SMD LED LTST-108TBL Datasheet - Blue InGaN - 3.2x1.6x1.1mm - 3.4V Max - 102mW - English Technical Document

1. Product Overview

The LTST-108TBL is a surface-mount device (SMD) light-emitting diode (LED) designed for automated printed circuit board (PCB) assembly. Its miniature size makes it suitable for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages

• Miniature Footprint: The compact EIA standard package allows for high-density PCB layouts.
• Automation Compatibility: Supplied in 8mm tape on 7-inch reels, it is fully compatible with automatic pick-and-place equipment.
• Robust Manufacturing: Compatible with infrared (IR) reflow soldering processes, supporting lead-free (Pb-free) assembly lines.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.
• Reliability: Devices are preconditioned to accelerate to JEDEC Level 3 moisture sensitivity levels, ensuring reliability during soldering.

1.2 Target Market & Applications

This LED is engineered for use in consumer, commercial, and industrial electronics where reliable, low-profile status indication is required.

• Telecommunications: Status indicators in routers, modems, and network switches.
• Office Automation & Computing: Power/activity lights in laptops, desktop PCs, and peripherals.
• Home Appliances & Consumer Electronics: Indicator lights on control panels.
• Industrial Equipment: Machine status and fault indicators.
• General Purpose: Front panel backlighting, signal and symbol luminary applications.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation (Pd): 102 mW at Ta=25°C. This is the maximum power the package can dissipate as heat.
• DC Forward Current (IF): 30 mA continuous. Exceeding this current significantly increases junction temperature and accelerates lumen depreciation.
• Peak Forward Current: 80 mA, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) for brief signal bursts.
• Derating Factor: 0.38 mA/°C linear from 25°C. The maximum allowable DC current must be reduced as ambient temperature increases to prevent exceeding the junction temperature limit.
• Operating & Storage Temperature: -40°C to +85°C and -40°C to +100°C, respectively, defining the environmental limits for operation and non-operation.

2.2 Electro-Optical Characteristics

Measured at Ta=25°C with IF=20mA, unless otherwise specified. These are the typical performance parameters.

• Luminous Intensity (Iv): Ranges from 330.0 mcd (min) to 520.0 mcd (max), with a typical value dependent on the bin rank. Measured using a sensor filtered to the CIE photopic eye-response curve.
• Viewing Angle (2θ½): A wide 110-degree (typical) angle, defined as the off-axis angle where intensity is half the axial (on-axis) intensity.
• Peak Wavelength (λp): Typically 471 nm, indicating the spectral peak of the emitted light.
• Dominant Wavelength (λd): Ranges from 457 nm to 467 nm. This is the single wavelength perceived by the human eye to define the color (blue). Tolerance is ±1 nm per bin.
• Spectral Line Half-Width (Δλ): Typically 26 nm, describing the spectral purity or bandwidth of the emitted blue light.
• Forward Voltage (VF): Between 2.6V (min) and 3.4V (max) at 20mA. This parameter is binned for consistency in circuit design.
• Reverse Current (IR): Maximum 5 µA at VR=5V. The device is not designed for reverse bias operation; this test is for quality assurance only.
• Capacitance (C): Typically 40 pF at VF=0V, f=1 MHz, relevant for high-speed switching considerations.

3. Bin Rank System Explanation

The product is sorted into bins based on key parameters to ensure performance consistency within a production batch. Designers can specify bins to match application requirements.

3.1 Forward Voltage (VF) Rank

Units: Volts @ 20mA. Tolerance on each bin is ± 0.10V.

• F4: 2.6V (Min) - 2.8V (Max)
• F5: 2.8V - 3.0V
• F6: 3.0V - 3.2V
• F7: 3.2V - 3.4V

3.2 Luminous Intensity (Iv) Rank

Units: millicandelas (mcd) @ 20mA. Tolerance on each bin is ± 11%.

• T2: 330.0 mcd (Min) - 410.0 mcd (Max)
• U1: 410.0 mcd - 520.0 mcd

3.3 Dominant Wavelength (WD) Rank

Units: nanometers (nm) @ 20mA. Tolerance for each bin is ± 1 nm.

• AC: 457.0 nm (Min) - 462.0 nm (Max)
• AD: 462.0 nm - 467.0 nm

4. Performance Curve Analysis

Typical characteristic curves provide insight into device behavior under varying conditions. All curves are at 25°C unless noted.

4.1 Relative Luminous Intensity vs. Forward Current

This curve shows a near-linear relationship between forward current (IF) and light output (Iv) within the recommended operating range. Driving the LED above 20mA yields diminishing returns in efficiency and increases heat.

4.2 Relative Luminous Intensity vs. Ambient Temperature

The light output decreases as ambient temperature increases. This thermal quenching effect is characteristic of semiconductor LEDs and must be accounted for in designs operating at elevated temperatures.

4.3 Forward Voltage vs. Forward Current

This exponential curve illustrates the diode's I-V characteristic. The specified VF at 20mA is the typical operating point. The curve helps in designing current-limiting circuitry.

4.4 Spectral Distribution

The graph shows a single peak centered around 471 nm (typical) with a half-width of approximately 26 nm, confirming the monochromatic blue emission from the InGaN semiconductor material.

5. Mechanical & Package Information

5.1 Package Dimensions

The LTST-108TBL is housed in a standard SMD package. Key dimensions (in millimeters, tolerance ±0.2mm unless noted) include a body size of approximately 3.2mm (L) x 1.6mm (W) x 1.1mm (H). The lens is water clear. The cathode is typically identified by a marking on the package or a green tint in the lens.

