Behavior Of Solder Research Articles

Effect of ultrasonic vibration on the wetting behavior of molten tin on copper substrate

The wetting behavior of molten tin solder on copper substrate under ultrasonic vibrations was investigated by the wetting balance method at 250 °C. The cross-section morphology and microstructure of the specimen were analyzed after the wetting test. The grain size and thickness of intermetallic compounds (IMCs) at the interface were measured by an image-pro software. The ultrasonic sound pressure distribution in the molten tin solder was simulated by finite element analysis. The results showed significant effect of ultrasonic vibrations on the wettability of the molten tin solder on the copper substrate. The wettability was conjunctively determined by the driving and additional forces caused by an interfacial reaction and acoustic streaming, respectively. Acoustic cavitation expedited the interaction of interfacial atoms and facilitated the interfacial reaction, resulting in an increased driving force that contributed to the spreading of the molten tin solder on the copper substrate.

Effect of Joint Design to In–Situ Observation Results of Molten Solder Behavior

Effect of Joint Design to In–Situ Observation Results of Molten Solder Behavior

Thermal behaviour and microstructural analysis of Sn-40Pb alloy and Sn-40Pb soldered on electroless nickel/immersion gold

Due to the toxicity of lead solder, the lead-free solder has been developing and improved in order to replace the lead solder. However, the behaviour and properties of lead solder is still better than the lead-free solder, especially in application when soldering on substrate. Hence, a common lead solder, Sn-40Pb is studied in this research by comparing with Sn-40Pb soldering on electroless nickel/immersion gold (ENIG) substrate. The thermal behaviour by differential scanning calorimeter (DSC) and microstructure formation with elemental analysis by scanning electron microscope (SEM) were carried out for Sn-40Pb solder alloy and Sn-40Pb soldered on ENIG substrate in this study. The result showed that the pasty range of Sn-40Pb was lower than Sn-40Pb/ENIG while the undercooling was higher. The diffusion and dissolution of Ni and Cu elements from ENIG substrate into the solder, forming the lead-rich phase with Ni elements and interfacial (Cu,Ni)6Sn5 with Pb elements in Sn-40Pb/ENIG. The diffusion and dissolution of elements from substrate into the solder affects the thermal behaviour and microstructural of solder.

Nanoindentation creep properties of lead-free nanocomposite solders reinforced by modified carbon nanotubes

In this research, creep properties and thermal behavior of Sn-3.5Ag-0.7Cu (SAC)/multi-walled carbon nanotubes (MW-CNTs) lead-free nanocomposite solders was studied by conducting the nanoindentation testing at different temperatures, in the range of 292–312 K. Solder materials were prepared by mechanical alloying followed by powder consolidation routes. Furthermore, nickel coating was electro-less plated on the surface of nanotubes to enhance their metallurgical compatibility with the SAC solder matrix. The content of Ni-coated MW-CNTs varied in the range of 0–0.2 wt%. Addition of Ni-coated nanotubes resulted in an improvement of the indentation creep behavior of SAC solder alloy in comparison with the non-coated agents. By increasing the fraction of Ni-coated MW-CNTs up to ~0.1 wt%, the creep resistance of solder nanocomposite was continuously enhanced. However, the higher contents of reinforcing agents led to the deterioration of creep behavior due to the aggregation of nanotubes and a considerable heterogeneous refinement of the microstructure. The activation energy for softening during localized deformation behavior of nanocomposite solders was estimated by two approaches based on Dorn constitutive and Lucas-Oliver creep models and found to be in the ranges of 8.8–18.2 kJ/mol and 17.3–48.4 kJ/mol, respectively. By changing in the activation energy for diffusion and sliding of grain boundaries, in dependency with the extent of grain structural refinement and generation of dislocations due to altering the content of nanotubes as the reinforcing agent, the time-dependent under-loading deformation phenomenon in terms of creep can be controlled. The experimental results revealed that modified carbon nanotubes which are located on sub-grain boundaries can reduce their chemical potential tremendously, suppress the sliding-based creep deformation up to an optimized content of ~0.1 wt%.

