Since the introduction of LED screen, the process continues to progress, the pixel density is getting higher and higher, which can not be separated from its progress in packaging technology.
Flip chip COB technology as the LED display industry is more advanced packaging technology, what is its process flow? What are the advantages? We together through this article to understand.
What is flip chip COB technology?
In the past, the development of more mature LED packaging technology is usually the LED chip front face up mounted on the substrate, and then between the LED chip and the bracket with metal lead welding, complete the electrical connection.
The flip chip COB technology is an improvement on the traditional LED packaging technology, directly mounting the LED chip upside down on the substrate, so that the LED chip contacts directly contact the substrate.
This way of mounting the LED chip saves the lead connection between the LED chip electrode and the bracket, reduces power consumption and heat loss, and the structure is much simpler, allowing for a more compact arrangement of the installation, i.e., smaller pixel pitch and greater pixel density.
Process Flow of flip chip COB technology
Quality Inspection and Cleaning of Wafers
Before we proceed with flip chip COB technology, we have to perform a quality inspection of wafers to ensure that the wafers are of good quality and the dimensions are in accordance with the requirements.
After screening out the appropriate wafers, the wafers are cleaned to ensure that the wafer surface is free of dirt and oil stains.
Bottom Metal Layer Deposition
The bottom metal layer is deposited on the wafer by magnetron sputtering, and it is more common to use metals such as titanium and copper as the seed layer.
Photoresist Coating
The insulating material polyimide is coated on the surface of the wafer where the deposition of the metal layer has been completed, and the wafer is sequentially exposed and developed to create the opening positions of the bumps.
Second Photolithography
Then for the next step, in order to open the area to be plated, we need to photolithograph the photoresist to create the opening.
Electroplating
A tin-silver alloy is electroplated on the open area to form the bump.
Removing the photoresist
Once the plating is complete, the photoresist is removed, leaving the metal seed layer that was deposited at the very beginning exposed.
UBM Etch
Only the metal seed layer underneath the bump formed by electroplating is retained and the rest of the metal layer is removed.
Reflow
The tin-silver alloy layers are melted and allowed to reflow through the reflow process, resulting in a smooth solder ball shape.
Chip Mounting
Align the LED chip bumps to the substrate and bond the LED chip to the substrate through the reflow process or hot press bonding process.
Bottom Filling
After the bonding of the chip and the substrate is completed, drop paint fills the remaining gap between the LED chip and the substrate to increase the connection strength of the LED chip and the substrate.
Curing
After completing the above steps, the flip chip COB technology package has been basically completed, but still need to carry out a final curing.
The encapsulated LED chip and substrate components will be placed in the curing oven for curing of the filler primer, to strengthen the reliability of the connection of all components.
Quality check
After the completion of all flip chip COB technology packaging steps, we also need to encapsulate the components after the quality check to ensure that no defective products into the next step of production.
Advantages of flip chip COB technology
Reduced heat loss
As long as the current passes through the metal, no matter how good or bad the metal is, there will be resistance heat caused by the resistance during the energization process, resulting in a part of the electrical energy converted into heat energy loss.
LED modules packaged with flip chip COB technology have fewer metal leads to weld and less heat energy to convert.
Higher efficiency
flip chip COB design of the LED component structure is simpler, the current transfer rate is faster, and reduces the heat loss in the process, the loss of electrical energy is less, that is, the conversion rate of electrical energy is higher, the efficiency of the LED is higher.
According to statistics, LED modules with flip chip COB technology have about 45% less power loss than ordinary LED modules.
Higher Reliability
As flip chip COB technology simplifies the structure of LED modules, reduces the number of many electronic components, and there is no lead soldering that may lead to failure rates, the overall stability and reliability of LED modules produced using flip chip COB technology is stronger, more robust and durable.
Better light quality
Higher utilization of electrical energy, stronger light output, flip chip COB technology can achieve higher brightness than traditional packaging technology, and due to the more reliable characteristics of the LED module manufactured by flip chip COB technology, the LED display of this packaging technology has excellent color uniformity and color consistency.
Compact design
By reducing the number of connectors and metal leads, flip chip COB technology produces a simpler LED module structure, which means that the chips can be mounted more compactly, realizing smaller pixel pitch LED displays.
Evolutionary history of flip chip COB technology
At the beginning of the 21st century, DIP technology began to be used in the market, and at that time, it was mostly single-color or dual color LED displays used for displaying some text information, which were used in stations and store entrances, and the pixel pitches of the LED displays made by DIP technology were large, and the resolution of the screen as a video playback monitor was low, and the quality of the picture was not clear enough, which was suitable for medium- to long-distance viewing only.
Followed by the arrival of SMD technology, SMD technology development a few years later, with low cost, high performance, high picture quality characteristics of the rapid occupation of the market, LED display also from the earliest low-resolution gradually evolved to high-definition images and dynamic video display, and SMD technology is still progressing, pixel pitch is getting smaller and smaller, the LED screen screen picture is more and more clear and delicate.
In 2016, COB technology began to come out, it can realize a smaller pixel pitch than SMD technology, and the process cost is within the market affordable range, so it is also quickly accepted by the market as soon as it is launched, and put into production on a large scale.
In 2017, flip chip COB technology appeared, which improves the performance and quality of LEDs on the basis of COB technology, but due to the cost and process problems did not put into production in large quantities, until the past two years only began to grow a lot of market share.
Difference between COB technology and flip chip COB technology
Installation
COB technology is to install the LED chip face up on the substrate, after installing the chip, you need to use metal leads to connect the LED chip and the substrate.
Flip chip COB technology is to install the LED chip upside down on the substrate, after the chip is installed, there is no need to connect the LED chip to the substrate with metal leads.
Thermal management
COB technology has more wire connection structure, more thermal energy conversion, and due to structural characteristics, COB technology LED chip is farther away from the heat sink, slower heat dissipation.
Flip chip COB technology reduces the lead connection, heat energy conversion is less, the structure of the chip layer closer to the substrate, heat dissipation faster.
Manufacturing complexity
COB technology has been used in the LED market for a long time, it has a mature process, simple manufacturing process, low cost, and currently occupies a large share of the market.
Flip chip COB technology manufacturing process is more complex, although from the overall performance of the LED module flip chip COB technology is better than the finished product of COB technology, but chip COB technology manufacturing cost is higher.
Pixel density
COB technology is able to realize the small pitch LED module of about 1mm, but the tiny pitch LED module of less than 0.4mm can not be done by COB technology.
The LED module chip and substrate connection structure made by flip chip COB technology is simpler, and the chip arrangement can be done more closely, on the basis of COB technology, flip chip COB technology can realize smaller pixel pitch and higher pixel density.
Conclusion
On the basis of traditional COB technology, flip chip COB technology allows LED packaging technology to have a higher level of technological breakthroughs. flip chip COB technology allows LED modules to reduce power consumption, increase stability and higher pixel density.
Although its current cost is higher than COB technology, with the growth of technology and process maturity, the production cost of flip chip COB technology will gradually converge to the basic level.
There is no doubt about the future market demand for flip chip COB technology.
