The fluids used in electrical engineering: coating varnishes, thermal pastes, adhesives, space fillers and other materials are constantly evolving to meet different technical and environmental requirements. During the development, while the desired technical properties are achieved, other properties influencing the use and usability of the liquid may change significantly. Since the attention of the circuit design engineer in most cases focuses on the improvement of the improved fluid in the operation, service life, reliability and performance of the PCB, the issue of the use of the fluid remains with the project engineer. The presentation tries to show project engineers different ways to address the challenges that arise.