Purpose This paper aims to present a new method of real-time monitoring of thermal profiles applied in vapour phase soldering (VPS) reflow processes. The thermal profile setting is a significant variable that affects the quality of joints. The method allows rapid achievement of a required thermal profile based on software control that brings new efficiency to the reflow process and enhanced joint quality, especially for power electronics. Design/methodology/approach A real-time monitoring system based on computerized heat control was realized in a newly developed laboratory VPS chamber using a proportional integral derivation controller within the soldering process. The principle lies in the strictly accurate monitoring of the real defined reflow profile as a reference. Findings Very accurate maintenance of the required reflow profile temperature was achieved with high accuracy (± 2°C). The new method of monitoring and control of the reflow real-time profiling was verified at various maximal reflow temperatures (230°C, 240°C and 260°C). The method is feasible for reflowing three-dimensional (3D) power modules that use various types of solders. The real-time monitoring system based on computerised heat control helped to achieve various heights of vapour zone. Originality/value The paper describes construction of a newly developed laboratory-scale VPS chamber, including novel real-time profiling of the reflow process based on intelligent continuously measured temperatures at various horizontal positions. Real-time profiling in the laboratory VPS chamber allowed reflow soldering on 3D power modules (of greater dimensions) by applying various flux-less solder materials.
Purpose The purpose of this paper is to investigate measurement and regulation of saturated vapour height level in vapour phase soldering (VPS) chamber based on parallel plate capacitor and retaining a stable saturated vapour level above the boiling fluid, regardless of the quantity and size of assembled components. Design/methodology/approach Development and realisation of capacitance sensor that sensitively senses the maximum height level of saturated vapour above the boiling fluid in the VPS chamber was achieved. Methodology of measurement is based on capacitor change from single air to a parallel plate, filled with two dielectric environments in a stacked configuration: condensed fluid and vapour (air). Findings An easy air plate capacitor immersed in the saturated vapour above the boiling fluid can serve as a parallel plate capacitor owing to the conversion of the air to the parallel plate capacitor. A thin film of fluid between the two capacitor plates corresponds to the height of the saturated vapour, which changes the capacity of the parallel plate capacitor. Originality/value Introducing the capacitive sensor directly into the VPS work space allows to achieve a constant height level of saturated vapour. Based on the capacity change, it is possible to control the heating power. There is a lack of information regarding measurement of stable height of vapour in the industry, and the present article shows how to easily improve the way to regulate the bandwidth of saturated vapour in the VPS process.
Purpose This paper aims to present a review of the recent developments in vapour phase soldering (VPS) technology. This study focuses on the following topics: recent developments of the technology, i.e. soft and vacuum VPS; measurement and characterization methods of vapour space, i.e. temperature and pressure; numerical simulation of the VPS soldering process, i.e. condensate layer and solder joint formation; and quality and reliability studies of the solder joints prepared by VPS, i.e. void content and microstructure of the solder joints. Design/methodology/approach This study was written according to the results of a wide literature review about the substantial previous works in the past decade and according to the authors’ own results. Findings Up to now, a part of the electronics industry believes that the reflow soldering with VPS method is a significant alternative of convection and infrared technologies. The summarized results of the field in this study support this idea. Research limitations/implications This literature review provides engineers and researchers with understanding of the limitations and application possibilities of the VPS technology and the current challenges in soldering technology. Originality/value This paper summarizes the most important advantages and disadvantages of VPS technology compared to the other reflow soldering methods, as well as points out the necessary further developments and possible research directions.
