SMD LED LTST-T180KEKT Datasheet - AlInGaP Red - 120° Viewing Angle - 30mA - 75mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a surface-mount device (SMD) Light Emitting Diode (LED). This component is designed for automated printed circuit board (PCB) assembly processes, making it ideal for high-volume manufacturing. Its miniature form factor caters to space-constrained applications across various electronic sectors.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, packaging in industry-standard 8mm tape on 7-inch reels for automated pick-and-place machines, and full compatibility with infrared (IR) reflow soldering processes. It is preconditioned to JEDEC Level 3 moisture sensitivity standards, ensuring reliability during assembly. Its target applications are broad, encompassing status indicators, signal and symbol illumination, and front-panel backlighting in telecommunications equipment, office automation devices, home appliances, and industrial control systems.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed. Key limits include a maximum continuous forward current (I_F) of 30 mA, a peak forward current of 80 mA under pulsed conditions (1/10 duty cycle, 0.1ms pulse width), a maximum reverse voltage (V_R) of 5V, and a power dissipation (P_D) limit of 75 mW. The operating and storage temperature range is specified from -40°C to +100°C.

2.2 Thermal Characteristics

Thermal management is critical for LED performance and longevity. The maximum allowable junction temperature (T_j) is 115°C. The typical thermal resistance from the junction to the ambient air (R_θJA) is 140 °C/W. This parameter indicates how effectively heat is transferred away from the semiconductor junction; a lower value is better. Proper PCB layout with adequate thermal relief is essential to maintain the junction temperature within safe limits, especially when operating at higher currents.

2.3 Electrical and Optical Characteristics

These are the typical performance parameters measured under standard test conditions (T_a=25°C, I_F=20mA). The luminous intensity (I_V) ranges from a minimum of 140 mcd to a maximum of 420 mcd, with specific values determined by the bin rank. The viewing angle (2θ_1/2) is 120 degrees, defined as the full angle where intensity drops to half of its on-axis value, indicating a wide, diffuse emission pattern. The dominant wavelength (λ_d) falls between 615 nm and 628 nm, characterizing the perceived red color. The forward voltage (V_F) typically ranges from 1.7V to 2.5V at the test current.

3. Bin Rank System Explanation

The luminous output of LEDs can vary from batch to batch. A binning system is used to sort devices into groups with consistent performance. This LED uses an intensity (I_V) bin rank system. The bins are labeled R2, S1, S2, and T1, with corresponding minimum and maximum luminous intensity values at 20 mA (e.g., S1: 185-240 mcd, T1: 315-420 mcd). A tolerance of +/-11% is applied within each bin. This system allows designers to select LEDs with the required brightness consistency for their application.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, typical curves for such a device would include the following relationships, crucial for design analysis:

• I-V Curve (Current vs. Voltage): Shows the exponential relationship between forward current and forward voltage. The knee voltage is typically around the specified V_F range. This curve is vital for designing the current-limiting driver circuit.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, usually in a near-linear relationship within the operating range, before potentially saturating or causing excessive heat at higher currents.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as the ambient (or junction) temperature increases. This is critical for applications operating in elevated temperature environments.
• Spectral Distribution: A plot of relative radiant power versus wavelength, showing a peak emission wavelength (λ_P) around 630 nm and a spectral half-width (Δλ) of approximately 15 nm, confirming a narrow-band red emission.

5. Mechanical and Package Information

The LED comes in a standard SMD package. The lens color is water clear, while the light source color is red, produced by an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material. Detailed package dimensions are provided in the datasheet drawings, including length, width, height, and pad spacing. All dimensions are in millimeters with a standard tolerance of ±0.2 mm unless otherwise noted. The polarity is indicated by the physical marking or pad design (typically a cathode mark).

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile

The device is compatible with lead-free (Pb-free) soldering processes. The recommended infrared reflow profile should comply with J-STD-020B standards. Key parameters include a preheat temperature of 150-200°C, a preheat time of up to 120 seconds, a peak temperature not exceeding 260°C, and a time above liquidus (TAL) as per the solder paste specification. The total time within 5°C of the peak temperature should be limited to a maximum of 10 seconds, and reflow should not be performed more than twice.

6.2 Cleaning

If cleaning is required after soldering, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is acceptable. Unspecified chemical cleaners may damage the epoxy lens or package.

