Al Solder Research Articles

Anand constitutive model of lead-free solder joints in 3D IC device

Anand constitutive relation of SnAgCu and SnAgCu-nano Al solders were studied under uniaxial tension, and the constitutive model was used in the finite element simulation to analyze the stress-strain response of lead-free solder joints in 3D IC devices. The results showed that the nine parameters of the Anand model can be determined from separated constitutive relations and experimental results. Based on Anand model, the finite element method was selected to calculate the stress-strain response of lead-free solder joints, it was found that in the 3D IC device the maximum stress-strain concentrated in the concern solder joints, the stress-strain of SnAgCu-nano Al solder joints was lower than that of SnAgCu solder joints, which represented that the addition of nano Al particles can enhance the reliability of lead-free solder joints in 3D IC devices.

Oxidation resistant effects of Ag2S in Sn–Ag–Al solder: A mechanism for higher electrical conductivity and less whisker growth

Oxidation resistant effects of Ag2S in a ternary Sn–Ag–Al solder were investigated from the aspect of electrical conductivity. Combined reactions, associated with combustion and ionization of Ag2S, contributed to the removal of the oxide layers of the Ag2S-containing solder; as a result, lowering the overall O concentration. Because the diffusion of Ag2S suppressed oxidation in the Sn matrix, the electrical resistivity was significantly decreased. With regard to the improvement of the oxidation resistance and electrical conductivity, these oxidation resistant functions of Ag2S also inhibited the formation of intermetallic compounds (IMCs) and interrupted the growth of Sn whiskers.

Effect of Al on the microstructure and properties of Sn–0.7Cu solder alloy

Effect of Al on the microstructure and mechanical properties were investigated. The results showed that Al could depress the formation of eutectic phase in Sn–Cu–Al solder alloy. The intermetallic compounds of Sn–0.7Cu–0.03Al were refined compared with that of Sn–0.7Cu–0.015Al. Segregated CuAl intermetallic compound was observed in Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al solder alloy. Sn-whisker was observed on the polished surface of Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al. The ultimate tensile strength of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was found to be higher than that of Sn–0.7Cu–xAl (x = 0, 0.015 and 0.15). The elongation of Sn–0.7Cu–0.015Al was the highest. The creep performance of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was similar and higher than that of Sn–0.7Cu and Sn–0.7Cu–0.15Al.

자동차 전장부품을 위한 Sn-0.5Cu-(X)Al(Si) 중온 솔더의 접합특성 연구

Joint properties of electric control unit (ECU) module using Sn-Cu-(X)Al(Si) lead-free solder alloy were investigated for automotive electronics module. In this study, Sn-0.5Cu-0.01Al(Si) and Sn-0.5Cu-0.03Al(Si) (wt.%) lead-free alloys were fabricated as bar type by doped various weight percentages (0.01 and 0.03 wt.%) of Al(Si) alloy to Sn-0.5Cu. After fabrications of lead-free alloys, the ball-type solder alloys with a diameter of 450 um were made by rolling and punching. The melting temperatures of 0.01Al(Si) and 0.03Al(Si) were 230.2 and 230.8℃, respectively. To evaluation of properties of solder joint, test printed circuit board (PCB) finished with organic solderability perseveration (OSP) on Cu pad. The ball-type sol- ders were attached to test PCB with flux and reflowed for formation of solder joint. The maximum tem- perature of reflow was 260℃ for 50s above melting temperature. And then, we measured spreadability and shear strength of two Al(Si) solder materials compared to Sn-0.7Cu solder material used in industry. And also, microstructures in solder and intermetallic compounds (IMCs) were observed. Moreover, thickness and grain size of Cu6Sn5 IMC were measured and then compared with Sn-0.7Cu. With increasing the amounts of Al(Si), the Cu6Sn5 thickness was decreased. These results show the addition of Al(Si) could suppress IMC growth and improve the reliability of solder joint.

Effect of the Soldering Process on the Microstructure and Mechanical Properties of Sn-9Zn/Al Solder Joints

Tin-zinc solder alloys are considered to be appropriate for soldering of aluminum alloys at low-temperature in electronics and radiators applications. In this paper, the effects of different soldering parameters on the microstructure and interfacial reaction behaviors of 1070Al/Sn-9Zn/1070Al joints were investigated. The results show that the Al substrate was dissolved by the liquid solder, but Al-related intermetallic was not observed in the interface. Two kinds of Al-rich phases formed in the solder matrix. Large butterfly-shaped solid solution (Al)″ phases (about 10 μm) were formed in the liquid alloys, and compact-shaped precipitations (nano-size) were dissolved out from solders during solidification process. With increasing of the soldering time, Al″ phases were migrated upwards in the solders and the amount of this phase increased. In addition, with the increase of the soldering temperature, the dissolution rate of Al into the solder increased and the formation time of (Al)″ phases was reduced. Shear test results indicate when soldered at 250 °C, the shear strength increased from 48.6 MPa to a maximum 60.5 MPa and then decreased to a stable value (about 55 MPa) with increasing of the soldering time. Similar trends were also observed at 300 and 350 °C, while the soldering time needed to obtain maximum shear strength was shortened. The formation of these Al-rich phases improves the shear strength but deteriorates the ductility.