In-situ EIS study on the initial corrosion evolution behavior of SAC305 solder alloy covered with NaCl solution

The corrosion performance of SAC305 solder joints is closely related to the working efficiency and life-span of electronic devices. Available studies on corrosion of SAC305 solder have seldom concentrated on its initial corrosion evolution behavior, which is critical in understanding its corrosion behavior in the long run. In this work, comb-like electrodes have been designed for in-situ EIS measurements to investigate the initial corrosion evolution process of SAC305 solder covered with 3.5 wt.% NaCl solution, and Raman, XRD, SEM and EPMA have also been employed to characterize the formed corrosion product layer. The results indicate that the initial corrosion evolution behavior of SAC305 solder mainly involves four stages, i.e. the corrosion degradation of the pre-existing SnO2 protective film in a short duration in contact with NaCl solution, the anodically dissolved Sn2+ undergoes hydrolysis under the effect of Cl− in electrolyte to form stannous hydroxychloride intermediates of various structures, the formation of Sn3O2(OH)2 from stannous hydroxychloride intermediates after Cl− releasing, and finally the formation of nano-SnO2 particles from Sn3O2(OH)2 after steps of dehydration and oxidation. Meanwhile, the acidified NaCl electrolyte can make the formed SnO2 slightly dissolved and favors the formation of SnCl4·4H2O crystals. These findings clearly demonstrate the initial corrosion evolution behavior and corrosion product formation mechanism of SAC305 solder, and are expected to provide potential guidelines on maintenance of microelectronic devices in marine atmosphere.

Removal of Oxide Film and Wetting Behavior of Sn9Zn–xSiC Composite Solder on 6061 Aluminum Alloy with Activated Organic Water-Soluble Flux

The effect of Sn9Zn–xSiC composite solder on the wetting and soldering behavior of 6061 aluminum alloys is investigated using a kind of new water-soluble organic flux through optical and electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The oxide film of 6061 aluminum alloys during the soldering process is composed of three-layer structure of different components, which are followed MgAl2O4, Al2O3 and Al from the outside to the inside. The flux removes the oxide film by the dissolution reaction. A solid solution layer can be developed by undergoing displacement reaction with the Al-rich phase. With the increasement of SiC micron particle content, the spreading area of the composite solders increases firstly and then decreases. When the weight percentage of SiC micro-particles in the composite solder was 0.75%, the spreading area reached the maximum value, which increased by 38.9% compared with Sn9Zn–0.25SiC composite solder.

Wetting behavior and vacuum soldering of novel Au-30Ga solder on Ni and Cu substrate

As a novel high-temperature solder with suitable eutectic temperature and high thermal conductivity, Au-30Ga solder is expected to be used in high-power device packaging. This research provides a timely and necessary study of its solderability. The wetting behavior and reactivity of Au-30Ga solder on Cu and Ni substrates was investigated through spreading tests in vacuum. The favorable wetting property of Au-30Ga solder on Ni and Cu substrate was observed. However, fundamental differences in the wetting behavior of liquid Au-30Ga alloy in contact with Ni and Cu substrates were immediately apparent. Their behavior changed from reactive wetting, characterized by formation of two thin Ni–Ga compound layers and a wide wetting ring, to dissolutive wetting, characterized by formation of a thick (Au, Cu)9Ga4 interface layer. Moreover, significant signs of solidification shrinkage of liquid solder are observed on the surface of wetting ring for the first time, which provides direct evidence for the formation mechanism of wetting ring. The wetting ring also reveals the microstructure of the Ni–Ga compounds during ripening. In addition, the soldering performance was evaluated by the shear strength of solder joints. The findings presented in this thesis add to understanding of solderability of the high-temperature Au-30Ga solder.

