Silver nanowires >60 μm and even 100 μm in length have been synthesized using a polyol process by adjusting the stirring speed at 130 °C. The length is over three times longer than that of normal ...AgNWs. These wires have a uniform ∼60 nm diameter, independent of the stirring speed. At 91% transmittance at 550 nm, AgNW films fabricated at room temperature achieved 25 Ω per square sheet resistance, which is superior to that of expensive ITO films.
New types of die attach pastes comprising micron-sized Ag particles hybridized with submicron-sized Ag particles were considered as lead-free die attach materials for SiC power semiconductors. ...Micron-sized Ag particles in alcohol solvent were prepared by mixing the die attach paste with submicron-sized Ag particles. The alcohol vaporizes completely during sintering and no residue exists in the bonding layer. The Ag layer has a uniform porous structure. The electrical resistivity of the printed tracks decreases below 1
×
10
−5
Ω
cm when sintered above 200
°C. When sintered at 200
°C for 30
min, the average resistivity reaches 5
×
10
−6
Ω
cm, which is slightly higher than the value obtained by using Ag nanoparticle paste. A SiC die was successfully bonded to a direct bonded copper substrate and the die-shear strength gradually increases with the increase in bonding temperature up to 300
°C. The Ag die attach bond layer was stable against thermal cycles between −40
°C and 300
°C.
The effects of alloy composition on microstructural, especially the formation of large intermetallic compounds, and mechanical properties of various Sn–Ag–Cu solder joints were investigated. The ...range of Ag–Cu content of Sn–Ag–Cu alloys was from 3.0 wt.%Ag–0.5 wt.%Cu to 3.9Ag–0.7 wt.%Cu. The high Ag content alloys exhibit the formation of large Ag
3Sn platelets especially at the solder–reaction layer interfaces, regardless of the kind of substrates. Long Cu
6Sn
5 whiskers are formed in all the solder–Cu joints and the high Cu content solder joints. Those whiskers have two shapes of needle and of hollow types. For the high Cu content solder joints with a 42 alloy substrate, long Ni–Cu–Sn whiskers are also formed at the interface and in the solder. The presence of large Ag
3Sn platelets does not degrade strength directly, but affects fracture mode. Large Ag
3Sn platelets induce brittle fracture at an interface and provide crack initiation sites. In order to avoid the formation of the large intermetallic compounds, especially Ag
3Sn platelets, the optimum composition of Sn–Ag–Cu alloy lies in the lower Ag–Cu content.
An ultra heat-shock resistant die-attach structure for a silicon carbide power device was developed. A silicon carbide die with a gold/titanium nitride coating was soldered with pure zinc onto a DBC ...with a silicon nitride insulator plate. This die-attach structure could resist severe thermal shock in air temperatures between -50°C and 300°C. No substantial change in microstructure was observed at the soldering interface, while conventional high-lead solder forms severe cracking. This die-attach structure can be also applied to other types of high-temperature device applications.
The microstructures and tensile properties of three typical Sn–Ag–Cu alloys, Sn–3.0wt.%Ag–0.5wt.%Cu, Sn–3.5wt.%Ag–0.7wt.%Cu and Sn–3.9wt.%Ag–0.6wt.%Cu, prepared under three different cooling ...conditions were evaluated after casting. The microstructures of all rapidly cooled specimens consisted of the eutectic phase of β-Sn with fine fibrous Ag
3Sn dispersion surrounding primary β-Sn grains. The slowly cooled Sn–3.5Ag–0.7Cu and Sn–3.9Ag–0.6Cu alloys exhibited additional large primary Ag
3Sn platelets, while the Sn–3.0Ag–0.5Cu did not. For all alloys, both ultimate tensile strength and 0.2% proof stress increased with increasing strain-rates in tensile tests. Lowering cooling speed decreased tensile strength. Elongation increased with an increasing strain rate from 10
−5 to 10
−2 s
−1, and decreased slightly at 10
−1 s
−1 for the rapidly cooled specimens. Elongation remarkably decreased for the slowly cooled Sn–3.5Ag–0.7Cu and Sn–3.9Ag–0.6Cu alloys, a degradation attributable to the formation of large primary Ag
3Sn platelets.
We have successfully developed a new Ag nanoparticle paste which can sinter at room temperature simply by drying the solvent from the paste. A small amount of alkylamine was incorporated into the Ag ...nanoparticle paste to form protective layers on the nanoparticles. By drying at room temperature, Ag nanoparticles are sintered, resulting in a low resistivity of 4.9
×
10
−6
Ωm. Since the new paste can be sintered even at room temperature without heat treatment, it should prove versatile for applications in electronics wiring.
