Heat-Resistant Microporous Ag Die-Attach Structure for Wide Band-Gap Power Semiconductors

Abstract

In this work, efforts were made to prepare a thermostable die-attach structure which includes stable sintered microporous Ag and multi-layer surface metallization. Silicon carbide particles (SiCp) were added into the Ag sinter joining paste to improve the high-temperature reliability of the sintered Ag joints. The use of SiCp in the bonding structures prevented the morphological evolution of the microporous structure and maintained a stable structure after high temperature storage (HTS) tests, which reduces the risk of void formation and metallization dewetting. In addition to the Ag paste, on the side of direct bonded copper (DBC) substrates, the thermal reliability of various surface metallizations such as Ni, Ti, and Pt were also evaluated by cross-section morphology and on-resistance tests. The results indicated that Ti and Pt diffusion barrier layers played a key role in preventing interfacial degradations between sintered Ag and Cu at high temperatures. At the same time, a Ni barrier layer showed a relatively weak barrier effect due to the generation of a thin Ni oxide layer at the interface with a Ag plating layer. The changes of on-resistance indicated that Pt metallization has relatively better electrical properties compared to that of Ti and Ni. Ag metallization, which lacks barrier capability, showed severe growth in an oxide layer between Ag and Cu, however, the on-resistance showed fewer changes.

Power Cycling Reliability with Temperature Deviation of Pressureless Silver Sintered Joint for Silicon Carbide Power Module

“…Recently, the use of SiC WBG devices has been increasing because their switching performance is significantly superior to that of currently used Si. Furthermore, wide bandgap (WBG) devices such as GaN power modules afford high-speed switching but are limited to operating in a power range of approximately 600-800 V. Consequently, for EV applications necessitating power modules of ‡ 1200 V/200 A, [4][5][6][7][8][9][10][11][12][13][14] SiC devices are indispensable. However, SiC devices, which exhibit maximum junction temperatures of only up to 300°C during operation, 9 preclude traditional soldering techniques owing to the risk of remelting.…”

“…Hence, Ag sinter bonding technology, which remains stable up to the melting point of Ag at 960°C, is actively being researched. However, despite active advancements in alternative Ag sintering bonding processes 2,4-14 and materials, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] a comprehensive comparison detailing the performance and long-term reliability differences between soldered and sintered modules…”

Microstructural and mechanical evolution of sintered nano-silver joints on bare copper substrates during high-temperature storage

“…Due to the size effect, the high surface activity of Ag nanoparticles (Ag-NPs) can drive the diffusive migration of silver atoms and achieve rapid structure densification at the temperature well below the melting point of bulk silver (Li et al , 2017; Yang et al , 2019; Wang and Benabou, 2020). At the same time, nano-silver paste has excellent electrical and thermal conductivity and “low-temperature sintering, high-temperature service” performance, which made its application in the field of high-temperature and high-power semiconductor have a very broad development prospect (Chen and Suganuma, 2021; Tan et al , 2017; Noh et al , 2018; Yoon and Back, 2022). Ogura et al (2010) found that repeated thermal cycling in an air atmosphere deepened the oxidation of the copper substrate in the nano-silver joints, resulting in a severe weakening of the bonding strength of the joints.…”

Low-Temperature Sinterable Cu@Ag Paste with Superior Strength Driven by Pre-Heating Process

“…Power devices based on wide-bandgap (WBG) semiconductors, including silicon carbide and gallium nitride, have attracted significant attention because of their ability to operate at higher temperatures, voltages, and frequencies [1][2][3][4]. Compared to conventional silicon-based power devices, the operating temperature of the power devices based on WBG semiconductors can exceed 200 • C [5][6][7][8], suggesting that their size and weight can be reduced by reducing the number and dimensions of the cooling parts. Therefore, there is an increasing demand for developing highly robust interconnection materials that help maintain the linkage between WBG chips and substrates at high temperatures and thus preserve the structural integrity of the devices [9].…”