LTST-C281KSKT-5A SMD LED Datasheet - 0.35mm Height - 1.7-2.3V - 75mW - AlInGaP Yellow - English Technical Document

1. Product Overview

The LTST-C281KSKT-5A is a surface-mount device (SMD) LED lamp designed for modern, space-constrained electronic applications. It belongs to a family of miniature LEDs specifically engineered for automated printed circuit board (PCB) assembly processes. This component is suitable for integration into a wide array of consumer and industrial electronics where reliable, compact, and bright indication is required.

1.1 Core Advantages and Target Markets

This LED offers several key advantages that make it a preferred choice for designers. Its primary feature is an extra-thin profile with a height of only 0.35mm, enabling its use in ultra-slim devices. It utilizes an Ultra Bright AlInGaP (Aluminum Indium Gallium Phosphide) chip, which provides high luminous efficiency and excellent color purity in the yellow spectrum. The device is fully compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. Its packaging in 8mm tape on 7-inch reels is standardized (EIA STD), ensuring compatibility with high-speed automated pick-and-place equipment. Furthermore, it is designed to withstand standard infrared (IR) reflow soldering processes, which is critical for modern surface-mount technology (SMT) assembly lines.

The target applications are diverse, spanning telecommunications equipment (e.g., cordless and cellular phones), office automation devices (e.g., notebook computers, network systems), home appliances, and indoor signage. Specific functional uses include keypad or keyboard backlighting, status indicators for power or connectivity, integration into micro-displays, and general signal or symbol illumination.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTST-C281KSKT-5A is defined by a comprehensive set of electrical, optical, and thermal parameters. Understanding these specifications is crucial for proper circuit design and ensuring long-term reliability.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation. For the LTST-C281KSKT-5A at an ambient temperature (Ta) of 25°C: the maximum continuous power dissipation is 75mW; the maximum DC forward current is 30mA; a peak forward current of 80mA is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating; the maximum reverse voltage that can be applied is 5V; the operating temperature range is from -30°C to +85°C; and the storage temperature range is from -40°C to +85°C. Notably, the device can withstand an infrared soldering condition of 260°C for a maximum of 10 seconds, which aligns with common lead-free (Pb-free) reflow profiles.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured under standard test conditions (Ta=25°C). The luminous intensity (Iv) ranges from a minimum of 7.1 millicandelas (mcd) to a maximum of 45.0 mcd when driven at a forward current (IF) of 5mA. The device features a very wide viewing angle (2θ1/2) of 130 degrees, meaning it emits light over a broad area, suitable for applications requiring wide-angle visibility. Its optical color is defined by a dominant wavelength (λd) between 587.0 nm and 594.5 nm, placing it firmly in the yellow region of the visible spectrum. The peak emission wavelength (λp) is typically 591.0 nm. Electrically, the forward voltage (VF) required to drive 5mA through the LED is between 1.7V and 2.3V. The reverse current (IR) is very low, with a maximum of 10 microamperes when a 5V reverse bias is applied.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance groups or "bins" based on key parameters. The LTST-C281KSKT-5A uses a three-dimensional binning system for forward voltage (VF), luminous intensity (IV), and dominant wavelength (Hue).

3.1 Forward Voltage (VF) Rank

LEDs are binned according to their forward voltage drop at a test current of 5mA. The bins are: E2 (1.70V to 1.90V), E3 (1.90V to 2.10V), and E4 (2.10V to 2.30V). A tolerance of ±0.1V is applied to each bin. This information is vital for designing constant-current drivers or predicting voltage drops in series configurations.

3.2 Luminous Intensity (IV) Rank

This bin defines the brightness output. The bins, measured in mcd at 5mA, are: K (7.1 to 11.2), L (11.2 to 18.0), M (18.0 to 28.0), and N (28.0 to 45.0). A tolerance of ±15% is applied to each bin. Designers can select a specific brightness bin to meet the visual requirements of their application, ensuring uniformity in multi-LED arrays.

