We focus on the analysis of power converters used in electrical engineering. These contain a metal ceramic assembly which serves both heat extraction and electromagnetic insulation. The metal is usually a copperplate and the ceramic’s an alumina. The assembly between the metal and ceramic plates proceeds by a ”Direct Bonding”, thus creating a ’natural’ interface. Under operating conditions, the assembly is subjected to a cyclic temperature variation, which can promote delamination along the interface. The objective of this study is to characterize mechanically the interface within a cohesive zone methodology. A traction-separation law with a triangular profile is adopted to mimicks the debonding process. Two key parameters are defined: Tmax (the maximum stress, at which debonding initiates) and Gc (the work of separation for the creation of a crack locally). An identification strategy is presented based on a two-scale observation of a four point bending test in which delamination is tracked [1]. Once the interface is described, together with the mechanical response of the copper and ce- ramic parts (elastic-plastic and elastic, respectively), the assembly is then subjected to a thermal cycling. The initial temperature corresponds to direct bonding one. The first cooling downto room temperature is first considered. At this stage, debonding initiation is numerically pre- dicted [1]. Subsequent cycling, of 200°C amplitude can further promote debonding but the initial state is found key to ensure the mechanical integrity of the assembly. Thus preventing damage right after the direct bonding stage is key, to improve the components durability. The resistance to the initial debonding can be prevented by optimising the ratio of the cop- per/ceramic thicknesses, also by considering a structuration of the metal perimeter. This results are then interprate with the calculation of the thermal (general-) stress intensity factors [2].