PCBs or Printed Circuit Boards for LEDs or light-emitting diodes are different from other circuit board designs, as the boards must help dissipate the excess heat generated by the LEDs when they are in operation. Although LED PCBs are the foundation of LED lighting systems, one of the core problems in LED PCB design is their thermal limitation. According to PCB Trace Technologies Inc., when measuring the quality of an LED circuit board, it is important to take into account the placement of each LED, the thermal capacities of the board, any capacitive coupling effects, and the overall performance.
Most modern commercial and residential lighting systems favor long-lasting, effective, and affordable lighting sources. Almost all outdoor, automotive, and housing lighting systems prefer LEDs as their lighting source due to their efficiency and output lumens. The typical assembly of an LED lighting system consists of LEDs mounted on a printed circuit board that also has a power circuit incorporated on it.
However, the design of LED PCBs is different from regular circuit boards. As LEDs in operation generate excess heat, suitable thermal management is necessary for these types of boards. Designers of LED PCBs make use of aluminum cladding, heat sinks, and other structural materials to remove thermal energy from the boards. It is necessary to explore the challenges, considerations, and types of design for LED PCBs.
Why Use LEDs?
As stated earlier, LED PCBs form the foundation of LED lighting systems. LEDs, as sources of light, offer several advantages:
Compact Design: The compact design of LEDs as light sources is a huge benefit in almost all applications, including traffic lights, floodlights, automobiles, smartphones, televisions, and computers.
Low Power Consumption: Because of their very high efficiency, LED lights can reduce power consumption by nearly 80% for the same luminance as compared to other types of sources. Most residential lighting has shifted from incandescent, fluorescent, and CFL, to LEDs to conserve power consumption.
Long Lifespan: Compared to traditional lighting sources, LEDs have a 25 times longer lifespan.
Non-Hazardous: Traditional fluorescent bulbs have mercury in them, a hazardous material. This presents a high environmental impact and requires special disposal procedures. As LEDs have no mercury in them, disposal is easier, without causing as much environmental pollution as traditional lights do.
Higher Efficiency: Unlike traditional lights like incandescent bulbs, LEDs generate much less heat. LEDs operate at a much higher efficiency, converting most of the energy they consume into producing light rather than heat.
Incandescent bulbs can convert only 10% of the energy they consume into useful light. The balance 90% they release as heat. On the other hand, heat dissipation in the case of LEDs is less than about 20% of their total energy consumption. Although their efficiency is high, the small amount of heat generation by LEDs, if allowed to accumulate, can pose a serious problem to LED circuits. To avoid performance degradation, it is necessary to dissipate the heat from LEDs when they are operating.
Design Challenges of LED PCBs
Among the many design considerations for LED PCBs, designers must give top priority to:
Cost and Quality: When designing LED PCBs, designers must consider cost and quality as major concerns as both are interdependent. For instance, the quality of an LED circuit board is related to the placement of components on it, its thermal capabilities, the capacitive coupling effects of the board, and its overall performance.
Thermal Efficiency: The quality of the LED PCB is highly dependent on its thermal efficiency. This is the rate at which the PCB can remove the heat from the LEDs. The greater the capability of heat removal of the PCB, the higher its quality.
Number of Layers: LED PCBs can be single-sided, double-sided, multi-layered, and rigid as well as flexible. The number of layers depends on the application, and depending on the requirement, the number of layers can vary. Irrespective of the number of layers, rigid LED PCBs typically have a metal cladding or a layer of aluminum on one side, and this acts as a heat sink. Because of the presence of the aluminum layer, these PCBs are also known as MCPCBs or metal-clad PCBs.
Lighting Color: The color of the light produced by the LED depends on its operating temperature. Unless the temperature of the LED is under careful control, the LED may not be able to maintain its specific color.
Life Span: A higher operating temperature is detrimental to the life span of the LED. The life span of an LED is inversely proportional to its operating temperature. To ensure the LED light has a long life span, the designer must carefully control the LED temperature, while aiming for a bright, and intense light output.