Purpose The purpose of this paper is to find an optimum between the quantity of solder paste and the desired properties of the soldered joint. A reduction of solder paste quantity is recognized as an opportunity to save money. On the other hand, the quantity of solder paste significantly influences the final properties of the soldered joint. The purpose is also to design recommendations for manufacturers of electronic assemblies. Design/methodology/approach The processing of the paper was initiated by a literature review. The expert analysis was the next step. The result of analysis was a fishbone diagram. Subsequently, the experiment was designed. Seven types and three volume of solder pastes and two aperture shapes of the stencil were used. The measured parameters were mechanical strength, electrical resistance, voids area and intermetallic compound (IMC) thicknesses. The results of the experiment were evaluated and recommendations for practice were defined. Findings The carried out research has confirmed the influence of solder paste quantity on the shear strength, electrical resistance, voids area and IMC thickness of solder joint. The article presents the results achieved for solders Sn42Bi58, Sn42Bi57.6Ag0.4, SnAg3.0Cu0.5, SnCu0.7Ag1.0NiGe, SnAg3.5Bi0.5In8.0 and Sn62.5Pb36.5Ag1.0. Reduction of solder paste quantity down to 74 per cent (i.e. one quarter of quantity) decreases mechanical shear strength less than 10 per cent. Recommendations relating to the optimal reduction of solder paste quantity have been designed for each solder paste. Originality/value Contribution of the paper is impact assessment of solder paste quantity on the properties of the soldered joint. It was carried out a large number of experiments and measurements which verify this effect. Such a comprehensive overview of the results is not yet available in the literature. Recommendations for manufacturers of electronic assemblies are also the benefit of article.
Purpose – The main advantages of vapour phase soldering are a non-oxygen environment, the elimination of overheating and the possibility of the vacuum application, which can guarantee undeniably higher quality of solder joints, especially as regards void formation. These features are less affected by the alloy composition. The paper aims to discuss these issues. Design/methodology/approach – The quality of solder joints made in two VPS options (with and without vacuum) was investigated in terms of voids formation. Solder alloys of 37%Pb63%Sn (PbSn) and 96%Sn3.5%Ag0.5%Cu (SAC 305) were applied to an etched Cu layer on a glass-epoxy substrate using the screen-printing method. 1206 SMD resistors were placed on the solder pads with a Quadra pick-and place machine. For the inspection of joint structure and void identification, 3D X-ray images of samples were taken using a computed tomography system with a 180 kV/15 W nanofocus. For comparison, traditional cross-sections of the samples were performed using a metallographic polisher. The cross-section analysis was done in a scanning electron microscope (SEM). To confirm the relevance of these data, a statistical analysis was carried out. Findings – The paper shows that alloy composition has less impact on the quality of joints as regards void formation. The tendency for a different arrangement of voids in a junction depending on the distance SMD element and the thickness of the solder layer was investigated using X-ray computed tomography. Originality/value – The use of 3D computed tomography for void investigation gives full information about the internal structure of the joint and allows for precise void identification. Vacuum application during the soldering allows significant voids elimination.
Purpose This study aims to investigate the chromium (Cr) effects on the microstructural, mechanical and thermal properties of melt-spun Sn-3.5Ag alloy. Design/methodology/approach Ternary melt-spun Sn-Ag-Cr alloys were investigated using X-ray diffractions, scanning electron microscope, dynamic resonance technique, instron machine, Vickers hardness tester and differential scanning calorimetry. Findings The results revealed that the Ag3Sn intermetallic compound (IMC) and ß-Sn have been refined because of the hard inclusions’ (Cr atoms) effects, causing lattice distortion increasing these alloys. The tensile results of Sn96.4-Ag3.5-Cr0.1 alloy showed an improvement in Young’s modulus more than 100 per cent (42.16 GPa), ultimate tensile strength (UTS) by 9.4 per cent (23.9 MPa), compared with the eutectic Sn-Ag alloy due to the high concentration of Ag3Sn and their uniform distribution. Shortage in the internal friction (Q−1) of about 54 per cent (45.1) and increase in Vickers hardness of about 7.4 per cent (142.1 MPa) were also noted. Hexagonal Ag3Sn formation led to low toughness values compared to the eutectic Sn-Ag alloy, which may have resulted from the mismatching among hexagonal Ag3Sn phase with orthorhombic Ag3Sn and ß-Sn phases. Mechanically, the values of Young’s modulus have been increased, with increasing chromium content, whereas the UTS and toughness values have been decreased. The opposite of this trend appeared in Sn95.8-Ag3.5-Cr0.7 alloy, which may have been due to high lattice distortion (ƹ = 16.5 × 10−4) compared to the other alloys. Increase in the melting temperature Tm, ΔH, Cp and ΔT was because of Ag3Sn IMC formation. The low toughness of Sn96-Ag3.5-Cr0.5 and Sn95.8-Ag3.5-Cr0.7 (109.56 J/m3 and 35.66 J/m3), relatively high melting temperature Tm (223.22°C and 222.65°C) and low thermal conductivity and thermal diffusivity (32.651 w.m−1.k−1 and 0.314 m2/s) make them undesirable in the soldering process. The high UTS, high E, high thermal conductivity and diffusivity, low creep rate and low electrical resistivity, which have occurred with “0.1 Wt.%” of Cr, make this alloy desirable and reliable for soldering applications and electronic assembly. Originality/value This study provides chromium effects on the structure of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors compared the elastic modulus of the melt-spun compositions, which have been resulted from the Static method with that have been resulted from the Dynamic method. This paper presents new improvements in mechanical and thermal performance.
