LTST-C281KSKT Yellow SMD LED Datasheet - 0.35mm Height - 2.4V Typ - 75mW - English Technical Documentation

1. Product Overview

The LTST-C281KSKT is an ultra-thin, surface-mount chip LED designed for modern electronic applications requiring minimal vertical profile. This device utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce a bright yellow light output. Its primary design goals are compatibility with automated assembly processes, adherence to environmental regulations, and reliable performance in a compact form factor.

The core advantage of this LED lies in its exceptionally low profile of 0.35mm, making it suitable for applications where space constraints are critical, such as in ultra-thin displays, backlighting for slim consumer electronics, and indicator lights in densely packed PCBs. It is packaged on 8mm tape and supplied on 7-inch diameter reels, facilitating high-speed pick-and-place manufacturing.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device's operational limits are defined under an ambient temperature (Ta) of 25°C. Exceeding these ratings may cause permanent damage.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED can dissipate as heat without degradation.
• Peak Forward Current (I_F(PEAK)): 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating.
• Continuous Forward Current (I_F): 30 mA DC. This is the maximum recommended current for continuous operation.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage beyond this limit can break down the LED's PN junction.
• Operating Temperature Range: -30°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +85°C.
• Infrared Reflow Soldering Condition: Withstands a peak temperature of 260°C for a maximum of 10 seconds, compatible with standard Pb-free (lead-free) soldering processes.

2.2 Electro-Optical Characteristics

Key performance parameters are measured at Ta=25°C and a standard test current of I_F = 20mA.

• Luminous Intensity (I_V): Ranges from a minimum of 28.0 mcd to a maximum of 180.0 mcd. The typical value falls within this wide binning range (see Section 3). Measurement is performed using a sensor filtered to match the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on-axis. It indicates a wide, diffuse light emission pattern suitable for area illumination or wide-angle indicators.
• Peak Emission Wavelength (λ_P): 588 nm. This is the wavelength at which the spectral power distribution reaches its maximum.
• Dominant Wavelength (λ_d): 587 nm to 597 nm. This is the single wavelength perceived by the human eye that defines the color (yellow) of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 15 nm. This parameter describes the spectral purity or bandwidth of the emitted light, measured at half the maximum intensity.
• Forward Voltage (V_F): Typical value is 2.4V, with a range from 2.0V to the maximum specified. This is the voltage drop across the LED when conducting 20mA.
• Reverse Current (I_R): Maximum of 10 μA when a reverse bias of 5V is applied.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters. The LTST-C281KSKT uses a three-code binning system (e.g., D4-P-K).

3.1 Forward Voltage Binning

Bins ensure LEDs in a circuit have similar voltage drops, preventing current imbalance in parallel configurations.

• Bin D2: V_F = 1.80V - 2.00V @20mA
• Bin D3: V_F = 2.00V - 2.20V @20mA
• Bin D4: V_F = 2.20V - 2.40V @20mA
• Tolerance per bin: ±0.1V

3.2 Luminous Intensity Binning

This groups LEDs by their light output brightness.

• Bin N: I_V = 28.0 mcd - 45.0 mcd @20mA
• Bin P: I_V = 45.0 mcd - 71.0 mcd @20mA
• Bin Q: I_V = 71.0 mcd - 112.0 mcd @20mA
• Bin R: I_V = 112.0 mcd - 180.0 mcd @20mA
• Tolerance per bin: ±15%

3.3 Dominant Wavelength Binning

Critical for color-matched applications, this defines the precise shade of yellow.

• Bin J: λ_d = 587.00 nm - 589.50 nm @20mA
• Bin K: λ_d = 589.50 nm - 592.00 nm @20mA
• Bin L: λ_d = 592.00 nm - 594.50 nm @20mA
• Bin M: λ_d = 594.50 nm - 597.00 nm @20mA
• Tolerance per bin: ±1 nm

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), their implications are standard for AlInGaP LEDs.

• I-V (Current-Voltage) Curve: Exhibits the typical exponential relationship of a diode. The forward voltage shows a positive temperature coefficient, meaning V_F decreases slightly as junction temperature increases for a given current.
• Luminous Intensity vs. Forward Current: Intensity is approximately proportional to forward current in the normal operating range (up to 30mA). Driving beyond this point leads to sub-linear increases due to efficiency droop and increased thermal effects.
• Luminous Intensity vs. Ambient Temperature: The light output of AlInGaP LEDs generally decreases as ambient (and junction) temperature rises. This thermal derating must be considered in high-temperature environments.
• Spectral Distribution: The emission spectrum is centered around 588nm (yellow) with a relatively narrow half-width of 15nm, indicating good color saturation.
• Viewing Angle Pattern: The 130-degree viewing angle suggests a near-Lambertian emission pattern, where intensity is roughly cosine-dependent on the viewing angle off-axis.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Polarity

The device conforms to an EIA standard package outline. Key dimensional features include the overall height of 0.35mm. The package incorporates a water-clear lens. Polarity is indicated by a cathode mark, typically a notch, green dot, or other visual indicator on the package or tape. The exact marking should be verified from the package drawing.

