SMD LED LTST-S110KGKT Datasheet - AlInGaP Green - 25mA - 62.5mW - English Technical Document

1. Product Overview

The LTST-S110KGKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It is part of a family of miniature LEDs intended for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages and Target Market

This LED offers several key advantages for modern electronics manufacturing. Its primary features include compliance with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. The device utilizes an ultra-bright AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip, which is known for high efficiency and good color purity in the green spectrum. The package is finished with tin plating, enhancing solderability and long-term reliability. It is fully compatible with automated pick-and-place equipment and infrared (IR) reflow soldering processes, which are standard in high-volume production. The LED is supplied in industry-standard 8mm tape on 7-inch reels, facilitating efficient handling and assembly.

The target applications are diverse, focusing on areas where compact size, reliability, and clear visual indication are critical. These include telecommunications equipment (e.g., cellular phones), office automation devices (e.g., notebook computers), network systems, various home appliances, and indoor signage or symbol illumination. Specific uses within these devices encompass keypad or keyboard backlighting, status indicators, micro-displays, and general signal luminaires.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical, optical, and thermal specifications is essential for proper circuit design and reliable operation.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (Ta) of 25°C. The maximum continuous DC forward current (IF) is 25 mA. Under pulsed conditions with a 1/10 duty cycle and a 0.1ms pulse width, the device can handle a peak forward current of 60 mA. The maximum allowable reverse voltage (VR) is 5 V. The total power dissipation should not exceed 62.5 mW. The operating temperature range is from -30°C to +85°C, and the storage temperature range is slightly wider, from -40°C to +85°C. Crucially, the LED can withstand infrared reflow soldering with a peak temperature of 260°C for a maximum of 10 seconds, which aligns with common lead-free (Pb-free) assembly profiles.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at Ta=25°C under standard test conditions. The luminous intensity (Iv), a measure of perceived brightness, ranges from a minimum of 18.0 millicandelas (mcd) to a maximum of 71.0 mcd when driven at the standard test current of 20 mA. The viewing angle, defined as 2θ1/2 (twice the half-angle), is 130 degrees. This wide viewing angle makes the LED suitable for applications where visibility from off-axis positions is important.

The spectral characteristics are defined by several wavelengths. The peak emission wavelength (λP) is typically 574 nm. The dominant wavelength (λd), which defines the perceived color, has a specified range from 567.5 nm to 576.5 nm at 20 mA. The spectral line half-width (Δλ) is typically 15 nm, indicating the spectral purity of the green light emitted.

Electrically, the forward voltage (VF) at 20 mA ranges from a minimum of 1.9 V to a maximum of 2.4 V. The reverse current (IR) is specified at a maximum of 10 μA when a reverse voltage of 5 V is applied.

3. Bin Ranking System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins based on key parameters. This allows designers to select parts that meet specific requirements for their application.

3.1 Forward Voltage (VF) Rank

LEDs are binned according to their forward voltage drop at 20 mA. The bin codes, minimum, and maximum voltages are as follows: Code 4 (1.9V - 2.0V), Code 5 (2.0V - 2.1V), Code 6 (2.1V - 2.2V), Code 7 (2.2V - 2.3V), and Code 8 (2.3V - 2.4V). The tolerance within each bin is ±0.1 volt. Selecting LEDs from the same VF bin helps maintain uniform brightness when multiple LEDs are connected in parallel without individual current-limiting resistors.

3.2 Luminous Intensity (IV) Rank

This binning categorizes LEDs based on their light output at 20 mA. The bins are: Code M (18.0 - 28.0 mcd), Code N (28.0 - 45.0 mcd), and Code P (45.0 - 71.0 mcd). The tolerance on each intensity bin is ±15%. This allows designers to choose a brightness level appropriate for the application, whether it requires high visibility or lower power consumption.

3.3 Hue (Dominant Wavelength) Rank

To control color consistency, LEDs are binned by their dominant wavelength. The bins are: Code C (567.5 - 570.5 nm), Code D (570.5 - 573.5 nm), and Code E (573.5 - 576.5 nm). The tolerance for each bin is ±1 nm. Using LEDs from the same hue bin is critical in applications where color matching between multiple indicators is important.

4. Performance Curve Analysis

Graphical data provides deeper insight into the device's behavior under varying conditions, which is vital for robust design.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The I-V characteristic curve shows the relationship between the current flowing through the LED and the voltage across it. For a typical AlInGaP LED like this one, the curve exhibits an exponential rise. The \"knee\" voltage, where current begins to increase significantly, is around 1.8-1.9V. Beyond this point, a small increase in voltage causes a large increase in current. This underscores the importance of using a constant current driver or a current-limiting resistor to prevent thermal runaway and ensure stable operation.

