Rong An

Low Temperature Sintering Cu6Sn5 Nanoparticles for Superplastic and Super‐uniform High Temperature Circuit Interconnections

Brittle intermetallics such as Cu6 Sn5 can be transformed into low cost, nonbrittle, superplastic and high temperature-resistant interconnection materials by sintering at temperatures more than 200 °C lower than its bulk melting point. Confirmed via in situ TEM heating, the sintered structure is pore-free with nanograins, and the interface is super-uniform.

Effect of Au-Sn IMCs’ formation and morphologies on shear properties of laser reflowed micro-solder joints

Purpose – The purpose of this paper is to investigate the effect of typical morphologies of Au-Sn IMCs (intermetallic compounds) at the interfaces of solder and pads on shear properties of laser reflowed micro-solder joints. Design/methodology/approach – Sn-2.0Ag-0.75Cu-3.0Bi (SnAgCuBi) solder balls (120 μm in diameter), pads with 0.1, 0.5, 0.9 or 4.0 μm thickness of Au surface finish, and different laser input energies were utilized to fabricate micro-solder joints with Au-Sn IMCs having different typical morphologies. The joints were performed by a shear test through a DAGE bond test system. Fracture surfaces of the joints were analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometry to identify fracture modes and locations. Findings – Morphologies of Au-Sn IMCs would affect shear properties of the joints remarkably. When needle-like AuSn4 IMCs formed at the interfaces of solder and pads, almost entire surfaces presented the manner of ductile fracture. Moreover, shear forces of ...

Effect of intermetallic compounds on fracture behaviors of Sn3.0Ag0.5Cu lead-free solder joints during in situ tensile test

In this paper, in situ tensile tests under various amounts of deformation were performed on Sn3.0Ag0.5Cu lead-free solder joints subjected to multi-reflow and isothermal aging processes by using a scanning electron microscope. Microstructure evolution and deformation behavior of the solder joints were observed. Effects of the intermetallic compound (IMC) Cu6Sn5 on fracture behaviors of the solder joints were investigated. Results showed that the Sn3.0Ag0.5Cu lead-free solder joints contained only a few Sn grains, and the sequence and degree of plastic deformation varied for the different grains in the same solder joint due to the strong anisotropic properties of Sn grains. Further experiments revealed that plastic deformation occured primarily in the form of slip bands in the solder joints during the in situ tensile test. Various fracture modes including intergranular and phase boundary fractures were observed. The fracture behaviors of solder joints were significantly affected by morphologies and distributions of the Cu6Sn5 IMCs. It was found that Cu6Sn5 particles located at the grain boundaries are apt to become crack sources, and that the long rod shaped Cu6Sn5 were easily broken. However, spherical Cu6Sn5 hardly deformed during the tensile test, resulting in dynamic recrystallization. In this case, fracture occured at the sub-grain boundaries.

One-Step Fabrication of 3D Nanohierarchical Nickel Nanomace Array To Sinter with Silver NPs and the Interfacial Analysis

Three-dimensional (3D) nanohierarchical Ni nanomace (Ni NM) array was fabricated on copper substrate by only one step with electroplating method, the unique structure was covered with Au film (Ni/Au NM) without changing its morphology, and in the following step, it was sintered with silver nanoparticle (Ag NP) paste. The structure of the Ni NM array and its surface morphology were characterized by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. The sintered interface was investigated by SEM, transmission electron microscopy, and energy-dispersive X-ray spectroscopy to analyze the sintering mechanism. The results showed that a metallurgical bond was successfully achieved at 250 °C without any gas or vacuum shield and extra pressure. The Cu substrate with Ni/Au NM array was able to join with the Ag NP paste without obvious voids. Due to the compatible chemical potential between Ag NPs and Ni/Au NM array, the Au element was able to diffuse into the Ag layer with about 800 nm distance. Based on the excellent 3D nanohierarchical structure, the shear strength of Ni/Au NM array was 6 times stronger than the flat Ni/Au coated substrate. It turned out that the substrate surface played a crucial role in improving the shear strength and sintering efficiency. The 3D Ni NM array had achieved an excellent bonding interface and had great potential application in the microelectronics packaging field.

Fabrication of Al2O3–Mullite–AlN Multiphase Ceramic Layer on W–Cu Substrates for Power Semiconductor Packaging

This paper proposes a novel method to manufacture ceramic insulated metal substrate for power semiconductor modules and high-temperature electronics. α-Al₂O₃-mullite (Al₆Si₂O₁₃)-AlN multiphase ceramic layer was fabricated on W80Cu20/Cr substrate at 1050 °C by firing. The polycarbosilaneAlN green ceramic layer was synthesized by spin processor, and then was fired under a steady flow of wet nitrogen Al-Si-O nanocrystalline rods were formed and their diameters were about 100 nm. The α-Al₂O₃-mullite-AlN multiphase ceramic layer had perfect interface bonding, and exhibited superior mechanical properties and thermal shock resistance.

