Properties Of Solder Joints Research Articles

Effects of soldering temperatures and composition on the microstructures and shear properties of Sn58Bi-xSAC0307/ENIG solder joints

PurposeThis paper aims to systematically study the effects of reflow temperature and SAC0307 (SAC) content on the micromorphology and mechanical properties of Sn58Bi-xSAC0307 composite solder joints to meet the requirements of high integration and low-temperature packaging of devices and provide references for the application of composite solder joints.Design/methodology/approachSn58Bi and SAC0307 solder paste was mechanically mixed in different proportions to prepare Sn58Bi-xSAC0307/ENIG solder joints. The thermal properties, microstructure and mechanical properties of the composite solder joints were studied.FindingsAs SAC content in the solder increases, the balling temperature of SnBi-SAC solder gradually increases. The addition of SAC alloy reduces the grain size of large Bi-rich phase, and there are small-sized dispersed Bi and Ag3Sn particles in the bulk solder. The intermetallic compounds composition of the SnBi-xSAC/ENIG solder joint changes from Ni3Sn4 to (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 with SAC increasing. As the soldering temperature increases, the strength of all solder joints shows a rising trend. Among them, the shear strength of SnBi-20SAC solder joints at a reflow temperature of 150°C is approximately 37 MPa. As the reflow temperature increases to 250°C, the shear strength of solder joints increases to approximately 67 MPa.Originality/valueThis study provides a reference for the optimization of low-temperature solder composition and soldering process under different package designs.

Effects of TiC nanoparticle addition on microstructures and mechanical properties of Sn-58Bi solder joints

The Sn58Bi solder has gained significant attention in the electronic packaging industry owing to its low melting temperature and excellent mechanical properties. However, the brittleness of Sn58Bi solder presents challenges in practical applications. This study investigates the effect of adding titanium carbide (TiC) nanoparticles on the mechanical properties of Sn58Bi solder joints. The study examines the melting behavior, spreadability, microstructure, and mechanical properties of Sn58Bi-xTiC (x = 0, 0.05, 0.1, 0.2 wt%) composite solders. The results indicate that adding TiC nanoparticles has merely a minor effect on the melting point of the Sn58Bi solder. However, the presence of TiC nanoparticles refined the solder’s microstructure, reduced the thickness of the intermetallic compounds, and enhanced the spreadability and mechanical properties. The Sn58Bi-0.1TiC composite solder exhibits the most favorable properties, including a 28.6 % increase in fracture energy compared with that of Sn58Bi solder. Consequently, incorporating TiC nanoparticles enhances the performance of the Sn58Bi solder by improving its spreadability and reducing its brittleness. These results hold great potential for advancing the development of lead-free solders with improved reliability and performance in electronic applications. The findings of this study could pave the way for the practical and widespread use of Sn58Bi-xTiC composite solders, offering a viable alternative to lead-containing solders while maintaining excellent mechanical characteristics.

The Effect of Thermal Aging on the Mechanical Properties of Gold-Containing Solder Joints

The Effect of Thermal Aging on the Mechanical Properties of Gold-Containing Solder Joints

Micromechanical and microstructure evolution of leaded (SnPb) and lead-free (SAC305 and SnCu) mixed solder joints during isothermal aging

This paper studies how isothermal aging affects the micromechanical and structural properties of mixed solder joints made of 60Sn-40Pb (SnPb) with Sn-3.0Ag-0.5Cu (SAC305) and SnPb with Sn-0.7Cu (SnCu). The nanoindentation test was done to measure the micromechanical properties of SnPb/SAC305 and SnPb/SnCu mixed solder joints. These properties are hardness, reduced modulus, and stress exponent. Scanning electron microscopy (SEM) was used to look at the microstructure of a cross-section of mixed solder joints. The micrographs that were taken were then examined with open-source image processing software called ImageJ. It was found that the rate and distribution of intermetallic compound (IMC) formation and the reduction of Sn-rich phase grain size affect how the hardness and stress exponent values of mixed solder joints change after 1000 h of high temperature storage (HTS). ImageJ analysis shows that the Pb-rich phase particle count and distribution can be used to figure out how mixed solder joints respond to indentation creep and how that relates to isothermal aging. Using ImageJ, it’s clear that the indentation creep behavior of the GBS mechanism of an as soldered SnPb/SnCu mixed solder joint is caused by the highest number and size of Pb-rich phase particles that are not well distributed across the dendritic area of Sn-rich phase grain boundaries.

