SMD LED LTST-C250TGKT Datasheet - Water Clear Lens - InGaN Green - 2.8-3.6V - 76mW - English Technical Document

1. Product Overview

The LTST-C250TGKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It features a miniature form factor suitable for space-constrained applications. The device utilizes an ultra-bright InGaN (Indium Gallium Nitride) chip to produce green light and is housed in a water-clear lens package. This LED is engineered for compatibility with high-volume, automated manufacturing processes including infrared reflow soldering.

1.1 Core Advantages

• RoHS Compliance: Manufactured to meet Restriction of Hazardous Substances directives.
• High Brightness: Features an ultra-bright InGaN semiconductor chip for excellent luminous output.
• Manufacturing Friendly: Packaged in 8mm tape on 7-inch reels, compatible with automatic pick-and-place equipment.
• Process Compatibility: Suitable for infrared (IR) reflow soldering processes, aligning with modern Pb-free assembly requirements.
• Reverse Mount Design: The chip configuration allows for mounting where light emission is desired from the side opposite the component placement.

1.2 Target Markets and Applications

This LED is versatile and targets a broad range of electronic equipment. Primary application areas include:

• Telecommunications: Status indicators in cordless phones, cellular phones, and network system equipment.
• Computing: Backlighting for keypads and keyboards in notebook computers.
• Consumer & Industrial Electronics: Indicators in home appliances, office automation equipment, and industrial control panels.
• Display & Signage: Micro-displays and indoor signage or symbol illumination.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. All values are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 76 mW. This is the maximum power the LED can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) and must not be used for continuous operation.
• Continuous Forward Current (I_F): 20 mA. This is the recommended DC operating current for reliable long-term performance.
• Operating Temperature Range: -20°C to +80°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -30°C to +100°C.
• Infrared Reflow Soldering Condition: Withstands a peak temperature of 260°C for a maximum of 10 seconds, which is standard for Pb-free solder processes.

2.2 Electro-Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and I_F=20mA, unless otherwise noted.

• Luminous Intensity (I_V): Ranges from a minimum of 71.0 mcd to a maximum of 450.0 mcd. The actual value is binned (see Section 3). Measurement follows the CIE eye-response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This wide viewing angle indicates a diffuse light pattern, suitable for area illumination or indicators requiring broad visibility.
• Peak Emission Wavelength (λ_P): Typically 525.0 nm. This is the wavelength at which the spectral output is strongest.
• Dominant Wavelength (λ_d): Ranges from 520.0 nm to 535.0 nm. This parameter, derived from the CIE chromaticity diagram, defines the perceived color of the light and is also binned.
• Spectral Line Half-Width (Δλ): Typically 17 nm. This indicates the spectral purity of the green light; a smaller value would indicate a more monochromatic source.
• Forward Voltage (V_F): Ranges from 2.8 V to 3.6 V at 20mA. The exact value is binned. This parameter is critical for designing the current-limiting circuitry.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage (V_R) of 5V. Important: This LED is not designed for reverse-bias operation; this test condition is for informational purposes only.

3. Bin Ranking System

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

3.1 Forward Voltage (V_F) Rank

Binning ensures LEDs have similar electrical characteristics, simplifying driver design. Tolerance on each bin is ±0.1V.

• D7: 2.8V - 3.0V
• D8: 3.0V - 3.2V
• D9: 3.2V - 3.4V
• D10: 3.4V - 3.6V

3.2 Luminous Intensity (I_V) Rank

This binning groups LEDs by brightness output. Tolerance on each bin is ±15%.

• Q: 71.0 mcd - 112.0 mcd
• R: 112.0 mcd - 180.0 mcd
• S: 180.0 mcd - 280.0 mcd
• T: 280.0 mcd - 450.0 mcd

3.3 Hue / Dominant Wavelength (λ_d) Rank

This ensures color consistency across multiple LEDs in an assembly. Tolerance for each bin is ±1 nm.

• AP: 520.0 nm - 525.0 nm
• AQ: 525.0 nm - 530.0 nm
• AR: 530.0 nm - 535.0 nm

4. Performance Curve Analysis

While specific graphs are not detailed in the provided text, typical curves for this type of LED would include:

• Forward Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship. Operating at the recommended 20mA ensures stable performance within the specified V_F range.
• Luminous Intensity vs. Forward Current: Intensity generally increases with current but may saturate or degrade at higher currents beyond specification.
• Luminous Intensity vs. Ambient Temperature: Light output typically decreases as junction temperature rises. Proper thermal management is essential for maintaining brightness.
• Spectral Distribution: A plot showing light intensity across wavelengths, peaking around 525nm with a ~17nm half-width.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The LED conforms to EIA standard package dimensions. All dimensions are in millimeters with a standard tolerance of ±0.1mm unless otherwise specified. The package features a water-clear lens.

5.2 Recommended PCB Attachment Pad Layout

A suggested land pattern is provided to ensure reliable soldering and proper alignment during reflow. Following this guideline helps prevent tombstoning and ensures good solder joint formation.

5.3 Polarity Identification

As a reverse mount chip LED, careful attention must be paid to the anode and cathode markings on the package or tape to ensure correct orientation on the PCB.

6. Assembly and Handling Guidelines

6.1 Soldering Process

Infrared Reflow Soldering (Pb-Free Process Recommended):

• Pre-heat Temperature: 150°C - 200°C
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Maximum 10 seconds. The device can withstand a maximum of two reflow cycles under these conditions.

