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Abstract: This study utilized a high speed lap-shear test to evaluate the mechanical behavior of Sn-37Pb/Cu under bump metallization (UBM) solder joints under high speed loading and hence the drop reliability. The samples were aged for 120h at different temperatures (150°С, 180°С) and then tested at different displacement rates in the range of 0.01mm/s to 500mm/s to examine the effects of aging on the drop reliability. The combination of the stress-strain graphs captured from the shear tests and the fracture morphology analysis discloses that the aging at high temperatures has influenced critically the deformation behavior of the solder joints and the effects appears more significant at high strain rates. This study demonstrates a unique capability of a drop reliability evaluation method that utilizes a high speed lap-shear test. [Copyright &y& Elsevier]

Abstract: Thermo-mechanical reliability of the anisotropic conductive film (ACF) joints in relation with flip chip bonding forces was evaluated by thermal shock testing. Two kinds of main failure modes were detected after thermal shock testing: formation of a conduction gap between conductive particles and Au bump or Ni/Au-plated Cu pad, and delamination of the adhesive matrix from the plated Cu pad on the flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. The main failure mode of the thermally shocked ACF joints was conduction gap for the joints with low bonding forces and adhesive matrix delamination for the joints with high bonding forces. Finite element analysis was also performed to determine the stress distributions within the two kinds of flip chip packages having different bonding gaps when it was stressed by the temperature rising. [Copyright &y& Elsevier]

Abstract: The effects of multiple reflows on the microstructural variation and joint strength of the flip chip solder joints were investigated. Conventional Sn–37Pb and a representative Pb-free Sn–3.0Ag–0.5Cu were used, and a popular low cost under bump metallurgy (UBM) of immersion Au/electroless Ni–P plating was employed. In case of Sn–37Pb, only Ni3Sn4 intermetallic compound layer was formed during multiple reflows. In case of Sn–3.0Ag–0.5Cu, (Cu,Ni)6Sn5 intermetallic compound layer was observed after a single reflow, while (Ni,Cu)3Sn4 layer was additionally settled at the interface between the (Cu,Ni)6Sn5 layer and Ni–P UBM. The thicknesses of the intermetallic compound layers increased and coarsened. The shear force of the both joints slightly decreased during the multiple reflows. The decrease of the joint strength was caused by different softening phenomena between the two cases, and that is discussed in the main text. [Copyright &y& Elsevier]

Abstract: The effect of displacement rate and intermetallic compound growth on the shear properties of the electroplated Sn–37Pb (wt.%) flip-chip solder bumps with Cu under-bump metallization (UBM) were investigated after multiple reflows. The compounds Cu6Sn5 and Cu3Sn were formed at the interface after one reflow, and their thicknesses increased with increasing reflow number up to 10. The shear properties peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force, but decreased the displacement until fracture. The tendency toward the brittle fracture characteristics was intensified with increasing displacement rate and reflow number. [Copyright &y& Elsevier]

Abstract: The reliability of adhesive interconnections using anisotropic conductive film (ACF) and non-conductive film (NCF) was evaluated by measuring connection resistance during 500cycles of thermal shock testing. The four-point probe method was used to measure the connection resistance of the adhesive joints constructed with Au bump on Si chip and Cu pad on flexible printed circuit (FPC). The connection resistance of the ACF joints was markedly higher than that of the NCF joints, mainly due to the constriction of the current flow and the intrinsic resistance of the conductive particles in the ACF joints. The connection resistances of both interconnections decreased with increasing bonding force, and subsequently converged to about 10 and 1mΩ at a bonding force of 70 and 80N, for the ACF and NCF joints, respectively. During the thermal shock testing, two different conduction behaviors were observed: increased connection resistance and the termination of Ohmic behavior. The former was due to the decreased contact area caused by z-directional swelling of the adhesives, whereas the latter was caused by either contact opening in the adhesive joints or interface cracking. [Copyright &y& Elsevier]

