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Shanghai, July 10, 2023 /PRNewswire/ -- In recent years, with technology maturing and costs decreasing, Mini LED has started to enter the market in large quantities. Currently, there are two main directions for Mini LED applications: one is to replace traditional LED as the backlight source for liquid crystal displays, improving LCD display effects through denser LED arrangements and under-screen backlight methods; the other is to realize Mini LED RGB direct display in the form of self-emission, utilizing small-pitch dense LED arrays to achieve delicate display effects.
Backlit Mini LED offers better display brightness, contrast, and color reproduction capabilities, with display performance and thickness approaching OLED, while surpassing OLED in terms of cost and lifespan. Due to issues such as high power consumption, low contrast, narrow color gamut, and relatively thick profiles of traditional LCD TVs, backlit Mini LED is beginning to replace LCD in medium-sized display devices. According to Yole's forecasts, LCD combined with Mini LED backlight will achieve good results in markets such as virtual reality, automotive electronics, monitors, and TVs. Furthermore, backlit Mini LED will also replace some LCD market share in the TV terminal sector.
Compared to OLED, direct-view Mini LED has the advantages of more precise brightness adjustment, higher brightness, and no risk of burn-in. OLED, on the other hand, boasts denser pixels, finer display, high contrast, thinner profiles, and better power savings. However, the risk of burn-in is currently the biggest flaw in OLED display devices. To balance lifespan, the brightness of OLED is also limited. As costs decrease, direct-view Mini LED will occupy more share in the high-end TV market above 60 inches, while OLED will dominate in the 40- to 60-inch high-end TV market.
The large-scale commercialization of Mini LED products has brought tremendous business opportunities to the Mini LED substrate manufacturing industry. Currently, there are three main Mini LED substrate solutions: PCB, FPC, and glass. FPC is used for flexible screens, while most other products employ PCB substrates or glass substrates. Both have their respective advantages and disadvantages:
PCB substrates excel in high structural strength, low process precision requirements, mature processes, and significantly higher yields compared to glass substrates. However, PCB substrates also face challenges: they are prone to bending and warping when heated, and smaller single-board sizes require multiple boards to be spliced together, potentially leading to issues with color difference and thickness uniformity.
Glass substrates, on the other hand, offer advantages such as low material costs, high processing precision, good thermal conductivity, excellent thickness uniformity, high flatness, strong stability, large single-board sizes, seamless splicing, no risk of light-emitting diode (LED) dropout, and long lifespan. However, glass substrates suffer from immature processes, lower brightness, fragility, low sputtering coating efficiency, graphical yield issues that need improvement, and higher costs. Additionally, glass substrate routing requires photolithography masks, which increases upfront costs. If the scale of production is not high, the average cost may exceed that of PCB substrates.
Overall, PCB substrates remain the mainstream solution in Mini LED products and are adopted by mainstream manufacturers' Mini LED solutions. Glass substrate solutions, due to their many advantages, are more suitable for Micro LED, which requires higher precision.
AT&S has long-term cooperation with renowned domestic and foreign manufacturers in producing Mini LED PCB substrates. Currently, AT&S' mass-produced products mainly include high-pixel-density Mini LED direct-view COB substrates (P0.6, P0.7, P0.8, P0.9, P1.0), as well as N-in-1 module direct-view boards, backlight substrates, and automotive display boards. Most of these products use 8-layer 3-stage HDI boards, with a minority using 6-layer 2-stage HDI and 10-layer 4-stage HDI.
Despite PCB substrates being the mainstream solution for Mini LED, they still face challenges. AT&S has accumulated rich experience in cooperation with large manufacturers and provides a complete set of solutions for the pain points in PCB substrate manufacturing:
Color difference: Due to optical characteristic requirements, direct-view MiniLED has very strict requirements for the ink smoothness and color difference on the PCB surface. AT&S uses suitable materials and new processes, strictly controlling ink thickness and window opening, avoiding the color difference issues encountered by most PCB manufacturers.
Warping and dimensional changes: In the assembly process of COB direct-view boards with small pixel pitches, a large number of chip transfer technologies are used. To avoid the risk of chip misalignment or displacement during transfer, there are very stringent requirements for PCB board warping and dimensional changes. AT&S addresses this by selecting materials, implementing layered control, and adjusting processes to ensure that PCB warping and dimensional changes remain within a very small range.
Pad size tolerance: Controlled within ±10 micrometers.
Pad spacing: The pad spacing is 40 micrometers, with a tolerance controlled within ±10 micrometers.
Line width and spacing: High-end SLP (substrates-like PCB) technology is used to achieve carrier-board-level line width and spacing.
