The development of SMD technology in the field of fine-pitch display has encountered bottlenecks: a large number of solder joints in SMD packaging, poor air tightness and poor protection, resulting in more reliability problems such as dead lights, caterpillars and so on.

1. Comparison of COB , SMD and 4in1SMD

2. What are COB, SMD, 4 IN 1 SMD?
SMD：
Surface Mounted Devices
For indoor Pixel＜2mm
Mainly use SMD1010,
SMD0808,SMD0606
Chip package
After the LED encapsulation,
then solder SMD legs to the
PCB.
COB：
chip on board
Chips directly integrated
packed on PCB board
4 IN 1 SMD:
Four SMD integrated packages
填充胶 SMT贴片LED灯
LED灯灯脚金属支架
PCB板
SMT贴片LED灯
LED灯灯脚金属支架
PCB板
Filling glue SMT chip LED lamp
LED lamp foot
metal bracket
PCB board
SMT chip LED lamp
LED lamp foot
metal bracket
Special made lamps for each pixels
Chip package
After the LED encapsulation,
then solder SMD legs to the PCB.

3. Time to market of COB, SMD, 4 IN 1 SMD
Crystal LED
2012 2018 2019
At ISE 2019, some
Chinese
manufacturers
exhibited four-in-
one products.
Ledman exhibited
COB products at
ISE 2018.
COB products were
exhibited for the first
time at the CES 2012.
SMD fine pitch
products are
launched.

4. COB SMD Four-in-one
Domestic listed
companies.
(excluding subsidiaries
of listed companies)
Ledman、Unilumin Leyard、Unilumin、
Absen、Ledman、
Leyard、Unilumin、
Absen、
Domestic unlisted
companies
Few companies can make it as
produce COB screen needs both
technology of LED package
and technology of LED
screen.
many Not much.
Foreign companies Sony、 Samsung、Daktronic many Not much.
Technical routes chosen by different companies in the
LED display industry (incomplete statistics)

5. Differences among different technical routes of COB, SMD, 4IN1-SMD,
SMD technology and 4 in 1 SMD route are similar,
COB technology route on the basis of SMD technology route, but it has get rid of soldering process and
reflow soldering process, which the reason why COB has a 10 times lower failure rate compare to SMD screen.

6. The biggest advantage of SMD technology is that it inherits all the engineering process characteristics of the
traditional pitch LED display screen, and the middle and upper reaches of the market is highly mature.
The development of SMD technology in the field of fine-pitch display has encountered bottlenecks: a large
number of solder joints in SMD packaging, poor air tightness and poor protection, resulting in more reliability
problems such as dead lights, caterpillars and so on. The welding area of the lamp bead welding pad is
small, and it is easy to damage the lamp bead when it is knocked in the process of handling, installation and
usage. The lamp bead welding pad is exposed, and people touches the screen in a dry environment, and the
influence of static electricity can easily lead to the breakdown of lamp beads. The dust between the lamp
beads cannot be cleaned. SMD is very difficult in the application of display screen where the point spacing is
less than 1.0mm.
Bottleneck of SMD fine pitch LED display technology

7. SMD: Due to the
uneven surface, the LED
is easily knocked off
and the dust cannot be
wiped at the same time.
SMD: due to the different
coefficient of thermal expansion of
different materials, the place where
marked by red arrow is easy to have
cracks, s and water or moist air can
easy to enter the inside and finally
corrode the chip。
Because the LED small spacing products
packaged by SMD need SMT on PCB,
calculated by P1.2mm, SMD small spacing
products have more than 2 million solder
joints than COB products, therefore, the
reliability of SMD small spacing products is
relatively poor, LED failure rate ≥ 50PPM.
Metal
Bottleneck of SMD fine pitch LED display technology

8. The Origin, advantages and disadvantages of 4IN1-SMD fine
pitch display Technology
In order to improve the anti-collision performance, and in order to make a LED display screen with less
than 1.0mm dot spacing, a four-in-one package SMD appeared.
However, the four-in-one welding foot is exposed, the air tightness is still not good, moisture-proof
performance, anti-static performance is still not good.
Four SMD integrated packages together, resulting in color separation is not easy to deal with.
It is very difficult to clean the dust between the lamp beads.
The specification is not flexible, and the spacing between a few points can only be fixed, so it is
impossible to produce in large quantities, and it is difficult to reduce the cost.

9. There is a color inconsistency
between the black screen lights.
There are splicing gaps.
Lamp foot reflection Up close, optical crosstalk between
four lights
The Origin, advantages and disadvantages of 4IN1-SMD fine
pitch display Technology

10. COB fine pitch display Technology
COB technology omits the SMD LED packaging process, color separation, braiding, patch and other
technological processes. COB greatly shortens the process path, and reduces the solder joints of LED which
help greatly improve the PPM(Failure rate of per million during a period of usage time) . (because the LED small
spacing products packaged by SMD need SMT on PCB. So, take 1 sqm P1.26mm for example, SMD P1.26
products have more than 2.5 million welding joints than COB products). From this aspect, COB improves the
reliability of the production process. )
The integral filling and sealing of the COB product panel has the advantages of moisture resistance, anti-
collision, no bare pins, anti-static breakdown, and improve the reliability of the use process. According to
the data statistics, the average failure rate of COB is 10 times lower than that of SMD, which effectively improves
the reliability and stability of LED display screen.

