Cu6Sn5 Layer Research Articles

Interfacial IMC growth behavior of Sn-3Ag-3Sb-xIn solder on Cu substrate

PurposeThe reliability of solder joints is closely related to the growth of an intermetallic compound (IMC) layer between the lead-free solder and substrate interface. This paper aims to investigate the growth behavior of the interfacial IMC layer during isothermal aging at 125°C for Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) solder joints with different In contents and commercial Sn-3Ag-0.5Cu/Cu solder joints.Design/methodology/approachIn this paper, Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) and commercial Sn-3Ag-0.5Cu/Cu solder were prepared for bonding Cu substrate. Then these samples were subjected to isothermal aging for 0, 2, 8, 14, 25 and 45 days. Scanning electron microscopy and transmission electron microscopy were used to analyze the soldering interface reaction and the difference in IMC growth behavior during the isothermal aging process.FindingsWhen the concentration of In in the Sn-3Ag-3Sb-xIn/Cu solder joints exceeded 2 Wt.%, a substantial amount of InSb particles were produced. These particles acted as a diffusion barrier, impeding the growth of the IMC layer at the interface. The growth of the Cu3Sn layer during the aging process was strongly correlated with the presence of In. The growth rate of the Cu3Sn layer was significantly reduced when the In concentration exceeded 3 Wt.%.Originality/valueThe addition of In promotes the formation of InSb particles in Sn-3Ag-3Sb-xIn/Cu solder joints. These particles limit the growth of the total IMC layer, while a higher In content also slows the growth of the Cu3Sn layer. This study is significant for designing alloy compositions for new high-reliability solders.

Enhanced Mechanical Properties with Ag Addition in Electroplated Ni-Sn Solder Joints: Sub-10 Micron Bond Thickness

Keywords: Micro-bump; Microstructure; Intermetallic compounds; Mechanical properties; thermocompression bondingThe advancement of electronic devices has garnered more extensive attention towards three-dimensional integrated circuit (3D-IC) technology due to microbump size reduction and increased power density. Microbumps play an important role in driving the development of this technology, especially in 3D chip-stacking involving multiple reflow processes. The reduction in microbump height spotlights the presence of intermetallic compounds (IMCs). In comparison to traditional ball grid array (BGA) solder joints, microbumps with smaller solder volumes exhibit a predominant fraction of IMCs at solder joints, especially with microbump dimensions potentially shrinking to less than 10 micrometers.The interface reaction within confined spaces has become a critical concern. Mechanical properties will be dominated by IMC properties rather than solder characteristics. In conventional Cu/Sn/Cu solder joints, grain coarsening and prolonged reflowing times, which result in IMC collisions from opposing substrates, forming columnar grains with a uniform orientation, make the solder joint less reliable. Furthermore, the Cu3Sn layer in Cu/Sn/Cu microbumps presents another challenges, indicating the formation of Kirkendall voids, increasing the risk of brittle interface fractures.This study investigates the mechanical reliability and microstructure of two sub-10um sandwiched structures: Cu/Ni/Sn/Ni/Cu and Cu/Ni/Sn-3.5Ag/Ni/Cu. In the 3D-IC manufacturing process, solder joints will experience multiple reflow processing. Different reflow heat treatment process to achieve different fractions of Ni3Sn4 IMCs were performed on both sandwiched structure. Despite the formation of internal voids due to volume shrinkage in Ni/Sn solder joints, the addition of silver in the solder, forming Ag3Sn, effectively fills these voids. The long-time reflowed sample showed outstanding mechanical properties via the addition of silver in solder. In this study, the influence of silver addition on the microstructure and mechanical properties of the overall joints under identical reflow conditions, the fracture path observation after shear test were investigated. The growth mechanism of Ag3Sn and its distribution in the solder would be further explored and addressed. Figure 1

Investigating the impact of cobalt incorporation on the transformation of Cu6Sn5 layer to (Cu, Co)6Sn5: Microstructural and mechanical insights

