Finite-element analysis of the static/dynamic mechanical reliability of adhesively bonded electronic components

The electronics on board of spatial equipment
undergos severe mechanical solicitations. Structural adhe-sives are used for bonding electronic components on Printed Circuit Boards (PCBs). To prevent these components from failing in vibration, experience and integration of failure cri-teria are very essential in practice. This paper leads to assess the reliability of a failure criterion being used long-time to predict the mechanical resistance of electronic boards. The latter simply supposes that an electronic board will with-stand if the ratio of the maximal deflection of its supporting PCB and its length is lower than a given safety value origi-nating from rules of good practice. When checking the valid-ity of the criterion it turns out that a physical quantity such as the maximum Von Mises equivalent stress at the adhesive joint is more proportional to the curvature of the plate after deformation than its maximum deflection value. Therefore, change of the criterion formula to express it in term of cur-vature seems to be more appropriate. Next, we propose to discuss the criterion quantitatively by means of finite ele-ment method simulations. Series of quasi-static analysis is performed by applying an out-of-plane acceleration to the assembly made up of a PCB, an epoxy adhesive and the elec-tronic component. Some effects of the assembly parameters, such as PCB dimensions, location and size of the component, bond-line thickness and the applied acceleration, are closely studied. The initial security value has demonstrated its ef-fectiveness when we chose to simulate worst cases because the value has never exceeded the yield strength of the adhesive. Besides, the behavior of assembly was studied in the case of harmonic acceleration. The obtained results could
permit a better design of the electronic boards and conse-quently reduce their weight.