Mechanical Properties Of Solder Joints Research Articles

Effect of non-standard SnAg surface finishes on properties of solder joints

In this study, the effects of nonstandard near-eutectic SnAg surfaces on the wettability, intermetallic compound growth and mechanical properties of solder joints were investigated. Four types of surface finishes based on near-eutectic SnAg alloys with different compositions and numbers of layers were analyzed. Design/methodology/approachThe effect of surface-finishes SnAg5NiP and SnAg7NiP, which were prepared with and without a Ni-P diffusion barrier, was tested. The Ni-P layer was produced either chemically or electrochemically. The effect of the SnAg surface finish on wettability, formation, and growth of intermetallic compound in the solder joint was analyzed. We further explored the impact of different PCB finishes on the quality of soldered joints. This investigation involved a comparative analysis of the behavior of SnAg finishes in comparison to pure copper, as well as the commonly employed HASL, ENIG, and ImSn finishes. FindingsIt was found that SnAg surface finishes with a Ni-P diffusion barrier are wetted by molten solder faster than surface finishes without a diffusion barrier. The mechanical properties of the joints on both surfaces are comparable to those on ENIG. SnAg that include a chemically created Ni-P diffusion layer is characterized by the formation of more thermally stable ternary intermetallic compounds based on (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4. On the contrary, the electrochemically formed Ni layer supports the increase in the rate of intermetallic compound formation, which affects the properties of the soldered joints. OriginalityNonstandard near-eutectic SnAg finishes, which contains a Ni-P diffusion layer can be used as promising replacement of ENIG or other standard finishes.

Growth of intermetallic compounds and their reinforcement on CrCoNi/Au80Sn20 soldering interfaces

To broaden the utility of the CrCoNi medium entropy alloy in engineering applications, it is imperative to conduct a comprehensive investigation into its soldering capabilities. This study is centered on a detailed examination of the microstructure and mechanical properties of solder joints formed between Au80Sn20 and CrCoNi through vacuum soldering. Nonetheless, the interaction between the solder and the alloy leads to the formation of an intermetallic compound layer with a specific thickness. Raising the soldering temperature results in an expanded contact area and an increase in the shear strength of the joints. This can be attributed to the enhanced diffusion and atom migration at elevated temperatures.Moreover, the hardness of the intermediate layer exceeds that of both the medium entropy alloy and the Au80Sn20 alloy. This is primarily due to the strengthening effects brought about by the presence of Ni and Co in the alloy. This study underscores the importance of thoroughly investigating soldering techniques for the medium entropy alloy. It also provides valuable insights into the mechanical characteristics and microstructure of the resulting solder joints.

Effect of gamma irradiation on microstructural evolution and mechanical properties of SnPb eutectic solder joints

Eutectic SnPb ball grid array (BGA) solder joints were exposed to 60Co source gamma irradiation at a dose rate of 1 Gy(Si)/s from 0, 50, 100, 150 and 200 h in air. The effects of gamma irradiation on the microstructure evolution and mechanical properties of the solder joints were investigated. After irradiation, β-Sn and Pb on the surface of the solder joint was oxidized to SnO2, PbO and PbO2, and an oxide layer covered with Cu oxide was formed on the surface of the solder joint. The formation process and mechanism of the oxide layer were analyzed. Sn and Pb depletion holes and Cu depletion areas appeared on the solder joint surfaces after various irradiation time. SnO2 nanocrystals and Sn wrinkles appeared in the FIB specimen after irradiation. After 200 h of irradiation, the melting temperature of the SnPb eutectic solder alloy decrease, and the shear force value of the solder joint first increase and then decrease.

Microstructure evolution and mechanical properties changes during the formation of full Cu41Sn11 joint in high-temperature electronic packaging

In this study, Cu/Sn/Cu structure under a pressure of 1.5 N was soldered at 390–450 °C. Then, microstructure evolution and changes in mechanical properties of solder joint during the formation of full Cu41Sn11 joint were systematically analyzed. Experimental results showed that Cu6Sn5 and Cu3Sn were observed in the interfacial region at 420 °C in the early stage of soldering. The Cu/Sn/Cu structure completely transformed into Cu/Cu3Sn/Cu at 1 h. With the further progress of the interfacial reaction, Cu41Sn11 appeared and grew at the expense of Cu3Sn. Eventually, the full Cu41Sn11 joint was formed at 10 h. The growth of Cu41Sn11 was controlled by volume-diffusion. Moreover, diffusion activation energy of Cu41Sn11 was about 108.19 kJ/mol. The shear strength of full Cu3Sn joints was 45 MPa, while that of the solder joints with 25, 50, 75 and 100% Cu41Sn11 was 50, 52.2, 59 and 64.5 MPa, respectively. For full Cu3Sn and full Cu41Sn11 joints, respectively, the fracture occurred partly within intermetallic compounds (IMCs) layers and partly along the Cu/IMC interface. However, for the joints composed of Cu3Sn and Cu41Sn11, all fractures occurred in the IMCs layer. Besides, all IMCs joints were brittle fracture, and the fracture of Cu3Sn was mainly intergranular, while the fracture that occurred in Cu41Sn11 was mainly transgranular.

