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This study investigates the mechanism and effects of incorporating different ZrO2 nano-particles into SAC0307 solder alloys. ZrO2 nano-powder and nano-fibers in 0.25–0.5 wt% were added to the SAC0307 alloy to prepare composite solder joints by surface mount technology. The solder joints were shear tested before and after a 4000 h long 85 °C/85% RH corrosive reliability test. The incorporation of ZrO2 nano-particles enhanced the initial shear force of the solder joint, but they decreased the corrosion resistance in the case of 0.5 wt%. SEM, EDS, and FIB analysis revealed intensive growth of SnO2 on the solder joint surfaces, leading to the formation of Sn whiskers. Density functional theory (DFT) simulations showed that, despite Sn being able to bond to the surface of ZrO2, the binding energy was weak, and the whole system was therefore unstable. It was also found that ZrO2 nano-particles refined the microstructure of the solder joints. Decreased β-Sn grain size and more dispersed intermetallic compounds were observed. The microstructural refinement caused mechanical improvement of the ZrO2 composite solder joints by dispersion strengthening but could also decrease their corrosion resistance. While ZrO2 nano-particles improved the solder joint mechanical properties, their use is recommended only in non-corrosive environments, such as microelectronics for space applications.

The effect of SiC nano-phases (nano-particles and nano-fibers) addition into SAC0307 solder paste was investigated on the thermal and microstructural properties of the composite solder joints. The nano-phases were used between 0.125 and 1 wt%, and they were mixed into the solder paste by ball milling process. For the study power MOSFET (metal oxide semiconductor field effect transistor) components were soldered onto metal core printed circuit boards (MCPCBs). The thermal impedance Zth(t) and thermal resistance Rth of MOSFETs were measured by an indirect electrical method. Furthermore, the void formation and the microstructure of solder joints were also studied. The solderability and voiding properties of the composite solder alloys were acceptable. It was found that in 0.5 wt% amount, SiC nano-particles have positive effects on the thermal parameters of the solder joints, which could be explained by the IMC (intermetallic compound) layer growth suppression effect of the nano-phases. The microstructural analysis revealed that the microstructural refinement of the composite solder joints differs in the case of nano-particles and nano-fibers.

This paper presents the effect of electromigration and isothermal ageing in lead-free SAC305 (Sn3Ag0.5Cu) solder joints of chip-size surface mounted (SMD) components, where different track-to-pad joining angles define the current density in the joint. The samples were based on 0402 and 0603 size components and were loaded for an extensive period of 4000 h with 2 and 2.5 A, respectively, in an increased temperature environment (40 °C). The solder joint reliability was assessed at selected times during the loading, with shear tests and cross-section analysis on metallurgic structures. Optical and scanning electron microscopy were used to analyse the microstructure of the solder joints. The shear strength of the solder joints was found to decrease with the increasing loading times. Intermetallic compound (IMC) was found on the 4000 h current stressed samples fracture surface, contrary to the other samples. The IMC layer thickness increased with the loading times and was slightly higher for the anode side of the current stressed components. The current stressing resulted in extensive copper dissolution from the pad and IMC layer accumulation at the component metallisation at the cathode side, affecting the reliability of the joints and pointing to electromigration.

The main joining process of the electronic industry is still soldering with different alloys of Sn. This work studied the relationship between Sn whisker growth and corrosion resistance of 99Sn0.3Ag0.7Cu–TiO2/ZnO (0.25wt%) composite solder alloys in a corrosive environment via scanning electron microscopy and focused ion beam techniques. The corrosive environment test showed that the application of TiO2 and ZnO nano-particles almost totally suppressed the Sn whisker growth and improved the corrosion resistance of the composite solder alloys compared to the reference 99Sn0.3Ag0.7Cu alloy. The microstructural analysis of the reference 99Sn0.3Ag0.7Cu solder alloy showed that the volumetric increase of the corroded β-Sn grains resulted in local mechanical stress in the solder joints, which was released by Sn whisker development. However, in the composite solder joints, the increased grain boundary fraction and segregation of the TiO2 and ZnO nano-particles to the grain boundaries resulted in a relatively uniform and compact protective oxide layer at the β-Sn grain boundaries. This suppressed the formation of SnOx, and via this, the corrosion-induced whisker growth.

The properties of Sn99Ag0.3Cu0.7 (SACX0307) solder alloy reinforced with ZnO nanoparticles were investigated. The primary ZnO particle sizes were 50, 100, and 200 nm. They were added to a solder paste at a ratio of 1.0 wt %. The wettability, the void formation, the mechanical strength, and the thermoelectric parameters of the composite solder alloys/joints were investigated. Furthermore, microstructural evaluations were performed using scanning electron and ion microscopy. ZnO nanoparticles decreased the composite solder alloys’ wettability, which yielded increased void formation. Nonetheless, the shear strength and the thermoelectric parameters of the composite solder alloy were the same as those of the SACX0307 reference. This could be explained by the refinement effects of ZnO ceramics both on the Sn grains and on the Ag3Sn and Cu6Sn5 intermetallic grains. This could compensate for the adverse impact of lower wettability. After improving the wettability, using more active fluxes, ZnO composite solder alloys are promising for high-power applications.