Chip-on-board (CoB) and Chip Scale Package (CSP) are the two most prominent LED chip configuration techniques. The two have nuanced differences that can be seen in their features. As the end user, you need to understand these differences for better decision-making. In this article, we compare CoB and CSP LEDs to bring out these differences.
What is LED Chip Configuration?
LED manufacturing is a quite complex process. One of the critical steps is usually the transfer of LED chips to the substrate layer.
These tiny semiconductor materials are grown using various means such as epitaxy. When they are ready for use, they need to be transferred to a substrate material. A typical LED luminaire has multiple layers, with one particular layer dedicated to the LEDs.
The process by which the LED chips are transferred and arranged on the substrate material is known as LED chip configuration. Since the inception of LEDs, SMD has been the most common method of LED packaging. This method is still in use today, but it is not as effective as CoB or CSP.
LED chip configuration methods are required to be fast and efficient to meet the growing demand for LED products. They also need to be safe to ensure minimal damage when transferring the tiny and delicate chips.
Standard LED Configuration Techniques
For the sake of standardizing the production of commercial LEDs, two LED configuration techniques are used. These are CoB and CSP.
Each method has its own characteristics. However, the goal remains the same — to configure and arrange LED chips on a conductive substrate. There are many applications of these techniques, with each having specific approaches. This is why you will find that the products are called CoB or CSP LEDs. Let us learn more about these techniques and what they entail.
The two methods are generally used in the manufacture of LED luminaires. In other words, light sources that use LED chips for light production. These lighting units are named after the method used to mount the LEDs.
Chip-on-board (CoB) configuration
As the name suggests, this technique involves the mounting of bare LED chips directly onto the substrate material.
One of the main reasons why these LEDs are mounted directly on the substrate is to increase the density of the chips. For applications such as LED displays, this leads to high pixel density while for lighting applications it leads to a bright light source. LED devices that are made using this technique are known as CoB LEDs.
After the LEDs have been transferred to the substrate, they are covered with a protective layer in a process known as encapsulation. Materials such as silicone epoxy are used in this process.
Chip scale package (CSP) configuration
This is an attempt at reducing the size of LEDs that can fit on a substrate, which effectively means more LED chips on the substrate.
The term chip-scale is used to emphasize the size of the substrate. When you hear chip, you immediately imagine something small. This is the goal of CSP LED configuration.
In this technique, there is no additional layer which is the case for CoB LEDs. This is done intentionally to ensure that the footprint of the LEDs is as minimal as possible. Resultantly, this approach leads to efficient luminaires and displays.
CoB vs CSP LEDs: Mounting Procedures
One of the points of comparison between CoB vs CSP LEDs is the mounting procedures. Let us delve into the different ways in which these LEDs are made.
CoB LED mounting process
The structure of a standard CoB LED includes the following;
- A PCB board
- The LED chip
- Gold wire
- Phosphor material
These four elements serve different purposes.
Starting with the PCB, or printed circuit board, is usually the substrate material to which the LED chip is attached. We will look at the different materials from which a PCB for this specific type of LED can be made.
The LED chip, which is usually a blue LED, is the semiconductor material that is responsible for emitting the light when current flows through. In most cases, the LED chips can be multiple, depending on the application of the luminaire.
On the other hand, the gold wire is used as the electrical connection between the substrate and the LED chips. In other words, it transmits the electrical energy needed to power the LED chip. Finally, the LEDs are covered with phosphor. This material is responsible for turning the color of the LED to white.
The configuration used in CoB LEDs gives the whole chip the capability of generating light at a 180-degree angle.
Depending on the size of the chip and the manufacturer, the process of mounting these chips differs. However, the general method of attaching these LEDs involves the use of thermally conductive adhesives.
After the chips have been attached to the PCB, the phosphor material is used as the encapsulation material. In particular, this step is also done for thermal management. This means that it is used to control the heat dissipation that happens when LED luminaires are working.
CSP LED mounting process
Chip scale package technology was originally used for backlighting LCD displays in early devices such as TVs and smartphones. Now, it is used mainly in the manufacture of LED strips and other LED luminaires.
The mounting of LEDs on substrates for CSP LEDs is quite different. In this technology, the chip is directly mounted on the substrate, but without a gold wire. The chip is directly crystallized on the PCB.
The surface of the LED chip is made of a very thin layer of fluorescent glue. This glue is responsible for light emission and distribution. Also, it acts as a protective barrier.
Using a die bonder, the LED chips are effectively lined up on the PCB board. This process is known as the linear extrusion process.
To understand the major difference between CoB and CSP, consider that an LED has two components;
- The LED chip – This is responsible for emitting light when excited by the electrons.
