As the name says this stage has the objective of functioning as a link between two different levels. The first is the flexible circuit developed with silver ink (the active zone of the sensors), and the second is to connect all the electronics in a reduced and efficient way.
It consists of a double face plate, type FR4 (fiberglass), which improves electromagnetic interference and allows it to have a longer duration over time. So that tracks that do not work as contacts are not exposed (reacting with oxygen, with its consequent oxidation), were coated with flux that also works as an insulator of the tracks and facilitates their welding.
In addition to this, the lower surface has 3 resistances of 15KOhm which are parts of the resistive divider needed by the sensors. These are SMD type because they take up less space, consume less energy and do not need to drill the plate.