Today, most of the companies understand that the reliability must be built in at the design phase and then, monitored during the whole manufacturing process. Reliability building means the totality of techniques and procedures having the goal to ensure a foreseen reliability level for a given product. This concept is linked with reliability assessing, which cover the whole evaluation system aiming to find out and record, during and after the manufacturing process, the reliability level of the batch of products. This evaluation system contains tests, electrical measurements, failure analysis and statistical processing of data.