High Temperature Lead-free Solder Research Articles

Electric current stressing enhanced damping properties in Sn5Sb solder

PurposeThe purpose of this paper is to investigate the effects of electric current stressing on damping properties of Sn5Sb solder.Design/methodology/approachUniformly shaped Sn5Sb solders were prepared as samples. The length, width and thickness of the samples were 60.0, 5.0 and 0.5 mm, respectively. The damping properties of the samples were tested by dynamic mechanical analyzer with a cooling system to control the test temperature in the range of −100 to 100°C. Simultaneously, electric current was imposed to the tested samples using a direct current supply. After tests, the samples were characterized using scanning electron microscope, electron backscatter diffraction and transmission electron microscope, which was aimed to figure out the damping mechanism in terms of electric current stressing induced microstructure evolution.FindingsIt is confirmed experimentally that the increase in damping properties is due to Joule heating and athermal effects of current stressing, in which Joule heating should make a higher contribution. G–L theory can be used to explain the damping properties of strain amplitude under current stressing by quantitative description of geometrically necessary dislocation density. While the critical strain amplitude and high temperature activation energy decrease with increasing electric current.Originality/valueThese results provide a new method for vibration reliability evaluation of high-temperature lead-free solders in serving electronics. Notably, this method should be also inspiring for the mechanical performance evaluation and reliability assessment of conductive materials and structures serving under electric current stressing.

A Drop-in High-Temperature Pb-Free Solder Paste that Outperforms High-Pb Pastes in Power Discrete Applications

Sn-based high-temperature lead-free (HTLF) solder pastes have been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. The pastes were designed to combine the merits of two constituent powders. A SnSbCuAg powder, with the melting temperature above 320°C, was designed to maintain a high-temperature performance. A SnAgCuSb powder, with a melting temperature around 228°C, was added to the paste to enhance wetting and improve joint ductility. In the design, the final joint will have the low-melting phase (the melting temperature >228oC) in a controllable quantity embedded into the high-melting SnSbCuAg matrix. HTLF-1, one of the designs, maintained the bond shear strength up to 15MPa, even around 290°C. Another design, HTLF-2, has a similar bond shear strength as Pb92.5/Sn5/Ag2.5 around 290°C, but exceeds substantially below 250°C. The power discrete components had been built with both HTLF solder pastes for both die-attach and clip-bond through the traditional high-Pb process, which demonstrated the drop-in processing compatibility. The components survived three additional SMT reflows (peak temperature of 260°C) and passed moisture sensitivity level 1. This confirmed that the maintained joint strength (comparable to or stronger than high-lead), helped to keep the joint integrity within the encapsulated components, even with melting phases in a controllable quantity existing above 228°C. Both HTLF solder pastes outperformed Pb92.5/Sn5/Ag2.5 in RDS(on) even after 1000cycles of TCT (-55/175oC), which is attributed to the intrinsic lower electrical resistivity of Sn of both HTLF pastes. Microstructural observation had shown no corner cracks for both die-attach and clip-bond joints after TCT.

Wetting behavior and mechanical properties of Sn-10Sb solder/Ni-plated Cu system with different surface structures

The Sn-10Sb alloy is a high-temperature lead-free solder for soldering with Cu substrates. It often causes brittle solder joints and poor reliability due to the generation of an over-thick interfacial layer. Adding Ni plating to Cu substrates can suppress the generation of an excessively thick interfacial layer. This paper investigated the wettability and bonding strength of two different surface structures of Ni-plated Cu substrates with Sn-10Sb solder. Sn-10Sb solder exhibited a contact angle of 69° on the rough Ni-plated Cu substrate and 80° on the smooth one. TEM and XPS analyses demonstrated that the interfacial reaction product between the Ni-plated Cu substrate and the solder was (Cu, Ni)6Sn5. The finer grains on the smooth Ni-plated surface inhibit the diffusion of Cu atoms into the solder and the slower the interfacial reaction rate, which is more conducive to the generation of stable (Cu, Ni)6Sn5 phase. Therefore, the bonding strength ratio between the Ni-plated Cu substrate with a smooth surface and the solder is better.

