Light emitting diodes (LEDs) are notorious for their high efficiency and long lifetimes. A diode is a semiconductor component which emits light in response to an electrical current being passed through it. The LED chip, when triggered by electrons, is responsible for the emission of light. It consists of semi-conductor layers that enable electrons and protons to move easily through. When this occurs the chip emits a blue light which is then converted by a layer of phosphor into various other wavelengths to produce the desired colour output.
LED technologies continue to develop, allowing for smaller packages to be produced. A LED package refers to the protective layer, typically plastic, that encases the LED chip and phosphor. This layer is responsible for focusing the light emitted, as well as helping with the transfer of heat from the LED chip to a heatsink. The most common LED packages on the market are chip-on-board (COB) or chip-scale-package (CSP). Each variation has its own benefits, but both are successful configurations of LED chips on a substrate.
Chip-scale-package (CSP) LEDs:
A chip scale LED package typically has an equal size to the LED chip, or no larger than 20% of that. They are being increasingly implemented in various lighting designs. Therefore, versatility is further increased, as a CSP LED does not require soldered wire connections, as its component features are integrated. Thus, removing the need to directly secure the LED chip to the PCB by sub-mounting. These chip structures guarantee that 70% of the elements within a COB LED are not present in its form factor. This means that thermal resistance between the LED chip and PCB is reduced, as there is improved heat dissipation from the LED chip to the heatsink, giving CPS LEDs a more robust form factor.
But a main drawback with CPS technologies is their cost. CPS LEDs are typically more expensive than COB LEDs. Yet, other advantages of CSP technology include:
- High lumen output. When compared to COB LEDS, CSP LEDs typically have higher illumination uniformity. CSP LEDs tend to have a visibility angle of around 180degrees. This helps add to the high lumen levels the LED emits.
- Wide range of applications. CSP LEDs can be easily implemented in compact devices due to their compact size.
- Flexibility in substrate material. Because the type of substrate material is not essential to the LED functionality, manufacturers can use various materials assuming it still has the desired properties. This allows for more cost-effective or readily available substrates to be chosen, there is flexibility in this choice. Whereas a COB LED will require particular substrate materials.
Chip-on-board Package (COB) LEDs:
A chip-on-board package consists of multiple LED chips mounted on a substrate material and coated by a uniform phosphor coating. This layer also works as a protective casing. This process is known as encapsulation. A common material used to do this is silicone epoxy.
A COB LED differs most clearly from CPS LEDs in the way the LED chip is mounted. A COB LED will be directly mounted onto the surface of the PCB, or a thermally efficient substrate material. Whereas CPS LEDs do not require soldered wire connections. By directly mounting COB LEDs to the substrate surface, the density of the chips is increased, leading to a brighter light source. For example, in applications like LED displays, this enables a high pixel density.
A key drawback of COB LEDs in comparison to CPS LEDs is their larger package size. But it is also worth noting that COBs like many other LEDs require adequate heat management. More than 70% of electric current delivered to LEDs converts into heat whilst only about 30% is converted to light emission. The placement of the LED chips within a COB LED package is very compact, and so heat management is essential for proper and effective LED operation.
Yet they have many other advantages, including:
- Large form factor. Although COB LEDs tend to be larger than CPS LEDs, they are still typically smaller than standard surface mount device LEDs (SMDs). Because of the technology involved in SMD LED mounting to a substrate, SMD LEDs tend to be a larger package.
- Cost-effective. The energy consumed by a COB LED is about half that of an incandescent bulb. Furthermore, a COBs generate about twice as much light output. They have a higher efficiency in power consumption, that does not compromise luminance and quality of light.