Low temperature SiC die-attach bonding technology by hillocks generation on Al sheet surface with stress self-generation and self-release

Abstract

this paper introduced an approach of die-attach bonding technology based on a low-cost high-purity aluminum (99.99%) sheet in a silicon carbide (SiC)/direct bonded aluminum (DBA) power module. Both sides of an Al sheet were sputtered by a thin Ti and Ag layer, which generated a tensile stress of 166 MPa on the Al surface. After heating, the Al surface displayed a large quantity of Ag hillocks by stress selfrelease due to the coefficient of thermal expansion (CTE) mismatch among Al, Ti, and Ag. The SiC/Al sheet/DBA substrate interfaces were bridged by the generation of these hillocks, which correspond to a robust shear strength of 33.4 MPa in a low-temperature process. Hillocks generation and the interface bonding mechanism by surface stress self-generation and self-release were systematically analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The shear strength remains constant at 32.1 MPa after high-temperature storage at 250 °C for 500 h, which suggests that the Al sheet possesses excellent high-heat resistance and thermal stability. this novel approach of die-attach bonding technology serves as an attractive alternative for Sic power devices that require high-temperature performance. Silicon carbide (SiC) forms a next-generation power semiconductor that realizes innovative energy saving in all types of electronic equipment, such as information communication equipment, electric vehicles, and electric railways 1-4. Next-generation super-heat-resistant packaging needs to secure reliability at extremely high operating temperatures (maximum temperature of 250 °C), which are substantially higher than the operating temperature of conventional Si devices (maximum temperature of 150 °C). Although the junction temperature of SiC is 250 °C, SiC can operate at high temperatures. The heat resistance of each part that constitutes the module is lower than 175 °C, which is representative of most solder die-attach materials. To address these challenges, a novel class of die-attach technologies is required due to the processability, compliance, and cost of solders. However, the electrical and thermal properties must match those of a pure metal. SiC power device modules comprise several components, including terminals, a SiC die, direct bonded copper (DBC) or direct bonded aluminum (DBA) substrate, and a heat sink. The bonding technology of SiC die devices, which can be employed for high operating temperature mounting, can be divided into three categories: (1) high melting point solder bonding 5-7 , (2) solid-liquid inter-diffusion bonding (SLID) 8-10 , (3) sinter silver paste joining 11-15 or copper paste joining 16,17. SLID bonding technology has a few advantages, such as a relatively short bonding time and some surface roughness tolerance; however, it is generally limited to material combinations with a favorable phase diagram 17 and interface voids generation 18. The use of sintered Ag paste as a bonding layer has received considerable attention due to its sup...

Effect of Annealing on the Microstructure and SERS Performance of Mo-48.2% Ag Films

“…Figure 4 a–d shows cross-sectional morphology of the Mo-Ag films before and after annealing. Obviously, the Ag particles are distributed on the Mo-48.2% Ag film, and the position relationship between Ag particles and the films is different from the hillock [ 36 ]. The thickness of the Mo-48.2% Ag film can be clearly seen from the cross-sectional morphology, and the film thickness gradually decreases as the annealing temperature increases as shown in Figure 4 e. The reason is that the formation and growth of polyhedral Ag particles on the annealed Mo-Ag film consumes abundant Ag atoms in the vicinity of the film surface.…”

“…The scanning range and acquisition time are, respectively, 200-2000 cm −1 and 1 s. Figure 4a-d shows cross-sectional morphology of the Mo-Ag films before and after annealing. Obviously, the Ag particles are distributed on the Mo-48.2% Ag film, and the position relationship between Ag particles and the films is different from the hillock [36]. The thickness of the Mo-48.2% Ag film can be clearly seen from the cross-sectional morphology, and the film thickness gradually decreases as the annealing temperature increases as shown in Figure 4e.…”

“…The thickness of the Mo-48.2% Ag film can be clearly seen from the cross-sectional morphology, and the film thickness gradually decreases as the annealing temperature increases as shown in Figure 4e. The reason is that the formation and growth of polyhedral Ag particles on the annealed Mo-Ag film consumes abundant Obviously, the Ag particles are distributed on the Mo-48.2% Ag film, and the position relationship between Ag particles and the films is different from the hillock [36]. The thickness of the Mo-48.2% Ag film can be clearly seen from the cross-sectional morphology, and the film thickness gradually decreases as the annealing temperature increases as shown in Figure 4e.…”