Affordable and durable lighting sources are the preferred option for modern commercial and residential lighting systems. LED lighting is the top choice for applications such as automotive, housing, & outdoor lighting due to its high output lumens & efficiency. To enhance their functionality, PCBs have LEDs mounted with an integrated power circuit. LED circuit designs differ from other circuit board designs because they tend to generate excess heat. To counteract this issue, LED printed circuit board designs utilize aluminum printed circuit board substances, heat sinks & structural substances to dissipate thermal power from the board. This article will explore the challenges, types, and considerations of LED printed circuit board design.
Why Use LED PCB Circuit Design?
LED illumination systems rely on LED PCBs as their foundation, which offer numerous advantages as light sources, including:
- Compact size: The small size of Light-Emitting Diodes makes them well-suited for various applications, including but not limited to computers, automobiles, smartphones, floodlights & traffic lights.
- Lower power consumption: LED lighting is the preferred choice for residential lighting due to its energy-saving properties. By using LED lights, power consumption can be reduced by approximately 80%
- Longer lifespan: Compared to traditional light sources, LEDs have a lifespan that is 25 times longer.
- Mercury-free: A traditional bulb has a significant environmental impact because they contain mercury, which necessitates special disposal ways. In contrast, LEDs are mercury-free and can be easily positioned, resulting in less pollution than traditional lights.
- Efficiency: LED lights generate less heat than incandescent lights. It is because the energy used by LED (Light-emitting Diode) lights is primarily used for lighting instead of heating.
Around 90 percent of the energy consumed by traditional bulbs is emitted as heat, whereas for LEDs, heat distortion accounts for approximately 20% of their total energy usage. Nevertheless, generating even 20 percent heat can pose a significant risk to LED circuits, and several challenges must be tackled in the design of LED PCBs.
Challenges for LED PCB Circuit Design
The design of LED PCBs must tackle the following problems that LED(Light emitting diode) lighting systems encounter.
- Temperature: Insufficient thermal management in LED PCBs can cause a rise in board temperature due to heat generation, which can significantly affect the longevity and color of the LEDs.
- Lifespan: Although LEDs are renowned for their extended lifespan, elevated temperatures in LED(Light emitting diode) circuits can diminish their longevity.
- Color of LED light: LEDs are utilized in various applications to produce specific colors, but when the temperature rises, it can result in color discrepancies in the LED illumination.
Effective thermal management is a crucial issue that must be tackled in LED printed circuit board design. To guarantee optimal efficiency, prolonged lifespan, and vivid LED illumination, precise temperature regulation is essential, particularly in critical LED applications.
Considerations for LED PCB Circuit Design
Several LED printed circuit board design factors require top priority consideration.
- Cost vs. quality: The design of LED printed circuit board boards involves considerations of both cost & quality, which are closely related. Factors such as the placement of LED components, thermal management capabilities, coupling effects & overall performance are crucial in evaluating the LED PCB quality.
- A number of layers: An LED printed circuit board can have a double-sided, single-sided/ multilayered design, with no. of layers determined by the specific application requirements.
Advantages of LED PCB Circuit Design
The popularity of LED PCBs among engineers & designers tasked with product upgrades or revisions can be attributed to several reasons.
- Generates light with minimal heat production
- Enables easy sourcing and assembly of products due to the layout of LED( Light emitting diode) membrane switches
- Exhibits strong resistance to moisture & dust impacts.
- The product boasts low & efficient power consumption, resulting in energy savings.
- It comes in a range of sizes, intensities, and colors, providing ample options for selection.
- The product can be seamlessly integrated into complex assemblies of interface with ease.
- Being lightweight, it can be effortlessly transported from one place to another.
- The product has high stability and a low profile.
- LED printed circuit board design provides a cost-effective option for backlighting icons and symbols.
- LED printed circuit board design has an extended lifespan, resulting in savings on maintenance & replacement costs.
- Like other PCBs, a backlit LED printed circuit board design is a more affordable choice.
- LED printed circuit board design is compatible with copper and silver flex membranes.
- The LED printed circuit board design provides ample flexibility, even in more complex assemblies.
Where to use LED PCB Circuit Design?