In this study, cobalt (Co) particles were incorporated as reinforcing agents into the Sn58Bi solder. The solderability of the solder and the strength of the solder joints were investigated. The results indicated that adding Co particles did not alter the low melting point characteristics of the Sn58Bi solder, yet its undercooling was reduced, and the wettability was enhanced. In the Sn58Bi/Cu solder joint, adding Co led to forming free (Cu, Co)6Sn5 intermetallic compound (IMC) and generating the CoSn2 phase through microalloying. The interfacial IMC was gradually transformed from a fan-shaped Cu6Sn5 to a flatter layer-like (Cu, Co)6Sn5 IMC, eventually exhibiting a coral-like structure with increased Co content. Adding Co particles increased the thickness of the IMC layer, but at low levels, the Co could refine the IMC grains. Simultaneously, implementing grain refinement and Orowan strengthening resulted in heightened microhardness and shear strength. In the shear test, the fracture of solder joints predominantly transpired within the solder matrix. Excessive Co particles were prone to aggregating within the solder, forming irregular block-shaped (Cu, Co)6Sn5. Concurrently, the coral-like IMC at the interface led to a decline in the mechanical performance of the solder joints, with some interfacial IMC being exposed in the fracture region.

Design Principles of Mediation Layer for Current Collectors Toward High‐Performance Anode‐Free Potassium‐Metal Batteries: A Case Study of Cu6Sn5 on Copper

AbstractAnode‐free potassium (K) metal batteries are promising candidates in high‐energy‐density batteries. Nevertheless, the notorious potassium dendrite growth and poor K plating/stripping efficiency originating from the potassiophobicity of conventional Cu current collectors impede their practical applications. Herein, by means of systematically multi‐scale theoretical simulations, the correlations among K deposition morphology, nucleation sites, and potassiophilicity of mediation layers are well illuminated from thermodynamics and dynamics perspectives. As a proof of concept, a potassiophilic alloy Cu6Sn5 layer is constructed on commercial Cu foils via a facile electroless plating approach. The designed Cu6Sn5@Cu can guide the homogeneous distribution of K+ flux and regulate the electronic field, promoting uniform K+ plating and stripping. Meanwhile, a KF‐rich solid electrolyte interphase (SEI) layer with high mechanical strength is electrochemically induced and formed, facilitating the transport of K+ through SEI and enhancing the stability of SEI. Consequently, Cu6Sn5@Cu delivers great performance with durable stability of up to 600 h (1 mA cm−2 and 1 mAh cm−2) in no‐reservoir half‐cells. Benefiting from the unique mediation layer design, a novel anode‐free K‐metal full‐cell prototype demonstrates ameliorative cyclic stability. This work advances a fundamental understanding and establishes the bridge between the potassium deposition morphology and mediation layer properties for anode‐free potassium‐metal batteries.

Influence of Isothermal Aging on Microstructure and Shear Property of Novel Epoxy Composite SAC305 Solder Joints.

With the rapid iteration of microsystem integrated technology, the miniaturization of electronic devices requires packaging materials with higher reliability. In this work, the microstructure evolution and mechanical properties of novel epoxy composite SAC305 solder joints were studied after isothermal aging to evaluate the enhanced effect of epoxy addition. The thickness variation and morphological evolution of the interfacial layer were analyzed. The results showed that, as the aging time was prolonged, the Cu6Sn5 interfacial layer remarkably coarsened and Cu3Sn compounds formed between the Cu6Sn5 layer and Cu pad due to the continuous atomic diffusion. Compared with the monolithic joint, the epoxy composite SAC305 joints had a lower overall IMC growth rate during aging, closely related to the initial morphologies of the interfacial layers. The shear test results showed an apparent decrease in the shear forces of all the solder joints as the aging time increased. Nevertheless, because of the extra mechanical support provided by the epoxy layer, the epoxy composite joints demonstrated notably enhanced mechanical properties. After 1000 h aging treatment, the shear force of SAC305 joints containing 8 wt.% epoxy was 26.28 N, showing a 24.08% increase over the monolithic joint. Cu-Sn IMCs were detected on the shear fracture of the monolithic joint after 1000 h aging, indicating the fracture occurred near the interface and displayed a ductile/brittle mixed fracture. Concerning the epoxy composite joints, cracks were still initiated and extended within the solder bulk, demonstrating a noticeable enhancement in ductility due to the addition of epoxy.

