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Due to the packages getting smaller, their power dissipation is henceforth mainly drained through the PCB. Besides the dissipation challenges that are seen today with single-chip components will only be magnified with the extended introduction of multi-chip packaging such as the System in Package devices These high density packages have increased the cooling issues and are demanding more complex board designs to transfer the heat from their chips to the PCB ground planes. To remove the heat more efficiently from the package, via structures are now currently incorporated into the PCB sub layers, which act as the thermal path to the Printed Circuit Board inner traces and power layers. So, to optimize board cooling the designer has now to deal with PCB layer layout with conventional via structures and, in the near future, with the implementation of High Density Interconnection circuit boards and their sophisticated technology. In comparison to the conventional printed circuit technology, HDI will create still denser interconnect substrates, containing multi-level micro-via structures that play a decisive role in the miniaturization of circuit boards and will increase the cooling design complexity. Unfortunately, their Detailed Thermal Modelling remains a great challenge so the "Compact Thermal Model“ defined by the European DELPHI methodology with for end to minimize the size of the numerical models and to preserve a great accuracy for large set of boundary conditions has been investigated to propose a behavioural thermal resistance network dedicated to HDI board. That customized methodology was applied to local via and micro-via structures which have to be tied to emerging component packaging. The first results demonstrate that the coupled CTM of the board and the component offers a real opportunity to take into account more details of local board structure with a very good compliance, better than 95%, to DTM thermal behaviour. The capability, for modelling th- - e thermal behaviour of this more complex devices is established in a work linked with EUREKA project IPITECH an acronym for Innovative PCB Integration Technologies for HDI board in Harsh environment.