Experimental Study On Dicing Evaluation Of Sapphire Substrate And Tool Failure Mode

Sapphire is widely used in aerospace,semiconductor lighting,biomedical and other fields due to its excellent mechanical properties,optical properties,strong corrosion-resistance,and good chemical stability.In the optoelectronic industry,sapphire is the most commonly used substrate material for LED chips.In the production of the LED chip,the sapphire substrate needs to be diced and cut.However,sapphire is a typically hard and brittle material,on which edge chipping is easily introduced to the dicing process.This not only reduces the yield rate but also influences the service reliability of LED chips.Therefore,a comprehensive study on the sapphire diced by ultrathin diamond blades is of scientific and practical implication for the development of diamond abrasive grinding tools.This study starts with the influence of processing parameters on dicing quality and it was found that the depth of cut,feed speed,and spindle speed affect the kerf width and the size of the chipping.Then,the surface morphology,and wear characteristics at cutting edge of the diamond blade were observed using a threedimensional video microscope,and the formation process of the kerf and chipping during the dicing process was analyzed.Next,the parameters of the diamond blade were optimized by studying the influence of blade thickness,concentration,grits size of diamond abrasives,and type of bonding metals on the chipping size.Through a careful analysis of the surface morphology of the diamond blade after different cutting distances on sapphire,the wear characteristics and failure modes of diamond blades were clarified.Finally,the influence of sapphire crystal orientation on dicing quality was discussed.The main conclusions are drawn as follows:(1)Among processing parameters investigated in this work,the depth of cut has the most significant influence on the chipping of sapphire dicing,followed by the feed speed,and the spindle speed has the least influence.When the depth of cut or feed speed is increased,the chipping on both sides of the kerf is asymmetrically distributed;(2)In the dicing process on sapphire,the diamond blade undergoes elastic deformation in the thickness direction under the grinding force.This results in only the abrasive grains on the deformed side of blades in contact with sapphire.Therefore,diamond abrasives on both circumferential surfaces and the side of blades are involved in the kerf formation.(3)Both geometric dimension and bonding metals of diamond blades have a significant influence on dicing quality.The increase of the thickness and reduction of the outer diameter of diamond blades improve the dicing quality.The sintered metal bond diamond blade offers a better dicing quality than that of the electroplated diamond blades,but the resin bond diamond blade fractures quickly due to insufficient mechanical strength.The concentration and grit size of diamond abrasive have limited influence on the dicing quality.When the abrasive particle size is small,the diamond blade will be fractured due to the insufficient cutting ability.(4)The sapphire dicing can be divided into two stages at the continuously increased length of cut: in the initial stage,the kerf width and chipping size increase rapidly,and diamond blades wear is mainly due to fracture of bonding metals and blunting of diamond abrasives;in the stable stage,the kerf width and the chipping size are stable,and diamond abrasives are mainly fractured and blunted.The insufficient cutting ability of blades caused by severe wear of diamond abrasive is the main reason for blade fracture during sapphire dicing.(5)Under the same processing parameters,the chipping size of sapphire diced along the [11 00] direction is smaller than that along with the [112 0] direction.