Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation–reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene. Encapsulation of single-atom and particulate gold within growing zeolite frameworks generates active catalysts with exceptionally high thermal stability.

/pdf/generation-of-subnanometric-platinum-with-high-stability-3mtyrisge0.pdf

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D

Pb-free solders have replaced Pb-containing SnPb solders in the electronic packaging industry due to environmental concerns. Both electromigration (EM) and thermomigration (TM) have serious reliability issues for fine-pitch Pb-free solder bumps in the flip-chip technology used in consumer electronic products. We review the unique features of EM and TM in flip-chip solder bumps, emphasizing the effects of current crowding and Joule heating. In addition, the challenges to a better understanding of EM and TM in Pb-free solders are discussed. For example, the anisotropic nature of Sn microstructure in Pb-free solders can enhance the dissolution rates of Ni and Cu in solders driven by EM and TM.

https://ir.nctu.edu.tw:443/bitstream/11536/6094/1/000280818700021.pdf

Electromigration and Thermomigration in Pb-Free Flip-Chip Solder Joints

The trend of continuing miniaturisation of microelectronics leads to new thermal management challenges. A key point in the heat removal process development is to improve the heat conduction across interfaces through improved thermal interface materials (TIMs). We identify the key areas for state-of-the art TIM research and investigate the current state of the field together with possible future advances.

Novel nanostructured thermal interface materials: a review

Failure mechanisms of solder interconnects under current stressing in advanced electronic packages

Coaxial waveguide microstructures are provided. The microstructures include a substrate (2) and a coaxial waveguide disposed about the substrate. The coaxial waveguide includes: a center conductor (20); an outer conductor including one or more walls (4, 10, 18, 24, 28), spaced apart from and disposed around the center conductor; one or more dielectric support members (12’) for supporting the center conductor in contact with the center conductor and enclosed within the outer conductor; and a core volume (30) between the center conductor and the outer conductor, where the core volume is under vacuum or in a gas state. Also provided are methods of forming coaxial waveguide microstructutres by sequentially building processes and hermetic packages which include a coaxial microstructure.

Coaxial waveguide microstructures and methods of formation thereof

Size-dependent melting properties of tin nanoparticles

In advanced electronic products, current crowding induced electromigration failure is one of the serious problems in fine pitch flip chip solder joints. To explore a strong resistance against current crowding induced electromigration failure, a very thick Cu column bump combined with a shallow solder interconnect at 100μm pitch for flip chip applications has been studied in this paper. Results revealed that these interconnects do not fail after 720h of current stressing at 100°C with a current density of 1×104A∕cm2 based on the area of interface between Cu column bump and solder. The reduction of current crowding in the solder region by using thick Cu column bumps increased the reliability against electromigration induced failure. The current distribution in a flip chip joint of a Cu column bump combined with a shallow solder has been confirmed by simulation. However, Kirkendall void formation was found to be much serious and enhanced by electromigration at the Cu∕Cu3Sn interface due to the large Cu∕Sn ratio. Since this is a system of a limited amount of Sn and an infinite supply of Cu, the Cu6Sn5 transforms to the Cu3Sn after all the Sn content in the solder bump is consumed and the Cu3Sn can grow very thick; the vacancy flux that opposes the Cu flux will condense to form Kirkendall voids. The mechanism of electromigration induced Kirkendall void formation in the Cu column with the shallow solder joint is discussed. Furthermore, a very large temperature gradient exists across the shallow solder interconnects, leading to thermomigration. Electromigration accompanied by thermomigration could replace current crowding as a serious reliability issue in using Cu column based interconnects.

Electromigration in flip chip solder joints having a thick Cu column bump and a shallow solder interconnect

This paper describes the creep behavior of three tin-rich solders that have become candidates for use in lead-free solder joints: Sn-3.5Ag, Sn-3Ag-0.5Cu, and Sn-0.7Cu. The three solders show the same general behavior when tested in thin joints between copper and Ni/Au metallized pads at temperatures between 60‡C and 130°C. Their steady-state creep rates are separated into two regimes with different stress exponents. The low-stress exponents range from ∼3–6, while the high-stress exponents are anomalously high (7–12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95°C to 60°C. The anomalous creep behavior of the solders appears to be due to the dominant tin constituent. Research on creep in bulk samples of pure tin suggests that the anomalous temperature dependence of the stress exponent may show a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating tin-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.

/pdf/the-creep-properties-of-lead-free-solder-joints-4v0lvq9i6t.pdf

The creep properties of lead-free solder joints

An electronic assembly including a die (40), having an integrated circuit formed therein, a thermally conductive heat spreader (16), and indium (14) located between the die and the heat spreader, is described. The heat spreader (16) has a layer of nickel (22). A gold layer (24) is formed on the nickel layer (22), and provides better wetting of indium than nickel. A better structural connection between the indium (14) and the heat spreader (16) is provided, especially during thermal cycling.

An electronic assembly having a wetting layer on a thermally conductive heat spreader

Developing new thermal interface materials (TIMs) is a key activity to meeting package thermal performance requirements for future generations of microprocessors. Indium solder is capable of demonstrating end-of-line performance to meet current technology targets due to its inherent high thermal conductivity. However, improving its reliability performance, particularly in temperature cycling, is a challenge. This study describes the failure mechanisms and reliability performance of indium solder TIM as a function of integrated heat spreader metallization thickness, TIM bond line thickness, and die size. Also studeited were the steps taken to improve its temperature cycle performance. Analyses were performed using thermal resistance measurements, scanning-electron microscopy, scanning-acoustic microscopy, and transmission-electron microscopy to characterize the solder TIM thermal performance, interfacial microstructure, and failure mechanisms.

Fay Hua

Papers

Size-dependent melting properties of tin nanoparticles

Electromigration in flip chip solder joints having a thick Cu column bump and a shallow solder interconnect

The creep properties of lead-free solder joints

An electronic assembly having a wetting layer on a thermally conductive heat spreader

The material optimization and reliability characterization of an indium-solder thermal interface material for CPU packaging