Interfacial Reactions

Zn-Al based alloys have been suggested as high temperature lead-free solder for Si die attach by different researchers. But, so far, these alloys have not been tested in the industrial environment. In this study, Zn-Al-Ge alloy solder wire was used for Si die attachment on Cu substrate in an automatic die attach machine. The back side of the die was metalized with Ti/Ni/Ag layers. Die attachment was performed in a forming gas environment at temperatures ranging from 370 o C to 390 o C. Interfacial structure at the Si die and Cu substrate interfaces, and the bulk solder microstructure were investigated using an optical microscope, scanning electron microscope (SEM), energy dispersive x-ray (EDX) and electron probe microanalyzer (EPMA). Wetting characteristics and die shear strength were also studied. Cross sectional microstructural investigation revealed that as many as three intermetallic (IMCs) layers form at the solder/copper interface. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5 Zn 8 forms at the middle. At the Si die-solder interface, with Ti/Ni/Ag metallization, no IMC layer was detected. Microstructural evidence suggests that Ni layer did not react with the Zn-Al-Ge solder. The microstructure of the bulk solder consists of mainly two phases: one with a lighter contrast and the other one being darker under the SEM. The phase with lighter contrast is a zinc rich phase containing an average of about 70.9% Zn. The darker one is found to be an aluminum rich phase containing an average of about 54.9% Al. In addition, some particles with brighter appearance are observed at different places in the bulk solder. These particles are rich in zinc and their composition closely resembles that of scallop type CuZn 4 IMC which forms at the solder side of the copper-solder interface. It is suggested that these particles are CuZn 4 IMC which have been spalled from the interface during soldering. Wetting of Zn-Al-Ge solder on Cu substrate was found to be lower at 370 o C as compared with that at 390 o C. Voids were found in the solder which were more in number at higher die attach temperatures. Die shear strength was found to be higher at the die attached temperature of 390 o C (22.3 MPa) as compared with those obtained at 370-380 o C (15.5-17.4 MPa). Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 28.2 MPa. The microstructure and properties of the solder joint are discussed.

Binary phase diagrams are important tools for designing desired alloys. In the Sn-rich region of the Sn-In alloy phase diagram, the solidus line appears as a dotted line in current literature plots to indicate uncertainty. The contour of the solidus has now been clarified as a result of the present investigation. Four alloys, Sn 70 In 30 , Sn 75 In 25 , Sn 80 In 20 , and Sn 85 In 15 were melted at 300°C for 10 h and annealed between 120 and 200°C in the (L + c) two-phase region. The morphology and chemical compositions of annealed specimens were analyzed using both field emission scanning electron spectroscopy and energy-dispersive x-ray spectrometry. The results reveal that the liquid phase, initially appearing at the eutectic temperature, invades the solid along grain boundaries with penetration gradually increasing with increasing annealing temperature and a granular structure form. The average compositions in grains of Sn 70 In 30 , Sn 75 In 25 , Sn 80 In 20 , and Sn 85 In 15 specimens correspond to the solidus concentrations, and the solidus line and (b + c)/c phase boundary can be determined as a fit to these temperaturecomposition points.

In this study, we investigate the impacts of working process, high-pressure torsion (HPT) and hot rolling (HR) on the microstructure and mechanical performance of aluminum-based nanocomposites containing fullerenes. HPT caused severe plastic deformations that generate numerous dislocations and lattice strains, and this stimulated the formation of aluminum carbides (Al 4 C 3) and reduced the hardness during heat treatment. In contrast, the HRed specimens experienced dynamic recovery, and their initial dislocation densities and lattice strains were lower than those of the HPTed specimens. Thus, the HRed composites formed supersaturated aluminum phases as well as aluminum carbides during the heat treatment. The supersaturated phases provided highdensity dislocations and severe lattice strains, resulting in an increase in the hardness during the heat treatment. This comparison suggests that the mechanical properties of aluminum-fullerene composites can be controlled by working processes in practical situations.

