Transient Liquid Phase Bonding Research Articles

Grain morphology and mechanical strength of high-melting-temperature intermetallic joints formed in asymmetrical Ni/Sn/Cu system using transient liquid phase soldering process

The grain morphology and mechanical strength of the high-melting-temperature intermetallic joints formed in the asymmetrical Ni/Sn/Cu system using a transient liquid phase (TLP) soldering process were investigated. The grain morphology of the (Cu, Ni)6Sn5 compounds subsequently exhibited fine rounded, needlelike and coarse rounded shapes from the Ni side to the Cu side, which was highly in accordance with the Ni concentration gradient across the intermetallic joints. The thermodynamic analysis indicates that the critical Ni concentration which determined the grain morphology between the needlelike shape and the coarse rounded shape is approximately 11 at% at the soldering temperature of 260 °C. The growth of the Cu3Sn compounds was suppressed and exhibited the grain morphology of fine rounded shape. The melting temperature and the shear strength of the intermetallic joints are 418.4 ± 0.1 °C and 49.8 ± 0.3 MPa, respectively. The shear fracture was inclined to occur in the area of (Cu, Ni)6Sn5 grains with the coarse rounded shape.

Transient Liquid Phase Bonding of Gamma Prime Precipitation Strengthened Ni Based Superalloy

Transient Liquid Phase Bonding of Gamma Prime Precipitation Strengthened Ni Based Superalloy

Strength and reliability of low temperature transient liquid phase bonded Cu[sbnd]Sn[sbnd]Cu interconnects

As power electronic devices have tendencies to operate at higher temperatures and current densities, the demand for reliable and efficient packaging technologies are ever increasing. This paper reports the studies on application of transient liquid phase (TLP) bonding of CuSnCu systems as a potential technology that could enable the realization of stacks with better thermal performance and reliability than those can be achieved using conventional soldering techniques. Low temperature TLP bonded CuSnCu samples are fabricated, and the strength of the achieved bonds is measured by shear testing. Micro-sectioning and optical microscopy studies of the samples reveal that the TLP bonds show good homogeneity with a small number of voids at the interface. Energy dispersive X-ray analysis is applied to examine at what rates Sn is converted into CuSn intermetallics since a full conversion is critical for achieving a strong and high temperature resistant bond. Finally, initial results from a thermal cycling test are presented and it is concluded that the achieved TLP bonding is a promising candidate for the fabrication of reliable interconnects in power electronics.

Effect of Bonding Temperature on Microstructure Development during Transient Liquid Phase Bonding of Ti<sub>2</sub>AlNb Alloy Using Ti-Zr-Cu Based Filler Alloy

Transient liquid phase (TLP) bonding of Ti2AlNb, used for vacuum brazing furnace, was carried out using Ti-Cu-Zr based foil as filler alloy at 950, 1000 and 1050°C. The effect of bonding temperature on joint interface, phase constitutions and their distributions were investigated by taking advantages of OM, SEM, EDS and XRD analyses. The result revealed that the TLP joint consisted of isothermally solidified zone and diffusion affected zone. A non-isothermally solidified zone existed only when the bonding temperature was not high enough. The interface morphologies of the joints were found to be very sensitive to the bonding temperature. With the bonding temperature increased from 950°C to 1000°C, the width of non-isothermally solidified zone decreased from 69 μm to 23 μm. When the bonding temperature was 1050°C, the non-isothermally solidified zone disappeared. Meanwhile, more alloying elements of Cu and Zr diffused most adequately into the base material. Phase analysis showed that along with the increasing of bonding temperature, the secondary phase constitution of joint changed from Ti (Cu,Al)2 + AlNb2 + Ti solid solution to Ti solid solution + Nb (CuAl) + Al4Cu9 + Al2Zr3, and the proportion of secondary phase was 35.7%, 20.2%, 6.7%, respectively. The morphology of base metal changed because of the relatively high bonding temperature was higher than 980°C, the α→β transition temperature.

