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In this research we investigated the contact angle of commercial SnAgCu solder paste mixing with some carbon allotropes such as graphite, graphene quantum dots, and fullerene of varying concentrations with melting temperature, wettability, interfacial microstructure. The wettability was assessed in terms of the contact angle. The in-line digital holography was used for determining the contact angle and morphological of samples at each temperature which the samples have been heating from room temperature until the melting temperature. In the experiment, only one beam was used as the object and reference beams which recorded by a CMOS camera. The recorded image was reconstructed by the angular spectrum digital holography numerical programing. Using the reconstructed images of our results, the shape and contact angle of solder pastes can be investigated.

The feasibility of transient liquid phase (TLP) bonding technology for high-temperature endurable power electronics packaging has been evaluated in this study. An Ag-Sn3.0Ag0.5Cu hybrid solder paste was fabricated and used as a bonding material. The bonding reactions between chip/substrate and hybrid solder paste and die shear strengths of the TLP-bonded joints were evaluated during conventional soldering and vacuum soldering processes. Compared to the conventional soldering, the vacuum-soldered joints had fewer voids and relatively good metallurgical microstructures. After TLP bonding, (Cu,Ni)6Sn5, Ag3Sn, and Cu6Sn5 intermetallic compounds formed at the chip interface, in the middle of the joint, and at the bottom interface, respectively. It was confirmed that the vacuum soldering process could create good interfacial uniformity with minimal voids in the Si chip/ceramic substrate joints. The formation of voids during TLP bonding significantly affected the mechanical shear strength of the TLP-bonded joints. The vacuum-soldered joints had high shear strength values of approximately 40 MPa. To ensure the high joint strength and long-term reliability of Sn-based TLP-bonded joints, critical void control in the joints is needed.

This article focuses on the study of voids in the solder joint interface of flip-chip LEDs. Additional flux is added to the solder paste to reduce the frequency of voids, and the mechanical properties of the solder joints are compared and analyzed. Two kinds of fluxes (NC559-TPF, TSF-6516) are selected. They are used in two kinds of solder pastes (lead and lead-free solder paste). The amount of flux added is 0 mL, 0.4 mL, and 0.8 mL. The other preparation conditions for all combinations are the same and are within the recommended scope of the manufacturer's documentation. X-rays are used to detect and analyze the distribution and quantity of voids in the solder layer. A push–pull tester is used to analyze and evaluate the mechanical strength of the solder joints. A scanning electron microscope was used to observe the microscopic morphology of the cross-section of the solder joint and the fracture morphology of the interface after the shear test. It was found that adding a proper amount of high-activity flux to the solder paste can reduce the frequency of voids and improve the mechanical reliability of the solder joints. Finally, we tested the thermal performance of the flip-chip LED filament for verification.

This paper investigates the effect of grain size on the evolution and shear behavior of lead-free solder joints. The grain size of the solder is 2-11 μm, 5-15 μm, 15-25 μm, respectively. The interface structure of the solder joint and the microstructure of the inferred surface are analyzed. The void ratio of the flip-chip solder layer is tested. In order to study the change of shear strength and fracture surface, the solder/copper joint was subjected to isothermal aging treatment (1000 h) under the environment of relative humidity of 85 °C/85%. The results show that the smaller the solder crystal grains, the larger the surface area of the crystal grains per unit mass. Because of the action of the liquid bridge force, tin powder agglomeration is prone to occur, which leads to a high void rate of the solder layer. At this time, a higher activity flux is required to remove oxides. Highly active flux (NC559-TPF) was added and verified. When the grain size is 5-15 μm, the solder paste has the best soldering performance. After the filament is aged for 1000 h, the junction temperature is the lowest. Secondly, the blue light flux is the highest.

Solder paste is mainly used for welding of resistance, capacitance, integrated circuit (IC) and other electronic components in surface mounted technology (SMT) industry, and the performance of solder paste has a significant impact on the reliability of electronic components. In this paper, processing defects, failure cases and mechanism of electronic components caused by solder paste are analyzed systematically. Improper application of solder paste during welding can lead to numerous processing defects including poor wetting, tombstoning, bridging, solder joint crack, solder ball spattering, corrosion and so on. Finally, an evaluation method of material compatibility is described in this paper, which provides a reference for ensuring the quality of electronic process material and improving the reliability of SMT products.

Effects of Mn-doped TiO2 nanoparticles on the wettability, printability and thickness of intermetallic layer of SAC30 on a Cu substrate were studied in this paper. Concentration of Mn-doped TiO2 nanoparticles was varied from 0.05 wt.% to 1[Formula: see text]wt.%. The wettability was evaluated in terms of contact angle of solder on the copper substrate and the printability was measured from the volume ratio of printed solder on the copper substrate to volume of stencil opening. The experimental results showed that 0.10[Formula: see text]wt.% Mn-doped TiO2 led to the lowest contact angle while the printability was decreased with the increase of the added nanoparticles and the thinnest intermetallic layer was found at 0.50[Formula: see text]wt.% Mn-doped TiO2 nanoparticles. Mn-doped TiO2 concentration was then optimized using a desirability function to find optimal values for the three responses. It was found that 0.07[Formula: see text]wt.% was the optimal concentration for the three metrics — wettability, printability and thickness of the intermetallic layer.

This paper investigates the effect of soldering temperature on solder joint voids and reliability of flip-chip LED chips during reflow soldering. Lead-free solder SAC305 was used as solder paste. The void ratio of the flip-chip LED solder joint at 250°C, 260°C, 270°C, 280°C, and 290°C reflow soldering temperatures was detected by x-ray detector. Shear tests were conducted to evaluate the influence of interfacial reactions on the mechanical reliability of solder joints. The distribution of voids in the shear section was observed by scanning electron microscope (SEM). Next, the photoelectric and thermal properties of FC-LED filament were tested and analyzed. Finally, a high-temperature and high-humidity aging experiment was carried out to test the reliability of the LED filament. The results show that the void ratio of the LED filament soldering joint is the lowest when the soldering temperature is 270°C. The small void ratio of the solder joints results in lower steady-state voltage and junction temperature of the flip-chip LED filament. As the void density in the solder joint decreases, the shear strength of the solder joint increases. At this time, the shear resistance and mechanical reliability are the highest.

