To Get Higher Screen-to-body Ratio, All Depend on It! What is the COP Package That is More Important Than Notched Display?
Xiaomi Mi Fans

To Get Higher Screen-to-body Ratio, All Depend on It! What is the COP Package That is More Important Than Notched Display?

Smartphones entered a prosperous stage of full screen in 2017. Numerous new coming smartphones (relative to previous mobile phones) obtain a broader view on-screen without increasing the phone body size. 

In 2018, the iPhone X notch display has become the mainstream in the smartphone world, which makes the parameter, screen-to-body ratio, become important competitiveness of new arrival in the future. Therefore, the smartphone screen’s packaging techniques will be the key to win competitiveness in the mobile phone market.

To improve the screen-to-body ratio, smartphone makers found a lot of new ways to explore a long time ago. More changes have been made to gradually create the smartphone we see today. 

Broadening display view begins with bezel

The Screen-to-body ratio refers to a ratio of the real visible display area and the phone screen surface area. A higher screen-to-body ratio will bring an illusion of a wide viewing angle on display and enjoyment when playing video games. In this era of 16:9 LCD panel dominating the mobile phone market, shrinking bezels naturally become the first choice to expend display vision.

Start with the sizes bezel

To expand display vision, the concept of edge to edge (aka bezel-less) emerged at the smartphones field at the earliest time, which starts with side bezels and lets palms directly touch the phone display edge.

Unfortunately, whether it be LCD or OLED screen, it is impossible to achieve a real edge to edge. In this way, Some brands smartphone represented by Nubia has accomplished the planning goal of edge to edge on vision by taking clever aRC (arc Refractive Conduction) technology.

To put it simply, aRC technology is to take an extremely narrow bezel-less design and uses an outer layer of curved glass to cover the BM area, then refracts the light by adopting unique edge cutting to achieve a stunning visual effect. ARC technology has gradually become mature from Nubia Z9 to Z11 and Z17, which have effectively solved the problems of the thick screen and rainbow colors accrued on both sides of the display.

In addition to Nubia, SONY manufacturers embarked on the path of bezel-less design after they launched Xperia C5 Ultra and Xperia M5. At the same time, the curved screen created through AMOLED screen can effectively reduce the size bezels’ impact to display vision.

Nubia Z17 Mini 4G Smartphone



Take the top and bottom bezels as an entry point

Compared to side bezels, the top and bottom bezels have more influence on-screen to body ratio. Lenovo Zuk Edge is the typical mobile phone to put a lot of effort into the top and bottom bezels. Zuk Edge makes it possible to fit a 5.5-inch screen in a 5.2-inch size body.

The present popular full screen has followed the display design style of ZUK Edge. Most smartphones’ top and bottom bezels have a similar width with ZUK Edge’s. The only difference is to put a higher ratio of 18:9 display on the phones. This is the consequence that the whole upstream and downstream industry chain promotes the display’s development and upgrading together. There is little to do with individual smartphone maker’s innovation.

iPhone X notch display displaces the full screen 

In this age of smartphone with full screen, smartphones have derived three kinds of full-screen. They are asymmetric display represented by Xiaomi MIX/MIX2, symmetrical display represented by SAMSUNG GALAXY S8, and unconventional cutout notched-display like iPhone X.

Xiaomi Mi Mix 2 4G Phablet 128GB ROM



Periodical success for notched screen

As we can see, display notches have won the periodical success among these three kinds of full screen in 2018, among them 95% newly released smartphones have followed the iPhone X display style. This is what we call the iPhone X notch display. Many advantages are taking the iPhone X notch style. One hand, its attention is easily improved by following the tide. On the other hand, the iPhone X notch style screen shows more information by retaining the display area on either side of the notch and it can also improve the screen-to-body ratio.

For the same reason for the full screen’s explosive growth in 2017, the iPhone X notch display became the king display in 2018 mainly due to the smartphone industrial chain’s optimization and upgrading. The unconventional cutout notched-displayS with 20:9/19.5:9/19:9 screen to body ratio have entered a stage of mass production, so why we need an old-type screen popular in the last year for a new mobile phone?

However, it is not hard to find that those new released smartphones with iPhone notch style display have a defect if we carefully observe them. The bottom bezel is generally wider than the top bezel, which looks a little bit odd.

The definition of no bottom “chin” bezel

The same important as side bezels, the top, and bottom bezels can not be abandoned completely for a smartphone. Even Vivo manufacturer launched APEX phone with the full-screen concept still has a relatively wider bottom bezel.

In that way, which kinds of design on earth maximally explains no bottom bezel?