Abstract: This study focused on the feasibility of using Ni flip chip bumps with a Sn–2.5Ag (wt.%) solder encapsulation. The interfacial reaction and die shear property of the Ni flip chip bump with a Sn–Ag solder cap bonded on the electroplated Cu/Sn–Ag substrate were investigated with increasing bonding time. After bonding for 1s (Cu x Ni1−x )6Sn5 and Cu6Sn5 intermetallic compound (IMC) layers were formed at the upper and lower interfaces, respectively, with the former IMC being the predominant phase during bonding. The transformation of the solder cap into the (Cu x Ni1−x )6Sn5 IMC depleted the solder after bonding for 30s, and then the Ni concentration in the IMC gradually decreased with increasing bonding time. The shear property peaked after 30s, and then decreased with increasing bonding time. The fractures occurred at the solder/Cu6Sn5 interface and inside the (Cu x Ni1−x )6Sn5 IMC after bonding for 1s and 30s, respectively, after which the fracture location shifted toward the (Ni x Cu1−x )3Sn4/(Cu x Ni1−x )6Sn5 interface with increasing bonding time. [Copyright &y& Elsevier]

Abstract: Rolled copper foil of 18μm thickness underwent nodule treatment via electro plating in a solution containing dissolved CuSO4 and NiSO4. The product formed on the surface of the copper foil varied from copper oxides to nickel compounds of the sphere type with increasing current density and plating time. The highest surface roughness and maximum peel strength of 680gf/cm were obtained with the formation of nickel compounds at a current density of 1.5A/dm2 and plating time of 30s. In addition, the fracture location varied according to the plating parameters and occurred at the interface between the polyimide film and adhesive layer at the condition of the maximum adhesion strength. [Copyright &y& Elsevier]

Abstract: This study was focused on the formation and reliability evaluation of solder joints with different diameters and pitches for flip chip applications. We investigated the interfacial reaction and shear strength between two different solders (Sn–37Pb and Sn–3.0Ag–0.5Cu, in wt.%) and ENIG (Electroless Nickel Immersion Gold) UBM (Under Bump Metallurgy) during multiple reflow. Firstly, we formed the flip chip solder bumps on the Ti/Cu/ENIG metallized Si wafer using a stencil printing method. After reflow, the average solder bump diameters were about 130, 160 and 190μm, respectively. After multiple reflows, Ni3Sn4 intermetallic compound (IMC) layer formed at the Sn–37Pb solder/ENIG UBM interface. On the other hand, in the case of Sn–3.0Ag–0.5Cu solder, (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMCs were formed at the interface. The shear force of the Pb-free Sn–3.0Ag–0.5Cu flip chip solder bump was higher than that of the conventional Sn–37Pb flip chip solder bump. [Copyright &y& Elsevier]

Abstract: The surface morphology, electrical property and reaction with solder alloy of two electroless nickel-phosphorus (EN–P) deposits (Ni–7wt.%P and Ni–10wt.%P) were investigated in this study. The P content of the EN–P layer decreased with increasing pH value. The EN–P plating layers had an amorphous structure and the electrical resistivity of the layer increased with increasing P content. Reaction layers of Ni3Sn4, Ni2SnP and Ni3P formed at the interfaces between the Sn–3.5Ag solder and the two EN–P deposit layers. The thickness of the interfacial Ni3Sn4 intermetallic compound (IMC) layer in the Sn–3.5Ag/Ni–7wt.%P joint was thicker than that in the Sn–3.5Ag/Ni–10wt.%P joint, whereas the thickness of the Ni3P layer increased with increasing P content. These study results confirmed that the interfacial reaction between solder and the EN–P layer is significantly affected by the composition (P content) of the EN–P layer. [Copyright &y& Elsevier]

In this study, we fabricated Sn-rich, Au–Sn flip-chip solder bumps by using a sequential electroplating method with Sn and Au. After reflowing, only a (Ni,Au)3Sn4 intermetallic compound (IMC) layer was formed at the Au–Sn solder/Ni interface. During aging for up to 1000h at 150°C, the solder matrix was transformed sequentially in the following order: β-Sn and η-phase, η-phase, η-phase and ε-phase. The microstructure variation resulted from the preferential consumption of more Sn atoms within the solder matrix during aging. [Copyright &y& Elsevier]

Abstract: The effects of plasma treatment on the surfaces of the flame resistant-4 (FR-4) and copper substrates are investigated in terms of X-ray photoelectron spectroscopy (XPS), contact angle, and atomic force microscopy (AFM). The adhesion strengths of the underfills/FR-4 substrate and underfills/copper substrate are also studied. As experimental results, the plasma treatments of FR-4 and copper substrate surfaces yield several oxygen complexes in hydrophilic surfaces, which can play an important role in increasing the surface polarity, wettability, and adhesion characteristics of the underfills/substrates. And, the curing temperature ranges of the underfills, which have the maximum adhesion strength of the underfills/FR-4 substrate and underfills/copper substrate, were 140–150°C. [Copyright &y& Elsevier]