Microstructure, wettability and strength of cryo‐deformed tin‐3.0 silver‐0.5 copper solder

AbstractThis project aims to assess the influence of cryogenic treatment prior to passing the solder sample through an equal channel angular pressing die in order to refine the microstructure of solder and thus, gain improvement of mechanical properties of solder joint. In this work, commercial tin‐3.0silver‐0.5copper solder alloy was subjected to severe plastic deformation by passing through the die for 1 pass, and prior to this, dipped in nitrogen for 10 minutes, 20 minutes and 30 minutes. Hardness and wettability of solder reflowed on bare copper substrate were measured along with strength of solder joint via lap joint shear strength test. Cryo‐deformed solder was found to have higher hardness, and wettability had also improved along with the strength of solder joint. Improvement could be due to grain refinement as observed in microstructure and also the more uniform distribution of eutectic network. Dipping for 10 minutes gave the best improvement, whereas longer dipping (20 and 30 minutes) seems to have deteriorating effect to the wettability and mechanical properties. Cryo‐deformation showed significant improvement on the wettability and mechanical properties of solder, and could potentially lead to higher reliability of solder joint.

Shear Strength Degradation Modeling of Lead-Free Solder Joints at Different Isothermal Aging Conditions

Abstract SAC-based alloys are one of the most common solder materials that are utilized to provide mechanical support and electrical connection between electronic components and the printed circuit board. Enhancing the mechanical properties of solder joints can improve the life of the components. One of the mechanical properties that define the solder joint structure integrity is the shear strength. The main objective of this study is to assess the shear strength behavior of SAC305 solder joints under different aging conditions. Instron 5948 Micromechanical Tester with a customized fixture is used to perform accelerated shear tests on individual solder joints. The shear strength of SAC305 solder joints with organic solderability preservative (OSP) surface finish is investigated at constant strain rate under different aging times (2, 10, 100, and 1,000 h) and different aging temperatures (50, 100, and 150°C). The nonaged solder joints are examined as well for comparison purposes. Analysis of variance (ANOVA) is accomplished to identify the contribution of each parameter on the shear strength. A general empirical model is developed to estimate the shear strength as a function of aging conditions using the Arrhenius term. Microstructure analysis is performed at different aging conditions using scanning electron microscope (SEM). The results revealed a significant reduction in the shear strength when the aging level is increased. An increase in the precipitates coarsening and intermetallic compound (IMC) layer thickness are observed with increased aging time and temperature.

Effect of Multiple Reflows on the Interfacial Reactions and Mechanical Properties of an Sn-0.5Cu-Al(Si) Solder and a Cu Substrate.

In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 °C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu6Sn5 IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

Influence of Ni foam/Sn composite solder foil on IMC growth and mechanical properties of solder joints bonded with solid-liquid electromigration

The effects of Ni foam addition and solid-liquid electromigration on the bonding of Cu/Sn-3.0Ag-0.5Cu/Cu joints under condition of 320 °C for 2, 4 and 8 h with the electric densities of 0, 3.33 and 6.67 × 102 A/cm2 were investigated. The results indicated that intermetallic compounds (IMCs) performed non-interfacial growth in the Cu/Ni foam/SAC305 system and were distributed in an island-like aggregation, and the asymmetric growth pattern of IMCs in both the cathode and anode sides disappeared after addition of Ni foam. In addition, the grain size of IMCs was significantly reduced and the tensile strength of the joints was enhanced by the addition of Ni foam. However, when the current density reached 6.67 × 102 A/cm2, the tensile strength of the joints containing Ni foam decreased dramatically after bonding for 8 h, this was due to the fact that IMCs grains were excessively coarse and the grain growth direction tended to be parallel to the current direction during bonding.