Creep behavior of SnAgCu solders containing nano-Al particles

In our previous work, a small amount of Al nanoparticles can improve the wettability and mechanical properties of SnAgCu lead-free solders. In this paper, creep properties of SnAgCu solder alloys containing 0.1 wt% Al nanoparticles were studied based on creep testing. It is found that with the addition of Al nanoparticles can enhance the creep resistance of SnAgCu solders. And the Garofalo–Arrhenius creep model was used to describe the creep behavior of SnAgCu and SnAgCu–0.1nano Al solder joints, the parameters were determined based on creep testing. And finite element analysis was utilized to represent the accumulated creep response and calculate the creep fatigue life of solder joints.

Effect of aluminum concentration on the microstructure and mechanical properties of Sn–Cu–Al solder alloy

The effect of aluminum on the microstructure and mechanical properties of Sn–0.7Cu–xAl (x=0–0.075) solder alloy is investigated. The results show that the microstructure of Sn–Cu solder alloy is refined by Al. The intermetallic compounds (IMC) in the Sn–Cu–Al solder alloy is varied from Cu6Sn5 in the Sn–Cu–(0.01–0.025)Al to Al2Cu in the Sn–0.7Cu–(0.05–0.075)Al. The volume fraction of the IMC and eutectic is raised with increasing aluminum concentration. The wettability of Sn–Cu–Al solder alloy is improved by aluminum. The spreading coefficient of Sn–0.7Cu–0.075Al is reached 70%. The tensile strength of Sn–Cu–Al alloy is decreased after aluminum adding to 0.025wt.% and then is increased after aluminum adding to 0.075wt.% due to the IMC variation and the volume fraction increasement of Al2Cu/Sn eutectic with high microhardness. The superior mechanical properties of Sn–0.7Cu–0.075Al are guaranteed by the refined microstructure, the dispersed IMC and the uniform stress distribution. The Sn–0.7Cu–0.075Al is an optimized lead-free solder alloy for the copper substrate.

Microstructure, interfacial IMC and mechanical properties of Sn–0.7Cu–xAl (x=0–0.075) lead-free solder alloy

• Microstructure and wettability of Sn–Cu–Al solder alloy are improved by adding Al. • IMC Cu 6 Sn 5 varies to Al 2 Cu with increasing Al concentration in the Sn–Cu–Al. • Scalloped interfacial IMC thickness is decreased with increasing Al concentration. • UTS and creep resistance of Sn–0.7Cu–(0.05–0.075)Al are guaranteed by disperse Al 2 Cu inhibiting the dislocation movement. • Sn–0.7Cu–(0.05–0.075)Al is considered as an applicable lead-free solder alloy. The effect of aluminum concentration on the microstructure, wettability, interfacial IMC and mechanical properties of Sn–0.7Cu lead-free solder alloy is investigated. The results show that the microstructure of Sn–Cu–Al solder alloy consists of β-Sn, eutectic and IMC, and the microstructure of Sn–0.7Cu alloy is refined by adding aluminum. The interfacial IMC at the boundary of β-Sn in the Sn–0.7Cu–(0.01–0.025)Al is Cu 6 Sn 5 , and it is varied to Al 2 Cu in the Sn–0.7Cu–(0.05–0.075)Al. The wettability of Sn–Cu–Al solder alloy is improved by aluminum, the spreading coefficient of Sn–0.7Cu–0.075Al reaches about 70%. The thickness of the scalloped interfacial IMC is dominated by the IMC variation, and the chemical reaction between Cu and segregated Al. The mechanical properties of Sn–Cu–Al solder alloy are decreased slightly by adding aluminum. The tensile strength and the creep resistance of Sn–0.7Cu–(0.05–0.075)Al are superior to Sn–0.7Cu–(0.01–0.025)Al due to the hindering dislocation slipping by the disperse Al 2 Cu. Sn–0.7Cu–(0.05–0.075)Al is an applicable lead-free solder alloy for the Cu substrate.