Thermodynamic Description of the Au-Sb-Sn Ternary System

Phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system are important for the design of Au-based alloys as high-temperature lead-free solders to replace high-Pb solders. In this work, phase transition temperatures of five Sb-Sn alloys were measured using differential thermal analysis (DTA), and the temperatures of three invariant reactions were determined. Based on the measured experimental results in this work and the reported results, the Sb-Sn binary system was re-optimized using the CALPHAD method. The calculated results were in good agreement with available phase equilibria and thermodynamic data. This work was further combined with the previous assessments of the Au-Sn and Au-Sb binary systems and the present optimization of the Sb-Sn binary system to calculate the phase equilibria and thermodynamic properties of the Au-Sb-Sn ternary system, according to the reported experimental results, including thermodynamic properties and phase equilibria. The calculated liquidus projection, isothermal sections, vertical sections, as well as enthalpy of mixing and activity of Sn in liquid alloys are consistent well with the reported experimental results. A self-consistent set of thermodynamic parameters was obtained to accurately describe Gibbs energies of various phases in the Au-Sb-Sn ternary system, which would serve as a sound basis for developing a thermodynamic database of multicomponent Au-Sn-based alloy systems.

Effect of Additive Element on Fatigue Properties of Sn-Sb-Ag High Temperature Lead-Free Solder

Effect of Additive Element on Fatigue Properties of Sn-Sb-Ag High Temperature Lead-Free Solder

A Drop-in High-Temperature Pb-Free Solder Paste that Outperforms High-Pb Pastes in Power Discrete Applications

Sn-based high-temperature lead-free (HTLF) solder pastes have been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. The pastes were designed to combine the merits of two constituent powders. A SnSb-based Ag/Cu-containing high temperature powder, with the melting temperature above 320° C, was designed to maintain a high-temperature performance. A Sn-rich SnAgCu-Sb powder, with a melting temperature around 228° C, was added to the paste to enhance wetting and improve joint ductility. In the design, the final joint will have the low-melting phase (the melting temperature >228o C) in a controllable quantity embedded into the high-melting SnSb matrix. HTLF-1, one of the designs, maintained the bond shear strength up to 15MPa, even around 290° C. Another design, HTLF-2, has a similar bond shear strength as Pb92.5/Sn5/Ag2.5 around 290° C, but exceeds substantially below 250° C. The power discrete components had been built with both HTLF solder pastes for both die-attach and clip-bond through the traditional high-Pb process, which demonstrated the drop-in processing compatibility. The components survived three additional SMT reflows (peak temperature of 260° C) and passed moisture sensitivity level 1. This confirmed that the maintained joint strength (comparable to or stronger than high-lead), helped to keep the joint integrity within the encapsulated components in the following SMT process, even with the controlled quantity of the melting phases above 228° C. Both HTLF solder pastes outperformed Pb92.5/Sn5/Ag2.5 in the resistance from drain to source when power is on (RDS(on)), even after 1000cycles of TCT (-55/175o C), which is attributed to the intrinsic lower electrical resistivity of Sn of both HTLF pastes. Microstructural observation had shown no corner cracks for both die-attach and clip-bond joints after TCT.

The impact of intermetallic compound on microstructure, mechanical characteristics, and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder

