SMD LED LTST-S220KGKT Datasheet - Side Looking Chip - Green (568nm) - 2.4V - 75mW - English Technical Document

1. Product Overview

This document details the technical specifications for a high-brightness, side-looking SMD (Surface Mount Device) LED. The device utilizes an advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip to produce green light. It is designed for automated assembly processes and is compatible with infrared (IR) reflow soldering, making it suitable for high-volume manufacturing. The package is supplied on industry-standard 8mm tape wound on 7-inch reels.

1.1 Core Advantages

• High Brightness: Features an ultra-bright AlInGaP chip for superior luminous intensity.
• Side-View Emission: The package is designed to emit light from the side, ideal for applications requiring lateral illumination or status indication on thin-profile devices.
• Manufacturing Friendly: Compatible with automatic pick-and-place equipment and standard IR reflow soldering profiles.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.
• Reliable Construction: Features tin-plated leads for good solderability and longevity.

1.2 Target Applications

This LED is intended for use in standard electronic equipment. Typical applications include, but are not limited to:

• Backlighting for LCD panels in consumer electronics.
• Status and indicator lights in communication devices, office equipment, and home appliances.
• Panel illumination on automotive dashboards or control panels (for non-critical functions, subject to specific qualification).
• Any application requiring a reliable, bright, green side-emitting light source in a compact SMD package.

2. In-Depth Technical Parameter Analysis

All parameters are specified at an ambient temperature (Ta) of 25°C unless otherwise noted.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation (Pd): 75 mW. This is the maximum power the package can dissipate as heat.
• Peak Forward Current (I_FP): 80 mA. This is the maximum instantaneous current, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current (I_F): 30 mA DC. This is the maximum recommended current for continuous operation.
• Reverse Voltage (V_R): 5 V. Exceeding this voltage in reverse bias can damage the LED junction.
• Operating Temperature Range: -30°C to +85°C. The ambient temperature range for reliable operation.
• Storage Temperature Range: -40°C to +85°C.
• Soldering Temperature: Withstands IR reflow soldering with a peak temperature of 260°C for up to 10 seconds.

2.2 Electro-Optical Characteristics

These are the typical performance parameters measured under standard test conditions (I_F = 20mA).

• Luminous Intensity (I_V): 18.0 - 35.0 mcd (millicandela). The amount of visible light emitted, measured on-axis. The actual value is binned (see Section 3).
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its peak (on-axis) value. A wide 130° angle indicates a broad, diffuse emission pattern suitable for side illumination.
• Peak Wavelength (λ_P): 574 nm. The wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λ_d): 568 nm. This is the single wavelength that best represents the perceived color of the LED to the human eye, derived from CIE chromaticity coordinates. This defines the "green" color.
• Spectral Bandwidth (Δλ): 15 nm. The width of the emission spectrum at half its maximum power (FWHM). A narrower bandwidth indicates a more spectrally pure color.
• Forward Voltage (V_F): 2.0V - 2.4V. The voltage drop across the LED when driven at 20mA. This parameter is also binned.
• Reverse Current (I_R): 10 μA (max). The leakage current when 5V is applied in reverse bias.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted (binned) based on key parameters. This allows designers to select parts that meet specific requirements for color, brightness, and voltage.

3.1 Forward Voltage Binning

Bins ensure LEDs in a circuit have similar voltage drops, promoting uniform brightness when driven in parallel. Tolerance within each bin is ±0.1V.

• Bin 4: 1.90V - 2.00V
• Bin 5: 2.00V - 2.10V
• Bin 6: 2.10V - 2.20V
• Bin 7: 2.20V - 2.30V
• Bin 8: 2.30V - 2.40V

3.2 Luminous Intensity Binning

Bins categorize LEDs by their brightness output. Tolerance within each bin is ±15%.

• Bin M: 18.0 mcd - 28.0 mcd
• Bin N: 28.0 mcd - 45.0 mcd
• Bin P: 45.0 mcd - 71.0 mcd

3.3 Dominant Wavelength Binning

This ensures color consistency. Tolerance within each bin is ±1nm.