Solidification Behaviour of Sn-40Pb Lead Solder and Sn-0.7Cu Lead-free Solder

Lead-free solder, especially Sn-0.7Cu has been evolving due to the restriction of the lead solder usage which is environmental and health unfriendly. However, most of the lead solder properties show a better result compared to the lead-free solder. To further improve the properties of lead-free solder, the solidification state of Sn-40Pb and Sn-0.7Cu, which is one of the important behaviour in thermal analysis that affects the solder properties and performance, was investigated and compared in this study by natural cooling curve method. The result showed that Sn-40Pb has two nucleation phase while Sn-0.7Cu has only one during the solidification. The primary lead-rich phase was first nucleated in Sn-40Pb following by the secondary tin-rich phase when cooling; while the phase of Cu6Sn5 was nucleated in Sn-0.7Cu. In addition, it is found that the undercooling of Sn-40Pb is lower than Sn-0.7Cu in the cooling curve.

Evaluation of creep properties for aged Pb-free solder joints/(Ni-P/Au) UBM with small addition Cu using shear punch creep testing method

The creep mechanical and physical properties of solder joints play an important role to ensure the service life of electronics products. In this paper, we investigated the creep properties of Pb-free Sn-4Ag and Sn-4Ag-0.5Cu (small additions Cu) solder joints on Ni-P/Au under bump metallization (UBM) using the shear punch creep test (SPCT) method at 30 °C. These results have been compared with the Pb-based Sn-37Pb solder joint after isothermal aging (150 °C) according to different times. In order to analyze the result of SPCT, the specific methods (i.e., Power-law relationship, Larson-Miller law and Monkman-Grant correlation) were used. Through the Power-law relationships, the stress exponents (n) of the Pb-free solder were higher than the Pb-based solder and generally, (n) value decreased with increasing aging time. Also, according to Larson-Miller law, the Pb-free solder joints revealed superior mechanical properties. The Monkman-Grant exponent (m) value of three solder joints which analyze by Monkman-Grant correlation is proximately 1. Furthermore, the failure fracture surface behavior of solder was investigated using scanning electron microscopy (SEM). Elongated dimple-like structures were detected on the fracture surfaces of all as-soldered (aging time 0 h) samples, but these gradually decreased with increasing aging time. The results indicated that the creep properties of Pb-free solder were better than Pb-based solders, and the Sn-4Ag-0.5Cu solder joint showed the best creep mechanical properties.

Microstructure induced galvanic corrosion evolution of SAC305 solder alloys in simulated marine atmosphere

Motivated by the increasing use of Sn-3.0Ag-0.5Cu (SAC305) solder in electronics worked in marine atmospheric environment and the uneven distribution of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in β-Sn matrix, comb-like electrodes have been designed for in-situ EIS measurements to study the microstructure induced galvanic corrosion evolution of SAC305 solder in simulated marine atmosphere with high-temperature and high-humidity. Results indicate that in-situ EIS measurement by comb-like electrodes is an effective method for corrosion evolution behavior study of SAC305 solder. Besides, the galvanic effect between Ag3Sn IMCs and β-Sn matrix can aggravate the corrosion of both as-received and furnace-cooled SAC305 solder as the exposure time proceeds in spite of the presence of corrosion product layer. Pitting corrosion can be preferentially found on furnace-cooled SAC305 with larger Ag3Sn grain size. Moreover, the generated inner stress during phases transformation process with Sn3O(OH)2Cl2 as an intermediate and the possible hydrogen evolution at local acidified sites are supposed to be responsible for the loose, porous, cracked, and non-adherent corrosion product layer. These findings clearly demonstrate the corrosion acceleration behavior and mechanism of SAC305 solder, and provide potential guidelines on maintenance of microelectronic devices for safe operation and longer in-service duration.

