1 Introduction
The optical performance and reliability of LEDs are influenced by the junction temperature of the LED itself, therefore reduction of the dissipated heat is a crucial point in high-power electronic applications [1] , [2] . Hence, in recent years, FR4 PCBs have been replaced by IMS PCBs in thermal applications to ensure a better heat dissipation and performance of the system [3] . However, several approaches to use FR4 technology in thermal applications have been investigated. By adding thermal vias below the heat dissipating electronic components, it is possible to reduce the thermal resistance and to improve the thermal performance of the system [4] , [5] . A typical IMS PCB consists of a high thermal conductive material, like Aluminium or Copper. Based on this material, an insulating layer is applied, which ensures an electrical insulation between the metal core and the conductor layer on top of the IMS PCB [3] , [4] . Since the thermal conductivity of the insulating layer is very low [6] , [7] , several approaches to improve the thermal conductivity already have been investigated [1] , [3] [4] , [8] . Hence, the insulating layer is the most critical part in an IMS PCB from a thermal point of view [3] , [6] . The result of applying an anodizing process to Aluminium is an insulating surface layer. This electro nonconductive layer consists of hexagonal structures with a pore in the middle of each cell [9] , [10] . These anodized coatings are usually applied to Aluminium to prevent the base material from environmental influence (e.g., corrosion, abrasion, etc.). By applying Nickel coating to the base material, it is possible to increase the thermal conductivity of the insulation layer. The common thickness of Nickel based coatings is varied from to [11] . Moreover, by applying Diamond coating, the thermal conductivity of the insulating layer results in a better thermal performance than anodizes based and Nickel based coatings [9] . By treat the heat sink (Copper or Aluminium) of a thermal system with a non-electro conductive insulating layer, it is possible to apply electro conductive adhesive onto the surface. However, it is possible to apply this adhesive in a defined structure, which can be used as tracks to provide the electronic connection between the components of the desired system. Hence, it is not required to implement a PCB onto such a system. Due to the reduction of the thermal resistance of the new adhesive based structure, the junction temperature of the LED is lower than using a regular IMS PCB. Nevertheless, the implementation of forced convection is also considered in this model to decrease the junction temperature.