SMD LED Green GaP Datasheet - 3.2x2.8x1.9mm - 2.6V - 72mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a high-brightness, surface-mount green LED. The device is designed for general-purpose indicator and backlighting applications in consumer electronics, office equipment, and communication devices. Its primary advantages include compatibility with automated placement equipment, suitability for infrared and reflow soldering processes, and compliance with lead-free (RoHS) requirements. The standard EIA package ensures broad compatibility within the industry.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device's operational limits are defined at an ambient temperature (Ta) of 25°C. Exceeding these ratings may cause permanent damage.

• Power Dissipation (Pd): 72 mW. This is the maximum power the LED can safely dissipate as heat under continuous operation.
• Peak Forward Current (IFP): 80 mA. This is the maximum allowable current under pulsed conditions, specified at a 1/10 duty cycle and 0.1ms pulse width. It is significantly higher than the DC rating to accommodate brief, high-intensity flashes.
• DC Forward Current (IF): 30 mA. This is the maximum recommended continuous forward current for reliable long-term operation.
• Reverse Voltage (VR): 5 V. Applying a reverse voltage beyond this limit can damage the LED's semiconductor junction.
• Operating Temperature Range: -40°C to +85°C. The device is rated for reliable performance across this wide industrial temperature range.
• Storage Temperature Range: -40°C to +100°C.

2.2 Electrical & Optical Characteristics

Key performance parameters are measured at Ta=25°C and a standard test current of IF=20mA.

• Luminous Intensity (Iv): Ranges from a minimum of 7.1 mcd to a typical value of 45.0 mcd. The actual intensity is binned, as detailed in Section 3.
• Viewing Angle (2θ1/2): 120 degrees. This wide viewing angle indicates a diffuse lens type, suitable for applications requiring broad visibility.
• Peak Emission Wavelength (λP): 565 nm. This is the wavelength at which the spectral output is strongest.
• Dominant Wavelength (λd): 569 nm. This single wavelength, derived from the CIE chromaticity diagram, defines the perceived color (green) of the LED.
• Spectral Line Half-Width (Δλ): 30 nm. This parameter describes the spectral purity; a narrower width indicates a more monochromatic light source.
• Forward Voltage (VF): Typically 2.6V, with a range from 2.0V to 2.6V at 20mA. A tolerance of +/- 0.1V is noted for the typical value.
• Reverse Current (IR): Maximum of 10 µA when a reverse voltage of 5V is applied.

3. Binning System Explanation

To ensure consistency in brightness across production batches, the luminous intensity is categorized into bins. The bin code is part of the part number selection.

• Bin Code K: 7.1 mcd (Min) to 11.2 mcd (Max)
• Bin Code L: 11.2 mcd to 18.0 mcd
• Bin Code M: 18.0 mcd to 28.0 mcd
• Bin Code N: 28.0 mcd to 45.0 mcd

A tolerance of +/-15% applies to each intensity bin. Designers should select the appropriate bin based on the required brightness level for their application.

4. Performance Curve Analysis

The datasheet references typical performance curves which illustrate the relationship between key parameters. While the specific graphs are not reproduced in text, their implications are critical for design.

• I-V Curve: Shows the relationship between forward current (IF) and forward voltage (VF). It is non-linear, typical of a diode. The curve helps in selecting the appropriate current-limiting resistor.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically in a near-linear relationship within the operating range. Operating beyond the maximum current leads to diminished returns and increased heat.
• Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as junction temperature increases. This is crucial for thermal management in high-power or high-ambient-temperature applications.
• Spectral Distribution: A graph of relative intensity versus wavelength, centered around 565nm with a 30nm half-width, confirming the green color output.

5. Mechanical & Package Information

5.1 Device Dimensions

The LED conforms to a standard EIA SMD package. Key dimensions (in millimeters) include a body size of approximately 3.2mm (length) x 2.8mm (width) x 1.9mm (height). Tolerances are typically ±0.2mm unless otherwise specified. Detailed dimensional drawings should be consulted for precise PCB footprint design.

5.2 Recommended PCB Pad Design

A land pattern recommendation is provided for infrared or vapor phase reflow soldering. Adhering to this recommended footprint is essential for achieving reliable solder joints, proper self-alignment during reflow, and effective heat dissipation. The design typically includes thermal relief patterns to manage soldering temperature.

