If you read the datasheets on the components they usually list a one time short duration high temperature period. This is intended for soldering it to the board. Basically they do start to fail. The plastic starts melting or evaporating and the wires might start oxidizing. But when it is such a short duration, and only once, it will usually not cause enough damage to the component. Even then you need to test each assembled board after soldering to make sure it still works. Some components fail as it is soldered.