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Modeling of delamination and interface strength in printed circuit boards

Abstract : In this thesis, the identification of the interface strength in Printed Circuit Boards (PCBs) is assessed. A PCB is a passive component, which allows to interconnect electronic components soldered on the outer layers in order to realize a complex electronic system. It is a multiple layer assembly made of woven composite and copper foil. Copper plays a major role in Printed Circuit Boards (PCBs) since it is the carrier of the electrical information. During its lifetime, the PCB undergoes a large number of thermal cycles, which can lead to the failure of copper path. In addition, it has been detected that the use of certain combinations of based materials leads to delamination, which limits the PCB service-life. The measurement of interface strength between copper layer and composite substrate is critical and the usual method for measuring the interface properties in PCB industry is the peel test. The PhD is divided in three main parts. In the first experimental part, peel tests at various peel angles are performed using specimens, which consist of a copper foil bonded on a woven composite substrate. Interface separation between the copper film and the composite substrate is observed. During the test, the peel force per unit width and the copper film radius at steady state are measured. Next, a theoretical analysis of the peel test for an elastic-plastic material is proposed. A precise definition of the work done by bending plasticity for a particular class of material response is established. Indeed, we have extended previous works of the literature by considering that the plastic hardening behavior of the film is modeled by a Voce type law. Finally, finite element (FE) simulations of peeling are conducted at various peel angles by considering that the copper material response is elastic-plastic. The isotropic hardening is identified based on uni-axial tensile tests. The woven composite is assumed to remain elastic with an orthotropic response. The interface is modeled by cohesive elements using a bilinear traction separation law. FE results are compared to experimental data. It is shown that the peel force and the film curvature are predicted accurately, for a large range of peel angles. 125 Therefore, from the dialog between finite element calculations and experiments, the interface fracture energy is obtained.
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Submitted on : Monday, June 22, 2020 - 11:53:23 AM
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Essossinam Simlissi. Modeling of delamination and interface strength in printed circuit boards. Materials Science [cond-mat.mtrl-sci]. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0326⟩. ⟨tel-02877354⟩



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