PurposeThis study aims to study the impact of intermetallic compound on microstructure, mechanical characteristics and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder.Design/methodology/approachIn this paper, a new group of lead-free high-temperature Pb-free solder bearing alloys with five weight percentages of different silver additions, Bi-Agx (x = 3.0, 3.5, 4.0, 4.5 and 5.0 Wt.%) have been developed by rapidly solidification processing (RSP) using melt-spun technique as a promising candidate for the replacement of conventional Sn-37Pb common solder. The effect of the addition of a small amount of Ag on the structure, microstructure, thermal and properties of Bi-Ag solder was analyzed by means of X-ray diffractometer, scanning electron microscopy, differential scanning calorimetry and Vickers hardness technique. Applying the RSP commonly results in departures from conventional microstructures, giving an improvement of grain refinement. Furthermore, the grain size of rhombohedral hexagonal phase Bi solid solution and cubic IMC Bi0.97Ag0.03 phase is refined by Ag addition. Microstructure analysis of the as soldered revealed that relatively uniform distribution, equiaxed refined grains of secondary IMC Bi0.97Ag0.03 particles about 10 µm for Bi-Ag4.5 dispersed in a Bi matrix. The addition of trace Ag led to a decrease in the solidus and liquidus temperatures of solder, meanwhile, the mushy zone is about 11.4°C and the melting of Sn-Ag4.5 solder was found to be 261.42°C which is lower compared with the Sn-Ag3 solder 263.60°C. This means that the silver additions into Bi enhance the melting point. The results indicate that an obvious change in electrical resistivity (?) at room temperature was noticed by the Ag addition. It was also observed that the Vickers microhardness (Hv) was increased with Ag increasing from 118 to 152 MPa. This study recommended the use of the Bi-Ag lead-free solder alloys for higher temperature applications.FindingsSilver content is very important for the soldering process and solder joint reliability. Based on the present investigations described in this study, several conclusions were found regarding an evaluation of microstructural and mechanical deformation behavior of various Bi-Ag solders. The effect of Ag and rapid solidification on the melting characteristics, and microstructure of Bi-Ag alloys were studied. In addition, the mechanical properties of Bi with different low silver were investigated. From the present experimental study, the following conclusions can be drawn. The addition of Ag had a marked effect on the melting temperature of the lead-free solder alloys, it decreases the melting temperature of the alloy from 263.6 to 261.42°C. Bi-Ag solders are comprised of rhombohedral Hex. Bi solid solution and cubic Ag0.97Bi0.03 IMC is formed in the Bi matrix. The alloying of Ag could refine the primary Bi phase and the Bi0.97Ag0.03 IMC. With increasing Ag content, the microstructure of the Bi-Ag gradually changes from large dimples into tiny dimple-like structures. The refinement of IMC grains was restrained after silver particles were added into the matrix. The inhibition effect on the growth of IMC grains was most conspicuous when solder was doped with Ag particles. As a result, the Vickers microhardness of the Bi-Ag lead-free solder alloys was enhanced by more than 100% ranging from 118.34 to 252.95 MPa. Bi-Ag high-temperature lead-free solders are a potential candidate for replacing the tin-lead solder (Sn-37Pb) materials which are toxic to human and the environment and has already been banned.Originality/valueThis study recommended the use of the Bi-Ag lead-free solder alloys for high-temperature applications.

Enhanced mechanical properties and corrosion behavior of Zn–30Sn–2Cu high-temperature lead-free solder alloy by adding Sm

Enhanced mechanical properties and corrosion behavior of Zn–30Sn–2Cu high-temperature lead-free solder alloy by adding Sm

A Novel Design of High-Temperature Lead-Free Solders for Die-Attachment in Power Discrete Applications

Abstract Development of high-temperature lead-free (HTLF) solders to replace high-lead solders for die-attachment in power device applications is driven by (1) the harmful effects of lead to human health and the environment, and (2) the demand of the improved bonding materials serving under high-power density and high-junction temperatures, especially for wide-band-gap power devices. A novel design, based on a mixed solder powder paste technology—Durafuse™—has been developed to deliver a Sn-rich HTLF paste, presenting the merits of both constituent powders. The combination of the rigid, high-melting SnSbCuAgX and the ductile, low-temperature Sn-rich solder in one paste enables reflow at a relatively low temperature (barely above the liquidus temperature of the final joint composition) and maintains the joint strength above 15MPa in the temperature range between 270°C and 295°C. The sufficient high-temperature strength has demonstrated the capability of maintaining the joint integrity during subsequent multiple SMT reflows below the 270°C peak temperature, regardless of the existence of a partial melting phase. Both X-ray inspection and cross-section microstructure have not shown any damage in the Si die or any noticeable cracks in the bonding joint, even after 3000 cycles of TCT (−40 to 150°C). In summary, Durafuse™ HT, the novel design of the high-temperature lead-free pastes, has shown the feasibility as a drop-in solution to replace high-lead solders for die-attachment in power discrete applications.