Growth of the nano-phase intermetallic compounds and its effect on mechanical behavior of Au80Sn20/CrMnFeCoNi solder joints during isothermal aging

High entropy alloy (HEA) like CrMnFeCoNi is deemed to be the next generation of novel structure materials because of its high strength and toughness. So it is really worth to probe the joining behavior of CrMnFeCoNi as a latent structure material. However, there are few studies on joining materials under actual service condition. In this paper, we investigated the microstructure and mechanical properties of Au80Sn20/CrMnFeCoNi solder joint after aging. The results indicate that there is no new phase in the time of aging based on XRD data. The thickness of intermetallic compound (IMC) layer aged for 360 h reaches 6.31 μm, 2.1 times larger than that of IMC without aging. Moreover, nanoscale Co3Fe7 particles grow gradually with extended aging time, reaching 560 nm at 360 h and growing nearly 1.5 times. But the Vickers hardness and shear strength decrease continuously with the extension of aging time. The results manifest the deterioration point of mechanical properties of solder joints, providing guiding significance for industrial application.

Fatigue Life Degradation Modeling of SnAgCu Solder Joints After Aging

The reliability of electronic assemblies is exceedingly reliant on the life of solder joints. Many factors may influence the fatigue life and mechanical properties of solder joints. Aging is one of the main factors that adversely affect the reliability of solder joints. In this article, the mechanical reliability of individual SnAgCu solder joints is studied at different aging conditions. The experiments include aging then cycling solder joints in stress-controlled shear fatigue at different stress amplitudes (16, 20, and 24 MPa) until complete failure. The aging conditions include three levels of aging temperatures (50 °C, 100 °C, and 150 °C) and four levels of aging time (2, 10, 100, and 1000 h). The effect of stress amplitude, aging time, and aging temperature on the fatigue life is investigated. The evolutions in the hysteresis loop, including the inelastic work dissipation, are explored by studying the stress–strain diagrams. The results showed that the fatigue life was affected by the stress amplitude, where increasing the stress by a factor of 2 leads to life reduction by a factor of 22. It was also found that increasing the aging time leads to nonlinear life reduction, where the first few hours of aging had the largest effect. Increasing the aging temperatures aggregates the aging time effect and leads to less fatigue resistance. Overall, increasing the aging time, temperature, and/or stress amplitudes leads to an increase in the work dissipation per cycle, which creates more damage and leads to less number of cycles to failure. The effect of these factors was fit into mathematical equations. Then, a general reliability model as a function of those parameters was developed.

Fabrication of Novel Ag Flake Composite Films Using a CMC/PEI Cross-Linking Process

The multifunctional properties of cross-liked carboxymethlycellulose (CMC) and polyethyleneimine (PEI) films with varied CMC:PEI ratios and Ag flake sizes were studied. Both the CMC and PEI were cross-linked through a sonication process to achieve dispersive equilibrium. Fourier-transform infrared spectroscopy (FT-IR) was used to identify the functional groups in the sample material, with thermogravimetric analysis and differential scanning calorimetry used to investigate the overall thermal behavior of the CMC–PEI cross-linked films. Thermal diffusivity and thermal conductivity were also analyzed using laser flash analysis. To analyze the effects of Ag flakes as a filler material, the distribution of the Ag flakes within the film was determined using scanning electron microscopy. The thermal conductivity and resistance of the CMC films increased when cross-linked with 20% PEI. The electrical and thermal properties of the films also improved with the addition of Ag flakes. The multifunctional properties of cross-liked carboxymethlycellulose and polyethyleneimine films with varied CMC:PEI ratios and Ag flake sizes were studied. The thermal, electrical and mechanical properties of solder joints were investigated by using various kinds of tests.

Role of alternating current shape on microstructure and damage evolution of solder joints

Motivated by recent works indicating the role of AC current on the reliability of electronic systems, the microstructural characterization and mechanical properties of solder joints, as vulnerable parts of electronic packages, under different alternating current shapes were investigated. The sine-, square- and triangle-waveform currents were considered for the experiments. The simulation results showed that the triangle shape current creates the highest thermal fluctuations and stress variations in the solder joints. This event was due to the lack of any relaxation time at the critical states, induced by triangle shape current, which leads to the intensification of stress in the solder material. On the other side, the sine- and square- currents have time to relax stresses at their peak temperatures. Moreover, it was found that the stress intensification in the solder exposed to the triangle-shape current leads to the increase of brittle intermetallic compounds and the degradation of mechanical properties. Moreover, thermal resistivity of solder joints was considered as failure indicator and found that the triangle AC current had the significant effect on the increase of thermal resistivity in the solder joint in a certain time compared with other AC current shapes.

