SMD LED LTST-C950RTGKT Datasheet - Water Clear Lens - InGaN Green - 20mA - 76mW - English Technical Document

1. Product Overview

This document details the specifications for a surface-mount device (SMD) LED lamp. This component is designed for automated printed circuit board (PCB) assembly and is suitable for applications where space is a critical constraint. The LED features a dome lens and utilizes an ultra-bright Indium Gallium Nitride (InGaN) semiconductor chip to produce green light.

1.1 Features

• Compliant with the Restriction of Hazardous Substances (RoHS) directive.
• Dome lens design for optimized light distribution.
• Ultra-bright InGaN chip technology.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place equipment.
• Standardized package dimensions compliant with Electronic Industries Alliance (EIA) standards.
• Input compatible with integrated circuit (IC) logic levels.
• Designed for compatibility with automatic placement machinery.
• Suitable for infrared (IR) reflow soldering processes.

1.2 Applications

This LED is intended for use in a broad spectrum of electronic equipment, including but not limited to:

• Telecommunication devices, office automation equipment, home appliances, and industrial control systems.
• Backlighting for keypads and keyboards.
• Status and power indicators.
• Micro-displays and panel indicators.
• Signal lighting and symbolic luminaries.

2. Package Dimensions and Configuration

The LED is housed in a standard SMD package. Critical mechanical dimensions are provided in engineering drawings, with all measurements specified in millimeters. The standard tolerance for dimensions is ±0.1 mm unless otherwise noted. The specific model documented here, LTST-C950RTGKT, features a water-clear lens and an InGaN chip that emits green light.

3. Ratings and Characteristics

All electrical and optical parameters are specified at an ambient temperature (Ta) of 25°C unless stated otherwise.

3.1 Absolute Maximum Ratings

Stresses beyond these limits may cause permanent damage to the device. Functional operation under these conditions is not implied.

• Power Dissipation (Pd): 76 mW
• Peak Forward Current (I_F(PEAK)): 100 mA (at 1/10 duty cycle, 0.1ms pulse width)
• Continuous Forward Current (I_F): 20 mA DC
• Operating Temperature Range (T_opr): -20°C to +80°C
• Storage Temperature Range (T_stg): -30°C to +100°C
• Infrared Reflow Soldering Condition: 260°C peak temperature for a maximum of 10 seconds.

3.2 Recommended IR Reflow Profile for Lead-Free Process

A suggested temperature profile for lead-free solder reflow is provided. This profile is a guideline; the optimal profile depends on the specific PCB design, solder paste, and oven characteristics. The profile should adhere to JEDEC standards, typically involving a pre-heat stage, a controlled ramp to a peak temperature not exceeding 260°C, and a controlled cooling phase.

3.3 Electrical and Optical Characteristics

These parameters define the typical performance of the device under normal operating conditions.

• Luminous Intensity (I_V): Ranges from 1120 mcd (minimum) to 7100 mcd (maximum), with a typical value dependent on the specific bin. Measured at I_F = 20mA using a sensor filtered to the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 25 degrees. This is the full angle at which the luminous intensity is half the value measured on the central axis.
• Peak Emission Wavelength (λ_P): 530 nm. The wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λ_d): Ranges from 520.0 nm to 535.0 nm at I_F = 20mA. This is the single wavelength perceived by the human eye that defines the color.
• Spectral Line Half-Width (Δλ): 35 nm. The spectral width at half the maximum intensity, indicating color purity.
• Forward Voltage (V_F): Ranges from 2.8 V to 3.8 V at I_F = 20mA.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage (V_R) of 5V. The device is not designed for operation under reverse bias.

3.3.1 Measurement Notes and Cautions

• Luminous intensity measurement follows CIE standards.
• The device is sensitive to Electrostatic Discharge (ESD). Proper ESD precautions, such as using grounded wrist straps and anti-static workstations, are mandatory during handling.
• Applying reverse voltage is for test purposes only; the LED is not intended for reverse-bias operation in application circuits.

4. Bin Ranking System

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

4.1 Forward Voltage (V_F) Rank

Binning at I_F = 20mA. Tolerance for each bin is ±0.1V.
Bin Codes: D7 (2.80-3.00V), D8 (3.00-3.20V), D9 (3.20-3.40V), D10 (3.40-3.60V), D11 (3.60-3.80V).

4.2 Luminous Intensity (I_V) Rank

Binning at I_F = 20mA. Tolerance for each bin is ±15%.
Bin Codes: W (1120-1800 mcd), X (1800-2800 mcd), Y (2800-4500 mcd), Z (4500-7100 mcd).

4.3 Hue (Dominant Wavelength) Rank

Binning at I_F = 20mA. Tolerance for each bin is ±1 nm.
Bin Codes: AP (520.0-525.0 nm), AQ (525.0-530.0 nm), AR (530.0-535.0 nm).

5. Typical Performance Curves

Graphical data representing device behavior under various conditions is typically provided. This includes, but is not limited to:

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, typically in a non-linear relationship, highlighting the importance of current regulation over voltage driving.
• Forward Voltage vs. Forward Current: Illustrates the diode's I-V characteristic curve.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the decrease in light output as junction temperature rises, a critical factor for thermal management in high-power or high-density applications.
• Spectral Power Distribution: A plot showing the intensity of light emitted at each wavelength, centered around the peak wavelength of 530 nm with a characteristic half-width.

6. User Guide for Assembly and Handling

6.1 Cleaning

Unspecified chemical cleaners may damage the LED package. If cleaning is necessary after soldering, use ethyl alcohol or isopropyl alcohol at room temperature. Immersion time should be less than one minute.

