SMD LED LTST-E682QETGWT Datasheet - Dual Color (Red/Green) - English Technical Document

1. Product Overview

This document details the specifications for the LTST-E682QETGWT, a surface-mount device (SMD) light-emitting diode (LED). This component integrates two distinct LED chips within a single package: one emitting red light using AlInGaP technology and another emitting green light using InGaN technology. It is designed for automated printed circuit board (PCB) assembly processes, making it suitable for high-volume manufacturing.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place equipment.
• Standard EIA (Electronic Industries Alliance) package footprint.
• IC-compatible low-voltage operation.
• Fully compatible with infrared (IR) reflow soldering processes.
• Preconditioned to JEDEC (Joint Electron Device Engineering Council) Moisture Sensitivity Level 3.

1.2 Target Applications

This dual-color LED is intended for a broad range of electronic equipment where compact size and reliable indication are required. Typical application areas include:

• Telecommunication devices (e.g., routers, modems, base stations).
• Office automation equipment (e.g., printers, scanners, multifunction devices).
• Home appliances and consumer electronics.
• Industrial control panels and equipment.
• Status and power indicators.
• Backlighting for front panels, symbols, or small signage.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under or at these conditions is not guaranteed and should be avoided in circuit design.

• Power Dissipation (Pd): 75 mW (Red), 76 mW (Green). This is the maximum power the LED can dissipate as heat at an ambient temperature (Ta) of 25°C.
• Peak Forward Current (I_FP): 100 mA (Red), 80 mA (Green). This is the maximum allowable instantaneous current under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is significantly higher than the continuous DC rating.
• DC Forward Current (I_F): 30 mA (Red), 20 mA (Green). This is the maximum recommended continuous forward current for reliable long-term operation.
• Operating & Storage Temperature Range: -40°C to +85°C (Operating), -40°C to +100°C (Storage). The device is rated for industrial temperature environments.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of Ta=25°C and I_F=20mA, unless otherwise specified. They define the typical performance of the device.

• Luminous Intensity (I_V): A measure of the perceived brightness. For the Red chip, the typical range is 450-1080 millicandelas (mcd). For the Green chip, the range is 780-1875 mcd. Measurement follows the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): Approximately 120 degrees (typical). This wide viewing angle, defined as the angle where intensity drops to half its on-axis value, is characteristic of a diffused lens, providing a broad, even illumination rather than a narrow beam.
• Peak Emission Wavelength (λ_P): 632 nm (Red, typical), 520 nm (Green, typical). This is the wavelength at which the spectral output is maximum.
• Dominant Wavelength (λ_d): 616-628 nm (Red), 515-530 nm (Green). This is the single wavelength that best represents the perceived color of the LED, derived from the CIE chromaticity diagram. Tolerance is ±1 nm for Green.
• Spectral Line Half-Width (Δλ): 20 nm (Red, typical), 30 nm (Green, typical). This indicates the spectral purity; a smaller value means a more monochromatic color.
• Forward Voltage (V_F): 1.7-2.5V (Red), 2.8-3.8V (Green) at 20mA. The Green InGaN chip typically requires a higher drive voltage than the Red AlInGaP chip. Tolerance is ±0.1V.
• Reverse Current (I_R): Maximum 10 µA for both colors at V_R=5V. LEDs are not designed for reverse bias operation; this parameter is primarily for IR testing.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters.

3.1 Luminous Intensity (I_V) Binning

LEDs are categorized by their measured brightness at 20mA.

Red (AlInGaP):

- R1: 450 - 600 mcd

- R2: 600 - 805 mcd

- R3: 805 - 1080 mcd

Green (InGaN):

- G1: 780 - 1045 mcd

- G2: 1045 - 1400 mcd

- G3: 1400 - 1875 mcd

Tolerance within each intensity bin is ±11%.

3.2 Wavelength (WD) Binning for Green

The Green LEDs are further sorted by their dominant wavelength to control hue variation.

- AP: 515 - 520 nm

- AQ: 520 - 525 nm

- AK: 525 - 530 nm

Tolerance for each wavelength bin is ±1 nm.

4. Mechanical and Package Information

4.1 Package Dimensions and Pin Assignment

The device uses a standard SMD footprint. Critical dimensions include body size and pad layout. All dimensional tolerances are ±0.2 mm unless otherwise specified. The pin assignment is as follows: Pins 1 and 2 are for the Green LED anode/cathode, and Pins 3 and 4 are for the Red LED anode/cathode. The specific anode/cathode assignment per pair should be verified from the detailed package drawing.

4.2 Recommended PCB Attachment Pad Layout

A land pattern design is provided to ensure proper solder joint formation during reflow soldering. Adhering to this recommended pad geometry is crucial for achieving good mechanical attachment, electrical connection, and thermal dissipation.

5. Soldering and Assembly Guidelines

5.1 IR Reflow Soldering Profile

The component is compatible with lead-free (Pb-free) soldering processes. A suggested reflow profile compliant with J-STD-020B is provided, typically including:

• Pre-heat: 150-200°C for a maximum of 120 seconds to gradually heat the board and activate flux.
• Peak Temperature: Maximum of 260°C. The time above liquidus (e.g., 217°C) should be controlled.
• Soldering Time at Peak: Maximum 10 seconds. Reflow should be performed a maximum of two times.