Quality and reliability of any solder joint depends on the interfacial morphology and distribution of the intermetallic compounds (IMCs) across the solder joint interface. In the present work, author shows the changes in microstructures and resistivity of the solder joints prepared with SN100C solder paste along with thin Sn film as interlayer using Cu pad as substrate. The micro-structural observations and the resistivity study of the samples with aging time were carried out by the optical microscope and 4 probe Source Measuring Unit (SMU) respectively. Result establishes the fact that the resistivity could be controlled by the addition of layers like Sn. It is also reported that the addition of Sn interlayer changes the microstructure and lowers the growth of the intermetallic compounds at the interface of the solder joint. It is concluded that, if alternate layers of Sn and solder paste (SN100C) are arranged, then the reliability and the performance of the soldered components will improve greatly and hence shall increase the service life of the gadgets.

An energy-based 3-D model was created to simulate the solder joint formation of the chip capacitor during reflow. The surface tension ( $F_{s}$ ) and hydrostatic force ( $F_{h}$ ) of molten solder and the gravitational force ( $F_{g}$ ) of a chip capacitor and solder paste were considered in this 3-D model. The initial geometry of solder joint is evolved into an equilibrium shape to minimize the internal energy of molten solder. In this study, we investigated the effect of various design parameters, such as solder paste volume, copper pad dimension, and component height on the solder joint shape of capacitor. Chip capacitor C1005 and C0603 with SAC305 solder paste and copper pads with electroless nickel immersion gold (ENIG) surface finish were used as examples. Actual capacitor samples were cross-sectioned and inspected to validate the simulation results from the 3-D model. Moreover, the self-alignment of the chip capacitor was studied in this work. The component self-alignment will affect the accuracy of component assembly and significantly affects the chip capacitor solder joint formation. Simulations were performed to address the mechanism of chip capacitor self-alignment during reflow soldering. The effect of solder paste volume on the capacitor self-alignment was summarized. The result showed relatively more solder paste that can improve the capacitor self-alignment because of the bigger restoring force generated by the molten solder. The inconsistency of solder paste volumes at the two terminations will cause the capacitor to offset from the center. It is found that the misalignment of capacitor C1005 can be reduced to $\pm 30~\mu \text{m}$ in component-length direction and $\pm 30~\mu \text{m}$ in component-width direction by the optimization of solder paste volume. The self-alignment is better in component-width direction than component-length direction. An extensive number of experimental studies were performed to develop a data-driven prediction model so that the manufacturing cost during trial tests can be reduced. In the experiments, the chip capacitors were placed intentionally with some initial offsets and their positions were measured before and after the reflow. Simulation results showed good agreement with the experimental data.

Stencil printing using solder paste material is one of the challenging processes in semiconductor assembly manufacturing. During evaluation of a semiconductor device, off-centered ball issue was encountered. The study aimed to mitigate the off-centered ball issue at stencil printing process by exploring the effect of different solder paste materials. Both solder paste materials were cured using the same reflow condition. However, solder paste material 1 (S1) resulted to cold solder joints while material 2 (S2) showed cured solder paste characteristic. With S2 material used in stencil printing, the off-centered ball occurrence was eventually eliminated. For future works, the solder paste material and configuration could be used for devices with similar requirement.

Recently, the addition of new materials into the conventional solder pastes provides a viable solution to optimize the material characteristics and properties of the nano-particle filled solder paste. Addition of titanium oxide (TiO2) nanoparticles shown that it can enable better performance of the solder. However, actual industry experiment in terms of its optimum thermal profile for improved strength through good spread of nano-particles in the solder is very costly and lengthy to set up. Hence, this paper presents a preliminary study of the interaction between two models of numerical simulation namely volume of fluid (VOF) and discrete phase model (DPM) then compare with previous experimental data. This paper aims to analyse the effect of peak temperature towards the fillet height of ultra-fine Sn-Ag-Cu (SAC) solder joints doped with TiO2 nanoparticles in an electronic assembly. For the purpose of this research, the weight percentage of the nanoparticles TiO2 with the SAC305 lead-free reinforced solder is varied at different peak temperature and investigated in terms of particles distribution, fillet height and thermal strain. This paper presents a 3D numerical simulation of nano-reinforced lead (Pb)-free solder at the ultra-fine joint component for 01005 capacitor with dimension of 0.2 x 0.2 x 0.4 mm³. The results obtained are confirmed by conducting an experiment using a field emission scanning electron microscope (SEM) joined with an EDS and X-ray diffraction machine. This study concludes that the best fillet height would be obtained at 250°C. The distributions of nanoparticles with 0.01 wt%, 0.05 wt%, and 0.15 wt% of weighted percentage are effectively observed by using the HRTEM analysis. Based on the study, higher temperature of the wetting region that range between 240°C and 255°C results in better particle distributions, and fillet height of the solder by using temperature in that range meets the requirement of IPC standards.

There are lots of companies manufacturing electronic components that have commonly used the Surface Mount Technology printing process. However, the temperature of solder paste printing on the Printed Circuit Board can influence the presence of defects in Surface Mount Technology. In this paper, the experiment called Surface Mount Technology printing is built and tested to characterize the temperature of solder pastes in order to prevent the electronic waste and rejection rate of the malfunctioning electronics due to poor soldering. The microstructures of solder paste on printed circuit board and copper substrate are inspected under Scanning Electron Microscopy. It is focused on two parameters that affect the performance of a printed circuit board, which includes the filling areas of solder paste and the distance between ball grid arrays. From the experiment and analysis results, the filling area decreases as the temperature increases during the Surface Mount Technology printing process. In short, when the temperature of SAC305 increases, the viscosity and filling areas decreases. In fact, SAC305 gave the second rank of smallest area (18.86%) and distance (43.43%) after SAC307. The average area and distance are fair enough for the solder to hold the component placement, unlike SAC307 which likely causes tombstone.

In this study, the influence of different reflow profiles and dosages of SnPb solder paste on the reliability of the SnAgCu/SnPb mixed assembly process was investigated. The interfacial microstructures were carefully examined through scanning electron microscopy, and two failures modes were found. Firstly, when reflowed at 245°C for 95 s, Pb-rich phases were buried within an intermetallic compound (IMC) layer and led to micro-voids and cracks under thermal stress or mechanical stress. However, upon increasing the reflow temperature or time further led to melting the solder ball totally, and the Pb element dissolved into a liquid phase and precipitated into uniform and small granules during the cooling process. Further, among the samples with different dosages of SnPb solder paste, severe shrinkage occurred at the solder joints with the addition of 12 wt.% eutectic SnPb component. Electron back-scattered diffraction analysis was conducted in order to determine the mechanism of different shrinkages. The solder ball consisted of several primary Sn grains, and the shrinkage and Pb-rich phase are preferred to appear at the grain boundary. When the solder ball consisted of a single grain, no preferred orientation of the shrinkage and Pb-rich phase were detected. The shrinkage appeared at the final solidification region, which is near the IMC layer. Moreover, the shrinkages connect to each other, and a continuous crack formed on the chip side, leading to the failure.