Properties of Sn‐Ag‐Cu Solder Joints Prepared by Induction Heating

In the present work, one near‐eutectic and three hypoeutectic Sn‐Ag‐Cu alloys have been employed for soldering by induction heating. The alloys were produced by induction melting of high purity Ag, Cu, and Sn lumps. The melting behavior of the alloys was investigated by differential scanning calorimetry. The solder alloys were subsequently applied for soldering by conventional hot‐plate heating as well as induction heating and both soldering times and peak temperatures were recorded during soldering. Solder joints of two copper sheets were produced. The electrical resistance, tensile strength, and microstructure were analyzed on each soldered joint. The results indicate that the physical and mechanical properties of solder joints are determined by their chemical composition and soldering technology. Induction soldered joints not only have a slightly higher electrical resistivity but also higher mechanical strength, except of the 0.3 wt.% Ag hypoeutectic solder. The highest increase in ultimate tensile strength (28%) was observed for induction soldered joints with 1 wt.% Ag hypoeutectic solder. This effect is ascribed to the homogenous distribution of the intermetallic compounds within the eutectic in the alloy microstructure. The homogenous distribution is aided by rotation of liquid solder due to eddy currents and high‐frequency magnetic field generated during induction heating.

Characterization of ultrasonic soldering of Ti and Ni with Ni/Al reactive multilayer deposition

The joining of Ti and Ni at low temperatures was analysed in this work. For joining pure Ti and Ni coins of 1.5 mm in thickness were used. Reactive multilayer thin films/foils with nanometric period (bilayer thickness), in particular Ni/Al multilayers, have been used to promote joining in two thickness of 28 and 55 nm. The ultrasonic soldering with SnAgTi active solder has been used for “hard-to-solder” material. The structural evaluation of soldered joint was studied by optical microscopy and EDX analysis. The structural analysis was focused to the creation of intermetallic layers in the joint interface. The mechanical properties of solder joints were tested by shear strength.

The effects of Ni addition on microstructure evolution and mechanical properties of solder joints undergoing solid-liquid electromigration

The effect of solid-liquid electromigration on Cu-xNi/Sn-3.0Ag-0.5Cu/Cu-xNi (x = 0, 1.5 and 5 wt%) joints bonded at 260 °C with electric density of 2.89 × 102 A/cm2 was investigated. The results showed that intermetallic compounds (IMCs) performed a non-interfacial growth in the Cu-5Ni/SAC305 system. The electron backscatter diffraction (EBSD) analysis revealed that the orientation of the Cu6Sn5 [1 0 0] direction parallelled to the direction of electric current, however, the addition of Ni could induce that the growth of (Cu,Ni)6Sn5 grain exhibited isotropy. Additionally, the additional Ni resulted in significant reduction in grain size and enhancement in the tensile strength of joints.

Investigations on elastic properties and electronic structures of α-CoSn3 doped with Ni via first-principles calculations and nano-indentation measurements

The low-temperature α-CoSn3 intermetallic compound (IMC) doped with Ni is an important component at the interface between Sn-based solder and printed circuit boards, which largely controls the mechanical properties of solder joints. However, the structure and elastic properties of α-CoSn3 doped with Ni are not well understood. In this work, first-principle calculations and nano-indentation have been performed to explore the influences of additional Ni on elastic properties of α-CoSn3 IMC. By means of nano-indentation, the Young’s modulus and hardness were recorded for α-CoSn3 and α-(Co,Ni)Sn3 to be 149.9 ± 8.6 GPa and 6.14 ± 0.96 GPa, and 142.5 ± 7.6 GPa and 5.84 ± 0.76 GPa, respectively. Systematic works of first-principle calculations indicated that the doped Ni weakened the mechanical properties while strengthened the ductility and elastic anisotropy of α-CoSn3. The calculated electronic structures demonstrated that the bonding energies of α-CoSn3 were obviously decreased with the doping of Ni, which led to the degeneration of mechanical properties.

Influence of Ni and Cu electrodeposits on the interfacial reaction between SAC305 solder and the Bi2(Te,Se)3 thermoelectric material

This research systematically investigated three joint systems (SAC305/Bi2(Te,Se)3, SAC305/Ni/Bi2(Te,Se)3 and SAC305/Cu/Bi2(Te,Se)3) and compared the influence of Ni and Cu electrodeposits on the interfacial reaction. The thermoelectric material possessed an isotropic microstructure, and hence its surface had no significantly effects on deposited direction of Ni or Cu atoms. The crystal orientations of Ni and Cu grains were indexed to be (111) and (200), and no noticeable impure products were formed in these two electrodeposits. Compared with the defective Cu plating, fully crystallization of the Ni plating was more beneficial to the spreadability of solder, and this advantage could dramatically promote the reliability of solder joints. Under aging treatment at 160 °C for various hours to 360 h, heterogenetic compounds grew excessively in the SAC305/Bi2(Te,Se)3 couple, which could result in brittle failure. This reliability of this joint system was improved by depositing Ni or Cu on the substrate. However, the poor interfacial contact between the Cu coating and TE substrates severely resulted in the deterioration of mechanical properties of solder joints. In contrast, the SAC305/Ni/Bi2(Te,Se)3 system were more reliable during the whole aging period.