Wetting characteristics of Sn-5Sb-CuNiAg lead-free solders on the copper substrate

PurposeThe purpose of this paper is to investigate the wetting behaviors of Sn-5Sb-CuNiAg solders on copper substrates in different soldering processes and the effects of alloying elements on the wettability.Design/methodology/approachSn-5Sb-CuNiAg solder balls (750 µm in diameter) were spread and wetted on 40 × 40 × 1 mm copper plates, in different fluxes, soldering temperatures and time. The contact angles were obtained by a home-made measuring instrument. The samples were polished and deep etched before analyzed by scanning electron microscopy. Energy dispersive X-ray spectroscopy was used to identify the composition of the joints.FindingsThe effects of different soldering processes and alloying elements on the wetting behaviors of Sn-5Sb-CuNiAg solders on copper substrates were calculated and expounded. The rosin-based flux could effectively remove oxidation layers and improve the wettability of Sn-5Sb-CuNiAg solders. Then with the increase of soldering temperature and time, the contact angles decreased gradually. The soldering processes suited for Sn-5Sb-CuNiAg solders were RMA218, 280°C and 30 s. Considered the effects of alloying elements, the wettability of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag was relatively favorable on copper substrates. Besides, Ni could accumulate at the solder/Cu interface and form a jagged (Cu,Ni)6Sn5 IMC.Originality/valueThis work was carried out with our handmade experiment equipment and the production of the quinary lead-free solder alloy used in wetting tests belongs to us. The investigated Sn-5Sb-CuNiAg alloys exhibited higher melting point and preferable wettability, that was one of the candidates for high-temperature lead-free solders to replace high-Pb solders, and applied extremely to high temperature and frequency working environments of the third-generation semiconductors components, with a greater potential research and development value.

The influence of Ag on the microstructure, thermal properties and mechanical behavior of Sn–25Sb-xAg high temperature lead-free solder

Abstract Adding Ag to Sn–25Sb solder to prepare Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5, x is the mass percentage) solder alloys. Using optical microscope, JSM-5610LV field emission scanning electron microscope, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Vickers hardness tester and tensile testing machine to test the microstructure of the solder alloy, thermal performance and mechanical performance. The microstructure test results of the solder alloys show that Ag3 (Sn, Sb) intermetallic compounds (IMCs) are formed in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) alloys after Ag is added, and they are dispersed in β-Sn phase. Ag3 (Sn, Sb) IMCs are pinned at the grain boundary of β-Sn and SbSn phases. Moreover, it is also found that the addition of Ag makes the β-Sn and SbSn phases in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) solder alloy refined. DSC analysis results show that the melting point of Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5) solder alloy decreases slightly after adding Ag. Among them, the pasty range of Sn–25Sb-2.5Ag solder alloy is the smallest at 12.84 °C, followed by Sn–25Sb-3.5Ag at 14.81 °C. In the mechanical performance test of the solder alloy, it is found that the ultimate tensile strength (UTS) and elongation of the Sn–25Sb-xAg solder alloy increase with the increase of Ag addition. Sn–25Sb-3.5Ag solder alloy has the highest UTS and elongation, which are 69.25 MPa and 8.02% respectively. The increase is mainly through fine-grain strengthening and dispersion strengthening mechanisms.