4.2 Luminous Intensity vs. Forward Current

This curve demonstrates how light output scales with drive current. Typically, luminous intensity increases approximately linearly with current up to a point. However, at very high currents, efficiency drops due to increased heat generation within the chip (efficiency droop). Operating at or below the recommended 20mA ensures optimal efficiency and longevity.

4.3 Luminous Intensity vs. Ambient Temperature

The light output of an LED is temperature-dependent. As the ambient temperature (or junction temperature) increases, the luminous intensity generally decreases. This derating curve is crucial for designing applications that must maintain a certain brightness level over a specified operating temperature range, especially towards the upper limit of +85°C.

4.4 Spectral Distribution

The spectral power distribution plot shows the relative intensity of light emitted at each wavelength. For a green AlInGaP LED, this curve is typically a single, relatively narrow peak centered around the dominant wavelength. The half-width (Δλ) of 15 nm indicates a moderately pure green color, which is desirable for clear, saturated indicators.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to an industry-standard SMD package outline. Key dimensions include the overall length, width, and height. The lens is water clear. All dimensions are provided in millimeters with a standard tolerance of ±0.1 mm unless otherwise noted. Precise dimensional data is essential for creating accurate PCB footprints and ensuring proper placement and soldering.

5.2 Recommended PCB Land Pattern and Polarity

A recommended solder pad layout (land pattern) is provided to ensure reliable solder joint formation and proper alignment during reflow. The design accounts for solder fillet formation and thermal relief. The cathode (negative) terminal is typically identified by a marking on the package body, such as a notch, dot, or green marking. Correct polarity orientation during assembly is mandatory for the device to function.

6. Soldering and Assembly Guidelines

6.1 Infrared Reflow Soldering Parameters

For lead-free (Pb-free) solder processes, a specific temperature profile is recommended. This profile typically includes a pre-heat zone (e.g., 150-200°C), a controlled ramp-up, a peak temperature zone, and a cooling zone. The critical parameter is that the device body temperature must not exceed 260°C for more than 10 seconds. Adherence to this profile is necessary to prevent damage to the LED's epoxy lens, internal wire bonds, or the semiconductor die itself.

6.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken. The soldering iron tip temperature should not exceed 300°C, and the contact time with the LED terminal should be limited to a maximum of 3 seconds for a single soldering operation. Applying excessive heat can irreversibly damage the component.

6.3 Cleaning

Post-solder cleaning must be performed with compatible solvents. Only alcohol-based cleaners, such as ethyl alcohol or isopropyl alcohol (IPA), should be used. The LED should be immersed at normal temperature for less than one minute. Harsh or unspecified chemical cleaners can degrade the plastic package, leading to discoloration, cracking, or reduced light output.

6.4 Storage and Handling

Proper storage is critical to maintain solderability. Unopened, moisture-proof bags with desiccant have a shelf life. Once the original packaging is opened, the LEDs are sensitive to ambient moisture (Moisture Sensitivity Level, MSL 3). They should be used within one week or stored in a dry environment (e.g., a sealed container with desiccant or a nitrogen cabinet). If exposed to ambient humidity for more than a week, a baking process (e.g., 60°C for at least 20 hours) is required before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.5 Electrostatic Discharge (ESD) Precautions

LEDs are sensitive to electrostatic discharge. Handling procedures must include proper grounding. Operators should use wrist straps or anti-static gloves. All workstations, equipment, and machinery must be correctly grounded to prevent ESD events that can degrade or destroy the semiconductor junction.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The product is supplied for automated assembly. It is packaged in 8mm wide embossed carrier tape. The tape is wound onto standard 7-inch (178mm) diameter reels. Each reel contains 3000 pieces of the LED. For quantities less than a full reel, a minimum packing quantity of 500 pieces is available. The packaging conforms to ANSI/EIA-481 standards, ensuring compatibility with standard tape feeders on pick-and-place machines.

8. Application Notes and Design Considerations

8.1 Current Limiting

An LED is a current-driven device. A series resistor is the simplest method to limit current when powered from a voltage source. The resistor value can be calculated using Ohm's Law: R = (V_source - VF_LED) / I_desired. For example, with a 5V supply, a VF of 2.1V, and a desired current of 20mA, the resistor value would be (5 - 2.1) / 0.02 = 145 Ohms. A standard 150 Ohm resistor would be suitable. The resistor's power rating must also be considered: P = I^2 * R = (0.02)^2 * 150 = 0.06W, so a 1/8W (0.125W) or larger resistor is adequate.