Interphases, solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) are the key influencers in determining battery life and performance. Especially, for technologies such as sodium ion batteries that are in development stage, it is crucial to tune the interphase chemistry without which it suffers at present from poor performance metrics for reaching real-life applications. In this study, we utilize optical sensors as a tool to follow operando, the thermal events of interfacial reactions and established the role of different electrolyte additives during the SEI/CEI formation. Using the acquired knowledge from sensing, together with complementary studies in Na-ion full-cells, we propose a new electrolyte formulation that showed stable cycling performance at 0-55 °C with very low self-discharge and improved safety due to mitigated 2 gassing during cycling. Finally, we nurture our studies by transferring the know-hows to prototype cylindrical 18650 cells. We hope such findings will accelerate the practical development of Na-ion batteries.

Co-deposition technique by means of simultaneous ion beam sputtering of nickel and silicon onto SiC was performed for tailoring of Nisilicide/SiC contacts. The prepared samples were analysed by means of XRD and XPS in order to obtain information about the surface and interface chemistry. Depth profiling was used in order to analyse in-depth information and chemical distribution of the specimens. XRD results showed that the main phase formed is Ni 2 Si. The XPS analysis confirmed the formation of the silicide on the surface and showed details about the chemical composition of the layer and layer/substrate interface. Moreover, the XPS depth profiles with detailed analysis of XPS peaks suggested that tailoring of C distribution could be monitored by the co-deposition technique employed.

Nickel and Tantalum thin films with 3:5 thickness ratios were deposited in succession onto 4H-SiC substrate at room temperature. The samples were then heated in situ in vacuum at 650, 800 or 950 8C for 30 min. Glancing angle X-ray diffraction (XRD), Auger electron spectroscopy (AES) and current-voltage (I-V) technique were used for characterising the interfacial reactions and electrical properties. Amorphous Ni-Ta can be formed by solid-state reaction at 650 8C. The minor dissolved Ni in the Ta metal promotes the reaction between Ta and SiC. With increasing annealing temperature up to 950 8C, the dominant carbide changes from Ta 2 C to TaC and a layer structure is developed. Electrical measurements show that ohmic contact is formed after annealing at or above 800 8C.

Interphases, solid-electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI) are the key influencers in determining battery life and performance. Especially, for technologies such as sodium ion batteries that are in development stage, it is crucial to tune the interphase chemistry without which it suffers at present from poor performance metrics for reaching real-life applications. In this study, we utilize optical sensors as a tool to follow operando, the thermal events of interfacial reactions and established the role of different electrolyte additives during the SEI/CEI formation. Using the acquired knowledge from sensing, together with complementary studies in Na-ion full-cells, we propose a new electrolyte formulation that showed stable cycling performance at 0-55 °C with very low self-discharge and improved safety due to mitigated 2 gassing during cycling. Finally, we nurture our studies by transferring the know-hows to prototype cylindrical 18650 cells. We hope such findings will accelerate the practical development of Na-ion batteries.

Mg-C composites offer a suitable alternative to Al alloys while allowing for a significant weight reduction, but their production can be impaired by the poor wettability of C substrates by Mg. In this study, a new ''liquid'' processing route has been investigated. By making use of the well-known effect of a pre-treatment of the C fibers with an aqueous solution of K 2 ZrF 6 in favoring spontaneous wetting of C with Al, C yarns have been pre-impregnated with Al and the feasibility of further using them as reinforcements in Mg matrix composites has been assessed. More particularly, it has thus been shown that the, under the thermal conditions involved in the process, C fibers did not suffer damage due to chemical reaction with Al, and also that special care should be taken to control the surface condition of the pre-infiltrated yarns. Keywords interfacial reactions, Mg/C composites, squeeze casting, wetting This article is an invited submission to JMEP selected from presentations at the Symposia ''Wetting, soldering and brazing'' and ''Diffusion bonding and characterization'' belonging to the Topic ''Joining'' at the European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2011), held September 12-15, 2011, in Montpellier, France, and has been expanded from the original presentation.

