According to Wikipedia (https://en.wikipedia.org/wiki/Soft_error https://en.wikipedia.org/wiki/Soft_error): "in modern devices, cosmic rays may be the predomina

According to Wikipedia (https://en.wikipedia.org/wiki/Soft_error https://en.wikipedia.org/wiki/Soft_error): "in modern devices, cosmic rays may be the predominant cause". However, radioactive isotopes in the packaging used to be a major cause. I liked this bit: "Controlling alpha particle emission rates for critical packaging materials to less than a level of 0.001 counts per hour per cm2 (cph/cm2) is required for reliable performance of most circuits. For comparison, the count rate of a typical shoe's sole is between 0.1 and 10 cph/cm2."