Lead-free Composite Solder Research Articles

Tensile characteristics of Sn–5wt%Sb–1.5wt%Ag reinforced by nano-sized ZnO particles

In this study the impact of adding 0.3 wt% ZnO nano-sized particles into Sn–5wt%Sb–1.5wt%Ag (SSA) lead free solder (LFS) was investigated for microstructure, thermal and tensile stress strain characteristics. The microstructure of both the plain and composite LFS was examined by utilizing the optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The addition of ZnOnano-sized particles drastically changed the microstructure and improved the tensile response of SSA LFS. The microstructure investigations showed the formation of the intermetallic compounds (IMCs) Ag3Sn and SnSb. Sizes of the formed IMCs were found finer in the ZnO-contained solder. In this work the alloy under investigation exhibited better tensile response with the refined IMC particle. Thermal analysis of the composite solder revealed a slight decrease (0.08 °C) in freezing point, low pasty range (6.55 °C) and low degree of undercooling (3.39 °C). These findings are expected to supply a correct guideline and reference in producing of electronic packages.

Microstructures and Properties of Sn2.5Ag0.7Cu0.1RE Composite Solders Reinforced with Cu-Coated Graphene Nanosheets Synthesized by Pyrolysis.

Composite solder is a promising route to improve the properties and reliability of Sn-based lead-free solder. In this study, Cu-coated graphene nanosheets (Cu-GNSs) were synthesized using pyrolysis. Cu-GNSs reinforced Sn2.5Ag0.7Cu0.1RE composite lead-free solders were prepared via powder metallurgy. The size, distribution, and adsorption type of Cu nanoparticles on the GNSs were studied. The relation of the Cu-GNSs content and microstructure to the physical, wettability, and mechanical properties of composite solders was discussed. The results show that Cu nanoparticles (with a mean size of 13 nm) present uniform distribution and effective chemisorptions on the GNS. Microstructural evolution of composite solders is dependent on the addition of Cu-GNSs. With increasing Cu-GNSs addition, β-Sn grains become finer and the eutectic phase proportion becomes larger, while the morphology of the eutectic phase transforms from dispersion to network-type. The improvement of the tensile strength of the composite solder can be attributed to grain refinement and load transfer. While the existence of Cu-GNSs can effectively improve the wettability and slightly change the melting point, it can also lead to the decline of elongation and electrical conductivity of the composite solder.

Effect of nickel (Ni) on the growth rate of Cu6Sn5 intermetallic compounds between Sn–Cu–Bi solder and Cu substrate

In this work, the lead-free composite solder was fabricated by mixing Ni element with Sn–0.7Cu–10Bi solder. The effect of nickel (Ni) addition on the growth behavior of intermetallic compounds (IMCs) between Sn–0.7Cu–10Bi–xNi (x = 0, 0.05, 0.10, 0.15 and 0.20, in wt%) solder and Cu substrate during the soldering process was studied. The microstructure and the IMCs growth of the solder joints under thermal aging were systematically investigated. The results shown that the addition of Ni element has a slightly influence on melting point of the solder. Moreover, the addition of Ni element can change Cu6Sn5 shape from scalloped-like structure into flat-like one. Moreover, the results reveal that Ni can considerably inhibit the growth and reduce the thickness of Cu6Sn5. The thickness of Cu6Sn5 ranges from 3.07 to 8.42 µm after aging process The diffusion coefficient (D) is 1.80 × 10−3 µm2 h−1 and growth rate (dH/dt) is 4.08 × 10−7 µm s−1 of the Cu6Sn5 when the Ni content come to 0.15 wt%. The (Cu,Ni)6Sn5 phase formed in the IMCs layer when Ni was added to the solder, and it can effectively hinder the diffusion of Cu atoms and depressed the growth rate of Cu6Sn5.

