1. A circuit card assembly, comprising:a circuit card;
a plurality of components disposed on a first surface of the circuit card, the plurality of components arranged in a path substantially perpendicular to an airflow path along the first surface of the circuit card;
a plurality of air-cooled heat sink structures, each disposed on one of the plurality of components;
wherein each of the plurality of heat sink structures comprises a plurality of impedance zones arranged in series substantially perpendicular to the airflow path, wherein the plurality of impedance zones comprise a first impedance zone having a first air impedance, and a second impedance zone having a second air impedance less than the first air impedance, and wherein the plurality of zones in the plurality of heat sink structures are aligned so that the first impedance zone in one of the plurality of heat sink structures does not overlap with the first impedance zone in another of the plurality of heat sink structures, relative to the airflow path.