According to the latest report from LEDinside, a division of the market research firm TrendForce, 3Q17 Micro LED Next Generation Display Industry Market Report- Micro LED Transfer Technology and Inspection Method Analysis, Mass transfer is a critical technology for Micro LED manufacturing, transferring Micro LED to a target backplane quickly and accurately will be one of the topics that manufacturers need to work on the most as well as on improving UPH and yield.
Micro LED Transfer Technology
Micro LED technology are facing lots of technology challenge, LEDinside research assistant manager Simon Yang indicates, there are four key technologies on Micro LED manufacturing, transfer technology takes the hardest part of manufacturing, however, driver IC, color conversion, inspection equipment and way of inspection, wafer wavelength uniformity, those are waiting for the technological bottleneck breakthrough.
There are many challenges in Micro LED mass transfer process, and LEDinside sorts the challenges into seven categories, including equipment accuracy, transfer yield, time of mass transfer process, manufacturing technology, inspection method, rework and processing cost. The upstream, midstream and downstream manufactures need to cooperate closely to achieve breakthrough and overcome related difficulties.
LEDinside assesses the feasibility on mass production of Micro LED according to Six Sigma. The transfer yield must be Four Sigma or higher so that the product has a chance to be commercialized but still with high processing and repair costs, while the transfer yield must be Five Sigma or higher to achieve mature commercialized products with competitive processing cost.
Feasibility of Micro LED Mass Producion
Generally, the traditional LEDs like 3030 LED with 3,000µm light source can be transferred by SMT equipment, it is available to transfer chip by die bonder when the size of light source reaches 100µm, the existing equipment for pick & place will facing serious challenges of accuracy when the size of light source reduces to 10µm.
In order to precisely transfer Micro LED to target backplane, the accuracy of equipment for Micro LED manufacturing is required to be less than ±1.5µm. However, currently, the accuracy of existing transfer equipment (Pick & Place) is ±34µm (Multi-chip per Transfer), while flip chip bonder features with accuracy of ±1.5µm (single-chip per Transfer), which are failed to meet the accuracy requirements of Micro LED mass transfer.
Chip bonding and wafer bonding cannot be applied to mass transfer due to low production capacity and high time cost, therefore, currently wafer bonding can be adopted to develop Micro LED technology and products featuring low pixel volume with the existing machines, while challenge exists in production capacity and time cost, so various thin-film transfer related technologies will be the mainstream in future.
Five thin-film transfer technologies include electrostatic adsorption, Van der Waals force-enabled transfer printing, laser ablation, phase-change transfer and fluidic assembly. The fluidic assembly is a high-speed assembly approach that achieves high UPH for various product applications, also it can reduce assembly time and cost greatly.
Mass transfer is a critical technology for Micro LED manufacturing, transferring Micro LED to a target backplane quickly and accurately will be one of the topics that manufacturers need to work on the most as well as on improving UPH and yield.
In view of the current situation, Micro LED will be firstly applied to indoor display, smart watch and smart bracelet, due to the high difficulty in transfer technology and various application products with different pixel volume, some manufacturers conduct R&D with existing wafer bonding equipment and take the application products with low pixel volume as targets to shorten the development period, also some manufacturers directly develop thin-film transfer technology, which required more resource investment and longer development period because the equipment needs to be adjusted even redesigned, moreover, there will be more manufacturing problems.