Numerical Studies On Failure Analysis Of Multilayer Ceramic Capacitors

With an increasing demand for electronic products in the electronic industry,miniaturization has become an inevitable development trend in electronic products.Multilayer ceramic capacitors (MLCCs) have been widely used in a variety ofapplications such as the information military, mobile communications, electronic,aerospace and other fields because of their small device size, high specific capacitance,high insulation resistance, low leakage current, long lifetime, high reliability and lowcost. In this paper, failure mechanisms of the multilayer ceramic capacitors (MLCCs)due to the thermal residual stress were analyzed by using the finite element method(FEM) base on commercial software ABAQUS6.8. This dissertation provides aconvenient tool for predicting the potential failure due to the thermal sintering processof the MLCCs, which is helpful for scientific research and engineering application.The main studies are as following:(1). The parameterization model was set up to meet the parametric design of theMLCCs through editing the input files.(2). MLCCs are made of the ceramic dielectric material (such as BaTiO3referredto as BT) and metallic electrodes (such as Ni) which are stacked with each other. Asimplified finite element model with the corresponding stress boundary conditionswas established. We predicted the thermal residual stresses of the MLCCs withdifferent thick dielectric layers base on the proposed model,. It is found that thethickness ratio of the dielectric layer to electrode layer plays a significant role. For agiven thickness of the electrode layer, a critical thickness of the dielectric ceramiclayer in MLCCs exists, below and above which the change trend of the residualstresses is quite different.(3). A simplified single layer model of the MLCCs was developed to investiagethe stress distributing near the center layer of the MLCCs. When the thickness of theNi layer is smaller than that of the BT layer, the results obtained by the proposedmodel show that the Von-Mises stress increases sharply with the decrease in thethickness of the ceramic layer. The residual stresses increase sharply as the thicknessratio of the dielectric layer to electrode layer is decreased below a critical value, and then they increase slightly and keep a high value with a further decrease in the thethickness ratio.(4). A simplified single layer FE model including cohesive layers with a zerothickness were developed to study the failure mechanizm during the sintering processof the MLCCs, where the cohesive elements were defined as potential failure paths inthe simulations. The Von-Mises stress, shear stress as well as cracking time wereinvestigated. The numerical results show that these two failure paths have differentfailure models. Cracking starts from the cohesive element near the electrode tip of thefailure paths I along the width direction, and then other elements were destroyedalmost at the same time, which is earlier than the failure of the paths II along thelength direction. By analyzing the total energy dissipated per unit volume in theelement by damage, it is concluded that the total energy dissipated increases with theincreasing Ni layer thickness for a given BT layer thickness, indicating that as thethickness of the Ni layer is increased, the MLCCs might readily lead to failure.(5). The effects of interface parameters on the failure evolution in the MLCCswere studied. The interface parameters mainly consist of the interface stiffness, thenominal stress, and the fracture energy of interface. The simulated results show thatwith the increasing interface stiffness, the failure model doesn’t change, but the timeof failure is advanced. Meanwhile as the nominal stress is increased, the MLCCs havebecome increasingly difficult to crack.