A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) throu...

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Joining of Silver Nanomaterials at Low Temperatures: Processes, Properties, and Applications

Silver (Ag) has been under development for use as interconnect material for power electronics packaging since the late 1980s. Despite its long development history, high thermal and electrical conductivities, and lead-free composition, sintered Ag technology has limited market penetration. This review sets out to explore what is required to make this technology more viable. This review also covers the origin of sintered Ag, the different types and application methods of sintered Ag pastes and laminates, and the long-term reliability of sintered Ag joints. Sintered Ag pastes are classified according to whether pressure is required for sintering and further classified according to their filler sizes. This review discusses the main methods of applying Ag pastes/laminates as die-attach materials and the related processing conditions. The long-term reliability of sintered Ag joints depends on the density of the sintered joint, selection of metallization or plating schemes, types of substrates, substrate roughness, formulation of Ag pastes/laminates, joint configurations (i.e., joint thicknesses and die sizes), and testing conditions. This paper identifies four challenges that must be overcome for the proliferation of sintered Ag technology: changes in materials formulation, the successful navigation of the complex patent landscape, the availability of production and inspection equipment, and the health concerns of Ag nanoparticles. This paper is expected to be useful to materials suppliers and semiconductor companies that are considering this technology for their future packages.

/pdf/are-sintered-silver-joints-ready-for-use-as-interconnect-2rnz0z0bm7.pdf

Are Sintered Silver Joints Ready for Use as Interconnect Material in Microelectronic Packaging

Review of silver nanoparticle based die attach materials for high power/temperature applications

Microstructural studies and bonding strength of pressureless sintered nano-silver joints on silver, direct bond copper (DBC) and copper substrates aged at 300 °C

Comparing the mechanical and thermal-electrical properties of sintered copper (Cu) and sintered silver (Ag) joints

As a heat-resistant die attach technology processed at low temperatures, three Ag filler-based sinter joining materials have been proposed. Among these, Ag flake pastes exhibited the greatest potential. Joining was carried out by sintering Ag nanoparticles/flakes in air at 200 °C for 60 min. All of the joined samples survived up to 1,000 thermal cycles in a temperature range from −40 to 180/250 °C with a 30 min dwell time. In particular, the joining strengths with the Ag micron and, Ag nano-thick flake pastes maintained excellent strength. Neither thermal fatigue cracks nor large voids were observed in the Ag sintered layers. Thus, low-temperature and low-pressure sinter joining with Ag flakes is expected to have an application in high power semiconductor devices for ultra-high temperature operation.

Microstructural stability of Ag sinter joining in thermal cycling

Emerging SiC power semiconductor devices are expected to work under the high temperature condition of 250–300 °C while the operation of Si devices is limited up to 180 °C. The die-bonding materials for emerging SiC power devices hence need to have sufficient capability in such extreme operating environments. In this study, we investigated the thermomechanical reliability of the die-attach technology using Ag flake paste, which can be processed by low-temperature and low-pressure sintering. The Ag flakes start to sinter immediately after the organic dispersant layer is removed from the flake surface at 160 °C, and die-bonding consequently becomes possible. The tested Si die-attachments joining with the paste maintained high strength (23 MPa) up to 1,000 thermal cycles from −40 to 180 °C. The stable microstructures without crack and no interfacial debonding assure the reliability of the Ag flake paste die-attach of Si. SiC die-attachments also maintained their high strength (24 MPa) up to 1,000 cycles of −40 and 250 °C, though a slight degradation appeared after 1,000 cycles. The debondings at the sintered Ag flake paste layer/SiC wafer interface were affected to the joining strength with the Ag flake paste. The obtained results indicate that our Ag flake paste die-attach can be applied to both Si and SiC power devices capable of high temperature operations.

Thermal fatigue of Ag flake sintering die-attachment for Si/SiC power devices

The developments of SiC power devices have been dramatically advanced for the last several years, and are gaining much attention as a key technology for the low carbon society. These SiC power devices are expected to work under the high temperature condition of 250-300°C because of the wide band-gap energy and the high heat resistance. To meet the high temperature operations, the die-bonding materials must have sufficient reliability under the extreme thermal environments. The present study hence focuses on the thermal reliability of the die-attach technology with using Ag flake paste, which can be sintered at about 200°C. For Si die-attachment on the Cu substrate, the Ag paste displays excellent reliability in the thermal cycles from -40°C to 180°C, and no serious degradation such as crack growth or interfacial debonding happens at either Si/Ag or Ag/Cu interfaces. The tested SiC die-attach samples maintained the high die-bonding strength up to 750 thermal cycles of -40°C and 250°C. However, thermal cracks and many voids appeared after 1000 cycles, and thus these damages due to thermal fatigue decreased the joining strength. These results indicate that the sintered Ag flake paste can withstand at the high operating temperature of new power devices, and our Ag paste can be employed as die-attach materials for both Si and SiC semiconductor power devices.

Thermomechanical reliability of Ag flake paste for die-attached power devices in thermal cycling

Surface modification of Cu flakes through Ag precipitation for low-temperature pressureless sintering bonding

Pressure-less sintering of Cu flake paste is achieved assisted by hydrogen plasma process toward die-attach technique of next-generation high-temperature power semiconductor devices The sintered paste shows high bond strength aver 50 MPa, showing large abnormal grain growth at the bonding interface, with homogeneously distributed void of porous interconnection layer Our results indicate that still the reduction of the surface oxide of Cu flake powders, and thus both the metal powder synthesis and the bonding process must be optimized to achieve a sound bonding interface

Pressure-less plasma sintering of Cu paste for SiC die-attach of high-temperature power device manufacturing

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