Cu/SnAgCu/Cu TLP with different thicknesses for 3D IC

PurposeThis paper aims to investigate Cu/SnAgCu/Cu transient liquid phase (TLP) bonding with different thicknesses for three-dimensional (3D) integrated circuit (IC).Design/methodology/approachThis paper includes experiments and finite element simulation.FindingsThe growth rate of the intermetallic compound layer during TLP soldering was calculated to be 0.6 μm/s, and the small scallop-type morphology Cu6Sn5 grains can be observed. With the decrease in thickness in solder joint, the thickness of intermetallic compounds represents the same size and morphology, but the size of eutectic particles (Ag3Sn, Cu6Sn5) in the matrix microstructure decrease obviously. It is found that with the increase in thickness, the tensile strength drops obviously. Based on finite element simulation, the smaller value of von Mises demonstrated that the more reliability of lead-free solder joints in 3D IC.Originality/valueThe Cu/SnAgCu/CuTLPbondingwithdifferentthicknessesfor3D IC was investigated.

고온동작소자의 패키징을 위한 천이액상확산접합 기술

고온동작소자의 패키징을 위한 천이액상확산접합 기술

Mechanism of Ag3Sn grain growth in Ag/Sn transient liquid phase soldering

Transient liquid phase (TLP) bonding is a potential high-temperature (HT) electron packaging technology that is used in the interconnection of wide band-gap semiconductors. This study focused on the mechanism of intermetallic compounds (IMCs) evolution in Ag/Sn TLP soldering at different temperatures. Experimental results indicated that morphologies of Ag3Sn grains mainly were scallop-type, and some other shapes such as prism, needle, hollow column, sheet and wire of Ag3Sn grains were also observed, which was resulted from their anisotropic growths. However, the scallop-type Ag3Sn layer turned into more planar with prolonging soldering time, due to grain coarsening and anisotropic mass flow of Ag atoms from substrate. Furthermore, a great amount of nano-Ag3Sn particles were found on the surfaces of Ag3Sn grains, which were formed in Ag-rich areas of the molten Sn and adsorbed by the Ag3Sn grains during solidification process. Growth kinetics of the Ag3Sn IMCs in TLP soldering followed a parabolic relationship with soldering time, and the growth rate constants of 250, 280 and 320 °C were calculated as 5.83×10−15 m2/s, 7.83×10−15 m2/s and 2.83×10−14 m2/s, respectively. Accordingly, the activation energy of the reaction was estimated about 58.89 kJ/mol.

Development and Evaluation of Equipment Enhancements for Transient Liquid Phase Bonding (TLPB) and Sintering

Operating devices at higher temperatures in automotive applications and the use of wide bandgap materials have driven the development of new bonding technologies as silver sintering and transient liquid phase bonding (TLPB). Considering their specific demands a dedicated tool for processing in batch was developed and characterized. Press unit containing a flexible elastomer membrane was implemented in a vacuum reflow soldering chamber. It allows bonding of various devices with different thickness without using height compensating tooling. Pressures up to 0.5 MPa, temperatures of maximum 300 °C and reducing atmosphere were utilized to demonstrate the process capability for void free low pressure silver sintering and Cu-Sn TLPB.

Cu@Sn Core–Shell Structure Powder Preform for High-Temperature Applications Based on Transient Liquid Phase Bonding

This paper presents a novel die-attach material for high-temperature applications based on transient liquid phase (TLP) bonding. Cu particles are electroless plated with Sn to achieve Cu@Sn structure, and the fabricated Cu@Sn particles are compressed into preforms for die attachment. This material can be reflowed at a low temperature ( I – V curve and breakdown voltages of the novel preform-bonded IGBTs are measured to examine the interconnection quality compared with those of Cu−Sn TLP-bonded IGBTs. This die-attach material is suitable for power devices operating under high temperatures or other harsh environments.