6.3 Storage and Handling

The LEDs are moisture-sensitive. When sealed in the original moisture-proof bag with desiccant, they should be stored at ≤30°C and ≤70% RH and used within one year. Once the bag is opened, the storage environment must not exceed 30°C and 60% RH. Components exposed to ambient conditions for more than 168 hours should be baked at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Packaging and Ordering Information

The standard packaging is 8mm wide embossed carrier tape on 7-inch (178 mm) diameter reels. Each reel contains 5000 pieces. A minimum packing quantity of 500 pieces is available for remainder orders. The tape is sealed with a cover tape. The packaging complies with ANSI/EIA-481 specifications.

8. Application Recommendations

8.1 Typical Application Circuits

LEDs are current-driven devices. To ensure uniform brightness and prevent current hogging, especially when multiple LEDs are connected in parallel, a current-limiting resistor must be used in series with each LED. The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F, where V_F is the forward voltage of the LED at the desired current I_F. Driving LEDs directly from a voltage source without a current limit is not recommended and will likely destroy the device.

8.2 Design Considerations and Cautions

This product is intended for general-purpose electronic equipment. For applications requiring exceptional reliability where failure could jeopardize safety (e.g., aviation, medical, transportation), specific qualification and consultation are necessary. PCB pad layout should follow the recommended design in the datasheet to ensure proper soldering and mechanical stability. Attention must be paid to thermal design on the PCB to manage the heat dissipation of 75 mW, especially in enclosed spaces or high ambient temperatures.

9. Technical Comparison and Differentiation

Compared to older technologies like GaAsP (Gallium Arsenide Phosphide) red LEDs, the AlInGaP material used in this device offers significantly higher luminous efficiency, resulting in brighter output at the same current, and better temperature stability. The 120-degree viewing angle provides a very wide and even illumination pattern suitable for panel indicators where viewing from off-axis angles is required, as opposed to narrower-angle LEDs used for focused light. Its compatibility with standard IR reflow processes differentiates it from LEDs that require manual or wave soldering, enabling cost-effective, high-speed automated assembly.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED with a 5V supply directly?
A: No. You must use a series current-limiting resistor. For example, with a typical V_F of 2.0V at 20mA and a 5V supply, R = (5V - 2.0V) / 0.020A = 150 Ω. A resistor is mandatory.

Q: What does \"Water Clear\" lens mean for a red LED?
A: The lens material itself is colorless/transparent. The red color is emitted solely by the AlInGaP semiconductor chip inside. A clear lens often allows for a wider viewing angle and less color distortion compared to a tinted diffused lens.

Q: The max current is 30mA, but the test condition is 20mA. Which should I use?
A: The 20mA condition is the standard test point for specifying optical characteristics. You can operate the LED at any current up to the absolute maximum of 30mA DC, but the luminous intensity and forward voltage will scale accordingly (see performance curves). Operating at lower currents increases longevity and reduces heat.

Q: Why is storage humidity so important?
A: SMD packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can crack the package or delaminate internal bonds—a phenomenon known as \"popcorning.\"

11. Practical Application Case Study

Scenario: Designing a status indicator panel for a network router. Multiple LEDs (Power, LAN, WAN, Wi-Fi) are needed. Using this LED model, the designer would: 1) Place the LEDs on the front panel PCB layout according to the recommended pad footprint. 2) For each LED, calculate a series resistor based on the system's 3.3V logic supply and a target current of 15mA (for balance of brightness and power). Assuming V_F = 2.0V, R = (3.3V - 2.0V)/0.015A ≈ 87 Ω (use 82 Ω or 100 Ω standard value). 3) Ensure the PCB layout provides some thermal copper area under the LED pads. 4) Specify the same intensity bin code (e.g., S1) for all LEDs in the Bill of Materials (BOM) to guarantee uniform brightness across the panel. 5) Follow the recommended reflow profile during assembly.

12. Operating Principle Introduction

A Light Emitting Diode is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, energy is released. In a standard silicon diode, this energy is released primarily as heat. In an LED, the semiconductor material (in this case, AlInGaP) has a direct bandgap, meaning the energy is released in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material. A wider bandgap produces shorter wavelength (bluer) light.

13. Technology Trends and Developments

The general trend in SMD indicator LEDs is toward higher efficiency (more light output per watt of electrical input), which reduces power consumption and heat generation. This allows for either brighter indicators at the same current or the same brightness at lower currents, extending device battery life. Package sizes continue to shrink, enabling denser indicator arrays and integration into ever-smaller consumer electronics. There is also a focus on improving color consistency and stability over temperature and lifetime through advanced binning techniques and more stable semiconductor materials. The drive for broader adoption of lead-free and halogen-free materials in compliance with global environmental regulations remains a key industry driver.