Sb powder is added to Sn-Ag-Cu solder so that the fusing point of the solder increases. The solder powder is expected to apply at essentially the same temperature as the process temperature for the base solder, and to improve thermal fatigue property of the solder joining area. We report Differential Thermal Analysis, Vickers hardness and the tensile test result of 7.0% Sb powder added Sn-3Ag-0.5Cu solder and the result of thermal fatigue test of the solder with Scanning Acoustic Tomography. As the results of experiments, we concluded that Sb powder addition elevates the melting point of Sn-3Ag-0.5Cu solder, and that 7.0% Sb powder added Sn-3Ag-0.5Cu solder have good thermal fatigue reliability.
In electronic products, lately increasing thermal radiation is demanding higher thermal conductivity of polymer composites. However, inaccurate observation of filler dispersion within the polymer do not allow for accurate quantification of Interface Thermal Resistance and subsequently prediction of thermal conductivity. Therefore optimum filler design could not be achieved. Firstly in this report, accurate stereoscopic filler dispersion was observed by FIB-SEM. Secondly, quantification of Interface Thermal Resistance could be achieved by thermal conduction analysis using filler dispersion model. Thirdly, this Interface Thermal Resistance enabled prediction of the thermal bulk conductivity. Lastly, prediction made above could be validated by comparison of predicted value and measured value. This result may lead to optimum filler design and thereby to the development of higher thermal radiation materials.
A high temperature soldering technique that enables to design the solidus temperature of the solder material has been developed by using Au-Ge-Ag system. By touching liquid phase Au-Ge to a solid phase Ag, Ag diffuses to the liquid and its solidus temperature rises up to the applied temperature. Authors have executed a series of sharing tests of die attached samples and confirmed solidus phase in 425°C which is much higher than 356°C, which is the solidus temperature of the eutectic alloy of Au-Ge. This technique will make possible to realize a high temperature operating power semiconductor module.
Recently, power semiconductor packages have been applied to various types of industrial equipment by increasing the energysaving consciousness. The thermal grease used in the attachment part of the heat sink of power semiconductor packages exhibits high thermal resistance. When a solder junction is formed with a Cu-plate structure, cracks might form in the junction. We propose a power semiconductor package structure that uses a Cu tray as heat spreader and potting seal case to reconcile low heat thermal resistance and high reliability. Numerical analysis showed that plastic strain reduced by about 72% by forming fillets around the solder junction. Through temperature cycling tests with these structures soldered on an Al board, the exfoliation of the solder junctions of the proposed structure about 70% decreased compared those of the Cu-plate structure.
When we estimate the fatigue life of lead-free solder joints under cyclic temperature load, we have to get equivalent inelastic strain range accurately. In this study, in order to show the example of using our previously proposed constitutive model, which can describe stress strain curves, stress strain hysteresis loops and stress relaxation curves, with these temperature dependencies and these rate dependencies, we conducted FE analysis of the chip component under thermal cycle using the constitutive model. We also conducted fatigue tests of Sn3.5Ag0.5Cu0.07Ni0.01Ge lead-free solder using micro test pieces and estimated the fatigue life.
The microstructure changes of solder joint caused by heat cycle load influence on the life against the thermal cycle loading. The creep characteristic changes were more influential than other parameters such as Young's modulus or yield stress. The thermal cycle loading consists of the heat and repeated mechanical strain. In this study, the effects of the material parameter changes caused by the microstructure change with thermal loading on the life against vibration load are estimated by FEM analysis focusing on the BGA solder joint as an example. The crack initiation caused by the mechanical load depends on the strain at the concentrated point of the solder joint. It has already been reported that the creep strain does not appear in the high strain rate loading such as vibration. The microstructure and material property changes caused by the high-temperature environment are measured. And the effect of the yield stress change on the strain under the vibration load is investigated with FEM analysis. The vibration test of the BGA mounted board with and without pre-thermal loading represented the deteriorated life of the solder joint caused by the thermal loading.
In this study, we observed the formation of the Sn-W reaction layer at the interface between Sn-3Ag-0.5Cu solder and an electrolesSni-B/Au plated W substrate. This was done by using repair process which was heat treated by replacing new melting solder. As a result, we confirmed that the Sn-W reaction layers are generated by 10 to 20 times solder repairs. This is repeated on the W substrate with Ni-B at 533K, getting through to the intermetallic compounds such a Sn-W and Sn-Ni-W-Cu at the interface. The structure was analyzed as two layers namely, a Sn:W=1:1 reaction layer, and a Sn:W=7:3 reaction layer. The Sn-W reaction layer shows excellent properties such as solder repair metallization, and is composed by each Sn grain and W grain, which does not show regular crystal structure. Furthermore, M5 edge EELS spectrum of the Sn-W reaction layer were measured with TEM samples, and the Sn-W bonding was analyzed by electron multiple scattering theory of FEFF8.2 calculation code. It was clarified that the Sn-W bond has more interaction with each other than Ni-W bond and W-W bond.
High-temperature joining is a key technology for electronic component assembly and other high-temperature applications. Recently, focusing on the sintering behavior of metal particles, the joining process using a nanoparticle paste has been proposed as an alternative to establish a new joining technology for high-temperature applications. In this study, a feasibility study was conducted to determine whether chestnut-burr-like micro-sized Ag particles can be used for joint material, and the effect of joining conditions such as heating temperature, bonding pressure and joining atmosphere on the joint strength of the Cu-to-Cu joint was investigated. Joining using micro-sized Ag particles was successfully achieved under a nitrogen atmosphere and the joint that was bonded at 300°C for 600 s under a bonding pressure of 10 MPa showed high shear strength (～30 MPa).
The electrically conductive adhesive (Isotropic Conductive Adhesive: ICA) is a paste-like and high-viscosity liquid composed of organic binder and inorganic filler. In recent years, ICA has gradually replaced lead solder as a jointing material for electronics packaging due to its-advantageous properties such as low-temperature junction, stress relaxation, safety, and ease of recycling. On the other hand, further improvements are still required in terms of electrical conductivity, heat conductivity and adhesion strength. In this research, in order to discuss the effect of polymer resin on electrical conductivity, the relationship between cure temperature, volume change, curing reaction in during the curing process and the emergence of conductivity was investigated by using ICA composed of atomized spherical silver particles and five different resins. As a result, it was confirmed that there was no obvious relationship between volume shrinkage of resin and electric resistivity of the ICA during the curing process and that the conductivity of the ICA was based neither on volume shrinkage of resin nor on the shortening of the distance between the fillers during the curing process. It was also confirmed that curing reactions in the polymer matrix were not necessarily required for the emergence of conductivity. These results suggest that there may be other influential factors such as the interaction between metal fillers and polymer resins.