Infant Mortality problems have been around for a long time (maybe that is why sometimes we have a shorter warranty period for many electronic products). Anyway, the explanation of infant mortality is that these are left over (or latent) defects. Defects that do not necessarily expose themselves and they can skip by all the manufacturing tests, including system test. However, with electrical and thermal stresses during use, they will eventually degrade to cause a significant functionality problem and will result as a failed system in the field. Product may last for hours to months if such a latent defect is trapped within.