3.3 Hue (Dominant Wavelength) Rank

This bin controls the precise shade of yellow. The dominant wavelength bins are: J (587.0 nm to 589.5 nm), K (589.5 nm to 592.0 nm), and L (592.0 nm to 594.5 nm). The tolerance for each bin is ±1 nm. Selecting a tight hue bin is critical for applications where color consistency is important, such as in status indicators or backlighting where multiple LEDs must appear identical.

4. Performance Curve Analysis

Graphical representations of LED characteristics provide deeper insight into performance under varying conditions, which is essential for robust design.

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

The I-V curve illustrates the nonlinear relationship between the current flowing through the LED and the voltage across it. For the AlInGaP material used in this LED, the curve will show a characteristic "knee" voltage around 1.8-2.0V, above which current increases rapidly with a small increase in voltage. This underscores the importance of using a current-limiting mechanism (resistor or constant-current driver) rather than a fixed voltage source to prevent thermal runaway and destruction of the device.

4.2 Luminous Intensity vs. Forward Current

This curve shows how light output increases with drive current. Typically, the relationship is relatively linear at lower currents but may saturate or become sub-linear at higher currents due to increased junction temperature and efficiency droop. Operating the LED within its specified DC current range (up to 30mA) ensures optimal efficiency and longevity.

4.3 Spectral Distribution

The spectral output curve for an AlInGaP yellow LED shows a relatively narrow emission band, typically with a spectral half-width (Δλ) of around 15 nm as specified. The peak will be centered near 591 nm. This narrow bandwidth results in a saturated, pure yellow color compared to broader-spectrum sources like phosphor-converted white LEDs.

5. Mechanical and Package Information

The physical construction and dimensions are critical for PCB layout and assembly.

5.1 Package Dimensions and Polarity Identification

The LED has a standard chip LED footprint. Key dimensions include the overall length, width, and the critically low height of 0.35mm. The cathode (negative) terminal is typically identified by a marking on the package, such as a green dot, a notch, or a differently shaped pad. The datasheet provides a detailed dimensional drawing with all critical measurements in millimeters, including pad positions, component outline, and lens size. Designers must adhere to these dimensions for their PCB land pattern (footprint) to ensure proper soldering and alignment.

5.2 Recommended PCB Attachment Pad Design

A suggested land pattern (solder pad layout) is provided to ensure reliable solder joint formation during reflow. This pattern accounts for solder fillet formation and prevents issues like tombstoning (where one end lifts off the pad). The design typically includes thermal relief connections if the pad is connected to a large copper plane, to manage heat during soldering.

6. Soldering and Assembly Guidelines

Proper handling and assembly are paramount for yield and reliability.

6.1 IR Reflow Soldering Parameters

For lead-free (Pb-free) processes, a specific reflow profile is recommended. The peak temperature should not exceed 260°C, and the time above 260°C should be limited to a maximum of 10 seconds. A pre-heat stage (typically 150-200°C) is necessary to slowly ramp up temperature and activate the flux, with a maximum pre-heat time of 120 seconds. The profile should be characterized for the specific PCB, solder paste, and oven to ensure all components are properly soldered without damage.

6.2 Storage and Handling Conditions

The LEDs are moisture-sensitive (MSL2a). When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤30°C and ≤90% relative humidity (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 should be subjected to IR reflow within 672 hours (28 days). If this time is exceeded, a bake-out at approximately 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" damage 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 normal temperature for less than one minute is acceptable. Harsh or unspecified chemicals can damage the plastic lens or package.

6.4 Electrostatic Discharge (ESD) Caution

The LED is susceptible to damage from static electricity and voltage surges. It is recommended to handle the device using a grounded wrist strap or anti-static gloves. All equipment, including workstations and machinery, must be properly grounded to prevent ESD events.

7. Packaging and Ordering Information

The LTST-C281KSKT-5A is supplied in a tape-and-reel format suitable for automated assembly. The tape width is 8mm, wound onto a standard 7-inch (178mm) diameter reel. Each reel contains 5000 pieces. For smaller quantities, a minimum packing quantity of 500 pieces is available for remnants. The tape and reel specifications conform to ANSI/EIA 481 standards, ensuring compatibility with standard feeder systems. The tape has a cover to protect the components, and there is a specification that no more than two consecutive component pockets can be empty.