Correction to: Characteristics of eutectic and near-eutectic Zn–Al alloys as high-temperature lead-free solders

Correction to: Characteristics of eutectic and near-eutectic Zn–Al alloys as high-temperature lead-free solders

The Microstructure, Thermal, and Mechanical Properties of Sn-3.0Ag-0.5Cu-xSb High-Temperature Lead-Free Solder

To obtain Sn-3.0Ag-0.5Cu-xSb (x = 0, 25, 28, and 31) high-temperature lead-free solder antimony was added to Sn-3.0Ag-0.5Cu solder. The microstructure, thermal properties, and mechanical behavior of the solder alloy prepared were studied by using JSM-5610LV scanning electron microscope, Germany STA409PC differential scanning calorimeter, AG-I250KN universal tensile testing machine, and other methods. The SEM-EDS results showed that after adding Sb, SnSb phase was formed in the β-Sn matrix phase. The newly formed SnSb phase and the existing Sb in the solder alloy can inhibit the generation of IMC and refine the IMC layer. The addition of Sb significantly increased the melting temperature of the solder alloy. Among them, the thermal performance of Sn-3.0Ag-0.5Cu-25Sb is the best. The melting temperature of Sn-3.0Ag-0.5Cu-25Sb is 332.91 °C and the solid–liquid line range of Sn-3.0Ag-0.5Cu-25Sb solder alloy is 313.28–342.02 °C. Its pasty range is 28.74 °C, lower than 30 °C, which is beneficial for soldering. The test results of the mechanical behavior of Sn-3.0Ag-0.5Cu-xSb solder alloy show that with the increase of Sb addition, the ultimate tensile strength of the solder alloy also increases. However, the change of the elongation of the solder alloy is the opposite. The ultimate tensile strength of the solder alloy increased from 29.45 MPa of Sn-3.0Ag-0.5Cu solder to 70.81 MPa of Sn-3.0Ag-0.5Cu-31Sb solder. The reason for the increase in the strength of the solder alloy is the reduction of the thickness of IMC and the solid solution hardening effect of Sb.

Effect of rare earth Ce on the thermal behavior, microstructure and mechanical properties of Zn–30Sn–2Cu high temperature lead-free solder alloy

The aim of the present study is to investigate the thermal behavior, microstructure and mechanical properties of high temperature Zn–30Sn–2Cu–xCe (x = 0, 0.05, 0.1, 0.5 wt%) Pb-free solders. The alloying of Ce refined the microstructure and increased the melting point of the solders. Zn–30Sn–2Cu–0.05Ce sample showed the best elongation, while the best ultimate tensile strength (UTS) and yield strength (YS) appeared in Zn–30Sn–2Cu–0.1Ce sample. The UTS of the alloys ranged from 44.02 to 64.95 MPa and the YS ranged from 32.73 to 51.83 MPa. Besides, the microhardness enhanced slightly with the addition of Ce. The analysis of the fractographies showed that the fracture mode turned from mixed brittle fracture into mixed ductile fracture with the addition of Ce.

Effect of isothermal ageing process on microstructural changes in Bi-Ag lead-free solder alloys

ABSTRACT Despite numerous studies on lead-free solder in recent years, only a limited number of publication is available on high temperature lead-free alternative solders to replace high lead solders. Therefore, this research focused on several candidate alloys (Bi-1.5–2.5-3.5 wt.% Ag) as alternative solders for high temperature application. Candidates of Bi-Ag alloys were aged at 160°C for 0, 100, 200, 350 and 500 hours. Morphological characteristics such as grain growth, wetting angle and Cu rich particles size distribution in solder bulk were investigated. The results show that physical and mechanical adhesion between Cu substrate and solder bulk occurred in all three percentages of Ag during isothermal ageing process. In the case of Cu-rich particle size analyses, by increasing the percentages of Ag in the solder alloys, the average size of Cu- rich phase increased. The average measurement of mechanical grain boundary grooving thickness and cross-sectional wetting angle also increased with addition of Ag percentage. However, the value for cross-sectional wetting angle analysis reduce with increasing ageing time. From this work, Bi-2.5 wt% Ag have been identified as the best candidate between the three solders to be explored for future analysis such as mechanical strength data collection and electrical conductivity test.

