Fabrication And Properties Of Eutectic Welding For Flip-chip Led Devices

Led(Light Emitting Diode)is the most promising cold light source in the 21 st century,because of its advantages such as energy saving,environmental protection,high reliability and design flexibility,it has been widely developed and applied in the lighting field.Flip-chip led has excellent optical,electrical and thermal properties.It is very important to use lead-free solder for eutectic welding in the packaging process of flip-chip led chip.Different eutectic welding methods may have a certain impact on the performance of the device.This subject takes flip-chip led filament as an example,the effect of glue filled between the silver on the performance of flip-chip led filament was investigated.The results showed that the use of glue filled increased the average shearing force of the chip.Make flip-chip led filament can better heat dissipation,reduce the temperature of flip-chip led filament;it has no harmful effect on the color temperature of filament under steady state and can effectively prevent the chip short circuit caused by solder paste adhesion in practical production,so it can be used as an improved process in eutectic welding to fabricate devices.Secondly,the influence of two welding methods on flip-chip led filaments properties is investigated.The results show that the shearing force of the two welding methods accord with the standard,but the shearing force of vacuum furnace welding is larger,the voltage of vacuum welding is more concentrated and the flux of light is higher under steady state.There is no significant difference in the rate of voltage change between the two before and after aging,and the maintenance rate of both luminous flux is within the standard range,but the maintenance rate of vacuum furnace welding is higher than that of vacuum furnace welding.In practical application,the selection of welding mode plays a guiding role: vacuum furnace welding can be used for the filament with higher requirements,more attention is paid to the production efficiency and the performance of the filament is not high,so direct welding can be adopted.Finally,the effect of welding temperature on the performance of flip-chip in direct welding process is investigated.The results show that when the welding temperature is 220 ?,the Au on the chip fully diffuses into the solder layer and reacts with the Sn in the solder.The Cu on the substrate has not begun to diffuse to the solder,and the average push tension of the chip is less than 200 gf,which is intact fracture from the Au layer.When the welding temperature is 260 C,the cu on the substrate begins to diffuse to the solder and react with the solder in the lower layer.The Sn content is relatively uniform,the average push tension ofthe chip increases,and the fracture occurs from the solder interior.When the welding temperature is 320 ?,the cu on the substrate begins to spread evenly to all parts of the solder and react with the Sn.The Ag in the solder has been completely melted.Due to the excessive welding temperature,a large number of uneven voids have been formed in the solder layer.As a result,the average push tension of the chip decreases and the average push tension of the chip increases.When the welding temperature is 320 ?,the flux in solder paste evaporates rapidly by heat,which results in the uneven thickness of IMC layer and the appearance of large voids.The negative effect on the push tension of the chip is greater than the positive effect of the fusion between elements on the push pull force of the chip.As a result,the average push tension of the chip is reduced,and the solder breaks from more places in the cavity.