The answer is very simple. Pls look at iPhone X, which is the only smartphone to make the top and bottom bezels’ width equal and adopts the perfectly symmetric design. It may be a little bit abstract in a literal description. We might as well compared several smartphones with the iPhone notch display. Ignore their display middle section and only focus on the top and bottom bezels, we will easily find the unique on iPhone X.

Here comes the question: 

Now that the symmetrical no bottom bezel of the iPhone X notch display is beautiful and fashionable, why can’t we find a new model for reference within numerous new mobile phones?

Packaging technique determines bottom bezel’s design

A smartphone display notch has to contain a front-facing selfie camera, ambient light/proximity sensor or a speaker, so the notches need to keep a certain width. However, now most smartphones have taken rear fingerprint scanner or a front fingerprint scanner on the bottom display. It seems that it is not necessary to put any hardware elements on the bottom bezel. Then some users may wonder why we can’t shrink the bottom bezel to extremes.

Getting stuck in the display packing

Smartphone display as an organic unity is made of many components like LCD(OLED), power management/touch IC and flex cable slot, etc., and connected to PCB motherboard by FPC board ( flex cable ), whether it is an ordinary screen, full screen or an iPhone X notch screen. Thus, the IC and display packaging technology determine whether smartphones can achieve no bottom bezel.

LCD structure schematic, smartphone display is more complex than it.

At present, the smartphone display packaging technique is mainly classified into COG, COF, and COP. Let’s analyze them in turn.

COG: traditional packaging

Before the flourish of the 18:9 full screen, the smartphone displays a widely used COG (Chip On Glass) packaging technique that an IC chip is directly bound to a glass surface of the LCD screen. This kind of packaging technique can effectively reduce the LCD module volume, enhance the qualified rate of the good display, and make it easy for mass production at low cost. So now comes a major problem, the COG is meant to require a wider bottom bezel because the glass is unable to fold and bend and consider another connected flex cable.

Xiaomi MIX brings a stunning bezel-less on three sides at the same time it has an impressive bottom bezel, resulting from the needs of containing a front camera and the main culprit of taking conservative COG packaging display. And a lot of flex cable needs to fit into a few millimeters space in display bottom.

COF: the best partner for fullscreen

COF is also called Chip On Flex or Chip On Film. Compare d with COG, the biggest improvements on COF are to fix touch IC and other chip in the soft grain film construct on flexible circuit boards and takes soft piggyback board as packaged chip / chip-carriers to joint flexible circuit board together. More directly, IC chip is inlaying on FPC flexible board, which means it is attached to the top of display and PCB board flex cable. 

FPC flexible board is free to bend, in this way, the smartphone makes can fold it in half in the back LCD display to shrink the top and bottom bezel. Compared with COG, COF packaging can at least reduce 1.5mm bottom bezel width. Xiaomi Max has a narrower bottom bezel mainly due to the folding property of COF packaging. In fact, mid-to-high-end full-screen and iPhone-notched display smartphones adopt COF packaged screens such as OPPO R15, Vivo X21 AND APEX full-screen conceptual machine, etc..

COP: flexible OLED’s exclusive perfect solution

COF packaging technique technology can be used in OLED ( including AMOLED ) screen, but it has not yet developed it’s 100% potential that OLED is flexible. But COP ( Chip On Pi ) packaging technique is regarded as a perfect solution especially for the flexible OLED screen.

To put it simply, a flexible OLED display’s backplane, not a specific glass existing on LCD, has adopted a similar material as FPC and its flexibility makes it free to bend. Therefore, a COP packaging display can fold the backplane directly based on COF to reduce space occupied by the display module maximally.

So the question remains, both iPhone X and SAMSUNG GALAXY S8/S9 use flexible OLED screen and COP packaging technology, then why does only iPhone X achieve no bottom bezel, but GALAXY S8/S9 still keep a wider bottom bezel(“chin”)? As we know, iPhone X screen is supplied by Samsung manufacturers, doesn’t SAMSUNG manufacturers want to keep the best display for themself?

The answer is simple, COP can narrow the display modules to an extreme, but a higher compression ratio will bring a higher cost and lower yield rate. To achieve the no bottom bezel design, iPhone X reportedly has a less 10% yield rate, and nine in ten of its models are defective in production. For the present smartphone manufacturers, no one else can optimize and improve COP packaging without considering cost except Apple manufacturer.


iPhone X notch display has dominated the smartphones’ world in 2018 The main competition of design on high-end phones is whose bottom bezel design can achieve a symmetrical design like iPhone X. It is hoped that the COP packaging technique will be used for more cost-effective models with industrial chain optimization and upgrading.

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