Acceleration factors for reliability analysis of electronic assemblies

There are several models for the calculation of the acceleration factor for the electronic assemblies subjected to stress tests. A correct reliability assessment requires an accurate analysis of these models and the evaluation of their real effectiveness and adequacy. As regard to the solder joints subjected to the thermo mechanical stresses given by temperature variation, applicable models are the original Coffin-Manson model, the Coffin-Manson model modified by Norris and Landzberg, and the model described in the standard IPC-SM-785. The last one is the most complete model to evaluate the acceleration factors given by slow temperature swings. However, the most effective method for the estimate of the solder joint aging is based on the analysis of the microstructure of the alloy. Regarding the acceleration factors of the electronic components, the international standardIEC 61709 can be used This standard provides the equations to determine the intrinsic failure rates of the electronic components. Those equations allow to calculate the acceleration factors for the different types of stress (caused by temperature, voltage, current, etc) This standard is more linked to the actual characteristics of the components than MIL-STD-217F, which was widespread in the past. IEC 61709 is also a useful tool for the design of electronic assemblies. A new method for the calculation of the acceleration factors is the analysis of the variation of the electrical parameters of the assembly when the stress is applied This new method allows to evaluate directly the effects of the stress on the functionality of the assembly.