SMD LED LTST-108TWET Datasheet - Yellow Lens, InGaN Blue Source - 3.2V, 102mW, 1500-2900mcd - English Technical Document

1. Product Overview

The LTST-108TWET is a high-brightness, surface-mount LED designed for automated assembly processes and space-constrained applications. It features a yellow lens with an InGaN (Indium Gallium Nitride) blue light source, producing a vibrant yellow output. This component is engineered for reliability and compatibility with modern manufacturing techniques, making it suitable for a broad spectrum of electronic devices.

1.1 Core Advantages

• Compliance: Meets RoHS (Restriction of Hazardous Substances) directives.
• Manufacturing Friendly: Packaged in 8mm tape on 7-inch reels, compatible with EIA standard packages and automatic placement equipment.
• Process Compatibility: Fully compatible with infrared (IR) reflow soldering processes, essential for lead-free (Pb-free) assembly lines.
• Reliability: Preconditioned to accelerate to JEDEC Level 3 moisture sensitivity levels, ensuring robustness against humidity during storage and assembly.

1.2 Target Markets

This LED is ideal for applications requiring compact, reliable status indicators and backlighting. Primary markets include telecommunications equipment (cordless/cellular phones), office automation (notebook computers), network systems, home appliances, and indoor signage or symbol illumination.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed breakdown of the LED's electrical, optical, and environmental specifications.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation should always be maintained within these boundaries.

• Power Dissipation (Pd): 102 mW. This is the maximum power the LED package can safely dissipate as heat.
• Peak Forward Current (I_F(PEAK)): 100 mA. This is the maximum pulsed current (1/10 duty cycle, 0.1ms pulse width) the LED can handle.
• Continuous Forward Current (I_F): 30 mA DC. The recommended maximum current for continuous operation.
• Operating Temperature Range (T_opr): -40°C to +85°C. The ambient temperature range for reliable operation.
• Storage Temperature Range (T_stg): -40°C to +100°C. The safe temperature range for the device when not powered.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at an ambient temperature (T_a) of 25°C under specified test conditions.

• Luminous Intensity (I_V): 1500 - 2900 mcd (millicandela) at I_F = 20mA. This indicates a high brightness level suitable for indicator applications.
• Viewing Angle (2θ_1/2): 110 degrees (typical). This wide viewing angle ensures the light is visible from a broad range of positions relative to the LED's axis.
• Chromaticity Coordinates (x, y): (0.3100, 0.3100) typical. These CIE coordinates define the precise yellow color point on the chromaticity diagram.
• Forward Voltage (V_F): 2.8V (Min) to 3.4V (Max) at I_F = 20mA. The voltage drop across the LED when conducting current. Tolerance is ±0.1V per bin.
• Reverse Current (I_R): 10 µA (Max) at V_R = 5V. The device is not designed for reverse bias operation; this parameter is for IR test purposes only.

3. Bin Ranking System Explanation

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

3.1 Forward Voltage (V_F) Binning

LEDs are categorized by their forward voltage at 20mA.

- Bin D8: V_F = 2.8V to 3.1V.

- Bin D9: V_F = 3.1V to 3.4V.

Tolerance within each bin is ±0.1V.

3.2 Luminous Intensity (I_V) Binning

LEDs are sorted by their light output at 20mA.

- Bin X1: I_V = 1500.0 mcd to 2100.0 mcd.

- Bin X2: I_V = 2100.0 mcd to 2900.0 mcd.

Tolerance on each intensity bin is ±11%.

3.3 Color (Chromaticity) Binning

LEDs are grouped based on their chromaticity coordinates (x, y) to guarantee a uniform yellow hue. The datasheet provides a detailed color bin table with specific coordinate boundaries for bins labeled Z1, Y1, Y2, X1, W1, and W2. The tolerance for each hue bin is ±0.01 in both x and y coordinates. A chromaticity coordinate diagram is typically referenced to visualize these bins on the CIE chart.

4. Performance Curve Analysis

While specific graphs are not reproduced in text, the datasheet includes typical characteristic curves. These are crucial for design engineers.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

This curve shows the relationship between the current flowing through the LED and the voltage across it. It is non-linear, with a characteristic \"knee\" voltage (around the typical V_F) above which current increases rapidly with small voltage increases. This highlights the importance of current-limiting circuitry (like a series resistor or constant current driver).

4.2 Luminous Intensity vs. Forward Current

This graph illustrates how light output (I_V) changes with drive current (I_F). Generally, intensity increases with current but may not be perfectly linear, especially at higher currents where efficiency can drop and heat generation rises.