5.3 Polarity Identification

The cathode is typically marked on the device, often with a notch, a green dot, or a truncated corner on the lens or package. The datasheet diagram must be consulted to confirm the exact marking scheme for correct orientation during assembly.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

The device is compatible with lead-free (Pb-free) reflow soldering processes. A suggested profile compliant with J-STD-020B is referenced. Key parameters include:

• Pre-heat Temperature: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Recommended duration as per solder paste specifications.
• Ramp Rates: Controlled to prevent thermal shock.

It is critical to note that the optimal profile depends on the specific PCB design, solder paste, and oven. Component-level and board-level verification is recommended.

6.2 Hand Soldering

If manual soldering is necessary, use a soldering iron with a temperature not exceeding 300°C. The contact time should be limited to a maximum of 3 seconds per joint, and it should be performed only once to avoid damaging the plastic package or the internal wire bonds.

6.3 Cleaning

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

6.4 Storage & Moisture Sensitivity

The LEDs are moisture-sensitive. When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤ 30°C and ≤ 70% RH and used within one year. Once the bag is opened, the storage environment should not exceed 30°C and 60% RH. Components exposed to ambient air for more than 168 hours should be baked at approximately 60°C for at least 48 hours before reflow soldering to prevent "popcorning" (package cracking due to vapor pressure).

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The device is supplied in 8mm carrier tape on 7-inch (178mm) diameter reels, compatible with standard automated pick-and-place equipment.

• Pieces per Reel: 2000.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Cover Tape: Empty pockets are sealed with top cover tape.
• Missing Components: A maximum of two consecutive missing lamps is allowed per specification (EIA-481-1-B).

7.2 Part Number Structure

The part number LTST-M670GKT encodes key attributes:

• LTST: Likely denotes the product family or series.
• M670: May refer to the specific chip/die type or optical design.
• G: Indicates the lens color (Water Clear).
• K: Represents the luminous intensity bin code (e.g., K bin: 7.1-11.2 mcd).
• T: Likely indicates tape and reel packaging.

Selecting the correct suffix (bin code) is essential for obtaining the desired brightness level.

8. Application Recommendations

8.1 Typical Application Scenarios

This LED is suitable for a wide range of applications requiring a bright, reliable green indicator, including:

• Status indicators on consumer electronics (routers, modems, audio equipment).
• Backlighting for membrane switches and panels.
• Illumination for instrumentation and control panels.
• General-purpose signage and decorative lighting where a wide viewing angle is beneficial.

8.2 Drive Circuit Design

LEDs are current-driven devices. For consistent brightness, especially when driving multiple LEDs in parallel, it is strongly recommended to use a series current-limiting resistor for each LED (Circuit Model A). Driving LEDs in parallel directly from a voltage source (Circuit Model B) is not recommended, as slight variations in the forward voltage (VF) characteristic between individual LEDs will cause significant imbalance in current sharing and, consequently, uneven brightness. The series resistor value can be calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use max value for reliability), and IF is the desired forward current.

8.3 Thermal Management

While the power dissipation is relatively low (72mW max), proper thermal design extends lifespan and maintains stable light output. Ensure the PCB pad design provides adequate thermal relief. Avoid operating the LED at or near its absolute maximum current and temperature ratings for prolonged periods.

8.4 ESD (Electrostatic Discharge) Precautions

Like most semiconductor devices, LEDs are sensitive to electrostatic discharge. Standard ESD handling procedures should be followed during assembly and handling, including the use of grounded workstations, wrist straps, and conductive containers.

9. Technical Comparison & Differentiation

Compared to older through-hole LED technologies, this SMD device offers significant advantages:

• Size & Profile: The compact 3.2x2.8mm footprint and low profile (1.9mm) enable miniaturization of end products.
• Manufacturability: Full compatibility with high-speed, automated SMT assembly lines reduces production cost and increases reliability over manual insertion.
• Optical Performance: The combination of high brightness (up to 45 mcd) and a wide 120-degree viewing angle provides excellent visibility.
• Reliability: The package is designed for robust infrared/reflow soldering processes and offers a wide operating temperature range (-40°C to +85°C).