Abstract: We fabricated YBCO film on an LAO substrate using the TFA-MOD method and evaluated the effects of the heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing processes were performed in the temperature ranges of 370–460°C and 750–800°C, respectively. We found that the phase purity, grain size and orientation, and degree of texture varied with the calcining and firing temperatures. The films fired at 775°C after calcining at 400–430°C showed the highest critical temperature (T C-onset) of 89.5K and critical current (I C) of 40A/cm-width, which corresponds to a critical current density (J C) of 1.8MA/cm2. According to the XRD, pole-figure, SEM images, and Raman analysis, these highest critical properties are probably due to the formation of a purer YBCO phase and stronger biaxial texture. In the multi-coated films, the I C value increased from 39 to 169A/cm-width as the number of coatings increased from one to four, while the corresponding J C was measured to be in the range of 0.8–1.2MA/cm2. Both the I C and J C decreased when a further coating was applied due to the degradation of the microstructure. [Copyright &y& Elsevier]

Abstract: YBCO film was fabricated by the TFA-MOD method based on the “211 process” in which precursors of Y2Ba1Cu1O x (Y211) and Ba3Cu5O8 powders, instead of Y-, Ba-, and Cu-based acetates, were dissolved in trifluoroacetic acid (TFA) in order to explore its possible application in coated conductors. We evaluated the effects of the humidity and firing temperature on the phase formation, texture formability, and critical temperature (T c) and current (I c) of the YBCO film. We successively synthesized pure YBCO films of which those fired in 12.1–20.0% humidified Ar gas showed the highest critical properties, viz. a T c-zero of 88.6K and I c of 30A/cm width. These improvements in the critical properties were attributed to the formation of pure YBCO phase, to the improved density and the large grain size. In addition, we observed that the I c varied significantly with the firing temperature. The variation of the I c with the firing temperature was correlated with the microstructural evolution. [Copyright &y& Elsevier]

Abstract: The microstructures and wear property of friction stir welded AZ91 Mg alloy/SiC particle reinforced composite (AZ91/SiC/10p) were investigated. The initial microstructures of the AZ91/SiC/10p were composed of irregularly distributed β-phases (Al12Mg17) and agglomerated SiC particles, while the friction stir weld zone was characterized by the homogeneous distribution of SiC particles, the recrystallized grain structure and the dissolution of β-phase. Thank to the microstructural modification, an improvement in the hardness and wear property of the weld zone were observed as compared to those of the base metal. The hardness near the weld zone was a higher and more homogeneously distributed and the wear resistance within the weld zone, as evaluated by the specific wear loss, was superior, as compared with the base metal. [Copyright &y& Elsevier]

The reaction layers of friction stir welded joints made from austenitic stainless steel and Al alloy consisted of mixed layers of elongated and ultra-fine grains and the intermetallic compound layer. The intermetallic compound layer was identified as Al4Fe with a hexagonal close-packed structure and a thickness of approximately 250nm. The elongated grains were shown to consist of a ferrite phase because of their ferromagnetism and a body-centered cubic crystal structure. [Copyright &y& Elsevier]

Abstract: We fabricated the textured Ni substrate for YBCO coated conductors and evaluated the effects of processing variables on microstructural evolution and texture transformation. Initial specimens were prepared by two different methods, i.e., powder metallurgy (P/M) and casting. To characterize the role of two preparation methods, the initial specimens of the same size were prepared under the same rolling and annealing conditions. The microstructure and texture were evaluated by orientation distribution function (ODF), electron backscattering diffraction and transmission electron microscopy with selected area diffraction. We observed that the microstructure of the rolled tape varied with preparation methods; the rolled tape prepared by P/M had more deformation bands and stronger β-fiber texture than that one obtained by casting, resulting in finer microstructure and stronger cube texture after recrystallization. The smaller grains in the former tape were explained by the “variation inhibition theory” together with in situ TEM result. Texture analysis indicated that the substrate made by P/M had a stronger cube texture and a wider annealing temperature range in which the cube texture became stable, compared to that of the casting-substrate. In addition, abnormal grain growth occurred and consequently formed high angle grain boundary for substrate by casting but not for substrate by P/M. [Copyright &y& Elsevier]

