You have to build a number of prototypes and "shake and bake" them to well beyond their specified limits, not necessarily to the breaking point, but certainly at least 10% (for commercial products) beyond the thermal, magnetic, electrical, environmental, and mechanical stresses they're specified to survive. That means that if the spec's incorporate a safety factor of 20%, you still need to go 10% beyond that.

You must know absolutely what the requirements of your target application are so that you can be sure that all your components are actually and not just putatively available in a version that will meet those requirements. If you need to operate in a 70-degree C environment at 40 MHz, you'd best know that sufficient supply of the components you need to operate at that speed in that environment under the conditions you require can be bought and delivered where you want them and when.

That applies to any component manufacturer, and not just ATMEL.

RE