4.3 Luminous Intensity vs. Ambient Temperature

This curve demonstrates the effect of ambient temperature on light output. Typically, luminous intensity decreases as the ambient temperature increases. Understanding this derating is vital for applications operating at high temperatures to ensure sufficient brightness is maintained.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED comes in a standard surface-mount package. All dimensions are in millimeters with a general tolerance of ±0.2mm unless otherwise specified. The drawing would typically show the length, width, height, and the placement/size of the solder pads and cathode/anode markings.

5.2 Polarity Identification

The cathode is typically indicated by a visual marker on the package, such as a notch, a dot, or a green marking. Correct polarity must be observed during PCB assembly.

5.3 Recommended PCB Pad Layout

A suggested land pattern (footprint) for the PCB is provided to ensure proper solder joint formation and mechanical stability during infrared or vapor phase reflow soldering. Adhering to this layout helps prevent tombstoning and ensures good thermal and electrical connection.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile (Pb-Free)

The datasheet recommends a reflow profile compliant with J-STD-020B for lead-free processes. Key parameters include:

- 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.

- Time Above Liquidus: Typically defined to ensure proper solder melting and wetting.

- Total Soldering Time: Maximum 10 seconds at peak temperature, with a maximum of two reflow cycles allowed.

6.2 Hand Soldering

If hand soldering is necessary:

- Iron Temperature: Maximum 300°C.

- Soldering Time: Maximum 3 seconds per joint.

- Frequency: Only one soldering cycle is permitted for hand soldering.

6.3 Storage Conditions

Sealed Package: Store at ≤30°C and ≤70% RH. Use within one year of opening the moisture barrier bag.

Opened Package: For components removed from their dry packaging, the storage ambient should not exceed 30°C and 60% RH. It is strongly recommended to complete IR reflow soldering within 168 hours (7 days) of exposure to ambient air (JEDEC Level 3). For longer exposure, a 48-hour bake at approximately 60°C is required before assembly to remove absorbed moisture and prevent \"popcorning\" damage during reflow.

6.4 Cleaning

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

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178mm) diameter reels. Standard reel quantity is 4000 pieces. A minimum packing quantity of 500 pieces is available for remainder orders. The packaging conforms to ANSI/EIA-481 specifications.

7.2 Reel Dimensions

Detailed mechanical drawings for the reel, including hub diameter, flange diameter, and overall width, are provided to ensure compatibility with automated pick-and-place equipment.

8. Application Notes & Design Considerations

8.1 Typical Application Circuits

The LED must be driven with a current-limiting device. The simplest method is a series resistor. 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 (3.4V) to ensure sufficient current at the lower end of the V_F bin. For example, with a 5V supply and target I_F of 20mA: R_s = (5V - 3.4V) / 0.020A = 80 Ohms. A standard 82 Ohm resistor would be suitable. For precision or varying supply voltages, a constant current driver is recommended.

8.2 Thermal Management

Although power dissipation is relatively low (102mW max), proper thermal design extends LED life. Ensure the PCB pad design follows recommendations to act as a heat sink. Avoid operating at the absolute maximum current and temperature limits for extended periods. In high-density or enclosed designs, consider airflow or thermal vias under the pad to dissipate heat.

8.3 Optical Design

The 110° viewing angle provides wide dispersion. For focused or directed light, external lenses or light guides may be necessary. The yellow color is achieved by combining the blue InGaN chip with a phosphor-coated yellow lens. This is a common and efficient method for producing white and other colors of light in modern LEDs.

9. Reliability & Cautions

9.1 Intended Use

This component is designed for general-purpose electronic equipment. It is not rated for safety-critical applications where failure could jeopardize life or health (e.g., aviation, medical life-support, transportation control). For such applications, consultation with the manufacturer for specialized components is mandatory.

9.2 ESD (Electrostatic Discharge) Sensitivity

While not explicitly stated, LEDs are generally sensitive to electrostatic discharge. Standard ESD precautions should be observed during handling and assembly: use grounded workstations, wrist straps, and conductive containers.

10. Technical Comparison & Trends

10.1 Technology Principle

The LTST-108TWET utilizes an InGaN semiconductor material for its light-emitting chip. InGaN is particularly efficient at producing light in the blue and green spectra. The yellow light is not emitted directly by the chip. Instead, the blue light from the InGaN chip excites a phosphor layer inside the yellow lens. The phosphor absorbs some blue light and re-emits it as yellow light. The mixture of the remaining blue light and the converted yellow light results in the perceived vibrant yellow color. This phosphor-conversion technique is highly efficient and allows for precise color tuning.

10.2 Industry Context

SMD LEDs like the LTST-108TWET represent the standard for modern indicator and backlighting applications due to their small size, reliability, and compatibility with automated high-volume assembly. The trend continues towards higher efficiency (more light output per watt), improved color consistency through tighter binning, and enhanced reliability under higher temperature and humidity conditions. The move to lead-free (Pb-free) soldering, for which this component is qualified, is now a global industry standard driven by environmental regulations.