Abstract: The interfacial reactions and shear strength of joints between Sn–9Zn solder and two different kinds of BGA (ball-grid-array) substrates (Cu and Au/Ni–P/Cu) were investigated for reflow conditions of 230°C up to 60min. For the Cu substrate, only Cu5Zn8 intermetallic compound was observed and other Cu–Sn IMCs were not observed. For the Au/Ni/Cu substrate, an AuZn3 IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, some of the AuZn3 IMC layer was detached from the interface after reflow. The thickness of the AuZn3 layer did not change with reflow time because the Au was consumed during the initial reflow process. After being reflowed for 60min, a Ni5Zn21 IMC formed between AuZn3 IMC and Ni substrate. Also, many voids existed inside the upper AuZn3 IMC layer. Ball shear tests for the Cu substrate showed the shear strength significantly decreased after reflow for 60min. A Cu5Zn8 IMC was also observed on the fracture surface. For the Au/Ni/Cu substrate, the shear strength value did not change much as a function of reflow time and fractures occurred within the solder. [Copyright &y& Elsevier]

Abstract: As a relatively high melting point material, Ti can be joined by the friction stir welding (FSW) using a sintered TiC welding tool and a water cooling system. The FSW zones of Ti were classified by the weld nugget (WN), the linear transition boundary (TB) and the heat affected zone (HAZ). The WN was characterized by the presence of considerable amount of twins and high density of dislocations. The TB was a linear region of rapid microstructural change from the WN to the HAZ and the HAZ was characterized by slight grain growth. The grain structures of the weld zone were closely related to the hexagonal close packed (HCP) crystal structure of Ti because the twin became dominant deformation mode. The hardness in the WN showed a scattered value, with higher hardness being observed in the region having denser twin structures. [Copyright &y& Elsevier]

Abstract: We fabricated YBCO coated conductors using a new TFA-MOD method and evaluated the phase formation, texture evolution, and critical properties as a function of the firing temperature and oxygen heat treatment time, in order to explore its possible application in CCs fabrication. In the fabrication process, Y2Ba1Cu1O x and Ba3Cu5O8 powders were used as precursors, instead of Y-, Ba- and Cu-based acetate or organics, and dissolved in trifluoroacetic acid followed by firing and oxygen heat treatment. We observed that for the films fired at 725°C, BaF2 and other second phases formed and T c was measured to be 66.5K. In contrast, when the film was fired at 775°C, strong and sharp (00 l) diffraction peaks of YBCO were observed, without the formation of the BaF2 phase. In addition, X-ray pole-figure analysis indicated that a strong biaxial texture was developed and the full-width at half-maximums of in-plane and out-of-plane textures were 4.38° and 4.26°, respectively. The critical temperature and current were also increased to 85.3K and 35.8A/cm-width, respectively, at 77K when the oxygen heat treatment time was increased to 20h. Microstructure observation indicated that a crack-free surface was obtained and that there was no a-axis grain growth. [Copyright &y& Elsevier]

Abstract: The interfacial microstructure of Sn–37Pb solder with immersion Au/electroless Ni–P under bump metallization (UBM) was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A Ni3Sn4 intermetallic compound (IMC) layer was formed at the interface between the solder and Ni–P UBM upon reflow. However, after isothermal aging, AuSn4 containing a certain amount of Ni dissolved in it, i.e. (Au,Ni)Sn4, appeared above the Ni3Sn4 layer. Two distinctive layers, P-rich and Ni–Sn–P, were additionally found from the TEM observation. Analytical studies using energy dispersive spectrometer (EDS) equipped in TEM revealed that the averaged composition of the P-rich layer is more close to that of a mixture of Ni3P and Ni, while that of the Ni–Sn–P layer is analogous to the P-rich layer but containing a small amount of Sn in it. The growth of the Ni3Sn4 IMC layer thickness obeyed a parabolic growth law which implies that the interfacial IMC growth is mainly controlled by volume diffusion of the elements to the reaction layer. The shear force of the joints decreased during isothermal aging at 373K. The decrease of the shear force could be mainly due to the coarsening effect of the microstructure within the solder. The failure behavior could be well explained with the results of finite element modeling (FEM) analyses. [Copyright &y& Elsevier]

