Printing technologies are typically used for printing different structures on 2D substrates (e.g. paper, films and flat plastic, silicon or metal surfaces). Jet printing methods such as inkjet and aerosol jet® enable printed structures on 3D surfaces and thus functional structures in electronics.
To do this, within the framework of a research project funded by the BMBF, we have researched printing of an intrusion sensor structure in an injection-molded cap. An intrusion sensor is used to protect sensitive devices (e.g. chip card readers) against unauthorized manipulation for the purpose of data theft. In an attempt to open the protected device (e.g. with a screwdriver), the intrusion sensor structures are damaged, disabling the device and preventing the theft of data. The more delicate the sensor structure, the better the protection. It was possible to implement intrusion sensor structures with a circuit path pitch of 400 µm and less. On a surface of 7x8 cm², it was possible to print four roughly 3.5 m long meander-shaped resistance structures, short-circuit-proof, and without interruption.
Further examples of printing on 3D surfaces are inkjet-printed through-connections via a transfer-molded thermoset package to the underlying circuit board, or printed silver structures on circuit board substrates with machined cavity as first circuit path level for printed coils, which are used in temperature sensors, for example.