Additive manufacturing methods have shown great potentials to substitute the costly and time‐consuming conventional subtractive methods in the processing of electronically conductive materials for applications in flexible and stretchable electronics. Herein, additive manufacturing of highly conductive, sandwich‐structured conductors with high‐temperature processibility and versatility in applicable substrates is reported. The sandwich‐structured conductors with silver nanoparticles (Ag NPs) as electronic conductors and polyimide (PI) as encapsulation are layer‐by‐layer deposited by aerosol printing into PI/Ag/PI composites. A high annealing temperature of 250 °C contributes to the high electronic conductivity of the Ag layer at 1.14 × 107 S m−1, which is in the same order of magnitude to the conductivity of bulk Ag at 6.3 × 107 S m−1. The high annealing temperature also significantly improves the interfacial bonding between the Ag and PI layers. For applications in flexible and stretchable electronics, the sandwich‐structured conductors are transferrable to various substrates through a thiol−epoxy bonding process, including polystyrene (PS), polyethylene terephthalate (PET), Kapton, and polydimethylsiloxane (PDMS) thin films. The sandwich‐structured conductors transferred to flexible and stretchable substrates exhibit highly retained electronic conductivity under deformations such as bending and stretching.

Currently, light-based three-dimensional (3D) printing with submicron features is mainly developed based on photosensitive polymers or inorganic-polymer composite materials. To eliminate polymer/organic additives, a strategy for direct 3D assembly and printing of metallic nanocrystals without additives is presented. Ultrafast laser with intensity in the range of 1 × 1010 to 1 × 1012 W/cm2 is used to nonequilibrium heat nanocrystals and induce ligand transformation, which triggers the spontaneous fusion and localized assembly of nanocrystals. The process is due to the operation of hot electrons as confirmed by a strong dependence of the printing rate on laser pulse duration varied in the range of electron–phonon relaxation time. Using the developed laser-induced ligand transformation (LILT) process, direct printing of 3D metallic structures at micro and submicron scales is demonstrated. Facile integration with other microscale additive manufacturing for printing 3D devices containing multiscale features is also demonstrated.