A mechanistic model for the life of solder joints under realistic long-term service conditions

A broad range of electronics applications involve the long-term exposure to combinations of thermal excursions and vibration with constantly varying amplitudes, and the ultimate life is very often limited by fatigue of the solder joints. The assessment of this is usually based on a combination of simplified accelerated tests and the assumption of simple acceleration factor expressions or models. Neither of the latter can, however, even account for observed effects of accelerated test parameters. To make matters worse common constitutive relations may be strongly misleading. Also, current damage accumulation rules cannot account for major interactions between thermal cycling and vibration or even just for ongoing variations in vibration amplitudes. Even if we are `just' aiming to decide between alternative material, design, or process parameters, or to compare a new product to a previous (supposedly similar) one, we should be concerned with the relative performance in service and not just in accelerated tests. Important parameters in a quantitative model still remain to be determined but a detailed understanding of the underlying mechanisms and the consequences of their interactions allows for the prevention of surprises, the definition of appropriate test protocols, the proper interpretation of results, and potentially the development of more reliable alloys.