5.2 Recommended Solder Pad Layout

A land pattern (solder pad footprint) is provided to ensure reliable solder joint formation during reflow. This pattern is designed to facilitate proper solder wetting, self-alignment of the component during reflow, and long-term mechanical reliability. Adhering to this recommended layout is crucial to prevent tombstoning or poor solder connections.

5.3 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound on 7-inch (178mm) diameter reels.

• Pocket Pitch: 8mm (standard for many small SMD components).
• Quantity per Reel: 5000 pieces.
• Minimum Order Quantity (MOQ) for remnants: 500 pieces.
• Missing Components: A maximum of two consecutive empty pockets is allowed.
• Standard: Packaging complies with ANSI/EIA-481 specifications.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared (IR) reflow profile is provided for Pb-free solder processes. Key parameters include:

• Preheat: 150°C to 200°C.
• Preheat Time: Maximum 120 seconds to allow for uniform heating and solvent evaporation from solder paste.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus (TAL): The duration within 5°C of the peak temperature should be limited to a maximum of 10 seconds. The component can withstand this peak temperature for a maximum of two reflow cycles.

The profile is based on JEDEC standards. Engineers must characterize the profile for their specific PCB design, solder paste, and oven to create reliable solder joints.

6.2 Hand Soldering

If manual soldering is necessary, extreme care must be taken:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per lead.
• Limit: Only one hand-soldering cycle is permitted to avoid thermal damage to the plastic package and the semiconductor die.

6.3 Cleaning

Cleaning is generally not required after reflow with no-clean solder paste. If cleaning is necessary (e.g., after hand soldering with flux):

• Recommended Solvents: Use only alcohol-based cleaners such as ethyl alcohol or isopropyl alcohol (IPA).
• Process: Immerse the LED at normal room temperature for less than one minute. Agitation may be used gently.
• Avoid: Do not use unspecified chemical liquids, ultrasonic cleaning (can cause mechanical stress), or harsh solvents that may damage the epoxy lens or package markings.

7. Storage and Handling

7.1 Moisture Sensitivity

The LED package is moisture-sensitive. Adherence to storage conditions is critical to prevent "popcorning" (package cracking) during reflow due to rapid vaporization of absorbed moisture.

• Sealed Bag (Original Packaging): Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life is one year when stored in the moisture-proof bag with desiccant.
• After Bag Opening: The exposure time out of the bag is limited. The recommended "floor life" before reflow is 672 hours (28 days) when stored at ≤30°C and ≤60% RH.
• Extended Storage (Opened): For storage beyond 672 hours, place components in a sealed container with desiccant or in a nitrogen desiccator.
• Rebaking: Components exposed for more than 672 hours must be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture.

7.2 Electrostatic Discharge (ESD) Protection

LEDs are susceptible to damage from electrostatic discharge. Precautions must be taken during all handling and assembly stages.

• Operators should wear a grounded wrist strap or anti-static gloves.
• All workstations, tools, and equipment must be properly grounded.
• Use conductive or dissipative mats on work surfaces.
• Transport and store components in ESD-protective packaging.

8. Application Suggestions

8.1 Typical Application Scenarios

• Status Indicators: Power, connectivity, and function status lights in consumer electronics (routers, set-top boxes, smart home devices), office equipment, and industrial control panels.
• Backlighting: Edge-lit or direct backlighting for LCD displays in thin devices, keypad illumination, and icon backlighting where height is constrained.
• Automotive Interior Lighting: Dashboard indicators, switch illumination, and ambient lighting (subject to verification of specific automotive-grade requirements).
• Portable and Wearable Devices: Battery level indicators, notification lights in smartphones, tablets, and fitness trackers benefiting from the ultra-low profile.

8.2 Design Considerations

• Current Limiting: Always use a series current-limiting resistor or a constant-current driver. Calculate the resistor value using R = (V_supply - V_F) / I_F. Do not connect directly to a voltage source.
• Thermal Management: Although power dissipation is low, ensure adequate PCB copper area or thermal vias under the solder pads to conduct heat away, especially when operating near maximum current or in high ambient temperatures. This maintains luminous output and longevity.
• Parallel Connections: Avoid connecting multiple LEDs directly in parallel from a single voltage source. Slight variations in V_F can cause significant current imbalance, with one LED hogging most of the current. Use separate current-limiting resistors for each LED or a constant-current driver with multiple channels.
• Optical Design: The wide 130-degree viewing angle provides good off-axis visibility. For focused light, external lenses or light guides may be required.

