Saipeng Li

Effect of indium addition on interfacial IMC growth and bending properties of eutectic Sn–0.7Cu solder joints

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.

Investigation of jet printing performance of lead-free solder paste

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.

Microstructure and mechanical properties of resistor chip joints fabricated by laser soldering using Sn-58Bi solder on Ni(P)/Cu pads

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. Ni3Sn4 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.

The influence of thermal aging on reliability of Sn-58Bi interconnects

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 effect of conductive filler on the properties of electrically Conductive Adhesives(ECAs)

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.

The effect of curing agent on the properties of silver paste Electrically Conductive Adhesives(ECAs)

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.

Investigation of properties and curing process of silver paste electrically conductive adhesives (ECAs)

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 morphology and rheological characteristics of silver paste electrically conductive adhesives (ECAs)

Jet printing technology solves the problem of control of solder pastes 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.