Improved shear property of Sn-3.0Ag-0.5Cu/Ni micro solder joints under thermal shock between 77 K and 423 K by adding TiO2 nanoparticles

The rapid development of space exploration technology was intensifying the desire for lead-free solders with high performance and reliability under extreme temperature environments. In this study, the influence of TiO2 nanoparticle addition on the microstructure, growth behavior of interfacial intermetallic compounds (IMCs) and shear property of Sn-3.0Ag-0.5Cu (SAC305)/Ni micro solder joints under thermal shock from 77 K to 423 K was systematically investigated. The results indicated that the grain size of β-Sn, IMC (Ag3Sn and (Cu,Ni)6Sn5) particles inside the solder was refined by adding 0.05 and 0.1 wt% TiO2 nanoparticles. Due to the spalling of interfacial IMCs into the solder occurring in all micro joints during thermal shock, the thickness of interfacial IMCs did not show a monotony increasing trend with increasing thermal cycles. However, the micro composite solder joint added with 0.05 and 0.1 wt% TiO2 nanoparticles always exhibited thinner interfacial IMC thickness and higher shear force compared with the plain micro joints during thermal shock. The inhibiting effect of TiO2 nanoparticles on the interfacial IMC growth could be explained by the adsorption theory and grain boundary pinning theory. The improvement in shear property of micro composite solder joints was primarily induced by the refinement of IMC particles in the solder and the reduced growth rate of interfacial IMCs by adding TiO2 nanoparticles.

Strong composite SnAgCu solder joints with internal aligned carbon fibers by magnetic field

Lightweight carbon fibers with high mechanical performance are referred to as an ideal reinforcement for an extensive variety of composite materials. However, the addition of carbon fibers into electronic interconnection solders is extremely limited so that the expected reinforcement in the mechanical properties of the composite solder joints has not been completely realized. Here, we used magnetic fields to align Ni-coated carbon fibers in the Sn-3.0Ag-0.5Cu solder vertically with the Cu substrate and prepared the oriented composite solder joints. We achieved a further improvement in the shear performance of composite solder joints (∼58 MPa) with a small addition of Ni-coated carbon fibers (0.5 wt%), which is 25% higher than that of pristine joints. It is found that these vertically oriented carbon fibers changed the propagation path of shear cracks and thus increased the shear resistance. Ni-coated carbon fibers also promoted nucleation of interfacial Cu6Sn5 in the solder joints during reflow, but prevented the formation of brittle Cu3Sn phase during isothermal aging, thus ensuring the high shear strength of composite solder joints after isothermal aging. This success provides a new pathway to fabricate a strong composite solder joint with a limited addition of reinforcements by aligning their orientation.

Effect of Nano-Cu6Sn5 upon development mechanism of Cu–Ni–Sn compounds and mechanical characteristics for mixed solder joints

This investigation aimed to examine the development mechanism of Cu–Ni–Sn compounds and analyze the mechanical properties of mixed solder (MS) joints. Results show that an intermetallic compound (IMC) layer was formed in an SAC305 solder joint prepared herein comprising (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 phases following the reflow process. The morphology of the (Cu, Ni)6Sn5 grains was identified to be dodecahedral. Meanwhile, the IMC layer of the prepared MS joints contained only the (Cu, Ni)6Sn5 phase, which exhibited a hexagonal prism morphology. The lattice characteristics of Cu6Sn5 changed after Ni dissolution, forming (Cu, Ni)6Sn5 crystals with an X-shaped morphology in the MS joints that exhibited a high Cu content during the aging process. After reflow, the MS joints exhibited slightly higher shear strength than the SAC305 solder joint. After aging at 165 °C for 1000 h, the shear strength of the SAC305 solder joint reduced by 21.72% compared to its value after reflow owing to the annexation of Sn grains. However, the number of Sn grains in the MS joints did not considerably decrease after aging. Further, the grain boundaries of β-Sn and (Cu, Ni)6Sn5 particles contributed to the strengthening of the MS joints. The shear strength of the MS joints decreased by 11.06%–18.35% after aging.

