SMD LED Blue Diffused Lens LTST-E681UBWT Datasheet - Package Dimensions - Voltage 3.8V - Power 114mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a surface-mount device (SMD) light-emitting diode (LED). The device features a blue light source utilizing InGaN (Indium Gallium Nitride) technology and is encapsulated with a diffused lens. This combination is designed to provide a wide viewing angle with softened light emission, suitable for applications requiring even illumination rather than a focused beam. The product is compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. It is supplied in industry-standard 8mm tape on 7-inch reels, making it fully compatible with automated pick-and-place assembly equipment and standard infrared (IR) reflow soldering processes.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (Ta) of 25°C. The maximum continuous power dissipation is 114 mW. The DC forward current should not exceed 30 mA under normal operating conditions. For pulsed operation, a peak forward current of 100 mA is permissible, but only under strict conditions: a 1/10 duty cycle and a pulse width of 1ms. The device is rated for operation within a temperature range of -40°C to +85°C and can be stored in environments ranging from -40°C to +100°C.

2.2 Electrical and Optical Characteristics

The performance is detailed under standard test conditions at Ta=25°C. The key optical parameter, luminous intensity (Iv), has a typical value of 900 millicandelas (mcd) at a forward current (IF) of 30mA, with a minimum specified value of 355 mcd. The device offers a very wide viewing angle (2θ1/2) of 120 degrees, defined as the angle where the intensity drops to half of its axial value. Electrically, the typical forward voltage (VF) is 3.8V at 30mA, with a maximum of 3.8V. The reverse current (IR) is limited to a maximum of 10 μA when a reverse voltage (VR) of 5V is applied. It is critical to note that the device is not designed for operation under reverse bias; this test condition is for characterization only.

2.3 Spectral Characteristics

The spectral properties define the color quality of the emitted light. The peak emission wavelength (λP) is typically 468 nanometers (nm). The dominant wavelength (λd), which is the single wavelength perceived by the human eye to define the color, falls within the range of 465 nm to 475 nm when driven at 30mA. The spectral line half-width (Δλ), a measure of the color purity, is typically 25 nm.

3. Binning System Explanation

To ensure consistency in applications, LEDs are sorted into bins based on key parameters. This system allows designers to select components that meet specific tolerance requirements for their circuit.

3.1 Forward Voltage Binning

Forward voltage (VF) is binned in 0.2V steps. The bin codes range from D7 (2.8V - 3.0V) to D11 (3.6V - 3.8V). The tolerance within each bin is +/-0.1V. Selecting LEDs from the same voltage bin is crucial for achieving uniform brightness when multiple devices are connected in parallel without individual current-limiting resistors.

3.2 Luminous Intensity Binning

Luminous intensity is categorized into bins with increasing minimum values. The bins are T2 (355-450 mcd), U1 (450-560 mcd), U2 (560-710 mcd), and V1 (710-900 mcd). The tolerance on each intensity bin is +/-11%. This binning allows for brightness matching in multi-LED arrays.

3.3 Dominant Wavelength Binning

The dominant wavelength, which determines the perceived blue color, is binned into two ranges: AC (465.0 nm - 470.0 nm) and AD (470.0 nm - 475.0 nm). The tolerance for each bin is +/- 1nm, ensuring tight color consistency.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet (e.g., Figure 1 for peak emission, Figure 5 for viewing angle), the typical curves for such a device would illustrate important relationships. These typically include the forward current vs. forward voltage (I-V curve), which shows the exponential relationship and helps in driver design. The relative luminous intensity vs. forward current curve demonstrates how light output increases with current, often in a near-linear region before efficiency drops at higher currents. The spectral power distribution curve would show the concentration of light energy around the 468nm peak with the defined 25nm half-width. Understanding these curves is essential for optimizing the LED's performance in a specific application, such as setting the correct drive current to achieve desired brightness and efficiency.

5. Mechanical and Package Information

5.1 Device Package Dimensions

The LED conforms to EIA standard SMD package dimensions. Detailed mechanical drawings are provided in the datasheet, specifying the length, width, height, lead spacing, and lens geometry. All dimensions are in millimeters, with a general tolerance of ±0.2mm unless otherwise specified. The diffused lens is integrated into the package, determining the final optical characteristics.

5.2 Recommended PCB Land Pattern

A recommended printed circuit board (PCB) attachment pad layout is provided for both infrared and vapor phase reflow soldering processes. Adhering to this land pattern is critical for achieving reliable solder joints, proper alignment, and effective heat dissipation during the soldering process. The pad design ensures sufficient solder volume and prevents issues like tombstoning.

5.3 Polarity Identification

Like all diodes, the LED has an anode and a cathode. The package includes markings or features (such as a notch, a dot, or a cut corner) to identify the cathode pin. Correct polarity must be observed during assembly to ensure the device functions. Applying reverse voltage can damage the LED.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The datasheet references a suggested IR reflow profile compliant with the J-STD-020B standard for lead-free soldering. A generic profile is provided, with key parameters including a pre-heat temperature of 150-200°C, a pre-heat time of up to 120 seconds maximum, a peak temperature not exceeding 260°C, and a total time above liquidus (soldering time) of 10 seconds maximum. It is emphasized that the actual profile must be characterized for the specific PCB design, components, solder paste, and oven used.

