I. Overview
Difficulties massive transfer is how to enhance the transfer of 99.9999% yield (called "six nine"), and each of the chips must be controlled within the accuracy of plus or minus 0.5 μm.
In the conventional LED package part, the main vacuum suction transfer manner. However, due to the vacuum in the physical limits can do about 80μm, and MicroLED size substantially less than 50μm, so the vacuum suction is no longer applied in the manner MicroLED age.
Industry was born out of at least three precise crawl (Fine Pick / Place) technology: "static electricity", "van der Waals force" and "magnetic" selective release of (Selective Release), self-assembly (Self-Assembly) and transfer (Roll Printing)
1. electrostatic force
Using electrostatic transfer head having a two-stage structure, in the transfer process, are applied to the positive and negative voltages, when the LED fetch from the substrate, on a silicon electrode via positively charged, LED will be adsorbed on the transfer head, when needed the LED into a predetermined position, through the addition of a negatively charged silicon electrode, to complete the transfer.
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2. van der Waals force
Transferring mode: elastic stamp, high precision motion control in conjunction with the print head, using the van der Waals force, by varying the speed of the print head, so that the transfer adhesive LED head, or print to a predetermined position on a target substrate sheet.
3. Magnetic
Before cutting, mixed with a magnetic material such as iron, cobalt and nickel on a Micro LED, by electromagnetic adsorption and release.
4. selective release sent
Selective release, be transferred directly from the original on the substrate the LED, the current approach is to achieve maximum laser lift off patterning (p-LLO), i.e., using the excimer laser, a gallium nitride sheet is irradiated on a growth interface sparse mold size separation zone, and then exposed to ultraviolet rays generated by gallium and nitrogen, do transferred in parallel to the substrate, to achieve accurate optical array.
5. Self-assembly camp
On the substrate using a brush barrel rolling, so that the LED is placed in a liquid suspension, by fluid force, so that the well corresponding to the LED falls on the substrate.
6. transfer school
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