Novel interface regulation of Sn1.0Ag0.5Cu composite solders reinforced with modified ZrO_(2):Microstructure and mechanical properties

With the trends of miniaturization and high density of electronic packaging,there has been an urgent demand to open up lead-free solders with high strength and ductility.In this study,a ZrO_(2)-reinforced Sn1.0Ag0.5Cu composite solder was designed.First,surface modification on ZrO_(2) was conducted with ball milling-pyrolysis method.Subsequently,NiO modified ZrO_(2)(NiO/ZrO_(2))was added to the solder matrix with ultrasonic stirring.The morphology and interface of NiO/ZrO_(2) were discussed.Moreover,the microstructure,interface and mechanical properties of the composite solders were systematically studied.The results showed that NiO nanoparticles were evenly adhered to the ZrO_(2) surface,and the interface relationship between them was semi-coherent and coherent.Further,an appropriate addition of NiO/ZrO_(2) could refine the microstructure of composite solders.The refinement mechanism was systematically investigated.Besides,a micro-mechanical lock and non-micropored clean interface was formed between NiO/ZrO_(2) and the solder matrix.The Sn/NiO/ZrO_(2) interface system based on mutual solid solution was ingeniously designed.The ultimate tensile strength and elongation were increased synergistically,and the fracture mechanism transformed from a ductile−brittle mixed fracture mode to a ductile fracture mode.Therefore,a lead-free solder with high strength and ductility was obtained.

Preparation and Properties of Particle Reinforced Sn-Zn-based Composite Solder

Particle reinforced Sn-Zn based composite solders were obtained by adding Cu powders to Sn-9Zn melts. The microstructure analysis reveals that in situ CusZn8 particles are formed and distributed uniformly in the composite solders. The strength and plasticity of the composite solders were improved, and creep resistance was considerably enhanced. The wettability of these composite solders is also better than that of Sn-9Zn.

Influence of stress on the creep behavior of Cu particle enhancement SnPb based composite solder joints

Lap joints with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancemem 63Sn37Pb based composite solder and 63Sn37Pb eutectic solder to examine the influence of stress on the creep behavior of the solder joints. The results indicate that the creep resistance of the composite solder joints is generally superior to that of the conventional 63Sn37Pb solder joints. At the same time, the creep rupture life of the composite solder joints is declined with increasing stress and drops faster than that of the 63Sn37Pb eutectic solder joints.

Environmentally friendly solders 3-4 beyond Pb-based systems

Based on environmental considerations, global economic pressures, enacted by legislations in several countries, have warranted the elimination of lead from solders used in electronic applications. Sn3.5Ag, SnAgCu, and Sn0.7Cu have emerged among various lead-free candidates as the most promising solder alloys to be utilized in microelectronic industries. However, with the vast development and miniaturization of modern electronic packaging, new requirements such as superior service capabilities have been posed on lead-free solders. In order to improve the comprehensive property of the solder alloys, two possible approaches were adopted in the current research and new materials developed were patented. One approach was involved with the addition of alloying elements to make new ternary or quaternary solder alloys. Proper addition of rare earth element such as La and Ce have rendered solder alloys with improved mechanical properties, especially creep rupture lives of their joints. Another approach, the composite approach, was developed mainly to improve the service temperature capability of the solder alloys. Composite solders fabricated by mechanically incorporating various reinforcement particles to the solder paste have again exhibited enhanced properties without altering the existing processing characteristics. The recent progress and research efforts carried out on lead-free solder materials in Beijing University of Technology were reported. The effects of rare earth addition on the microstructure, processing properties, and mechanical properties were presented. The behaviors of various Sn-3.5Ag based composite solders were also explicated in terms of the roles of reinforcement particles on intermetallic growth, steady-state creep rate, the onset of tertiary creep, as well as the overall creep deformation in the solder joints. Thermomechanical fatigue (TMF) behavior of the solder alloys and composite solders were investigated with different parameters such as ramp rate, dwell time, etc. The damage accumulation features and residual mechanical properties of the thermomechanically-fatigued composite solder joints were compared with non-composite solder joints. To match the lead-free alloys, various types of water soluble no-clean soldering flux have also been developed and their properties were presented.

Nano ZrO_(2) Particulate-reinforced Lead-Free Solder Composite

A lead-free solder composite was prepared by adding ZrO2 nanopowders in eutectic Sn-Ag alloy. Microstrucrural features and microhardness properties of those solders with different ZrO2 nanopowder fraction were examined. Results indicate that the addition of ZrO2 nanopowders reduced the size of β-Sn grains and restrained the formation of bulk Ag3Sn intermetallic compounds （IMCs） due to the adsorption effect of the ZrO2 particles. The Vicker＇s hardness of the obtained lead-free solder composites fits well with the HalI-Petch relationship. The refinement of β-Sn grains favors to improve the microhardness of composite solders.