• Bin C: 567.5 nm - 570.5 nm
• Bin D: 570.5 nm - 573.5 nm
• Bin E: 573.5 nm - 576.5 nm

The specific part number LTST-S220KGKT implies a combination of these bins (likely a specific V_F, I_V, and λ_d bin).

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (e.g., Fig.1, Fig.5), the following analysis is based on standard LED behavior and the provided parameters.

4.1 Current vs. Voltage (I-V) Characteristic

The forward voltage (V_F) has a positive temperature coefficient and increases logarithmically with current. Operating at the typical 20mA ensures stable performance within the specified V_F range of 2.0-2.4V. Driving the LED above the absolute maximum DC current (30mA) will generate excessive heat, reduce efficiency (luminous efficacy), and shorten lifespan.

4.2 Temperature Dependence

AlInGaP LEDs exhibit performance changes with temperature. Typically, luminous intensity decreases as junction temperature increases. The specified operating range of -30°C to +85°C defines the ambient conditions where the LED will function within its published specifications. For optimal longevity and stable light output, maintaining a lower operating temperature through proper PCB thermal design is recommended.

4.3 Spectral Distribution

With a dominant wavelength of 568nm and a spectral bandwidth of 15nm, this LED emits a relatively pure green light. The peak wavelength (574nm) is slightly higher than the dominant wavelength, which is typical for green AlInGaP LEDs. The wide viewing angle of 130° results from the package lens design, which diffuses the light emitted from the side-looking chip.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity

The LED conforms to an EIA standard package outline for side-view LEDs. Detailed dimensional drawings are provided in the datasheet, including body length, width, height, and lead spacing. The cathode is typically identified by a visual marker on the package, such as a notch, green dot, or a shorter lead. Correct polarity must be observed during assembly to prevent damage.

5.2 Recommended Solder Pad Layout

A suggested land pattern (solder pad design) for the PCB is provided to ensure reliable soldering and proper alignment. Adhering to this pattern helps achieve good solder fillets, mechanical strength, and correct positioning of the side-emitting lens. The datasheet also suggests an optimal orientation for the solder wave or reflow process to minimize potential soldering defects.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

The LED is qualified for lead-free (Pb-free) soldering processes. A detailed reflow temperature profile is suggested, compliant with JEDEC standards. Key parameters include:

• Preheat: 150-200°C for a maximum of 120 seconds to gradually heat the assembly and activate flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus (TAL): The time within 5°C of the peak temperature should be limited to a maximum of 10 seconds.
• Number of Cycles: The LED can withstand a maximum of two reflow cycles under these conditions.

It is critical to note that the optimal profile depends on the specific PCB design, solder paste, and oven. The provided profile serves as a starting point that must be validated for the actual production setup.

6.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken:

• Use a temperature-controlled soldering iron set to a maximum of 300°C.
• Limit soldering time per lead to a maximum of 3 seconds.
• Apply heat to the PCB pad, not directly to the LED body.
• Allow sufficient cooling time between joints.

6.3 Cleaning

If post-solder cleaning is required, only use specified solvents to avoid damaging the plastic lens and package. Recommended agents are ethyl alcohol or isopropyl alcohol (IPA). The LED should be immersed at normal room temperature for less than one minute. Harsh or unspecified chemicals must be avoided.

6.4 Storage and Handling

ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Proper ESD controls must be in place during handling, including the use of grounded wrist straps, anti-static mats, and conductive containers.

Moisture Sensitivity: The package is moisture-sensitive. Unopened reels (sealed with desiccant) should be stored at ≤30°C and ≤90% RH and used within one year. Once the original packaging is opened, the LEDs should be stored at ≤30°C and ≤60% RH. For extended storage outside the original bag, store in a sealed container with desiccant. Components stored open for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied on embossed carrier tape for automated assembly.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 4000 pieces (standard full reel).
• Minimum Pack Quantity: 500 pieces for partial reels or remainders.
• Packing Standard: Complies with ANSI/EIA-481 specifications.
• Cover Tape: Empty pockets on the carrier tape are sealed with a top cover tape.