Oxidation behavior and intermetallic compound growth dynamics of SAC305/Cu solder joints under rapid thermal shock

Oxidation behavior of SAC305/Cu solder joints and kinetics of intermetallic compound (IMC) growth were investigated using an electromagnetic induction heating device. The results show that the solder joint undergoes oxidation when subjected to rapid thermal shock. The oxidation behavior of the solder joint itself is the main factor, which is exacerbated by the presence of the internal Cu6Sn5 IMC. The growth of the Cu6Sn5 layer is controlled by grain boundary diffusion, while that of the Cu3Sn layer is controlled by bulk diffusion. The dissolved Cu of the substrate diffuses mainly into the interfacial IMC and the interior of the solder. Under rapid thermal shock, the shear strength of the solder joint decreases substantially, by 49.2% after 72 h. The fracture mechanism changes from ductile fracture to mixed tough−brittle fracture and finally, to brittle fracture.

Effect of Thermal Aging on the Interfacial Reaction Behavior and Failure Mechanism of Ni-xCu/Sn Soldering Joints under Shear Loading.

Ni-xCu/Sn soldering joints were aged at 200 °C, and the microstructure evolution and mechanical properties during the solid-state reaction were studied under shear loading. Results showed that the intermetallic compounds (IMCs) exhibited a Cu content-dependent transformation from the (Ni,Cu)3Sn4 phase to the (Cu,Ni)6Sn5 phase at the Ni-xCu/Sn interface. Furthermore, a Cu3Sn layer was observed exclusively at the Cu/Sn interface. The shear strength of the soldering joints after thermal aging exhibited an initial decrease followed by an increase, except for a significant enhancement at the Cu content of 60 wt.%. In addition, the evolution law of mechanical properties and failure mechanism of the thermal aging joints were elucidated based on the fracture microstructure and the fracture curve of the joints.

Metal deposited nanoparticles as “bridge materials” for lead-free solder nanocomposites

An influence of carbon nanotubes and carbon nanospheres coated by Au–Pd and Pt on the microstructure of solder/copper joints at room temperature and after aging at sub-zero temperature. The carbon nanosized admixtures were mixed with ternary Sn3.0Ag0.5Cu matrix to prepare a composite solder. The microstructure of the solder joints between the nanocomposite solders and a copper substrate was studied by scanning electron microscopy. It was found that minor (0.05 wt. %) admixtures of both the carbon nanospheres and nanotubes increase the shear strength of the solder joints and reduce the growth rate of the intermetallic Cu6Sn5 layer, formed at the interface between solder and copper. This effect may be related to the adsorption of nanoinclusions on the grain surface during the solidification process. Comparative analysis suggests that exposure for 2 months at 253 K does not lead to deterioration of such an important mechanical characteristic of the solder joint as shear strength, indicating the possibility of using these nanocomposite solders in microelectronic equipment even at temperatures below 0 ℃.

