Shuang Tian

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 (xu2009=u20090–5.0 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.

Rheological characterization and jet printing performance of Sn–58Bi solder pastes

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 50xa0°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.

Effect of bonding time on the microstructure and mechanical properties of Co/Sn/Cu joint

The bonding process of Co/Sn/Cu couple has been conducted at 270u2009°C. The microstructure evolution was observed. The spreading test of Cu/Sn–xCo and Co/Sn–xCu was conducted to explain the microstructure evolution of Co/Sn/Cu couple. The results showed that the main interfacial intermetallic compounds (IMCs) layer of Cu/Sn side of Co/Sn/Cu couple was (Cu, Co)6Sn5, as the dissolution of Co from Co substrate to solder layer. The (Cu, Co)6Sn5 IMCs layer only thickened slightly during bonding process as large amount of the (Cu, Co)6Sn5 IMCs layer dissociated into solder alloy layer. As the adsorbing effect of Co substrate on the dissociating (Cu, Co)6Sn5 IMCs, there was a thick (Cu, Co)6Sn5 IMCs layer covered on the surface of Co substrate at the early stage of bonding process. For longer bonding time (>u200930xa0min), the (Co, Cu)Sn and (Co, Cu)Sn3 IMCs generated on the Co/(Cu, Co)6Sn5 interface as the diffusion of Sn atom from liquid solder alloy to Co/(Cu, Co)6Sn5 interface. The Co/Sn/Cu joint bonded for 60xa0min could work at the temperature of 300u2009°C. The shear strength of joints bonded for 20 and 30xa0min was approximate 45xa0MPa. The shear strength of joints bonded for a time more than 30xa0min declined gradually as the generation of (Co, Cu)Sn3 IMCs.

Microstructure, interfacial reactions and mechanical properties of Co/Sn/Co and Cu/Sn/Cu joints produced by transient liquid phase bonding

In this paper, the wettability and growth behaviors of interfacial intermetallic compounds (IMCs) in the Sn/Co and Sn/Cu liquid/solid couples were comparatively investigated. In situ tensile tests were conducted to evaluate the mechanical properties of the Co/Sn(IMCs)/Co and Cu/Sn(IMCs)/Cu joints. The wettability of Sn on Cu substrate was better than that of Co substrate. The lath-like CoSn3 IMCs limited the improvement of wettability of Sn on Co substrate, even if the soldering temperature was increased. The Sn/Co couples showed an acceptable wettability for electronic application. During liquid aging, the rapid growing interfacial CoSn3 were controlled by the combination of chemical reaction and atomic diffusion. Grain boundary diffusion should be responsible for the growth of Cu6Sn5 in the Sn/Cu liquid/solid couples. The tensile strength and elongation of the Co/CoSn3/Co joints were basically equal to that of the Cu/IMCs/Cu full IMCs joints. Interfacial IMCs cracks were more likely to occur in the joints fabricated by Co substrate. The Co/CoSn3/Co sandwich structure can be fabricated within a remarkable short period of time at low temperature without pressure.

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.

Effect of interfacial intermetallic compounds morphology on mechanical properties of solder joint with finite element simulation

The morphology of interfacial intermetallic compounds (IMCs) can have serious impact on the reliability of solder joints. This paper investigated the effect of interfacial IMC (Intermetallic Compound) morphology on mechanical properties of solder joint by finite-element method. The joint model is consisted of copper, Cu6Sn5 interfacial IMC and Sn-3.0Ag-0.5Cu solder alloy. The surface of interfacial IMC was simplified into a cyclical one. In finite-element analysis, these joints with different interfacial IMC morphology were extruded to fracture. The results show that there are three stages for load-displacement curve of every kind of joint including quasi-elastic deformation stage, plastic deformation stage, and damage stage. Ultimate tensile load, fracture energy and interfacial crack length are influenced by the surface morphology of interfacial IMC.