- LED package – This is responsible for focusing light emitted, providing support on the substrate, and transferring heat to the heat sink.
A CSP LED contains three major components; the LED chip, yellow phosphor, and connection pads. Stripping away the frame and the reflector results in much reduction in the size of an individual LED. As such, there is more space to mount as many chips as possible.
CoB vs CSP LED: LED Chip Packaging Substrates
The type of substrate used in each configuration determines the features of the end product. In manufacturing, a substrate just means the surface material. These materials are required to be able to handle electrical conductivity, thermal management, and overall functionality of the luminaire.
CoB LED substrates
The material making up the CoB LED substrate needs to have certain properties. Some of the common materials used for making these substrates include;
- Sapphire. This is one of the rare gemstones. It is made of aluminum oxide, which makes it a good conductor of electricity. Sapphire is also used as a wafer in the epitaxial processes of growing micro LEDs.
- Silicon carbide. Carbide is a hybrid material made up of carbon and a metal oxide. It is metallic in nature. This material is known for its resistance to rust, heat, and corrosion. These are qualities that make it a suitable substrate.
Other substrates that can be used in CoB LEDs include ceramic and CooLam. All these materials have demonstrated the ability to withstand the electromagnetic properties of LEDs.
These LED luminaires are mounted directly to the substrate which can be made of different materials. Except for specific applications, the material used is similar to that used in CoB LEDs.
The substrate needs to be able to withstand the structural difference between CoB and CSP LEDs. In other words, it has to be able to provide mechanical support for the LEDs. The common material used in CSP LEDs is usually ceramic and other types of glass.
Factors Influencing the Choice of Substrate
The type of substrate used depends on a number of factors. Most of these substrates are desired because they have;
- High-temperature resistance
- High strength
- Good electrical insulation
- Low dielectric loss
These properties of substrates enable the manufacturer to be in control of;
- Thermal management. This is the removal of heat from the vicinity of an LED chip for it to perform at maximum capacity. Luckily, some LEDs are manufactured to have the lowest heat dissipation possible. Still, the small heat needs to be managed to avoid overheating of the luminaire.
- Design. The design of the LED chip is also controlled by the choice of the substrate. For instance, when designed for LED strip lights, the choice of substrate needs to have a lot of flexibility.
- Application. The use of the LED chip is a factor that influences the choice of the substrate. Some applications have specific requirements where the manufacturer has specified the use of a certain material for its properties.
CoB vs CSP LED: Characteristics
The characteristics of these types of LED chips can help us understand more about them. Think of these characteristics as the defining features of the luminaire. We are going to discuss them separately since they are unique to each type.
Characteristics of CoB LEDs
The common features of chip-on-board LEDs include;
Larger Form Factor
The technology used in the packaging of CoB LEDs makes them quite small. However, they are not smaller than CSP LEDs. However, they are smaller than SMD or surface mount device LEDs. SMDs are much larger due to the packaging technology used to mount the LED chips on the substrate.
Poor Heat Management
As we saw, heat management is an important process that ensures LED chips are functioning optimally. One of the major reasons for this is the nature of the mounting which leaves the LED chips closely tangled together.
Over time, the continuous heat dissipation from the chips builds up and it needs to be dissipated through the heat sink. Actually, over 70% of the electric current supplied to LEDs turns into heat while 30% turns to light. Therefore, power management is quite essential.
Used in General Lighting Applications
CoB LED chips are used mostly in luminaires such as headlights. Some of the common applications of this type of LED chip include;
- Lighting: COB LEDs are used in indoor and outdoor residential lighting. They can also be used in retail stores, restaurants, offices, and workspaces.
- Solid-state lighting: COB LEDs can replace metal-halide lamps in high-bay lighting, street lights, downlights, and high-output track lights.
- Outdoor lighting: COB LEDs can be used in streetlights, floodlights, and security lights.
- Museum displays: COB LEDs can create a spotlight effect on artifacts.
- Smartphone camera flash: COB LED display technology can improve photo results.
When referring to the cost-effectiveness of CoB LEDs, we are considering the initial fees, running costs, and maintenance costs. Generally, these costs are usually low.
For instance, a CoB LED consumes less energy than an incandescent light but produces twice as much light. This means it’s more efficient in power consumption, without compromising its luminance.
Depending on the luminaire being manufactured, the design of the LED chip will vary. For applications such as light strips, they will be manufactured in the form factor that is applicable to this form of luminaire. This is important since it ensures that there is flexibility in the field.
Characteristics of CSP LEDs
Chip scale package LEDs have different characteristics from those of CoB LEDs. CSPs are focused on the miniaturization of LED chips. This is done with the intention of making the smallest most capable luminaire for specific applications.
