Effect of bismuth–tin alloy particle diameter on bonding strength of copper nanoparticles/bismuth–tin solder hybrid joints

The effect of the diameter of Bi–Sn alloy particles on the bonding strength of hybrid joints formed between SiC chips and direct-bonded copper (DBC) plates using a Cu nanoparticles/Bi–Sn solder was studied. The bonding strength was the highest at 40 MPa for a Bi–Sn alloy particle diameter of 10 µm. Further, the bonding strength was dependent on the area of the bonding layer adhering to the SiC-side fracture surface, as determined by the die-shear test. Ni, which was deposited on the SiC chips and DBC plates before the bonding process, remained near the interfacial area of the bonding layer in the joints formed using the 5 µm particles. In contrast, Ni diffused all over the bonding area, with the exception of the interfacial area where Cu–Sn compounds were formed, in the joints produced using the larger alloy particles. The distribution of Sn in the bonding layer became more uniform and the segregation of Bi at the interface became more pronounced as the particle size was reduced. Further, with an increase in the particle size, the Ag layers deposited on the surfaces of the SiC chips and DBC plates diffused into the bonding layer after the first firing step at 473 K, which was performed before the secondary firing step at 623 K. These results imply that the diameter of the Bi–Sn solder particles in hybrid joints affects the interfacial structure, as it governs the wetting behavior of the Bi–Sn solder and hence has a determining effect on the bonding strength.     

Effect of adding Ce on interfacial reactions between Sn–Ag solder and Cu

We investigated the effect of adding cerium (Ce) to low Ag content Sn–1.0wt.%Ag solder on the interfacial reactions between the Sn–1.0Ag solder and Cu substrate. The formation and growth of interfacial intermetallic compounds (IMCs) between the Sn–1.0Ag–0.3Ce solder and Cu substrate were studied and the results were compared to those obtained for the Ce-free Sn–1.0Ag/Cu and most promising Sn–3.0Ag–0.5Cu/Cu systems. The addition of Ce to the Sn–Ag solder significantly reduced the growth of the interfacial Cu–Sn IMCs, retarded the interfacial reactions between the solder and the substrate, and prevented the IMC from spalling from the interface. The Sn–1.0Ag–0.3Ce solder alloy had a good interfacial stability with the Cu substrate during solid-state isothermal aging in the viewpoint of IMC growth.     

Evolution of interfacial IMCs and mechanical properties of Sn–Ag–Cu solder joints with Cu-modified carbon nanotube

Cu-modified carbon nanotube (Cu-CNT) was mechanical mixed with Sn-3.0Ag-0.5Cu (SAC305) solder powder to fabricate composite solder. Experiments were carried out on the composite solder to investigate its thermal behavior and mechanical properties. Evolution of interfacial intermetallic compounds (IMCs) and shear fracture behaviors of composite solder joints were explored as well. Differential scanning calorimetry results showed that the addition of Cu-CNT increased the melting point of SAC305. Nanoindentation indicated that the hardness and modulus of composite solder increased with the increase of Cu-CNT content, indicating that the addition of Cu-CNT could improve the mechanical properties of SAC305 solder. SAC-xCu-CNT/Cu (x?=?0, 0.1 and 0.2 wt%) composite solder joints were obtained by reflow soldering, aging experiment was carried out subsequently. The results showed that Cu-CNT as the reinforcement phase of SAC305 solder could inhibit the growth of IMC. The suppression effect was enhanced when the content of Cu-CNT increased from 0.1 to 0.2 wt% in SAC305. The growth rate of the IMC layer of the composite solder joint with 0.2 wt% Cu-CNT was the lowest. Shear tests showed that adding Cu-CNT could improve the shear strength of solder joints and the fracture mode of the solder joint changed from mixed fracture to ductile fracture.