Thermal behaviour and microstructural analysis of Sn-0.7Cu alloy and Sn-0.7Cu soldered on electroless nickel/immersion gold

Lead-free solder has been developing since decades due to the environmental and health harmful of lead solder. To compete with the lead solder, the behaviour and properties of lead-free solder have been continually researched and improved. Sn-0.7Cu is one of the most common solder in application and suitable to be used as a control in research. The thermal behaviour by differential scanning calorimeter (DSC) and microstructure formation with elemental analysis by scanning electron microscope (SEM) of Sn-0.7Cu solder alloy was compared to Sn-0.7Cu soldered on electroless nickel/immersion gold (ENIG) substrate in this study. The result showed that the pasty range of Sn-0.7Cu was lower than Sn-0.7Cu/ENIG while the undercooling was higher. Primary and interfacial (Cu,Ni)6Sn5 were formed in Sn-0.7Cu/ENIG due to the diffusion and dissolution of elements from ENIG substrate. The β-Sn dendrites and eutectic phase of Sn-0.7Cu/ENIG was coarser than Sn-0.7Cu due to the decreasing of undercooling.

Effect of graphene nano-sheets additions on the density, hardness, conductivity, and corrosion behavior of Sn–0.7Cu solder alloy

Graphene nano-sheets (GNSs) are considered a functional (excellent/good) material at solder alloy modification. In this study, GNSs were doped into Sn–0.7Cu solder by powder metallurgy to form Sn–0.7Cu–xGNSs (x = 0.025, 0.05, 0.075, 0.1 wt%) composite solders. The density, hardness, and electrical conductivity of the composite solders were investigated. At the same time, Potentiodynamic polarization method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were applied to analyze the electrochemical corrosion behavior of composite solders in the 3.5 wt% NaCl solution. The results revealed that as the content of GNSs increased, the hardness of composite solders decreased, but the density enhanced when compared with original Sn–0.7Cu. Simultaneously, the conductivity reached highest as the GNSs content was 0.025 wt%. Potentiodynamic polarization showed that GNSs affected the anodic reaction of the solders. The corrosion resistance of Sn–0.7Cu–0.075GNSs was better than that of other alloys. Sn3O(OH)2Cl2 and Tin oxides were the formation of the corrosion product by XPS and XRD analysis. SEM analysis confirmed that when the GNSs content was 0.075 wt%, the corrosion products were dense and the corrosion resistance of the alloy was improved.

Evaluation of Reliability of Lead-free Solders in Silver-free Hybrids

Abstract Silver and silver-filled materials are widely used for hybrid substrate conductors, component terminals and conductive attachment materials. However, some concerns exist about using silver, especially for high-voltage hybrid assemblies that must operate in harsh non-hermetic or semi-hermetic applications. This paper discusses the reliability testing of silver-free components attachment materials. The target application temperature for this research was 185°C. Target duration at temperature was 500 hours. The evaluation of Sn100C solder was performed in comparison to solders of Sn96 and Au80Sn20. Two types of Ag-free thick-film substrates were tested with different type of solders to mount surface-mounted technology (SMT) components. The assembled test samples were subjected to thermal aging and thermal cycle tests. At each test interval, shear tests were performed to evaluate the mechanical performance. Cross sections of the solder joint and thick-film interface were used to understand the intermetallic compounds (IMC) formation and failure mechanisms under thermal stress. Tests for conductive filament growth was performed to evaluate the behavior of Sn-based solders in powered assemblies under target environmental conditions. Test results were discussed and suggestions for achieving a reliable, silver-free thick-film hybrid were made.

Control of Solder Bump Growing Morphology in Lead Free Plating

Abstract Plating Solder bump is one of the key enabling technologies for flip chip assembly methodology. Flip chip assembly has advanced to support higher levels of interconnect and small feature sizes. Electroplating is a very promising technology for finer bump features when compared with solder printing and ball mounting. Hence, the plated-solder bump morphology is quite important for process quality control and design realization. This paper aims to study the plated solder behavior from as-plated mushroom structure to after reflowed bump stage photoresist sizing. In addition, this activity will consider the full bumping process integration relative to the electroplated solder bump design rules.

