Modern power electronics has the increased demands in current density and high-temperature reliability. However, these performance factors are limited due to the die attach materials used to affix power dies microchips to electric circuitry. Although several die attach materials and methods exist, nanosilver sintering technology has received much attention in attaching power dies due to its superior high-temperature reliability. This paper investigated the sintering properties of nanosilver film in double-side sintered power packages. X-ray diffraction results revealed that the size of nanosilver particles increased after pressure-free sintering. Compared with the pressure-free sintered nanosilver particles, the 5-MPa sintered particles showed a higher density. When increasing sintering pressure from 5 to 30 MPa, the shear strength of the sintered package increased from 8.71 to 86.26 MPa. When sintering at pressures below 20 MPa, the fracture areas are mainly located between the sintered Ag layer and the surface metallization layer on the fast recovery diode (FRD) die. The fracture occurs through the FRD die and the metallization layer on the bottom molybdenum substrate when sintering at 30 MPa.

In this paper, moisture absorption/desorption and hygroscopic swelling of silicone/phosphor composite film and epoxy mold compound (EMC) used in chip-on-board (COB) LED packaging is studied with in-situ characterization. Material properties, including diffusivity, activation energy, saturated moisture concentration and the coefficient of hygroscopic swelling, are extracted from the experimental data. For silicone/phosphor film, the moisture diffusion can be described by the conventional Fickian diffusion model. However, the saturated moisture concentration increases with temperatures under the same relative humidity condition. The dependence of saturated moisture concentration on temperature is characterized by an Arrhenius-like equation, and the net absorption heat is found to be 8–11 kJ/mol. Furthermore, the silicone/phosphor composite film shows reversible diffusion process during absorption and desorption cycle, which confirms the Fickian behavior of moisture absorption. Moisture diffusion in EMC, on the other hand, exhibits non-Fickian diffusion, and thus, a dual stage diffusion model is adopted to fit experimental data. Moreover, EMC shows partially non-reversible moisture absorption during absorption and desorption cycle, which is consistent with the dual-stage model description. In hygroscopic swelling testing, silicone/phosphor film shows a permanent swelling during moisture absorption despite that the moisture absorption is completely reversible. EMC shows partially reversible swelling after moisture is removed, which indicates the residual moisture in material. Further study is needed to understand the mechanism of permanent hygroscopic swelling for silicone/phosphor composite during moisture absorption and desorption.