermal expansion (PCB) (CTE)
When materials are heated, they expand. The degree of expansion with temperature is the coefficient of thermal expansion,CTE.
The coefficient of thermal expansion is shown by the expansion of a body in all three dimensions. The coefficient of thermal expansion depends on the material and is expressed in parts per million( ppm) relative to Kelvin (ppm/K). For quartz, the coefficient of thermal expansion is `0.6 * 10^-6` per Kelvin, for copper `17 * 10^-6` per Kelvin, and for lead `29 * 10^-6` per Kelvin.
There are also materials that contract rather than expand as the temperature rises. This is called contraction. An example of this is water at temperatures between 4 °C and 0 °C.