Heterogeneous nucleation of Cu6Sn5 in Sn–Cu–Al solders

Cu6Sn5 is a common intermetallic in Pb-free soldering. We explore the influence of dilute aluminium additions on the heterogeneous nucleation and grain refinement of primary Cu6Sn5 in Sn–4Cu–xAl solders. For cooling rates relevant to soldering, it is found that 0.02 and 0.2wt%Al cause significant grain refinement of Cu6Sn5 with 0.2wt%Al increasing the number of Cu6Sn5 grains per unit area by a factor of ∼8. Grain refinement is shown to be due to heterogeneous nucleation of Cu6Sn5 on either delta-Cu33Al17 or gamma1-Cu9Al4, coupled with significant constitutional supercooling ahead of growing Cu6Sn5 crystals. Reproducible orientation relationships are measured between the Cu–Al intermetallics and Cu6Sn5, with a planar lattice mismatch of less than 2.5%. The role of potent nuclei and solutal growth restriction are discussed with reference to the grain refinement of structural casting alloys.

Effect of aluminium additions on wettability and intermetallic compound (IMC) growth of lead free Sn (2 wt. % Ag, 5 wt. % Bi) soldered joints

The effect of a trace Al addition (0, 0.01, 0.05 and 0.1 wt. %) in the Sn-2Ag-5Bi solder alloy on wettability and intermetallic compound (IMC) formation of the alloy was investigated. The interface between the solder and a Cu(17 μm)/Ni(4 μm)/Au (0.02 μm) under bump metallized (UBM) substrate was studied. The microstructure of the bulk solder and the interface of the soldered joints was observed in a scanning electron microscope (SEM), and the thickness of the interface reaction layers was estimated. Various IMC phases were identified by energy dispersive spectroscopy (EDS) and by the electron probe micro analyzer (EPMA). The experimental results indicated that the addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder alloy significantly improved the wettability of the solder more than the other Al additions did. The IMC layer between the bulk Sn-2Ag5Bi-0.01Al solder and the Cu/Ni/Au UBM substrate was almost uniform and thinner than those between the solders containing 0, 0.05, and 0.1 wt. % Al and their respective Cu/Ni/Au UBM substrates. Furthermore, the growth rate of the IMC layer between the Sn-2Ag-5Bi-0.01Al solder and Cu/Ni/Au UBM after 1 to 10 reflow times was lower than that of the IMC layer between the Sn-2Ag-5Bi solder and Cu/Ni/Au UBM. The IMCs in the solder joint interface (e.g., Ni3Sn4) of the Sn-2Ag-5Bi-0.01Al solder were well distributed near the Bi and fine Ag3Sn. The addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder yielded the best wetting properties for the solder and the minimum growth rate of the IMCs because it increased the nucleation rate of Ag3Sn and uniformly segregated the Bi phase.

Development of an Er-doped Mg–Zn–Al solder by ultrasonic treatment and its joint property

A novel Er-doped Mg–Zn–Al solder was developed by using ultrasonic vibration technology. The inclusions in the solder were analyzed. The microstructure of the solder and its soldering lap joint was investigated, and the shear strength of the joint was measured. It was found that the inclusions in the solder decreased greatly, the α-Mg phase and Al3Er compound were broken up into granular structure after ultrasonic vibration treatment. The α-Mg phase and Al3Er compound in the soldered joint showed similar structure as that of the original solder. The average shear strength of the soldered joints by using the ultrasonic treated filler metal was almost 1.25 times as large as that soldered by the traditional one.

Effect of doping Al on the liquid oxidation of Sn–Bi–Zn solder

The liquid oxidation behaviors of Sn–40Bi–2Zn and Sn–40Bi–2Zn–0.005Al solders were investigated from thermal dynamics and kinetics analysis. The characteristics of surface oxidation film at 170 °C were studied by thermo gravimetric analysis and X-ray photoelectron spectroscopy (XPS). Sn–40Bi–2Zn solder performed inferiorly in oxidation prevention performance, due to the formation of ZnO, which exhibits lower Gibbs free energy of formation and higher growth rate. Trace amount of Al addition, however, alleviated the oxidation behavior of Zn. XPS depth profile results indicated that the surface layer of Sn–40Bi–2Zn–0.005Al consisted of oxides of Al and Zn formed on the outer surface of the solder film and in the subsequent layer, mainly formed by the oxides of Sn, Bi. Al, basically formed as Al2O3, segregated towards the outer surface, seemed to deter the Zn oxidation on the solder surface.

