Research Of Microstructure Of Solder And Interconnected Defects Based On The Selfpropagating Reaction Of Al/Ni Nanofoil

The self-propagating exothermic reaction of nanofoil can be used as a local,rapid heat source to connect different substrate materials.Due to its high efficiency of heat release,high concentration of heat,and small heat affected zone,it is suitable for the packaging of thermal mismatch,heat sensitive materials or devices.It has broad application prospects in3D packaging and multi-chip packaging such as MEMS devices,micro-systems,and micro-analysis systems.However,due to its extremely high rate of heat release,the rate of heating and cooling of the solder is too high,the melting and solidification process is highly unsteady,and the solidification microstructure of the solder is different from the conventional heating process.The main work of this paper is as follows:The self-propagating exothermic reaction of Al/Ni nanofoils were used in this article to complete the rapid solidification experiment of solder.In the experiment,observation and analysis were performed on the solidification structure in the fusion zone of the four kinds of solder preforms,and the finer microstructure were obtained under rapid heating and cooling conditions.The change of melt zone size in different thickness of solder preform and preheat temperature process parameters was analyzed respectively.It was found that with the decrease of the thickness of Sn42Bi58 solder preform from 400?m to 300?m,the size of fusion zone increased by 52?m.As the preheat temperature increases from 25°C to75°C,the fusion zone size increases by 20?m.Compared with the fusion zone of the four solders under the same parameters,the thickness of the fusion zone decreases gradually with the increase of the melting point of the solder,and the melting zone of Sn42Bi58 and Sn solder is different by 80?m.A finite element model of solder melting based on Al/Ni self-propagating exothermic reaction was established to analyze the influence of structural temperature field and temperature cycle on the melting and solidification process of the solder.The temperature field in the reaction process was compared with the thickness of different thickness of solder preforms and the preheating temperature.The thickness of the fusion zone and the temperature rise and fall rate at different positions were analyzed.It was found that with the thickness of the Sn solder preform decreased from 400?m to 300?m,the thickness of fusion zone increased from 86?m to 107?m.With the preheating temperature increased from25°C to 75°C,the fusion zone increased from 107?m to 180?m.However,when the two kinds parameters were changed,the maximum increase and decrease rate of the solder temperature did not change significantly,and they were all maintained at about 8.0×10~7°C/s and 9.0×10~7°C/s.The Si/Si and Si/PCB substrates were interconnected based on the self-propagation exothermic reaction of Al/Ni foils.The microstructures of the interconnected joints were observed,and the defects were analyzed.The thickness and porosity of the welds were statistically analyzed.The interconnected joints obtained under different preheating temperatures and applied pressures were compared and analyzed.It was found that when the applied pressure was increased,the weld thickness decreased by 15?m and the porosity decreased by 40%.When the preheating temperature was increased,the weld thickness decreased by 15?m,and the porosity decreases by 20%.