77GHz Millimeter wave radar PCB

As is typical of all polytetrafl uoroethylene (PTFE) based circuit board materials in which the cop per cladding

is bonded to the dielectric at elevated temperatures, RT/duroid® laminates show some degree of dimensional

shrinkage after copper is etched off. When the laminate is cooled to room temperatures after the copper

has been bonded to the dielectric, the copper and dielectric are at dif ferent dimensions than they would be

if not bonded together due to differences in the thermal coef fi cients of expansion (CTE’s). The dielectric is

trying to shrink but is restrained by the copper foil. Similarly the copper is trying to grow, but is restrained

by the dielectric.