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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 microstructure and mechanical properties of Sn-0.7Cu solder alloy and Sn-0.7Cu with 1.0–5.0 wt% indium addition were investigated in this study. With indium added into Sn-0.7Cu solder, the melting temperature decreased and the reaction temperature increased. Coarse grains of Cu6(Sn,In)5 intermetallic compounds (IMCs) were formed in the alloy matrix when the indium content increased to 1.0 wt%. Indium was evenly distributed in the β-Sn phase and Cu6(Sn,In)5 IMCs in as-prepared In-containing solder alloys. After isothermal aging, indium accumulated gradually in the Cu6(Sn,In)5 IMCs while decreasing its content in the β-Sn phase. Tensile test results indicated that the ultimate tensile strength increased obviously and that the elongation decreased significantly with indium addition. Sawtooths were observed in the stress-strain curves of all aged In-containing alloys. A model describing a coherent relationship between the β-Sn phase and the Cu6(Sn,In)5 phase was proposed to explain this phenomenon. The fracture surface of the Sn-0.7Cu alloy exhibited a ductile fracture mode while a mixed ductile-brittle fracture mode occurred when excessive indium was added into Sn-0.7Cu alloys.

The rheological character and jet printing performance of the lead-free solder paste (Sn–58Bi) with four solid phases were investigated. The rheology tests, containing oscillation test, creep recovery test, viscosity test and thixotropic loop test, were conducted by an Anton Paar MCR302 rheometer. Jet printing technology is a new packaging method with many advantages such as high precision, customization, low cost, etc. The jet printing test was carried out with the spray nozzle heated to 50 °C. From this study, it is found that the G″/G′ ratio of the pastes obtained by the oscillation stress test can influence the jet printing performance of the pastes. Paste 2 with the lowest ratio of G″/G′ can form the most complete hemispherical droplet. In addition, the solder paste with better liquid-like character at the nozzle and more solid phase property and surface tension when crashing on the base plate could be reverted to the hemispherical morphology easily. As the demand for pastes applied to jet printing increases, rheological measurement can assist with the research of the new high viscosity lead-free solder pastes.

The microstructure and growth behaviors of interfacial IMCs between the Sn–0.7Cu–xIn (x = 0–5.0 wt%) solder and Cu substrate under solid aging were investigated. Bending test was conducted to evaluate the mechanical properties of Cu/Sn–0.7Cu–xIn/Cu solder joints. The needle-like Cu6(Sn,In)5 IMCs formed at interface instead of Cu6Sn5 in as-soldered In-containing solder joints. During solid aging, indium addition had little influence on the growth of Cu6Sn5 IMCs, but strongly suppressed the growth of Cu3Sn IMCs. In Sn–0.7Cu–5.0In/Cu couple, the maximum solubility of indium in Cu6Sn5 and Cu3Sn was about 4.9 and 3.1 at.% respectively which was independent of aging temperature. The average composition of Cu6(Sn,In)5 and Cu3(Sn,In) were given as Cu6(Sn0.89,In0.11)5 and Cu3(Sn0.88,In0.12). After indium addition, the diffusion coefficients were found to be lower than that of Sn–0.7Cu/Cu couple and the activation energy for the growth of Cu3Sn increased with the increase of indium content. Doping indium into Sn–0.7Cu solder improved the bending properties of solder joints. Interfacial cracks were suppressed effectively after long time aging with indium addition.

Solder paste plays an important role in the processing of surface mount technology in electronic packaging. In this study, the Sn-0.3Ag-0.7Cu solder powder was used as the alloy powder, in combination with different lead-free solder pastes. The effect of active agents on the rheological properties of solder paste was investigated systematically with a combined method including oscillation stress sweep test, thixotropic loop test and creep-recovery test. The results show that the loss coefficient of the solder paste containing succinic anhydride was high and its flow stress was small as well at room temperature, which structure is unstable and have a poor jet printing performance. At low shear rate, Dimethylol Propionic Acid (DMPA) plays a role in the viscosity increasing of the solder paste, When the value of G″/G′ was between 0.4 and 0.5 and the flow stress was about 100 Pa, the jet printing condition of the solder paste was better, and there was less phenomenon of nozzle jam at room temperature.

