| Full-screen mobile phone has become a hot spot in smartphone market competition because of its beautiful in appearance and sense of technology.In order to achieve high screen occupation ratio,the screen-to-body ratio has been switched from 16:9 to 18:9,19:9,19.5:9 or even 21:9.The display form has changed from the mainstream narrow frame screen to the current notch screen,water drop screen and hole digging screen.The main work of this paper is to design and develop a 6.2-inch new Chip-On-Film(COF)structure water drop full screen Liquid-Crystal-Module(LCM)for a well-known mobile phone manufacturer in China,which accounts for more than 90%of the screen-to-body ratio.Firstly,the characteristics of traditional Chip-On-Glass(COG)module structure and new COF structure are analyzed,and the differences of COF structure in design,assembly and material use are pointed out.COF structure can greatly reduce the screen borders by bonding IC transfer to FPC and folding it back to the back of the module,and matching the reverse backlight.Secondly,the dimension tolerance of the structure design is analyzed in detail,and the related influencing factors are decomposed.The processing tolerance of raw materials,assembly tolerance of equipment and calculation of expansion and contraction clearance of materials are sorted out and analyzed.The theoretical calculation and analysis show that the structure design can meet the performance requirements of the phone.In addition,the accuracy disassembly analysis of COF bonding,theoretical calculation of expansion coefficient of Film-On-Glass(FOG)and Film-On-Film(FOF)side and optimization of actual bonding effect ensure that the offset range of FPC pin after bonding will not affect the normal display.At the same time,the improvement measures are put forward according to the contrastive analysis of the rebound force caused by COF base material,the calculation of bright line angle of view,the prevention of reliability testing in advance,and the detection method of profile and the monitoring method of optimizing the activation rate of BLU tapes are put forward.Finally,the LCD modules are tested under the reliability test conditions required by customers.For the problem of film waving caused by module over-heat in the testing process,based on the results of the model simulation and the analysis of the heat conduction and dissipation way of the module,several improving schemes include decreasing Light-Emitting-Diode(LED)forward current,enhancing radiation dissipation by Nano-coatings and enhancing heat conduction by graphite sheet or copper alloy iron frame.The improving effects are evaluated by comparing and measuring the temperature difference between COF and COG.The measured results show that the maximum temperatures of the module can be reduced by 9℃ and 12℃ by using graphite sheet and copper alloy iron frame,respectively.Further reliability tests of the module using graphite sheet or copper alloy iron frame are pass by thermal shock testing and high temperature and high humidity testing,which show that the improved scheme can meet the requirements.Compared with copper alloy,graphite sheet has advantages of mature technology,simple installation and low price.As a result,by comprehensive considering the effect of the heat dissipation,the cost of the material cost as well as the feasibility of the installation,the graphite sheet heat-reducing scheme has been adopted in this project finally. |
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