Effect of nano-ZnO particles on wettability, interfacial morphology and growth kinetics of Sn–3.0Ag–0.5Cu–xZnO composite solder

The influence of nano-ZnO particles addition on wettability, thermal behavior and interface morphology of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated in present study. SAC305-xZnO composite solder with five different mass fractions of nano-ZnO particles ranging from 0 to 2.0 wt% were synthesized with SAC305 powder, nano-ZnO particles and flux. Solder joints were soldered in a reflow furnace with the maximum temperature of 255 °C for 7 min and followed by isothermal aging at 170 °C up to 240 h. The results reveal that the wettability improves first and then reduces whereas the thickness of intermetallic compounds (IMCs) layer declines first and then increases with the amount of nano-ZnO particles increasing where the threshold occurs at 0.5 wt% nano-ZnO particles, meaning slight addition of nano-ZnO particles can effectively improve wettability as well as restrain IMCs layer growth. The thermal behaviors of SAC305-xZnO composite solder increases slightly as nano-ZnO particles adds from 0 to 2.0 wt%. Moreover, the diffusion coefficient of solder is 0.92 μm2/h, 0.21 μm2/h, 0.22 μm2/h, 0.37 μm2/h and 0.48 μm2/h in sequence with nano-ZnO particles increased from 0 to 2.0 wt%, revealing nano-ZnO particles can inhibit atoms diffusion so as to suppress IMCs layer. Furthermore, the grain size of Cu6Sn5 is observed that it increases with power function of aging time describing as \(d = 1.70t^{0.38}\). In the end, it reveals that Cu6Sn5 grows both longitudinally controlled by volume diffusion as well as transversely in the form of boundary diffusion.

Experimental and numerical study on dynamic mechanical behaviors of low-silver lead-free solder under combined compression-shear loadings

In this paper, the behaviors of low-silver lead-free solder Sn0.3Ag0.7Cu were studied by quasi-static and dynamic compression-shear tests and finite-element analysis. The quasi-static tests were performed on MTS-809 material tester, while the dynamic tests were carried out on a modified split Hopkinson pressure bar (SHPB) system that uses inclined cropped cylinders as incident and transmitter bars. The inclination angle, which is formed between the ends of the incident and transmitter bar, allows dynamic combined compression-shear loadings. Inclination angles from 0° to 45° were tested under the same strain rate of 2157 s−1. Experimental results show that a larger inclination angle results in lower normal stress amplitude but higher tangential stress, given the same strain rate. The effect of strain rate was further studied by fixing the inclination angle as 30°. When the strain rate is below 2445 s−1, the strain rate effect is limited. However, from 2445 to 2875 s−1, the strain rate effect becomes significant, not only in normal direction but also in tangential direction. The experimental findings on both inclination angle and strain rate were then simulated by finite element method using the Cowper–Symonds material model. It was found that the adopted material model is able to predict the same trending as experimental data, but an accurate prediction requires a more sophisticated material model.

Power Module Interconnection Reliability in BTS Applications

In this paper, the reliability of RF power transistors’ solder attachments is characterized through experiments and simulations. Test cases consisted of power amplifier (PA) modules on AlSi10Mg substrates with either a low or high mutual thermal mismatch. The module’s flange interconnections were stressed by means of thermal cycling testing (TCT) in the 15 °C–95 °C range. Scanning acoustic microscopy (SAM) was used intermittently to inspect the interconnections of selected structures during cycling breaks. Optical cross-polarization microscopy and scanning electron microscopy were used in the failure analysis of the solder joints. Different materials and dimensional variations were tested in simulations to observe differences in thermal stress. The viscoplastic behavior of lead-free solder in the interconnection was modeled using Anand’s constitutive equations. The first cracks could be observed with SAM after 100 cycles. SAM imaging showed that in the worst case, 72% of the interconnection area had cracked at the end of the 1100-cycle TCT. Only a marginal amount of cracks could be observed in PA modules with a better coefficients of thermal expansion match to the substrate. Simulations indicated that it is possible to decrease creep energies significantly and thereby increase the lifetime expectancy of interconnections by selecting the correct materials and structures.