► We enhanced the characteristics of pure Zn as die-attach material. ► The new die-attach materials were made by addition of minor elements in pure Zn. ► We selected Ca, Mn, Cr, and Ti as minor ...elements. ► The mechanical properties of pure Zn were enhanced by the minor elements addition. ► In addition, the minor elements addition improved oxidation resistance.
Pure Zn is one of the best die-attachment candidates for use in next-generation wide-gap semiconductor power devices operating at temperatures up to 300°C. However, it has certain drawbacks when used at high operating temperatures: poor ductility and limited oxidation resistance. In this study, we investigated the effect of adding minor elements – Ca, Mn, Cr, and Ti – in improving Zn ductility and oxidation resistance. This addition significantly reduced the grain size of the microstructure, thus improving the tensile strength and elongation of pure Zn. In addition, the minor elements addition significantly improved oxidation resistance of pure Zn. Consequently, because of higher ductility and oxidation resistance, the interconnection ability of Zn alloys as die-attachment candidates was significantly enhanced.
The objective of this work is to develop bioactive glass coatings for metallic orthopedic implants. A new family of glasses in the SiO
2–Na
2O–K
2O–CaO–MgO–P
2O
5 system has been synthesized and ...characterized. The glass properties (thermal expansion, softening and transformation temperatures, density and hardness) are in line with the predictions of established empirical models. The optimized firing conditions to fabricate coatings on Ti-based and Co–Cr alloys have been determined and related to the glass properties and the interfacial reactions. Excellent adhesion to alloys has been achieved through the formation of 100–200 nm thick interfacial layers (Ti
5Si
3 on Ti-based alloys and CrO
x
on Co–Cr). Finally, glass coatings, approximately 100 μm thick, have been fabricated onto commercial Ti alloy-based dental implants.
•We demonstrate a novel Pb-free die-attachment structure using Sn-plated Zn solder.•The bonded microstructure can be controlled by the process time.•The current bonding structure shows high bonding ...strength above 30MP.•The fracture of current bonding system occurred in the β-Sn matrix soldered layer.•The β-Sn phase in the fracture layer can be expected to reduce the brittleness of Zn.
A novel die-attachment method is demonstrated through quasi-transient liquid-phase bonding using Sn-plated Zn sheets. The bonding temperature can be decreased to 250°C, which is ∼100°C lower than that for typical Zn–Sn high-temperature solders. The bonded interface consists of primary α-Zn and Sn–Zn eutectic phases, and the microstructure can be controlled according to the diffusion velocities of metals. The high die-shear strength exceeding 30MPa from the controlled microstructure is superior to typical Pb–5Sn solders strength around 20MPa.
The effects of the fourth elements, i.e., Fe, Ni, Co, Mn and Ti, on microstructural features, undercooling characteristics, and monotonic tensile properties of Sn–3 wt.%Ag–0.5 wt.%Cu lead-free solder ...were investigated. All quaternary alloys basically form third intermetallic compounds in addition to fine Ag
3Sn and Cu
6Sn
5 and exhibit improved solder structure. The precipitates of Sn–3Ag–0.5Cu (–0.1 wt.%X; X=Ni, Ti and Mn) alloy are very fine comparing with the other alloys. The effective elements for suppressing undercooling in solidification are Ti, Mn, Co and Ni. All quaternary bulk alloys exhibit similar or slightly larger tensile strengths; especially Mn and Ni can improve elongation without degrading strength. The interfacial phases of Sn–3Ag–0.5Cu (–0.1 wt.%X; X=Fe, Mn and Ti)/Cu joints are typical Cu
6Sn
5 scallops. Sn–3Ag–0.5Cu (–0.1 wt.%X; X=Ni and Co)/Cu joints form very fine Sn–Cu–Ni and Sn–Cu–Co scallops at interface. The Cu/Sn–3Ag–0.5Cu–0.1Ni/Cu joint exhibits improved tensile strength prior to thermal aging at 125 and 150 °C. The fracture surface of Cu/Sn–3Ag–0.5Cu/Cu joint exhibits mixture of ductile and brittle fractures, while Cu/Sn–3Ag–0.5Cu (–0.1X; X=Ni and Co)/Cu joints exhibit only brittle fracture at interface. The Sn–3Ag–0.5Cu–0.1Ni alloy is more reliable solder alloy with improved properties for all tests in the present work.
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