SMD LED LTST-C990KRKT Datasheet - Red AlInGaP - 20mA - 1.6-2.4V - English Technical Document

1. Product Overview

This document details the specifications for a compact, high-brightness Surface Mount Device (SMD) LED lamp. Designed for automated printed circuit board (PCB) assembly, this component is ideal for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Features

• Compliant with RoHS environmental directives.
• Incorporates a dome lens for optimized light distribution.
• Utilizes an Ultra Bright Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor chip for high luminous efficiency in the red spectrum.
• Packaged in 8mm tape on 7-inch diameter reels, compatible with standard automated pick-and-place equipment.
• Conforms to EIA (Electronic Industries Alliance) standard package outlines.
• Designed to be driven directly by integrated circuit (IC) outputs.
• Fully compatible with infrared (IR) reflow soldering processes.

1.2 Applications

This LED is suitable for a wide range of applications, 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 luminaires and symbolic illumination.

2. Technical Parameters: In-Depth Objective Interpretation

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): 62.5 mW. This is the maximum amount of power the LED package can dissipate as heat without degradation.
• Peak Forward Current (I_F(PEAK)): 60 mA. This is the maximum allowable pulsed forward current, typically specified under conditions of a 1/10 duty cycle and 0.1ms pulse width to prevent overheating.
• DC Forward Current (I_F): 25 mA. This is the maximum continuous forward current recommended for reliable long-term operation.
• Reverse Voltage (V_R): 5 V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Operating Temperature Range: -30°C to +85°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range: -40°C to +85°C. The temperature range for non-operational storage.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which is standard for lead-free (Pb-free) reflow processes.

2.2 Electrical & Optical Characteristics

These parameters define the typical performance of the device under standard test conditions (Ta=25°C, I_F=20mA unless noted).

• Luminous Intensity (I_V): 180.0 - 1120.0 mcd (millicandela). Measured using a sensor filtered to match the CIE photopic (human eye) response curve. The wide range is managed through a binning system.
• Viewing Angle (2θ_1/2): 75 degrees. This is the full angle at which the luminous intensity is half the value measured on the central axis (0°). The dome lens creates this wide viewing pattern.
• Peak Emission Wavelength (λ_P): 639 nm (typical). The wavelength at which the spectral power output is maximum.
• Dominant Wavelength (λ_d): 624.0 - 636.0 nm. Derived from the CIE chromaticity diagram, this is the single wavelength perceived by the human eye that defines the color (red).
• Spectral Line Half-Width (Δλ): 20 nm (typical). The bandwidth of the emitted spectrum measured at half the peak intensity, indicating color purity.
• Forward Voltage (V_F): 1.6 - 2.4 V. The voltage drop across the LED when driven at 20mA. This range must be considered for driver design.
• Reverse Current (I_R): 10 μA (maximum). The leakage current when 5V is applied in reverse bias.

3. Binning System Explanation

To ensure consistency in applications, LEDs are sorted (binned) based on key optical parameters.

3.1 Luminous Intensity Bin Code

The device is categorized into bins based on its minimum and maximum luminous intensity measured at 20mA. The tolerance within each bin is +/-15%.

• Bin S: 180.0 - 280.0 mcd
• Bin T: 280.0 - 450.0 mcd
• Bin U: 450.0 - 710.0 mcd
• Bin V: 710.0 - 1120.0 mcd

Selecting the appropriate bin is crucial for applications requiring uniform brightness across multiple LEDs.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (e.g., Fig.1, Fig.5), the following analysis is based on the provided tabular data and standard LED behavior.

4.1 IV (Current-Voltage) Curve Implication

The forward voltage (V_F) range of 1.6V to 2.4V at 20mA indicates the characteristic exponential relationship of a diode. The actual V_F for a specific unit will depend on the semiconductor material properties and junction temperature. Designers must ensure the current-limiting circuit can accommodate this range to maintain consistent current and, therefore, consistent brightness.

4.2 Temperature Characteristics

The specified operating temperature range is -30°C to +85°C. It is important to note that LED characteristics are temperature-dependent. Typically, the forward voltage (V_F) has a negative temperature coefficient (decreases with increasing temperature), while luminous intensity also decreases as junction temperature rises. Adequate thermal management on the PCB is essential to maintain performance and longevity, especially when operating near the maximum current rating.

4.3 Spectral Distribution

With a dominant wavelength between 624nm and 636nm and a typical spectral half-width of 20nm, this LED emits a saturated red light. The relatively narrow spectrum is characteristic of AlInGaP technology, offering good color purity compared to older technologies like GaAsP.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD package outline. All dimensions are in millimeters with a typical tolerance of ±0.1mm unless otherwise noted. The specific footprint and height are defined in the package drawing, which is essential for PCB layout and clearance checks.

5.2 Recommended PCB Attachment Pad Layout

A suggested land pattern (copper pad design) is provided to ensure reliable soldering and mechanical stability. Following this recommendation helps achieve proper solder fillet formation and alignment during the reflow process.

5.3 Polarity Identification

The cathode is typically marked on the device, often by a notch, a green marking, or a shorter lead within the package. Correct polarity orientation is critical during assembly to ensure the device functions.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Parameters (Pb-Free Process)

The device is rated for IR reflow soldering with a peak temperature of 260°C for a maximum of 10 seconds. A sample profile is suggested, including a pre-heat stage (150-200°C for up to 120 seconds) to gradually heat the assembly and minimize thermal shock. The profile should be developed in accordance with JEDEC standards and validated with the specific PCB design and solder paste.