6.2 Storage Conditions

Proper storage is vital to maintain solderability. Unopened, moisture-proof bags with desiccant should be stored at ≤30°C and ≤70% Relative Humidity (RH), with a shelf life of one year. Once the original packaging is opened, the components should be stored at ≤30°C and ≤60% RH. Components exposed to ambient conditions for more than 168 hours (7 days) should be baked at approximately 60°C for at least 48 hours before soldering to remove absorbed moisture and prevent "popcorning" damage during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. The use of unspecified or aggressive chemical cleaners can damage the plastic package and lens.

7. Packaging and Ordering Information

The standard packaging consists of 8mm wide embossed carrier tape that holds the LEDs. The tape is wound onto 7-inch (178mm) diameter reels. Each full reel contains 2000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces is specified for remainders. The packaging follows ANSI/EIA-481 specifications. The part number LTST-E681UBWT uniquely identifies this specific variant: blue color, diffused lens, with the defined electrical and optical bins.

8. Application Notes and Design Considerations

8.1 Drive Method

LEDs are current-driven devices. To ensure uniform brightness and prevent current hogging, it is strongly recommended to use a series current-limiting resistor for each LED, especially when connecting multiple LEDs in parallel. Driving the LED directly from a voltage source without current regulation is not advised, as small variations in forward voltage can lead to large differences in current and brightness, and potentially overcurrent failure.

8.2 Thermal Management

Although the power dissipation is relatively low (114mW max), proper thermal design extends LED life and maintains stable light output. The maximum operating junction temperature is a key factor. Ensuring adequate PCB copper area for heat sinking, avoiding placement near other heat sources, and adhering to the specified current limits are essential practices.

8.3 Application Scope

This LED is intended for use in ordinary electronic equipment, including office equipment, communication devices, and household appliances. For applications requiring exceptional reliability where failure could jeopardize safety (e.g., aviation, medical devices, transportation systems), additional qualification and consultation with the component manufacturer are mandatory.

9. Technical Comparison and Differentiation

The primary differentiating factors for this LED are its combination of a blue InGaN chip with a diffused lens, resulting in a wide 120-degree viewing angle. Compared to clear-lens LEDs, the diffused lens provides a more uniform, softer light emission, reducing glare and hotspots. The specific binning structure for voltage, intensity, and wavelength allows for high-precision selection in color- and brightness-sensitive applications. Its compatibility with standard IR reflow processes and tape-and-reel packaging makes it a drop-in solution for automated, high-volume manufacturing lines.

10. Frequently Asked Questions (FAQ)

Q: Can I drive this LED without a current-limiting resistor?

A: No. An LED must be driven with a controlled current. A series resistor is the simplest method to set the current when using a voltage source. Without it, the current is determined by the power supply's voltage and the LED's dynamic resistance, which is very low and can lead to thermal runaway and destruction.

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λP) is the wavelength at which the spectral power output is maximum (468nm here). Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength that the human eye perceives as the color of the light (465-475nm here). For a monochromatic source like a blue LED, they are often close.

Q: Why is storage humidity so important?

A: SMD plastic packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can crack the package or delaminate internal bonds—a phenomenon known as "popcorning." The specified storage and baking procedures prevent this.

11. Practical Application Examples

Example 1: Status Indicator Panel: An array of these LEDs can be used behind a translucent or frosted panel to create uniform blue status backlighting for buttons or icons on a consumer electronics device. The wide viewing angle ensures visibility from various positions.

Example 2: Decorative Lighting: Multiple LEDs can be spaced along a strip to create ambient blue accent lighting. The diffused lens helps blend individual points of light into a more continuous glow. Designers must calculate the appropriate series resistor value based on the supply voltage (e.g., 5V or 12V) and the desired forward current (e.g., 20mA for lower power/longer life or 30mA for maximum brightness).

12. Operating Principle Introduction

This LED is based on a semiconductor chip made of InGaN. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The specific bandgap energy of the InGaN material determines the wavelength of the emitted photons, which in this case is in the blue region of the visible spectrum. The diffused lens, made of epoxy or silicone, contains scattering particles that randomize the direction of the emitted light, broadening the beam angle and softening its appearance.

13. Technology Trends

The underlying technology for blue LEDs, InGaN, was a groundbreaking development that enabled white LEDs (via phosphor conversion) and full-color displays. Current trends in SMD LED technology focus on increasing luminous efficacy (more light output per watt of electrical input), improving color rendering index (CRI) for white LEDs, achieving higher power densities in smaller packages, and enhancing reliability under higher temperature and current stress. Packaging innovations also aim for better thermal management and more precise optical control. The device described represents a mature, cost-effective implementation of this core technology for general indicator and lighting applications.