SMD LED LTST-108TGKT Datasheet - Water Clear Lens - InGaN Green - 2.8-3.8V - 80mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-108TGKT, a surface-mount device (SMD) light-emitting diode (LED). This component is designed for automated printed circuit board (PCB) assembly processes and is suitable for applications where space is a critical constraint. The LED features a water-clear lens and utilizes an Indium Gallium Nitride (InGaN) semiconductor material to produce green light.

The primary design goals for this LED series include miniaturization, compatibility with high-volume pick-and-place equipment, and reliability through standard infrared (IR) reflow soldering processes. These characteristics make it a versatile component for modern electronics manufacturing.

1.1 Features

• Compliant with Restriction of Hazardous Substances (RoHS) directives.
• Packaged in 8mm tape on 7-inch diameter reels for automated handling.
• Standardized package outline compliant with Electronic Industries Alliance (EIA) specifications.
• Input/output characteristics are compatible with standard integrated circuit (IC) logic levels.
• Designed for compatibility with automatic component placement machinery.
• Suitable for infrared reflow soldering processes commonly used in surface-mount technology (SMT).
• Preconditioned to accelerate to Joint Electron Device Engineering Council (JEDEC) moisture sensitivity level 3.

1.2 Applications

This LED is intended for use in a broad spectrum of electronic equipment. Typical application areas include:

• Telecommunication Equipment: Status indicators on routers, modems, and network switches.
• Office Automation: Panel lights on printers, scanners, and multifunction devices.
• Consumer Appliances: Power and function indicators on various home electronics.
• Industrial Equipment: Machine status and fault indication panels.
• Status Indication: General-purpose power-on, standby, or activity lights.
• Signal and Symbol Luminary: Backlighting for icons or symbols on control panels.
• Front Panel Backlighting: Illumination for buttons or keypads.

2. Package Dimensions

The mechanical outline of the LTST-108TGKT follows a standard SMD LED footprint. All critical dimensions are provided in the official datasheet drawings. Key notes regarding dimensions include:

• All linear dimensions are specified in millimeters (mm).
• The standard tolerance for unspecified dimensions is ±0.1 mm (which is approximately ±0.004 inches).

Part Number Identification:
Lens Color: Water Clear
Light Source Color: InGaN Green

3. Ratings and Characteristics

This section defines the operational limits and performance parameters under specified test conditions. Exceeding the absolute maximum ratings may cause permanent damage to the device.

3.1 Absolute Maximum Ratings

Ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 80 mW - The maximum total power the device can dissipate.
• Peak Forward Current (I_F(peak)): 100 mA - Maximum allowable current under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current (I_F): 20 mA - The recommended maximum continuous DC operating current.
• Operating Temperature Range (T_opr): -40°C to +85°C - The ambient temperature range for normal operation.
• Storage Temperature Range (T_stg): -40°C to +100°C - The safe temperature range for the device when not powered.

3.2 Suggested IR Reflow Profile

For lead-free (Pb-free) soldering processes, a reflow profile compliant with the J-STD-020B standard is recommended. The profile typically includes a pre-heat zone, a thermal soak zone, a reflow zone with a peak temperature, and a cooling zone. The critical parameters are:

• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus (TAL): Typically recommended to be within specified limits (e.g., 30-90 seconds).
• Ramp Rates: Controlled heating and cooling rates to prevent thermal shock.

It is crucial to note that the optimal profile depends on the specific PCB design, solder paste, and oven characteristics. The provided profile serves as a generic guideline based on JEDEC standards.

3.3 Electrical and Optical Characteristics

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

• Luminous Intensity (I_V): 355 - 900 millicandelas (mcd). Measured using a detector filtered to match the CIE standard photopic eye-response curve.
• Viewing Angle (2θ_1/2): 110 degrees (typical). Defined as the full angle at which the luminous intensity drops to half of its axial (on-axis) value.
• Peak Emission Wavelength (λ_p): 518 nm (typical). The wavelength at which the optical output power is greatest.
• Dominant Wavelength (λ_d): 520 - 535 nm. The single wavelength perceived by the human eye that defines the color. Tolerance is ±1 nm.
• Spectral Line Half-Width (Δλ): 35 nm (typical). The width of the emission spectrum at half of its maximum intensity.
• Forward Voltage (V_F): 2.8 - 3.8 Volts. The voltage drop across the LED when conducting 20mA. Tolerance is ±0.1V.
• Reverse Current (I_R): 10 μA (maximum) at a Reverse Voltage (V_R) of 5V. Important: This device is not designed for operation under reverse bias; this parameter is for informational/testing purposes only.

4. Bin Ranking System

To ensure consistency in production, LEDs are sorted (binned) according to key parameters. This allows designers to select components that meet specific performance criteria for their application.

4.1 Forward Voltage (V_F) Rank

Binned at I_F = 20mA. Tolerance within each bin is ±0.10V.

• D7: 2.8V (Min) - 3.0V (Max)
• D8: 3.0V - 3.2V
• D9: 3.2V - 3.4V
• D10: 3.4V - 3.6V
• D11: 3.6V - 3.8V

4.2 Luminous Intensity (I_V) Rank

Binned at I_F = 20mA. Tolerance within each bin is ±11%.

• T2: 355.0 mcd (Min) - 450.0 mcd (Max)
• U1: 450.0 mcd - 560.0 mcd
• U2: 560.0 mcd - 710.0 mcd
• V1: 710.0 mcd - 900.0 mcd

4.3 Dominant Wavelength (WD) Rank

Binned at I_F = 20mA. Tolerance within each bin is ±1 nm.

