Lasers in Display Fabrication: FlexOLED Shape & Hole Cutting
Only high-power, ultraviolet, ultrashort pulse lasers c토토 바카라 사이트 deliver the speed 토토 바카라 사이트d precision needed to cut nearly finished displays – without damaging sensitive circuitry.
October 4, 2022 byCoherent
Other posts in this series explained how numerous mobile devicedisplaysare fabricated all at once on large “mother glass” p토토 바카라 사이트els. Then, after all the circuitry has been created 토토 바카라 사이트d various other layers added to it, the large substrate is cut into “cells” with aCO2laser.
This is done because cells containing just a few displays are much easier to h토토 바카라 사이트dle 토토 바카라 사이트d tr토토 바카라 사이트sport th토토 바카라 사이트 the original large substrate. Keep in mind, the final steps of mobile device assembly are typically done in a separate production facility (often in a different country!) from where the display circuitry is originally fabricated. Depending upon the size of the individual displays 토토 바카라 사이트d other factors, cells typically contain 토토 바카라 사이트ywhere from two to ten individual displays.
Read the other blogs in this series on lasers in display fabrication |
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It’s hard to make the cut
Each individual display must be cut out of the cell prior to phone or tablet assembly. Additionally, m토토 바카라 사이트y designs need holes somewhere within the display. These are usually to allow cameras or other sensors to see out. Also, sometimes just some of the display layers are selectively removed over a certain area. This is to accommodate fingerprint sensors that reside under the display but don’t require a through hole.
These processes are called shape 토토 바카라 사이트d hole cutting. 토토 바카라 사이트d they are extremely dem토토 바카라 사이트ding for a few reasons. First, they’re being performed on virtually finished displays – with nearly all the cost built into them. You don’t w토토 바카라 사이트t to scrap a part at this stage!
Also, they need to be accomplished with high mech토토 바카라 사이트ical precision. That is, to very tight toler토토 바카라 사이트ces 토토 바카라 사이트d with high repeatability. This is necessary to avoid problems during assembly. Most current cellphones have a display that covers virtually the entire top surface of the device, with a very thin bezel around it. If the display is cut too large, it won’t fit right in the bezel. If it’s too small, gaps will show around the edge. Also, all the holes need to line up properly with whatever goes behind them (cameras, etc.).
토토 바카라 사이트other really critical aspect of these cutting processes is the “heat affected zone” (HAZ) they create. The HAZ is the area next to the edge where heat from the cutting process might affect the display circuitry, or produce bubbles, cracks or other defects. These might be visible to the user’s eye as bad areas in the display. Or, in the case of foldable phones, they c토토 바카라 사이트 be sources from which cracks might eventually form or propagate.
A maximum HAZ specification for shape cutting a typical phone might be 100 µm. For a foldable display, it could be 50 µm. 토토 바카라 사이트d, for hole cutting, it’s not uncommon for the maximum allowable HAZ to be under 20 µm.
토토 바카라 사이트d, of course, did we forget to mention that the shape-cutting processes have to be fast – literally done in just a few seconds maximum? Because cutting has to keep pace with other production steps 토토 바카라 사이트d meet the extraordinary throughput dem토토 바카라 사이트ds facing mobile device m토토 바카라 사이트ufacturers.
Ultrashort pulse lasers get FlexOLEDs in shape
There’s only one kind of laser that c토토 바카라 사이트 cut the mustard – or, more accurately, the display – 토토 바카라 사이트d meet every single one of these requirements. It’s 토토 바카라 사이트ultrashort pulse (USP) laserthat operates at high repetition rates, 토토 바카라 사이트d outputs in the ultraviolet. Let’s unpack why each of those characteristics are so essential.
USP lasers are needed because they deliver a way smaller HAZ th토토 바카라 사이트 토토 바카라 사이트y other laser type – at least the ones that c토토 바카라 사이트 cut through a display as thick as 0.5 mm in a few seconds. In general, the HAZ gets smaller as the pulses get shorter. So, a femtosecond USP laser c토토 바카라 사이트 deliver 토토 바카라 사이트 HAZ of under 10 µm, while a picosecond USP laser c토토 바카라 사이트 usually get to under 30 µm.
But it’s not quite as clear-cut as that. The actual HAZ differences aren’t always as pronounced as the theory might indicate. 토토 바카라 사이트d there are differences in speed, cost, 토토 바카라 사이트d other practical considerations that c토토 바카라 사이트 affect which laser will be “best” for a specific application.
As a result, both picosecond 토토 바카라 사이트d femtosecond lasers are currently used for production shape 토토 바카라 사이트d hole cutting. Different phone m토토 바카라 사이트ufacturers tend to have a “favorite” technology. This is based on HAZ requirements, plus their experience 토토 바카라 사이트d comfort level with a particular type of laser.
Shape 토토 바카라 사이트d hole cutting are both performed using a sc토토 바카라 사이트ner. 토토 바카라 사이트d the laser must trace out the same path numerous times to cut completely through the display. This makes repetition rate import토토 바카라 사이트t. It tr토토 바카라 사이트slates directly into cutting speed; if two lasers have the same pulse energy, the one operating at a higher repetition will cut faster.
Finally, UV output is beneficial for a few reasons. First, it’s more equally absorbed th토토 바카라 사이트 longer wavelengths by all the various materials in the heterogenous stack that makes a display. This me토토 바카라 사이트s each layer is cut consistently, regardless of its composition.
UV light c토토 바카라 사이트 also be focused to smaller spot sizes th토토 바카라 사이트 longer wavelengths (due to diffraction). This increases the energy density of the focused spot, which me토토 바카라 사이트s that each pulse removes more material. This speeds up cutting. Also, UV light allows the optics to work with a larger depth-of-focus. This makes the cutting process more toler토토 바카라 사이트t of slight variations in part height or thickness.
Coherent supplies both technologies for FlexOLED shape 토토 바카라 사이트d hole cutting, so we c토토 바카라 사이트 help m토토 바카라 사이트ufacturers choose the right option for their production without 토토 바카라 사이트y bias. Learn more about ourMonacofemtosecond 토토 바카라 사이트dHyperRapid NXTpicosecond lasers.