Microstructure and interfacial reaction of Sn–Zn–x(Al,Ag) near-eutectic solders on Al and Cu substrates

Sn–Zn–x(Al,Ag) near-eutectic solders, namely Sn–8.3Zn–0.73Ag, Sn–8.4Zn–0.44Al and Sn–7.4Zn–0.26Al–0.68Ag (in wt%) with melting points of 200.74, 198.00 and 197.32 °C, respectively, as well as the Sn–9Zn eutectic solder, were used to join Al and Cu substrates. The addition of Ag led to the formation of dendritic AgZn3 phases, while the addition of Al obviously refined the microstructure of Sn–Zn eutectic, as well as the AgZn3 phases. The Sn–Zn–Al solder possessed the best wettability on both Cu and Al substrates among the four solders. Al4.2Cu3.2Zn0.7 intermetallic compound (IMC) layers formed at the Sn–Zn–x(Al,Ag)/Cu interfaces while Al-rich (Zn) solid solutions at the Sn–Zn–x(Al,Ag)/Al interfaces of all the as-soldered joints. The shear strength of the Al/Sn–Zn–Al/Cu solder joints was the highest among the four solder joints. The declining degree of the shear strength of the Sn–Zn–x(Al,Ag) solder joints in 3.5 % NaCl solution was in agreement with the corrosion-resistance order of the bulk solders. The Al/Sn–Zn–Ag/Cu joint thus owned the best corrosion resistance.

Development of extremely ductile lead-free Sn-Al solders for futuristic electronic packaging applications

In the present study, new lead-free Sn-Al solders are developed incorporating varying amount of Al (0.4 and 0.6% by weight) into pure Sn using disintegrated melt deposition technique. Solder samples were then subsequently extruded at room temperature and characterized. Microstructural characterization studies revealed equiaxed grain morphology, minimal porosity, reasonably uniform distribution of Al particles and good Sn-Al interfacial integrity. Melting temperature of Sn-0.6Al (228°C) was found to be close to the eutectic Sn-0.7Cu (227°C) solders. Microhardness was increased with increasing amount of Al in pure Sn. Room temperature tensile test results revealed that newly developed Sn-0.6Al solders exhibited significant improvement in 0.2% yield strength (∼67%), ultimate tensile strength (∼18%) and ductility (∼123%) when compared to commercial Sn-0.7Cu solder. Ductility was improved about 222%, 263% and 81% when compared to commercially available Sn-3.5Ag-0.7Cu, Sn-3.5Ag and Sn-37Pb solders, respectively without compromising strength.

Effects of Al and Fe additions on microstructure and mechanical properties of SnAgCu eutectic lead-free solders

In this study, Sn–3.5Ag–0.9Cu (wt%) lead-free solder was modified with minor additions of Al and Fe. The thermal, microstructural and mechanical behaviors after and before compositional modifications were investigated by a combined study of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and shear strength measurements. EDS results and Darken–Gurry predictions indicated a high concentration of Fe substitution within the Cu6Sn5 at the solder/copper interface which induced desirable effects on undercooling and microstructure evolution. Eutectic SAC and SAC+0.05wt% Al solder joints exhibit considerable number of brittle proeutectic phases (i.e., Ag3Sn). Proeutectic Ag3Sn formation was found to be suppressed after Fe modification. A new type of Al–Sn–Cu intermetallic compound was detected for Al added specimens. The rod-like morphology of this IMC appears to cause a sharp decrease in the shear strength of Al modified solder joints. The shear strength values for Fe modified solder joints were found to be higher in a wider composition range (0.01–0.1wt% Fe) as compared to eutectic SAC and SAC+0.05wt% Al.

The Effects of Small Additions Ga and Al on the Microstructure and Tensile Properties of Sn-Zn Based Lead-Free Solders

The melting temperature, microstructures, and mechanical properties of the Sn-Zn-0.5Ag-0.5Ga, Sn-Zn-0.5Ag-0.45Al and Sn-Zn-0.5Ga-0.45Al lead-free solders were investigated. The results indicate that the addition of 0.5 wt% Ag to the Sn-Zn based alloys destroy the eutectic structure and results in the formation of Ag-Zn compound and hypoeutectic structure. The variation in the microstructure lowers the UTS. By the addition of Al the UTS and elongation of the 0.5Ag-0.45Al alloy can be decreased due to the Al diffused to the interface of the Ag-Zn compound/Sn-Zn eutectic structure to form Al-Zn compound. The 0.5Ga-0.45Al alloy shows a typical eutectic structure with the light contract β-Sn and the darker needle-like phase, as well as a small amount of Al-Zn phase with a near diamond shape. Gallium uniformly distributes in the Sn matrix and Zn rich phases. The 0.5Ga-0.45Al solder had the highest UTS and elongation, while 0.5Ag-0.45Al had the lowest UTS and elongation. The results indicate that Ga and Al exhibits prominent influence on the microstructure as well as the mechanical properties of the solders.

