Research And Improvement Of Drop Mura In TFT-LCD

In the Liquid Crystal Display(LCD)industry,it is becoming more and more important to reduce costs and improve product yield and quality.The traditional Liquid Crystal(LC)filling method has problems such as long-time consumption and material waste,and has been completely replaced by One Drop Filling(ODF),which can greatly reduce the time of LC filling and the consumption of LC material.However,the ODF process brings a defect called Drop Mura,which seriously affects the yield of the product.In particular,for products using Polymer Stabilized Vertically Aligned(PSVA)photoalignment technology,the transmittance,contrast and resolution are relatively high,and the phenomenon of Drop Mura is more serious.Therefore,it is urgent to put forward corresponding solutions.The causes of Drop Mura are complex,the mechanism is inconclusive,and there is not much related literature and research.It was born along with the invention of ODF technology,and it has been a difficult problem for LCD panel manufacturers for a long time.It is generally believed that Drop Mura may be related to factors such as contamination of the liquid crystal,moisture on the PI film,and damage to the PI film by liquid crystal drops.Traditional panel manufacturers mainly improve the problem of Drop Mura by changing liquid crystal materials,adjusting liquid crystal dropping parameters,or increasing rubbing intensity.At the same time,some manufacturers have improved Drop Mura by increasing the height and density of the spacer.However,all the methods failed to fundamentally solve Drop Mura.In this paper,Drop Mura was investigated by LC materials,color filter(CF)photoresist materials,Polyimide(PI)Inkjet process,ODF process and PSVA process.The results show that within a certain range,the higher the viscosity of the liquid crystal,the higher the content of the reactive monomer(RM)and the higher the transmittance of the CF photoresist,the higher probability of Drop Mura.In terms of process,it indicated that longer post baking time of PI,smaller size of LC drop and lower curing voltage of PSVA process could reduce the ratio and degree of LC Drop Mura effectively.Drop Mura defect rate was reduced from 63% to 6% after process parameters optimazation.In addition,this paper proposed that incidence of Drop Mura could be further reduced to 0% by using a new PI with initiator unit or using LC Inkjet equipment.The problem of Drop Mura was completely solved.