Phase analysis and growth kinetics of intermetallic compound (IMC) layers formed between low cost Sn–Cu–Ni solder for wave soldering and Cu substrate by solid state isothermal aging were examined at temperatures between 80 and 150 °C for 0 to 60 days. The IMC layer was composed of two phases; Cu6Sn5 (also (Cu,Ni)6Sn5) adjacent to the solder, Cu3Sn adjacent to the copper. The Cu3Sn layer was absent at all time periods for the aging temperatures of 80 and 100 °C. After isothermal aging at 120 °C for 30 days and at 150 °C for all time periods, the solder/Cu interface exhibited a duplex structure of Cu6Sn5 and Cu3Sn intermetallics. From the EPMA analysis, a comparatively high Ni concentration is found between the Cu6Sn5 and Cu3Sn layer. The Ni concentration in the (Cu,Ni)6Sn5 intermetallic was about 4.3 at.%. The total IMC layer thickness was approximately 11.5 μm after 60 days of aging at 150 °C. The apparent activation energies for growth of total and Cu6Sn5 IMC layer were 76.17 and 66.35 kJ/mol, respectively. [Copyright &y& Elsevier]

High heat-endurance bonding between Cu Ni was investigated by hybrid transient liquid phase sintering bonding. By simultaneously adding Cu and Ni to SAC305, the IMC was stably formed, and the bonding strength of hybrid TLPS joint was the highest. It is expected to be used for SiC die attachment of power module packaging. [Display omitted] • Novel hybrid transient liquid phase sintering bonding is developed for Cu Ni bonding. • Fast and stable ternary (Cu,Ni)-Sn IMCs were formed by hybrid transient liquid phase sintering bonding. • Electron probe micro-analyzer was used for investigating the atomic distribution of TLPS joints. A novel approach to copper-nickel bonding was investigated by hybrid transient liquid phase sintering (TLPS) method. Hybrid bonding material containing copper, nickel, and Sn-3.0Ag-0.5Cu (SAC305) and an organic solvent was fabricated to form a fast and stable ternary Cu Ni Sn intermetallic compound (IMC) joint between Cu to Ni joint. The atomic distribution was analyzed by an electron probe micro-analyzer, showing full IMC formation of the hybrid TLPS joint. In addition, by simultaneously adding Cu and Ni to SAC305, the IMC was stably formed, and the bonding strength of hybrid TLPS joint was the highest. [ABSTRACT FROM AUTHOR]

• Low temperature sintering process was performed with intensive pulsed light. • The pulse condition of intensive pulsed light affected on printed Cu circuit. • Electrochemical migration behavior of Cu circuit was investigated. Problems associated with the oxidation of Cu nanopaste have been widely studied in efforts to develop a replacement for Ag nanopaste. The intensive pulsed light (IPL) sintering process has been suggested to solve the oxidation problem because it is a method with a short processing time and is conducted at room temperature. Cu nanopaste was fabricated with Cu nanoparticles and a functional organic matrix. Cu nanopaste screen-printed onto a polyethylene terephthalate substrate was subjected to various IPL sintering conditions, and the effects of pulse power and pulse width on the microstructure, electrical resistivity, and electrochemical migration behavior of the printed Cu patterns were investigated. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrochemical migration behavior was varied because of leaked ethylene glycol from organic matrix. The dendrites from lower pulse condition has finer microstructure and increased nucleation. [ABSTRACT FROM AUTHOR]

Cu–Cu bonding was successfully achieved through the transient liquid phase sintering (TLPS) bonding method using Cu and an eutectic Sn–Bi alloy. The bonding process was performed for total bonding process time of 2 h under a pressureless condition in air. The bonding temperature was 220 °C considering that the Cu 6 Sn 5 intermetallic compound (IMC) and Bi react at 195.9 °C to transform into Cu 3 Sn and a liquid. The shear strength of Cu-70(Sn–58Bi) was approximately 22.06 MPa with the formation of the Cu 3 Sn. The residual eutectic Sn–Bi structure remained at Cu-90(Sn–58Bi), and the voids were largely observed at Cu-50(Sn–58Bi). In case of Cu-70(Sn–58Bi) and Cu-50(Sn–58Bi), the remelting temperature increased to 270 °C by the IMC reaction between Cu and Sn. On the other hand, the remelting temperature of Cu-90(Sn–58Bi) joint remained at 139 °C due to residual eutectic Sn–Bi structure. The salt spray test was conducted at 35 °C under the 5% NaCl condition for 24, 48, and 96 h to evaluate the bonding reliability under the salt spray condition. The corrosion behavior was evaluated using the electrochemical impedance spectroscopy measuring method. In addition, the thermal bonding reliability was investigated through a high-temperature storage test at 200 °C for 100, 500, and 1000 h. Analysis results of the experiment showed that the electrochemical and thermal bonding reliabilities were improved with the Cu 3 Sn formation owing to its high resistance properties under the salt spray and high-temperature conditions. • Pressureless transient liquid phase sintering bonding was achieved by composite paste consisted of Cu and Sn–58Bi. • TLPS joint consisted of Cu 3 Sn and Bi, was formed for high heat endurance and high reliable bonding. • Electrochemical and thermal bonding reliability was confirmed by salt spray and high-temperature storage test. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) is increasingly considered for various industrial applications. CFRP has been applied to the automotive industry to increase fuel efficiency due to its excellent strength and lightweight. Therefore, the demand for dissimilar material joining techniques is gradually increasing. In this study, we investigated the intense pulsed light (IPL) as surface treatment for CFRP. The IPL surface treatment requires a very short processing time and can be easily automated compared with other processes such as chemical and mechanical treatments. The change in morphology and chemical composition of the CFRP-treated surfaces was analyzed using scanning electron microscopy, profiler, and X-ray photoelectron spectroscopy. The bonding strength due to varying IPL exposure time was evaluated by the lap shear test. The apparent shear strength increased by up to 159% in this study. The IPL treatment is very simple and requires short processing time to produce enhanced adhesive joints. [ABSTRACT FROM AUTHOR]