Wetting kinetics of SiC nanoparticle reinforced Sn-Pb eutectic solders

SiC nanoparticles reinforced eutectic Sn-Pb solder were prepared by mechanical mixing method. Reactive wetting of the resultant composite solders on Cu substrates was investigated using real time, in-situ visualization of the triple-line movement. It was found that spreading rates of all solder pastes in this work do not obey Tanner＇ s law of non-reactive spreading. SiC nano-particles slow down both the pre-melting and post-melting spreading rates of composite solder pustes. As the content of SiC nano-particles increase, the melting point of composite solders decrease, and the spreading time of molten composite solder pastes increases.

The influence of temperature on creep behavior of Cu particle enhanced SnPb based composite soldered joints

Creep property of solder alloys is one of the important factors to affect the reliabdity of soldered joints in SMT （surface mount technology）. Particle-enhancement is a way to improve the properties of solder alloys and has caused much more attention than before. Temperatures applied to soldered joints are one of the primary factors of affecting creep properties of particle enhancement composite soldered joints. In this paper single shear lap creep specimens with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancement 63Sn37 Pb based composite soldered joints and 63Sn37 Pb eutectic soldered joints to examine the influence of temperature on creep behavior of soldered joints. Results indicated that the creep resistance of soldered joints of Cu particle enhancement 63Sn37Pb based composite soldered joint was generally superior to that of the conventional 63Sn37Pb soldered joint. At the same time, creep rupture life of the composite soldered joint was declined with increasing temperature and drop faster than that of the conventional 63Sn37 Pb eutectic soldered joint.

Effects of nano-sized Ag reinforcing particulates on the microstructure of Sn-0.7Cu solder joints

Composite solders were prepared by mechanically dispersing different volumes of nano-sized Ag particles into the Sn-0.7Cu eutectic solder. The effects of Ag particle addition on the microstructure of Sn-0.7Cu solder joints were investigated. Besides, the effects of isothermal aging on the microstructural evolution in the interfacial intermetallic compound （IMC） layer of the Sn-0.7Cu solder and the composite solder reinforced with 1vol% Ag particles were analyzed, respectively. Experimental results indicate that the growth rate of the interfacial IMC layer in the Ag particles reinforced composite solder joint is much lower than that in the Sn-0.7Cu solder joint during isothermal aging. The Ag particles reinforced composite solder joint exhibits much lower layer-growth coefficient for the growth of the IMC layer than the corresponding solder joint.

Morphologies and evolution of intermetallic compounds formed between Sn_(1.0)Ag_(0.7)Cu composite solder and Cu substrate

This study investigated the morphologies of the intermetallic compounds(IMC)formed during soldering reaction between Sn_(1.0)Ag_(0.7)Cu-1.0SnO_(2) composite solder and Cu substrate at various temperatures.The prismtype Cu_(6)Sn_(5) forms when the soldering temperature is 260or 2800C,while those grains transform from prism type to scallop type at the temperatures of 300 and 320℃.It can be found that the morphologies of Cu6Sn5 grains affect adsorption of Ag_(3)Sn nanoparticles during soldering reaction.The scallop-type grains with a higher growth rate need to adsorb large amounts of Ag_(3)Sn particles.In terms of mechanical behavior,the shear strength of solder joint is improved from 40 to 46 MPa at soldering temperature of 300℃.In addition,the thickness of IMC increases with the extension of aging time.During aging,the morphology of Cu6Sn5 grains remains scallop type,but the number of Ag_(3)Sn nanoparticles is reduced largely.The scallop-type Cu^(6)Sn_(5) can increase in size and flatten in morphology with the aging time increasing.

Influence of Temperature on Creep Behavior of Ag Particle Enhancement SnCu Based Composite Solder

The creep properties of solder alloys are an important factor affecting the reliability of soldered joints in surface mount technologies. Particle-enhancement is one way to improve the properties of solder alloys. The temperature of the solder joint is one of the primary factors affecting the solder joint creep properties. Single shear lap creep specimens with a 1 mm2 cross-sectional area were fabricated using Ag particle enhancement 99.3Sn0.7Cu based composite solder and 99.3Sn0.7Cu eutectic solder to examine the influence of temperature on the creep behavior of solder joints. The results show that the solder joint creep resistance of the composite solder joint was generally superior to that of the 99.3Sn0.7Cu solder joint. The creep rupture life of the composite solder joint was reduced by increasing temperatures at a faster rate than that of the 99.3Sn0.7Cu eutectic solder joint.

Effect of Diamond Additions on Wettability and Distribution of SnAgCu Composite Solder

Diamond/SnAgCu composite solder bumps were prepared on Cu pad by mechanically incorporating diamond particles into Sn3.0Ag0.5Cu （SAC） solder powders, mixing with flux and reflowing at 260℃ for 60 s. The spreading areas of composite solder were calculated and the distributions of copper-coated diamonds were characterized. When diamond additions were below 3 wt%, the spreading area decreased with diamond additions, and the diamonds distributed mainly at the interface between solder and Cu pad; however, when additions were beyond 4 wt%, the discharge of diamond particle occurred, and the spreading area increased due to the reduction of surface energy.