3D CT scan metrology for solder void formation analysis in ball grid array electronic chips

The miniaturization of silicon chips and the complexity of device functionality has driven the electronic packaging industry to find new methods to enhance the reliability of chips at a smaller size. Solutions such as Ball Grid Array (BGA) packages have contributed to the miniaturization of integrated circuits (ICs) and the reduction in their overall size. However, void formation in the solder joint is a weakness that can affect the robustness of the solder joint integrity, both mechanically and electrically. To detect these voids, metrology methods such as 3D Computed tomography (CT)-scan are used. 3D CT-scans can identify submicron-sized void defects in real-time during thermal tests, which can be utilized to help improve the quality control lines in the electronic chip manufacturing industries. In this paper, two types of BGA packages will be evaluated for solder joint properties. The prepared samples will be subject to high temperature stress conditions to assess the mechanism of void formation in solder joint. The prepared samples will be heated at 260 °C four times where the heating lasts 0, 5, 10, and 15 min, respectively. The prepared samples will be mounted on a PCB board and the results of the thermal stress tests will be analyzed using 3D X-ray CT scans. These 3D-CT scans used in tandem with a reconstruction and visualization software suite, will be utilized to observe changes such as void formation in the solder joint after each heating time. Unexpectedly, void size reduced between the first and second heat cycles on both samples but increased for the third and fourth heat cycles then.

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.

Influence of Isothermal Aging on Microstructure and Shear Property of Novel Epoxy Composite SAC305 Solder Joints.

With the rapid iteration of microsystem integrated technology, the miniaturization of electronic devices requires packaging materials with higher reliability. In this work, the microstructure evolution and mechanical properties of novel epoxy composite SAC305 solder joints were studied after isothermal aging to evaluate the enhanced effect of epoxy addition. The thickness variation and morphological evolution of the interfacial layer were analyzed. The results showed that, as the aging time was prolonged, the Cu6Sn5 interfacial layer remarkably coarsened and Cu3Sn compounds formed between the Cu6Sn5 layer and Cu pad due to the continuous atomic diffusion. Compared with the monolithic joint, the epoxy composite SAC305 joints had a lower overall IMC growth rate during aging, closely related to the initial morphologies of the interfacial layers. The shear test results showed an apparent decrease in the shear forces of all the solder joints as the aging time increased. Nevertheless, because of the extra mechanical support provided by the epoxy layer, the epoxy composite joints demonstrated notably enhanced mechanical properties. After 1000 h aging treatment, the shear force of SAC305 joints containing 8 wt.% epoxy was 26.28 N, showing a 24.08% increase over the monolithic joint. Cu-Sn IMCs were detected on the shear fracture of the monolithic joint after 1000 h aging, indicating the fracture occurred near the interface and displayed a ductile/brittle mixed fracture. Concerning the epoxy composite joints, cracks were still initiated and extended within the solder bulk, demonstrating a noticeable enhancement in ductility due to the addition of epoxy.

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.

In-situ delamination detection in multi-layered semiconductor packages

Accurately determining the material properties of large-area solder joints is crucial for developing precise lifetime models in modern power electronic devices, as these joints play a vital role in providing both electrical and mechanical connections between components. This study presents a novel, non-destructive, and in-situ technique based on laser Doppler vibrometry for detecting crack initiation and monitoring crack growth in semiconductor structures. This method was successfully applied to determine various stages of die attach degradation during accelerated mechanical cyclic tests of large area solder joints, and was verified by scanning acoustic microscopy (SAM) measurements as well as optical methods. Furthermore, analysis of the acoustic emission (AE) signal was conducted as an alternative method for monitoring crack propagation. Optical and electron microscopy were employed to analyse crack initiation, crack paths, and crack surface morphologies. The in-situ delamination detection technique can provide essential information for robust lifetime prediction modelling of material systems in advanced semiconductor components.

Solder Joint Degradation and Electrochemical Metallic Ion Migration Property of Solder Joints with Surface Finish