A carbon nanotube (CNT) has remarkable properties, but it has disadvantages in application because of its dispersal- and bonding-related issues. Metal–CNT composite materials are necessary in solving these problems. In this study, nickel (Ni)–multi-walled CNTs (Ni–MWCNTs) are synthesized through sequential processing, functionalizing, and electroless plating processes to deposit Ni nanoparticles on MWCNTs. The synthesized Ni–MWCNTs are used to fabricate composite solders with various contents (0, 0.05, 0.1, and 0.2 wt%). The test kit used for the 3-point bending test in this study is designed with a differential package structure to evaluate the bending reliabilities of the Ni–MWCNT composite materials with various contents. The crack initiation and propagation in the microstructure evolution solder joints are also investigated. The bending reliabilities improve with the BGA structure and indicate that the highest bending cycle fails with 0.1 wt% of Ni–MWCNTs. The chemical composition and distribution of the Ni–MWCNTs in the solder joints are investigated with electron probe microanalysis. • Test-kits for 3-point bending test were designed with differential structure. • Bending test was performed to evaluate the mechanical properties of solder joints. • Ni-MWCNTs composite solder could improve the bending reliability of Sn58Bi solder. [ABSTRACT FROM AUTHOR]

A Cu-cored solder ball (CCSB) is often used as the interconnection material for 3D package. The CCSB has a Cu core surrounded by Sn-Ag-Cu alloy. The effect of the Cu core on mechanical reliability of the CCSB was investigated using thermal shock test. Microstructure and thermal shock reliability of the CCSB with organic solderability preservative (OSP) surface finish was compared with that of Sn-3.0wt.%Ag-0.5wt.%Cu (SAC) solder. The thermal shock test was performed in the temperature range of −40 °C to 125 °C in compliance with JESD22-A104. Failure mechanism was analyzed by finite element method analysis. Average number of thermal shock cycles for the CCSB/OSP joints was 1.15 times higher than that for SAC/OSP joints. Maximum value of simulated plastic strain for the SAC/OSP joints was 1.25 times higher than that for the CCSB/OSP joints because the stand-off height of the CCSB/OSP joints could be maintained by the Cu core. • Thermal shock reliability of Cu cored solder joint was investigated. • Simulated stress and strain were reduced because stand-off height of solder ball was maintained by Cu core. • Crack of solder joint was propagated through the solder matrix that was highest simulated plastic strain regions. • Thermal shock reliability of solder joint was improved due to stand-off height. [ABSTRACT FROM AUTHOR]

Abstract: System-on-Chip and System-on-Package technologies have advantages depending on application needs. As a number of electrical and electronic equipment manufacturers have an interest in increasing CMOS technology densities, a range of two- and three-dimensional silicon integration technologies are emerging which will support next-generation high-end semiconductors such as high speed microprocessors and high speed memories. However, there are many issues regarding process integration, thermal management, and reliability of 3D stacked package. In this study, the printed circuit board (PCB), silicon carrier and silicon chip are integrated with ultrasonic vibration. Die shear tests of the joints were carried out with increasing bonding time and input power to optimize the bonding condition. The integrated chips were successfully bonded to the PCB with and without NCF using a transverse ultrasonic bonding. Electrical resistance of multi-chip bonded with NCF (10mΩ) measures lower than that bonded without NCF (28.9mΩ). The voids and delamination were easily found on the joint bonded without NCF that caused lower shear strength. [Copyright &y& Elsevier]