Design Considerations of LED PCBs
When designing LED PCBs, designers must consider certain important factors that will allow fabricators to create a board that will work as intended for LED lighting applications.
Materials
For LED PCBs, the designer must use materials that can remove and dissipate the extra heat generated by the LEDs. Furthermore, it must act as an electrical insulator for the copper conductors and the metal cladding.
A single-layer LED PCB typically uses an aluminum backing, with a dielectric layer separating the aluminum from the copper conductors on the dielectric layer. A solder mask covers the exposed copper conductors except for the solderable pads. Structures of this type are also known as IMS or Insulated Metal Substrate. The aluminum backing works to absorb the extra heat from the PCB components and thereby assist in thermal management.
Thermal Management
One of the most crucial aspects of LED PCB design is thermal management. Increasing the temperature of components on the PCB can shorten the life of the LEDs and affect the color purity of the light emitted by them. The addition of the aluminum backing or core and the use of heat sinks help in extracting as much of the heat as possible from the components.
The placement of LEDs and the arrangement of other components on the LED PCB also impact the distribution and removal of heat to the ambient. Designers must consider the thermal management aspect of the design as thoroughly as possible.
Routing
Proper track routing on the LED PCB is necessary to avoid common pitfalls like shorts, opens, and crosstalk between circuits creating manufacturing problems. With proper trace routing, designers can ensure that network connections are in their proper places without causing interference to other network connections.
As LEDs are current-sensitive components, proper width of traces is necessary for supplying them with the necessary current without overheating. Designers must consider proper spacing for traces, pads, and mounting holes in the design so that manufacturing will not face any issues.
Surface Finish
The surface finish on the board ensures protection for the circuit layer and the pads on which the components will be soldered. Various types of PCB surface finishes are available, each with advantages and disadvantages. The designer must decide on the right surface finish based on the final application and the budget for the project.
Types of LED PCBs
As stated above, LED PCBs can be flexible or rigid.
Flexible LED Strips
LED strip PCBs are special circuit boards designed as long flexible strips mounted with a string of multiple LEDs. The PCB serves as the base or substrate onto which the manufacturer solders the LEDs, with copper tracks providing the electrical connections.
The copper tracks on the LED strip PCB connects the LEDs in a specific configuration, allowing them to power up individually. While the PCB provides structural stability and protection for the LEDs, the substrate aids in thermal management for dissipating the heat generated by the LEDs.
The flexible substrate is typically polyimide, a material that is flexible enough to allow the LED strip to bend and conform to different shapes and surfaces. Apart from the LEDs themselves, the LED strip PCB may also have additional components such as resistors, capacitors, and even integrated circuits mounted on it to regulate the voltage and current to the LEDs. They may enable various lighting effects, such as control of brightness and color.
Rigid LED PCBs
Unlike flexible LED strips, rigid LED PCBs cannot bend, as they are made of a stiff material like fiberglass. Moreover, they also have a metal backing, typically of aluminum, to aid in thermal dissipation. Rigid LED PCBs can be single-sided, double-sided, or multi-layered.
The aluminum-backed PCB is the most common among metal-core LED PCBs. This type of PCB has an aluminum alloy base, with a thermal insulation layer on it. This layer is very important for the proper functioning of the PCB. It must have dielectric properties with high thermal conductivity, but a good electrical insulator. It must also protect the board from mechanical or thermal damage. It must be capable of absorbing heat from the components on the circuit layer on its top surface and transferring it to the aluminum layer, which ultimately disperses the heat to the ambient.
Conclusion
For LED PCB solutions, it is essential to understand the factors influencing the success of the board during its operation. As these factors go into the design of the circuit board, eminent PCB manufacturers like PCB Trace Technologies Inc. suggest looking for solutions that ensure proper thermal management to allow the removal of excess heat for effective and long-life operation.
