COB Packaging Challenges Outdoor Small Pitch New Limits & SMD
Packaging Will Face Great Challenges
COB packaging has gradually matured in the field of LED display
applications, especially in the field of outdoor small pitch with
its unique technological advantages have emerged, has now exceeded
the outdoor P3.0 level, and in the near future to break through the
outdoor P2.0 level is inevitable . So what is the COB packaging
technology? Why is it so impressive to see the emergence of an
Egyptian? Where is its technical advantage? What are the
application prospects of future COB products?
I. What is COB packaging?
COB package in English is called Chip On Board, literal translation
is the chip on the board. as the picture shows:
In the field of LED display technology, the COB packaging process
is to fix LED bare die with conductive adhesive or insulating
adhesive on the pad of the PCB's lamp position, and then use
ultrasonic welding technology to conduct lead bonding of the LED
chip, and finally use epoxy. The resin glue encapsulates the lamp
position and protects the LED light-emitting chip.
II. The difference between COB packaging process and DIP and SMD
The DIP and SMD packaging processes are no different from COB
encapsulation in terms of die bonding wires. The biggest difference
is in the use of red brackets. As we all know, the bracket has four
solder legs that need to be soldered to the PCB board by SMT.
Therefore, the biggest difference between the COB packaging process
and the DIP and SMD packaging process is the elimination of a lamp
surface over-reflow soldering process.
III. The advantages of COB packaging technology
1. High reliability:
An important indicator for evaluating reliability is the failure
The current national standard applied in the LED display industry
COB packaging process can make this indicator achieve:
Full color screen: less than 100,000; single, dual color screen:
less than 8 parts per million;
Why COB packaging display has such high reliability, we analyze
through the following five points:
A: The number of control loops in the single lamp production
process is reduced.
As we all know, a full-color lamp requires five wires:
The COB packaging process only needs to control the quality of the
five bonding wires in the production process. In addition to the
quality of the five bonding wires, the SMD process needs to be
controlled, and it is necessary to control the soldering of the
four soldering legs of the support when the lamp surface is
reflowed quality, as shown:
According to the principle of reliability, the fewer control links
in a system, the higher the reliability. The control links for COB
and SMD are 5 and 9, respectively, so the reliability of SMD is at
least nearly twice as low as COB in this respect.
If one square meter of P10 is produced, the SMD packaging process
requires an additional 40,000 control points. If the pixel density
is reduced by a factor of two, that is, the spot density reaches
the P5 level, the SMD packaging process requires 160,000 solder
joints per square meter to be controlled. If the pixel density is
further reduced to the P2 level, the SMD packaging process requires
1 million solder joints per square meter to be controlled. How to
ensure that 1 million solder joints do not exhibit false soldering,
continuous soldering, and false soldering under the condition of P2
dot pitch is a very serious problem.
The COB packaging process has created a revolutionary step and has
eliminated the welding of this bracket.
B. COB eliminates the lamp bead surface reflow process and there is
no microscopic damage to the LED chip and wire caused by the high
temperature in the reflow oven.
The SMD lamp needs to be surface-mounted and soldered to the PCB
board, so the oven is subjected to a test temperature of 240°C. If
the epoxy resin TG point is too low, the high temperature causes a
sharp increase in the coefficient of thermal expansion of the
colloid. Destruction failure of LED conductive wire. In addition,
the possibility that the high temperature is transmitted to the
chip through the stent pin to cause crystal fragmentation failure
C. The COB packaging process directly fixes the bare LED chip to
the pad, so the heat dissipation area is larger than the SMD, the
thermal conductivity is also high, and the heat dissipation is
The SMD is to fix the LED bare chip on the pad inside the bracket.
The pad needs to transfer heat to the PCB board through the bracket
D. The COB packaging process circuit board adopts a gold-immersed
process, and does not adopt the SMD-packaged PCB board spraying
process, so the anti-oxidation capability of the PCB board circuit
E. COB packaging process lamp surface curve is semi-spherical, as
The SMD has a quadrangular shape with sharp edges and corners. COB
has no shadow area and no processing dead corner when the outdoor
nano-coating, anti-ultraviolet coating and three anti-paint
spraying outdoor protection treatment process are performed. And
SMD is faced with a huge challenge in how to deal with the
antioxidant capacity of these millions of solder joints when
dealing with the outdoor protection of four-legged or six-legged
pads on surface-mounted lamp beads.
2. Cost cut down
Compared with the SMD packaging process, COB packaging process
saves costs, mainly from the following four aspects:
A. Saving raw material costs
COB packages no longer use metal materials such as brackets and
B. Save process costs
The COB package saves the cutting, splitting, braiding, and lamp
reflow processes of the lamp bead circuit board;
C. Save on transportation costs
The COB package no longer uses brackets, saving the weight of the
bracket. For example, a square meter of SMD P3 full color screen
will use 111111 brackets.