Solder paste is an integral part of surface mount technology which an adequate understanding of its behavior and properties is essential to comprehend the relationship solder paste has to the overall manufacturing process. The jet printing technology of solder pastes is a new packaging method which provides customized packaging solutions for different requirements with a cost advantage. Jet printing technology solves the problem of control of solder paste's height in screen printing and it is also suitable for soft substrate printing, which may possible make it have wide application in complex integrated circuit. This study concerns the rheological characterization of different solder paste component used for jet printing. A series of rheological tests were carried out (viscosity, oscillation stress sweep, thixotropic loop and creep recovery test) to aid with understanding the characteristic of the pastes in the flowing processing. Besides, the pastes samples were tested on a jet printing machine with piezoelectric ceramics actuator as driving force. The solder pastes were jet printed onto a pad and the imagination of droplets were collected by a 3D microscope. Our results show that the nonlinear flow curve obtained in the viscosity test revealed the “shear thinning” behavior of solder paste samples as typical non Newtonian fluid. The linear viscoelastic region(LVR) of three solder paste samples was obtained by the oscillation stress sweep test curve and the transition point between liquid and solid was determined when the storage modulus (G') equal to the loss modulus (G″). Paste 1 indicated the biggest LVR while Paste 3 occupied the highest value of G' and G″. The Paste 3 indicated the largest thixotropic loop area and the least unrecovered stress. The creep recovery properties were further tested according to the LVR under shear stress of 5Pa and 50Pa, respectively. In the recovery test Paste 3 indicated the best recovery and the lowest values of creep and recovery compliance in the LVR (more than 5Pa) while the opposite results at the stress of 50Pa, which proved that the irreversible deformation happened in the internal structure of solder paste. Jet printing results show that Pastel could obtain excellent droplet morphology similar to the perfect hemispherical. While Paste 2 obtained highest points in three samples as the largest ratio of height to diameter. Fracture and collapse arose after the droplets of Paste 3 were printed.

With the miniaturization of electronic devices and the utilization of heat-sensitive electronic components, the couple of solder with low melting temperature and laser soldering technology would be applied in electronic packaging. In this study, the microstructure and mechanical properties of resistor chip joints fabricated by laser soldering were investigated. The energy input of the laser was 1 W and the soldering time was more than 0.3 s, resistor chip could be bonded with pads reliably. Precipitated Bi phase was not observed in the laser soldering joints due to the rapid cooling rate. Ni 3 Sn 4 IMCs layer formed between Sn-58Bi solder and Ni(P)/Cu pads. The thickness of IMCs layer was less than 1.0 µm even if the laser soldering time was more than 1.0 s. The maximum shearing force of laser soldered joints increased with increasing the soldering time which was slightly lower than that of reflow soldered joints.

Silver paste electrically conductive adhesives (ECAs) are adhesives containing silver particles and resin matrix, forming by specific technology. The conductive adhesive has better printing performance than the solder paste, which can meet the requirements of higher precision. However, the relationship between curing process and properties of conductive adhesive has not been developed completely and it is time to explore a kind of conductive adhesive which is suitable for fast curing. The effects of curing time and temperature of conductive adhesives on electrical and mechanical properties are studied in this paper. Several analysis methods are used to test scanning electron microscope photograph, electrical and mechanical properties and so on. Besides, the TG and DSC curves are studied to seek the appropriate curing temperatures of three conductive adhesives with different volume percentages. The curing process has influence on the electrical and mechanical properties of the conductive adhesive after curing. When the curing temperature is lower than the temperature of the crosslinking reaction, the curing process is not complete, and the resistivity shows large. The shear strength of the conductive adhesive increases with the increase of curing time. The conductive adhesive can be cured completely when the curing temperature reaches the temperature of crosslinking reaction and the resistivity decreases with the increase of the curing temperature. The shear strength increases with the increase of curing time in the initial stage of curing process and the conductivity and shear strength begin to decrease when the curing time reaches a certain range. Curing temperature over 140°C can be difficult to get good conductivity and shear strength.

Jet printing technology solves the problem of control of solder paste's height in screen printing and it is also suitable for soft substrate printing, which may possible make it have wide application in complex integrated circuit. Conductive adhesive is a kind of adhesive containing conductive particles and resin matrix, forming by specific technology. The ECAs own better printing performance than the solder paste, which meeting the requirements of higher precision. However, jet printing technology of ECAs has not been developed completely and it is time to explore a kind of conductive adhesive which is suitable for jet printing and fast curing at the same time. The effects of different components of ECAs on printing are studied in this paper. Different analysis methods were used to test viscosity, scanning electron microscope photograph, jet printing performance and so on. Besides, the rheological behavior, morphology, points dimension were studied in printing performance. Compared with the conductive adhesive containing triethanolamine which could be printed well, the conductive adhesives containing methyl hexahydrophthalic anhydride and dicyandiamide are difficult to be printed. According to the results of viscosity test, when the shear rate is low, the viscosity-shear rate curves of conductive adhesives which contain triethanolamine and dicyandiamide are similar, which means that they own the similar rheological properties.