Purpose The purpose of this paper is to investigate the effect of carbon nanotube (CNT) addition on microstructure, interfacial intermetallic compound (IMC) layer and micromechanical properties of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint under blast wave condition. This work is an extension from the previous study of microstructural evolution and hardness properties of Sn-Ag-Cu (SAC) solder under blast wave condition. Design/methodology/approach SAC/CNT solder pastes were manufactured by mixing of SAC solder powder, fluxes and CNT with 0.02 and 0.04 by weight percentage (Wt.%) separately. This solder paste then printed on the printed circuit board (PCB) with the copper surface finish. Printed samples underwent reflow soldering to form the solder joint. Soldered samples then exposed to the open field air blast test with different weight charges of explosives. Microstructure, interfacial IMC layer and micromechanical behavior of SAC/CNT solder joints after blast test were observed and analyzed via optical microscope, field emission scanning microscope and nanoindentation. Findings Exposure to the blast wave induced the microstructure instability of SAC305/Cu and SAC/CNT/Cu solder joint. Interfacial IMC layer thickness and hardness properties increases with increase in explosive weight. The existence of CNT in the SAC305 solder system is increasing the resistance of solder joint to the blast wave. Originality/value Response of micromechanical properties of SAC305/CNT/Cu solder joint has been identified and provided a fundamental understanding of reliability solder joint, especially in extreme conditions such as for military applications.

Purpose The purpose of this paper is to investigate the effect of different viscosity models (Cross and Al-Ma’aiteh) and different printing speeds on the numerical results (e.g. pressure over stencil) of a numerical model regarding stencil printing. Design/methodology/approach A finite volume model was established for describing the printing process. Two types of viscosity models for non-Newtonian fluid properties were compared. The Cross model was fitted to the measurement results in the initial state of a lead-free solder paste, and the parameters of a Al-Ma’aiteh material model were fitted in the stabilised state of the same paste. Four different printing speeds were also investigated from 20 to 200 mm/s. Findings Noteworthy differences were found in the pressure between utilising the Cross model and the Al-Ma’aiteh viscosity model. The difference in pressure reached 33-34% for both printing speeds of 20 and 70 mm/s and reached 31% and 27% for the printing speed of 120 and 200 mm/s. The variation in the difference was explained by the increase in the rates of shear by increasing printing speeds. Originality/value Parameters of viscosity model should be determined for the stabilised state of the solder paste. Neglecting the thixotropic paste nature in the modelling of printing can cause a calculation error of even approximately 30%. By using the Al-Ma’aiteh viscosity model over the stabilised state of solder pastes can provide more accurate results in the modelling of printing, which is necessary for the effective optimisation of this process, and for eliminating soldering failures in highly integrated electronic devices.

Ag-decorated multi-walled carbon nanotubes (Ag-MWCNT) were investigated for use in Sn58Bi solder joints for FCLED packages. Among lead-free solders, Sn58Bi solder has been identified as a candidate for widespread use because of its low melting temperature and high tensile strength. However, Sn58Bi solder is brittle, and it is difficult to relieve it from an impact shock. To overcome these limitations, the bonding characteristics of Sn58Bi solder have been improved with Ag-MWCNT. Ag-MWCNT composite solder paste is fabricated by mixing Ag-MWCNTs of various concentrations with solder paste, and the FCLED chips are bonded on the printed circuit board. The thermal, electrical, and mechanical properties of the solder joints are investigated using various tests. The bonding strength of the Sn58Bi solder with the Ag-MWCNTs increased by 16% compared to that without it. Furthermore, the thermal resistance of the solder alloy decreased by a factor of 2 with the addition of 0.1 wt% Ag-MWCNT.

Purpose This paper aims to investigate voiding phenomena in solder joints under thermal pads of light-emitting diodes (LEDs) assembled in mass production environment by reflow soldering by using seven low-voiding lead-free solder pastes. Design/methodology/approach The solder pastes investigated are of SAC305 type, Innolot type or they are especially formulated by the manufacturers on the base of (SnAgCu) alloys with addition of some alloying elements such as Bi, In, Sb and Ti to provide low-void contents. The SnPb solder paste – OM5100 – was used as a benchmark. The solder paste coverage of LED solder pads was chosen as a measure of void contents in solder joints because of common usage of this parameter in industry practice. Findings It was found that the highest coverage and, related to it, the least void contents are in solder joints formed with the pastes LMPA-Q and REL61, which are characterized by the coverage of mean value 93.13% [standard deviation (SD) = 2.72%] and 92.93% (SD = 2.77%), respectively. The void diameters reach the mean value equal to 0.061 mm (SD = 0.044 mm) for LMPA-Q and 0.074 mm (SD = 0.052 mm) for REL61. The results are presented in the form of histograms, plot boxes and X-ray images. Some selected solder joints were observed with 3D computer tomography. Originality/value The statistical analyses are carried out on the basis of 2D X-ray images with using Origin software. They enable to compare features of various solder pastes recommended by manufacturers as low voiding. The results might be useful for solder paste manufacturers or electronic manufacturing services.

Transient liquid phase-like soldering technique has been successfully applied to prepare lead-free solder joints at 230 °C. Multiple interlayers of tin thin films in combination with a Sn-3.0Ag-0.5Cu (SAC305) solder paste have been used as filler for joining. Microstructural analysis was carried out by electron microscopy and energy-dispersive spectroscopy. For interlayer containing samples (Cu-Sn-SAC305-Sn-Cu), interfacial intermetallics layers found to be more homogeneous compared to the samples without interlayers (Cu-SAC305-Cu). Quality of the joints has been investigated nondestructively by ultrasonic method. On measuring the electrical resistivity by four-probe method, Cu-Sn-SAC305-Sn-Cu solder joint shows lower electrical resistivity compared to that of the Cu-SAC305-Cu solder joint, wherein nonlinear ultrasonic parameters confirm the superiority of former over later.