Purpose This paper aims to use nano-silver paste to design a new bonding method for super-large-area direct-bonded-aluminum (DBA) plates. It compared several frequently used bonding methods and proved the feasibility of an optimized low-pressure-assisted double-layer-printed silver sintering technology for large-area bonding to increase the thermal conductivity of power electronic modules with high junction temperature, higher power density and higher reliability. Design/methodology/approach The bonding profile was optimized by using transparent glasses as substrates. Thus, the bonding qualities could be directly characterized by optical observation. After sintering, the bonded DBA samples were characterized by nondestructive X-ray computed tomography system, scanning electron microscopy equipped with an energy dispersive spectrometer. Finally, bonding stress evolution was characterized by shear tests. Findings Low-pressure-assisted large-area double-layer-printed bonding process consisting of six-step was successfully developed to bond DBA substrates with the size of 50.8 × 25.4 mm. The thickness of the sintered-silver bond-line was between 33 and 74 µm with the average porosity of 12.5 per cent. The distribution of shear strength along the length of DBA/DBA bonded sample was from 9.7 to 18.8 MPa, with average shear strength of 15.5 MPa. The typical fracture primarily propagated in the sintered-silver layer and partially along the Ni layer. Research limitations/implications The bonding stress needs to be further improved. Meanwhile, the thermal and electrical properties are encouraged to test further. Practical implications If nano-silver paste can be used as thermal interfacial material for super-large-area bonding, the thermal performance will be improved. Social implications The paper accelerated the use of nano-silver paste for super-large-area DBA bonding. Originality/value The proposed bonding method greatly decreased the bonding pressure.
PurposeCrack and stress distribution on dies are key issues for the pressure-assisted sintering bonding of power modules. The purpose of this research is to build a relationship among stress distributions, sintering sequences and sintering pressures during the sintering processes. Design/methodology/approachThree sintering sequences, S(a), S(b) and S(c), have been designed for the double-side assembly of power module in this paper. Experiments and finite element method (FEM) analysis are conducted to investigate the crack and stress distribution. FindingsThe sintering sequence had significant effects on the crack generation in the chips during the sintering process under 30-MPa pressure. The simulation results revealed that the module sintered by S(a) showed lower chip stress than those by the other two sintering sequences under 30 MPa. In contrast, the chip stress is the highest when the sintering sequence follows S(b). The simulation results explained the crack generation and prolongation in the experiments. S(a) was recommended as the best sintering sequence because of the lowest chip stress and highest yield rate. Originality/valueThis study investigated the stress distributions of the double-side sintered power modules under different sintering pressures. Based on the results of experiments and FEM analysis, the best sintering sequence design is provided under various sintering pressures.
