SMD LED LTST-M140KSKT Datasheet - Yellow AlInGaP - 30mA - 72mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-M140KSKT, a surface-mount device (SMD) light-emitting diode (LED). This component belongs to a family of LEDs designed for automated printed circuit board (PCB) assembly, featuring miniature sizes and configurations suitable for space-constrained applications. The LED utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce a yellow light output, encapsulated in a water-clear lens package.

The core design philosophy centers on compatibility with modern high-volume electronics manufacturing. The device is engineered to be compatible with automatic pick-and-place equipment and withstand the thermal profile of standard infrared (IR) reflow soldering processes, making it ideal for streamlined production lines.

The target markets and applications are broad, reflecting the component's versatility and reliability. Primary applications include status indicators, backlighting for front panels, and signal or symbol illumination within telecommunications equipment, office automation devices, home appliances, and various industrial equipment.

2. Technical Parameters Deep Dive

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. These values are specified at an ambient temperature (Ta) of 25°C. The maximum continuous forward current (DC) is 30 mA. Under pulsed conditions with a 1/10 duty cycle and a 0.1ms pulse width, the device can handle a peak forward current of 80 mA. The maximum permissible reverse voltage applied across the LED is 5 V. The total power dissipation must not exceed 72 mW. 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 typical electrical and optical performance is measured at Ta=25°C with a forward current (IF) of 20 mA, which is the standard test condition. The key parameters include:

• Luminous Flux (Φv): Ranges from a minimum of 0.42 lumens (lm) to a typical maximum of 1.35 lm. This measures the total perceived power of light emitted.
• Luminous Intensity (Iv): Corresponds to the luminous flux, with a minimum of 140 millicandelas (mcd) and a typical maximum of 450 mcd. Intensity is measured along the central axis.
• Viewing Angle (2θ1/2): The full angle at which the luminous intensity is half the axial value is typically 120 degrees, indicating a wide viewing pattern.
• Peak Wavelength (λP): The wavelength at which the spectral emission is strongest is typically 591 nanometers (nm).
• Dominant Wavelength (λd): The single wavelength that defines the perceived color, specified between 584.5 nm and 594.5 nm, ensuring a consistent yellow hue.
• Spectral Line Half-Width (Δλ): Typically 15 nm, describing the spectral purity or bandwidth of the emitted light.
• Forward Voltage (VF): Ranges from 1.8 V to 2.4 V at 20 mA, with a tolerance of ±0.1 V for binned parts.
• Reverse Current (IR): Maximum of 10 microamperes (μA) when a 5 V reverse bias is applied.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific requirements for their application.

3.1 Forward Voltage (VF) Binning

LEDs are categorized into three voltage bins (D2, D3, D4) at 20 mA. Bin D2 covers 1.8V to 2.0V, D3 covers 2.0V to 2.2V, and D4 covers 2.2V to 2.4V. Each bin has a ±0.1V tolerance. Selecting a tighter voltage bin can help in designing more consistent driver circuits, especially when multiple LEDs are connected in series.

3.2 Luminous Flux and Intensity Binning

The luminous output is binned into five primary codes (C2, D1, D2, E1, E2). For example, bin C2 specifies a luminous flux between 0.42 lm and 0.54 lm (corresponding to 140-180 mcd), while the highest output bin, E2, covers 1.07 lm to 1.35 lm (355-450 mcd). The tolerance for each intensity bin is ±11%. This binning is crucial for applications requiring uniform brightness across multiple indicators or backlighting arrays.