• We prepare Sn-coated Cu particles of different diameters as a micro paste. • We use the paste to bond a dummy chip and a DBC substrate. • The bonding is carried out via transient liquid-phase sintering (TLPS) technology. • The paste affords a high shear strength value of ~40 MPa. • Our approach is suitable for power electronics packaging and allied applications. Cu paste has been considered as a promising substitute for Ag paste for high-temperature-endurable chip-bonding applications, particularly for power electronics packaging, because it is cheaper than Ag. However, the primary disadvantage of using Cu paste is its possible oxidation during the handling and bonding process. In this context, to overcome the oxidation problem of the Cu sinter paste and to exploit the advantages of transient liquid-phase sintering (TLPS) bonding technology, we prepare Sn-coated Cu micro paste in this study, and we evaluate its feasibility as a die-attach material for power electronics packaging. We first prepare various Sn-coated Cu powders under various plating conditions, and we successfully perform TLPS bonding with Sn-coated Cu paste at a relatively low bonding temperature and a short bonding time. During the TLPS bonding, Sn is completely consumed, and the resulting bonded joint is composed of the Cu–Sn intermetallic compounds and remnant Cu particles. The TLPS-bonded joints exhibit relatively high shear strength values of ~40 MPa, and all fractures mainly occur at the chip-side interfaces irrespective of the Cu particle size. We believe that our findings can contribute to the use of Sn-coated Cu paste as an alternative bonding technology for power electronics applications. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructure of Sn-58 wt%Bi solder including various levels of Ag-decorated MWCNTs (0, 0.05, 0.1, and 0.2 wt%) were investigated for use in solder joints. The electronic industry relies on Pb-free solders because lead can have harmful effects on the environment and human health. The Sn-58 wt%Bi solder is a representative low temperature Pb-free solder with high tensile strength and good creep resistance. However, the Sn-58 wt%Bi solder has poor ductility for relieving shock impact. To address this drawback, Ag-decorated MWCNTs were used to reinforce the mechanical properties of Sn-58 wt%Bi solder. The Sn-58 wt%Bi-nanocomposite solder paste was fabricated by mechanically mixing Ag-decorated MWCNTs with solder paste. The Sn-58 wt%Bi solder pastes including Ag-decorated MWCNTs were printed on a printed circuit board (PCB), and the joints were aged in an isothermal environment. Inclusion of 0.1 wt% Ag-decorated MWCNTs increased the shear strength of the solder by about 15%. The thickness of the IMC of Sn-58 wt%Bi solder increased with age. • The Ag-decorated MWCNTs were synthesized with functionalizing process. • The Ag-decorated MWCNTs increased shear strength of Sn-58 wt%Bi solder. • Furthermore, Ag-decorated MWCNTs have an effects on microstructure of Sn-58 wt%Bi solder. [ABSTRACT FROM AUTHOR]

Ag particles have been attractive candidates for highly reliable interconnections in electronic packages due to an absence of IMCs, high melting temperature, and high electrical and thermal conductivity. We fabricated various Ag-nanoparticle (NP) pastes containing different epoxy/binder percent weight (epoxy: 4.5, 9.0, 13.5, and 18 wt%) to investigate the effect on the bonding strength and electrical performance of multilayer ceramic capacitor (MLCC) components. MLCC joints were obtained by stencil printing Ag NP pastes on an Al 2 O 3 substrate with Cu electrodes followed by pressureless bonding at 250 °C for 15 min. When using Ag NP pastes containing higher epoxy compositions, more residues were identified while the other organic additives, such as the binder and dispersant, were removed by debinding during the bonding process. The Ag NP-18 wt% epoxy paste showed bonding strength approximately 8.6 times that of the paste containing 4.5 wt% epoxy. However, the electrical resistivity of MLCC components of 18 wt% epoxy paste showed an electrical resistance of 3.5 Ω, which was about 1.8 times that with the 4.5 wt% epoxy paste. We designed Ag NP pastes with varying epoxy ratio, and studied their chemical, bonding, and electrical characteristics for the development of advanced interconnection. • Ag nanoparticle paste containing epoxy was fabricated for pressureless MLCC bonding. • Robust bonding strength, 44.59 MPa, was achieved with Ag NP-epoxy (18 wt%) paste. • Epoxy filled voids and covered the circuit, deteriorating electrical conductance. • Moderate electrical and mechanical characteristics were achieved with 13.5 wt% epoxy. [ABSTRACT FROM AUTHOR]

