Study On Automatic Optical Inspection Technology For LCD Module ACF Bonding

In recent years,with the rapid development of smartphone industry,HDTV industry and other industries containing liquid crystal display(LCD)display terminal,LCD modules which are the core components of LCD display terminals are becoming more and more precision.In the production process of LCD modules,anisotropic conductive film(ACF)bonding is one of the most important technologies that achieve LCD modules having higher and higher resolution,size and integration level.ACF bonding is widely used in LCD industry.It implements circuit connection between pads of integrated circuits(ICs)or flexible printed circuits(FPCs)and indium tin oxide(ITO)bumps on glass substrates using conductive microspheres of ACF materials trapped between those pads and bumps.ACF bonding is one of key factors that influence LCD module quality,so it requires to inspect ACF bonding to ensure LCD module quality and improve LCD module production technology in the production process of LCD modules.Moreover,because of the wide use of LCD modules in daily living and production,the large capacity demand of LCD modules requires achieving rapid on-line LCD module ACF bonding inspection.Automatic optical inspection(AOI)has been widely used in industrial production inspection for its non-contact and high speed.However,because of the size of conductive microspheres,pads and bumps used in LCD module ACF bonding,electrical conduction mechanism of ACF bonding,etc,conventional AOI technology widely used in industrial inspection can't be used in LCD module ACF bonding inspection directly.In this thesis,the main work is to achieve AOI inspection of LCD module ACF bonding online.The main research achievements and innovations are listed below: 1)AOI inspection method for LCD module ACF bonding based on differential interference contrast(DIC)imaging has been proposedIn LCD module ACF bonding,it implements electrical conductance between screens and FPCs or ICs based on trapped conductive microspheres in ACF materials.The electrical conductance performance of LCD modules is one of the key factors that influence LCD quality,which is affected by conductive microspheres trapped between ITO bumps and Pads.The quantity and shape deformation rate of trapped conductive microspheres affect the electrical conductance performance of LCD module ACF bonding.However,because conductive microspheres' size widely used in ACF materials is in the range of 3-5 mm and conductive microspheres are trapped between ITO bumps on glass substrate and metal pads,it is too difficult to quickly obtain the information of trapped conductive microspheres using conventional imaging methods of AOI in industrial inspection,such as using the conventional imaging method of printed circuit board(PCB)AOI to obtain the quantity and shape deformation rate of trapped conductive microspheres in LCD module ACF bonding.In this thesis,based on research of LCD module production process and ACF bonding,it has proposed a method to quantitatively analyze the quantity and shape deformation rate of trapped conductive microspheres in LCD module ACF bonding using DIC imaging and back propagation neural network technology,achieved online AOI inspection of LCD module ACF bonding,and the miss rate is lower than 0.1%,and the false inspection rate is lower than 2%.2)Rapid quantitative AOI estimation method for LCD module ACF bonding resistance based on DIC imaging has been presentedThe electrical conductance performance of ACF bonding in LCD module has an important influence on the reliability of LCD modules,and ACF bonding interconnect conductance can be directly reflected by the interconnection resistance of ACF bonding.At the same time,quantitatively evaluating LCD module ACF bonding interconnection resistance can be beneficial to the digital analysis of LCD module ACF bonding quality,which is of great value to the improvement of LCD module production process.In LCD module factories,the conentional method to obtain LCD module ACF bonding interconnection resistance is realized by electric measurement.Although interconnect resistance of LCD module ACF bonding using electric measurement can have a good measurement precision,it is too inconvenient to achieve electric measurement for LCD module ACF bonding because the sizes of bumps and pads in LCD modules ACF bonding,especially in the case of precision LCD modules which have hundreds of tiny and closely bumps and pads.It is extremely difficult and time consuming to measure the interconnect resistance using electric measurement in this case.With study of LCD module ACF bonding technology and ACF bonding interconnect resistance model,this thesis has proposed an optical method to inspect the quantity and shape deformation of trapped conductive microspheres by DIC imaging and image analyzing,and further quantitatively evaluated interconnect resistance of LCD module ACF bonding online.3)High-resolution line scan imaging and precision position positioning using linear optical encoder have been proposed in LCD module ACF bonding AOI inspectionIn LCD module ACF bonding AOI inspection,the trapped conductive microspheres have a micrometer size,so the reliability of the image pixels which reflect those conductive microspheres can affect the reliability of LCD module ACF bonding AOI inspection results.Compared with conventional PCB AOI inspection,LCD module ACF bonding AOI inspection is in the micron level while the inspection region size of LCD module ACF bonding is close to that of PCB AOI inspection.Those require highresolution imaging without compression or stretching using scan imaging in large regions.Linear optical encoder is a measurement feedback device based on grating principle,which is often used in precision computer numerical control machine tool.In this thesis,precision imaging and positioning control using linear optical encoder have been proposed for LCD module ACF bonding AOI system.Line scan camera uses hardware triggering mode with linear optical encoder to obtain high-quatily images.Feedback signals from linear optical encoder are used as input signals of proportion integral derivative(PID)control to achieve precision motion position control.By those,high resolution and nondestructive imaging of large inspection regions is realized in LCD module ACF bonding AOI inspection system.All of those are significant for AOI inspection in LCD module industry and other fields which require imaging large regions with high resolution.4)High-resolution imaging opto-mechatronics for precision LCD module ACF bonding online AOI inspection has been designedWith the development of LCD module industry,LCD modules become more and more precision with larger sizes,which demands harsh imaging requirements for AOI inspection.Here we report a high-resolution and clearly focused imaging optomechatronics for precision LCD module ACF bonding AOI inspection.It firstly presents and achieves high-resolution imaging for LCD module ACF bonding AOI inspection using line scan camera triggered by linear optical encoder,self-adaptive focusing for the whole large imaging region using line scan camera and laser displacement sensor,which reduces the requirements of machining,assembling and motion control of AOI devices.Results show this system can directly achieve clearly focused imaging for AOI inspection of large LCD module bonding with high image resolution and no limited imaging width theoretically for LCD module ACF bonding AOI inspection.It has achieved inspecting LCD modules having 7 inches size in 4 seconds.All of those are significant for AOI inspection in LCD module industry and other fields which require imaging large regions with high resolution.