High Strength Die-Attach Joint Formation by Pressureless Sintering of Organic Amine Modified Ag Nanoparticle Paste

Sintered silver (Ag) die-attach has attracted much attention in power systems with high power density and high operating temperature. In this paper, we proposed a novel surface modification method for Ag nanoparticles with organic amines as a coating agent for enhancing the pressureless sintering performance. This work systematically introduced the Ag nanoparticle modification process, Ag paste preparation, and sintering process and compared the changes in the sintering performance of Ag nanoparticles after modification with four different alkyl chain lengths of amines. The study showed that the sintered films of Ag nanoparticle pastes modified with n-octylamine (NOA) can achieve the lowest resistivity of the sintered film and the highest shear strength of the bonded joints. The resistivity of the sintered Ag film is affected by the grain size and microscopic morphology, and the strength of the bonded joints is also related to the sintering density and the amount of organic residues. The thermal behavior of the Ag particles coated with different amines is measured by thermal analysis. Finally, the mechanism of NOA-modified Ag nanoparticles to improve the sintering performance is proposed. This study can provide effective data and theoretical support for the further promotion and application of nano-Ag pressureless sintering.

Effectiveness of Oxygen during Sintering of Silver Thin Films Derived by Nanoparticle Ink

Silver nanoparticle (NP) inks have been widely used in the ink-jet printing field because of their excellent properties during low-temperature sintering. However, the organic dispersant used to prevent the aggregation and sedimentation of NPs can hinder the sintering process and result in the high resistivity of sintered films. In this study, silver thin films derived from silver NP ink with polyvinylpyrrolidone (PVP) dispersant were sintered in different atmospheres of pure nitrogen, air, and pure oxygen. The effect of the oxygen content in the sintering atmosphere on the thermal properties of the ink, the electrical resistivity and microstructure of the sintered films, and the amount of organic residue were studied by using differential scanning calorimetry, the four-point probe method, scanning electron microscopy, Fourier transform infrared spectroscopy, etc. The mechanism of optimizing the film resistivity by influencing the decomposition of the PVP dispersant and the microstructure evolution of the silver thin films through the sintering atmosphere was discussed. The results demonstrated that an oxygen-containing atmosphere could be effective for silver NPs in two ways. First, the oxygen content could enhance the diffusion ability of silver atoms, thus accelerating the stage transition of microstructural evolution at low temperatures. Second, the oxygen content could enable the PVP to decompose at a temperature much lower than in conditions of pure nitrogen, thus helping to finalize the densification of a silver film with a low resistivity of 2.47 μΩ·cm, which is approximately 1.5-fold that of bulk silver. Our findings could serve as a foundation for the subsequent establishment of ink-jet printing equipment and the optimization of the sintering process for printing silver patterns on flexible substrates.

Size-tunable synthesis of iron oxide nanocrystals by continuous seed-mediated growth: role of alkylamine species in the stepwise thermal decomposition of iron(II) oxalate

The properties of inorganic nanoparticles (NPs) are governed by their size. Therefore, tuning the size of NPs is a fundamental technique in nanoscience. However, the size-tunable synthesis of inorganic NPs is generally carried out in a dilute solution, which produces large quantities of waste. Herein, we report the predictable size-tunable synthesis of Fe₃O₄ NPs by the stepwise thermal decomposition of iron(II) oxalate (Fe(ox)). Monodisperse Fe₃O₄ seed crystals were synthesized by the thermal decomposition of oleylamine-coordinated iron oxalate (Fe(ox)-OAm) in a small amount of oleylamine, followed by continuous seed-mediated growth of Fe₃O₄ NPs. The thermal decomposition behavior of Fe(ox) in oleylamine with and without N,N-diethyl-1,3-diaminopropane (dedap) revealed the important role of dedap in the stepwise thermal decomposition of Fe(ox). The size of the Fe₃O₄ NPs was easily tuned via the stepwise thermal decomposition of Fe(ox) by controlling the amount of decomposed Fe(ox) in a small amount of an alkylamine mixture. The particle diameter was predicted from the size of the Fe₃O₄ seed crystals and the amount of decomposed Fe(ox). Finally, the size dependency of magnetic properties of the synthesized Fe₃O₄ NPs was studied. This continuous seed-mediated growth method based on the stepwise thermal decomposition of metal oxalate can be applied to control the size of a variety of metal and metal oxide NPs.