Purpose The purpose of this paper is to investigate the influence of pulse plating current density on the morphology and solderability of Pb-free Sn-Cu solder coatings prepared from alkaline stannate baths. Design/methodology/approach Sn-Cu solder coatings were produced from a plating solution containing sodium stannate, copper stannate, sodium hydroxide and sorbitol additive on copper substrates. The pulse plating experiments were conducted in galvanostatic mode. The plating current density was varied from 5 to 25 mA/cm2, and the morphology of the coatings was studied. The solderability of the coatings was assessed by spread ratio measurement after reflowing the solder coatings at 250°C. Findings The composition control of eutectic solders is always a challenge in plating. The findings show that Sn-Cu coatings prepared by pulse plating are composed of tetragonal ß-Sn structure and Cu6Sn5 compounds irrespective of bath composition and conditions. The final coatings were very dense and smooth with nodular morphology. It was shown that a eutectic composition can be achieved if we apply a current density of ∼15-20 mA/cm2. The solderability studies suggest that solder coatings plated at and beyond 15 mA/cm2 are more suitable for solder finish applications. Originality/value The work presents key issues in pulse electroplating of Sn-Cu solder coatings from an alkaline bath. Possible strategies to control the eutectic Sn-Cu composition by plating process are recommended.
Purpose This paper aims to investigate the effect of ultrasonic vibration (USV) on the evolution of intermetallic compounds (IMCs), grain morphology and shear strength of soldered Ni/Sn/Ni samples. Design/methodology/approach The Ni/Sn/Ni joints were obtained through ultrasonic-assisted soldering. The formation of IMCs, their composition, grain morphology and the fractured-surface microstructures from shear tests were characterized using scanning electron microscopy and energy-dispersive x-ray spectroscopy. Findings Without USV, a planar interfacial Ni3Sn4 layer was formed at the Ni/Sn interface, and a few Ni3Sn4 grains were distributed in the soldered joint. The morphology of these grains was needle-shaped. With USV, several grooves were formed at the interfacial Ni3Sn4 layer due to ultrasonic cavitation. Some deepened grooves led to “neck” connections at the roots of the Ni3Sn4 grains, which accelerated the strong detachment of Ni3Sn4 from the substrate. In addition, two types of Ni3Sn4 grains, needle-shaped and granular-shaped, were observed at the interface. Furthermore, the shear strength increased with longer USV time, which was attributed to the thinning of the interfacial IMC layers and dispersion strengthening from the Ni3Sn4 particles distributed evenly in the joint. Originality/value The novelty of the paper is the detailed study of the effect of USV on the morphology, size changes of interfacial IMC and joint strength. This provides guidance for the application of ultrasonic-assisted soldering in electronics packaging.
Purpose The purpose of this study is to investigate the addition of 0.05 Wt.% carbon nanotube (CNT) into the Sn-1.0Ag-0.5Cu (SAC) solder on the intermetallic (IMC) growth. Lead-based solders play an important role in a variety of applications in electronic industries. Due to the toxicity of the lead in the solder, lead-free solders were proposed to replace the lead-based solders. Sn-Ag-Cu solder family is one of the lead-free solders, which are proposed and considered as a potential replacement. Unfortunately, the Sn-Ag-Cu solder faces some reliability problems because of the formation of the thick intermetallic compounds. So the retardation of intermetallic growth is prime important. Design/methodology/approach The solder joint was aged under liquid state aging with soldering time from 1 to 60 min. Findings Two types of intermetallics, which are Cu6Sn5 and Cu3Sn were observed under a scanning electron microscope. The morphology of Cu6Sn5 intermetallic transformed from scallop to planar type as the soldering time increases. The addition of carbon nanotube into the SAC solder has retarded the Cu6Sn5 intermetallic growth rate by increasing its activation energy from 97.86 to 101.45 kJ/mol. Furthermore, the activation energy for the Cu3Sn growth has increased from 102.10 to 104.23 kJ/mol. Originality/value The increase in the activation energy indicates that the growth of the intermetallics was slower. This implies that the addition of carbon nanotube increases the reliability of the solder joint and are suitable for microelectronics applications.