     

Effects of Al,Pr additions on the wettability and interfacial reaction of Zn–25Sn solder on Cu substrate

Zn–25Sn alloy suffers from easy oxidation during soldering. This study investigated the feasibility of Al and rare earth Pr addition for enhancing the wettability of the Zn–25Sn solder. The wettability and interfacial reaction of Zn–25Sn, Zn–25Sn–0.05Al, Zn–25Sn–0.05Al–XPr (X = 0.01, 0.05, 0.08, 0.15 wt%) on Cu substrate were investigated. The additions of 0.05 wt% Al in Zn–25Sn and 0.01, 0.05 wt% Pr in Zn–25Sn–0.05Al enhanced the wettability of solders and depressed the growth of intermetallic compounds. However, the additions of 0.08, 0.15 wt% Pr in Zn–25Sn–0.05Al degraded the wettability and enhanced the growth of the intermetallic compound. Pr and Al were shown to accumulate at the surface of solders and the interfaces between solder and substrate by the Secondary Ion Mass Spectroscopy, Scanning Electron Microscope and Transmission Electron Microscopy. The phases PrZn₃, Pr₃Sn₅ and (Cu, Al)₄Zn were formed at the solder/substrate interface.     

Characterization of interfacial IMCs in low-Ag Sn–Ag–xCu–Bi–Ni solder joints

This research investigated the effects of Cu content on the interfacial IMCs in low-Ag Sn–0.7Ag–xCu–3.5Bi–0.05Ni (x = 0.3, 0.5, 0.7, and 1.5 wt%, respectively) solder joints by deep-etching method and SEM observation. Experimental results indicated that as Cu content increased in the solder, the grain size of the IMCs increased and the thickness of the IMCs decreased on Cu substrate. When the concentration of Cu in the solder was 0.3 wt%, the IMC on the soldering interface was (Cu, Ni)₆Sn₅. The concentration of Ni in (Cu, Ni)₆Sn₅ IMC was significantly suppressed by the increase of Cu content in the solder. As Cu content increased to 1.5 wt%, the concentration of Ni in the IMC decreased to 0 and the IMC transformed from (Cu, Ni)₆Sn₅ to Cu₆Sn₅. Due to the increase of Cu content, more and more (Cu, Ni)₆Sn₅ grains nucleated on Ni substrate, and the morphology of (Cu, Ni)₆Sn₅ transformed from polyhedrons to tiny prisms.     

Effects of antimony on the microstructure,thermal properties,mechanical performance,and interfacial behavior of Sn–0.7Cu–0.05Ni–xSb/Cu solder joints

Journal of Materials Science: Materials in Electronics - We investigated a new, lead-free solder alloy to replace traditional lead-based solder alloys. A Sn–0.7Cu–0.05Ni solder alloy...     

Physical properties of Sn58Bi–xNi lead-free solder and its interfacial reaction with copper substrate

The aims of this research are to investigate the effects of Ni on the physical properties of Sn58Bi–xNi lead-free solder, and to examine its interfacial reaction with the copper substrate. In the experiments, four concentrations of Ni (i.e. 0.05, 0.1, 0.5 and 1.0 wt.%) were individually added into Sn58Bi and their respective microstructure, tensile strength, elongation, melting temperature, wettability and electrical resistivity of Sn58Bi–xNi were subsequently measured. The results indicated that Ni refined the microstructure of the solder matrix and induced the formation of Ni₃Sn₄ intermetallic phase, and that the size and volume fraction of Ni₃Sn₄ were positively correlated to the Ni content. The optimal concentration of Ni to enhance the tensile strength of the alloy was 0.1 wt.%, but the elongation of the alloy was inversely correlated to the Ni content. The addition of Ni contributed positively to the melting temperature and wetting behavior of the alloy, whereas no significant change in the electrical resistivity of Sn58Bi–xNi was detected. In addition, Ni increased the thickness of the intermetallic layer at the interface, and only monoclinic η′-Cu₆Sn₅ phase was present at the intermetallic layer. Nevertheless, the intermetallic phase of this research was dissimilar from the findings of existing literature.     