Elimination of pores in Ag–Sn TLP bonds by the introduction of dissimilar intermetallic phases

Low-temperature transient liquid phase (TLP) bonding is a very promising technology for achieving die attachment in high-temperature power devices. However, the Ag–Sn TLP-bonded joint has high sensitivity to shrinkage pores, which will lead to the deterioration of mechanical, thermal, and electrical properties. In this study, we have proposed two novel methods to solve the problem of pores in Ag–Sn TLP bonding through the introduction of second phases. The first method is replacing Ag substrate on one side with Cu substrate to create dual layers of dissimilar intermetallic compounds (IMCs). Consequently, the dual layers of Cu6Sn5 (or Cu3Sn) and Ag3Sn IMCs emerge on the cross-sections of bonded joint, resulting in the effective elimination of pores, which can be attributed to the change of the microstructure and the interface migration between two dissimilar IMC layers (e.g., Cu6Sn5/Ag3Sn). The second method is coating a thin Cu film on the Ag substrate to introduce Cu–Sn IMC particles. As a result, a great number of Cu6Sn5 particles disperse in the middle of the Ag3Sn layer, filling the micropores efficiently, such that a significant decrease in shrinkage pores is achieved. Both methods have been experimentally verified to improve the mechanical properties, and they have high potential to be implemented in other TLP systems.

Non-interfacial growth of Cu3Sn in Cu/Sn/Cu joints during ultrasonic-assisted transient liquid phase soldering process

The non-interfacial growth of Cu3Sn intermetallic compounds (IMCs) in a Cu/Sn/Cu interconnection structure during the ultrasonic-assisted transient liquid phase (TLP) soldering process was investigated. In the traditional TLP soldering process, the Cu3Sn phase always nucleated at Cu6Sn5/Cu interfaces and grew at the expense of the Cu6Sn5 phase and towards the joint centre, eventually forming a full intermetallic joint consisting of a single Cu3Sn phase with columnar grains. While in the ultrasonic-assisted TLP soldering process, the Cu3Sn phase nucleated and grew randomly within the whole joint, the resulting intermetallic joint consisted of a single Cu3Sn phase with equiaxed grains. This anomalous behaviour can be wholly ascribed to the effects ultrasonic on the nucleation and growth mechanisms of Cu3Sn.

HOT-300 – A Multidisciplinary Technology Approach Targeting Microelectronic Systems at 300 °C Operating Temperature

Abstract Several applications in the fields of industrial sensors and power electronics are creating a demand for high operating temperature of 300 °C or even higher. Due to the increased temperature range new potential defect risks and material interactions have to be considered. As a consequence, innovation in semiconductor, devices and packaging technologies has to be accompanied by dedicated research of the reliability properties. Therefore various investigations on realizing high temperature capable electronic systems have shown that a multidisciplinary approach is necessary to achieve highly reliable solutions. In the course of the multi-institute Fraunhofer internal research program HOT-300 several aspects of microelectronic systems running up to 300 °C have been investigated like SOI-CMOS technology and circuits, silicon capacitor devices, a capacitive micromachined ultrasonic transducer (CMUT), ceramic substrates and different packaging and assembly techniques. A ceramic molded package has been developed. Die attach on different leadframe alloys were investigated using silver sintering and transient liquid phase bonding (TLPB). Copper and gold wire bonding was studied and used to connect the chips with the package terminals. Investigations in flip chip technology were performed using Au/Sn and Cu/Sn solder bumps for transient liquid phase bonding. High operating temperatures result in new temperature driven mechanisms of degradation and material interactions. It is quite possible that the thermomechanical reliability is a limiting factor for the technology to be developed. Therefore investigations on material diagnostics, reliability testing and modeling have been included in the project, complementing the technology developments.

