## 4 Micro/Nanojoining for Microelectronics  
Recently, there was significant progress in the development of bonding materials and joining processes for power electronic devices and flexible electronics. Furthermore, new advances in the bonding of nanostructures, an important step toward the transition to nanoelectronics, were reported. In the field of power electronics, the focus is directed at the development of novel materials for transient liquid phase bonding (TLP) and nanoparticle sintering routes. [PERSON] et al. [42] proposed an Sn-coated Cu-multiwalled CNT (MWCNT) composite (Sn-Cu-MWCNT) paste for Cu interconnections, and [PERSON] et al. [43] developed a Cu-solder-resin composite paste for pressure-less die-attach technology for bonding Kovar chips onto Cu electrodes on Si\({}_{3}\)N\({}_{4}\) substrates. The Sn-Cu-MWCNT composite powder [42] was fabricated by subsequent electroless plating of Cu and Sn on a multi-walled carbon nanotube. It can be applied as a paste for the fabrication of Cu interconnects with improved mechanical properties at temperatures of 260 \({}^{\circ}\)C and applied pressure of 10 MPa. During the process, the Sn-Cu-MWCNT composite material transformed to MWCNT-Cu\({}_{3}\)Sn in the Cu joint zone. The Cu-solder-resin composite pastes developed by [PERSON] et al. [43] allowed a TLP sintering (TLPS) process at a temperature of 250 \({}^{\circ}\)C without pressure application. The as-produced TLPS joints showed excellent thermal reliability (only 14% decrease in shear strength after thermal aging at 200 \({}^{\circ}\)C for 1000 h). This was due to their unique microstructure consisting of a Cu particle-IMC skeleton partially filled with polyimide resin in the as-bonded state. The growing interest in soft electronic components and devices drives the development of micro/nanojoining technology. The aim is to provide solutions for the integration of diverse passive and active components on flexible (elastic) substrates for various applications from wearables to robotics, energy storage applications, bioelectronics, and functional textiles. [PERSON] et al. [44] reported the development of binder-free conductive composite inks with adjustable electrical and mechanical properties for flexible electronics applications. The developed binder-free composite inks were composed of silver nanoparticles, binary solvents, and conductive nanofillers of various architecture and composition. The inks were successfully used for laser-based fabrication of soft electrodes with low electrical resistance and good mechanical performance. It was shown that, using graphene filler, the electrical resistivity of electrodes could be significantly reduced, while adding silver nanowires to the ink improved the electrode flexibility. Thus, the properties of the joints could be tailored by the selection of the paste nanofiller according to the product requirements. An alternative method to fabricate conductive electrodes, capacitors, and other flexible radio frequency (RF) devices is laser-direct writing (LDW), which gained a lot of interest as a simple and low-cost manufacturing method [45]. The LDW process is a noncontact, maskless, and gentle patterning method with a resolution that can go down to the submicrometer range. [PERSON] et al. [45] demonstrated that the transmission and reflection characteristics of laser-scribed microstrip transmission lines, basic components of RF circles, on flexible substrates can be simply tuned by accommodating the resistance of the conductors with a variation of the laser power. Ultrafast laser ablation can be used for the reshaping, cutting, and joining of nanostructures, as well as for the formation of nanostructures with required optical properties and surface plasmon resonance [46]. [PERSON] et al. [46] demonstrated that Ag nanorods can be transformed into bone-shaped nanorods, T-shaped nanorods, and nanodots by controlling laser polarization direction and wavelength during the femtosecond pulse laser near-field ablation process. In the same way, nanojoints can be formed.