Purpose The research on lead-free solder alloys has increased in past decades due to awareness of the environmental impact of lead contents in soldering alloys. This has led to the introduction and development of different grades of lead-free solder alloys in the global market. Tin-silver-copper is a lead-free alloy which has been acknowledged by different consortia as a good alternative to conventional tin-lead alloy. The purpose of this paper is to provide comprehensive knowledge about the tin-silver-copper series. Design/methodology/approach The approach of this study reviews the microstructure and some other properties of tin-silver-copper series after the addition of indium, titanium, iron, zinc, zirconium, bismuth, nickel, antimony, gallium, aluminium, cerium, lanthanum, yttrium, erbium, praseodymium, neodymium, ytterbium, nanoparticles of nickel, cobalt, silicon carbide, aluminium oxide, zinc oxide, titanium dioxide, cerium oxide, zirconium oxide and titanium diboride, as well as carbon nanotubes, nickel-coated carbon nanotubes, single-walled carbon nanotubes and graphene-nano-sheets. Findings The current paper presents a comprehensive review of the tin-silver-copper solder series with possible solutions for improving their microstructure, melting point, mechanical properties and wettability through the addition of different elements/nanoparticles and other materials. Originality/value This paper summarises the useful findings of the tin-silver-copper series comprehensively. This information will assist in future work for the design and development of novel lead-free solder alloys.
Purpose This paper aims to introduce a new indicative parameter of filling efficiency to quantify the performance and productivity of the flip-chip underfill encapsulation process. Additionally, the variation effect of the bump pitch of flip-chip on the filling efficiency was demonstrated to provide insight for flip-chip design optimization. Design/methodology/approach The filling efficiency was formulated analytically based on the conceptual spatial and temporal perspectives. Subsequently, the effect of bump pitch on filling efficiency was studied based on the past actual-scaled and current scaled-up underfill experiments. The latter scaled-up experiment was validated with both the finite volume method-based numerical simulation and analytical filling time model. Moreover, the scaling validity of scaled-up experiment was justified based on the similarity analysis of dimensionless number. Findings Through the scaling analysis, the current scaled-up experimental system is justified to be valid since the adopted scaling factor 40 is less than the theoretical scaling limit of 270. Furthermore, the current experiment was qualitatively well validated with the numerical simulation and analytical filling time model. It is found that the filling efficiency increases with the bump pitch, such that doubling the bump pitch would triple the efficiency. Practical implications The new performance indicative index of filling efficiency enables the package designers to justify the variation effect of underfill parameter on the overall underfill process. Moreover, the upper limit of scaling factor for scaled-up package was derived to serve as the guideline for future scaled-up underfill experiments. Originality/value The performance of underfill process as highlighted in this paper was never being quantified before in the past literatures. Similarly, the scaling limit that is associated to the scaled-up underfill experiment was never being reported elsewhere too.
Purpose Stencil cleaning is an important operation in solder paste printing process. Frequent cleaning may interrupt printing process and increase idle time, as well as loss for performing cleaning. This paper aims to propose a method to optimize the stencil cleaning time and reduce unnecessary cleaning operations and losses. Design/methodology/approach This paper uses a discrete-time, discrete-state homogeneous Markov chain to model the stencil printing performance degradation process, and the quality loss during the stencil printing process is estimated based on this degradation model. A stencil cleaning decision model based on renewal reward theorem is established, and the optimal cleaning time is obtained through a balance between quality loss and the loss on idle time. Findings A stencil cleaning decision model for solder paste printing is established, and numerical simulation results show that there exists an optimal stencil cleaning time which minimizes the long-term loss. Originality/value Stencil cleaning control is very important for solder paste printing. However, there are very few studies focusing on stencil cleaning control. This research contributes to developing a model to optimize the stencil cleaning time in solder paste printing process.