· LED Strip PCB Design
A PCB with SMD Light Emitting Diodes mounted on its surface, which can be either flexible/rigid, is commonly known as an LED strip. The layout of an LED strip PCB must take into account various critical factors such as water resistance, as well as current and voltage considerations. The color variation and if the Light Emitting Diode is addressable are also significant factors that impact the design.
Several options are available for LED strip printed circuit board design, including uni-color non-configurable, flexible white non-configurable, multicolor non-configurable, & RGB addressable. These options have various uses in appliances like decorative lighting, fluorescent lighting, and even in the production process for UV inspections. Therefore, proper LED strip PCB design is crucial for achieving the desired outcome in these applications.
· SMD LED PCB Design
SMT LEDs apply in various electric equipment, such as notebooks, network systems & cellular phones. Similar to other LED printed circuit board designs, these PCBs offer exceptional heat dissipation capabilities.
· LED Street Light PCB
LED Street light PCBs are specifically engineered for street lighting purposes, incorporating VMS technology that proves beneficial for traffic guidance systems. Besides, LED lighting ensures consistent luminance, contributing to enhanced visibility during the night and facilitating traffic management. Consequently, these printed circuit boards are made to ensure optimal street illumination and seamless communication (signalization).
· PCB Design for LED Bulb
LED PCBs are widely utilized for producing LED bulbs, making them one of the most popular applications of this technology. This technology is the driving force behind most bulbs available today.
Moreover, the design of LED PCBs for bulbs is also implemented in various other LED( Light Emitting Diode) light products, such as LED( Light Emitting Diode) panel lights & LED( Light Emitting Diode) floor lights. It is instrumental in achieving LED( Light Emitting Diode) ceiling lights as well.
· LED Matrix PCB Design
It is a dot matrix display that can showcase a vast amount of information, albeit with low resolution. This type of display consists of a 2-dimensional array of diodes, with cathodes arranged in rows and anodes arranged in columns. Moreover, the printed circuit boards (PCBs) used in LED matrix appliances are designed to have a life of more than 50,000 hours, ensuring their longevity.
LED matrix displays have multiple applications, ranging from displaying animated images and information on enterprise premises to use in television, computer monitors, headsets, and medical monitors. They come in various types, such as 88 dot matrix, 12816 dot matrix, and others. These displays facilitate easy control of color and brightness.
· COB LED PCB Board
An array of diodes is through direct contact between multiple bare diodes and an MCPCB substrate, forming Chip on Board (COB). COB MCPCBs exhibit exceptional thermal conductivity, facilitating perfect heat distortion.
COB MC printed circuit boards offer a simple LED assembly & can reduce space consumption while being relatively inexpensive. They find various applications, such as backlighting for Light Emitting Diode TVs, street & parking lighting, car lighting, horticulture lighting, and high-energy LED applications.
Other PCB Design for LED Light Systems
LED PCBs have a range of lighting applications, each with unique design characteristics. For instance, LED lighting printed circuit boards in the telecommunication sector prioritize low weight & noise resistance.
LED equipment in telecommunications generates significant amounts of heat, and here the superior heat dissipation property of aluminum-based materials proves valuable. These PCBs find application in high-speed equipment such as filter circuits.
How to Choose LED PCB Circuit Design Material?
· Fire Retardant
The chosen material must possess fire-resistant properties capable of slowing down or halting the fire spread during an outbreak. It is through the chemical reactions that render fuels minimally flammable and prolongs the combustion phase, thus averting the risk of the LED circuit board caught fire.
· Dielectric Constant
It’s important to take into account the electrical power storage capabilities of the material. Additionally, the electrical force strength from the dielectric constant, making it a crucial factor to consider. Keep in mind that LED circuit boards use in electrical appliances, so make sure to evaluate the material’s electrical power storage capability.
· Loss Factor
A substrate substance serves the function of dielectric loss, which the dissipation factor can measure to determine performance differences between materials. A lower dissipation factor indicates less dielectric loss in the laminate. It’s important to select a laminate material with a lower dielectric loss for use in the substrate.
· Tensile Strength
Tensile strength refers to a substance’s ability to resist breaking under tension or the maximum load it can sustain. It indicates that the material can withstand stretching without breaking. Ensure the LED printed circuit board material has the necessary tensile strength.