Effects of tin particles addition on structural and mechanical properties of eutectic Sn–58Bi solder joint

Due to the inherent environmental and health toxicities associated with lead, the use of environmental friendly lead-free solder materials has become an unavoidable trend in the electronic packaging industry. Sn-58Bi alloy is gaining attention for its good material properties such as low melting point, reliability and high tensile strength. The presence of the bismuth-rich phase increases the brittleness of Sn-58Bi alloy. The purpose of this study is to suppress the brittleness of Sn-58Bi alloy by the addition of different wt% (0, 10, 20, 30) of Sn powder. The powder metallurgy method was used to prepare the samples. Scanning electron microscopy and energy-dispersive X-ray analysis were done to study the structural properties and a tensile test was done by a universal tensile machine to study the mechanical properties. The results reveal that the Sn particles partially dissolved in the Sn-58Bi solder matrix. The dissolution of Sn particles significantly improved the mechanical strength by 30%, suppressed the brittleness and improved the strain value by 1.3 times.

     

Kinetics of intermetallic compound layer growth and interfacial reactions between Sn–8Zn–5In solder and bare copper substrate

Abstract

The growth kinetics of the intermetallic compound layer formed between Sn–8Zn–5In solder and bare Cu substrate by solid-state isothermal aging were examined at temperatures between 70 and 150°C for times up to 100 days. Experimental results showed that the intermetallic compound observed on the bare copper substrate was γ-Cu₅Zn₈ and its thickness increased with ageing temperature and time. The layer growth of the intermetallic compound in the couple of the Cu/Zn satisfied the parabolic law at the given temperature range. As a whole, because the values of time exponent (n) were approximately 0·5, the layer growth of the intermetallic compound was considered to be mainly controlled by diffusion mechanism over the temperature range studied. The apparent activation energy for growth of the γ-Cu₅Zn₈ intermetallic compound was 62 kJ mol^?1.     

Effects of zinc coating on magnesium alloy–steel joints produced by cold metal transfer method

Magnesium alloys are lap-joined to galvanised and bare steel sheets by a cold metal transfer method. The weld appearance, cross-section, tensile strength and fracture behaviour of these joints are characterised by scanning electron microscopy, tensile tests and energy-dispersive spectroscopy. The joints were found to have good weld appearance and satisfactory tensile strength. The spreadability and wettability of the Mg alloy–galvanised steel joint are superior to those of the Mg alloy–bare steel joint, but the tensile strength is lower. In particular, the presence of Zn on the galvanised steel sheet improves wettability but decreases tensile strength. Aluminium has a high affinity for Fe, and the thinner layer of Fe–Al improves the mechanical properties of the Mg alloy–bare steel joint.     

Growth mechanisms of interfacial intermetallic compounds in Sn/Cu–Zn solder joints during aging

The interfacial reactions of Sn/Cu–xZn (x = 15 and 30 at.%) solder joints were investigated. Before aging, [Cu₆(Sn,Zn)₅] and [Cu₆(Sn,Zn)₅/Cu–Zn–Sn] intermetallic compounds (IMCs) formed at the [Sn/Cu–15Zn] and [Sn/Cu–30Zn] interfaces, respectively. After thermal aging at 150 °C for 80 days, [Cu₆(Sn,Zn)₅/Cu₃(Sn,Zn)/Cu(Zn,Sn)/CuZn] and [Cu₆(Sn,Zn)₅/Cu(Zn,Sn)/CuZn] IMCs, respectively, formed at the [Sn/Cu–15Zn] and [Sn/Cu–30Zn] interfaces. Increasing the amount of Zn in the Cu–Zn substrates evidently suppresses the growth of Cu₃Sn and Kirkendall voids at the solder joint interfaces. Transmission electron microscopy images show the different microstructure of CuZn and Cu–Zn–Sn phases in Sn/Cu–Zn joints. These Cu–Zn phases act to inhibit the growth of Cu₆Sn₅ and Cu₃Sn IMCs. As the content of Zn increased in Cu–Zn substrates, both CuZn and Cu(Zn,Sn) grew significantly. In addition, the growth of the Cu₆(Sn,Zn)₅/Cu₃Sn IMCs approached a reaction-controlled process. The formation mechanisms of the CuZn and Cu(Zn,Sn) phases were probed and proposed with regard to the interfacial microstructure, elemental distribution, and the compositional variation at Sn/Cu–xZn interfaces.     