The effect of bimetallic monodisperse CoPd nanoparticles on the microstructure and the shear strength of the Cu/ SAC305/Cu solder joint was investigated. The nanocomposite Sn–3.0Ag–0.5Cu (SAC305) solders with 0.1, 0.3, 0.5, and 1.0 wt% nanoCoPd were prepared through a paste mixing method. The employed bimetallic nanoparticles were produced via a modified oleylamine method. The microstructural analysis of as-solidified Cu/solder/Cu joints was performed by scanning electron microscopy. The results showed that initial additions of CoPd nanoparticles into the SAC305 solder promoted the growth of the interfacial planar-type Cu3Sn IMC layer; while the average thickness of the interfacial scallop-type Cu6Sn5 IMC layer slightly decreased. Further additions of the nanosized CoPd admixtures to the SAC305 solder paste lead to a significant increase of the average thickness of the Cu6Sn5 intermetallic compound layer up to 40%. The shear strength measurements were performed to investigate a relationship between the microstructure and mechanical properties of the investigated solder joints. The results indicated a decrease in the shear strength of the SAC305 solder joint by addition of 0.1 wt% CoPd NPs, while a difference in absolute values between solder joints with 0.3, 0.5, and 1.0 wt% nanoCoPd was practically insignificant.

Purpose The purpose of this paper is to investigate the wettability and intermetallic (IMC) layer formation of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint according to the formulation of solder paste because of different types of fluxes. Design/methodology/approach Solder pastes were prepared by mixing SAC305 solder powder with different flux and different wt.% of carbon nanotube (CNT). Fourier transform infrared spectroscopy was used to identify functional groups from different fluxes of as-formulated solder paste. The solder pastes were then subjected to stencil printing and reflow process. Solderability was investigated via contact angle analysis and the thickness of cross-sectionally intermetallic layer. Findings It was found that different functional groups from different fluxes showed different physical behaviour, indicated by contact angle value and IMC layer thickness. “Aromatic contain” functional group lowering the contact angle while non-aromatic contain functional group lowering the thickness of IMC layer. The higher the CNT wt.%, the lower the contact angle and IMC layer thickness, regardless of different fluxes. Relationship between contact angle and IMC layer thickness is found to have distinguished region because of different fluxes. Thus it may be used as guidance in flux selection for solder paste formulation. Research limitations/implications However, detail composition of the fluxes was not further explored for the scope of this paper. Originality/value The quality of solder joint of SAC305/CNT/Cu system, as indicated by contact angle and the thickness of IMC layer formation, depends on existence of functional group of the fluxes.

Low temperature reflow is promising to relieve the warpage issue caused by the mismatch of thermal expansion coefficients (CTE) of PCB and BGA components during assembly. While Sn58Bi with a melting point of 138°C has a low reflow temperature, its brittleness can lead to solder joint reliability problems. SAC305 solder alloy has excellent soldering yield and reliability performance, however, the reflow temperature is difficult to be reduced further by element addition or modification. In this paper, the mixed solder of SAC305 and Sn58Bi was prepared by solid-liquid low temperature soldering. low temperature reflow is promising to relieve the warpage issue caused by the mismatch of thermal expansion coefficients (CTE) of PCB and BGA components during assembly. We found that after reflowing at 210°C for 5 min, the solder ball and solder paste were completely mixed. This temperature is much lower than that of SAC305, which can effectively reduce the thermal warpage and thermal budget. In addition, according to the shear test data of solder joints under each reflowing condition, the shear strength increases obviously with the increase of mixing degree. The shear strength of samples refluxed at 210°C for 5 min (63.68 MPa) is about 10 MPa higher than that refluxed for 1 min (52.42 MPa). The results show the mitigation of brittleness in Bi contained solder joints. Our research results provide a promising solution for low-temperature soldering technology in 3D package.

Traditional packaging materials such as solder paste were studied for decades, which is possible to detect initial cracks for a reliability lifetime estimation. While novel die-attach materials such as sintered silver are developing towards higher working temperature and higher current density, it is not clear whether initial cracks are also helpful for reliability assessment. Therefore, in this work, a series of FEM simulations were established for a response surface model with power electronics chip sizes to predict sintered silver joint reliability. Impact factors for resistance were analyzed and compared such as die size and the thickness of the joint. Sintered silver layer sandwiched by copper substrate and terminals with constant current supply was generated and simulated for resistance fluctuation. Through the high-precision DC resistance measurement setup based on the four-probe method, the resistance over ${50 \mathrm{n}\Omega}$ is possible to detect, thus lead to crack growth. In order to study the geometry sensitivity of cracks, preset arc-shape cracks were modeled to simulate crack generation. The coupling of resistance and crack were analyzed through von Mise strain distribution. With a proper geometric configuration of the die-attach layer, it is possible to minimize the testing time for new joint materials through a high precision electrical resistance measurement and simulation-assisted models.

VIPPO design enabled a better signal quality and speed, but it also suffered side-effect caused by this design. At VIPPO location with or without a solid-Cu-hole-fill, the coefficient of thermal expansion (CTE) typically around 17ppm/°C which is quite lower than that of non- VIPPO pads nearby, which is around 45ppm/°C. For double-sided PCB, at ramp-up stage of the second reflow, the difference in CTE of neighboring pads would result in excessive tension on the joint on VIPPO pads, and consequently resulted in Hot-Tear (HT) before reaching melting point of solder joints. Epoxy Flux (EF) was developed to eliminate HT problem. EF dip process did not work due to insufficient EF volume to bond BGA strongly to PCB to nullify the ΔCTE factor. EF dispense process wet well, exhibited low voiding, and allowed sufficient EF volume to fill the gap between BGA and PCB, thus enabled a strong bonding force to nullify the ΔCTE factor, and consequently eliminated the HT defect. The EF developed had the epoxy stress balanced around the solder joints and avoided joint-drifting and solder-extrusion problem. EF dispense process was recommended to be used without solder paste when the BGA was to be assembled. It cured fully in the reflow process, and was non-tacky on touch, and also met IPC SIR requirement. Commercial underfills tested did not work on preventing HT from happening, due to the joint-drifting and solder-extrusion problem. Edge bond or corner bond was also expected to be unable to prevent HT defect. Compared with other polymeric reinforcement materials, EF dispense process minimized the process steps hence was a lower cost valid solution than other reinforcement approaches.

In the present study, SACX0307-ZnO and SACX0307-TiO 2 nano-composite solder pastes were fabricated. The ceramic reinforcements were used in 1wt% and with different primary particle sizes between 50-200nm. The soldering properties and microstructure of the solder joints were investigated. The nano-particles were mixed into the solder paste by standard ball milling process. Reflow soldering technology has been applied to prepare solder joints and spreading tests from the different solder alloys. The solder joints were evaluated by shear test, and cross-sections were prepared to investigate the metallographic properties by Scanning Electron Microscopy (SEM). The different ceramic nano-particles had different effects on the solderability of solder alloys. Best results were observed in the case of TiO2 nano-particles with improved wetting and mechanical strength. The microstructural investigations showed considerable grain refinement and the modified grain boundary/interfacial properties, which could cause the increase of the mechanical parameters.