· Glass Transition Temperature (Tg)
When considering the use of polymers, it’s essential to consider their Tg. At this temperature, the properties of plastic transition to a crystalline state. Above this temperature, the same substance becomes rubbery. This property is crucial to consider when using polymers for end use.
When designing the LED printed circuit board, it’s important to select a material with a sufficiently high Tg to ensure that the board can perform well even under harsh temperature conditions.
· Z-axis Expansion Coefficient
Dimensional stability of an object refers to its changes in size when subjected to varying temperatures, also called thermal expansion. Determine the coefficient of thermal expansion under constant pressure. Different ways for measuring the expansion, including volumetric, area, and linear methods.
Guidelines for LED PCB Circuit Design
· Never Place Vias at the End of Pads
To avoid creating weak solder joints, it’s important to ensure that vias are not positioned too closely to SMT pads, especially when not masked. Maintain a minimum distance of 0.025″ between the edge of the via & SMT trade. Additionally, it’s advisable to apply a mask via a pad.
· Avoid Routing Wide Traces
It is recommended that the width of the surface mount pads be greater than that of the traces that connect to them. If the traces extend beyond the pads, the amount of surface area available for the solder finish will be limited by the size of the solder mask opening. It can result in insufficient coverage by the solder paste, as well as diminished heat dissipation. To ensure proper coverage and heat sinking, the surface finish area determine the size of the pad rather than the size of the trace.
· Designing Sides of SMT Pads
To prevent potential issues, it is advisable to refrain from routing along the edges of surface-mount technology (SMT) pads. Instead, the traces should be routed to connect with the pads at a midpoint along the edge. When there is a gap between the trace & pad etchant can become trapped and corrode the trace during the rinse cycle. Additionally, such connections are prone to failure due to thermal shock during assembly and may even result in oversized pads. We advise to review and amend any trace routing for these connections as necessary.
· Don’t Route Circuit Trace at an Acute Angle
Routing at acute angles, which are less than 90 degrees, can lead to issues that may fail. Acute angles tend to concentrate stress, harming the system’s integrity. To mitigate this issue, we advise to reroute corners in a manner that results in angles mohan 90 degrees. It can help to distribute stress more evenly, reducing the likelihood of failure.
· Don’t Place Components Too Close to the Board’s Outline
Positioning elements too near the size of the PCB can be risky, as they may get damaged during a de-penalization process. It is advisable to keep SMT components at least a hundred inches away from the board’s edge to prevent any potential damage.
To ensure the safe placement of components during PCB design, it is recommended to include a tab location. It can help you determine if the element is properly positioned or if adjustments are necessary to avoid any potential damage during the de-penalization process.
· Don’t Export Gerber files at 2:3 Decimal.
The 2:3 ratio, a popular method for transferring files onto floppy disks, is unsuitable for more compact designs. This approach often results in the loss of crucial data and can cause issues with arc points.
· Consistency in Solder Mask Openings
To minimize issues with design rules and streamline the manufacturing process of your printed circuit board (PCB), it’s important to apply consistent oversizing to your pad stack definitions for all components. It will help prevent potential flaws and simplify the PCB production process.
· Use Direct Connects for Vias
Merely addressing the circuit problems is insufficient; it is also crucial to guarantee the effective operation of the holes. Incorporating thermal pads in vias, particularly crowded ones, may result in an open circuit situation. It is advisable to omit these features since they are unnecessary during manufacturing and can cause issues.
· Thermal Pad Sizing
Ensuring the accurate size of the thermal pad in the element hole is also essential. Congested pads in element holes can result in an open circuit. Thus, the interior diameter should match that of the exterior layer pads to avoid any issues.
· On the Through Holes
To maintain accuracy, the distance between a plated through hole (PTH) and the trace must be a minimum of 0.006″, particularly for multilayer printed circuit boards. Several factors impact the precision of this space in multilayer PCBs, such as:
- Material movement
- pinning setup
- Artwork scaling
- Drill depletion
Defects of LED PCB Circuit Design and How to overcome?