Note: The optimal profile depends on the specific PCB design, solder paste, and oven. The provided profile is a guideline based on JEDEC standards.

5.2 Hand Soldering (If Necessary)

If manual soldering is required, use a temperature-controlled soldering iron set to a maximum of 300°C. The contact time with the LED terminal should not exceed 3 seconds, and this should be done only once to prevent thermal damage to the plastic package and the semiconductor die.

5.3 Cleaning

Do not use unspecified or aggressive chemical cleaners. If cleaning after soldering is necessary, use alcohol-based solvents such as ethyl alcohol or isopropyl alcohol (IPA). Immerse the LED for less than one minute at normal room temperature. Ensure the cleaning agent is fully evaporated before applying power.

6. Storage and Handling Cautions

6.1 Storage Conditions

• Sealed Package (Moisture Barrier Bag): Store at ≤30°C and ≤70% Relative Humidity (RH). The shelf life is one year from the bag seal date.
• Opened Package: The ambient should not exceed 30°C and 60% RH. Components exposed to ambient air should be reflow-soldered within 168 hours (7 days).
• Extended Storage Out of Bag: For periods longer than 168 hours, store in a sealed container with desiccant or in a nitrogen desiccator. If exposed beyond this limit, a bake-out at approximately 60°C for at least 48 hours is recommended before assembly to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.2 Application Caution

This LED is intended for general-purpose electronic equipment. It is not designed or qualified for applications where failure could directly jeopardize life, health, or safety (e.g., aviation, medical life-support, critical transportation controls). For such high-reliability applications, consult the manufacturer for specifically qualified components.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The standard packaging is embossed carrier tape (8mm width) wound on a 7-inch (178mm) diameter reel. Key specifications include:

• 2000 pieces per full reel.
• Minimum order quantity for remnants is 500 pieces.
• Empty pockets in the tape are sealed with a cover tape.
• Packaging complies with ANSI/EIA-481 specifications.

8. Application Suggestions and Design Considerations

8.1 Current Limiting

Always operate the LED with a series current-limiting resistor or a constant-current driver. Never connect it directly to a voltage source. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet to ensure sufficient current under all conditions. For the Red LED at 20mA with a 5V supply: R = (5V - 2.5V) / 0.02A = 125Ω. A standard 120Ω or 150Ω resistor would be appropriate.

8.2 Thermal Management

While SMD LEDs are efficient, they still generate heat. Exceeding the maximum junction temperature degrades light output and lifespan. Ensure the PCB has adequate thermal relief, especially if operating near the maximum DC current or in high ambient temperatures. Avoid placing heat-generating components nearby.

8.3 ESD (Electrostatic Discharge) Precautions

LEDs are sensitive to electrostatic discharge. Handle them in an ESD-protected environment using grounded wrist straps and conductive work surfaces.

9. Typical Performance Curves Analysis

The datasheet includes graphical representations of key relationships, which are essential for design.

• Relative Luminous Intensity vs. Forward Current: Shows how brightness increases with current, typically in a sub-linear fashion. Operating above the recommended current yields diminishing returns and increases heat.
• Forward Voltage vs. Forward Current: Demonstrates the diode's exponential I-V characteristic. The voltage increases with current and decreases with rising temperature (negative temperature coefficient).
• Relative Luminous Intensity vs. Ambient Temperature: Illustrates the thermal quenching effect. Light output decreases as the ambient (and thus junction) temperature rises. This is more pronounced in AlInGaP (Red) LEDs than in InGaN (Green/Blue) LEDs.
• Spectral Distribution: Depicts the relative power output across wavelengths, showing the peak and half-width.

10. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive the Red and Green LEDs simultaneously at their maximum DC current?

A1: No. The Absolute Maximum Ratings are per chip. Driving both at 20mA (Red) and 20mA (Green) simultaneously means the total power dissipation in the package would be significant. You must consider the combined thermal load and ensure the local temperature does not exceed specifications. It is often advisable to drive them at lower currents or use multiplexing.

Q2: What is the difference between Peak Wavelength and Dominant Wavelength?

A2: Peak Wavelength (λ_P) is the physical wavelength where the spectral output is highest. Dominant Wavelength (λ_d) is a calculated value that corresponds to the perceived color on the CIE chart. For a monochromatic source, they are similar. For LEDs with some spectral width, λ_d is the more relevant parameter for color matching.

Q3: Why is the storage humidity requirement stricter after the bag is opened?

A3: The Moisture Barrier Bag (MBB) and desiccant protect components from ambient humidity. Once opened, the plastic LED package can absorb moisture. During the high-temperature reflow process, this trapped moisture can vaporize rapidly, causing internal delamination or cracking (\"popcorning\"), leading to failure.

11. Operating Principle Introduction

An LED 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, they release energy. In standard silicon diodes, this energy is released as heat. In LEDs made from direct bandgap semiconductor materials like AlInGaP (for Red/Amber) and InGaN (for Green/Blue/White), a significant portion of this energy is released as photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material used in the active region.