This paper reported the enhancement in thermo-mechanical properties and chemical stability of porous SiCOH dielectric thin films fabricated with molecularly scaled pores of uniform size and distribution. The resulting porous dielectric thin films were found to exhibit far stronger resistance to thermo-mechanical instability mechanisms common to conventional SiCOH dielectric thin films without forgoing an ultralow dielectric constant (i.e., ultralow-k). Specifically, the elastic modulus measured by nano-indentation was 13 GPa, which was substantially higher than the value of 6 GPa for a porous low-k film deposited by a conventional method, while dielectric constant exhibited an identical value of 2.1. They also showed excellent resistance against viscoplastic deformation, as measured by the ball indentation method, which represented the degree of chemical degradation of the internal bonds. Indentation depth was measured at 5 nm after a 4-h indentation test at 400 °C, which indicated an ~89% decrease compared with conventional SiCOH film. Evolution of film shrinkage and dielectric constant after annealing and plasma exposure were reduced in the low-k film with a self-organized molecular film. Analysis of the film structure via Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated an increase in symmetric linear Si–O–Si molecular chains with terminal –CH₃ bonds that were believed to be responsible for both the decrease in dipole moment/dielectric constant and the formation of molecular scaled pores. The observed enhanced mechanical and chemical properties were also attributed to this unique nano-porous structure.

The nucleation kinetics and morphology of Cu₆Sn₅ IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu₆Sn₅ IMCs. The smallest Cu₆Sn₅ IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 °C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu₆Sn₅ IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

In this study, a Ag sintered joint was applied to replace the high-Pb solder to bonding materials between Aluminum Nitride (AlN) substrates and terminals used in wafer bake processes. The Ag sintered joint was fabricated using an optimized temperature profile. The high-Pb solder specimens were fabricated using a conventional reflow process. An X-ray analysis and mechanical properties evaluation of the specimens were performed. Subsequently, a high temperature storage test was performed for a high temperature reliability evaluation. The initial void analysis result showed that the Ag sintered joint and high-Pb solder joint had approximately 1%, and 20% voids, respectively. After being stored at a high temperature of 280 ℃ for 1000 h, the shear strength of the high-Pb solder joint decreased by approximately 27% owing to the Pb degradation. However, the shear strength of the Ag sintered joint was maintained. After 1000 h of a high temperature storage test, growth of Ni3Sn4 intermetallic compound and Kirkendall voids were observed at the high-Pb solder interface. Furthermore, a Ag-Au layer was observed at the sintered Ag interface. In addition, the sintered Ag joints densificated after the high temperature storage test.

Conventional hot air reflow soldering is one of major bonding technology when bonding is proceeded on automotive electronics applications. However, here we focus on modifying the bonding process and composition of solder to enhance mechanical and thermal properties. This study experimentally investigated the mechanism of how laser-assisted bonding (LAB) form a small size of initial intermetallic compounds (IMC), and 0.2 wt% Cr element was added to Sn-0.7Cu eutectic solder to suppress the IMC growth. As a result, Sn-0.7Cu and Sn-0.7Cu-0.2Cr initial grain refinement was achieved by LAB. Isothermal aging was conducted to observe the mechanical and thermal properties depending on the IMC growth under 100, 125, 150 ℃ respectively. Sn-0.7Cu-0.2Cr tended to inhibit the growth of IMC at solder matrix and interface compared to Sn-0.7Cu throughout all aging temperature and time. The shear test was proceeded and Sn-0.7Cu-0.2Cr shear force was achieved 18% higher than Sn-0.7Cu. Even after isothermal aging, Sn-0.7Cu-0.2Cr showed lower reduction rate of shear force compared to Sn-0.7Cu.