Dependence of shear strength of Sn–3.8Ag–0.7Cu/Co–P solder joints on the P content of Co–P metallization

The mechanical properties of solder joints highly depend on the interfacial reaction between the solders and the metallization on substrates. In this work, we electroplated Co–P films with various compositions on the Cu pads of printed circuit boards and fabricated Sn-3.8 wt% Ag-0.7 wt% Cu/Co–P ball grid array (BGA) solder joints. The BGA solder joints were annealed at 150 °C for 100, 200, 500, and 1000 h and the shear strength of these joints was measured. When the P content of the Co–P metallization was increased from 2.3 to 18.8 at.%, the shear strength after 1000 h annealing initially rose to 107.9 MPa at a P content of 8.5 at.%, then decreased to 84.3 MPa at a P content of 12.5 at.%, and again increased to 96.0 MPa at a P content of 18.8 at.%. The enhancement of the shear strength of the joints with Co-8.5 at.% P, Co-12.5 at.% P, and Co-18.8 at.% P films was 109.5%, 63.7%, and 86.4% in comparison to the joints without Co–P metallization, respectively. The interfacial reaction between the Sn–Ag–Cu (SAC) solder and Co–P films during annealing and the fractured surfaces of the solder joints after the shear test were studied. For the joints with Co-8.5 at.% P and Co-18.8 at.% P films, a thick layer of CoSn3 was formed at the interfaces during annealing, which enhanced the shear strength. For the joints with Co-12.5 at.% P metallization, a thin layer of Co–Sn–P was formed at the interfaces and was peeled off layer by layer with prolongation of the annealing time. The spalled Co–Sn–P was mixed with the solder matrix, increasing the shear strength of the solder joints. The shear strength of the SAC/Co-12.5 at.% P joints was less than that of the joints with Co-8.5 at.% P and Co-18.8 at.% P films because no CoSn3 formed. Therefore, the composition of Co–P metallization played an important role in the interfacial reaction of the SAC/Co–P solder joints, which in turn affected the shear strength of the solder joints. Our experimental results show that the electroplated Co–P film is a promising candidate as the metallization for BGA solder joints.

Critical Review of Size Effects on Microstructure and Mechanical Properties of Solder Joints for Electronic Packaging

With the miniaturization of electronic packaging and devices, the size of solder joints in electronics is also decreasing from bulk solder joints to micro-bumps. Both the microstructure and mechanical properties of the solder joints are also evolving with the decreasing size, which brings great concern for the reliability of different sizes of solder interconnections. In this paper, the effect of solder size on the microstructure (i.e., interfacial intermetallic compound (IMC) growth, precipitation in the solder matrix, dendrite arms, and undercooling) and mechanical properties (i.e., tensile property, shear and compression strength, fracture toughness, and creep deformation) are reviewed from the mechanical point of view. In addition, some areas for further researches about size effects on solder joints are discussed.

Effect of gamma-ray irradiation on microstructure and mechanical property of Sn63Pb37 solder joints

In order to meet the reliability requirement of solder joints for future small satellite, the effect of γ-ray irradiation on the microstructure and mechanical property of Sn63Pb37 solder joints was investigated by scanning electron microscope observation and mechanical testing. The results showed that γ-ray irradiation possessed few influence on the thickness and morphology of intermetallic compound layer of Sn63Pb37/Cu. But the mechanical properties of solder joints were reduced with micro-voids and micro-cracks appearing in Pb-based solid solution during irradiation process. Energetic electrons created by γ-ray through Compton Effect, generated dislocated atoms which eventually resulted in the formation of microscopic defects and the decrement of mechanical property. After 960 h γ-ray irradiation at the dose rate of 0.25 Gy(Si)/s, the shear force of Sn63Pb37 solder joints was decreased by 11.47%. Compared with as-soldered joint, the ductility of irradiated solder joints was reduced with more unobvious shear dimples and lower impact toughness.