Mechanical properties degradation of Sn 37Pb solder joints caused by interfacial microstructure evolution under cryogenic temperature storage

The interfacial microstructure, shear property and fracture behaviors of Sn37Pb joints after cryogenic temperature storage for different durations were investigated in this study, storage test at room temperature (298 K) and thermal aging test at 423 K were also carried out as comparison. The morphology of interfacial Cu6Sn5 IMCs for the joints stored under 77 K and 173 K transformed from scallop-like to column-like, moreover, the IMC layer thickness slowly increased with prolonged storage time. The growth rate of Cu6Sn5 layer in Sn37Pb joint stored at 77 K was slightly faster as compared with that stored at 173 K. However, the morphology and thickness of Cu6Sn5 IMC layer still remained roughly unchanged after storage at 298 K for up to 40 days. The Cu6Sn5 IMC growth of Sn37Pb joint stored at 77 K and 173 K was expected to be caused by Cu atom diffusion from Cu pad towards Sn37Pb solder, which was induced by the stress gradient. Additionally, the shear force declined and fracture position changed from in Sn37Pb solder to primarily in Sn37Pb solder and partly along the interface with the prolonging of storage time at 77 K and 173 K, which were induced by IMC layer growth.

Nanosecond Pulsed Laser‐Assisted Deposition to Construct a 3D Quasi‐Gradient Lithiophilic Skeleton for Stable Lithium Metal Anodes

AbstractThe continuous growth of Li dendrites and volumetric deformation of Li severely impede the commercial application of Li metal anodes. To regulate Li stripping/plating, electrodeposition or magnetron sputtering is extensively utilized to fabricate lithiophilic‐metal deposited 3D Li hosts. However, the binding force between lithiophilic‐metal and host is weak, inevitably leading to numerous cracks/defects of lithiophilic‐surface‐layer during Li plating/stripping. Herein, a quasi‐gradient (Cu‐Cu3Sn‐Sn‐SnO2) 3D skeleton consisting of hierarchical Sn/SnO2 composite metallurgically bonded to copper foam through Cu3Sn alloy (LAD‐SSC@CF) is designed, and prepared in one‐step by a nanosecond‐pulsed‐laser‐assisted deposition strategy. The homogeneous Li nucleation sites provided by Li22Sn5 formed by the reaction of Sn/SnO2 with Li can inhibit Li dendrites growth. Meanwhile, the porous space and strong bonding of Cu3Sn layer avoid structural deterioration of anodes. Consequently, a symmetric cell based on LAD‐SSC@CF@Li exhibits an outstanding cycling stability of 1500 h at 1 mA cm−2. In particular, a full cell with LiFePO4 cathode provides good capacity retention of 81.3% at 5 C after 600 cycles. Moreover, the successful preparation of other composite materials (In, Zn, Sn‐Bi, etc.) loading on various substrates (Kapton film, ceramic, copper foil, etc.) demonstrates the versatility of pulsed‐laser‐assisted deposition strategy for preparing battery materials.

In Situ Reaction Fabrication of a Mixed‐Ion/Electron‐Conducting Skeleton Toward Stable Lithium Metal Anodes

Lithium metal batteries are emerging as a strong candidate in the future energy storage market due to its extremely high energy density. However, the uncontrollable lithium dendrites and volume change of lithium metal anodes severely hinder its application. In this work, the porous Cu skeleton modified with Cu6Sn5 layer is prepared via dealloying brass foil following a facile electroless process. The porous Cu skeleton with large specific surface area and high electronic conductivity effectively reduces the local current density. The Cu6Sn5 can react with lithium during the discharge process to form lithiophilic Li7Sn2 in situ to promote Li‐ions transport and reduce the nucleation energy barrier of lithium to guide the uniform lithium deposition. Therefore, more than 300 cycles at 1 mA cm−2 are achieved in the half‐cell with an average Coulombic efficiency of 97.5%. The symmetric cell shows a superior cycle life of more than 1000 h at 1 mA cm−2 with a small average hysteresis voltage of 16 mV. When coupled with LiFePO4 cathode, the full cell also maintains excellent cycling and rate performance.