8.2 Thermal Management

Although small, LEDs generate heat at the semiconductor junction. Excessive junction temperature reduces light output, shifts wavelength, and shortens lifespan. For designs operating at high ambient temperatures or near maximum current, consider the PCB layout. Using a PCB with a ground plane or thermal vias under the LED's thermal pad (if present) can help dissipate heat. Avoid placing LEDs near other heat-generating components.

8.3 Application Scope and Reliability

This LED is designed for use in standard commercial and industrial electronic equipment. For applications requiring exceptional reliability where failure could jeopardize safety or health (e.g., aviation, medical life-support, critical transportation systems), additional qualification and specific consultation are necessary. The standard device may not be suitable for such high-reliability applications without further assessment.

9. Technical Comparison and Differentiation

The LTST-S110KGKT, based on AlInGaP technology, offers distinct advantages compared to other green LED technologies like traditional GaP (Gallium Phosphide) or InGaN (Indium Gallium Nitride) for certain wavelengths. AlInGaP LEDs generally provide higher efficiency and better temperature stability in the amber to red spectrum, and for specific green wavelengths, they can offer superior performance in terms of brightness and color stability compared to older GaP technology. Its 130-degree viewing angle is wider than some side-view or top-view packages designed for more directional light, making it a versatile choice for status indication where wide-angle visibility is beneficial. The combination of a clear lens and a bright AlInGaP chip results in a vibrant, saturated green color that is easily distinguishable.

10. Frequently Asked Questions (FAQ)

10.1 What is the difference between peak wavelength and dominant wavelength?

Peak wavelength (λP) is the wavelength at which the spectral power distribution curve reaches its maximum intensity. Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength of a pure monochromatic light that would match the perceived color of the LED. For LEDs with a narrow spectrum, these values are often close, but λd is the more relevant parameter for color specification.

10.2 Can I drive this LED with a voltage source directly?

No. An LED's forward voltage has a negative temperature coefficient and varies from unit to unit. Connecting it directly to a voltage source will cause an uncontrolled current to flow, likely exceeding the maximum rating and destroying the device. Always use a current-limiting mechanism, such as a series resistor or a constant-current driver.

10.3 Why is there a binning system for luminous intensity and wavelength?

Manufacturing variations cause slight differences in performance between individual LEDs. Binning sorts them into groups with closely matched characteristics. This allows designers to purchase parts with guaranteed minimum/maximum performance (e.g., brightness, color) for their application, ensuring consistency in the final product, especially when using multiple LEDs.

10.4 What happens if I exceed the 10-second limit at 260°C during reflow?

Exceeding the time-temperature profile can cause several failures: thermal stress cracking of the epoxy lens, degradation of the internal silicone encapsulant (leading to darkening), failure of the wire bonds, or damage to the semiconductor chip itself. This will result in reduced light output, color shift, or complete device failure.

11. Practical Design and Usage Examples

11.1 Status Indicator for a Consumer Device

In a portable Bluetooth speaker, a single LTST-S110KGKT can be used as a power/charging status indicator. Driven at 10-15 mA via a current-limiting resistor from the main 3.3V or 5V rail, it provides a clear, bright green light. The wide 130-degree viewing angle ensures the status is visible from almost any angle. The design must include the correct PCB footprint and ensure the LED is not placed behind a deeply tinted or diffusing lens that would require higher drive current.

11.2 Backlighting for Membrane Keypad

For a medical device keypad, multiple LEDs from the same intensity bin (e.g., Code N) can be arranged around the perimeter to provide even backlighting. They would be connected in series-parallel combinations with appropriate current-limiting resistors to ensure uniform brightness. Thermal management must be considered if many LEDs are driven simultaneously in a confined space.

12. Technology Introduction

The LTST-S110KGKT utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material grown on a substrate. When a forward voltage is applied, electrons and holes recombine in the active region of the chip, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy and thus the wavelength (color) of the emitted light, in this case, green. The chip is mounted in a leadframe package, wire-bonded, and encapsulated with a clear epoxy lens that protects the chip and shapes the light output beam. Tin plating on the external leads ensures good solderability and resistance to oxidation.

13. Technology Trends

The general trend in SMD indicator LEDs continues towards higher efficiency (more light output per unit of electrical power), improved color consistency and saturation, and smaller package sizes to enable denser PCB designs. There is also a focus on enhancing reliability under harsh conditions, such as higher temperature and humidity. The drive for miniaturization persists, with chip-scale package (CSP) LEDs becoming more prevalent for the most space-constrained applications. Furthermore, integration of control electronics directly with the LED die (e.g., for constant current driving or color mixing) is an area of ongoing development.