9. Technical Comparison and Differentiation

The LTST-C281KSKT offers specific advantages in its class:

• vs. Standard Thickness LEDs (0.6mm+): The primary differentiator is the 0.35mm height, enabling design in space-critical applications where traditional LEDs cannot fit.
• vs. Other Yellow LED Technologies: The use of AlInGaP semiconductor material, compared to older technologies like GaAsP, provides higher luminous efficiency (more light output per unit of electrical power), better temperature stability, and superior color purity (narrower spectrum).
• vs. Non-Reel Packaged LEDs: The 8mm tape-on-reel packaging is a significant advantage for mass production, ensuring compatibility with high-speed automated pick-and-place machines, reducing assembly time and cost.
• Compliance: It meets RoHS (Restriction of Hazardous Substances) directives and is classified as a Green Product, which is a mandatory requirement for electronics sold in many global markets.

10. Frequently Asked Questions (FAQ)

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

Peak Wavelength (λ_P): The literal, physical wavelength at which the LED emits the most optical power. It is measured directly from the spectrum.
Dominant Wavelength (λ_d): A calculated value based on human color perception (CIE chart). It is the single wavelength of monochromatic light that would appear to have the same color as the LED's broad-spectrum output. For color definition and matching, the dominant wavelength is the more relevant parameter.

10.2 Can I drive this LED at 30mA continuously?

Yes, 30mA is the maximum rated DC forward current. However, for optimal longevity and to account for real-world conditions like elevated ambient temperature, it is considered good engineering practice to derate this value. Operating at 20mA (the standard test condition) or lower will significantly extend the LED's operational life and maintain more stable light output.

10.3 Why is binning important, and which bin should I choose?

Binning is crucial for consistency in appearance and performance within an application. For example, in a panel of multiple status LEDs, using LEDs from different intensity or wavelength bins would result in visibly different brightnesses and color shades.
Choose bins based on your application's needs: For tight color matching (e.g., brand-specific yellow), specify a narrow dominant wavelength bin (J, K, L, or M). For consistent brightness across multiple units, specify a luminous intensity bin (N, P, Q, or R). For current balancing in parallel strings, specify a forward voltage bin (D2, D3, D4).

10.4 Is a heat sink required?

A dedicated heat sink is not typically required for a single LED operating at or below 30mA due to its low 75mW power dissipation. However, effective thermal management at the PCB level is essential. This means providing adequate copper area (thermal pad) connected to the LED's solder pads to conduct heat into the PCB substrate, which acts as a heat spreader. This is especially important for arrays of LEDs or operation in high-temperature environments.

11. Practical Design Case Study

Scenario: Designing a low-battery indicator for a handheld medical device. The device housing has an internal height limitation of 0.5mm for the PCB and all components in the indicator area.
Challenge: A standard LED with 0.6mm height would not fit.
Solution: The LTST-C281KSKT, with its 0.35mm height, is selected. A current-limiting resistor is calculated for a 3.3V supply: R = (3.3V - 2.4V) / 0.020A = 45Ω. A 47Ω standard value resistor is chosen, resulting in I_F ≈ 19mA. The wide 130-degree viewing angle ensures the indicator is visible from various angles. The yellow color is chosen as a universal caution/warning indicator. The tape-and-reel packaging allows for automated assembly, ensuring manufacturing efficiency and reliability.

12. Technology Principle Introduction

The LTST-C281KSKT is based on AlInGaP semiconductor technology. This material is a compound semiconductor from the III-V group. When a forward voltage 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 Aluminum, Indium, Gallium, and Phosphide in the active layer determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. For yellow light (~590nm), a specific bandgap energy is engineered. The water-clear epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output pattern.

13. Technology Trends

The general trend in SMD LEDs for indicator and backlight applications continues toward:

• Increased Efficiency: Developing materials and structures that produce more lumens per watt (lm/W), reducing power consumption for the same light output.
• Miniaturization: Further reduction in package size (footprint and height) to enable ever-slimmer electronic devices. The 0.35mm height of this device is part of this trend.
• Improved Color Rendering and Gamut: For display backlighting, there is a move toward LEDs with narrower spectral peaks and specific wavelengths to enable wider color gamuts (e.g., Rec. 2020).
• Higher Reliability and Lifetime: Advancements in packaging materials (epoxy, silicone) and die attach technologies to withstand higher junction temperatures and harsher environmental conditions, extending operational lifetime.
• Integration: Incorporating multiple LED chips (RGB, RGBW) into a single package or integrating driving electronics (IC) with the LED for simplified design ("smart LEDs").