SMD LED LTST-T680UBWT Datasheet - Diffused Blue - 120° Viewing Angle - 2.6-3.4V - 30mA - English Technical Documentation

1. Product Overview

This document provides the complete technical specifications for a surface-mount device (SMD) LED. This component is designed for automated printed circuit board (PCB) assembly, featuring a miniature form factor ideal for space-constrained applications. The LED utilizes an InGaN (Indium Gallium Nitride) semiconductor material to produce a diffused blue light output. Its primary function is as a status indicator, signal luminary, or for front panel backlighting in a wide range of electronic equipment.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place assembly.
• Standard EIA (Electronic Industries Alliance) package footprint.
• IC (Integrated Circuit) compatible drive levels.
• Fully compatible with automated placement equipment.
• Suitable for infrared (IR) reflow soldering processes.
• Preconditioned to accelerate to JEDEC (Joint Electron Device Engineering Council) moisture sensitivity Level 3.

1.2 Applications

This LED is suitable for diverse applications across multiple industries, including:

• Telecommunication equipment (e.g., cordless and cellular phones).
• Office automation devices (e.g., notebook computers, network systems).
• Home appliances and consumer electronics.
• Industrial control and monitoring equipment.
• Status and power indicators.
• Signal and symbol illumination.
• Front panel and display backlighting.

2. Technical Parameters Deep Analysis

2.1 Absolute Maximum Ratings

The following 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): 102 mW. This is the maximum power the LED package can dissipate as heat.
• Peak Forward Current (I_FP): 100 mA. This is the maximum allowable instantaneous current, typically under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): 30 mA. This is the maximum continuous forward current recommended for reliable long-term operation.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range within which the LED is designed to function.
• Storage Temperature Range: -40°C to +100°C. The temperature range for non-operational storage.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and a forward current (I_F) of 20mA, unless otherwise noted.

• Luminous Intensity (I_V): 280.0 - 710.0 mcd (millicandela). The amount of visible light emitted, measured using a sensor filtered to match the human eye's photopic response (CIE curve). The wide range indicates the device is available in different brightness bins.
• Viewing Angle (2θ_1/2): 120 degrees (typical). This is the full angle at which the luminous intensity is half of the intensity measured on-axis (0°). A 120° angle indicates a wide, diffused light pattern suitable for indicator applications.
• Peak Emission Wavelength (λ_P): 468 nm (typical). The wavelength at which the optical output power is maximum.
• Dominant Wavelength (λ_d): 465 - 475 nm. This is the single wavelength perceived by the human eye that defines the color of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 20 nm (typical). The spectral bandwidth measured at half the maximum intensity (Full Width at Half Maximum - FWHM).
• Forward Voltage (V_F): 2.6 - 3.4 V. The voltage drop across the LED when driven at 20mA. This range is subject to binning.
• Reverse Current (I_R): 10 μA (max) at V_R=5V. The device is not designed for reverse bias operation; this parameter is for test purposes only.

3. Binning System Explanation

To ensure consistency in production runs, LEDs are sorted into bins based on key electrical and optical parameters. This allows designers to select parts that meet specific application requirements for brightness, color, and voltage.

3.1 Forward Voltage (V_f) Rank

Binned at I_F = 20mA. Tolerance on each bin is ±0.1V.

• D6: 2.6V (Min) - 2.8V (Max)
• D7: 2.8V (Min) - 3.0V (Max)
• D8: 3.0V (Min) - 3.2V (Max)
• D9: 3.2V (Min) - 3.4V (Max)

3.2 Luminous Intensity (I_V) Rank

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

• T1: 280.0 mcd (Min) - 355.0 mcd (Max)
• T2: 355.0 mcd (Min) - 450.0 mcd (Max)
• U1: 450.0 mcd (Min) - 560.0 mcd (Max)
• U2: 560.0 mcd (Min) - 710.0 mcd (Max)

3.3 Dominant Wavelength (W_d) Rank

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

• AC: 465.0 nm (Min) - 470.0 nm (Max)
• AD: 470.0 nm (Min) - 475.0 nm (Max)

4. Performance Curve Analysis

Typical performance curves (not shown in the provided excerpt but referenced) would normally illustrate the relationship between key parameters. Designers should consult the full datasheet for these graphs, which typically include:

• Relative Luminous Intensity vs. Forward Current (I-V Curve): Shows how light output increases with drive current, up to the maximum rating.
• Forward Voltage vs. Forward Current: Illustrates the non-linear V-I characteristic of the diode.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the decrease in light output as junction temperature rises, a critical factor for thermal management.
• Spectral Distribution: A graph showing the relative optical power across wavelengths, centered around the peak wavelength of ~468 nm with a typical FWHM of 20 nm.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED comes in a standard surface-mount package. All dimensions are in millimeters (mm) with a general tolerance of ±0.2 mm unless otherwise specified. The specific dimensional drawing would show the length, width, height, and lead/pad spacing.

5.2 Polarity Identification and Pad Design

The component has an anode and cathode. Polarity is typically indicated by a marking on the package or by an asymmetric pad design. The datasheet provides a recommended PCB land pattern (attachment pad) for both infrared and vapor phase reflow soldering to ensure proper solder joint formation and alignment.

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile (Pb-Free)

The soldering profile should comply with J-STD-020B standards for lead-free processes. Key parameters include:

• Pre-heat Temperature: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: Should be controlled according to paste specifications.
• Total Soldering Time: Maximum 10 seconds at peak temperature (maximum two reflow cycles allowed).

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

6.2 Hand Soldering (Soldering Iron)

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per joint.
• Limit: One-time soldering only when using an iron.