Solder paste quality can be improved from microstructure and surface status of the solder powder. In this work, the micro-morphology of solder paste was observed and the particle surface condition was analyzed. Also, the conditions of corrosion and the corrosion products in different organic acid groups (activators) were analyzed. The result shows that the SnO passive film on the solder powder surface reacts with the COO– in the active agent of the solder paste. This reaction led the passivation layer to be peeled off. It also caused the change in solder powders’ physical and chemical properties and made the metal boundary to be cold-welded. This is the root cause of solder paste exsiccation and deterioration. The study on the details shows that to obtain high-quality solder paste, one of the key methods is using the solder powder with ideal passivation shell structure and defect-free surface.

The improvement in the hardness of Sn-3.0Ag-0.5Cu solder alloy reinforced with 1.0 wt % TiO2 nanoparticles was evaluated by nanoindentation. A specific indentation array was performed on four different horizontal cross sections of the composite solder with different heights and diameters, in order to verify the mixing homogeneity of TiO2 nanoparticles within the Sn-3.0Ag-0.5Cu solder paste during the ball milling process. The phase analysis indicated successful blending of the Sn-3.0Ag-0.5Cu with the TiO2 nanoparticles. According the scanning electron microscopy micrographs, presence of the TiO2 nanoparticles reduced the size of the Cu6Sn5 and Ag3Sn intermetallic compound phases. Incorporation of the 1.0 wt % TiO2 nanoparticles improved the hardness values up to 26.2% than that of pure SAC305. The hardness values increased gradually from the top cross sections towards adjacent to the solder/substrate interface. The mechanism of the hardness improvement attained by the TiO2 nanoparticles addition were also investigated on the horizontal cross sections of the samples.

Purpose The presence of voids in the solder layer has been considered as one of the main issues causing reliability problems in optoelectronic devices. Voids can be created due to trapped gas, clean-up agent residues (fluxes), poor wettability at interface or shortcoming of the reflow process. The voids hinder the heat conduction path and subsequently, the thermal resistance will increase. The purpose of this paper is to investigate the influence of lead-free water-washable Sn96.5Ag3.0Cu0.5 (SAC305) solder paste (SP) voids on the thermal and optical performance of white high-power (HP) surface-mounted device (SMD) light-emitting diode (LED). Design/methodology/approach Five LEDs are mounted on five SinkPAD substrates by using the SP. The SMT stencil printing is used to control the thickness of the SP and reflow oven for the soldering process. The fraction of voids in the SP layer is calculated using the X-ray machine software. The thermal parameters of the LEDs with different voids fraction and configuration are measured using a thermal transient tester (T3Ster) system. In addition, the optical characterizations of the LEDs are determined by the thermal and radiometric characterization of power LEDs (TeraLED) and the electroluminescence by using the spectrometer. Findings The results showed that the thermal performance and temperature distribution are improved for the LED with lower voids fraction and good filling state of soldering. In addition, luminous flux, efficacy and color shift of the LEDs with different fraction and configurations of voids on the SP layer are compared and discussed. It is found that the color shift of LED1 of low voids fraction and higher thickness are less than other LEDs. Originality/value The paper provides valuable information about the effect of water-washable SAC305 SP voids fraction and filling state of solder on the thermal and optical performance of ThinGaN HP SMD LED. A comprehensive overview of the outcomes is not available in the literature. It was shown experimentally that the voids fraction, height and configuration of the SP layer could strongly influence the heat dissipation efficiency and thermal resistance. This study can help in heat diffusion investigation and failure analysis of HP SMD LEDs.

The effects of printing force and different squeegee geometries on the process of stencil printing were investigated in this paper. Numerical models were established, which included squeegees with different geometries (different overhang sizes of 6, 15, 20, 25 mm) and took the printing force (specific value 0.3 N/mm) into account by using loaded squeegee angles instead of unloaded ones. The flow behaviour of the solder paste was captured by utilising non-Newtonian fluid parameters, which were determined by fitting a curve to the prior measurement results of a lead-free solder paste (particle size 20–38 μm). The effect of different squeegee geometries was characterised by calculating the pressure distribution over the stencil. Results showed a significant difference in the pressure using the unloaded and the loaded squeegee geometries. In the case of unloaded squeegee angle of 60°, the increase was ˜22%, ˜45% and ˜90% for overhang sizes of 15, 20, 25 mm respectively by applying loaded squeegees. In the case of unloaded squeegee angle of 45°, the increase in pressure was even more noticeable; ˜45%, ˜102% and ˜250% for the overhang sizes of 15, 20, 25 mm respectively. This increase in pressure implies that neglecting the printing force and squeegee geometries in numerical investigation of the stencil printing process results in significant calculation errors.

Solder joint with Sn58Bi/Sn3.0Ag0.5Cu/Cu superposition structure was designed and fabricated by two-step soldering process. Sn, Ag, and Cu atoms diffused from the Sn3.0Ag0.5Cu bulk into the molten Sn58Bi solder paste during the second soldering process. The Sn3.0Ag0.5Cu bulk in the composite solder joint increased the concentration and grain size of β-Sn in the Sn58Bi bulk. Moreover, a large amount of tiny Bi-rich particles were found in the Sn58Bi solder bulk. The formation and growth of the β-Sn phases in the Sn58Bi solder bulk was affected by the microstructure of the Sn3.0Ag0.5Cu bulk. Additionally, the β-Sn dendritic in Sn58Bi bulk grew along the Sn3.0Ag0.5Cu bulk like the sunlight. The composite solder joint showed more ductile features than the traditional Sn58Bi eutectic solder joint due to its microstructural transformation occurred during the second soldering process. The Sn3.0Ag0.5Cu bulk with superposition structure works as a barrier to propagate cracks and effectively suppresses the brittle failure of the solder joint.