8. Application Notes and Design Considerations

8.1 Current Limiting

An LED is a current-driven device. A series current-limiting resistor is mandatory when driving from a voltage source. The resistor value can be calculated using Ohm's Law: R = (V_source - V_F) / I_F. Always use the maximum V_F from the datasheet (2.4V) for a worst-case design to ensure the current does not exceed the desired level (e.g., 20mA). For precision or long-term stability, consider using a constant current driver circuit.

8.2 Thermal Management

Although power dissipation is low (75mW max), effective thermal management is crucial for reliability and maintaining light output. Ensure the PCB has adequate copper area connected to the LED's thermal pad (if applicable) or solder pads to conduct heat away from the junction. Avoid placing the LED near other heat-generating components.

8.3 Optical Design

The side-view emission and 130° viewing angle make this LED suitable for applications where light needs to be directed parallel to the PCB surface, such as into a light guide plate for edge-lit displays or for illumination of adjacent components. Consider the lens profile and emission pattern when designing light pipes, diffusers, or apertures to achieve the desired optical effect.

9. Technical Comparison and Differentiation

Compared to older technology like GaP (Gallium Phosphide) green LEDs, AlInGaP offers significantly higher brightness and efficiency. Compared to InGaN (Indium Gallium Nitride) based green LEDs, AlInGaP typically offers superior performance in the true green to yellow-green spectrum (around 570nm) with higher efficacy and more stable wavelength over temperature and current. The side-looking package differentiates it from top-emitting LEDs, solving specific spatial constraints in design.

10. Frequently Asked Questions (FAQ)

10.1 What resistor should I use with a 5V supply?

Using the maximum V_F of 2.4V and a target I_F of 20mA: R = (5V - 2.4V) / 0.02A = 130 Ohms. The nearest standard value is 130Ω or 150Ω. A 150Ω resistor would yield a slightly lower current, which is safe and conserves power.

10.2 Can I drive this LED without a current-limiting resistor?

No. Connecting an LED directly to a voltage source will cause excessive current to flow, rapidly overheating and destroying the device. A series resistor or constant current circuit is always required.

10.3 Why is there a binning system?

Semiconductor manufacturing has natural variations. Binning sorts LEDs into groups with tightly controlled parameters (color, brightness, voltage), allowing designers to source parts with consistent performance for their application, ensuring uniform appearance and function in the final product.

10.4 How do I identify the cathode?

Refer to the package outline drawing in the datasheet. For this side-view package, the cathode is typically marked by a green dot on the top of the package or a notch/chamfer on one end of the body. The lead connected to the cathode may also be slightly shorter.

11. Practical Application Example

Scenario: Status Indicator on a Portable Device

A designer is creating a slim handheld scanner. They need a low-power, bright green light to indicate "ready" status. Space is extremely limited on the edge of the main PCB.

Solution: The LTST-S220KGKT is an ideal choice. Its side-looking emission allows it to be mounted flat on the PCB, with its lens positioned right at the edge of the board. A small light pipe or a clear window in the housing can channel the light to the exterior. The designer drives it at 15mA (below the 20mA typical) using a GPIO pin from a microcontroller with a series resistor, conserving battery life while still providing ample brightness. The compatibility with reflow soldering simplifies the automated assembly of the entire PCB.

12. Technology Principle Introduction

This LED is based on AlInGaP semiconductor technology. The chip is composed of layers of Aluminum, Indium, Gallium, and Phosphide alloys grown epitaxially on a substrate. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, green at 568nm. The side-view package incorporates the chip mounted on a lead frame, wire-bonded, and encapsulated in a molded plastic lens that shapes the light output.

13. Industry Trends and Developments

The general trend in LED technology is toward higher efficiency (more lumens per watt), increased power density, and greater color consistency and control. For indicator and backlight applications, miniaturization continues while maintaining or improving optical performance. There is also a growing emphasis on broader operating temperature ranges and enhanced reliability for automotive and industrial applications. While this specific part represents a mature and reliable technology, ongoing material science and packaging innovations continue to push the boundaries of what is possible in solid-state lighting and indication.