Rework on electronic assemblies becomes necessary if, for example, a solder joint is judged to be defective according to the common acceptance criteria, a component is defective or has been incorrectly mounted and the assembly cannot be used in this condition. Rework requires skilled employees (see soldering training!). In true rework, production-equivalent processes are used and the assembly looks the same afterwards as an assembly that has not been reworked. In the case of a repair, on the other hand, non-production-equivalent methods are also permitted and the appearance may differ afterwards. A modification means a functional change of the assembly (controlled by drawings).