Thermal Fatigue Properties Of SAC305and Influences Of Compound/Alloying On The Properties Of Solders

In mordern times, the flourish of the electronics technology benefits from the rapiddevelopment of the microelectronic technology on some level. Nowadays, the world isenjoy a moment of electronic information technology, which requires that electronicproducts have high performance, multi-function, high reliability, miniaturization, thin,facilitation, low cost, and requires that packaging technology has high densitypackaging, high reliability and low cost.Microelectronic packaging field follows the development formula of a generationcircuit, a generation packaging and a generation material. Among them, as packagingmaterials, solder alloys can protect the microchips and offer necessary electrical,thermal and mechanical connections to perform the functions of microchips throughforming metallurgical connections with substrate materials. The weldability of solderalloy with subatrate directly determines the reliability and service life. Therefore, thedevelopment of the high performance solder alloy during super-fine process is veryimportant. In this paper, new multiple solder alloys were prepared by adding PolyhedralOligomeric Silsesquioxanes (POSS) nano-particle and Bi/Ni elements intoSn-3Ag-0.5Cu (SAC305) and Sn-0.7Cu (SC) solders, respectivly; the effects of addingparticles and the third, or fourth element on the melting characteristics, wettability andmicrostructure were studied systermically; the microstructure evolution and the fracturemechanism of alloying solder alloy joints under different thermal stress were discussedalso. The main content and main conclusion in this paper are as follows:The shear experiment and tensile experiment were performed on the solder joints ofGraphic&Central Processing Unit (GCPU). Before that, all the GCPU were dealed withthermal cycling, thermal shock and isothermal aging, respectively. And then the shearstrength and tensile strength of SAC305/Cu solder joints and the fracture mechanicalunder shear stress and tensile stress of SAC305/Cu solder joints were discussed; besidesthat, the influences of different thermal stress on the fracture mechanism wereanalysised. The results shows the shear strength decreases with the increase of thecycles of thermal cycling and thernal shock and the extension of isothermal aging time.During thernal cycling, the shear strength declined fatest. That’s because the extent ofthe microstructure evolution of the solder joints under different thermal stress and thegeneration and the extension path of the cracks in the solder joints have discrepancies, which influenced shear strength of the solder joints. The tensile strength of the solderjoints did not decrease but increase with the cycles of thermal cycling and thermal shockand the extension of isothermal aging time, which indicated that thermal stress was notthe major factor inducing the tensile fracture of the solder joints.Polyhedral oligomeric silsesquioxanes (POSS) nano-particles reinforcedSn-3Ag-0.5Cu-xPOSS (x=1,3,5) composite solders were prepared and were reflowedon Cu substrates at543K. Then, the solder joints were isothermal aged at393K for24and48hours, respectively. Microstructural evolution of the solder joints were observedby scanning electron microscopy (SEM) and the influence of POSS nano-particles onthe solder joint were investigated. The results showed that β-Sn primary phase wasrefined and the number of grain boundary increased with the addition of POSSnano-particles. The growth rates of intermetallic compounds (IMC) layer weresuppressed by the adsorption affection of POSS nano-particles to the IMC layer duringisothermal aging. Moreover, the dissolution process of the IMC layer, which wasaccompanied by the growth of the IMC layer, changed the morphology of the IMC layer.The growth rate and the dissolution rate of the IMC layer in SAC305-3POSS/Cucomposite solder joint were the lowest.The influences of Bi, Ni elements on the melting characteristics, wettability andmicrostructure of SC solders were studied systermically. Besides that, the effects of Bi,Ni elements on IMC of the solder joints after1cycle reflow,10cycles reflow andisothermal aging, respectively. The results showed that the adding of3.5wt.%Bielement into SC solders decreased the melting temperature of SC solder alloy, butbroadened the concomitant zone of ice and liquid. Meanwhile the wettability of SCsolder alloy was improved as the addition of Bi elements. Bi elements extracted fromβ-Sn primary phase, existed on the grain boundary and pinned the grain boundary,strengthening the shear property and suppressing the growth of IMC. The addition of Nielement into the SC matrix refined the grain size while it did not much affect themelting characteristics and wettability of SC solder alloys. And the shear strength ofsolder joint was improved when the joint was isothermal aged at a high temperature.