The use of GaP (Gallium Phosphide) on GaP substrate technology is a mature and reliable process for producing green LEDs with stable color and performance.

10. Frequently Asked Questions (FAQ)

Q1: What is the difference between Peak Wavelength (λP) and Dominant Wavelength (λd)?
A1: Peak Wavelength (565 nm) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (569 nm) is a calculated value from colorimetry that represents the single wavelength of the perceived color. For monochromatic sources like this green LED, they are typically close.

Q2: Can I drive this LED at 30mA continuously?
A2: Yes, 30mA is the maximum rated DC forward current. For maximum reliability and longevity, it is often advisable to operate slightly below this maximum, for example, at 20mA (the standard test condition), which also provides ample brightness for most indicator applications.

Q3: Why is a series resistor necessary even if my power supply is current-limited?
A3: A dedicated series resistor provides a simple, cost-effective, and robust method of setting the current. It also helps absorb minor variations in supply voltage and LED forward voltage, ensuring stable operation. It is considered a best practice for most general-purpose LED circuits.

Q4: How critical is the 168-hour floor life after opening the moisture barrier bag?
A4: It is very important for process reliability. Exceeding this time without baking increases the risk of moisture-induced package damage during the high-temperature reflow soldering process, which can lead to immediate failure or reduced long-term reliability.

11. Design-in Case Study

Scenario: Designing a status indicator panel for a network switch with 24 identical green port activity LEDs.
Design Steps:

1. Brightness Selection: For indoor equipment viewing distance of 1-2 meters, a mid-range brightness is sufficient. Select Bin Code L (11.2-18.0 mcd) from the ordering information.
2. Drive Circuit: The system uses a 3.3V rail. Using the maximum VF of 2.6V and a target IF of 20mA, calculate the series resistor: R = (3.3V - 2.6V) / 0.020A = 35 Ohms. The nearest standard value of 33 Ohms or 39 Ohms would be chosen, slightly adjusting the current.
3. PCB Layout: Use the recommended pad layout from the datasheet. Route the 3.3V and GND traces to all 24 LEDs. Place the current-limiting resistor close to the anode of each LED.
4. Thermal Consideration: With 24 LEDs at ~20mA each, total power is low (~1.5W). No special heatsinking is required, but ensure general airflow in the enclosure.
5. Assembly: Follow the recommended reflow profile. After opening the reel, plan to complete the SMT assembly for all boards within the 168-hour window or implement a baking schedule.

This approach ensures uniform brightness, reliable soldering, and long-term performance.

12. Technology Principle Introduction

This LED is based on Gallium Phosphide (GaP) semiconductor material. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. In GaP, this recombination process releases energy in the form of photons (light) with a wavelength corresponding to the bandgap energy of the material, which for this specific composition results in green light (~565-569 nm). The "Water Clear" lens is made of epoxy and is designed to diffuse the light, creating the wide 120-degree viewing angle. The SMD package encapsulates the semiconductor die, wire bonds, and lead frame, providing mechanical protection and thermal/electrical connections.

13. Industry Trends & Developments

The optoelectronics industry continues to evolve. While this GaP-based green LED represents a mature and highly reliable technology, trends include:

• Increased Efficiency: Ongoing development of materials (like InGaN for broader color ranges) and chip designs to achieve higher lumens per watt (lm/W), reducing power consumption for a given light output.
• Miniaturization: Development of even smaller package footprints (e.g., 0201, 01005) for space-constrained applications like wearable devices and ultra-compact consumer electronics.
• Integrated Solutions: Growth of LEDs with built-in drivers (constant-current ICs), protection diodes (for ESD/reverse voltage), or multiple colors (RGB) in a single package, simplifying circuit design.
• High-Reliability Demands: Expansion of applications in automotive, industrial, and medical fields drives requirements for extended temperature ranges, higher vibration resistance, and longer operational lifetimes (often rated at L70 or L90, meaning time to 70% or 90% of initial luminance).

The device described in this datasheet sits firmly in the established, high-volume segment of the market, prized for its proven performance, cost-effectiveness, and ease of integration.