Comparison study of SAC405 and SAC405+0.1%Al lead free solders

Purpose – The purpose of this paper is to study the effect of the addition of a small amount of Al (0.1 percent) on the properties of lead‐free solder type Sn‐4Ag‐0.5Cu (SAC 405).Design/methodology/approach – The soldering properties of wettability and spreadability on a Cu substrate were studied, and the effect of Al on the growth of intermetallic compounds (IMCs) was observed. The shear strength of soldered joints was assessed. For comparison, soldering and strength tests were carried out on SAC 405 and SAC 405+ Al solders. Soldering was performed with an activated flux type ZnCl2‐NH4Cl, with non‐activated flux (rosin), and without flux in the air.Findings – Experimental results show that Al addition slightly reduces the wettability and spreadability of SAC 405 solder. Also, the shear strength is moderately reduced, dropping by 8 MPa on average. Differential scanning calorimetry (DSC) analysis showed that the melting point of SAC 405+0.1%Al solder was increased to 221°C.Originality/value – The positive ...

Elevated-temperature shear strength and hardness of Zn–3Cu–xAl ultra-high-temperature lead-free solders

This study examines the shear strength and hardness of the ultra-high-temperature Zn—3wt% Cu—4wt% Al (ZCA34), Zn—3wt% Cu—5wt% Al (ZCA35), and Zn—3wt% Cu—6wt% Al (ZCA36) solder alloys in the temperature range of 25–225°C. Evaluation of the data revealed that the ZCA34 alloy, with the lowest aluminum content, had the highest shear yield stress (SYS), ultimate shear strength (USS) and hardness (Hv) at elevated temperatures. This behavior was in contrast to that of the more concentrated ZCA36 alloy which exhibits the best mechanical properties at room temperature. Higher Al contents of the alloys resulted in the evolution of a refined spheroidized structure, and encouraged the four phase transformation α+ε→T′+η. The refined structure may give rise to grain boundary sliding at high temperatures, and the four phase transformation results in a lesser amount of the harder ε-phase in the microstructure, thus causing softening. The shear strength of these high temperature solder alloys is found to be much higher than those of the Zn–Sn and Pb–Sn high-temperature solders.

Effect of Ga on the Oxidation Properties of Sn–8.5Zn–0.5Ag–0.1Al–xGa Solders

The oxidation properties of Sn–8.5Zn–0.5Ag–0.1Al–xGa lead-free solders in the liquid state (250 °C) under O2 atmosphere were investigated using a thermal gravimetric analyzer. The Ga content of the investigated solders was 0.05–2 wt%. The results indicate that Ga enhances the oxidation resistance of Sn–Zn–Ag–Al solder. Cross-sections of the solder surfaces were examined using focus ion beam milling. The thickness of the oxidation layer, which was about 30–100 nm, increased with increasing Ga content. The oxidation layer was found to be nonuniform at low Ga content. The oxide layers on the surface of solders were investigated using Auger electron spectroscopy and thin-film XRD. The results showed that the oxide layer formed was ZnO. Al and Ga tended to segregate on the surface of the solder.

Development of Sn-Ag-Cu-X Solders for Electronic Assembly by Micro-Alloying with Al

Of Pb-free solder choices, an array of solder alloys based on the Sn-Ag-Cu (SAC) ternary eutectic (Teut = 217°C) composition have emerged with potential for broad use, including ball grid array (BGA) joints that cool slowly. This work investigated minor substitutional additions of Al ( 0.05Al), but the suppression effect faded for >0.20Al. Undercooling suppression did not correlate specifically with blade suppression since it became significant at 0.10Al and increased continuously with greater Al to 0.25Al. Surprisingly, an intermediate range of Al content (0.10 wt.% to 0.20 wt.% Al) promoted formation of significant populations of 2-μm to 5-μm faceted Cu-Al particles, identified as Cu33Al17, that clustered at the top of the solder joint matrix and exhibited extraordinary hardness. Clustering of Cu33Al17 was attributed to its buoyancy, from a lower density than Sn liquid, and its early position in the nucleation sequence within the solder matrix, permitting unrestricted migration to the top interface. Joint microstructures and implications for the full nucleation sequence for these SAC + Al solder joints are discussed, along with possible benefits from the clustered particles for improved thermal cycling resistance.