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52 DESIGN007 MAGAZINE I OCTOBER 2022 I haven't written anything on thermal man- agement for some time, and from my perspec- tive, it continues to get more complicated as applications become more complex. Even applications at millimeter-wave frequencies, which typically use lower power, also have thermal management issues. It is a large topic, and this article will focus on practical issues related to PCB design and construction. To start, heat can be generated for a circuit application in a variety of ways. Sometimes the heat is generated from an active device, sometimes from the resident power within the PCB, sometimes from the operating environ- ment, and sometimes it is a mix of these issues. It is easier to deal with thermal management if you take one issue at a time. Heating due to an active device usually occurs on the outside layer of a PCB and typically the Thermal Management Isn't Getting Easier heat needs to transfer through the PCB to a heat sink below. For this example, the main thermal issue is related to thermal conductiv- ity of the PCB laminate(s) and the PCB design. For the PCB design, placing many grounding plated through-hole (PTH) vias near the heat source is commonly used. e via has copper plating. Copper is extremely high in thermal conductivity (~400 W/m∙K) and the via can act like an efficient thermal path to the ground plane on the bottom of the circuit which would be in contact with the heat sink. In some cases, which oen depends on the active device gen- erating the heat, the grounding vias cannot be made and then the thermal conductivity of the laminate(s) becomes more critical. Laminate thermal conductivity is typically in the range which would be regarded as a thermal insulator and not the desired thermal Lightning Speed Laminates by John Coonrod, ROGERS CORPORATION

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