Full-Color LED Screen Packaging Introduction:
LEDs are available in discrete or integrated packaging. LED discrete devices are part of traditional packaging, and they’re widely used in related fields. They have been developed for more than 40 years and now form a range of mainstream products.
Chip-integrated modules are currently confined to customized packaging. They are primarily designed and manufactured for individual application products and have yet to become mainstream products.
It is laborious and expensive to use the traditional LED method because there aren’t any ready-made core light source components. However, we can actually combine the “LED light-source discrete device /MCPCB module light source” into one – transfer and mount directly on the semiconductor chip and then integrate it onto MCPCB in order to create a COB module light source.
Wire stitching is used to make the electrical connection between chip and substrate. It is implemented and covered with resin for reliability. This saves not only labor and time but also the cost of packaging.
Compared to discrete LED devices, COB modules can reduce costs for LED primary packaging, production of light engine modules, and distribution of secondary light in applications. Calculations show that light source costs can be reduced by up to 30%.
Through a reasonable design, and the use of micro-lensing, COB modules can avoid performance issues such as glare and spotlight that are present when using discrete light sources. The color rendering can be improved by adding a combination of red chips without affecting the efficiency or life of the source. The COB modules are easier to install and produce, resulting in a reduction in costs.
Existing process technology and equipment are capable of supporting the production of COB modules at large scales with high yield rates.
What is the COB Packaging?
Chip-on board packaging is also known as COB. This is a new full-color COB LED product developed using solid-crystal technology and SMD precise dispensing.
Cover the silicon placement point on the substrate with thermally-conductive epoxy resin, usually epoxy resin with silver particles, place the silicon directly on the substrate surface, heat treat the wafer until it is fixed, and then solder the chip directly onto the substrate. It is easier to mass produce than SMD full-color and dot matrix LED modules.
These are the photos of COB module developed independently by Doitvision.
Compare COB with traditional SMD LED Packaing
1) Costs of raw materials and processing
full-color SMD LED: This LED display product has a higher raw material cost and a more complex production and processing process, which results in heftier investment and costs.
full-color COB LED: COB reduces the time by 1/3, eliminates brackets and electroplating and does not require reflow soldering or patches. In terms of die-bonding and wire-bonding processes, COB packaging has similar efficiency to SMD. However, in terms of dispensing, separation and packaging, COB packaging’s efficiency is higher.
COB packaging only represents 10% of the cost of materials, while labor and manufacturing costs are about 15%. The cost is at least 5% more than full-color SMD LED packaging.
2) Optical and Electrical Properties
Full-color COB LED has a good color consistency and a large viewing angle. It also has a uniform light spot with high brightness. SMD and dot matrix color full color LED cannot match these characteristics and benefits.
High brightness and wide viewing angle.
COB uses heat sink technology to guarantee that LEDs have an industry-leading (95%) thermal lumen maintenance.
This is a picture that compares the angle light and appearance of COB and SMD LED module.
COB is more consistent in appearance.
It is evident that the board has hundreds of luminous spots, which are all on the same PCB, or horizontal plane. The luminous points all have the same reference point. This is why the light that is emitted from them will be the same.
Since SMDs will be affixed one by one to the PCB, the result will be a visual effect that is worse than COB packaging.
COB has better light quality.
The picture shows how COB has better light quality.
As shown in the image on the right, SMD packaging is a traditional way to package LEDs. It involves mounting multiple discrete devices onto a PCB to create an application. As can be seen in the image, this approach is prone to problems such as ghosting and glare. COB, on the other hand, is an integrated package that also acts as a surface-light source.
It not only has a large viewing area in image 1, but it also reduces light refraction.
COB offers a larger perspective.
Below image shows that full-color COB LED has a larger viewing angle than full-color SMD LED.
full-color SMD LED viewing angles are approximately 110 degrees. The viewing angle for full-color COB can reach up to 140-170° without affecting the brightness. The vertical angle has a viewing angle that is 140-170°. These features can be very useful in certain applications.
COB angular light and SMD angular light pattern
According to the diagram of luminous effects, this is what you can see:
Dispensing luminous effect diagram /SMD luminous effect diagram
The COB visual effect is superior to that of SMD in terms of viewing angles and luminescence diagrams.
Placement of solid Crystals
RGB chips are arranged in a line. The lens is smooth and curved. The lens exhibits a good refraction of light. The three-color light will be refracted by the lens and the three colors will be reflected. The color mixing will be improved if the color light is more evenly mixed. Also, a uniform light spot will create a better visual effect while SMD does not have the same feature.
Since the top surface of SMD has a flat pattern, which means that the refraction is average. This makes the color matching worse than COB. Here is a comparison between the light distribution curves, so you can see more clearly the advantages of full-color COB.
COB full-color R/G/B light distribution curve /SMD full-color R/G/B light distribution curve
The light distribution curve can tell us that the SMD Packaging curves do not have a consistent pattern. The COB Packaging curve is superior because the red light and blue/green light are a little separated.
Reliability
Low thermal resistance
The system thermal resistance of traditional SMD packaging applications is: chip/glue/solder/ paste/copper/foil-insulation layer-aluminum material, while COB packaging is: chip/glue/aluminum material.
The COB packaging system’s thermal resistence is lower than traditional SMD packaging. This increases the LED’s life.
The COB chip dispensing is also fixed directly on the board. This means that there is a large heat dissipation surface, resulting a better heat dissipation. The chip junction temperature will rise and result in greater light absorption. These are the bottlenecks for the development of SMD technology.
Waterproof, UV-proof and moisture-proof
COB uses a packaging technique to disperse glue onto the board, and performs better when used outdoors in terms of waterproofing and moisture-proofing. SMD, on the other hand, uses a PPA bracket that is waterproof, humidity-proof and UV-proof. When the waterproofing and moisture-proofing problems are not resolved, it can lead to quality issues such as failures, dimming and rapid attenuation.
Conclusion:
Comparing the COB packaging LED screen developed by Doitvision to the mainstream SMD LED Packaging, it has many advantages in terms of optical characteristics, process and cost. It is sure to become a standard product in the near future.