Purpose The purpose of this paper is to study the mechanism of electrochemical dissolution of SAC305 solder in mild acid solution. Design/methodology/approach Cyclic voltammetry (CV) was used to obtain electrochemical dissolution peaks followed by chronoamperometery (CA) to investigate the dissolution mechanism at each peak. Structural and microstructural characterization was performed to verify the CA analysis. Potentiodynamic polarization was performed afterwards to determine the corrosion potential of every phase in SAC305. Findings The early cycle of CV exhibits only dissolution peaks of β-Sn until intermetallic compound (IMC) peaks emerged at a later cycle. CA performed for 24 h at selected potentials reveals that β-Sn can be removed completely from the sample without disrupting the IMC network at a suitable potential. This was later verified by XRD and SEM. Potentiodynamic polarization determined the corrosion potential of IMC as −0.36 V. Originality/value The mechanism of anodic dissolution of SAC305 was studied and proposed.
Purpose This study aims to develop a bimodal nano-silver paste with improved mechanical property and reliability. Silicon carbide (SiC) particles coated with Ag were introduced in nano-silver paste to improve bonding strength between SiC and Ag particles and enhance high-temperature stability of bimodal nano-silver paste. The effect of sintering parameters such as sintering temperature, sintering time and the proportion of SiC particles on mechanical property and reliability of sintered bimodal nano-silver structure were investigated. Design/methodology/approach Sandwich structures consist of dummy chips and copper substrates with nickel and silver coating bonded by nano-silver paste were designed for shear testing. Shear strength testing was conducted to study the influence of SiC particles proportions on the mechanical property of sintered nano-silver joints. The reliability of the bimodal nano-silver paste was evaluated experimentally by means of shear test for samples subjected to thermal aging test at 150°C and humidity and temperature testing at 85°C and 85 per cent RH, respectively. Findings Shear strength was enhanced obviously with the increase of sintering temperature and sintering time. The maximum shear strength was achieved for nano-silver paste sintered at 260°C for 10 min. There was a negative correlation between the proportion of SiC particles and shear strength. After thermal aging testing and humidity and temperature testing for 240 h, the shear strength decreased a little. High-temperature stability and high-hydrothermal stability were improved by the addition of SiC particles. Originality/value Submicron-scale SiC particles coated with Ag were used as alternative materials to replace part of nano-silver particles to prepare bimodal nano-silver paste due to its high thermal conductivity and excellent mechanical property.
Purpose This paper aims to consider the practical production environment of electronics manufacturing industry firms, and the large quantities of information collected on machine processes, testing data and production reports, while simultaneously taking into account the properties of the processing environment, in conducting analysis to obtain valuable information. Design/methodology/approach This research constructs a prediction model of the circuit board assembly process yield. A decision tree is used to extract the key attributes. The authors also integrate association rules to determine the relevance of key attributes of undesirable phenomena. Findings The results assure the successful application of the methodology by reconfirming the rules for solder skip and short circuit occurrence and their causes. Originality/value Measures for improvement are recommended, production parameters determined and debugging suggestions made to improve the process yield when the new process is implemented.
Purpose The purpose of this paper is to investigate the effect of nickel-plated graphene (Ni-GNS) on the microstructure and mechanical properties of 96.5Sn3Ag0.5Cu (SAC305) lead-free solder joints before and after an electro-migration (EM) experiment. Design/methodology/approach In this paper, SAC305 solder alloy doped with 0.1 Wt.% Ni-GNS was prepared via the powder metallurgy method. A U-shaped sample structure was also designed and prepared to conduct an EM experiment. The EM experiment was carried out with a current density of 1.5 × 104 A/cm2. The microstructural and mechanical evolutions of both solder joints under EM stressing were comparatively studied using SEM and nanoindentation. Findings The experimental results showed that for the SAC305 solder, the interfacial intermetallic compounds (IMC) formulated a protrusion with an average height of 0.42 µm at the anode after 360 h of EM stressing; however, despite this, the surface of the composite solder joint was relatively smooth. During the stressing period, the interfacial IMC on the anode side of the plain SAC305 solder showed a continuous increasing trend, while the IMC at the cathode presented a decreasing trend for its thickness as the stressing time increased; after 360 h of stressing, some cracks and voids had formed on the cathode side. For the SAC305/ Ni-GNS composite solder, a continuous increase in the thickness of the interfacial IMC was found on both the anode and cathode side; the growth rate of the interfacial IMC at the anode was higher than that at the cathode. The nanoindentation results showed that the hardness of the SAC305 solder joint presented a gradient distribution after EM stressing, while the hardness data showed a relatively homogeneous distribution in the SAC305/ Ni-GNS solder joint. Originality/value The experimental results showed that the Ni-GNS reinforcement could effectively mitigate the EM behavior in solder joints under high current stressing. Specifically, the Ni particles that plated the graphene sheets can work as a fixing agent to suppress the diffusion and migration of Sn and Cu atoms by forming Sn-Cu-Ni IMC. In addition, the nanoidentation results also indicated that the addition of the Ni-GNS reinforcement was very helpful in maintaining the mechanical stability of the solder joint. These findings have provided a theoretical and experimental basis for the practical application of this novel composite solder with high current densities.
