SMD LED LTST-S270KDKT Datasheet - Red AllnGaP Chip - 20mA - 50mW - English Technical Document

1. Product Overview

The LTST-S270KDKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It features a miniature form factor suitable for space-constrained applications. The device utilizes an ultra-bright Aluminum Indium Gallium Phosphide (AllnGaP) semiconductor chip to produce red light, housed in a water-clear lens package. This combination is engineered for applications requiring high reliability and compatibility with modern manufacturing processes.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Side-looking chip configuration with tin-plated leads for improved solderability.
• Utilizes an ultra-bright AllnGaP chip technology for high luminous intensity.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place assembly.
• Conforms to EIA (Electronic Industries Alliance) standard package outlines.
• IC-compatible drive characteristics.
• Designed for compatibility with automatic placement equipment.
• Suitable for infrared (IR) reflow soldering processes.

1.2 Applications

This LED is targeted at a broad range of electronic equipment where compact size, reliability, and efficient assembly are critical. Typical application areas include:

• Telecommunications: Status indicators in cordless phones, cellular phones, and network equipment.
• Office Automation & Consumer Electronics: Backlighting for keypads and keyboards in notebook computers and other portable devices.
• Home Appliances & Industrial Equipment: Power, mode, or status indicators.
• Display and Signage: Micro-displays and symbol illumination in indoor applications.

2. Package Dimensions and Mechanical Information

The LED is provided in a standard SMD package. The lens color is water clear, and the light source color is red from the AllnGaP chip. All dimensional tolerances are \u00b10.1 mm unless otherwise specified. Detailed mechanical drawings for the component, recommended PCB attachment pads, and tape-and-reel packaging are provided in the source document, which are essential for PCB layout design and assembly process planning.

3. Ratings and Characteristics

3.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. All values are specified at an ambient temperature (Ta) of 25\u00b0C.

• Power Dissipation (Pd): 50 mW
• Peak Forward Current (I_F(PEAK)): 40 mA (at 1/10 duty cycle, 0.1ms pulse width)
• DC Forward Current (I_F): 20 mA
• Reverse Voltage (V_R): 5 V
• Operating Temperature Range (T_opr): -30\u00b0C to +85\u00b0C
• Storage Temperature Range (T_stg): -40\u00b0C to +85\u00b0C
• Infrared Soldering Condition: 260\u00b0C peak temperature for a maximum of 10 seconds.

3.2 Electrical and Optical Characteristics

These are the typical operating parameters measured at Ta=25\u00b0C and I_F=20 mA, unless noted.

• Luminous Intensity (I_V): 4.5 - 45.0 mcd (millicandela). Measured with a filter approximating the CIE photopic eye-response curve.
• Viewing Angle (2\u03b8_1/2): 130 degrees. Defined as the full angle at which intensity is half the axial (on-axis) value.
• Peak Emission Wavelength (\u03bb_P): 650.0 nm (typical).
• Dominant Wavelength (\u03bb_d): 630.0 - 645.0 nm. This single wavelength defines the perceived color of the LED on the CIE chromaticity diagram.
• Spectral Line Half-Width (\u0394\u03bb): 20 nm (typical). The width of the emission spectrum at half its maximum intensity.
• Forward Voltage (V_F): 1.6 - 2.4 V.
• Reverse Current (I_R): 10 \u03bcA (maximum) at V_R=5V.

3.3 Electrostatic Discharge (ESD) Caution

LEDs are sensitive to electrostatic discharge and voltage surges. Proper ESD control measures must be implemented during handling and assembly. This includes the use of grounded wrist straps, anti-static gloves, and ensuring all equipment and workstations are properly grounded to prevent latent or catastrophic device failure.

4. Bin Rank System

To ensure color and brightness consistency in production, LEDs are sorted into bins based on luminous intensity. The LTST-S270KDKT uses the following bin codes for its red output, measured at 20 mA.

• Bin J: 4.5 - 7.1 mcd
• Bin K: 7.1 - 11.2 mcd
• Bin L: 11.2 - 18.0 mcd
• Bin M: 18.0 - 28.0 mcd
• Bin N: 28.0 - 45.0 mcd

A tolerance of \u00b115% is applied to the limits of each luminous intensity bin. Designers should specify the required bin code to guarantee the desired brightness level in the final application.

5. Performance Curve Analysis

The source document includes typical performance curves which are crucial for understanding device behavior under various conditions. These curves typically illustrate the relationship between forward current and luminous intensity (I_F vs. I_V), forward current and forward voltage (I_F vs. V_F), and the effect of ambient temperature on luminous intensity. Analyzing these curves allows designers to optimize drive current for efficiency and brightness, understand voltage requirements for power supply design, and account for thermal derating in high-temperature environments.

6. Assembly and Handling Guidelines

6.1 Cleaning

Unspecified chemical cleaners can damage the LED package. If cleaning is necessary after soldering or due to contamination, use ethyl alcohol or isopropyl alcohol at room temperature. Immersion time should be less than one minute to prevent potential harm to the epoxy lens or internal structure.

6.2 Soldering Process

The device is compatible with infrared (IR) reflow soldering processes, which is standard for SMD assembly. A lead-free (Pb-free) process profile is recommended.

• Pre-heat: 150\u00b0C to 200\u00b0C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260\u00b0C.
• Time Above Liquidus: Maximum 10 seconds at peak temperature. Reflow should not be performed more than twice.

