Thermal reliefs are structures that decouple a via thermally from a large conductor plane and as such create a thermal barier in order to obstruct heat conduction through these planes during the soldering process. Two models have been developed that describe the impedance of a thermal relief structure at DC and at RF. The first model gives an estimate of the excess resistance that is added by introducing a thermal relief on the connection of a hole to a large conductor plane, which is directly related to the thermal resistance. The second model estimates the excess inductance that is introduced in the connection by the thermal relief at RF frequencies.
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