Reliability prediction is fundamental to system design. It involves the quantitative assessment of systems reliability prior to development. For many years the reliability of an electronic system was based, to a great extent, upon the junction temperatures of the semiconductor devices. Substantial efforts were made in the fabrication methods, mounting methods, and cooling techniques of the electronic devices to reduce these hot spot temperatures below 100 °C. This has produced a significant improvement in the reliability and effective operating life of the equipment. However, the electronic failure rates are still too high. Additional reductions in the failure rates must be achieved to further improve the reliability of our electronic equipment. Some of the failure mechanisms that can cause malfunctions in electronic systems are examined in this paper Experience has shown that most of these failures are produced by a mismatch in the thermal coefficients of expansion (TCE) of the different types of materials typically used in electronic assemblies. The mismatch often generates high forces and stresses, which produce fractures and cracks in the electronic components and assemblies. An examination of a large number of avionics failures has shown that most of them are mechanical in nature. They typically involve fractures in solder joints, electrical lead wires, plated through holes (PTH), electrical cables, connectors, adhesive bonded joints, and hermetic seals. These failures are often produced by various combinations of thermal, vibration, shock, humidity, and salt environments, combined with poor manufacturing processes and poor design practices. These failures must be reduced in order to achieve a substantial improvement in the system reliability. The paper aims at presenting the numerical evaluation by finite element analysis of the common class of PCBs under the mechanical stress. This work contributes to the study of vulnerability in packaged electronics by comparing the numerical result with finite element analysis.