LED PCB

An LED PCB (Light‑Emitting Diode Printed Circuit Board) is a specialised circuit board that forms the core of LED‑based airfield ground lighting fixtures. It is designed to mechanically support and electrically interconnect LED chips, drivers, resistors, and other passive components, while also providing a path for thermal dissipation to prevent overheating. Unlike standard PCBs, LED PCBs are often constructed with metal‑core substrates (MCPCB – Metal Core Printed Circuit Board) to enhance heat transfer away from the LEDs.

Key functions of an LED PCB in AGL applications include:

• Electrical Interconnection: Providing traces and pads to connect LEDs in series or parallel configurations, and to interface with the LED driver.
• Thermal Management: Using copper planes, thermal vias, and a metal substrate to conduct heat away from the LED junctions to the fixture's heat sink or housing.
• Mechanical Support: Holding the LEDs and other components securely in place, with mounting holes or pads for attachment to the fixture.
• Optical Alignment: Ensuring that LEDs are precisely positioned to achieve the required beam pattern when combined with lenses or reflectors.
• Reliability: Designed to withstand extreme temperatures, vibration, moisture, and thermal cycling typical of airfield environments.

LED PCBs are custom‑designed for each fixture type, with specific layouts to accommodate the number and arrangement of LEDs, and are often potted or coated to protect against moisture and corrosion.

The LED PCB's purpose is to hold the fixture's actual light-emitting elements in the precise electrical and thermal environment they need to perform reliably — carrying current to each LED without excessive voltage drop, and carrying heat away from each LED junction fast enough to keep it within its rated temperature. Because an LED's light output, colour, and lifespan are all directly sensitive to junction temperature, the PCB's metal-core construction and thermal-via design are not just a manufacturing convenience but a core part of what keeps the fixture's photometric performance stable over its service life. Its role in physically positioning each LED also feeds directly into the fixture's optical performance, since the beam pattern produced by the lens or reflector above it depends on the LEDs being placed exactly where the optical design assumes they are.

LED PCBs are used in every LED‑based AGL fixture, including:

• Runway Edge and Centreline Lights: PCBs with multiple high‑power LEDs arranged to produce the required beam pattern and colour.
• Taxiway Edge and Centreline Lights: Similar PCBs but with blue or green LED chips.
• Approach Lighting Systems: High‑intensity LED arrays on PCBs for sequenced flashing lights and barrettes.
• Obstruction Lights: PCBs with red or white high‑power LEDs for aviation warning beacons.
• PAPI and VASI Units: PCBs with closely matched LED pairs to achieve the required colour‑transition characteristics.
• Apron Floodlights: Large PCBs with many high‑power LEDs for area illumination.
• Stop Bars and Guard Lights: PCBs with LEDs arranged in linear arrays for visual barriers.

They are also used in:

• Retrofit Upgrades: Replacing halogen lamps with LED modules that include a custom PCB.
• Prototyping and R&D: Developing new fixtures and testing LED configurations.
• Spare Parts: Replacement PCBs for field maintenance of LED fixtures.

The PCB mounts directly onto the fixture's internal heat sink, usually via a thermal interface pad or paste, and secured so the full board area makes even thermal contact rather than being fastened only at the corners. Positioning within the housing is set by the fixture's optical design (the PCB sits at the reflector's focal point or the lens's designed working distance) rather than by a general rule, since even a small misplacement shifts the beam pattern out of specification. Power and control leads from the LED driver terminate on the PCB's own connector or solder pads, kept short and strain-relieved so vibration in the fixture housing doesn't fatigue the joint over time; no separate field cabling is involved beyond the fixture's existing driver leads.

The LED PCB serves as the central hub for the LED module:

• Substrate Material: Most AGL LED PCBs are fabricated on an aluminium‑core (or copper‑core) substrate, which is a sandwich of a metal base, a dielectric layer, and a copper circuit layer. The metal core provides excellent thermal conductivity, transferring heat from the LEDs directly to the fixture's heat sink.
• Circuit Traces: Copper traces on the top layer carry current from the connector or driver to the LED pads. The trace width is designed to handle the required current without excessive voltage drop or heating. For high‑power LEDs, thick copper (≥ 2 oz) is common.
• Thermal Vias: In some designs, thermal vias (plated holes) connect the top copper layer to the metal core, further enhancing heat transfer.
• LED Placement: LEDs are soldered onto the PCB pads using reflow soldering. The pads are designed to match the LED's footprint, with proper spacing to avoid short circuits and to allow for optical alignment.
• Additional Components: The PCB may also hold resistors for current limiting, Zener diodes for ESD protection, and connectors for wiring. Some advanced PCBs integrate the LED driver circuitry directly.
• Optical Interface: The PCB often includes alignment markers or mounting features for secondary optics (lenses, reflectors) to ensure that the light output is directed correctly.
• Environmental Protection: After assembly, the PCB may be coated with a conformal coating or potted in resin to protect against moisture, dust, and corrosive agents.

The PCB's design must balance electrical performance, thermal dissipation, and mechanical robustness to meet the stringent requirements of airfield lighting.

The LED PCB is the lowest, purely passive layer of the fixture's control architecture — it carries no logic, makes no decisions, and holds no feedback loop of its own. Everything that determines the intensity the board's LEDs actually emit — the ALCMS's chosen step, the CCR's regulated loop current, the driver's constant-current or constant-voltage output — is decided upstream and simply arrives at the PCB's input connector as a current the copper traces are sized to carry without excessive voltage drop or resistive heating. The board's only "response" to that incoming current is physical rather than logical: proportionally more light output, and proportionally more heat generated at each LED junction, conducted down through the dielectric layer and metal core toward the fixture's heat sink (or, in higher-power designs, into a heat pipe). Because the PCB has no sensing or protection circuitry of its own, it depends entirely on the driver upstream to keep the delivered current within the LEDs' rated limits and on the metal-core substrate's thermal design to keep junction temperature within range — if either of those upstream safeguards fails, the PCB itself has no mechanism to intervene. Its place in the architecture is therefore purely as the electrical and thermal interface where the control chain's final output becomes visible light: everything before it is logic and regulation, everything at it is fixed, physical response.

The board is built on either an aluminium-core (MCPCB) substrate — a thin dielectric layer sandwiched between the copper circuit layer and an aluminium base, chosen specifically for its thermal conductivity — or a standard FR4 board with thermal vias drilled through to a copper pour, used where cost matters more than peak heat extraction. Copper layer thickness runs 1–4oz depending on the current the LEDs draw, and 1 to 48 LEDs are reflow-soldered directly onto the board per fixture design, with a conformal coating applied afterward to protect the joints from moisture and the pavement or fixture environment. The finished board bolts to the fixture housing through pre-drilled mounting holes positioned to press the aluminium core (or thermal via field) flat against the housing's own heatsink surface, since the PCB's construction only works as a thermal path if that mechanical contact is solid.