The trend toward miniaturization in electronic devices requires printed circuit board (PCB) manufacturers to enhance their expertise due to thermal stresses experienced by PCBs from heat generated by electronics or the surrounding environment. PCBs are intricate assemblies comprising various materials, each with distinct mechanical properties, especially thermal expansion coefficients. These coefficients contribute to thermal stresses that may lead to layer delamination, occurring between insulating substrates or between copper and insulating substrates. Traditionally, the peel test has been the predominant method for assessing interfacial energy in PCBs, providing an estimate based on the IPC standard. However, this method, involving peeling, often results in copper experiencing plasticity. Consequently, the literature extensively explores the analysis of peel tests with plasticity development in the film. Recent studies have delved into the elastic-plastic response of copper, serving as a valuable tool for characterizing the cohesive behavior of the substrate/copper interface. However, challenges arise when seeking a precise evaluation of the mechanical response of the interface using this approach. To overcome these challenges, we propose the Double Cantilever Beam (DCB) test designed to investigate both the substrate/substrate and copper/substrate interfaces. Our focus primarily lies on Mode I interface fracture to determine the critical strain energy release rate (GIc). Our approach involves combining experimental data with numerical simulations to estimate the critical stress. Additionally, we delve into a detailed discussion on the shape of the traction-separation law. This innovative method aims to provide a more comprehensive understanding of interface behavior in PCBs and offers improved precision in evaluating their mechanical response.