ESS profiles with step stress level

Environmental Stress Screening (ESS) is usually referred to the process of exposing a product to environmental stresses for detecting and eliminating latent defects made in manufacturing process. The common ESS profiles are using thermal cycling, random vibration or their combinations as the screening stresses. Various guidelines and standards have been available for determining an ESS profile. Nevertheless, there are cases that the standard ESS profiles may not be efficient enough to detect the latent defects in some manufacturing process. This paper reports the results of one industrial project on the ESS profile design for circuits. In the project, a comparative study was carried out for the evaluation of the ESS strength under the ESS profiles with incremental step stresses (ISS). The ISS profile under the study is firstly to implement a step thermal cycling and then perform the test with two screening stimuli concurrently: ordinary thermal cycling and random vibration of step increasing intensity levels. For the purpose of the comparative study, the ESS test samples were consisted of two groups A and B that were made at two different levels of manufacturing: soldering by skilled and unskilled workers, respectively. The comparative study shows that the ISS profiles are effective for exposing the latent defects in sample group A and B. Based on the project results, an ESS profile is recommended in this paper.