The soldering process, essential for electrical and mechanical connections in the microelectronics industry, is crucial for IGBT die attachment as well. This paper investigates the impact of the vacuum reflow process on IGBT assembly using fluxless solder paste activated by formic acid. The paste demonstrates excellent print quality, formability, and consistent solder joint formation. Achieving satisfactory wetting, it compares favorably to traditional solder materials. Key optimized parameters include reflow temperature profiles, activation, and vacuum conditions, such as preheat time, time above liquid (TAL), peak temperature, formic acid concentration, and vacuum ratio. Crucially, formic acid's concentration and activation duration play significant roles in reducing void percentages, effectively decreasing voids from 7.5% to as low as 1%. Vacuum pressure also critically influences void behavior, with reductions in pressure resulting in increased void percentages from 1% to a high of 30%. This study underscores the potential of fluxless solder methodology as a sustainable and economic advancement in the power electronics industry.

The rise of 5G, artificial intelligence, and other applications drives the demand for planar inductors based on PCB processes, due to the advantages of compatible processes, flat shapes, high power densities, reduced volumes, etc. In this paper, six kinds of soft magnetic encapsulation materials (SMEs) were selected to prepare planar dual-layer spiral inductors (PDSI). The actual PDSI device, as well as the six kinds of SMEs, were then processed. Based on the tested relative permeability of SMEs, FEM models were built and calibrated through the actual PDSI structures. Furthermore, FEM models of single-layer, double-layer, and multilayer inductors were established respectively, with analysis of the differences in magnetic properties. The results reveal that both Land Q of the PDSI exhibit a positive linear correlation with the relative permeability of the SMEs, and SMEs with high permeability limit the magnetic leakage. The multilayer inductor could achieve similar Land Q values with a smaller area compared with the planar inductor. However, the increase in thickness limits their application in thin devices. The models can be adjusted to match the SME properties and size parameters of the actual manufacturing process, contributing to simplified calculations for inductor design and performance analysis. Based on such analysis, the planar inductor designs based on in-house SME and PCB-compatible processes are adjusted for high-frequency applications.

Power modules applied in offshore applications are facing risks of corrosion failures on die-attach materials due to high humidity and H₂S exposure. To investigate such corrosion behavior for sintered die-attach materials, we conducted a study with four groups of samples fabricated using copper and silver metal particles under different solvent systems. Such samples were firstly subjected to high-humidity-H₂S conditions for 168 h to simulate the harsh offshore environment. After undergoing corrosion, the primary compounds formed were CuO/Cu₂O and Ag₂S through SEM, XRD, and XPS analysis. Notably, the incorporation of epoxy resin into sintered copper joints resulted in a remarkable reduction in corrosion and a substantial improvement in electrical conductivity after the reaction. In contrast, while the addition of epoxy did not evidently reduce corrosion in silver joints, it did lead to a significant increase in shear strength. Furthermore, to gain further insights into the effect of epoxy resin on corrosion behavior, electrochemical analysis, and molecular dynamics simulations were conducted. Finally, the mechanical reliability of the corroded copper and silver joints was evaluated through thermal shock tests. In summary, sintered copper joints exhibited better anti-corrosion behaviors than sintered silver under high humidity and H₂S exposure, especially with the addition of epoxy resin. However, the corrosion products of sintered copper suffered from a sharp decrease in shear strength after thermal shock tests than sintered silver, which is probably due to the coefficient of thermal expansion mismatch.