5.2 Recommended PCB Attachment Pad Layout

A land pattern design is provided for infrared or vapor phase reflow soldering. This pattern ensures proper solder fillet formation, mechanical stability, and thermal relief during assembly. Adherence to this layout is critical for achieving reliable solder joints and managing heat dissipation from the LED die.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile (Pb-Free Process)

A detailed temperature profile compliant with J-STD-020B is specified for lead-free assembly.

• Pre-heat: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Recommended profile shows a specific duration.
• Soldering Time: Maximum 10 seconds at peak temperature (max two reflow cycles).

Note: The optimal profile depends on the specific PCB design, solder paste, and oven. The provided profile serves as a generic target based on JEDEC standards.

6.2 Hand Soldering (If Necessary)

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per pad (one time only).

6.3 Storage Conditions

• Sealed Package: Store at ≤ 30°C and ≤ 70% RH. Use within one year when the moisture-proof bag with desiccant is intact.
• Opened Package: Store at ≤ 30°C and ≤ 60% RH. It is recommended to complete IR reflow within 168 hours (1 week) of exposure.
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen ambient. If exposed for >168 hours, bake at approximately 60°C for at least 48 hours before soldering to remove moisture and prevent \"popcorning\" during reflow.

6.4 Cleaning

If cleaning is necessary after soldering, use only specified solvents. Immerse the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Do not use ultrasonic cleaning or unspecified chemicals.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The device is supplied in embossed carrier tape per ANSI/EIA 481 specifications.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Pocket Sealing: Empty pockets are sealed with cover tape.
• Missing Components: A maximum of two consecutive missing lamps are allowed per specification.

8. Application Suggestions & Design Considerations

8.1 Drive Method

LEDs are current-operated devices. To ensure uniform brightness, especially when connecting multiple LEDs in parallel, each LED should be driven by a constant current source or have its own current-limiting resistor. Driving with a constant voltage source without a series resistor is not recommended as it can lead to thermal runaway due to the negative temperature coefficient of VF.

8.2 Thermal Management

While the package is small, proper thermal design is essential for longevity. Ensure the PCB pad design provides adequate thermal relief. Avoid operating at maximum current (30mA) in high ambient temperatures without considering the derating factor (0.38 mA/°C). High junction temperatures accelerate lumen depreciation and can reduce operational lifetime.

8.3 Optical Design

The wide 110-degree viewing angle makes this LED suitable for applications requiring broad visibility. For focused or directed light, secondary optics (lenses, light guides) may be required. The water-clear lens is optimal for applications where the true chip color is desired.

9. Technical Comparison & Differentiation

Compared to older technology like GaP-based blue LEDs, this InGaN (Indium Gallium Nitride) LED offers significantly higher luminous efficiency and a more saturated blue color. Within its form factor, key differentiators include its wide viewing angle, specific binning structure for color and intensity consistency, and robust construction for IR reflow compatibility, which may not be present in all low-cost SMD LEDs.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive this LED at 30mA continuously?

Yes, 30mA is the maximum rated DC forward current at 25°C. However, for optimal lifetime and reliability, it is often advisable to drive LEDs below their absolute maximum rating, such as at the test condition of 20mA. Always apply the derating factor if the ambient temperature exceeds 25°C.

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

Peak Wavelength (λp) is the wavelength at the highest point in the LED's spectral power distribution (typically 471 nm). Dominant Wavelength (λd) is a colorimetric quantity derived from the CIE chromaticity diagram; it is the single wavelength that best matches the perceived color of the LED (457-467 nm). λd is more relevant for color specification in visual applications.

10.3 Why is there a storage time limit after opening the bag?

SMD packages can absorb moisture from the atmosphere. During the high-temperature reflow soldering process, this trapped moisture can rapidly vaporize, creating internal pressure that may delaminate the package or crack the die (\"popcorning\"). The 168-hour floor life and baking procedures are countermeasures against this failure mode.

11. Practical Application Case Study

Scenario: Designing a status indicator panel for a network switch with 24 identical blue power/activity LEDs.

Design Considerations:

1. Current Drive: Use a constant current driver IC or 24 identical current-limiting resistors (calculated for ~20mA from the system voltage and the LED's VF bin, e.g., F5: ~2.9V typ).
2. Brightness Uniformity: Specify a tight Iv bin (e.g., U1: 410-520 mcd) and VF bin (e.g., F5) from the supplier to ensure all 24 LEDs appear equally bright.
3. PCB Layout: Implement the recommended solder pad layout for each LED to ensure reliable automatic soldering and heat dissipation.
4. Assembly: Follow the specified Pb-free reflow profile. Ensure the panels are assembled within 168 hours of opening the LED reel or that the LEDs have been properly baked if stored longer.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region (the junction). When these charge carriers recombine, energy is released in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material used in the active region. The LTST-108TBL uses an Indium Gallium Nitride (InGaN) compound semiconductor, which is engineered to emit photons in the blue spectrum (~470 nm).

13. Technology Trends

The development of efficient blue InGaN LEDs was a foundational achievement in solid-state lighting, enabling the creation of white LEDs (via phosphor conversion) and full-color displays. Ongoing trends in SMD LED technology include continued improvements in luminous efficacy (lumens per watt), higher maximum power density in smaller packages, enhanced color rendering indices (CRI) for white LEDs, and the integration of more sophisticated features like built-in drivers or control circuitry. The drive towards miniaturization and compatibility with advanced assembly processes, as seen in this datasheet, remains consistent across the industry.