Reliability Characterization of Au–In Transient Liquid Phase Bonding Through Electrical Resistivity Measurement

Transient liquid phase (TLP) die-attach bonding is an attractive technique for high-temperature semiconductor device packaging. In this paper, the material reliability of gold–indium (Au–In) TLP bonding is investigated utilizing electrical resistivity measurement as an indicator of material diffusion. Samples were fabricated featuring a TLP reaction, representative of TLP die-attach, by depositing TLP materials on glass substrates with various Au–In compositions, but with identical barrier layers, and were then used for reliability investigation. The samples were annealed at 200 °C and then stressed with thermal cycling. Samples containing high indium content in the TLP bond are shown to have poor reliability due to material diffusion through barrier layers, whereas the samples containing sufficient gold content proved reliable through electrical resistivity measurement, energy-dispersive X-ray spectroscopy, focused ion beam, and scanning electron microscope characterization.

Advanced packaging methods for high-power LED modules

LED luminaires are already beyond retrofit systems, which are limited in heat dissipation due to the old fitting standards. Actual LED luminaries are based on new LED packages and modules. Heat dissipation through the first and second level interconnect is a key issue for a successful LED package. Therefore the impact of known bonding technologies as gluing and soldering and new technologies like sintering and transient liquid phase soldering were analyzed and compared. A realized hermetic high power LED package will be shown as example. The used new techniques result in a module extremely stable against further assembly processes and harsh operating conditions.

X-Ray Characterization of Intermetallic Phases in Al/Ni Multilayer System

The attractive properties of Al-Ni intermetallic phases and their extensive field of technological applications demands a thorough understanding of the system. In particular, kinetic experiences with Al/Ni diffusion-reaction couples using Transient Liquid Phase Bonding (TLPB) process deals with the simultaneous growing of intermetallic phases as multilayers in the interconnection zone. This work complements the first stages of morphology, chemical composition and microhardness characterization of these layers with conventional X-Ray Diffraction (XRD) experiments. XRD results obtained for the multilayer sequence in Al/Ni diffusion-reaction couples in range of 800-1170°C were analyzed. Al-rich phases Al3Ni, Al3Ni2 and Al1.1Ni0.9 were identified and associated with layers L1, L2 and L3, respectively. Nevertheless, singular layer experiments are required for Ni-rich phases identification.

Engineering of Fuel Plates on Uranium-Molybdenum Monolithic: Critical Issues

Engineering of nuclear fuels using monolithic plates of uranium-molybdenum and Al-6061 cladding is the current challenge for research and test reactors. The main drawback of the manufacture of monolithic nuclear fuel was analyzed using two surface coating methods: aluminum sputtering and transient liquid phase bonding (TLPB). Coating was done with a commercial alloy of Al-Si (R-4047). These techniques were used to improve the metallurgical bonding between the UMo and the cladding by rolling. Finally, design parameters and manufacture of UMo plate fuels were established. Mechanical tests were used to characterize the plates, resulting in UTS values of about 700 and 1000 MPa for the UMo alloys. These results are complemented with metrological analyses, X-Ray diffraction (XRD), thermal analyses, and metallography. X-rays and ultrasound scanners were used to monitor bonding and the co-rolling effects. These initial results show the main obstacles to the engineering development of UMo monolithic plate fuels with Al-6061 cladding, and these are discussed herein.

Electro- and thermomigration induced Cu3Sn and Cu6Sn5 formation in SnAg3.0Cu0.5 bumps

Two important trends in the microelectronics business are the development of three dimensional packaging solutions which increase the number electronics components on the same area, and the application of VLSI electronics under harsh environment conditions. Both trends lead to a growing importance of intermetallic compound (IMC) formation in Sn based solder joints. Due to miniaturization a growing part of the solder joint volume is transformed into IMCs and finally the reflow process becomes a transient liquid phase soldering (TLPS) process. For harsh environment applications TLPS enables the transformation of low melting Sn contacts into high melting IMC joints. In both cases a model for the prediction of migration-induced IMC formation is required for the fabrication of IMC joints.For the general prediction of the migration induced IMC formation the related material parameters are needed. Against this background the Cu3Sn and Cu6Sn5 formation was observed during temperature storage tests on Amkor® Package-on-Package packages (12×12mm) with SnAg3.0Cu0.5 ball grid arrays. A mathematical model was developed to calculate the average mass flux of Sn and Cu during the stress tests. Based on the mass flux values the activation energies and diffusion constants for Cu and Sn in Cu3Sn and Cu6Sn5 were determined. Afterwards the temperature storage was combined with an AC and a DC current load to investigate thermo- and electromigration-related phenomena. Based on the IMC formation speed during the AC and the DC tests the heat of transport Q* and the effective charge of the moving ion Z* were calculated. An interpretation of the material parameters is given in consideration of the high defect density in Cu3Sn and Cu6Sn5.