Impact of Isothermal Aging on Mechanical Properties of 92.8%Sn-3%Ag-0.5%Cu-3.3%Bi (Cyclomax) Solder Joints

During operation, electronic components are exposed to high temperatures that may last for long periods, depending on the operating duration. Solder joints are one of the components most affected by thermal aging while in service. In this research, the effect of thermal aging duration and temperature on the mechanical properties of 92.8%Sn-3%Ag-0.5%Cu-3.3%Bi (Cyclomax) was investigated. The novelty of this work lies in the study of the important properties of a new generation of Sn-Ag-Cu (SAC) materials (i.e., Cyclomax). Cyclomax is rare in industry and immature in research. To understand the effect of thermal aging, the microstructure was investigated, and changes in it and its mechanical properties were observed. To simulate solder joints in electronic devices, samples of solder balls were prepared and attached to copper pads on electronic boards. Most samples were then treated at 150 °C or 100 °C for up to 1000 h and some samples were left untreated for comparison. A scanning electron microscope (SEM) was used to obtain images of the microstructure. The shear stress–shear strain relationships, including the ultimate shear strength (USS), the modulus of elasticity and the ultimate energy (UE), were investigated. The microstructure images indicated the presence of a layer of Cu6Sn5 on top of the copper pad before thermal aging was applied. The thickness of this layer increased with the application of thermal aging over time. The results for the shear stress–shear strain relationship indicate that all of the USS, the total energy (TE) to shear off the solder balls and the UE decreased at the beginning of the thermal aging and then reversed to increase later. In general, isothermal aging reduces the performance of Cyclomax solder joints in terms of the minimum force and energy required to separate and subsequently damage electronic components.

The Study of the Reliability of Complex Components during the Electromigration Process

With the increasing number of inputs and outputs, and the decreasing interconnection spacing, electrical interconnection failures caused by electromigration (EM) have attracted more and more attention. The electromigration reliability and failure mechanism of complex components were studied in this paper. The failure mechanism and reliability of complex components during the electromigration process were studied through the simulation and the experiment, which can overcome the limitation of experimental measurement at a micro-scale. The simulation results indicated that the solder joint has obvious current crowding at the current inlet, which will significantly enhance the electromigration effect. Based on the atomic flux divergence method, the void formation of solder joints can be effectively predicted, and life prediction can be more accurate than Black's equation. Experimental results indicated that the resistance of the daisy chain could be significantly increased with the process of void formation in the solder and corrosion of the leads. Moreover, the growth of intermetallic compounds can be obviously promoted under current stress. The main composition of the intermetallic compounds changes from almost entirely Cu5Sn6 to Cu5Sn6 and Cu3Sn; the cracks can be detected at the Cu3Sn layer. Specifically, the mean time to failure is 1065 h under 1.4 A current and 125 °C based on IPC-9701A guidelines.

Investigation of the Microstructure, Thermal Properties, and Mechanical Properties of Sn-Bi-Ag and Sn-Bi-Ag-Si Low Temperature Lead-Free Solder Alloys

In this study, we investigated the microstructure, mechanical properties, and thermal performance of Sn-xBi-1Ag (x = 35, 37, 45, and 47 wt.%) solders, with a particular focus on the effect of adding trace Si atoms. The impact of different Ag concentrations on the properties of Sn-xBi-Ag-0.5Si solders was also studied. The results indicated that as the amount of Bi added to Sn-xBi-1Ag solder alloys increased, the tensile strength, microhardness, melting temperature, and melting range decreased somewhat, but the wettability improved. The Cu6Sn5 layer between the soldering alloy and the Cu substrate became thinner upon increasing the Bi content. Adding microcrystalline Si atoms to the Sn-Bi-1Ag alloy improved the tensile strength and microhardness, but the melting point and melting range were not significantly changed. The wettability was optimized, and the diffusion layer formed with the Cu matrix was significantly thinner. By increasing the Ag content in the Sn-Bi-(1,3)Ag-0.5Si alloy, the tensile strength of the alloy was continuously strengthened, while the hardness decreased slightly and the melting point and melting range increased slightly. The wettability was greatly improved, and the Cu6Sn5 layer became thinner.