Structural Assessment of Lead Free Solder Joint of Miniaturized Electronics Assembly

This paper presents a study on structural assessment of ultra-fine package assembly with nano-composites lead free solder joint after reflow soldering process. In this work, various nanoparticles (i.e. TiO2, Fe2O3 and NiO) with different weightage percentage (i.e., 0.01, 0.05 and 0.15 wt.%) were successfully incorporated into SAC305 solder paste using the mechanical solder paste mixer to synthesize novel lead-free composite solders. Effects of the nanoparticles addition on the quality of joining and fillet height between various weightage (wt.%) for the ultra-fine package assembly in the reflow soldering process have been investigated after the reflow soldering process by using the scanning electron microscope (SEM) system equipped with an energy dispersive X-ray spectroscopy (EDS) and XTV 160 x-ray inspection system. The experimental results show the increment of TiO2, Fe2O3 and NiO nanoparticles addition to 0.15wt.%, 0.05wt.% and 0.01wt.%, respectively, produce highest fillet height of each composition of nanoparticles solder paste. Among all these new composition of nanoparticles solder paste, NiO nanoparticles reinforced solder paste with 0.01wt.% yielded highest fillet height The miniaturized solder joints do not cause any problem in terms of solder voids. The findings show the capability of the reflow soldering process in assembling miniaturized electronics assembly and expected to provide a reference in electronic package industry.

Microstructural evolution of 96.5Sn\u20133Ag\u20130.5Cu lead free solder reinforced with nickel-coated graphene reinforcements under large temperature gradient

In this study, 96.5Sn–3Ag–0.5Cu (SAC305) lead-free composite solder containing graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS) was prepared using a powder metallurgy method. A lab-made set-up and a corresponding Cu/solder/Cu sample design for assessing thermo-migration (TM) was established. The feasibility of this setup for TM stressing using an infrared thermal imaging method was verified; a temperature gradient in a solder joint was observed at 1240 K/cm. Microstructural evolution and diffusion of Cu in both plain and composite solder joints were then studied under TM stressing conditions. Compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder joint was significantly reduced. The interfacial intermetallic compounds (IMCs) present in the composite solder joint also provide a more stable morphology after the TM test for 600 h. Furthermore, during the TM test, the Ni-GNS reinforcement affects the formation, migration and distribution of Ni–Cu–Sn and Cu–Sn IMCs by influencing the dissolution rate of Cu atoms.

Effect of TiO2 additions on Sn-0.7Cu-0.05Ni lead-free composite solder

The effect of TiO2 addition on the microstructure, melting behavior, microhardness and interfacial reaction between Sn-0.7Cu-0.05Ni and a Cu-substrate were explored. Samples with various TiO2 percentages (0, 0.25, 0.5, 0.75 and 1.0wt.%) were prepared using a microwave-assisted sintering powder metallurgy method. Microstructural analysis reveals that TiO2 was uniformly distributed along the grain boundary of the bulk solder. Differential scanning calorimetry (DSC) results showed a decrease in the undercooling while melting temperature of the solder slightly increase. The thickness of the interfacial intermetallic compounds of the solder joint was reduced with the addition of TiO2 particles. This thickness reduction indicates that the presence of a small amount of TiO2 particles is effective in suppressing the growth of the intermetallic compound layer. Small dimples on the fracture surface have revealed that the Sn-Cu-Ni composite solder exhibits typical ductile failure. Overall, the addition of TiO2 to Sn-0.7Cu-0.05Ni solder dramatically increases its shear strength and hardness and improves its wetting properties and fracture surface.

Effect of ageing time on the tensile behavior of Sn–3.5 wt% Ag–0.5 wt% Cu (SAC355) solder alloy with and without adding ZnO nanoparticles

In this work, lead-free composite solder was produced by mixing ZnO-nano-sized particles with Sn–3.5% Ag–0.5% Cu solder. The effects of nano-particle addition on the melting behavior, microstructure and tensile properties of the as-solidified composite solder are systematically investigated. In comparison with solder without the addition of ZnO nanoparticles metallographic observations revealed that the grain size of β-Sn, the intermetallic compounds (IMCs) average grain size and distance decreased significantly in the composite solder matrix. This was possibly ascribed to the strong absorption effect and high surface free energy of ZnO nanoparticles. Our results show that 0.5wt% addition of ZnO nanoparticles led to an improvement in microstructure, proof stress (ơy0.2), ultimate tensile stress (ơUTS) and fracture stress (ơf) compared with non-composite solder. Differential scanning calorimetry (DSC) revealed that the melting temperature of SAC355 composite solder is slightly higher by about 1.1K than that of the conventional SAC355 solder. The observed increase of mechanical properties was rendered to refined IMCs, acting as a strengthening phase in the solder matrix. Ageing the specimens of both solders for different aging times at all different testing temperatures, resulted in the decrease of tensile properties investigated. This was attributed to ripening of IMC particles leading to decrease of their pinning action of dislocation movements which was emphasized by SEM examinations. This interpretation is in consistence with the theoretical prediction from dispersion strengthening theory.