For manual rework with a soldering iron, the tip temperature should not exceed 300\u00b0C, and contact time should be limited to a maximum of 3 seconds per joint. It is critical to follow JEDEC-standard reflow profiles and solder paste manufacturer recommendations to ensure reliable solder joints and prevent thermal damage to the LED.

6.3 Storage Conditions

Proper storage is vital to maintain solderability and device reliability.

• Sealed Package: Store at \u2264 30\u00b0C and \u2264 90% Relative Humidity (RH). The shelf life is one year when stored in the original moisture-proof bag with desiccant.
• Opened Package: For components removed from their original packaging, the storage environment must not exceed 30\u00b0C or 60% RH. It is recommended to complete IR reflow within one week (Moisture Sensitivity Level 3, MSL 3). For longer storage outside the original bag, use a sealed container with desiccant or a nitrogen desiccator. Components stored for more than one week should be baked at approximately 60\u00b0C for at least 20 hours before soldering to remove absorbed moisture.

7. Packaging and Ordering Information

The standard packaging for high-volume assembly is 8mm wide embossed carrier tape wound on 7-inch (178mm) diameter reels. Each reel contains 4000 pieces. The tape is sealed with a top cover tape. Packaging follows ANSI/EIA-481 specifications. For smaller quantities, a minimum pack of 500 pieces is available. The tape is designed to allow a maximum of two consecutive missing components (empty pockets).

8. Application Design Considerations

8.1 Drive Circuit Design

LEDs are current-driven devices. To ensure uniform brightness when driving multiple LEDs, especially in parallel configurations, it is essential to use a current-limiting resistor in series with each LED. This compensates for the natural variation in forward voltage (V_F) from one device to another. Driving LEDs directly from a voltage source without current regulation can lead to excessive current, thermal runaway, and reduced lifespan. The simple series resistor method (Circuit A in the source document) is a reliable and common approach.

8.2 Thermal Management

While the package is small, power dissipation (50 mW maximum) and the operating temperature range (-30\u00b0C to +85\u00b0C) must be respected. Luminous output typically decreases as junction temperature increases. In applications where the LED is driven at or near its maximum current, or in high ambient temperatures, consideration should be given to the PCB layout to provide adequate thermal relief via copper pads and traces.

8.3 Application Scope and Reliability

This product is intended for use in standard commercial and consumer electronic equipment. For applications requiring exceptional reliability where failure could jeopardize safety or health (e.g., aviation, medical life-support, transportation control), additional qualification and consultation are necessary. The device is not designed for continuous outdoor exposure or harsh environments unless properly protected.

9. Technical Comparison and Trends

The use of AllnGaP technology for red LEDs represents a significant advancement over older technologies like Gallium Arsenide Phosphide (GaAsP). AllnGaP offers superior luminous efficiency, resulting in higher brightness for the same drive current, and better temperature stability. The side-looking package (as opposed to top-emitting) is specifically advantageous for applications where light needs to be directed parallel to the PCB surface, such as in edge-lit panels or light guide applications for keyboard backlighting. The trend in SMD LEDs continues toward higher efficiency, smaller packages, and broader compatibility with automated, high-temperature assembly processes like lead-free reflow soldering.

10. Frequently Asked Questions (FAQ)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (\u03bb_P) is the wavelength at which the optical output power is maximum. Dominant wavelength (\u03bb_d) is the single wavelength perceived by the human eye, calculated from the CIE color coordinates. \u03bb_d is more relevant for color specification.

Q: Can I drive this LED without a series resistor?
A: It is strongly discouraged. The forward voltage has a range (1.6V to 2.4V). Connecting it directly to a voltage source even slightly above its V_F can cause a large, uncontrolled current to flow, potentially destroying the LED instantly or over time.

Q: Why is the viewing angle so wide (130\u00b0)?
A> A wide viewing angle is characteristic of the side-looking package and lens design. It is beneficial for applications requiring broad, even illumination over an area, rather than a focused spot of light.

Q: How do I select the correct bin code?
A> The bin code selection depends on the required minimum brightness for your application. If your design needs at least 15 mcd, you should specify Bin L or higher (L, M, N). Using a higher bin ensures your brightness requirement is met even with the -15% tolerance.

11. Design and Usage Case Study

Scenario: Backlighting a Membrane Keypad.
A designer is creating a medical device with a silicone rubber keypad that requires red backlighting for low-light operation. Space is extremely limited behind the keypad.

Design Choices:
1. The LTST-S270KDKT is selected for its side-looking emission, which is ideal for coupling light into the edge of a light guide or directly illuminating the side of a translucent keypad legend from the PCB level.
2. The ultra-bright AllnGaP chip ensures sufficient light output even when diffused through the rubber keypad material.
3. A drive current of 15 mA is chosen (below the 20 mA maximum) to ensure long-term reliability and minimize heat generation within the sealed device enclosure.
4. Bin M (18.0-28.0 mcd) is specified to guarantee a bright, consistent appearance across all keys.
5. The PCB layout includes the recommended solder pad dimensions and uses a 0805-size current-limiting resistor in series with each LED, calculated based on the power supply voltage and the typical V_F of the LED.
6. The assembly house follows the provided IR reflow profile, and the devices are stored in a controlled environment before use to comply with MSL3 requirements.

This approach results in a reliable, uniformly lit keypad that meets the aesthetic and functional requirements of the end product.