The COB package uses a point-by-point precise dispensing process to
protect the bare LED chips. Therefore, the amount of glue used is
very small. Take P3 full-color as an example. The amount of glue
used by a 1024-lamp module is less than 3 grams. Therefore, the
weight of the module is also saved.
Save on weight saves logistics costs;
D. Simplified production organization process
The COB packaging process integrates the production processes of
the midstream and downstream companies in the LED display industry
chain. Within a company, it can complete the production process
from encapsulation of LED light beads to LED display screens,
saving the cost of production organization, and packaging and
intermediate links, logistics costs, quality control costs, etc.
The SMD packaging process is the lamp packaging factory will do a
good job of lamp encapsulation, and transportation to LED display
3. Easy to achieve small pixel pitch
For the application trend of small pitch led display, it is
possible to break through the P1.0 level in the future. If only
from the perspective of reliability, the advantages of the COB
packaging process are much stronger than those of the SMD packaging
process. The reasons are as follows.
Take the P1.0 level as an example: The P1.0 pixel density per
square meter is calculated as follows:
For 1 million points, with 4 legs for each point, the total
production process needs to control 4 million feet. This will be
very difficult, and the COB package will not have such
difficulties, so it is reliable. Also, the COB package is no longer
limited by the size of the bracket when designing the lamp
diameter, as shown in the following figure:
The current technology can design the lamp pixel pitch to 1.2mm,
and the safety distance between the lamp distance and the lamp
distance can reach 0.5mm. In theory, the small pixel pitch can
achieve P1.7 level. In the future, with the advancement of LED chip
technology, the size will further shrink, or there will be the
emergence of flip chip LED chips. Breaking through the P1.0 level
is no longer a dream.
4. Thin 180° wide viewing angle
A. Thin and light:
The COB package module will weigh less than 1/2 the weight of the
SMD package module.
Compared with outdoor modules with the same density, the COB module
is about 10kg lighter per square meter than the SMD module.
B. 180° wide viewing angle
Since the COB package uses a hemispherical lens to emit light,
there is no masking of the face, so in theory the light emission
angle can reach 180°.
The SMD is generally at 125° and can reach up to about 160°.
Because the COB package is not brazed and the LED chip is sealed by
the epoxy resin in the lamp position, it can be arbitrarily bent.
The bending capacity is determined by the size of the module and
the thickness of the PCB. The SMD module cannot be bent.
5. Compression resistance, impact resistance, wear resistance, easy
A. Compression resistance, impact resistance, wear resistance
The lamp position of the COB module is encapsulated with epoxy
resin, and the high TG point glue has good physical properties as
Compressive strength: 8.4kg/mm2
Shear strength: 4.2kg/mm2
Impact strength: 6.8kg*cm/cm2
Hardness: Shore D 84
Take P4 lamp beads as an example: Lamp diameter is D=2.8mm
The lamp bead package area is: S=πr2=3.14X1.42=6.15mm2
The individual lamp beads withstand the pressure: 6.15X8.4=51.66kg
The individual lamp beads withstand the lateral shear force:
6.15X4.2 = 25.83kg
B. Easy to clean
Because the mask of the COB module lamp panel is no longer used, it
can be directly washed with water after being used outdoors for a
period of time after the pollution.
IV. in conclusion
In the future application fields of small-pitch LED display
products, SMD will face enormous challenges in terms of
reliability, achieving smaller pixel pitch, and cost. COB packaging
will have a revolutionary breakthrough and will eliminate the big
burden of brackets. COB encapsulation has a much bright future.
|Module composition||Pixel structure||COB 3-in-1|
|Module maximum power consumption||21W|
|Cabinet composition||Cabinet module composition||4×2|
|Cabinet size||500(W)×500(H)× 70(D)|
|Cabinet Pixel density||8192pixels/sq.m|
|Cabinet form||Die-cast aluminum Cabinet|
|Optical parameters||White balance||≥1800-2500nits|
|Viewing angle(Level / vertical)||≥170/170|
|max power consumption(W/ Cabinet；W/m2)||168/672|
|aver power consumption(W/ Cabinet；W/m2)||67/269|
|Processing performance||Change frame frequency(Hz)||50&60|
|Color processing bits||8bit|
|Use parameters||Service life(hrs)||50,000H|
|Working temperature / humidity(℃/RH)||-40 – 80 / 10%-90%RH|
|Lamp beads compression Forward / Lateral(KG)||38/19|
|Lamp beads wear-resistant||D84|
|application environment||window display||Transparent,waterproof|
|stage display||High Transparent|
|rental display||Thin and light,Wear-resistant,Not afraid of bumping|
|landscape display||For fountain,waterproof|
|advertising led poster||Ultra-thin and ultra-light,Easy to install|