Purpose The purpose of the paper is to experimentally evaluate the impact of voids on thermal conductivity of a macro solder joint formed between a copper cylinder and a copper plate by using reflow soldering. Design/methodology/approach A model of a surface mount device (SMD) was developed in the shape of a cylinder. A copper plate works as a printed circuit board (PCB). The resistor was connected to a power supply and the plate was cooled by a heat sink and a powerful fan. A macro solder joint was formed between a copper cylinder and a copper plate using reflow soldering and a lead-free solder paste SAC305. The solder paste was printed on a plate through stencils of various apertures. It was expected that various apertures of stencils will moderate the various void contents in solder joints. K-type thermocouples mounted inside cylinders and at the bottom of a plate underneath the cylinders measured the temperature gradient on both sides of the solder joint. After finishing the temperature measurements, the cylinders were thinned by milling to thickness of about 2 mm and then X-ray images were taken to evaluate the void contents. Finally the tablets were cross-sectioned to enable scanning electron microscopy (SEM) observations. Findings There was no clear dependence between thermal conductivity of solder joints and void contents. The authors state that other factors such as intermetallic layers, microcracks, crystal grain morfologyof the interface between the solder and the substrate influence on thermal conductivity. To support this observation, further investigations using metallographic methods are required. Originality/value Results allow us to assume that the use of SAC305 alloy for soldering of components with high thermal loads is risky. The common method for thermal balance calculation is based on the sum of serial thermal resistances of mechanical compounds. For these calculations, solder joints are represented with bulk SAC305 thermal conductivity parameters. Thermal conductivity of solder joints for high density of thermal energy is much lower than expected. Solder joints’ structure is not fully comparable with bulk SAC305 alloy. In experiments, the average value of the solder joint conductivity was found to be 8.1 W/m·K, which is about 14 per cent of the nominal value of SAC305 thermal conductivity.

This paper offers a statistical methodology for evaluating Pb-free solder alloy performance for high–reliability products using Cox proportional regression analysis and provides a detailed application of the technique based upon a 15-mm BGA package. Specifically, the effects of doping SAC305 solder balls with small amounts of Bi, Co, In, Mn, Ni, and Sb either directly or from the solder paste used for assembly have been studied. The test results have led to a downselection of optimum material combinations that offer a potential solution to the well-known material degradation of SAC305 solder alloys with aging. The test conditions had two different time/temperature periods: 10 days at 25 °C and an accelerated condition of 180 days at 125 °C. Each test board was temperature shocked 3000 times (−40 °C–125 °C) with a 15-min thermal profile (5-min dwell time and 2.5-min transition time). The electrical continuity of solder interconnect was examined during the tests, and the effect of solder doping and aging on the failure rate (hazard rate) were assessed at 90% confidence level using the proportional hazard model. We found that the solder doping combination, aging time and temperature, and the interactions between these parameters have significant impacts on the failure rate. BGA with Sn–Ag–Cu doped with Sb, Bi, Co, and Ni can significantly reduce the failure rate after aging with a 90% level of confidence. The failure analysis shows recrystallized assisted crack nucleation in the solder joints.

In this study, the nanoporous copper (NPC) sheets were fabricated by dealloying Cu40Al60 precursor alloy in 1.45 mol/L dilute hydrochloric acid solution under water bath at 80 °C for 12 h. The NPC sheets had a typical homogeneous ligament-pore microstructure with the average pore size of 320 nm. The NPC sheet was sandwiched between two Cu substrates with Sn3.0Ag0.5Cu (SAC305) solder paste. The melted solder infiltrated the NPC sheets and reacted with the Cu ligaments rapidly. A Cu/Cu-Sn IMCs/Cu interconnection can be achieved after reflow at 240 °C for 10 min under a pressure of 5 MPa. The average shear strength of the bondlines was 37.68 MPa, and the maximum shear strength can reach up to 57.38 MPa. The average resistivity of the bondlines was measured to be 13.38 μΩ·cm. At last, the evolution of microstructure, Vickers hardness and shear strength of the bondlines during aging test at 200 °C for 15 days were characterized. The bondline can be fabricated at a low temperature but can service at a much higher temperature with a high re-melting point, which can provide a new die attach method for high temperature power device packaging.

Good wetting, strong bonding and low electrical resistance are the most important properties of the solder in microelectronic packaging. Aim of this study was to improve the mechanical and wetting properties of commercially available lead-free solders. Different type and sized ceramic particles treated with different surface modification methods were added to lead-free SAC305 solder paste to form composites. The reinforcement particles were subjected to various surface modification processes. We made reflow soldering in the same way as in industrial application. Solder joints were formed between a novel designed test PCB board and microelectronic components. The mechanical properties of the composite joint were tested by microhardness measurement and shear test, while the microstructure and the IML layer were examined by scanning electron microscope.

The effects of the flux formulation temperature on the printing and wetting properties of solder paste were evaluated in this study. The tested flux formulation temperatures were 100, 150, and 200 °C. The fluxes were mixed with Sn–3.0Ag–0.5Cu (SAC305) solder powders to produce solder pastes. The slump ratio of the solder paste increased with increasing flux formulation temperature. Slump and bridge tests revealed that low flux formulation temperatures provided good slump properties. The flux viscosity decreased with the flux formulation temperature, which also decreased the solder paste viscosity. Hence, the high slump with high flux formulation temperature was due to low flux viscosity. The wetting properties of the flux were observed by wetting balance testing. The wettability was the lowest for the lowest flux formulation temperature because of its high viscosity. Although the viscosity was the lowest at a formulation temperature of 200 °C, the wettability was not the highest because of the low flux activation. Therefore, the flux formulated at 150 °C provided the best solder printing and wetting properties.

Purpose This study aims to investigate the NiO nano-reinforced solder joint characteristics of ultra-fine electronic package. Design/methodology/approach Lead-free Sn-Ag-Cu (SAC) solder paste was mixed with various percentages of NiO nanoparticles to prepare the new form of nano-reinforced solder paste. The solder paste was applied to assemble the ultra-fine capacitor using the reflow soldering process. A focussed ion beam, high resolution transmission electron microscopy system equipped with energy dispersive X-ray spectroscopy (EDS) was used in this study. In addition, X-ray inspection system, field emission scanning electron microscopy coupled with EDS, X-ray photoelectron spectroscopy (XPS) and nanoindenter were used to analyse the solder void, microstructure, hardness and fillet height of the solder joint. Findings The experimental results revealed that the highest fillet height was obtained with the content of 0.01 Wt.% of nano-reinforced NiO, which fulfilled the reliability requirements of the international IPC standard. However, the presence of the NiO in the lead-free solder paste only slightly influenced the changes of the intermetallic layer with the increment of weighted percentage. Moreover, the simulation method was applied to observe the distribution of NiO nanoparticles in the solder joint. Originality/value The findings are expected to provide a profound understanding of nano-reinforced solder joint’s characteristics of the ultra-fine package.

A method for directly bonding thermoelectric elements onto copper electrodes without applying a solder paste was developed in this study. A tin coating of thickness approximately 50 μm was deposited via electroplating onto the surface of a Bi₂Te₃-based thermoelectric element, which had a nickel diffusion barrier layer. The resulting structure was subsequently subjected to direct thermocompression bonding at 250 °C on a hotplate for 3 min at a pressure of 1.1 kPa. Scanning electron microscopy imaging confirmed that a strong and uniform bond was formed at the copper electrode-thermoelectric element interface, and the melted or solidified tin layer remained defect-free. The thermoelectric module fabricated using tin plating had an average bonding strength similar to that fabricated using soldering.