Mechanical Properties and Solderability of Robust Sn-0.7Cu Lead-Free Composite Solder

A composite solder with Sn-0.7Cu based solder was successfully fabricated via powder metallurgy routes which consist of mixing, compacting and sintering. Varying amount of activated carbon (AC) was used as reinforcement to obtain a novel lead-free composite solder. Following fabrication, the sintered composite solder was analyzed in terms of their microstructure, microhardness and solderability properties. The distribution of the various percentages of AC particles along the grain boundaries was observed. The addition of AC particles into the Sn-0.7Cu solder matrix has increased the hardness values up to 22.9%, while reducing the contact angle of composite solder up to 12.9% for a good wettability performance. As overall, addition of AC into Sn-0.7Cu based solder has indicated an enhancement of reliability performance of Sn-0.7Cu/AC composite solder for electronic application.

Research on Al Particles Reinforced Thermal Stress Aging Treatment Behavior of Composite Lead-Free Solder

Studying Al particles reinforced composite lead-free solder by experiments of constant temperature thermal stress aging treatment. Scanning electron microscope was used to observe the micro-structure of composite solder. The results show that composite lead-free solder after constant 125°C aging treatment for 24 hours, Al particles has two types of morphologies: one is small amount of solid solution,another type is a large number of aluminum particles structure.The existence of Al particles slowed down the coarsening rate of the Bi Phase grain, and obtained uniform refined the Bi Phase grain.

Design of Experiment (DOE) of Powder Metallurgy Technique in Fabricating SnCu/Carbon Lead-Free Composite Solder with Different Mixing Parameters

Physical and mechanical properties of a solder joint will be improved by adding the high performance of reinforcement particulates in the monolithic lead-free solder. In this study, 0.1wt% of activated carbon (AC) was added into Sn-0.7Cu lead-free solder which fabricated via powder metallurgy (PM) techniques. Various parameters used in PM technique such as mixing time, compacting load and sintering temperature has been carried out in fabricating the composite solder. In this study, the best mixing time has been optimized. The distribution of carbon in SnCu matrix for each mixing time was observed by using optical microscope. Microstructural observation showed that the increasing in mixing time has increased the number of AC particles to become agglomerated. It is found out that 1hour of mixing time is the best parameter to fabricate SnCu/AC composite solder via powder metallurgy route since the distribution of reinforcement particles has distributed uniformly at the grain boundaries without any agglomeration.

Effect of TiO<sub>2</sub> Reinforcement on Microstructure and Microhardness of Low-Silver SAC107 Lead-Free Solder Composite Solder

This research has investigated the physical performances of low-silver Sn-Ag-Cu (SAC) lead-free composite solder reinforced with titanium dioxide (TiO2). The SAC/TiO2 composite solder were fabricated via powder metallurgy (PM) technique. The five different composition chosen were 0, 0.25, 0.5, 0.75, and 1.0. The results showed that distribution of TiO2 along the grain boundaries has increased the hardness of the SAC/TiO2 composite solders compared to monolithic SAC solder alloy.

Dissolutive wetting process and interfacial characteristic of molten Sn–17Bi–0.5Cu alloy on copper substrate

The reactive spreading processes of Sn–17Bi–0.5Cu melt alloy on Cu substrate were studied by sessile drop method in the temperature range of 523–673 K. Dynamic contact angles between the solder and Cu substrate at different times were recorded with high-resolution CCD digital video. The smallest contact angle was observed at 623 and 673 K. Ultimate spreading radius does not increase monotonously with the temperature increasing. These can be attributed to the strong dissolution of Cu substrate into the liquid solder, which hinders the solder from spreading. Triple line area configuration of the Sn–17Bi–0.5Cu/Cu system was discussed by the description of the equilibrium state. The calculated results based on experiments of the tension balances along each of the three interfaces show good agreement with theoretical analysis. Intermetallic compounds at the Sn–17Bi–0.5Cu/Cu interface are identified as Cu6Sn5 adjacent to the solder and Cu3Sn adjacent to the Cu substrate, respectively. These results are of practical interest for composite lead-free solders’ preparations and joining of Sn–17Bi–0.5Cu to Cu substrate.

Non-Metal Reinforced Lead-Free Composite Solder Fabrication Methods and its Reinforcing Effects to the Suppression of Intermetallic Formation: Short Review

To increase the solder joint robustness, researches and studies on composite solder carried out by many researchers in an effort to develop viable lead-free solders which can replace the conventional lead-based solders.This paper reviews the fabrication processes of the lead-free composite solder and its non-metal reinforcing effects to the suppression of intermetallic formation. Most researchers using different solder fabrication methods have found that byadditions of non-metal reinforcement from micron up to nanoparticle size had suppressed the intermetallic compound formations of lead-free composite solders.