Cu3Sn joint based on transient liquid phase bonding of Cu@Cu6Sn5 core–shell particles

With the development of high-integration and high-power electronics, the lack of matching chip connecting materials that can withstand high temperatures has been a challenge. In this manuscript, a Cu@Cu6Sn5 core–shell bimetallic particles (approx. 1 μm in diameter) are successfully prepared and introduced as a new solder material for the packaging of power devices to obtain a Cu3Sn all-IMC solder joint. The joint consisted mainly of equiaxed Cu3Sn grains, and a small portion of columnar Cu3Sn grains. In columnar-type growth, Sn is the dominant diffusing species, which comes from the depletion of Sn in Cu6Sn5. The depleted Cu6Sn5 is transformed into columnar Cu3Sn. In equiaxed-type growth, Cu is the dominant diffusing species. Cu reacts with Cu6Sn5 to grow a Cu3Sn layer. This conclusion was confirmed by the orientation relationship. The equiaxed Cu3Sn grain nucleates at the Cu/Cu3Sn interface have an orientation relationship with the Cu substrate. Columnar Cu3Sn grains at the Cu6Sn5/Cu3Sn interface have an orientation relationship with Cu6Sn5.

Nucleation and growth of intermetallic compounds on the prefabricated Cu6Sn5 layer

In the 3D advanced packaging process, solder joints undergo multiple reflows and the intermetallic compounds will continue to grow on the Cu6Sn5 layer. However, the nucleation and growth mechanism of intermetallic compounds on the Cu6Sn5 layer is not clear. In this paper, the Cu6Sn5 layer was prefabricated on (001) Cu and the reaction between the prefabricated Cu6Sn5 layer and the Sn-based solder under the influence of solder composition was investigated. Results show that when the prefabricated Cu6Sn5 layer has a preferred orientation, the orientation can be retained after reflowing. When the orientation of the prefabricated Cu6Sn5 layer is randomly distributed, small Cu6Sn5 grains nucleate on the surface of the prefabricated Cu6Sn5 layer and grow along the <0001> crystal direction. Besides, the addition of Ag is beneficial to the heritability of orientation and inhibits the nucleation of small Cu6Sn5 grains on the surface of the prefabricated Cu6Sn5 layer.

Localized Induction Heating of Cu-Sn Layers for Rapid Solid-Liquid Interdiffusion Bonding Based on Miniaturized Coils.

Considering the demand for low temperature bonding in 3D integration and packaging of microelectronic or micromechanical components, this paper presents the development and application of an innovative inductive heating system using micro coils for rapid Cu-Sn solid-liquid interdiffusion (SLID) bonding at chip-level. The design and optimization of the micro coil as well as the analysis of the heating process were carried out by means of finite element method (FEM). The micro coil is a composite material of an aluminum nitride (AlN) carrier substrate and embedded metallic coil conductors. The conductive coil geometry is generated by electroplating of 500 µm thick copper into the AlN carrier. By using the aforementioned micro coil for inductive Cu-Sn SLID bonding, a complete transformation into the thermodynamic stable ε-phase Cu3Sn with an average shear strength of 45.1 N/mm2 could be achieved in 130 s by applying a bond pressure of 3 MPa. In comparison to conventional bonding methods using conduction-based global heating, the presented inductive bonding approach is characterized by combining very high heating rates of about 180 K/s as well as localized heating and efficient cooling of the bond structures. In future, the technology will open new opportunities in the field of wafer-level bonding.

