Research On White LED Filament Based On Flip-chip

Under globe ban of incandescent lamps,LED filament as a new light source with the characteristics of low energy,environmental protection,special appearance and omni light,is taking place of incandescent.Flip-chip LED(FC-LED)has reasonable heat dissipation structure and high light efficiency,and the filament fabricated by FC-LED can effectively enhance the filaments thermal performance.In this paper,white LED filament was fabricated by coating the phosphor on the surface,and flip-chip was die-bonded by high temperature solder paste.The influence of substrates,chip attached solder and phosphor-coated method on the properties of the FC-LED filament was investigated by measuring the chip die shear strength,photoelectric parameters and thermal parameters.The experiment results show that FC-LED filament was prepared by the same conditions,the light efficiency of ceramic substrate products(125.2 Lm/W)is higher than aluminum substrate(118.4 Lm/W),ceramic substrate can be double-sided light emitting,which is more suitable for the filament with high requirement of light efficiency.The surface temperature of aluminum substrate(332.2 K/336.6 K)is lower than ceramic substrate(339.7 K/341.6 K)and thermal distribution of aluminum substrate is more uniform,which is more suitable for the filament with high requirement of high power,high heat dissipation.Under the directly-baking conditions,the more voids was generated in the joint,for flux than for solder paste.The lumen maintenances 87.07 % for flux and 91.51 % for solder paste after 1000 h aging test.When the thickness of solder paste layer from 32 μm to 82 μm,chip die shear was increased by 135 %,voltage of chip was decreased by 2.56 mV(at current of 30 mA),and junction temperature was increased by 1.5 K.Color temperature difference between positive and negative is 235 K in the filament coated by phosphor on single side,and the light efficiency is 112 Lm/W.Color temperature difference between positive and negative is 285 K in the filament coated by same phosphor on the two side,and the light efficiency is 115 Lm/W.The negative side phosphor concentration was reduced to 20% of positive sidephosphor concentration,color temperature difference between positive and negative is 53 K,the light efficiency is up to 121 Lm/W,and the concentration had little effect on color temperature.Die-bond process and phosphor coating process with low cost,high efficiency were offered,suitable for flip LED white light filament.