Nanocomposite Inks Based on Nickel–Silver Core–Shell and Silver Nanoparticles for Fabrication Conductive Coatings at Low-Temperature Sintering

Nanocomposite inks composed of nickel–silver core–shell and silver nanoparticles (NPs) can combine the advantages of lower cost, high conductivity, and low-temperature sintering processes, which have attracted much attention in the development of materials for printed flexible electronics. In this context, in the present paper, we report the process of preparation of nanocomposite ink containing nickel–silver core–shell nanoparticles, as the main filler, and silver nanoparticles, as doping material, and their application for the fabrication of conductive coatings. It was found that the addition of a low concentration of Ag NPs to ink formulation based mainly on low-cost Ni-Ag NPs improves the conductive properties of coatings fabricated by ink deposition on a glass substrate. Two types of prepared nanocomposite ink coatings showed promising properties for future application: (1) doped with 0.5% of Ag NPs sintered at 200 °C as low cost for larger industrial application and, (2) containing 1% of Ag NPs sintered at 150 °C for the fabrication of conductive printed patterns on flexible substrates. The conductivity of such nanocomposite films was similar, about of 6 × 106 S/m, which corresponds to 35% of that for a bulk nickel.

Reactive Sintering of Cu Nanoparticles at Ambient Conditions for Printed Electronics

A new approach is presented to overcome the disadvantages of oxidation and harsh sintering conditions of Cu nanoparticle (Cu NP) conductive inks simultaneously. In this process, oleylamine (OAM) adsorbed on particles was effectively eliminated via the reactive desorption by formic acid in alcohols; meanwhile, Cu ion was generated on the surface. The desorption of OAM resulted in more severe surface oxidation of Cu NPs. The oxide (Cu₂O) and Cu²⁺ distributed on the Cu NP surface could be reduced to Cu(0) by NaBH₄ solution and take on the role of soldering flux to weld particles into a blocky structure. With the compact coalescence of particles without oxides, the resistivity of metal patterns could fall below 20 μΩ·cm and exhibit proper adhesion. Thanks to the sintering of Cu NPs at ambient conditions, the conductive patterns could be facilely formed on thermosensitive substrates. As the oxide state of Cu would be reduced during sintering, the partially oxidized Cu nanoparticles could be directly applied to conductive inks.

Silver Nanoparticles Based Ink with Moderate Sintering in Flexible and Printed Electronics

Printed electronics on flexible substrates has attracted tremendous research interest research thanks its low cost, large area production capability and environmentally friendly advantages. Optimal characteristics of silver nanoparticles (Ag NPs) based inks are crucial for ink rheology, printing, post-print treatment, and performance of the printed electronics devices. In this review, the methods and mechanisms for obtaining Ag NPs based inks that are highly conductive under moderate sintering conditions are summarized. These characteristics are particularly important when printed on temperature sensitive substrates that cannot withstand sintering of high temperature. Strategies to tailor the protective agents capping on the surface of Ag NPs, in order to optimize the sizes and shapes of Ag NPs as well as to modify the substrate surface, are presented. Different (emerging) sintering technologies are also discussed, including photonic sintering, electrical sintering, plasma sintering, microwave sintering, etc. Finally, applications of the Ag NPs based ink in transparent conductive film (TCF), thin film transistor (TFT), biosensor, radio frequency identification (RFID) antenna, stretchable electronics and their perspectives on flexible and printed electronics are presented.

Structural evolution of Ag/BN hybrids via a polyol-assisted fabrication process and their catalytic activity in CO oxidation

Enhanced catalytic activity of Ag/BN nanohybrids is ascribed to the formation of a thin intermediate Ag–O–B layer.

Silver Ink Formulations for Sinter-free Printing of Conductive Films

Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering.

Tannic acid stabilized silver nanoparticles for inkjet printing of conductive flexible electronics

Tannic acid stabilized silver nanoparticles were prepared as conductive inks for fabricating conductive patterns using a common color inkjet printer.

Sintering mechanism of the Cu–Ag core–shell nanoparticle paste at low temperature in ambient air

Cu–Ag core–shell nanoparticles owned good anti-oxidation ability, and as-fabricated joints using the Cu–Ag core–shell nanoparticles paste showed high shear strength.

Bimodal sintered silver nanoparticle paste with ultrahigh thermal conductivity and shear strength for high temperature thermal interface material applications

A bimodal silver nanoparticle (AgNP) paste has been synthesized via the simple ultrasonic mixing of two types of unimodal AgNPs (10 and 50 nm in diameter). By sintering this paste at 250 °C for 30 min, we obtained an ultrahigh thermal conductivity of 278.5 W m(-1) K(-1), approximately 65% of the theoretical value for bulk Ag. The shear strength before and after thermal cycling at 50-200 °C for 1000 cycles was approximately 41.80 and 28.75 MPa, respectively. The results show that this excellent performance is attributable to the unique sintered structures inside the bimodal AgNP paste, including its low but stable porosity and the high density coherent twins. In addition, we systematically discuss the sintering behavior of this paste, including the decomposition of the organic layers and the formation of the coherent twins. On the basis of these results, we confirm that our bimodal AgNP paste has excellent potential as a thermal interface material for high temperature power device applications.