The paper used Sn-58Bi interconnects to perform the thermal aging treatment under different times, namely one day, three days, fine days, seven days, fifteen days under 120°C. Then the tensile experiment was launched, the mechanical properties of solder joints were analyzed by looking at the joint defect, fracture and the IMC layer with SEM, combining with the tensile properties and fractograph analysis of the samples under different temperature, namely room temperature, 60°C, 80°C and 120°C, finally came to conclusions about reliability. According to the above experiments, some results can be found that as the aging time goes on, the IMC layer thickens, the strength of micro bumps has a tendency to continue to decrease, the fracture model is the brittle fracture and fracture position is given priority to internal fracture in solder, which may be associated with low tensile velocity. Under the condition of low strain rate, the decrease of the solder joint strength is mainly embodied in the damage of solder structure during the formation of chemical compounds. In addition, with the increase of temperature, the fracture model has been changed from the brittle fracture to the ductile fracture.

The Electrically Conductive Adhesives(ECAs) has better printing performance than the solder paste, which can meet the requirements of higher precision. In this paper, three different kinds of organic matter were used as curing agents in an ECAs to find out the effect on that. The effect of curing agent on the conductive properties of silver paste ECAs has been systematically investigated by volume resistivity test, and the curing loss rate was used to indicate the curing properties. In addition, the mechanical properties on different curing time were analyzed by comparing the shear stress through shear strength test. The analysis of volume resistivity test indicated that extension curing time will make the unevenness of silver particle become larger, which can benefit the conductivity of silver paste ECAs. Whats more, and the result of shear strength tests show that when curing time up to 20 minutes, the shear strength of containing triethanolamine and dicyandiamide silver paste ECAs will be more than 10MPa when curing time up to 20 minutes. The curing loss rate indicate that the silver paste ECAs which contains triethanolamine is the most stable one.

The conductive filler in the Electronic Conductive Adhesives(ECAs) have been widely investigated for decades. In this paper, the mass fraction of silver powder ranging from 30% to 50% was added as conductive filler into ECAs. To study the influence of the content of the conductive filler, volume resistivity, shear strength and jet printing test were carried out to assess the conductivity, shear stress and the shape of jetting dots, respectively. According to the percolation theory and the result of conductivity test, it reached its percolation when the mass fraction of silver powder increased up to 40%, and the shear strength decreased as the mass fraction of silver powder progressively increased. The result of jet printing test showed that the probability of contact between silver particles increased with the content of silver powder increasing, which results in jam problem.

Solder paste is the most important strategic bonding material for surface mounting components in electronics manufacturing field. The aim of this study was to investigate the effect of thixotropic agents on the rheology of SnAgCu lead-free solder pastes and grope for materials suitable for jet printing process. The rheological behaviors consisting of viscosity, oscillation, creep recovery and thixotropy of solder pastes added with four thixotropic agents were investigated. The jet printing test was carried out at room temperature. In this paper, it is found that thixotropic agents ST and CVS can reduce the G''/G' ratio of solder pastes calculated by the oscillation stress curve. Besides, ST and CVS can effectively improve the area of thixotropic loop and the value of unrecovered stress, which is suitable for the jet printing. T4 samples with CVS can be jetted continuously for more than 5000 points with a minimum diameter of 372.3 μm. As the demand for solid-liquid two-phase fluid materials applied to jet printing increases, rheological methods can assist with the exploration of new high viscosity lead-free solder pastes.

Surface Mounted Technology (SMT) is a universal technology used in electronics packaging industry. Electronic manufacturing industries have utilized advanced Integrated Circuits(IC) packages to achieve the manufacture of smaller, lighter, faster and cheaper products. However, the assembly of these surface mounts packages and the reliability of the products are challenged by solder paste printing process. A novel solder paste jet printing technology can solve the problem well, which demands a new-type solder paste suitable for jetting process. The solder paste is the homogeneous mixture of alloy solder powder and flux. In this paper, the viscosity and stability properties of Sn-3Ag-0.5Cu lead-free solder pastes have been systematically investigated by viscosity test, slump test and other material analysis methods. The impacts of different metal content, alloy type, and size distribution on the viscosity, thixotropy and slump properties have also been discussed. The requirements of solder powder used for jet printing have also been concluded by jet printing test. In addition, the rheology and jet printing performance of solder pastes with different kinds of flux have been compared and the influence of thixotropic agents was explored preliminarily.