The assembly technology being developed is designed for the so-called critical applications used in the defense sector, the medical sector, the broadly defined area of means of transport, in many electronic applications, created for the fast-growing Internet of Things (loT) and in advanced electronic devices, created for the needs of many areas of "Industry 4.0". Currently, newer and newer projects are being created, using flexible boards in their construction. They are one of the most versatile and electronically useful solutions for building electronic assemblies and systems. The boards can be folded and formed around other elements in order to fit them into the available space, without having to divide the assembly into separate parts. By allowing for the construction of complex electronic systems in three dimensions, the devices can be more ergonomic and fit to their functions. Before the era of flexible circuits, assemblies were usually a set of different circuits and connections, often made by means of wire harnesses. As a result of the use of flexible systems, the number of required parts was reduced, which directly translated into lower production costs and reduced use of natural resources - environmental protection. Depending on the elements used, the assembly technology or the design of the device, the flexible boards contribute to the reduction of weight and space of the final product, compared to solutions based on rigid printed circuit boards.