Zn-Al based alloys have been suggested as high temperature lead-free solder for Si die attach by different researchers. But, so far, these alloys have not been tested in the industrial environment. In this study, Zn-Al-Ge alloy solder wire was used for Si die attachment on Cu substrate in an automatic die attach machine. The back side of the die was metalized with Ti/Ni/Ag layers. Die attachment was performed in a forming gas environment at temperatures ranging from 370 o C to 390 o C. Interfacial structure at the Si die and Cu substrate interfaces, and the bulk solder microstructure were investigated using an optical microscope, scanning electron microscope (SEM), energy dispersive x-ray (EDX) and electron probe microanalyzer (EPMA). Wetting characteristics and die shear strength were also studied. Cross sectional microstructural investigation revealed that as many as three intermetallic (IMCs) layers form at the solder/copper interface. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5 Zn 8 forms at the middle. At the Si die-solder interface, with Ti/Ni/Ag metallization, no IMC layer was detected. Microstructural evidence suggests that Ni layer did not react with the Zn-Al-Ge solder. The microstructure of the bulk solder consists of mainly two phases: one with a lighter contrast and the other one being darker under the SEM. The phase with lighter contrast is a zinc rich phase containing an average of about 70.9% Zn. The darker one is found to be an aluminum rich phase containing an average of about 54.9% Al. In addition, some particles with brighter appearance are observed at different places in the bulk solder. These particles are rich in zinc and their composition closely resembles that of scallop type CuZn 4 IMC which forms at the solder side of the copper-solder interface. It is suggested that these particles are CuZn 4 IMC which have been spalled from the interface during soldering. Wetting of Zn-Al-Ge solder on Cu substrate was found to be lower at 370 o C as compared with that at 390 o C. Voids were found in the solder which were more in number at higher die attach temperatures. Die shear strength was found to be higher at the die attached temperature of 390 o C (22.3 MPa) as compared with those obtained at 370-380 o C (15.5-17.4 MPa). Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 28.2 MPa. The microstructure and properties of the solder joint are discussed.

The present work was intended to judge the influence of superheat and mould preheat temperature on the fluidity of 6xxx Al-alloys. The fluidity spirals were made using magnesia filler materials and the colloidal silica binder. The fluid increases with the increase of super heat and shell mould preheat temperature. The fluidity was higher for 6061 Al-alloy than that of 6013 Al-alloy.

In the present work an attempt has been made to arrive at the optimum values of control factors, which govern the quality of investment shell moulds. The effect of control factors and subsequent optimization have been carried by Taguchi’s design method. The predicted optimum value of hot bending strength, hot permeability and %thermal expansion of shells are respectively 2.42 N/mm2, 7.94 and 0.24.

The ceramic shells were fabricated with ceramic slurry containing zirconia as filler material and colloidal silica binder to cast Zr-alloy 705. The investment shell mould characteristics in terms of hot bending strength, thermal expansion and metal-mould reaction were measured. On account of phase transformation (confirmed by Raman spectra) of zirconia at high temperatures the hot bending strength zirconia shells decreases with increasing temperature. A hard ZrO2 case layer was noticed beneath the surface of the casting.

Interfacial reactions during Si die attachment with Zn-Al-Mg-Ga high-temperature lead (Pb)-free solder on bare Cu lead-frame (Tamac 4) and Ni metallized Cu lead-frame were investigated using an optical microscope, scanning electron microscope (SEM) and energy dispersive x-ray (EDX). Die attachment was performed in an automatic die attach machine in a forming gas environment at temperature 380C. The back side of the die was metallized with Ti/Ni/Ag layers. Comparative studies of die attach properties such as wetting, void and die shear strength on bare and Ni metallized Cu lead-frame was made. Cross sectional microstructural investigation revealed that as many as three intermetallic compound (IMCs) layers form at the solder/lead-frame interface for bare Cu lead-frame. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn4 forms at the solder side, while Cu5Zn8 forms at the middle. At the interface with Si die, IMC layer could not be detected by SEM. With Ni metallized Cu lead-frame, no IMC layer was observed at the solder/lead-frame as well as Si die/solder interface by SEM. Wetting on Ni metallized Cu lead-frame was found to be lower as compared to that at bare Cu lead-frame. Die shear strength was found to be higher on bare Cu lead-frame (24.2 MPa) as compared to Ni metallized Cu lead-frame (20.5 MPa). Die shear strength of standard Pb-5Sn solder was also measured for comparison and found to be 28.2 MPa. © 2010 IEEE.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5746721&tag=1