Reliability Investigation of Cu/In TLP Bonding

Die-attach bonding was evaluated using a transient liquid phase (TLP) bonding method on a Cu/In, Au/In and Cu-Sn3Ag metal stack. TLP bonding is a relatively low cost process since thin layers of material are used and, at the same time, has higher reliability due to the good thermal resistance of the intermetallic compounds (IMCs) formed. The bonded samples were aged at 300°C for 500 h and thermal cycled from −40°C to 125°C for 500 cycles. The results showed that the shear strength of the Cu/In joint was higher than that of the Au/In joint with increasing aging time. Cu/In specimens on a ceramic substrate also showed good reliability results during the thermal cycling test. Even though Cu/In TLP bonding is not popular in conventional electronics, it is suitable for high temperature electronics due to the simplicity of the IMC formation.

Early stage growth characteristics of Ag3Sn intermetallic compounds during solid–solid and solid–liquid reactions in the Ag–Sn interlayer system: Experiments and simulations

Transient Liquid Phase Bonding (TLPB) makes use of the isothermal solidification of a liquid interlayer through the formation of intermetallic compounds (IMC). This work investigates the Ag3Sn IMC formation in a thin, electroplated Ag–Sn interlayer system appropriate for TLPB – while covering as-coated conditions, growth initiation up to a few minutes of holding time – with experimental and numerical methods. Both solid-state and solid–liquid reactions at 200, 250 and 300°C, respectively, were covered under identical and near-isothermal conditions with a novel experimental setup. Morphological aspects like the lateral IMC grain size or the scallop roughness were proven to strongly depend on temperature. Growth kinetics were captured by power laws, growth exponents n were determined as 0.24, 0.36 and 0.29, parabolic growth constants k as 1.32⋅10−11, 4.04⋅10−10 and 7.24⋅10−10cm2/s at 200, 250 and 300°C, respectively, and the activation energy Q as 30.6kJ/mol. Predominant diffusion mechanisms, i.e. volume or GB diffusion, as well as coarsening effects were identified as temperature and time dependent at early stages. A mathematical model was developed based on the Arrhenius relationship including a growth correction function zIMC,corr to calculate and predict IMC growth as a function of temperature and time. The study was completed by multiphase-field simulations which targeted to mimic kinetic and morphological features of Ag3Sn IMC under various conditions. Good agreement between experiments and simulations was found for a limited set of parameters which allowed drawing conclusions about the dominant transport mechanisms for the reacting elements.

Application of Ni and Cu nanoparticles in transient liquid phase (TLP) bonding of Ti-6Al-4V and Mg-AZ31 alloys

The transient liquid phase (TLP) bonding of Ti-6Al-4V alloy to a Mg-AZ31 alloy was performed using an electrodeposited Ni coating containing a dispersion of Ni and Cu nanoparticles. Bond formation was attributed to two mechanisms; first, solid-state diffusion of Ni and Mg, followed by liquid eutectic formation at the Mg-AZ31 interface. Second, the solid-state diffusion of Ni and Ti at the Ti-6Al-4V interface resulted in a metallurgical joint. The joint interface was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. The use of Cu nanoparticles as a dispersion produced the maximum joint shear strength of 69 MPa. This shear strength value corresponded to a 15 % enhancement in joint strength compared to TLP bonds made without the use of nanoparticles dispersion.