3.3 Hue (Dominant Wavelength) Binning

The dominant wavelength, which defines the precise shade of yellow, is binned into four categories: H (584.5-587.0 nm), J (587.0-589.5 nm), K (589.5-592.0 nm), and L (592.0-594.5 nm). Each bin has a tolerance of ±1 nm. This allows for precise color matching in applications where specific yellow tones are required, such as in traffic signals or specific status indicators.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, typical performance curves for such LEDs provide essential design insights. These generally include:

• Current vs. Voltage (I-V) Curve: Shows the exponential relationship between forward voltage and current. The curve is crucial for determining the operating point and designing current-limiting circuitry.
• Luminous Intensity vs. Forward Current (I-L Curve): Demonstrates how light output increases with current, typically in a near-linear relationship within the recommended operating range. It helps in selecting the drive current for desired brightness.
• Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as the junction temperature rises. Understanding this derating is vital for applications operating in elevated temperature environments.
• Spectral Distribution Curve: Plots relative intensity against wavelength, showing the peak at ~591 nm and the 15 nm half-width, confirming the monochromatic yellow emission.
• Viewing Angle Pattern: A polar plot showing the angular distribution of light intensity, typically confirming the 120-degree viewing angle with a Lambertian or similar emission pattern.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED comes in a standard SMD package. All dimensions are provided in millimeters with a general tolerance of ±0.2 mm unless otherwise specified. The datasheet includes a detailed mechanical drawing showing the top view, side view, and footprint, including key dimensions like body length, width, height, and the placement and size of the solder pads.

5.2 Pad Design and Polarity Identification

A recommended PCB land pattern (attachment pad) is provided for both infrared and vapor phase reflow soldering processes. This pattern is optimized for reliable solder joint formation and mechanical stability. The component features polarity markings, typically indicated by a cathode marker on the package itself (like a notch, dot, or trimmed lead). Correct orientation is essential as LEDs are diodes and only allow current flow in one direction.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The datasheet provides a suggested IR reflow profile compliant with J-STD-020B for lead-free processes. Key parameters include a pre-heat zone, a controlled ramp-up to a peak temperature, and a controlled cooling phase. The maximum peak temperature recommended is 260°C, with the time above 217°C (liquidus temperature for typical lead-free solder) carefully controlled to prevent thermal damage to the LED package or the semiconductor die.

6.2 Storage and Handling Precautions

The LEDs are moisture-sensitive devices. When sealed in their original moisture-proof packaging with desiccant, they should be stored at ≤30°C and ≤70% relative humidity (RH) and used within one year. Once the sealed bag is opened, the "floor life" begins. Components should be stored at ≤30°C and ≤60% RH and are recommended to be IR-reflowed within 168 hours (JEDEC Level 3). For storage beyond this period, baking at approximately 60°C for at least 48 hours is required before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is recommended. Unspecified chemical cleaners may damage the epoxy lens or the package material.

7. Packaging and Ordering Information

The standard packaging for automated assembly is a 12 mm wide embossed carrier tape wound on a 7-inch (178 mm) diameter reel. Each reel contains 3000 pieces. The tape and reel specifications comply with ANSI/EIA-481 standards. A minimum packing quantity of 500 pieces is available for remainder orders. The tape includes a cover tape to seal the component pockets, and the maximum allowed number of consecutive missing components in a reel is two.

8. Application Suggestions

8.1 Typical Application Circuits

The most common drive method is a constant current source or a simple series resistor. The resistor value (R) is calculated using the formula: R = (Vsupply - VF) / IF, where VF is the forward voltage of the LED at the desired current IF. For example, with a 5V supply, a VF of 2.0V, and a target IF of 20mA, the required series resistor is (5V - 2.0V) / 0.02A = 150 Ohms. A resistor rated for at least (5V-2.0V)*0.02A = 0.06W should be selected, with a 1/8W or 1/10W resistor being typical.

8.2 Design Considerations

• Current Limiting: Always use a current-limiting device (resistor or driver IC). Connecting directly to a voltage source will cause excessive current and immediate failure.
• Thermal Management: While the power dissipation is low, ensuring adequate PCB copper area or thermal vias around the solder pads can help dissipate heat, especially in high ambient temperature conditions or when driven at higher currents.
• ESD Protection: Although not explicitly stated as highly sensitive, standard ESD handling precautions should be observed during assembly.
• Optical Design: The wide 120-degree viewing angle makes it suitable for applications requiring broad visibility. For focused light, secondary optics (lenses) would be required.