The Effect of Multi-Walled Carbon Nanotubes Reinforcement and Multiple Reflow Cycles on Shear Strength of SAC305 Lead-Free Solder Alloy

Abstract In this study, the effect of multi-walled carbon nanotubes (MWCNT) reinforcement on joint shear strength and microstructural development of tin-3.0silver-0.5copper (SAC305)/copper solder joint subjected to multiple reflow cycles was investigated. The MWCNT-reinforced SAC305 solder systems (SAC305-x MWCNT; x = 0.01, 0.05, 0.1, and 0.5 wt.%) were developed by a mechanical dispersion method. The microstructural, mechanical, and melting properties of SAC305 composite solders were evaluated as a function of different wt.% of MWCNT addition. The melting behavior of composite solders was analyzed using differential scanning calorimetry. The morphology and intermetallic compound growth at the solder joint interface were studied using scanning electron microscopy. The copper/solder/copper micro-lap-shear solder joint specimens reflowed for multiple reflow cycles were systematically characterized to evaluate the joint shear strength. The results showed that the reinforcement in the range of 0.01–0.05 wt.% of MWCNT resulted in the improvement of joint shear strength and better wettability compared to plain SAC305 solder alloy. Amongst all compositions analyzed, SAC305-0.05MWCNT nanocomposite suppressed the intermetallic compound layer growth effectively leading to improvement in the joint shear strength under multiple reflow cycles.

Effects of Ag contents in Sn–xAg lead-free solders on microstructure, corrosion behavior and interfacial reaction with Cu substrate

Abstract The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn–xAg lead-free solders, and on the formation of intermetallic layer of the solders with Cu substrate were investigated. The Ag contents (x) were 0, 3.0, 3.5, 4.0, and 5.0 wt.%. The Ag content played a role in the morphology of Ag3Sn phase in the solders. The microstructure analysis showed that the β-Sn phase was surrounded by eutectic networks in the 3.0Ag and 3.5Ag solders and large plate-like Ag3Sn formed in the 4.0Ag and 5.0Ag solders. Nonetheless, the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test. After soldering, only a single layer of a Cu6Sn5 intermetallic compound formed at the Sn–xAg/Cu interface. By comparison, the Cu6Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder. The fine Ag3Sn particles in the eutectic networks precipitating in the 3.0Ag and 3.5Ag solders effectively hindered the growth of Cu6Sn5 grains compared to large plate-like Ag3Sn in the 4.0 and 5.0Ag solders.

Wettability, Interfacial Behavior and Joint Properties of Sn-15Bi Solder

Sn-15Bi solid solution solder provides a potential replacement for Sn-40Pb solder due to lower cost and similar melting point. Sn-15Bi solder was compared with Sn-40Pb solder to assess the microstructure, wettability, bulk tensile properties, interfacial microstructures in solder joints with a Cu substrate, the interfacial evolution in joints during isothermal aging, and the shear strength on ball solder joints with the effect of aging conditions. The microstructure of Sn-15Bi bulk solder was composed of the primary β-Sn phase with Bi in solid solution and with precipitated Bi phases along the grain boundaries. The wettability of solder alloys was evaluated with wetting balance testing, and the results showed that Sn-15Bi solder had a lower wetting force and longer wetting time than Sn-40Pb solder. The poorer wettability of Sn-15Bi solder was not influenced by different types of soldering flux, but improved with increasing temperature. Tensile tests on bulk solder alloys indicated that Sn-15Bi solder had a higher tensile strength but lower elongation than Sn-40Pb solder. Also, the tensile strength of Sn-Bi solder decreased with decreasing strain rate and with increasing temperature, while the elongation of Sn-Bi solder was independent of the temperature and strain rate. In as-soldered joints, Sn-15Bi solder produced a thicker Cu6Sn5 layer than Sn-40Pb solder. Following isothermal aging, the thickness of the interfacial Cu-Sn intermetallic compound (IMC) increased with the aging time, and the growth rate of the IMC layer in Sn-15Bi solder joints was slightly higher than that in Sn-40Pb solder joints during aging. Ball shear test on solder joints illustrated that Sn-15Bi solder joint had a higher shear strength than Sn-40Pb solder joint, and that with increased aging time, the solder became stronger due to precipitation of Bi, leading to a change in the fracture mode from ductile failure in the solder to brittle fracture at the IMC interface.