Purpose The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows. Design/methodology/approach The solder balls with diameters from 250 to 760 µm were mounted on the copper-clad laminate by 1-5 reflows. The strength of the solder balls was tested by the single ball shear test and pull test, respectively. The failure modes of tested samples were identified by combing morphologies of fracture surfaces and force-displacement curves. The stresses were revealed and the failure explanations were assisted by the finite element analysis for the shear test of single solder ball. Findings The average strength of a smaller solder ball (e.g. 250 µm in diameter) is higher than that of a larger one (e.g. 760 µm in diameter). The strength of smaller solder balls is more highly variable with multiple reflows than larger diameters balls, where the strength increased mostly with the number of reflows. According to load-displacement curves or fracture surface morphologies, the failure modes of solder ball in the shear and pull tests can be categorized into three kinds. Originality/value The strength of solder balls will not deteriorate when the diameter of solder ball is decreased with a reflow, but a smaller solder ball has a higher failure risk after multiple reflows. The failure modes for shear and pull tests can be identified quickly by the combination of force-displacement curves and the morphologies of fracture surfaces.
Purpose Tin-Silver-Copper is widely accepted as the best alternative to replace Tin-Lead solders in microelectronics packaging due to their acceptable properties. However, to overcome some of the shortcomings related to its microstructure and in turn, its mechanical properties at high temperature, the addition of different elements into Tin-Silver-Copper is important for investigations. The purpose of this paper is to analyse the effect of lanthanum doping on the microstructure, microhardness and tensile properties of Tin-Silver-Copper as a function of thermal aging time for 60, 120 and 180 h at a high temperature of 150°C and at high strain rates of 25, 35 and 45/s. Design/methodology/approach The microstructure of un-doped and Lanthanum-doped Tin-Silver-Copper after different thermal aging time is examined using scanning electron microscopy followed by digital image analyses using ImageJ. Brinell hardness is used to find out the microhardness properties. The tensile tests are performed using the universal testing machine. All the investigations are done after the above selected thermal aging time at high temperature. The tensile tests of the thermally aged specimens are further investigated at high strain rates of 25, 35 and 45/s. Findings According to the microstructural examination, Tin-Silver-Copper with 0.4 Wt.% Lanthanum is found to be more sensitive at high temperature as the aging time increases which resulted in coarse microstructure due to the non-uniform distribution of intermetallic compounds. Similarly, lower values of microhardness, yield strength and ultimate tensile strength come in favours of 0.4 Wt.% Lanthanum added Tin-Silver-Copper. Furthermore, when the thermally aged tensile specimen is tested at high strains, two trends in tensile curves of both the solder alloys are noted. The trends showed that yield strength and ultimate tensile strength increase as the strain rate increase and decrease when there is an increase in thermal aging. Originality/value The addition of higher supplement (0.4 Wt.%) of Lanthanum into Tin-Silver-Copper showed a lower hardness value, yield strength, ultimate tensile strength, ductility, toughness and fatigue in comparison to un-doped Tin-Silver-Copper at high temperature and at high strain rates. Finally, simplified material property models with minimum error are developed which will help when the actual test data are not available.