6.3 Storage Conditions

• Sealed Package (with desiccant): Store at ≤30°C and ≤70% RH. Use within one year.
• Opened Package: Store at ≤30°C and ≤60% RH. It is recommended to complete IR reflow within 168 hours (7 days) of opening.
• Extended Storage (out of bag): Store in a sealed container with desiccant or in a nitrogen atmosphere.
• If exposed >168hrs: 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 unspecified chemical liquids.

7. Packaging and Handling

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape for automated assembly.

• Reel Diameter: 7 inches.
• Tape Width: 8 mm.
• Quantity per Reel: 2000 pieces.
• Empty pockets are sealed with cover tape.
• Packaging conforms to ANSI/EIA-481 specifications.
• The maximum number of consecutive missing components (empty pockets) is two.

8. Application Notes and Design Considerations

8.1 Drive Method

LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a series current-limiting resistor for each LED or to drive them with a constant current source. Driving LEDs in parallel directly from a voltage source can lead to significant brightness variations due to the natural spread in forward voltage (V_F) characteristics, even within the same bin.

8.2 Thermal Management

While the power dissipation is relatively low (102 mW max), proper thermal design is essential for maintaining LED lifetime and consistent performance. Ensure the PCB pad design provides adequate thermal relief, especially when operating at or near the maximum DC current (30mA) or in high ambient temperatures. Excessive junction temperature will reduce light output and accelerate degradation.

8.3 Application Scope and Cautions

This component is designed for use in ordinary electronic equipment. For applications requiring exceptional reliability where failure could jeopardize life or health (e.g., aviation, medical, safety systems), a specific technical consultation is required prior to design-in. The device is not designed for reverse voltage operation.

9. Technical Comparison and Differentiation

The key differentiating features of this LED include its 120° wide viewing angle with a diffused lens, providing a soft, even illumination ideal for panel indicators. The use of InGaN technology enables efficient blue light emission. Its compatibility with standard IR reflow processes and JEDEC Level 3 preconditioning makes it suitable for modern, high-volume PCB assembly lines. The comprehensive binning structure for voltage, intensity, and wavelength allows for precise selection to meet application-specific color and brightness consistency requirements.

10. Frequently Asked Questions (Based on Technical Parameters)

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

Peak Wavelength (λ_P): The wavelength at the highest point of the LED's spectral output curve (468 nm typical). Dominant Wavelength (λ_d): The single wavelength that defines the perceived color to the human eye, calculated from the CIE color coordinates (465-475 nm). For monochromatic LEDs like this blue one, they are often close, but dominant wavelength is more relevant for color specification.

10.2 Can I drive this LED at 30mA continuously?

Yes, 30mA is the maximum recommended DC Forward Current. However, operating at the absolute maximum rating will generate more heat and may reduce long-term reliability. For optimal lifetime and stability, driving at a lower current such as 20mA (the test condition) is advisable if the application's brightness requirements allow it.

10.3 Why is the luminous intensity range so wide (280-710 mcd)?

This range represents the total spread across all available brightness bins (T1, T2, U1, U2). A specific order will be for a single bin (e.g., U1: 450-560 mcd). The binning system ensures you receive LEDs with consistent brightness within a defined, narrower range.

10.4 How do I interpret the "120° viewing angle"?

This is the full viewing angle (2θ_1/2). It means the angle from one side where intensity drops to 50% of the on-axis value, to the opposite side where it also drops to 50%. So, the LED emits usable light across a very wide 120-degree cone, making it visible from many side angles.

11. Design and Usage Case Example

Scenario: Designing a status indicator panel for a network router with multiple blue LEDs showing link activity and power.

1. Component Selection: Choose the U1 brightness bin (450-560 mcd) for good visibility in an office environment. Select the AC wavelength bin (465-470 nm) for a consistent blue hue across all indicators.
2. Circuit Design: Use a 3.3V supply rail. Assuming a typical V_F from the D7 bin (2.9V) and a target I_F of 20mA, calculate the series resistor: R = (V_supply - V_F) / I_F = (3.3V - 2.9V) / 0.02A = 20 Ω. Use a 20 Ω, 1/10W resistor per LED.
3. PCB Layout: Implement the recommended solder pad footprint from the datasheet. Ensure adequate spacing between LEDs for the diffused light patterns not to bleed together.
4. Assembly: Follow the provided IR reflow profile. After opening the moisture-barrier bag, complete board assembly within 168 hours.
5. Result: A panel with uniform, bright blue indicators that are clearly visible from a wide angle, reliable for the product's lifetime.

12. Operating Principle Introduction

This LED is a semiconductor photonic device. Its core is a chip made of InGaN materials forming a p-n junction. When a forward voltage exceeding the junction's threshold (approximately 2.6-3.4V) is applied, electrons and holes are injected across the junction. When these charge carriers recombine, they release energy in the form of photons (light). The specific bandgap energy of the InGaN semiconductor determines the photon's wavelength, which in this case is in the blue region of the visible spectrum (~468 nm). The built-in diffused lens scatters the light, broadening the emission pattern to a 120-degree viewing angle.

13. Technology Trends

Surface-mount LEDs continue to evolve towards higher efficiency (more lumens per watt), smaller package sizes, and improved color consistency. There is a growing emphasis on tighter binning tolerances for both chromaticity and flux to meet the demands of applications requiring precise color matching, such as full-color displays and architectural lighting. Furthermore, advancements in packaging materials are enhancing thermal performance, allowing for higher drive currents and greater light output from miniature footprints. The compatibility with standard, high-speed SMT assembly processes remains a fundamental requirement, driving designs that are robust against the thermal and mechanical stresses of reflow soldering.