9. Technical Comparison and Differentiation

The LTST-M140KSKT differentiates itself through its use of AlInGaP technology for yellow emission. Compared to older technologies like GaAsP, AlInGaP LEDs offer significantly higher luminous efficiency, resulting in brighter output at the same drive current, and better temperature stability. The wide 120-degree viewing angle is a key feature for indicator applications. Its compatibility with standard IR reflow processes and tape-and-reel packaging makes it a cost-effective choice for automated, high-volume manufacturing compared to through-hole LEDs requiring manual insertion.

10. Frequently Asked Questions (FAQs)

Q: What is the difference between luminous flux (lm) and luminous intensity (mcd)?
A: Luminous flux measures the total amount of visible light emitted in all directions. Luminous intensity measures the brightness in a specific direction (typically the central axis). For a wide-angle LED like this, the mcd value is a reference point, but the total light output is better represented by the lumen value.

Q: Can I drive this LED with a 3.3V supply?
A: Yes. Using the formula with a typical VF of 2.0V and a target current of 20mA, the required series resistor would be (3.3V - 2.0V) / 0.02A = 65 Ohms. Ensure the resistor power rating is sufficient.

Q: Why is binning important?
A: Binning ensures color and brightness consistency. If you are using multiple LEDs in a product (e.g., an array of status lights), ordering from the same voltage, intensity, and wavelength bins guarantees a uniform appearance.

Q: What happens if I exceed the absolute maximum reverse voltage of 5V?
A> Applying a reverse voltage beyond the rating can cause a sudden, catastrophic breakdown of the LED's PN junction, leading to immediate and permanent failure.

11. Practical Use Case Example

Scenario: Designing a status indicator panel for a network router. The panel requires four yellow LEDs to show link activity on different ports. Uniform brightness and color are critical for user experience.
Design Steps:
1. Select the LTST-M140KSKT for its yellow color, suitable brightness, and SMD form factor.
2. Specify bins: Choose a single luminous intensity bin (e.g., D2 for 224-280 mcd) and a single dominant wavelength bin (e.g., J for 587.0-589.5 nm) to ensure consistency. A mid-range voltage bin (D3) is acceptable.
3. Circuit Design: Use a common 3.3V rail on the router's PCB. Calculate the series resistor for each LED. Assuming a VF of 2.1V (middle of bin D3) and a target 20mA: R = (3.3V - 2.1V) / 0.02A = 60 Ohms. Use a standard 62-ohm, 1/10W resistor.
4. Layout: Place the LEDs symmetrically on the PCB front panel. Follow the recommended land pattern from the datasheet to ensure good solderability.
5. Assembly: Follow the recommended reflow profile. Ensure the opened reel of LEDs is used within the 168-hour floor life or is properly baked if stored longer.

12. Operating Principle

Light emission in this LED is based on electroluminescence in a semiconductor PN junction made of AlInGaP materials. When a forward voltage exceeding the junction's built-in potential is applied, electrons from the N-type region and holes from the P-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, yellow (~591 nm). The water-clear epoxy lens encapsulates the semiconductor chip, provides mechanical protection, and shapes the light output pattern.

13. Technology Trends

The development of SMD LEDs like the LTST-M140KSKT is part of the broader trend in electronics towards miniaturization, increased reliability, and automated manufacturing. AlInGaP technology represents a mature and efficient solution for red, orange, and yellow LEDs. Ongoing trends in the industry include the push for even higher luminous efficacy (more light output per watt of electrical input), improved color consistency through tighter binning, and the development of ever-smaller package sizes (e.g., chip-scale packages) to enable denser integration. Furthermore, there is a focus on enhancing reliability under harsh environmental conditions, such as higher temperature and humidity ranges, to meet the demands of automotive and industrial applications.