Effect of Addition of Trace Ni and Ge into Sn-Sb-Ag High Temperature Lead-free Solder Alloy on its Mechanical Properties

Effect of Addition of Trace Ni and Ge into Sn-Sb-Ag High Temperature Lead-free Solder Alloy on its Mechanical Properties

Characteristics of eutectic and near-eutectic Zn–Al alloys as high-temperature lead-free solders

Lead-based alloys are conventionally used for soldering interconnections that are expected to perform at high temperatures. Because of the concerns of lead toxicity, the development of lead-free solders became important. Till now, none of the proposed alloys have the characteristics that can completely substitute the Pb-bearing solders for high-temperature soldering application. Recently, researchers studied many ternary and quaternary systems near Zn–Al binary eutectic composition and reported prospects in soldering applications. However, the bulk solder properties of the Zn–Al binary system near the eutectic composition is rare in the literature. In the present study, the microstructure and thermal, mechanical and electrical characteristics of eutectic and near-eutectic Zn–Al alloys are investigated as replacement of traditional lead-bearing high-temperature solders. Mechanical and electrical properties of Zn was enhanced by alloying with Al, without altering much of the thermal expansion co-efficient. Finally, the material properties of the prepared Zn–Al alloys and other Zn-based alloys are compared with the conventional Pb–Sn solders. Research shows, 7 wt% Al–Zn alloy has multiple times higher magnitude of ultimate tensile strength, Vicker’s microhardness and electrical conductivity than the traditional Pb–Sn high-temperature solders. The melting temperature of the alloys was a bit higher than the Pb–Sn solders. A suitable ternary element addition to the system can potentially replace the conventional Pb-based high-temperature solders.

Effects of aluminum addition (x = 0–1 wt%) on the thermal behavior, microstructure and mechanical properties of Zn–30Sn high temperature lead-free solder alloy

The thermal behavior, microstructure and mechanical properties of the modified lead-free Zn–30Sn–xAl (x = 0, 0.1, 0.5, 1.0 wt%) composite solder alloys had been investigated in the present study. Addition of Al tended to refine the microstructure and decrease the melting point. The analysis of microstructure showed that the supersaturated precipitation of Al (0.5 wt%) in η-Zn phase would result in the formation of Zn–Al phase. Due to the peritectic reaction, the Zn–Sn–Al phase was observed when the Al content was 1 wt%. The refinement of eutectic structure and η-Zn phase improved the elongation when the minor Al element (0.1 and 0.5 wt%) was added into Zn–30Sn solder. However, when the Al content was 1.0 wt%, the elongation of Zn–30Sn-based solder decreased because of the stress concentration. Besides, the ultimate tensile strength (UTS) of the alloy increased from 45.48 to 91.26 MPa, and the yield strength increased from 35.26 to 37.53 MPa. The analysis of the fractography showed that the brittle fracture gradually turned into mixed fracture mode of ductile fracture and ductile fracture with the increasing content of Al.

Effects of Ni Addition to Sn–5Sb High-Temperature Lead-Free Solder on Its Microstructure and Mechanical Properties

Effects of Ni Addition to Sn–5Sb High-Temperature Lead-Free Solder on Its Microstructure and Mechanical Properties

Effect of Rare Earth Metals on the Properties of Zn-20Sn High-Temperature Lead-Free Solder

Cerium–lanthanum mixed rare earth (RE) (0.5 wt.%) was added to Zn-20Sn high-temperature lead-free solder to study the effect of RE on the solder properties. The Zn-20Sn-0.5RE solder has a better corrosion resistance than that of Zn-20Sn alloy. RE addition increases the γ-Cu5Zn8 layer thickness, promotes growth of a e-CuZn5 layer shaped like bamboo shoots, and increases the roughness of the e-CuZn5 layer, which increases the shear strength of the solder joints. Compared with the Zn-20Sn alloy, the creep resistance of the Zn-20Sn-0.5RE solder was improved after soldering. The indentation hardness increases in an order of Zn-20Sn-0.5RE solder, Zn-20Sn solder, e-CuZn5 layer, and γ-Cu5Zn8 layer.