Purpose To explore substitutes for traditional Sn-Pb solder, Sn-20In-2.8Ag was considered because of its appropriate melting temperature, good reliability and high ductility at less than 100°C. However, the mechanical properties of Sn-20In-2.8Ag were not satisfactory. The reason for the poor mechanical properties of the Sn-20In-2.8Ag/Cu joint was revealed, and a way to solve the problem was found. Design/methodology/approach The microstructure evolution, characteristics of melting and solidification and joining performance with Cu were investigated using scanning electron microscopy (SEM), electron probe microanalysis, differential scanning calorimetry (DSC) and mechanical testing. Findings SEM results showed that the microstructure of Sn-20In-2.8Ag was composed of coarse dendritic Ag2In and γ phases, with Ag2In distributed at the grain boundaries. DSC measurements revealed that small amount of low temperature eutectic reaction, L → Ag2In + β + γ, occurred at 112.9°C. This reaction was caused by the segregation of indium, which is a process that has a strong driving force. In the lap-shear testing, a crack propagated along the grain boundary of the solder, and failure showed an intergranular fracture. This failure was connected with the three-phase eutectic and coarse Ag2In. Thus, to improve the mechanical properties, segregation of indium should be reduced and coarsening of Ag2In should be prevented. Originality/value The reason for the unsatisfactory mechanical properties of Sn-20In-2.8Ag was revealed via microstructural observations and solidification analysis, and the way to solve this problem was found.

The present study examines the effect of squeegee load, squeegee speed, and separation speed on the printing performance of lead-free solder paste, and solder printing was carried out to evaluate the effect of the filled volume of the solder paste during stencil printing. Application of pressure on the squeegee affects the filled volume of the solder paste in the stencil aperture, and the incorrect pressure setting could cause incomplete filling. Herein, an experiment was conducted on a printing machine employing surface mount technology. The solder paste used in the study was Sn/Ag/Cu (SAC305), and four components, namely, 0603, small outline transistor (SOT), 1210, and tantalum-D, were tested. The filled volume and height of the solder paste under different squeegee loads, squeegee speeds, and separation speeds were determined, and the solder volume was found to vary with the squeegee load and component type. Response surface method (RSM) optimization is conducted to obtain optimum filled volume and solder paste height and area during the printing process. The method showed squeegee load, squeegee speed, and separation speed have considerable effects on filled volume, solder paste height, and solder paste area.

The jet printing process of Sn-58Bi lead-free solder paste involving expansion, necking, pinch-off and satellite droplet formation was observed and analyzed with the aid of high-speed photography. The viscosity and phase angle of the solder paste at three temperatures were measured using a rheometer. Spattering behavior of the solder paste was observed at 55°C. The spatter on the substrate came from a second satellite droplet which was produced in the second pinch-off of the solder paste and collided with the nozzle. Satellite droplets were produced at three temperatures when droplets break off, and the number of satellite droplets was determined at each temperature. The appropriate temperature could reduce the viscosity of the solder paste and improve the liquid-like behavior, which is conducive to realizing the jet printing process with an ideal ratio of height to diameter of the solder joints. According to the demand for jet solder paste, high-speed photography and rheological methods can help establish the relationship between jet printing performance and materials design.

The properties of Sn99Ag0.3Cu0.7 (SACX0307) solder alloy reinforced with ZnO nanoparticles were investigated. The primary ZnO particle sizes were 50, 100, and 200 nm. They were added to a solder paste at a ratio of 1.0 wt %. The wettability, the void formation, the mechanical strength, and the thermoelectric parameters of the composite solder alloys/joints were investigated. Furthermore, microstructural evaluations were performed using scanning electron and ion microscopy. ZnO nanoparticles decreased the composite solder alloys’ wettability, which yielded increased void formation. Nonetheless, the shear strength and the thermoelectric parameters of the composite solder alloy were the same as those of the SACX0307 reference. This could be explained by the refinement effects of ZnO ceramics both on the Sn grains and on the Ag3Sn and Cu6Sn5 intermetallic grains. This could compensate for the adverse impact of lower wettability. After improving the wettability, using more active fluxes, ZnO composite solder alloys are promising for high-power applications.

We have transferred and bonded a $\mu \text{LED}$ array to the patterned substrate using SITRAB (Simultaneous transferring and bonding) and ASP (Anisotropic Solder Paste). ASP contained epoxy as a base matrix, solder powder, and a small fraction of polymer balls and was applied to the substrate using screen printing. We have arrayed $\mathrm{20}\times \mathrm{20}$ of $\mu \text{LEDs}$ on the interposer, which is PDMS laminated glass wafer. The interposer was picked-up by quartz bonder-head and aligned to the substrate. After aligning the interposer to the substrate, the bonder-head moved to the substrate and applying pressure. While applying the pressure, the homogenized laser with a wavelength of 980nm was irradiated through the quartz bonder-head for a few seconds. In this process, transferring and bonding the $\mu \text{LED}$ array are performed simultaneously, so we named this process SITRAB. After the SITRAB process, the $\mu \text{LED}$ array bonded substrate was cured at 120°C for 2 hours. Because the ASP contains no vaporizable substance, there is no fume during the SITRAB process, and the cleaning is unnecessary after the post-cure process. Using ASP material and the SITRAB process, a $\mathrm{20}\times \mathrm{20}\ \mu \text{LED}$ -array was successfully transferred and bonded to the substrate. We observed the light output from the $\mu \text{LED}$ array bonded to the electrodes and measured a cross-sectional SEM image to analyze the bonding joint.

Durafuse™ LT paste was designed as an alternative low temperature solder targeting at enabling hierarchy design for portable devices with good temperature cycling and superior drop-shock performance. It is formulated with the mixed solder powder technology to allow the paste reflowable at around 200°C or above. Durafuse™ LT formed solder joints with a melting temperature above 189°C and a plateau type reflow profile was recommended. Impact of reflow profiles on both drop shock and temperature cycling performance was investigated. The drop number increased with increasing peak temperature up to 210°C, presumably due to an improved homogeneity of solder joint. It also increased with increasing plateau time at peak temperature for temperature below 210 °C. At 210 °C, the drop number decreased with increasing plateau time, presumably due to increasing IMC thickness at pad interface. Homogeneous solder joints were more resistant to drop failure than mixed alloy system, and could be attributed to better homogeneity for the former system. Regardless of reflow profile impact, Durafuse™ LT showed at least two-order-of-magnitude higher drop shock resistance than Bi-Sn-Ag solder. Using the optimized reflow profiles, Durafuse™ LT outperformed SAC305 in drop-shock test. For LGA with homogeneous solder joint, Durafuse™ LT exhibited a characteristic life about 2.5X of BiSn0.4Ag. For chip resistor reliability in TCT, no significant difference in reliability could be discerned when comparing ENIG with OPS. Durafuse™ LT was slightly lower in reliability than SAC305. Higher peak temperature resulted in a better reliability for Durafuse™ LT. The chip size appeared to be an insignificant factor.

