A flexible LED PCB is a printed circuit board made of flexible PCB material and used in LED devices. Flexible LED circuit board is used in a variety of applications due to its compact size and low-power application. Due to its versatility, LEDs are used in several places ranging from small interior lights to automotive lighting. Flexible PCB for LED strip is manufactured by arranging or installing the LED circuits in a series or parallel fashion, to form all kinds of patterns and shapes.
Classification of Flexible LED PCBs
LED PCBs can be classified as single-layer and double-layer.
Single-layer Flexible LED PCB:
- Generally, a single flexible LED PCB consists of a substrate made up of dielectric material. A thin conductive layer for electrical conductivity is made up of copper.
- This is followed by a protective layer called overlays. In addition, to connect several Flexible PCBs (FPCBs), an adhesive layer made up of polyethylene or epoxy resin can be used.
Two-layer Flexible LED PCB:
- When two-layer FPCBs are considered, we can find that there is more than one conductive layer, which is also used for power circuits called the power circuit layer.
- There is more than one protective layer made up of PVC film. An adhesive layer consisting of double tape is also present.
Flexible Material Used in LED PCBs
Characteristics: The most important aspect of led flex PCB is the heat dissipation available through metal sinks and heat sinks.
Commonly Used Materials: While metal core PCB was predominantly the choice, aluminum was preferred later due to its efficiency in heat dissipation. Kaplon was used earlier for dielectrics, which was replaced by ceramic polyester and its byproducts due to effective heat dissipation and thermal considerations.
Copper Weight of Flex PCBs
- The weight of copper chosen for the PCB became important as the quality and standard of the copper used in the manufacturing of Flex PCBs plays a vital role in determining the quality of the board.
- The thickness preferred is 2 ounces or more. When the thickness is higher, the heat dissipation is better and the conductivity is found to be improved in the PCBs
Advantages of LED Printed Circuit Boards
- Durable: The LED PCBs are highly durable and can withstand temperature variations. With suitable management of thermal resistance, flex PCB LEDs are robust.
- Dimmable: The dimmable nature of LED is important to be used in a variety of residential applications and smart lighting systems.
- Spotlighting: LEDs are advantageous to use in spotlighting and other applications where the illumination is required in a specific direction.
- Hazardous-free: While normal incandescent bulbs use mercury and other hazardous substances, flex PCB LEDs are free from such chemicals.
Application of Flexible LED Circuit Boards
Ranging from home appliances to industrial LEDs, the applications of LEDs are enormous.
- Street Lighting: LEDs are used in smart street lighting and residential lighting systems. It is preferred for its aesthetic sense and is widely used in interior design.
- Electronic Systems: The electronic systems use LEDs for light and power indications.
- Automobiles and Vehicles: The flexible LED PCBs are used prominently in automobiles and vehicles for all types of lighting sources.
- Consumer Electronics: They are used where power requirements are to be reduced and power saving is required, for example in industries and for all consumer electronics as a backlight option.
- Display Systems: They are also used for large display systems and gaming units in peripherals.
- Harsh Environments: In places where harsh environments are observed, flexible LED PCBs are preferred due to their durability.
- Greenhouse: For plants in the greenhouse, wherein they grow in suitably designed environments, LEDs are the preferred choice.
Design Considerations of Flexible PCBs
1. Electrical Characteristics
- To begin with, it is important to note the electrical characteristics of a flex PCB LED, usually the conductivity, forward voltage drop, electrical resistance, and other factors as LEDs form the base for the flexible PCB LED strip.
2. Excessive Heat Issues
- Thermal stability becomes the main consideration in FPCBs, as LEDs face issues due to high-temperature effects.
- The overall heat along the LED strip is very high, affecting the durability. To avoid this, heat sinks and thermal vias are used.
- It can also be solved by having other copper layers which can assist in heat dissipation.
3. Cost and Quality
- Component placement is an important design consideration as it can impact capacitance between the components.
- This can lead to the capacitive coupling effect, affecting the quality of the circuits.
4. Heating Effect on the Color of LED
- The temperature rise in the LED circuit has a huge impact on the color of the LED.
- The high current and voltage spikes disrupt the stability of the LED. This affects the PI layer present in the PCB, and because of heating effects and reflection, we can observe the changes in the color of the LED
5. Need for Current and Voltage Regulators
- The over-current and voltage issues can be addressed by current-limiting resistors and voltage regulators.
- The current and voltage spike can also cause overheating issues in the circuits.
6. Environmental Conditions
- Environmental conditions like dust and corrosion are important considerations while designing Flexible LED PCBs.
- This depends on the application where the LEDs are to be installed and depending on the moisture present, the longevity is affected.
7. Designing Efficient Power Systems for LED
- The use of the regulators to stabilize the power to the LED is necessary to design a compatible power system, thereby reducing the heating issues in the LEB PCBs.
- The use of driver ICs can act as a protecting device to turn off the system when it is overheated.
8. Simulation and Analysers
- With the never-ending advancements in technology, the use of a power distribution analyzer and other thermal analyzers becomes important to predict and fan out the necessary parts of the device to ensure thermal stability.
9. Design and Implementation of Improvised Technology: COB
- Typically the LEDs are mounted using traditional technology- SMT, where the LED strips are soldered onto the surface.
- The new technology is the chip on board technology, alternatively known as COB, where the LED strips are mounted onto the single flex PCB and wounded together on the chip.
- The advantage is the high-density package which is an integrated technology, leading to miniaturization in size.
- The LED strips are segregated into pieces of wafers made up of LED crystals attached to the PCB using the integrated COB technology.
- This indeed can help in reducing the thermal resistance and improving heat dissipation