Thermal Properties of Sn-0.7Cu/re-Al Composite Lead-Free Solder

Composite approach in lead-free solder development was perceived as an expectation in finding new robust solder. Accordingly, Sn-0.7Cu/re-Al composite lead-free solder with varying amount of recycled-Aluminum (0, 3.0, 3.5 and 4.0 wt.% re-Al) particulates produced from aluminum beverage cans were successfully fabricated via powder metallurgy techniques in this study. This paper focuses on the thermal properties focusing on the melting temperature of the new developed Sn-0.7Cu/re-Al lead-free composite solder. The melting temperature (Tm) of the new solders was determined using differential scanning calorimetry (DSC). The melting temperature of the composite solders has showed comparable results with the monolithic solders of Sn-0.7Cu lead-free solder.

Development of a lead-free composite solder from Sn–Ag–Cu and Ag-coated carbon nanotubes

The microelectronic applications of lead-free solders pose ever-increasing demands. We seek to improve the solder by forming composites with Ag-coated single-walled carbon nanotubes (Ag-coated SWCNTs). These were incorporated into 96.5Sn–3.0Ag–0.5Cu solder alloy with an ultrasonic mixing technique. Composite solder pastes with 0.01–0.10 wt% nanotube reinforcement were prepared. The wettability, melting temperature, microstructure and mechanical properties of the composite solders were determined, and their dependency on nanotube loading assessed. Loading with 0.01 wt% Ag-coated SWCNTs improved the composite solder’s wetting properties, and the contact angle was reduced by 45.5 %, while over loading of the coated nanotubes up to 0.10 wt% degraded the wettability. DSC results showed only slight effects on the melting behavior of the composite solders. Cross-section microstructure analysis of the spreading specimens revealed uniform distribution of the intermetallic compounds throughout the solder matrix, and EDS analysis identified the phases as β-Sn, Ag3Sn and Cu6Sn5. The mechanical properties of composite specimens, compared with those of unloaded 96.5Sn–3.0Ag–0.5Cu solder, had a maximal improvement in the shear strength of 11 % when the nanotube loading was 0.01 wt% of Ag-coated SWCNTs.

Effect of ZnO nanoparticles addition on thermal, microstructure and tensile properties of Sn–3.5 Ag–0.5 Cu (SAC355) solder alloy

Regarding to the development of Sn–Ag–Cu (SAC) lead-free solders for advance electronic components, the effect of 0.5 wt% nano-sized ZnO particles on the thermal, microstructure and tensile properties of Sn–3.5 wt% Ag–0.5 wt% Cu (SAC355) lead-free solder alloy is investigated. The results showed that addition of 0.5 wt% nano-sized ZnO particles into the conventional lead-free SAC355 solder caused a slight increase of its liquidus temperature by about 1.1 K. Metallographic observations of SAC355–0.5 wt% ZnO (composite solder) revealed an obvious refinement in the microstructure compared with the SAC355 (non-composite) solder. Consequently, addition of nano sized-ZnO particles could improve the stress–strain characteristics proof stress (σy0.2) and ultimate strength (σUTS). This was rendered to suppressing effect of ZnO on the coarsening of the intemetallic compounds (IMCs) Ag3Sn and Cu6Sn5 during the solidification process in the composite solder and subsequently dispersion strengthening is considered to be the dominating mechanism. This will allow the use of SAC355 composite lead-free solder alloy, to be consistent with the conditions of usage for conventional SAC solder alloys and to overcome the serious problem of the excessive growth of IMCs and the formation of microvoids in the SAC lead-free solder alloys.