The study attends to the evaluation of solder joints from a mechanical point of view. Two lead-free alloys Sn99.7Cu0.3 and Sn96.5Ag3Cu0.5 (SAC305) were selected for samples preparation. To compare the results of current alloys with the most utilized solder in the past, the study comprises eutectic lead solder paste Sn63Pb37, too. Solder joints intended for observation were created by assembling chip resistors. Assembled boards were reflowed employing a hot air convection oven. Mechanical properties were evaluated by performing shear tests and microhardness measurements. Microhardness of bulk solder and intermetallic compounds (IMC) was measured using the micro-indentation Vickers test. For this purpose, a metallographic cross-section of some samples was accomplished. Solder pads on testing boards were coated by Organic Solder Preservative (OSP) and Hot Air Solder Levelling (HASL). Depending on solder paste type, the results show more or less impact of surface finish on the solder hardness. Some difference in microhardness of IMC layers and shear strength was also detected but, in these tests, results are not in favour of one surface treatment.

In the present research, the solderability of SACX0307 nano-composite solder alloys was studied. The SACX0307 solder alloys were reinforced by ZnO or TiO2 nanoparticles. The nanoparticles were mixed into the solder paste in different volume fractions between 0.25 and 1 wt%, using the ball milling process. Wetting and mechanical tests were performed with the nano-composite solder alloys and with the reference SACX0307 as well. It was found that the ceramic reinforcements did not have a considerable effect on the wetting of the composite solder alloys. However, the shear strength of the nano-composite solder joints increased compared to the reference SACX0307. Generally, the application of TiO 2 nanoparticles resulted in a bit better solderin properties than the ZnO nanoparticles. No straightforward correlation was found between the volume fraction of the ceramic nanoparticles and the soldering properties of the nano-composite solder alloys. Expect in the case of the ZnO nanoparticles, when the volume fraction should not exceed 0.5wt% since it can inhibit the proper reflow of the solder paste.

This paper is focused on the dynamic stretch testing of SMD chip resistors which were contacted on a textile conductive ribbon by a thermo-compression method. In this method, the plastic housing made from Acrylonitrile Butadiene Styrene (ABS) material with a cavity for SMD component is placed on the textile ribbon, melted and subsequently cooled under continuous pressure (variant 1). The electrical contact resistance can be decreased by applying SnBi solder paste on the conductive textile pads (variant 2) or by realizing SnBi bumps on the leads of the SMD component (variant 3). Low-temperature solder based on Bismuth material can be melted altogether with plastic housing in one step. The electrical contact resistance was measured right after the manufacturing and subsequently after every 2000 stretching cycles up to 12000 cycles. This paper is focused on the dynamic stretch testing of SMD chip resistors which were contacted on a textile conductive ribbon by a thermo-compression method. In this method, the plastic housing made from Acrylonitrile Butadiene Styrene (ABS) material with a cavity for SMD component is placed on the textile ribbon, melted and subsequently cooled under continuous pressure (variant 1). The electrical contact resistance can be decreased by applying SnBi solder paste on the conductive textile pads (variant 2) or by realizing SnBi bumps on the leads of the SMD component (variant 3). Low-temperature solder based on Bismuth material can be melted altogether with plastic housing in one step. The electrical contact resistance was measured right after the manufacturing and subsequently after every 2000 stretching cycles up to 12000 cycles.

Since lead is a pollutant to the environment, therefore lead-free solder paste compounds have been interested in many research teams. The objective of this research is the investigation properties of solder paste with graphene oxide and reduced graphene oxide. In our experimental method the solder pastes of SnAgCu mixed with graphene oxide with bad electrical conductivity at different concentration by weight of 0.00%, 0.05%, 0.1% and 0.2% respectively. Subsequently, the shape changes of the compounds have been investigated by using digital in-line holography using laser diode wavelength 635 nm as the light source. The solder paste compounds were melted at $250\pm 5^{\ \circ}\ C$ and were recorded for every 5 seconds. Then, the contact angles of the melted solder paste compound have been determined using their digital holographic reconstructed images.

Due to pressure to meet consumer requirements, miniaturization, reliability, and increased functionality have become more important. To achieve good assembly of electronic devices, there must be smooth deposition of tiny and consistent paste deposits on the board which must be up to an acceptable height and volume based on desirable process parameters in the output. The printing performance of the solder paste is dependent on conditions such as paste deformation behavior, good paste roll, complete aperture filling, and paste release onto the substrate pads. Eighteen tests were performed using two types of lead-free solder paste. Three temperatures were investigated under three different time intervals. Results analysis showed that variability of the paste distribution was lowest and more uniform for paste stored at 25˚C for 48 hours. From the analysis, it is obvious that temperature has tremendous effects on the printing performance of solder paste. This study recommends 25˚C as a good temperature for solder paste printing.

The SiP module market has grown significantly over the past several years and is now becoming one of the fastest growing packaging technologies in the semiconductor industry owing to its lower cost, smaller form factor, higher levels of integration, and better electrical performance. The assembly of these miniature components requires advanced solder paste with finer particles size, such as Type 7 ( $2-11\mu \mathrm{m}$ ) and smaller. Increase in powder surface area as the powder size decreases might lead to formation of more void, if the flux is not capable of removing the surface oxides. Voids in solder joints are considered one of the most detrimental defects in electronic assembly as it reduces mechanical robustness of interconnection and consequently affect the reliability, especially on fine pitch devices with increasing functionality. Ideally, achieving zero void is the goal, but this is not easy to achieve. Factors, such as flux chemistry, solder paste printing, and reflow profile, have significant influences on the amount of void. While water soluble chemistry solder paste is still the mainstream in SiP modules assembly, no clean solder paste is getting increased attention. In this work, a solder paste with no clean flux chemistry will be evaluated in comparison to a water-soluble counterpart. The paper will report the printability performance of both solder pastes along with the effect of reflow parameters such as ramp-up rate, soak time, time above liquidus (TAL) and peak temperature (within the allowable process limits) towards minimizing the occurrence of voids.