Hand Soldering (If Necessary):

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per pad. Limit to one soldering cycle only.

Note: Profile must be characterized for the specific PCB design, components, and solder paste used.

6.2 Cleaning

If cleaning is required after soldering, only use specified solvents to avoid damaging the epoxy lens. Recommended methods include:

• Immersion in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute.
• Avoid ultrasonic cleaning unless verified to be safe for the package.

6.3 Storage and Moisture Sensitivity

The LEDs are moisture-sensitive (MSL 3).

• Sealed Package: Store at ≤30°C and ≤90% RH. Use within one year of the pack date.
• Opened Package: Store at ≤30°C and ≤60% RH. Use within one week. For longer storage out of the original bag, store in a sealed container with desiccant or in a nitrogen atmosphere.
• Rebaking: If exposed for more than one week, bake at approximately 60°C for at least 20 hours before reflow soldering.

6.4 Electrostatic Discharge (ESD) Precautions

LEDs are susceptible to damage from static electricity. Always handle with ESD precautions:

• Use wrist straps or anti-static gloves.
• Ensure all workstations and equipment are properly grounded.

7. Packaging and Ordering

7.1 Tape and Reel Specifications

The standard packaging is compliant with ANSI/EIA-481.

• Reel Size: 7 inches (178 mm) in diameter.
• Tape Width: 8 mm.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Pocket Coverage: Empty pockets are sealed with cover tape.
• Missing Components: A maximum of two consecutive missing LEDs is allowed per specification.

8. Application Notes and Design Considerations

8.1 Current Limiting

Always operate the LED with a series current-limiting resistor or a constant-current driver. The resistor value can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F from the bin or datasheet to ensure the current does not exceed 20mA under worst-case conditions.

8.2 Thermal Management

While power dissipation is low (76mW), maintaining a low junction temperature is key to long-term reliability and stable light output. Ensure the PCB has adequate thermal relief, especially if multiple LEDs are used or if the ambient temperature is high.

8.3 Optical Design

The 130-degree viewing angle provides a wide, diffuse beam. For focused light, secondary optics (lenses, light guides) will be required. The water-clear lens is optimal for applications where the LED chip itself should not be visibly colored when off.

9. Technical Comparison and Differentiation

The LTST-C250TGKT differentiates itself through several key features:

• Reverse Mount Capability: Unlike standard top-emitting LEDs, this design allows for innovative PCB layouts where light is emitted from the opposite side of the board, useful in backlighting applications.
• InGaN Technology: Offers higher efficiency and brighter output compared to older technologies like AlGaInP for green wavelengths.
• Wide Viewing Angle: The 130-degree angle is broader than many indicator-type LEDs, making it suitable for area illumination.
• Comprehensive Binning: Three-parameter binning (V_F, I_V, λ_d) provides designers with high consistency for color-critical and brightness-matched applications.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive this LED with a 5V supply without a resistor?

No. This is a common cause of immediate failure. The forward voltage is only ~3.2V. Applying 5V directly would cause excessive current to flow, destroying the LED. A current-limiting resistor or regulator is mandatory.

10.2 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λ_P): The single wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d): The single wavelength of monochromatic light that would appear to have the same color as the LED's output to the human eye. λ_d is more relevant for color specification.

10.3 How do I interpret the bin codes when ordering?

Specify the required bin codes for V_F (e.g., D8), I_V (e.g., R), and λ_d (e.g., AQ) to ensure you receive LEDs with the desired electrical and optical characteristics for your application. If not specified, you may receive a mix from production.

11. Practical Use Case Example

Scenario: Designing a status indicator panel for a network router.

1. Requirement: Multiple green LEDs to show link activity and power status. Uniform brightness and color are important for aesthetics.
2. Design Choice: Select the LTST-C250TGKT for its brightness, wide viewing angle (visible from various angles), and available binning.
3. Implementation:
   • Order LEDs from a single production lot or specify tight bins (e.g., I_V Rank S, λ_d Rank AQ).
   • Design PCB with the recommended pad layout.
   • Use a 3.3V rail. Calculate resistor: R = (3.3V - 3.2V_max) / 0.020A = 5Ω. Use a 5.1Ω or 5.6Ω standard resistor.
   • Follow the IR reflow profile during assembly.
4. Result: A panel with consistent, bright green indicators that are reliably soldered and have a long operational life.

12. Technology Introduction

The LED is based on InGaN (Indium Gallium Nitride) semiconductor technology. InGaN materials are capable of emitting light in the blue, green, and ultraviolet parts of the spectrum. By adjusting the ratio of indium to gallium, the bandgap of the material is tuned, which directly determines the wavelength (color) of the emitted light. The \"water clear\" lens is made of epoxy or silicone that is transparent across the visible spectrum, allowing the true color of the chip's emission to be seen without tinting.

13. Industry Trends

The market for SMD LEDs like the LTST-C250TGKT continues to be driven by several key trends:

• Miniaturization: Demand for smaller components in portable and wearable devices.
• Increased Efficiency: Ongoing development of semiconductor materials and package designs to achieve higher luminous efficacy (more light output per watt of electrical input).
• Automation Compatibility: Components are increasingly designed from the ground up for compatibility with high-speed, precision automated assembly lines.
• Color Consistency and Binning: As LEDs are used in more demanding applications (e.g., large video walls, automotive lighting), tighter binning and better color uniformity are becoming standard requirements.
• Reliability and Lifetime: Focus on improving thermal management within the package to enhance longevity and maintain light output over tens of thousands of hours.