Effects of strain rate and temperature on the stress–strain response of solder alloys

To ensure reliable design of soldered interconnections as electronic devices become smaller, requires greater knowledge and understanding of the relevant mechanical behavior of solder alloys than are presently available. The present paper reports the findings of an investigation into the monotonic tensile properties of bulk samples of three solder alloys; a lead–tin eutectic and two lead-free solders (tin–3.5 copper and a tin–3.5 silver alloy). Temperatures between–10 and 75°C and strain rates between 10^–1 and 10^–3 s^–1 have been studied. Both temperature and strain rate may have a substantial effect on strength, producing changes well in excess of 100%. Strength is reduced by lowering strain rate and increasing temperature, and Sn–37 Pb is usually most sensitive to the latter. Expressions for strain and strain rate hardening have been developed. The Sn–0.5 Cu alloy is usually the weakest and most ductile. Sn–37 Pb is strongest at room temperature but with increasing temperature and lower strain rates it becomes inferior to Sn–3.5 Ag. Ductility changes with temperature and strain rate for all three alloys are generally small with inconsistent trends. The role of such data in stress analysis and modeling is considered and the paramount importance of employing data for conditions appropriate to service, is emphasized.     

Effect of the soldering time on the formation of interfacial structure between Sn–Ag–Zn lead-free solder and Cu substrate

The evolution of interfacial structure between the Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate were systematically explored for different soldering times (1, 5, and 10 min). According to microstructural observations, it is found that the longer the soldering time is, the thicker the soldered interface becomes. The interface soldered for 1 min is composed of the Cu₅Zn₈ intermetallic compounds (IMCs) layer locating above the Cu₆Sn₅ IMCs layer. The interfaces soldered for 5 and 10 min are mainly made up of the Cu₆Sn₅ IMCs with some bulk Ag₃Sn IMCs randomly distributing within it. The evolution of the IMCs layer in the soldered interface can be divided into three stages: the Cu₅Zn₈ IMCs firstly forms, then Cu₆Sn₅ IMCs separated out from the bottom (controlled by diffusion of Sn in the Cu₅Zn₈), finally, subsequent growth of the Cu₆Sn₅ IMCs layer is controlled by diffusion of Sn in Cu₆Sn₅ IMCs.     

Influence of Co addition on microstructure evolution and mechanical strength of solder joints bonded with solid–liquid electromigration

Journal of Materials Science: Materials in Electronics - The influence of solid–liquid electromigration on Cu-xCo/Sn-3.0Ag-0.5Cu/Cu-xCo (x?=?0, 30 and 50 wt.%) joints bonded at...     

Reactive wetting of Sn–2.5Ag–0.5Cu solder on copper and silver coated copper substrates

In the present work, wetting characteristics and morphology of intermetallic compounds (IMCs) formed between Sn–2.5Ag–0.5Cu lead-free solder on copper (Cu) and silver (Ag) coated copper substrates were compared. It was found that, Ag coated Cu substrate improved the wettability of solder alloy. The average values of contact angles of solder alloy solidified on Ag coated Cu substrate were reduced to about 50 % as compared to contact angles obtained on Cu substrates. Flow restrictivity for spreading of solder on Ag coated Cu was found to be lower as compared to Cu substrate. The spreading of solder alloy on Ag coated Cu exhibited halo zone. Coarse needle shaped Cu₆Sn₅ IMCs were observed at the solder/Cu substrate interface whereas at the solder/Ag coated Cu interface Cu₆Sn₅ IMCs showed scallop morphology. The formation of Cu₃Sn IMC was observed for the spreading of solder alloy on both substrates. The solder/Ag coated Cu substrate interface exhibited more particulates of Ag₃Sn precipitates as compared to solder/Cu substrate interface. The improved wettability of solder alloy on Ag coated Cu substrate is due to the formation of scallop IMCs at the interface.