Abstract
Sintering of nano Ag paste on bare Cu has attracted more interests recently for high-temperature electronics packaging, which offers the advantages of high reliability, cost-effective and direct bonding process. However, the current bonding methods normally need a protective atmosphere or metallization on Cu substrate to avoid oxidation. In this study, self-assembled monolayers (SAMs) were deposited on Cu substrate to suppress oxidation prior to nano Ag sintering. Thermal-compression bonding process of Cu/nano Ag/Cu joints was conducted and analysed with and without SAMs treatment. The cross-sectional characterization and shear tests were conducted to evaluate the influence of SAMs treatment. When SAMs applied, shear strength of 12.72 MPa has been achieved in the ambient atmosphere, which is much higher than the value without SAMs treatment (3.77 MPa). It has been identified that the shear mode changed from the interfaces of sintered nano Ag/Cu to inside of sintered nano Ag due to the applied SAMs. This technological approach provides a tangible and cost-effective method for high-temperature electronics packaging.
Highlights
With the rapid development of third generation wide-band-gap de vices such as SiC and GaN, it is possible for semiconductors operated at high temperatures with higher power density and switching speeds [1]
It is apparent that nano Ag has sintered and bonded strongly onto bare Cu and the joints were more likely broken from the middle of bulk nano Ag layers
Ag was partially delaminated on righthand side from the Cu/Nano Ag interface in sample 1, and similar fail ures were found in sample 2 & 3 but on the left-hand side
Summary
With the rapid development of third generation wide-band-gap de vices such as SiC and GaN, it is possible for semiconductors operated at high temperatures with higher power density and switching speeds [1]. After a typical thermal-compressing sintering process, the nano Ag paste could be sintered with die and Cu substrate. Such metallization presents a po tential reliability problem, because of the frequent formation of cracks at the interface between the barrier layers and Cu substrate. Shinji et al [9] investigated the reliability of electroless plating Ni on Cu substrate after 500 thermal cycles with the temperature range from − 40 to 250 ◦C. Direct sintering of nano Ag onto bare copper without the interlayer could provide a simpler bonding process and reduce costs if the joints can meet the reliability requirements [10]. Self-assembled monolayers (SAMs) have been applied in electronic packaging for fluxless soldering, which offer the ability to prevent the
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