Some of the characteristics of this technology include;
Good Thermal Performance
One of the major differences between CoB and CSP LEDs is the thermal management qualities of the two chips. CSPs are made to have a better heat dissipation approach.
The thermal performance of these luminaires is perfect because of the stripped disturbances. To clarify, the structure of these chips ensures that 70% of the elements found in the COB LED are absent in its form factor. Therefore, it gives it a more robust form factor, especially the path of transferring heat to the heat sink.
High Lumen Output
The luminance of an LED light is measured in lumens (lm). One of the factors that affect the luminance intensity of these lights is the type of LED used.
Blue light is known to have a relatively high wavelength, at about 450 nanometers. This light is usually converted to a white light by the phosphor material. The conversion also works as an amplifier where the light becomes more intense when passed through the phosphor material. CoB LEDs are known to produce light of up to 1500 lumens.
Used in Compact Devices
The application of CSP LEDs is wide. One of the common features of the devices that use this type of LED is that they are compact. By this, we mean that they are portable and efficient in space confinement. The main reason for this is that a small-sized LED can light up to a high degree, thereby reducing the need for large chips except in certain use cases.
Flexibility in Substrate Material
Since the substrate does not influence most of the functionality of this type of LED, the choice does not have a huge impact. Therefore, the manufacturer can use any material, as long as it has the desired properties. This is in contrast to CoB LEDs which require quite specific substrates.
CoB vs CSP LED: Similarities and Differences
What do CSP and CoB LEDs have in common? Also, what is unique to them? Let us answer these questions by studying the similarities and differences of these luminaires.
Similarities Between CoB vs CSP LED
Given that both of these luminaires share an almost similar form factor, you would expect them to share a number of similarities. These similarities can be used to compare them and put them in the same category. Some of these similarities include;
Direct LED Chip Mounting
In the production process, we saw that the LED dies are attached directly to the substrate. This ensures that there are reduced barriers between the photons (light electrons) and the semiconductor material. This approach leads to more efficient design and light efficacy.
Compact Form Factor
The small size of the LED makes its form factor compact enough for applications where this is essential. In today’s world where devices are striving to become smaller, compactness is an integral feature at the center of all this.
While CSP LEDs have better thermal management than CoB LEDs, they both can be said to contain heat produced by LEDs and dissipate it appropriately. This is important since it ensures that the heating component of the device is contained.
The uses of these types of LED chips are not limited to something particular. As long as the application supports these luminaires, it can use either CSP or CoB LEDs. The only difference is that the choice of the specific type might vary depending on the requirements. In most general cases, CoB is sufficient since it has most of what CSP LEDs have.
Differences Between CoB vs CSP LED
Some of the aspects of these two luminaires vary greatly from each other. These unique characteristics are what make the two different from each other. Some of the common ones include;
In this context, the term configuration refers to the form factor and set-up of the LED chip. While the CSP has a minimalistic form factor, the CoB has more of a clunky configuration. This is particularly due to the borders that cover each LED chip.
When comparing them at face level, we see that they appear different. This is because the glue used in CSP does not have phosphor which makes it appear milk white. CoB LED appears yellow due to the phosphor material that is usually yellow in color.
CSP LEDs are known to have better illumination uniformity when compared to CoB LEDs. This uniformity is required to provide higher luminance. In particular, CSPs have a lighting angle of about 180 degrees. This is what contributes to the high level of lumens that it gives off.
On the other hand, the uniformity of CoB LEDs is sufficient. They are known to have a better beam angle than SMDs but are slightly inferior when compared to CSPs. This explains why they have a lower lumen output than CSPs.
As we saw in the characteristics of both, CSPs have a better way of handling unwanted heat than CoB LEDs. This ensures that CSPs have a better heat dissipation system than CoB LEDs.
Luckily, there are a few ways that COB LEDs can be made to have better thermal management. Some of the tried and tested techniques include;
- Using a high-volume heat sink
- Using thermally conductive material for the cooling block
- Include ventilation in the final product
The cost of LED chips is based on factors such as design and form factor. These two factors are considered during the manufacture of CSP and CoB LEDs. Therefore, it makes sense for them to have different costs. In this case, CSP LEDs are more expensive than CoBs.
The design of these LEDs depends on the intended application. In most cases, they have a specific appearance. Design is all about the physical attributes of the product.
CSP LEDs are known to have design flexibility since they are stripped of most of the components found in CoB LEDs. This allows CSP LEDs to have more efficiency, which in turn means more use cases as opposed to CoB LEDs.
LED lighting solutions are constantly evolving to become more efficient. This is evidenced by the characteristics of CoB and CSP LEDs. Consequently, these luminaires have been adopted for the production of highly efficient lighting solutions. We hope the article helped you compare CoB and CSP LEDs side by side.