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Deep dive into Apple’s iPad Pro’s miniLED backlight: how the company balanced cost and performance

System Plus Consulting reveals the Apple’s iPad Pro’s MiniLED secrets…

OUTLINE:

  • MiniLEDs and their assembly in the display’s backlight unit of the iPad Pro 2021, developed by Apple
  • The new backlighting system:

It is composed of 10,384 mini-LEDs, divided up into 2,596 local dimming zones.

MiniLEDs are GaN[1]-based dies on patterned sapphire substrate with top & back dielectric reflectors for light emission shape control.

COB[2] assembly includes more than 10,000 miniLEDS

The miniLEDS are driven by 9 drivers from STMicroelectronics.

The main part of the backlight unit cost is due to the mini-LEDs at 37%…

  • Supply chain

Epistar, STMicroelectronics, Zhen Ding Tech (China) and TSMT are part of the Apple’s supply chain.


After years of excitement, Apple finally released its first miniLED based product with its latest iPad Pro. System Plus Consulting has just released a full teardown report of the backlight unit with technology and cost analyses. We learned a lot.

Liquid Crystal Display (LCD) manufacturers have long been using full-array local dimming (FALD) to improve the contrast in their panels. In LCDs, depolarization effects in the TFT transistor substrate, liquid crystal cell, and color filters result in light leakage. Therefore, even when a pixel is turned off, there is always a residual amount of light leaking from the backlight unit (BLU), resulting in poor contrast. To enhance the performance of the LCD, global and local backlight dimming are used. In local dimming, the display is segmented into multiple zones, in each of which the backlight can be controlled individually and completely shut down in dark areas of the image, as shown below.

FALDs have till now only been used in TVs and desktop IT monitors, but not in mobile displays such as laptops, tablets, or mobile phones. One reason is that by placing the LEDs on the back of the display facing the viewer, the thickness of the device increases. Not only is the LED package itself relatively thick, but a sufficient distance is required for the light from individual chips to spread evenly throughout the display, eliminating hot spots.

Here come the miniLEDs

MiniLEDs solve the issue by multiplying the number of LED chips, thereby reducing the spacing between each light source and the thickness of the backlight. More interestingly, they also can significantly increase the number of zones, which should reduce blooming – the halo effect when bright objects or highlights much smaller than the individual dimming zones are displayed against a very dark background.

Ultimately, well-designed miniLED backlights can enhance LCD contrast performance to levels close to OLEDs while maintaining the LCD’s high brightness characteristics and long lifetime (no “burn-in” concerns). They can also reduce power consumption, since most zones will be off in dark images or the brightness will be dimmed.

Why don’t we see miniLED backlights everywhere? The answer is cost. More LEDs mean higher chip cost, and a higher number of zones means more driver ICs. One possible way to reduce cost is to make the chips as small as possible. However, this makes chip manufacturing more complicated, increases sensitivity to defects, and reduces yields. By reducing the gap between the bonding pads, miniLEDs also make attaching the die onto the printed circuit board (PCB) more difficult: higher placement accuracy is required, and the demands on the PCB flatness and lithography accuracy become more stringent. Cost increases further.

Apple’s iPad Pro’s MiniLED secrets

The design and manufacture of a miniLED BLU is a complex art that must balance technology, performance, and cost.  System Plus consulting’s iPad Pro miniLED backlight unit teardown reveals that the device uses 10,384 miniLED chips assembled directly on a special PCB to form 2,596 zones. The miniLEDs (manufactured by Epistar) are not as small as would have been expected, leading to a relatively high chip cost. In addition, the die presents some features such as DBR dielectric mirrors that are more often found on higher-end, larger chips used for general lighting or automotive applications.

However, Apple manages to drive the full backlight with a small number of custom drivers provided by ST Microelectronics. The partners appear to have found a good balance between cost and performance by optimizing the number of channels and each driver’s multiplexing capabilities.