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

The most common drive method is a series current-limiting resistor connected to a voltage supply (Vcc). The resistor value (R) is calculated using Ohm's Law: R = (Vcc - VF) / IF, where VF is the forward voltage of the LED (use the maximum value from the bin or datasheet for a conservative design) and IF is the desired forward current (e.g., 5mA, 10mA, up to 30mA max). For applications requiring consistent brightness or operation over a wide voltage range, a constant-current driver IC is recommended.

8.2 Thermal Management

Although the power dissipation is low (75mW max), effective thermal management is still important for maintaining LED lifetime and preventing color shift. The PCB itself acts as a heat sink. Connecting the LED's thermal pad (if present) to a sufficient copper area on the PCB helps dissipate heat. Avoid operating the LED at its absolute maximum current and temperature simultaneously for extended periods.

8.3 Optical Design Considerations

The wide 130-degree viewing angle makes this LED suitable for applications where light needs to be seen from various angles without additional diffusers. For more directed light, external lenses or light guides can be used. The water-clear lens of this particular model allows the native chip color (yellow) to be emitted without filtering.

9. Technical Comparison and Differentiation

The LTST-C281KSKT-5A differentiates itself primarily through its ultra-thin 0.35mm profile, which is thinner than many standard chip LEDs (e.g., 0603 or 0805 packages which are often 0.6-0.8mm tall). This makes it ideal for the latest generation of ultra-slim mobile devices and wearables. The use of AlInGaP technology provides higher efficiency and better color saturation in the red-amber-yellow range compared to older technologies like GaAsP. Its compatibility with standard IR reflow and tape-and-reel packaging aligns it with high-volume, automated manufacturing processes, offering a cost-effective and reliable solution.

10. Frequently Asked Questions (Based on Technical Parameters)

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

Peak wavelength (λp) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is a calculated value derived from the CIE chromaticity diagram that represents the perceived color of the light; it is the single wavelength that would match the color sensation of the LED's mixed output. For a monochromatic source like this yellow AlInGaP LED, they are typically very close, but λd is the more relevant parameter for color specification.

10.2 Can I drive this LED with a 3.3V supply without a resistor?

No, this is not recommended and is likely to destroy the LED. The forward voltage is only 1.7-2.3V. Applying 3.3V directly would cause a very large, uncontrolled current to flow (far exceeding the 30mA maximum), leading to immediate overheating and failure. A current-limiting resistor or regulator is always required.

10.3 How do I interpret the bin codes when ordering?

When placing an order, you may specify a combination of VF, IV, and Hue bin codes to get LEDs with tightly matched characteristics. For example, requesting "E3, M, K" would get you LEDs with a forward voltage of 1.9-2.1V, a luminous intensity of 18.0-28.0 mcd, and a dominant wavelength of 589.5-592.0 nm. If no bin is specified, you will receive parts from standard production bins.

11. Operational Principles

The LTST-C281KSKT-5A is a semiconductor light source based on the AlInGaP material system. When a forward voltage exceeding the diode's built-in potential is applied, electrons and holes are injected into the active region of the semiconductor chip. These charge carriers recombine, releasing energy in the form of photons (light). The specific bandgap energy of the AlInGaP alloy determines the wavelength of the emitted photons, which in this case is in the yellow region (~590 nm). The water-clear epoxy lens encapsulates the chip, providing mechanical protection, shaping the light output beam (wide 130-degree angle), and enhancing light extraction efficiency.

12. Industry Trends and Context

The development of LEDs like the LTST-C281KSKT-5A is driven by several key trends in electronics. There is a continuous push for miniaturization, demanding components with smaller footprints and lower profiles to enable thinner end products. Increased efficiency and brightness from semiconductor materials like AlInGaP allow for lower power consumption and longer battery life in portable devices. Furthermore, the industry-wide adoption of lead-free soldering and RoHS compliance mandates components that can withstand higher reflow temperatures and are free of restricted substances. The standardization of packaging (tape-and-reel, EIA standards) supports the highly automated, high-volume manufacturing that defines modern consumer electronics production.