11. COB fine pitch display Technology
COB technology to achieve the "point" light
source to "surface" light source, no pixel particle
sense; the pixel center brightness can be
effectively controlled, reduce light intensity
radiation, suppress moire, glare and glaring
damage to the retina, suitable for close-up,
long-time viewing, not easy to produce visual
fatigue, is the best solution for scenes that
require close viewing of the display screen., such
as meetings, monitoring, command and
control center.

12. Brief introduction of Moire pattern
The generation of moire pattern is the interference of waveforms between different
objects, which is a manifestation of the beat principle.
Because the photographic element (CCD or CMOS) such as the camera has a spatial
frequency, the spatial frequency of the pixel of the photosensitive element (CCD or
CMOS) is close to the spatial frequency of the image to be photographed, which will
produce a new pattern, which is the moire pattern.
The LED display screen is made up of discrete pixels, and there is an obvious non-
luminous black area between the pixels, forming a grid pattern, which forms a moire
pattern in the process of being photographed by the camera.
The solution to the moire pattern is to optically treat the surface of the display screen,
enlarge and display the discrete LED luminous points, and convert the point
luminescence into surface luminescence to eliminate the moire pattern.

13. Comparison of COB, SMD, 4IN1-SMD
In terms of technology, COB involves two very important technologies: one is point-by-point
correction technology, and the other is single-point maintenance technology.
At present, the luminance chromaticity point-by-point homogenization correction technology and the field
correction technology have been very mature.
Compare with the traditional watch paste LED display screen, the vast majority of people in the industry
think that the COB display screen is more complex and more difficult to maintain, which is actually a
misunderstanding. Because the protective performance of COB products is quite excellent, there is
actually no cost for after-sale maintenance, but customers and integrators can only repair part of
the PCB board, so they feel that the maintenance process is complicated. In fact, the repairable
degree of COB technology is better than that of table stickers.
Watch sticker products break a lamp, which is easy to leave a very obvious mark after maintenance, while
COB products use special equipment for single point maintenance, there is no such problem.

14. Comparison of COB, SMD, 4IN1-SMD
From the user's point of view, many users are
government departments and confidential units, and
outsiders are not allowed to enter the site for
maintenance, and users can not reach the technical
level of on-site maintenance, so many SMD small
spacing displays actually require users to change
modules and send them to manufacturers for repair,
which is the same as COB maintenance process.
After the SMD product module
changes the light on the spot

15. COB vs SMD, 4IN1-SMD, summary
Name COB SMD 4IN1-SMD
Time to market 2012 (Ledman is 2018) 2012 2019
Large
companies
adopting the
technology
Sony、 Samsung、Daktronic、Ledman、Unilumin Basically have Leyard、Unilumin、Absen、
Brightness and
chromaticity
uniformity
The pixel parameters of COB package can not be sorted and mixed,
and the chromaticity and luminance consistency of the whole screen is
worse than that of SMD. However, Through the specially optimized
point-by-point chromaticity correction technology, COB can ensure that
the brightness consistency of the whole screen is more than 98%, and
the difference of color coordinates is less than 0.003.
SMD products are
tested and sorted after
packaging, "mixed
lights" are carried out
before braiding, and
then mixed again when
SMT is affixed with lamp
beads, the overall
consistency is good.
Worse than SMD.
Black screen
color
consistency
COB products are prone to chromatic aberration between modules,
which is worse than SMD.
basically no color
difference in the whole
screen of SMD
products.
Worse than SMD.
Moiréeffect The surface light source basically has no Moir éeffect. The moire effect of point
light source is obvious.
The moire effect of point
light source is obvious.

16. COB vs SMD, four-in-one, summary
Name COB SMD 4IN1-SMD
Moistureproof
performance
Good, up to 90%. Not good, ≤80%. Not good, ≤80%.
Anti-collision
performance
Module-level packaging, good. Single lamp package, very poor. Better than SMD.
Antistatic
performance
The metal pins are not exposed. Good. The metal pin is exposed, easy to touch,
not good.
金The metal pin is exposed,
easy to touch, not good.
LED failure rate <2PPM ≥50PPM ≥50PPM
Maintenance
performance
LED cannot be repaired on site. LED can be repaired on site. LED can be repaired on site.
Maturity of
industrial chain
With the gradual improvement of technology
maturity, there are predictions in the industry that
there will be a big outbreak in 2021.
The upstream and downstream
industries are mature and have a high
degree of technological maturity.
The specification is not
flexible and it is not easy to
produce on a large scale.
The technology is relatively
mature.

17. WWW.LEDMAN.COM
Some of
LEDMAN
COB
screen
photos
LEDMAN COB P1.5 in reception hall in Japan

18. WWW.LEDMAN.COM
Some of
LEDMAN
COB
screen
photos
Ledman COB P1.2 in command center

19. WWW.LEDMAN.COM
Some of
LEDMAN
COB
screen
photos

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