SMD LED LTST-S320TBKT Datasheet - Side View - 3.2x1.6x1.2mm - 2.8-3.8V - 76mW - Blue InGaN - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a miniature, side-viewing Surface Mount Device (SMD) Light Emitting Diode (LED). The device is designed for automated printed circuit board (PCB) assembly and is suitable for applications where space is a critical constraint. Its compact form factor and reliable performance make it an ideal component for modern electronic equipment.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its ultra-bright output from an InGaN (Indium Gallium Nitride) semiconductor chip, a wide 130-degree viewing angle, and full compatibility with standard infrared (IR) reflow soldering processes used in high-volume manufacturing. The package features tin plating for improved solderability and is supplied on industry-standard 8mm tape and 7-inch reels for efficient pick-and-place automation.

The target applications span a broad range of consumer and industrial electronics. It is commonly used for status indication, keypad or keyboard backlighting, symbol illumination on control panels, and integration into micro-displays. Its reliability and performance suit it for telecommunications equipment, office automation devices, home appliances, and various industrial control systems.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical parameters is essential for proper circuit design and achieving desired performance.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the device can safely dissipate as heat.
• Continuous Forward Current (IF): 20 mA DC. This is the recommended maximum current for reliable long-term operation.
• Peak Forward Current: 100 mA, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Exceeding the DC current rating, even briefly, can degrade the LED.
• Operating Temperature Range: -20°C to +80°C. The device is guaranteed to function within this environmental temperature range.
• Storage Temperature Range: -30°C to +100°C.
• Soldering Temperature: Withstands IR reflow soldering with a peak temperature of 260°C for up to 10 seconds, which is standard for lead-free (Pb-free) assembly processes.

2.2 Electro-Optical Characteristics

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

• Luminous Intensity (Iv): Ranges from a minimum of 28.0 millicandelas (mcd) to a maximum of 180.0 mcd. The actual value is determined by the device's bin rank (see Section 3).
• Viewing Angle (2θ1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on the central axis. The side-view package is designed to emit light perpendicular to the mounting plane, making this a critical parameter for side-illumination applications.
• Peak Emission Wavelength (λP): Typically 468 nanometers (nm), placing it in the blue region of the visible spectrum.
• Dominant Wavelength (λd): Ranges from 465.0 nm to 475.0 nm. This is the single wavelength perceived by the human eye that defines the color.
• Spectral Line Half-Width (Δλ): Approximately 25 nm. This indicates the spectral purity or bandwidth of the emitted blue light.
• Forward Voltage (VF): Ranges from 2.8 Volts to 3.8 Volts at 20 mA. This is the voltage drop across the LED when operating and is crucial for driver design.
• Reverse Current (IR): Maximum 10 microamperes (μA) when a reverse voltage (VR) of 5V is applied. LEDs are not designed for reverse bias operation; this parameter is for test purposes only.

3. Bin Ranking System Explanation

Due to manufacturing variations, LEDs are sorted into performance bins. This system allows designers to select devices with tightly controlled characteristics for consistent application performance.

3.1 Forward Voltage (VF) Binning

LEDs are grouped by their forward voltage drop at 20 mA. Bins range from D7 (2.80V - 3.00V) to D11 (3.60V - 3.80V), with a tolerance of ±0.1V per bin. Selecting LEDs from the same VF bin ensures uniform brightness and current distribution when multiple devices are connected in parallel.

3.2 Luminous Intensity (Iv) Binning

This is the primary brightness binning. Bins are defined as N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd), and R (112.0-180.0 mcd), with a tolerance of ±15% per bin. This allows for precise control over the light output level in the final application.

3.3 Dominant Wavelength (λd) Binning

LEDs are sorted by color point. For this blue LED, the bins are AC (465.0-470.0 nm) and AD (470.0-475.0 nm), with a tight tolerance of ±1 nm. This ensures minimal color variation between different LEDs in an array or display.

4. Performance Curve Analysis

Graphical data provides deeper insight into device behavior under varying conditions.

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

The I-V characteristic is non-linear. The curve shows that a small increase in voltage beyond the turn-on threshold (~2.8V) causes a rapid increase in current. Therefore, LEDs must be driven by a current-limited source, not a constant voltage source, to prevent thermal runaway and destruction.

4.2 Luminous Intensity vs. Forward Current

This curve demonstrates that light output is approximately proportional to forward current within the rated operating range. However, efficiency (lumens per watt) may decrease at very high currents due to increased heat generation.

4.3 Spectral Distribution

The spectral output graph shows a single peak centered around 468 nm, characteristic of InGaN-based blue LEDs. The relatively narrow half-width indicates good color saturation.

5. Mechanical and Package Information

5.1 Package Dimensions

The device conforms to an industry-standard SMD footprint. Key dimensions include a body length of approximately 3.2 mm, a width of 1.6 mm, and a height of 1.2 mm. All tolerances are typically ±0.1 mm. The side-view design means the primary light-emitting surface is on the smaller side of the package.

