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16 SMT Magazine • June 2014 mK) in respect to standard FR-4 material (ca. 0.3 W/mK). The copper design layer is on top of the dielectric layer. IMS show a very short heat conduction path through the thin dielectric layer, because the metallic base material serves already as first heat sink. There are several different IMS varia- tions available depending on the requested per- formance. Further build up concepts using a short heat conduction path to the heat sink are conventional through-hole plated glass fiber reinforced PCB technologies. A sufficient ther- mal performance in the lower power loss range up to several watts can frequently be achieved by reasonable numbers for via count, via di- ameter, and hole plating thickness [4] . Figure 2a shows a scheme of a PCB with open through holes serving as open thermal vias. In figure 2b an example of a footprint design is shown. It ADvAnCeD THeRMAL MAnAgeMenT SOLuTIOnS continues can be seen that the thermal vias are situated in the extended thermal pads beside the pad, where the component will be placed. So, to avoid the well-known problem of solder soak- ing, it is not possible to place open thermal vias directly underneath a component. Due to this fact, the thermal path is elongated, because the heat has to be spread first later- ally on the surface before it can be guided per- pendicular through the PCB to the heat sink shown in Figure 2c. A schematic cross section as depicted in Fig- ure 3a demonstrates a special via plating tech- nology featuring plugged vias with a homoge- neous copper layer on the front faces. In con- trast to the concept with open vias, this build up allows vias directly beneath a component, which also reduces the thermal path. Figure 3b shows a microscopic view of a cross section of this type of PCB. feaTure figure 2: pCb with open thermal vias: a) scheme; b) design; c) thermal path. figure 3: pCb with plugged thermal vias: a) scheme; b) cross section; c) thermal path.