Effects of bonding pressures on microstructure and mechanical properties of silver–tin alloy powders synthesized by ball milling for high-power electronics packaging

Silver (Ag) sintering is widely adopted as a die attach method for power electronics packaging. However, oxidation, massive grain growth, and increasing porous structure occur in sintered Ag joints at high temperatures, resulting in decreasing mechanical properties of the die attachment in power devices. To solve the problems of sintered Ag joints, a novel die attach material consisting of silver–tin (Ag–Sn) alloy particles is developed in this study. Ag–Sn alloy powders were newly fabricated by high-energy ball milling technique. The microstructural evolutions of the Ag–Sn alloy joints bonded at different pressures were systematically analyzed. With increasing high-temperature storage time at 300 °C, the reactions between sintered Ag–Sn alloy joints and Cu substrates increased, which resulted in the formation of Cu3Sn or Ag-rich diffusion layer. The relationships between microstructures and the formation of each phase were discussed. In addition, the robust sintered Ag–Sn alloy joints exhibited low porosity without pore coarsening and limit oxidation at high temperatures, indicating a dense and stable microstructure of sintered Ag–Sn alloy joints. As a result, high bonding strength did not deteriorate even after high-temperature storage for 2000 h. It is concluded that the novel Ag–Sn alloy paste produced by high-energy ball milling has long-term high-temperature reliability to be used as a die attach material for the power electronics packaging, thus enabling high-power devices to have higher operating temperatures and thermal stability.

PREPARATION OF CZTS THIN FILM EMPLOYING RAPID THERMAL PROCESSING METHOD

CZTS thin film was fabricated by sulfurization process of deposited thin films on Mo coated glass substrates. Cu, Zn, and Sn thin film layers were deposited sequentially to form Glass/Mo/CuSn/Zn/Cu. The CuSn layer in the stacked structure was formed by annealing process in the sputtering chamber after sequential deposition of Cu and Sn, respectively. The sulfurization process was performed by rapid thermal processing method (RTP) so as to obtain kesterite CZTS structure. The obtained CZTS thin film was analyzed using several characterization methods such as EDX, XRD, Raman spectroscopy, SEM and PL measurements. The EDX measurements showed that elemental loss was not observed after the annealing process in sulfur atmosphere. The fabricated CZTS thin film showed Cu stoichiometric and Zn rich composition. The XRD pattern of annealed sample revealed formation of kesterite CZTS structure. The Raman spectra of the sample proved formation of kesterite CZTS structure. In addition, some CTS phases were detected in the structure by Raman spectroscopy. Polycrystalline surface microstructure was seen in SEM surface measurement. The room temperature PL measurement exhibited a transition around at 1.39 eV that is very close to band gap of kesterite CZTS structure. Overall, with this study, it has been shown that the CZTS thin film structure can be easily produced using the RTP method with very high heating rate.

Effect of Thermal Aging on the Mechanical Properties of SAC305.

Many electronic products are subjected to heat for long periods, depending on their operations. Thus, it is expected that the physical and mechanical properties of electronic elements, including the soldering joints, will be affected. In this study, the impact of thermal aging time and temperature on the microstructure and mechanical properties of 96.5Sn–3.0Ag–0.5Cu (SAC305) was investigated. The samples used were SAC305 solder balls attached to copper pads. The research began by examining the microstructure of the aged samples at 150 °C for 100 and 1000 h. Then, this was compared to the microstructure of the same samples without thermal aging. Then, five groups of 10 samples were prepared from a shear stress–shear stain experiment. The first group was as produced, the second group was aged for 2 h, the third group was aged for 10 h, the fourth group was aged for 100 h, and the fifth group was aged for 1000 h. All groups were aged at a temperature of 150 °C. An Instron testing machine was used to plot a shear stress–shear stain curve until the ball was completely sheared off the pad. The mechanical properties, including the ultimate shear strength, the ultimate energy used to shear the ball, and the total energy used to shear the ball at all thermal aging times were then estimated. The results of this study indicated the formation of a layer of Cu6Sn5 over the copper pad, which thickened with thermal aging time. Furthermore, the ultimate and total shear strengths decreased with thermal aging time. The same procedure was repeated to assess the ultimate shear strength at 100 °C. The decrease in ultimate shear strength was more severe with increasing thermal aging temperature.