When working with LED printed circuit boards, you may come across various defects that can affect their efficiency. While some of these issues are specific to LED PCBs, others can also be found in others. It is crucial to address these problems comprehensively and effectively to maintain the functionality of your LED PCB. In this article, I will guide you to some most common defects and provide solutions for overcoming them.
· Circuit Scratch
When the pads on a circuit board are together, it can result in recessive defects by scratching. This defect can expose the underlying copper, which can have serious consequences. To prevent this, we advise adding more copper foil to the circuit board to minimize the occurrence of open and short circuits. It can help to reduce the amount of scrap and improve the overall quality of the circuit board.
Defects exposed to copper may not always be noticeable until after the surface-mount technology (SMT) process. One solution to this issue is to reduce the line & pad pitch, which can cause the shrinking of the pitch. It can help to mitigate circuit scratching and lead to an overall improvement in the quality of the circuit board.
· Solder Mask Oil Peeling
If you choose to use the solder mask in your LED printed circuit board design, you must apply a significant amount of exposure energy. Additionally, using a thicker oil than usual can make it challenging to ensure that the oil at the lower layer is adequately exposed, resulting in the peeling of the (oil)solder mask. To overcome this issue, we advise applying exposure energy. However, when doing so, it’s important to consider the consignment ability of a solder mask to ensure optimal results.
· Bad Board Outline
A frequent occurrence during the application of Light Emitting Diode through-holes in smaller-sized boards without margins is the bulging of the board outline. Loose screws can lead to this effect, as well as board displacement during the process. To overcome this issue, we advise establishing appropriate margins that aid in the marking-up process. By doing so, the defect can be resolved.
· Solder Mask Oil Color Unconformity
It is a prevalent flaw with PCB, particularly in the LED sector of an LED circuit board. It is difficult to measure and meet the appropriate standards due to the lack of widely accepted standards for this issue. Numerous factors affect the conformity of oil color.
Attaining oil conformity requires adherence to stricter manufacturing standards compared to regular circuit boards. The best approach to achieve this is to explore suitable manufacturing ways and control parameters. However, this can only be achievable through years of experience in production and using new technologies.
· Board Angle Defects
When dealing with circuit boards with a relatively high thickness, it’s crucial to be mindful of the fragility of sides( angles). Board angle problems are likely to occur while transporting printed circuit boards. To prevent such defects, it’s essential to handle the delicate side angles of LED printed circuit boards with utmost care.
Moreover, it’s advisable to make the base plates relatively larger than standard single-margin printed circuit boards.
· Warpage
Typically, the warping of a LED PCB is caused by an uneven distribution of stress on the board, mainly due to multiple dense pads on a Light Emitting Diode side of a circuit board. The arrangement of large copper blocks on the driver side of the circuit board can also contribute to this issue.
One effective solution to this problem is maintaining a warpage of less than 0.5 percent, which assists in keeping the board flat and stable.
· Pad Outline
The intricate arrangement of pads often leads to omissions during inspection due to the strain & fatigue it causes. As a result, long inspection times and a low pass rate are common problems of arrangement.
It is essential to address pad outline issues. It’s important to define favorable production procedures to minimize the omission ratio and overcome these issues. Additionally, it’s worth noting that visual fatigue can significantly affect the performance of visual inspectors.
· Degrading Functions
You may have already observed that LED PCBs differ technically from other types of PCB. LED Printed Circuit Boards typically feature dense pads & black solder masks, which can present challenges during error analysis in PCB assembly. The dense pads and black masks can make it difficult to identify any malfunctioning LEDs accurately.
When a PCB experiences a function failure, the PCBA typically only indicates the failure without specifying which pad is at fault. The failure is an issue with a whole row of Light Emitting Diodes. If you encounter this issue, it may be necessary to take extra steps to discover the problem. Pinpointing the specific Light Emitting Diode causing the issue may require removing components and solder oil through demolition.
Conclusion
LED PCBs have a significant impact on our daily lives in numerous ways. By following this article, you will know how to create your LED Printed circuit board design and have a comprehensive understanding of the assembly & fabrication processes involved. Based on our discussion, you can select the best LED PCB option for your application. Overall, this guide has equipped you to handle any matters related to LED PCBs confidently.