The tear-down analysis reveals many other unique design choices. We invite our readers to study this new release to understand better Apple’s miniLED supply chain and technological choices from chip design to the overall backlight architecture and the consequences for the bill of material of this newly released miniLED backlight unit.

While OLEDs were once thought to be the sure winner in many applications, miniLEDs provide LCD makers a credible opportunity to reduce the performance gap and leverage their massive installed LCD capacity. For midsize panels, such as tablets and laptops, it brings an opportunity to establish a strong foothold in the high-end product segments, at a time when OLED makers are finally making a strong push and investing in new fabs and technologies to address laptop and tablet applications. But as is often the case in the display and LED industry, cost reduction will be key to enabling significant adoption. This first miniLED backlight teardown and reverse costing by System Plus Consulting shows that balancing cost and performance is not as straightforward as some would think. Teardowns of various devices (TVs, monitors) are in progress at SPC. These will allow us to get a good picture of the miniLED BLU technology landscape and see the cost /performance tradeoffs made by different companies in different devices.

Of course, with Apple’s acquisition of LuxVue back in 2014, the company also has its eyes on microLED. As discussed extensively in our latest MicroLED Displays – Market, Industry and Technology Trends 2021, the momentum is strong for microLED, but many technical and supply chain challenges remain. Many solutions look great on paper, but real-life process integration in a high-volume manufacturing environment is much more challenging. Apple has strong incentives to succeed. MicroLED could offer the company a unique, highly differentiating technology and allow it to ultimately control a fabless microLED display supply chain, independent of traditional panel makers and with multiple suppliers at each critical step.

But for Apple, miniLED is also a strategic decision. The iPad is only the first step. MiniLED is anticipated to be a key differentiator in Apple’s new generation of upcoming MacBooks.

In addition to the analysis of the miniLED backlight unit of the iPad Pro, Yole Group is launching a multi-customer action in order to do the reverse engineering and teardown of 4 major miniLED backlight displays and monitors, analyzes the performance of these displays, highlight the supply chain and compare the choices and strategies of the different companies. If you want to learn more and tailor this multi-customer action to your needs, feel free to contact Jean-Christophe Eloy (eloy@yole.fr).

Authors

Eric Virey, PhD, serves as a Principal Display Market and Technologies Analyst within the Photonics, Sensing & Display division at Yole Développement (Yole).
Eric has spoken in more than 50 industry conferences over the last 10 years and has been interviewed or quoted in multiple media including: The Wall Street Journal, CNN, Fox News, CNBC, Bloomberg, Financial Review, Forbes, Technology Review, etc.
Prior to joining Yole, Eric held R&D, engineering, manufacturing and marketing positions with Fortune 500 Company Saint-Gobain in France and the United States. Eric received a PhD in Optoelectronics from the National Polytechnic Institute of Grenoble. He is based in Portland, OR.

Zine Bouhamri, PhD. Team Lead Analyst, Imaging & Display Activities at Yole Développement (Yole).
Zine is managing the expansion of the technical expertise and the market know-how of the company.
In addition, he actively assists and supports the development of dedicated imaging collection of market & technology reports and monitor as well as custom consulting projects.
Prior to Yole, Zine oversaw numerous R&D programs at Aledia. During more than three years, he developed strong technical expertise as well as a detailed understanding of the display industry. He is author and co-author of several papers and patents.
Zine Bouhamri holds an Electronics Engineering Degree from the National Polytechnic Institute of Grenoble (FR), one from the Politecnico di Torino (IT), and a Ph.D. in RF & Optoelectronics from Grenoble University (FR).

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MiniLED Backlight Unit in the 2021 Apple iPad Pro
In-depth technical and cost analysis of the first consumer miniLED backlight unit and its assembly.

MicroLED Displays – Market, Industry and Technology Trends 2021
Strong momentum for MicroLED with progress on all fronts. Cost is the biggest challenge, but Apple and Samsung are carving paths toward the consumer.

MicroLED Displays – Intellectual Property Landscape and Analysis 2021

Next Generation TV Panel Technology and Market Trends 2020


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