Recent Development of Novel Lead-Free Composite Solders Using Microwave-Assisted Sintering Powder Metallurgy Route

This review paper discusses on the recent lead-free composite solders developed using powder metallurgy (PM) routes. However, the review will focus on the sintering part in the powder metallurgy techniques which the application of microwave technology can be utilized in the development of robust lead-free composite solders. Comprehensive reviews of the published literatures were carried out to understand the requirements and problems in fabricating the lead-free composite solder by using microwave-assisted sintering PM route. This paper describes the improvement of the recent development of lead-free composite solders using microwave-assisted sintering application. It can be summarized that by adding appropriate amounts of a third element as reinforcement in lead-free base matrix system has mostly improved mechanical properties of the monolithic solder. Nevertheless, the review discovered with microwave-assisted sintering, most lead-free bulk samples exhibited a superior microstructural feature which has brought to surprisingly a better mechanical properties in the solder compared to conventionally sintered samples. With microwave-assisted sintering application, the issues related to the implementation of microwave-assisted sintering in lead-free solder development based solder system reinforced with ceramic particulates are also introduced. Furthermore, with the implementation of new hybrid microwave sintering technique which arises from the coalition of conventional and microwave sintering, will yield a staggering advancement in lead-free nanocomposite solder development.

Research Advances of Composite Solder Material Fabricated via Powder Metallurgy Route

Researches and studies on composite solder have been done by many researchers in an effort to develop viable lead-free solders which can replace the conventional lead-based solders as lead is considered as toxic. Solder materials developed by composite approach showed improvement in their properties and importantly it improved their service performance when compared with solder materials developed by other methods. This paper reviews the solder properties of various types of composite lead-free solder that were fabricated via powder metallurgy route. The fabrication processes of the composite solder material by using powder metallurgy route which involved mixing the powder homogeneously, compaction of the mixed powder and sintering the green body were discussed in detail. The types of reinforcements used in order to enhance its properties and the roles of the reinforcement used were also discussed in detail. Properties of a desirable composite solder and the effects of the reinforcement addition to the composite solder microstructure, changes in its wettability and improvement of its mechanical properties were later discussed in this paper. In conclusion, by reviewing various research advances in composite solder material, a solder material with high solder joint reliability at elevated temperature have yet to be found. Thus, a novel composite solder material with higher solder joint reliability at room and elevated temperature was proposed.

Influence of TiO2 nanoparticles on thermal property, wettability and interfacial reaction in Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The influence of TiO2 nanoparticles on thermal property, wettability, and interfacial reaction in Sn–3.0Ag–0.5Cu–xTiO2 (x = 0, 0.05, 0.1, and 0.6) lead-free composite solder was investigated in this study. Results show that the solidus temperatures of the TiO2-containing composite solder have no obvious change compared with TiO2-free solder. However, the liquidus temperatures of the TiO2-containing composite solders increase by 4.4 °C with an increase in amounts of TiO2 nanoparticles. The wetting angle of the composite solder decreases with the addition of TiO2 nanoparticles ranging from 0.05 to 0.1 wt%, while the spreading area increases. Based on the spherical cap model, the mathematical relation between the wetting angle and spreading area is analyzed. Scanning electron microscopy was used to observe the interfacial microstructure evolution of solder joints and to estimate the thickness of the intermetallic layer. Energy dispersive x-ray and x-ray diffractometry were used to identify the intermetallic compound (IMC) phases. Results reveal that both the thickness of IMCs and the size of Cu6Sn5 grains formed in the solder matrix decrease when TiO2 nanoparticles were added. It was also observed that some of the TiO2 nanoparticles are adsorbed on the surfaces of the scallop-like Cu6Sn5 grains. According to the adsorption theory, the surface energy of the Cu6Sn5 grains decreases with adsorption of TiO2 nanoparticles. Therefore, the diffusion of Sn and Cu atoms might be retarded, resulting in suppressing the growth of the IMCs layer.

Mechanical properties of Sn–0.7Cu/Si3N4 lead-free composite solder

The use of reinforcing high performance ceramic particulates in monolithic lead-free solder is one way to improve the service temperature and mechanical behavior of a solder joint. In this study, various compositions of Sn–0.7Cu/Si3N4 lead-free composite solder were fabricated via the application of powder metallurgy (PM) techniques. The influences of the Si3N4 particulates in the monolithic matrix solder on the melting point temperature (Tm), microhardness value, lap-shear strength, and surface fracture mechanisms were investigated based on the weight percentage addition used (0.5wt%, 1.0wt%, and 1.5wt%). Minimal alteration of the melting point temperature of the composite solder sample was obtained. Improvements in the microhardness value and lap-shear strength were found for higher reinforcements of Si3N4 particulates, which revealed the formation of a more ductile fracture mode in the composite solder samples. The increasing addition of Si3N4 allowed the formation of homogeneous and finer dimples. Overall, the addition of Si3N4 particulates to the Sn–0.7Cu lead-free solder should be higher than 1.0wt%, as these compositions showed superior mechanical properties.