• AP: 520.0 nm (Min) - 525.0 nm (Max)
• AQ: 525.0 nm - 530.0 nm
• AR: 530.0 nm - 535.0 nm

5. Typical Performance Curves

The datasheet includes graphical representations of key characteristics, typically plotted against forward current or ambient temperature. These curves provide insight into device behavior under non-standard conditions. Common curves include:

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, often becoming sub-linear at higher currents due to heating.
• Forward Voltage vs. Forward Current: Demonstrates the diode's I-V characteristic.
• Relative Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as junction temperature rises.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the shape and width of the emitted light spectrum.

These curves are essential for designing drive circuits and thermal management systems to achieve consistent performance.

6. User Guide and Handling

6.1 Cleaning

If cleaning after soldering is necessary, use only approved solvents. Immerse the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute. Do not use unspecified chemical cleaners as they may damage the epoxy lens or package.

6.2 Recommended PCB Pad Layout

A recommended land pattern (footprint) for the PCB is provided to ensure proper soldering and mechanical stability. This includes the size and shape of the copper pads for the anode and cathode, as well as the recommended solder mask opening. Adhering to this layout helps achieve reliable solder joints during reflow.

6.3 Tape and Reel Packaging

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178mm) diameter reels. Standard packaging contains 4000 pieces per reel. Key packaging notes:

• Empty pockets in the tape are sealed with the cover tape.
• A minimum order quantity of 500 pieces is available for remnants.
• A maximum of two consecutive missing components is allowed per reel specification.
• Packaging complies with ANSI/EIA-481 standards.

7. Important Cautions and Usage Notes

7.1 Intended Application

These LEDs are designed for use in standard commercial and industrial electronic equipment. They are not rated or intended for safety-critical applications where failure could lead to direct risk to life or health, such as in aviation, medical life-support, or transportation control systems. For such applications, components with appropriate reliability certifications must be used.

7.2 Storage Conditions

Proper storage is critical to prevent moisture absorption, which can cause \"popcorning\" (package cracking) during reflow soldering.

• Sealed Package: Store at ≤30°C and ≤70% Relative Humidity (RH). The shelf life is one year when the moisture barrier bag with desiccant is intact.
• Opened Package: For components removed from their sealed bag, the storage environment must not exceed 30°C and 60% RH.
• Floor Life: It is recommended to complete the IR reflow process within 168 hours (7 days) after opening the moisture-proof bag.
• Extended Storage/Baking: If components are exposed beyond 168 hours, they must be baked at approximately 60°C for at least 48 hours prior to soldering to remove absorbed moisture.

7.3 Soldering Instructions

Detailed soldering parameters are provided to ensure reliability:

Reflow Soldering (Recommended):

• Pre-heat Temperature: 150-200°C
• Pre-heat Time: Maximum 120 seconds
• Peak Body Temperature: Maximum 260°C
• Time at Peak/Soldering Time: Maximum 10 seconds (maximum of two reflow cycles allowed)

Hand Soldering (Soldering Iron):

• Iron Tip Temperature: Maximum 300°C
• Contact Time: Maximum 3 seconds per solder joint (one-time soldering only).

7.4 Drive Method Principle

An LED is a current-controlled device. Its light output (luminous intensity) is primarily a function of the forward current (I_F) passing through it, not the voltage. Therefore, to ensure consistent brightness, especially when multiple LEDs are used in parallel, each LED should be driven by a controlled current source or have its own current-limiting resistor. Driving LEDs in parallel directly from a voltage source is not recommended due to variations in forward voltage (V_F) from device to device, which can lead to significant differences in current and thus brightness.

8. Design Considerations and Application Notes

8.1 Thermal Management

While the power dissipation is relatively low (80mW max), effective thermal management is still important for longevity and stable performance. The forward voltage and luminous intensity are temperature-dependent. Designing the PCB with adequate thermal relief, using a ground plane, and avoiding placement near other heat-generating components can help maintain a lower junction temperature.

8.2 Current Limiting Resistor Calculation

When using a simple voltage source and series resistor to drive the LED, the resistor value (R_s) can be calculated using Ohm's Law: R_s = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet (3.8V) to ensure the current does not exceed 20mA even with a low V_F device. For example, with a 5V supply: R_s = (5V - 3.8V) / 0.020A = 60 Ohms. A standard 62-ohm resistor would be a safe choice. The power rating of the resistor should be at least P = I_F² * R_s.

8.3 Optical Design

The 110-degree viewing angle provides a wide, diffuse light pattern suitable for status indicators meant to be seen from various angles. For applications requiring a more focused beam, secondary optics (such as lenses or light pipes) would be necessary. The water-clear lens is optimal for achieving the true color of the InGaN chip without tinting.

9. Comparison and Selection Guidance

The LTST-108TGKT sits in a category of standard, mid-brightness green SMD LEDs. Its key differentiators are its specific binning structure for color and intensity, its compliance with automated assembly processes, and its detailed handling and soldering specifications. When selecting an LED, engineers should compare:

• Wavelength/Color: Ensure the dominant wavelength bin (AP, AQ, AR) meets the color requirements of the application.
• Brightness: Select the appropriate luminous intensity bin (T2, U1, U2, V1) for the required visibility.
• Viewing Angle: A 110-degree angle is standard for wide viewing. Narrower angles provide more focused light.
• Forward Voltage: The V_F bin impacts the design of the driving circuit and power consumption.

This component is a robust, general-purpose choice where reliable performance and manufacturability are prioritized over ultra-high brightness or specialized optical characteristics.