6.2 Hand Soldering

If hand soldering is necessary, it should be performed with a temperature-controlled iron set to a maximum of 300°C. The contact time with the LED terminal should not exceed 3 seconds, and soldering should be limited to one time only per pad to prevent thermal damage to the epoxy package and the semiconductor die.

6.3 Storage Conditions

LEDs are moisture-sensitive devices (MSL 3). When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤30°C and ≤90% RH and used within one year. Once the bag is opened, the storage environment should not exceed 30°C and 60% RH. Components exposed to ambient air for more than one week should be baked at approximately 60°C for at least 20 hours before reflow to remove absorbed moisture and prevent "popcorning" during soldering.

6.4 Cleaning

If post-solder cleaning is required, only alcohol-based solvents such as isopropyl alcohol (IPA) or ethyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. Unspecified chemical cleaners may damage the plastic lens or package material.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The components are supplied on embossed carrier tape, 8mm in width, wound onto 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. The tape is sealed with a cover tape to protect the components. Industry standards (ANSI/EIA 481) are followed for pocket spacing and orientation.

7.2 Minimum Order Quantity

The standard packing quantity is 3000 pieces per reel. For remainder quantities, a minimum pack of 500 pieces is available.

8. Application Suggestions

8.1 Drive Circuit Design

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, even when multiple LEDs are connected in parallel to a voltage source (as shown in the datasheet's "Circuit model A"). Driving LEDs directly from a voltage source without current regulation ("Circuit model B") is not recommended as it leads to brightness variation and potential overcurrent damage due to the spread in V_F from unit to unit.

8.2 Design Considerations

• Current Setting: Operate at or below the recommended 20mA DC forward current for optimal lifespan. Use the minimum current that achieves the required brightness.
• Thermal Management: Ensure the PCB has adequate copper area or thermal vias to dissipate heat, especially in high ambient temperature environments or high-current applications.
• ESD Protection: The device is sensitive to electrostatic discharge (ESD). Proper ESD controls (wrist straps, grounded workstations) must be used during handling and assembly.

9. Technical Comparison & Differentiation

This AlInGaP red LED offers several advantages:

• Higher Efficiency & Brightness: Compared to traditional GaAsP red LEDs, AlInGaP technology provides significantly higher luminous intensity for the same drive current.
• Better Temperature Stability: AlInGaP LEDs generally exhibit less luminous intensity drop with increasing temperature than some other technologies.
• Standardized Package: The EIA-standard SMD footprint ensures compatibility with a vast array of automated assembly equipment and PCB design libraries, reducing design and manufacturing complexity.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Why is there such a large range in Luminous Intensity (180-1120 mcd)?

This range represents the total spread across the entire production. Through the binning system (S, T, U, V), units are sorted into much tighter groups. Designers specify the required bin to ensure consistency in their application.

10.2 Can I drive this LED at 25mA continuously?

While 25mA is the absolute maximum DC current rating, for reliable long-term operation and to account for real-world thermal conditions, it is advisable to design the drive circuit for a lower current, such as the typical test condition of 20mA. Derating increases reliability.

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

Peak Wavelength (λ_P) is the physical wavelength where the spectral output is strongest. Dominant Wavelength (λ_d) is a calculated value based on human color perception (CIE chart) that defines the perceived color. For a monochromatic source like this red LED, they are close but not necessarily identical.

11. Practical Design Case

Scenario: Designing a status indicator panel requiring 5 uniformly bright red LEDs powered from a 5V rail.

1. Bin Selection: Choose Bin U (450-710 mcd) for high, consistent brightness.
2. Drive Current: Target 18mA per LED for a good balance of brightness and longevity.
3. Series Resistor Calculation: Using Ohm's Law: R = (V_supply - V_F) / I_F. To accommodate the V_F range (1.6V-2.4V), use the maximum V_F for a conservative design: R = (5V - 2.4V) / 0.018A ≈ 144 Ω. The nearest standard value is 150 Ω. Re-calculating current for the minimum V_F: I_F = (5V - 1.6V) / 150Ω ≈ 22.7mA, which is still within a safe limit. Therefore, a 150Ω, 1/8W resistor in series with each LED is appropriate.
4. Layout: Place the LEDs and resistors according to the recommended pad layout. Ensure some copper pour around the LED pads for heat sinking.

12. Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons and holes recombine in the active region (the AlInGaP chip in this case). This recombination releases energy in the form of photons (light). The specific material composition of the semiconductor (Aluminum, Indium, Gallium, Phosphide) determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this instance, red. The dome-shaped epoxy lens serves to protect the chip, enhance light extraction from the semiconductor, and shape the radiation pattern into a wide viewing angle.

13. Development Trends

The general trend in SMD LED technology continues toward higher luminous efficacy (more light output per watt of electrical input), improved reliability, and smaller package sizes enabling higher density designs. There is also a focus on tighter binning tolerances for color and intensity to meet the demands of applications requiring precise color matching and uniformity, such as full-color displays and automotive lighting. Furthermore, advancements in packaging materials aim to provide better thermal performance and resistance to harsh environmental conditions like high humidity and temperature cycling.