The effect of voids on thermal conductivity of solder joints

In this paper, the influence of voids on thermal conductivity of solder joints is analyzed using the finite element method. The conclusions come that: for single-void case, with the size of void increasing, the influence of void on thermal conductivity growing, void near the heat source has a greater influence than that far away. Then, the situation of multi-voids get similar results, but the temperature distribution of solder joints presents the comprehensive function of the two factors, particularly, the voids far away from the heat source may have little influence on the thermal conducting performance.

Elastic Property of Cu 3 Sn Determined by a First-Principles Calculation on the Basis of its Crystal Substructure

As compared with the significance for controlling reliability of solder joints, research on elastic behavior of Cu3Sn has not been given enough consideration mainly because of the difficulty in preparing acceptable single-phase sample. In this paper, independent elastic constants of single crystal Cu3Sn are determined from first-principles calculations with a pseudopotential plane-wave method to completely characterize its polycrystalline elastic behavior and elastic anisotropy. The ideal elastic, shear and bulk modulus (E=147GPa, G=56GPa and K=132GPa) as well as the Poissons ratio (v=0.315) of Cu3Sn were predicted by Voigt-Reuss-Hill method. Cu3Sn exhibited distinct anisotropy in Youngs modulus, as shown by the large difference between maximum and minimum of 44GPa, which may be partially responsible for the discrepancy in the experimental results. The Youngs modulus of Cu3Sn with texture in real solder joints was also explored.

Recent Progress in Rapid Sintering of Nanosilver for Electronics Applications

Recently, nanosilver pastes have emerged as one of the most promising high temperature bonding materials for high frequency and high power applications, which provide an effective lead-free electronic packaging solution instead of high-lead and gold-based solders. Although nanosilver pastes can be sintered at lower temperature compared to bulk silver, applications of nanosilver pastes are limited by long-term sintering time (20–30 min), relative high sintering temperature (>250 °C), and applied external pressure, which may damage chips and electronic components. Therefore, low temperature rapid sintering processes that can obtain excellent nanosilver joints are anticipated. In this regard, we present a review of recent progress in the rapid sintering of nanosilver pastes. Preparation of nanosilver particles and pastes, mechanisms of nanopastes sintering, and different rapid sintering processes are discussed. Emphasis is placed on the properties of sintered joints obtained by different sintering processes such as electric current assisted sintering, spark plasma sintering, and laser sintering, etc. Although the research on rapid sintering processes for nanosilver pastes has made a great breakthrough over the past few decades, investigations on mechanisms of rapid sintering, and the performance of joints fabricated by pastes with different compositions and morphologies are still far from enough.

Characterization of the Microstructure of an AlN-Mullite-Al2O3 Ceramic Layer on WCu Composite Alloy for Microelectronic Application

An AlN composite ceramic layer was designed and fabricated on WCu substrates by hydrolysis-assisted solidification and firing. First, the surface of WCu substrates were pre-coated with polycarbosilane/AlN ceramic layers by spinning; the layers were then fabricated by firing. The phase composition, microstructure, and element distribution of the ceramic layer and interfacial reaction layer were investigated by use of scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction. The results showed that the ceramic layers were composed of AlN, mullite, and Al2O3. There were many nanocrystalline rods on the surface of the ceramic layers. The Cr layer prevented the WCu substrate from reacting with water vapor during firing, and the Ni layer prevented diffusion of tungsten into the Cr layer. Study of the cross section of the ceramic layer fired on the Cr/Ni/WCu substrate revealed a perfect interfacial reaction layer.

Robust tuning of Kirkendall void density in circuit interconnections through substrate strain annealing

Unpredictable Kirkendall void formation at the interface of circuit interconnections underlies degradation in electronics, yet there is a lack of effective approaches to curb the amount of these voids. In this paper, we developed a modified strain-anneal method to tailor grain size distributions in the copper substrate of interconnections by inhomogeneous recrystallization, and demonstrate quantitatively that not only the removal of the impurities but also an increase in the grain size of the substrates leads to an appreciable decline in the void density. The interconnections on the substrate recrystallized at a high annealing temperature show the massive porosity and the increased sensitivity of the voiding to the grain size. Our results highlight an example of how grain size of substrates can be tailored to enable manipulation of void propensity in hetero-interfaces, and suggest a promising strategy for high-stability circuit bonding in electronics, particularly in high temperature/high power electronic devices based on wide band gap semiconductors.