RESUMEN
In this study, the electrochemical performance of an electroless nickel/immersion gold (ENIG) surface finish was evaluated as a function of the Au immersion time by the water immersion migration test. As the Au plating time increased, the electroless nickel phosphorous (EN-P) changed from amorphous to crystalline and then increased in crystallinity. X-ray diffraction (XRD) was used to evaluate the crystallinity of the plating layer. The electrical resistance of the electrodes was tracked as the sample was immersed in water with a 5 V bias. The microstructures of the electrodes after the electrochemical migration test were observed by using secondary electron microscopy (SEM) and energy dispersive spectroscopy (EDS). As the Au immersion time increased, the EN-P's crystallinity and Au thickness increased. This enhanced the electrochemical migration protection of the surface finish layer.
RESUMEN
We investigated the feasibility of a printing technology for Ag circuit formation on a FR4 substrate. A conductive paste containing Ag nanoparticles (73 wt%) of 20-50 nm diameter was screen printed on an FR4 substrate and sintered under a sintering temperature ranging from 100 degrees C to 200 degrees C for 30 min. We carried out the thermal analysis of the Ag nanopaste to confirm the suitability of the set-up conditions. To investigate the sintering degree with various temperatures, fractured cross-sections were observed by field emission scanning electron microscopy (FESEM). For electrical characterization of the printed Ag circuit, a four-point probe method was used to measure the direct current (DC) resistivity, while a network analyzer and Cascade's probe system in the frequency range from 10 MHz to 20 GHz were used to measure the scattering parameters (S-parameter) of the sintered Ag conducting patterns. The resistivity under the application of a DC signal decreased as the temperature increased. The measured S-parameters indicated that the electrical losses decreased as the sintering temperature increased due to the interparticle neck formation after heat treatment at high temperatures.
RESUMEN
In this study, the feasibility of low-cost Cu-sintering technology for power electronics packaging and the effect of sintering conditions on the bonding strength of the Cu-sintered joint have been evaluated. A Cu paste with nano-sized Cu powders and a metal content of ~78% as a high-temperature bonding material was fabricated. The sinter-bonding reactions and mechanical strengths of Cu-sintered joints were evaluated at different sinter bonding pressures, temperatures, and durations during the sintering process. The shear strength of the Cu-sintered joints increased with increasing sintering pressure. Good interfacial uniformity and stable metallurgical microstructures were observed in the Cu joints sintered at a high sintering pressure of 10 MPa, irrespective of the sintering time. It was confirmed that a high-pressure-assisted sintering process could create relatively dense sintered layers and good interfacial uniformity in the Cu-sintered joints, regardless of the sintering temperatures being in the range of 225â»300 °C. The influence of the sinter bonding pressure on the shear strengths of the Cu-sintered joints was more significant compared to that of the sintering temperature. Durations of 10 min (at 300 °C) and 60 min (at 225 and 250 °C) are sufficient for complete sintering reactions between the Si chip and the direct bond copper (DBC) substrate. Relatively good metallic bonding and dense sintered microstructures created by a high sintering pressure of 10 MPa resulted in high shear strength in excess of 40 MPa of the Cu-sintered joints.