5.2 PCB Pad Layout and Polarity

A recommended land pattern (footprint) for PCB design is provided. The cathode (negative) terminal is typically identified by a visual marker on the LED package, such as a notch, green dot, or cut corner. The PCB silkscreen should clearly indicate polarity to prevent assembly errors. Proper pad size and spacing are critical for achieving reliable solder joints and preventing tombstoning during reflow.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

The device is rated for lead-free (Pb-free) soldering processes. The recommended profile includes a pre-heat zone (150-200°C), a controlled ramp-up, a peak temperature not exceeding 260°C, and a time at peak temperature of 10 seconds maximum. The total number of reflow cycles should be limited to two. This profile is based on JEDEC standards to ensure package integrity and reliable electrical connections.

6.2 Storage and Handling

The LEDs are moisture-sensitive (MSL 3). When stored in their original sealed moisture-barrier bag with desiccant, they have a shelf life of one year at ≤30°C and ≤90% RH. Once the bag is opened, components should be used within one week under ambient conditions of ≤30°C and ≤60% RH. If exposed for longer, a bake-out at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" (package cracking during reflow).

6.3 Cleaning

If post-solder cleaning is necessary, only alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol should be used. The LED should be immersed at room temperature for less than one minute. Harsh or unspecified chemicals can damage the epoxy lens or package.

6.4 Electrostatic Discharge (ESD) Precautions

This LED is susceptible to damage from electrostatic discharge. Proper ESD controls must be in place during handling and assembly. This includes the use of grounded workstations, wrist straps, conductive floor mats, and anti-static packaging.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The components are supplied on embossed carrier tape with a width of 8 mm. The tape is wound on a standard 7-inch (178 mm) diameter reel. Each reel contains 3000 pieces. The tape is sealed with a protective cover tape. Packaging conforms to ANSI/EIA-481 standards.

7.2 Minimum Order Quantities

The standard packing quantity is one reel (3000 pieces). For quantities less than a full reel, a minimum pack of 500 pieces is available for remainder stock.

8. Application Notes and Design Considerations

8.1 Driver Circuit Design

Always use a constant current driver or a current-limiting resistor in series with the LED when powered from a voltage source. The resistor value can be calculated using Ohm's Law: R = (V_source - VF_LED) / I_desired. Given the VF range (2.8-3.8V), design for the worst-case scenario to ensure the current never exceeds the absolute maximum rating, even with a low-VF device.

8.2 Thermal Management

While the power dissipation is low (76 mW), effective thermal management is still important for longevity and maintaining light output. Ensure the PCB has adequate copper area connected to the LED's thermal pad (if applicable) or solder pads to conduct heat away. Operating at high ambient temperatures or at maximum current will reduce the device's lifetime.

8.3 Optical Integration

The side-view emission profile is ideal for edge-lighting light guides, illuminating symbols on a vertical surface, or providing backlighting for keys adjacent to the PCB. Consider the 130-degree viewing angle when designing light pipes or diffusers to ensure even illumination of the target area.

9. Technical Comparison and Differentiation

Compared to top-view SMD LEDs, this side-view variant offers a distinct mechanical advantage for space-constrained designs where light needs to be emitted parallel to the PCB plane. The use of an InGaN chip provides higher efficiency and brighter blue output compared to older technologies. Its compatibility with standard IR reflow and tape-and-reel packaging makes it cost-effective for automated, high-volume production, distinguishing it from LEDs requiring manual soldering.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive this LED directly from a 5V supply?

No. Connecting it directly to 5V would cause excessive current to flow, destroying the LED instantly. You must always use a series current-limiting resistor or a dedicated constant-current LED driver.

10.2 What is the difference between peak wavelength and dominant wavelength?

Peak wavelength (λP) is the wavelength at which the spectral power output is maximum. Dominant wavelength (λd) is derived from the color coordinates on the CIE chromaticity diagram and represents the perceived color. For a monochromatic source like this blue LED, they are very close, but λd is more relevant for color specification.

10.3 Why is the storage condition so strict after opening the bag?

The epoxy packaging material 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 ("popcorning"). The MSL 3 rating and baking procedure prevent this failure mode.

11. Practical Application Example

Scenario: Designing a status indicator panel for a network router. The panel has small, vertical slots for status icons (Power, Internet, Wi-Fi). A side-view LED is mounted on the main PCB directly behind each slot. Its 130-degree viewing angle ensures the icon is evenly illuminated from within the slot. The designer selects LEDs from the same luminous intensity bin (e.g., Bin Q) and forward voltage bin (e.g., Bin D9) to guarantee all status lights have identical brightness and color when driven by a common current source. The PCB layout follows the recommended pad geometry, and the assembly house uses the specified JEDEC-compliant reflow profile.

12. Operating Principle

This is a semiconductor photonic device. It is based on an InGaN heterostructure. When a forward bias voltage is applied, electrons and holes are injected into the active region from the n-type and p-type semiconductor layers, respectively. These charge carriers recombine radiatively, releasing energy in the form of photons. The specific bandgap energy of the InGaN material determines the wavelength of the emitted light, which in this case is in the blue spectrum (~468 nm). The epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output beam.

13. Technology Trends

The underlying technology for blue LEDs, InGaN, was a groundbreaking development in solid-state lighting, enabling 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), improving color rendering index (CRI) for white LEDs, achieving higher reliability and longer lifetimes, and enabling even smaller package sizes for ultra-miniature applications. Advancements in packaging materials also aim to better manage heat and provide wider viewing angles or more controlled beam patterns.