A silver-multi-walled carbon nanotube (Ag-MWNT) nanocomposite was utilized as a thermal interface material for a high-power light-emitting diode (LED) package. The nanocomposite was fabricated by screen printing and sintering of a nanocomposite paste comprising Ag-decorated MWNTs mixed with Ag nanoparticles dispersed in an organic solvent. The Ag-MWNT nanocomposite sintered at 300 °C for 30 min with 3 wt.% MWNT exhibited the highest thermal conductivity of 21.1 W/mK at room temperature and the lowest thermal resistance of ∼6.6 K/W. Percolation networks of Ag-decorated MWNTs between Ag nanoparticles led to improved thermal conduction, resulting in excellent heat dissipation and luminous efficiency of the high-power LED package. The LED package fabricated with an Ag nanocomposite paste containing 3 wt.% MWNT exhibited a 7% decrease in operating temperature of LED chips compared with that of the basic structure of a metal printed circuit board. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid silver (Ag)-multiwalled carbon nanotube (MWNT) nanopaste was screen-printed onto a thermoplastic polyurethane (TPU) substrate to create a stretchable electronic interconnection. The effects of various ratios of MWNT contents on the direct current electrical resistivity and the stretchability were investigated by a four-point probe method and a single tensile test, respectively. Square and dog-bone patterns were fabricated by using a 400-mesh stencil mask on a TPU substrate. All samples were pre-dried and then sintered at 140 °C for 1 h in air. The experimental results showed the electrical resistivity of the hybrid Ag-MWNT nanopaste increased with increasing MWNT volume fraction. On the other hand, the hybrid Ag-MWNT nanopaste containing a higher composite ratio of MWNT showed larger tensile resistance. Through optical microscope (OM) observation, we found there were Ag nanoparticles on the MWNT networks under a tensile load of 5%. Prior to rupture-failure, the maximum displacement rate was measured to evaluate the stretchability. The hybrid Ag-MWNT pattern containing 1.2 wt% of MWNT showed the largest displacement rate, 3.4%, this is a 2.70 times increase compared to the Ag nanopaste without MWNTs. To improve both the electrical and mechanical properties of the hybrid Ag-MWNT nanopaste, further research is required. [Copyright &y& Elsevier]

Abstract: Copper (Cu) was deposited on a polyimide via pulsed electrodeposition for use as a conduction layer in flexible copper clad laminates. The influence of the peak current density on the mechanical hardness and electrical resistivity of the Cu films was investigated. In the fabrication process, electroless deposition was first employed to create a Cu seed layer on the polyimide. A Cu film was subsequently electro-deposited using a square wave pulse with different peak current densities. As the peak current density was increased from 1.5 to 4.0 A/dm2, the grain size and degree of (220) preferred orientation decreased, while the hardness and electrical resistivity increased from 0.75 to 1.19 GPa and from 17.00 to 26.26 nΩm, respectively. Such changes were believed to be due to grain refinement. The relationship between grain size and resistivity was correlated with the Mayadas and Shatzkes’s model. [Copyright &y& Elsevier]

Abstract: The interfacial reactions between Sn–3.0wt.% Ag–0.5wt.% Cu solder and an electroless nickel–electroless palladium–immersion gold (ENEPIG) substrate were investigated. After initial reflowing, discontinuous polygonal-shape (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed at the interface. During reflowing for up to 60min, the interfacial IMCs were sequentially changed in the following order: discontinuous (Cu,Ni)6Sn5, (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4, and embedded (Cu,Ni)6Sn5 in (Ni,Cu)3Sn4. The interfacial product variation resulted from the preferential consumption of Cu atoms within the solder and continuous Ni diffusion from the Ni(P) layer. [Copyright &y& Elsevier]

Abstract: In this study, it was aimed to develop a novel interconnect material simultaneously possessing high electrical conductivity and strength. Cu composite sheets were fabricated by forming the high electrical conduction paths of Ag on the surface of high strength Cu alloy substrates by damascene electroplating. As a result, the electrical conductivity increased by 40% thanks to mesh type Ag conduction paths, while the ultimate tensile strength decreased by 20%. Because of macro damascene interface profile, the peel strength of Cu composite sheet prepared by damascene electroplating increased by above 50 times compared to Cu composite sheet by conventional electroplating. As Ag conduction path became finer, pressing formability improved. Al wire wedge bonding was able to be carried out without bondable pads patterning process. [Copyright &y& Elsevier]