Zn-Al based alloys have been suggested as high temperature lead-free solder for Si die attach by different researchers. But, so far, these alloys have not been tested in the industrial environment. In this study, Zn-Al-Ge alloy solder wire was used for Si die attachment on Cu substrate in an automatic die attach machine. The back side of the die was metalized with Ti/Ni/Ag layers. Die attachment was performed in a forming gas environment at temperatures ranging from 370°C to 390°C. Interfacial structure at the Si die and Cu substrate interfaces, and the bulk solder microstructure were investigated using an optical microscope, scanning electron microscope (SEM), energy dispersive x-ray (EDX) and electron probe microanalyzer (EPMA). Wetting characteristics and die shear strength were also studied. Cross sectional microstructural investigation revealed that as many as three intermetallic (IMCs) layers form at the solder/copper interface. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5Zn 8 forms at the middle. At the Si die-solder interface, with Ti/Ni/Ag metallization, no IMC layer was detected. Microstructural evidence suggests that Ni layer did not react with the Zn-Al-Ge solder. The microstructure of the bulk solder consists of mainly two phases: one with a lighter contrast and the other one being darker under the SEM. The phase with lighter contrast is a zinc rich phase containing an average of about 70.9% Zn. The darker one is found to be an aluminum rich phase containing an average of about 54.9% Al. In addition, some particles with brighter appearance are observed at different places in the bulk solder. These particles are rich in zinc and their composition closely resembles that of scallop type CuZn 4 IMC which forms at the solder side of the copper-solder interface. It is suggested that these particles are CuZn 4 IMC which have been spalled from the interface during soldering. Wetting of Zn-Al-Ge solder on Cu substrate was found to be lower at 370°C as compared with that at 390°C. Voids were found in the solder which were more in number at higher die attach temperatures. Die shear strength was found to be higher at the die attached temperature of 390°C (22.3 MPa) as compared with those obtained at 370-380°C (15.5-17.4 MPa). Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 28.2 MPa. The microstructure and properties of the solder joint are discussed.

ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5643009

Interfacial reactions during Si die attachment with Zn-Al-Mg-Ga high-temperature lead (Pb)-free solder on bare Cu lead-frame (Tamac 4) and Ni metallized Cu lead-frame were investigated using an optical microscope, scanning electron microscope (SEM) and energy dispersive x-ray (EDX). Die attachment was performed in an automatic die attach machine in a forming gas environment at temperature 380C. The back side of the die was metallized with Ti/Ni/Ag layers. Comparative studies of die attach properties such as wetting, void and die shear strength on bare and Ni metallized Cu lead-frame was made. Cross sectional microstructural investigation revealed that as many as three intermetallic compound (IMCs) layers form at the solder/lead-frame interface for bare Cu lead-frame. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5Zn 8 forms at the middle. At the interface with Si die, IMC layer could not be detected by SEM. With Ni metallized Cu lead-frame, no IMC layer was observed at the solder/lead-frame as well as Si die/solder interface by SEM. Wetting on Ni metallized Cu lead-frame was found to be lower as compared to that at bare Cu lead-frame. Die shear strength was found to be higher on bare Cu lead-frame (24.2 MPa) as compared to Ni metallized Cu lead-frame (20.5 MPa). Die shear strength of standard Pb-5Sn solder was also measured for comparison and found to be 28.2 MPa.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5746721