6.2 Recommended PCB Pad Layout

A suggested land pattern (footprint) for the PCB is provided to ensure proper soldering and mechanical stability. This includes pad dimensions, spacing, and solder mask definitions to achieve a reliable solder fillet.

6.3 Tape and Reel Packaging Specifications

The LEDs are supplied in embossed carrier tape wound onto 7-inch (178mm) diameter reels. The tape width is 8mm. Key specifications include:

• Pocket pitch and dimensions for component housing.
• Cover tape specifications for sealing.
• Reel hub, flange diameter, and winding direction.

6.4 Reel Packaging Details

• Standard reel contains 2000 pieces.
• Minimum order quantity for non-full reels is 500 pieces.
• A maximum of two consecutive empty pockets is allowed per reel.
• Packaging conforms to ANSI/EIA-481 standards.

7. Application Notes and Cautions

7.1 Intended Use and Reliability

This LED is designed for standard commercial and industrial electronic equipment. It is not rated for safety-critical applications where failure could lead to direct risk to life or health (e.g., aviation, medical life-support, transportation control). For such applications, consultation with the manufacturer for high-reliability grades is essential.

7.2 Storage Conditions

Sealed Package: Store at ≤30°C and ≤90% 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. Components should be subjected to IR reflow soldering within one week (Moisture Sensitivity Level 3, MSL 3). For storage beyond one week, bake at 60°C for at least 20 hours before assembly, or store in a sealed, dry environment (e.g., with desiccant or nitrogen).

7.3 Soldering Recommendations

Reflow Soldering (Recommended):
- Pre-heat: 150-200°C.
- Pre-heat Time: Maximum 120 seconds.
- Peak Temperature: Maximum 260°C.
- Time at Peak: Maximum 10 seconds. The reflow process should not be performed more than twice.
Hand Soldering (If necessary):
- Iron Temperature: Maximum 300°C.
- Soldering Time: Maximum 3 seconds per lead. This should be performed only once.
Note: The optimal reflow profile is board-specific. The provided values are limits; characterization for the specific PCB assembly is recommended.

8. Technical Deep Dive and Design Considerations

8.1 Photometric and Colorimetric Principles

The performance is defined using photometric units (luminous intensity in millicandelas) which account for the sensitivity of the human eye, unlike radiometric units (watts). The dominant wavelength is the key parameter for color specification in applications where human perception is important, while peak wavelength is more relevant for optical sensor matching. The narrow spectral half-width of 35 nm is characteristic of InGaN-based green LEDs, offering good color saturation.

8.2 Electrical Drive Considerations

LEDs are current-driven devices. The forward voltage has a negative temperature coefficient and varies from unit to unit (as indicated by the V_F binning). Therefore, driving with a constant voltage source is not recommended as it can lead to thermal runaway or inconsistent brightness. A constant current driver or a current-limiting resistor in series with a voltage source is essential. The maximum DC current of 20mA defines the standard operating point, while the 100mA pulsed rating allows for brief overdrive in multiplexed applications.

8.3 Thermal Management

With a maximum power dissipation of 76mW, effective heat sinking through the PCB is crucial, especially when operating at high ambient temperatures or at the maximum current. The decrease in luminous intensity with rising junction temperature must be factored into the optical design to ensure consistent brightness over the operating range. The PCB pad layout serves as the primary thermal path.

8.4 Optical Design

The 25-degree viewing angle (full width at half maximum) indicates a relatively focused beam from the dome lens. This makes it suitable for indicator applications where directed light is needed. For backlighting or area illumination, secondary optics (light guides, diffusers) are typically required to spread the light evenly.

8.5 Comparison with Alternative Technologies

InGaN-based green LEDs, like this one, offer higher efficiency and brightness compared to older technologies like Gallium Phosphide (GaP). The water-clear lens provides the true chip color, which is a saturated green, unlike diffused lenses that can scatter light and slightly alter perceived color. The SMD package offers significant advantages in assembly speed, placement accuracy, and board space savings over through-hole LEDs.

8.6 Application-Specific Guidance

Status Indicators: A simple series resistor calculated for ~10-15mA at the system voltage is sufficient. Consider the viewing angle for panel placement.
Backlighting: Multiple LEDs are often used. Consistency in luminous intensity (I_V bin) and dominant wavelength (Hue bin) is critical to avoid visible hotspots or color variation across the display. A constant-current driver array is recommended.
High-Speed Signaling: The fast switching capability of LEDs can be utilized. The pulsed current rating allows for brief high-current pulses to achieve higher peak brightness in multiplexed or PWM-dimmed applications.

8.7 Troubleshooting Common Issues

Inconsistent Brightness: Likely caused by driving LEDs in parallel from a voltage source without individual current limiting. Use a constant current source or individual resistors.
Color Shift Over Time/Temperature: The dominant wavelength can shift slightly with temperature and current. Ensure proper thermal design and stable current drive.
ESD Damage: Failure to light or intermittent operation can result from ESD. Always follow ESD protocols during handling and assembly.
Poor Solder Joints: Can result from incorrect pad design, excessive solder paste, or deviation from the recommended reflow profile. Refer to the land pattern and soldering guidelines.

9. Industry Context and Trends

SMD LEDs represent the dominant packaging technology for modern optoelectronics due to their compatibility with high-volume, automated PCB assembly lines. The shift to InGaN materials for green and blue LEDs has enabled higher efficiencies and brighter outputs. Trends continue towards miniaturization (smaller package sizes), increased power density (higher flux from smaller areas), and improved color consistency through tighter binning. Furthermore, integration with onboard drivers and control circuitry in more advanced packages is an ongoing development. The emphasis on RoHS and lead-free soldering compatibility, as seen in this datasheet, reflects broader environmental regulations in the electronics industry.