To confirm the degradation property of solder joints by substrate surface finish, chip resistors are reflow soldered to organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG) finish substrate in a nitrogen atmosphere using the type 6 Sn-3.0Ag-0.5Cu (SAC305) solder paste. To confirm the electrochemical metallic ion migration (ECM) sensitivity with and without photo solder resist (PSR) ink-coated printed circuit board (PCB), comb patterned test vehicles were prepared by the hot air reflow soldering process in nitrogen atmosphere, and the SAC305 solder paste was printed on the conductor of the ECM test PCB. The ECM test was conducted under high temperature and high humidity conditions of 85℃ and 85% RH, respectively. As a result of measuring the void content of the 2012 chip resistor, the average void content of the OSP substrate was higher than that of the ENIG substrate. The thermal shock test (TST) indicated that the degradation rate of the OSP substrate was higher than that of the ENIG substrate. Microstructure analysis showed that the OSP substrate had more crack propagation and thicker intermetallic compound (IMC) thickness than the ENIG substrate. The ECM test revealed that the substrate with PSR-coated PCB coupon generated more dendrites than that without PSR-coated coupon. Because the PSR coated substrate decreased the moisture absorption into the substrate, moredendritesweredeterminedtobe generated.

Effect of Trace Boron Nitride Nanoparticles on the Microstructure and Shear Properties of Sn58Bi Solder Joint

Effect of Trace Boron Nitride Nanoparticles on the Microstructure and Shear Properties of Sn58Bi Solder Joint

Microstructure and mechanical properties of Sn-xGa alloys and solder joints

Though Ga is a promising addition used in third-generation lead-free solders for harsh-environment applications, its influences on βSn structure and mechanical properties of solder alloys/joints are still unknown. This study demonstrated that Ga additions in Sn-XGa (X = 0.5, 1.0, 2.0 in wt%) can moderately refine βSn grains but render the alloys more susceptible to recrystallization during cross-section and polishing. Sn-1.0Ga shows substantially elevated yield/tensile strengths (45.1 MPa/64.9 MPa) compared with pure Sn, attributed to the strong solid-solution strengthening effect of Ga, and it also possesses good tensile ductility of >25%. Compared with pure Sn and Sn-3.0Ag-0.5Cu (SAC305) solder joints on Cu, Sn-XGa/Cu solder joints show significantly reduced dissolution of Cu substrate that benefits in suppressing the formation of primary Cu6Sn5. Among Sn-XGa/Cu, Sn-2.0Ga/Cu joint exhibits high shear strength (69.4 MPa) comparable to that of SAC305/Cu joint (70.5 MPa), owing to the Ga solid-solution strengthening and the extra second-phase strengthening from Cu9Ga4.

Effect of Cu on the diffusion behavior of Bi in Sn matrix during electromigration

The segregation of Bi phase during current stressing deteriorates the mechanical property of Sn-58Bi solder joint. To improve the reliability of Sn-58Bi solder joint, a thorough understanding of the diffusion behavior of Bi elements is necessary. In this study, a Cu/SnBi/Sn-xCu/SnBi/Cu multi-layer solder joint structure was adopted to reveal the diffusion path of Bi element and the effect of Cu on the diffusion behavior of Bi during electromigration. The result showed that the Bi element diffused along the grain boundary. The presence of Cu had two competing mechanisms on the diffusion of Bi: it slowed the process by forming Cu6Sn5 intermetallic compounds that blocked and prolonged the diffusion path, yet also accelerated it by refining the Sn and creating more diffusion channels. A data processing method was used to estimate the diffusion rate of Bi and determine the dominant mechanism. The results indicated that the diffusion rate was accelerated by Cu doping, confirming that the dominant mechanism was the refining effect, which promoted the diffusion of Bi element.

Effect of temperature on the low cycle fatigue properties of BGA solder joints

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature.

Reliability and prediction of Sn36Pb2Ag solder joints under thermal aging test

In this work, the capacitor solder joints were aged at 50 °C, 75 °C, 100 °C, 125, and 150 °C from 100 h to 1000 h. The intermetallic compounds (IMCs) layer growth of Sn36Pb2Ag on hot air solder leveled (HASL) pad and electroless nickel/immersion gold (ENIG) pad was measured. Based on the empirical power-law of the IMC growth and the Arrhenius relationship between diffusion coefficient and aging temperature, a method to predict the IMC growth at a selected temperature was developed. The mechanical property of capacitor solder joints after thermal aging was investigated through the shear test. Through analysis of the fracture surface, the mixed fracture mode of ductile and brittle was exhibited. The porous structure of the Cu coating on the capacitor electrode was determined to be the origin of the crack.

Effects of Cu foam on microstructure and mechanical properties of SAC305 solder joints bonded with solid–liquid electromigration

Effects of Cu foam on microstructure and mechanical properties of SAC305 solder joints bonded with solid–liquid electromigration