Sintering of Copper Particles for Die Attach
10 Jul 2012-IEEE Transactions on Components, Packaging and Manufacturing Technology (IEEE)-Vol. 2, Iss: 10, pp 1587-1591
TL;DR: In this paper, a feasibility analysis of sintering of copper particles for die attach is presented, where porosity, Young's modulus as well as electrical and thermal conductivities of sintered layers are analyzed.
Abstract: First steps are taken toward a low-cost alternative to silver sintering as a highly reliable die attach technology for deep drilling applications and future power electronic modules. In this feasibility analysis, we evaluate sintering of copper particles for die attach. Particulate copper pastes are pretreated in H2 atmosphere (50 mbar) in order to gain oxide-free particles. Subsequently, particles are sintered at a pressure of 40 N/mm2 and a temperature of 350°C for 2 min. Porosity, Young's modulus as well as electrical and thermal conductivities of sintered layers are analyzed. Moreover, shear tests at ambient temperature are performed for evaluating the adhesion of monometallic as well as Cu-Au bonds according to the American military standard for chip-substrate contacts (MIL-STD-883H, method 2019.8).
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TL;DR: In this paper, the authors discuss the main methods of applying Ag pastes/laminates as die-attach materials and the related processing conditions, and the long-term reliability of sintered Ag joints.
Abstract: 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.
239 citations
TL;DR: 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, and the future outlook for joining applications with silver nanomaterials is explored.
Abstract: 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...
232 citations
TL;DR: In this article, a complete intermetallic-phases (IPs)-composed joints during die bonding for high temperature applications was achieved by pressureless and fluxless ultrasonic assisted soldering in air within seconds.
90 citations
TL;DR: In this paper, the authors compared the mechanical and thermal-electrical properties of sintered copper (Cu) with Sintered silver (Ag) as bonding materials in the microelectronics joint applications.
71 citations
TL;DR: The developed copper NPs could provide promising advances as nanopastes for sustainable fabrication of copper electrodes and die attachment materials for the production of next-generation power semiconductors.
Abstract: Copper nanoparticles (NPs) with an average particle diameter of 50–60 nm were successfully obtained by reducing an aqueous solution of a copper(II)-nitrilotriacetic acid complex with an aqueous hydrazine solution at room temperature under an air atmosphere. Copper NP-based nanopastes were printed onto a glass substrate using a metal screen mask and pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min. The electrical resistivity of the resulting copper electrode was 16 μΩ · cm. For a metal-to-metal bonding test, copper nanopaste was printed on an oxygen-free copper plate, another oxygen-free copper plate was placed on top, and the bonding strength between the copper plates when pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min was 39 MPa. TEM observations confirmed that highly crystalline metal bonding occurred between the copper NPs and the copper plate to introduce the ultrahigh strength. The developed copper NPs could provide promising advances as nanopastes for sustainable fabrication of copper electrodes and die attachment materials for the production of next-generation power semiconductors.
51 citations
References
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TL;DR: The results show the importance of kinetic effects for the formation of well-defined suboxides during a reduction process and the activation of oxide catalysts.
Abstract: Time-resolved X-ray diffraction, X-ray absorption fine structure, and first-principles density functional calculations were used to investigate the reaction of CuO and Cu(2)O with H(2) in detail. The mechanism for the reduction of CuO is complex, involving an induction period and the embedding of H into the bulk of the oxide. The in-situ experiments show that, under a normal supply of hydrogen, CuO reduces directly to metallic Cu without formation of an intermediate or suboxide (i.e., no Cu(4)O(3) or Cu(2)O). The reduction of CuO is easier than the reduction of Cu(2)O. The apparent activation energy for the reduction of CuO is about 14.5 kcal/mol, while the value is 27.4 kcal/mol for Cu(2)O. During the reduction of CuO, the system can reach metastable states (MS) and react with hydrogen instead of forming Cu(2)O. To see the formation of Cu(2)O, one has to limit the flow of hydrogen, slowing the rate of reduction to allow a MS --> Cu(2)O transformation. These results show the importance of kinetic effects for the formation of well-defined suboxides during a reduction process and the activation of oxide catalysts.
477 citations
01 Dec 2005
Abstract: DESCRIPTION This Third Edition updates a landmark text with the latest findings The Third Edition of the internationally lauded Semiconductor Material and Device Characterization brings the text fully up-to-date with the latest developments in the field and includes new pedagogical tools to assist readers. Not only does the Third Edition set forth all the latest measurement techniques, but it also examines new interpretations and new applications of existing techniques.
465 citations
"Sintering of Copper Particles for D..." refers background in this paper
...which is commonly used to measure the resistivity of a semiconductor wafer [27]....
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01 Oct 1989
TL;DR: In this paper, a diffusion welding-based low-temperature joining technique based on the principle of diffusion welding has been developed for joining a silicon wafer to suitable substrates.
Abstract: Conventional techniques for joining a silicon wafer to suitable substrates do not satisfy the demands of future power devices. Therefore, a low-temperature joining technique based on the principle of diffusion welding has been developed. The surfaces to be joined are metallized with Ag or Au, and the molybdenum substrate is coated with a thin layer of silver flakes. The parts to be joined are then sintered together at about 240 degrees C and a pressure of approximately 40 N/mm/sup 2/ within a few minutes. The joining technique does not affect the silicon wafer and accordingly is compatible with conventional power device and IC fabrication techniques. Both sides of the wafer can be joined with substrates even if IC structures are present. This possibility allows an increased surge current. Numerical calculations for different wafer thicknesses have been performed and compared with results on test devices. The technical usefulness of this approach has been proved by additional tests such as thermal cycling. >
207 citations
"Sintering of Copper Particles for D..." refers background in this paper
..., operating temperature >200 °C, like in deep drilling or nextgeneration power electronics), sintering of silver particles has been investigated to a great extent due to its excellent thermal, electrical, and mechanical properties [1]–[13]....
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TL;DR: In this article, the effect of electroless silver coating on fine copper powder (3.4 μm) and its effects on oxidation resistance were investigated by varying the silver contents.
156 citations
"Sintering of Copper Particles for D..." refers background in this paper
...Therefore, silver-coated fine copper powders have already been proposed for die attach, though in this case the price reduction versus pure silver is negligible [17]....
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...has become a major cost factor in the industry [17], making the sinter die attach using silver particles less attractive....
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TL;DR: In this article, a low-temperature sintering of nanoscale silver paste was used to achieve high temperature operation of SiC power semiconductor devices by using stencil-printed layers of the nano-scale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for die-attachment.
Abstract: In this paper, we present the realization of high-temperature operation of SiC power semiconductor devices by low-temperature sintering of nanoscale silver paste as a novel die-attachment solution. The silver paste was prepared by mixing nanoscale silver particles with carefully selected organic components which can burn out within the low-temperature firing range. SiC Schottky diodes were placed onto stencil-printed layers of the nanoscale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for the die-attachment. After heating up to 300degC and dwell for 40 min in air to burn out the organic components in the paste and to sinter the nanoscale silver, the paste consolidated into a strong and uniform die-attach bonding layer with purity >99% and density >80%. Then the die-attached SiC devices were cooled down to room temperature and their top terminals were wire-bonded to achieve the high-temperature power packages. Then the power packages were heated up from room temperature to 300degC for high-temperature operation and characterization. Results of the measurement demonstrate the low-temperature silver sintering as an effective die-attach method for high-temperature electronic packaging. An advanced packaging structure for future SiC transistors with several potential advantages was also proposed based on the low-temperature sintering technology.
153 citations