LTST-C281KRKT-5A SMD LED Datasheet - Dimensions 2.8x1.6x0.35mm - Voltage 1.7-2.3V - Color Red - English Technical Document

1. Product Overview

The LTST-C281KRKT-5A is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. It belongs to a category of extra-thin chip LEDs, featuring a remarkably low profile. The device utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce a high-brightness red light output. This combination of a thin form factor and efficient material technology makes it suitable for integration into a wide range of consumer and industrial electronics where board space and component height are critical design parameters.

Its core advantages include compliance with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. The package is supplied in industry-standard 8mm tape on 7-inch diameter reels, ensuring compatibility with high-speed automated pick-and-place assembly equipment. Furthermore, it is designed to withstand infrared (IR) reflow soldering processes, which is the standard for mass production of printed circuit board assemblies (PCBAs).

2. Technical Parameter Deep Dive

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. The maximum continuous forward current (DC) is rated at 30 mA. For pulsed operation, a peak forward current of 80 mA is permissible under specific conditions: a 1/10 duty cycle and a pulse width of 0.1 ms. The maximum power dissipation is 75 mW, which is a function of forward current and voltage. The device can withstand a reverse voltage of up to 5 V. The operating and storage temperature ranges are specified from -30°C to +85°C and -40°C to +85°C, respectively, defining its environmental robustness.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of an ambient temperature (Ta) of 25°C and a forward current (IF) of 5 mA, unless otherwise noted.

• Luminous Intensity (Iv): Ranges from a minimum of 4.5 millicandelas (mcd) to a maximum of 45.0 mcd. The typical value falls within this range. Intensity is measured using a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ1/2): Defined as 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on the central axis (0 degrees). A wide viewing angle like this indicates a more diffused light output pattern.
• Peak Wavelength (λP): Typically 639 nanometers (nm). This is the wavelength at which the spectral power distribution of the emitted light is at its maximum.
• Dominant Wavelength (λd): Typically 631 nm at IF=5mA. This is a colorimetric parameter derived from the CIE chromaticity diagram, representing the perceived color of the light. It is the single wavelength that best matches the LED's color point.
• Spectral Bandwidth (Δλ): Typically 20 nm. This is the full width at half maximum (FWHM) of the emission spectrum, indicating the color purity. A smaller value indicates a more monochromatic light source.
• Forward Voltage (VF): Ranges from 1.7 V to 2.3 V at IF=5mA. This is the voltage drop across the LED when it is conducting current.
• Reverse Current (IR): Maximum of 10 microamperes (μA) when a reverse voltage (VR) of 5 V is applied. This parameter indicates the quality of the semiconductor junction.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins based on key parameters. The LTST-C281KRKT-5A uses a two-dimensional binning system.

3.1 Forward Voltage Binning

LEDs are categorized by their forward voltage (VF) measured at 5 mA. The bin codes and their ranges are:
- E2: 1.70 V to 1.90 V
- E3: 1.90 V to 2.10 V
- E4: 2.10 V to 2.30 V
A tolerance of ±0.1 V is applied to each bin.

3.2 Luminous Intensity Binning

LEDs are also sorted by their luminous intensity (Iv) measured at 5 mA. The bin codes and their ranges are:
- J: 4.50 mcd to 7.10 mcd
- K: 7.10 mcd to 11.20 mcd
- L: 11.20 mcd to 18.00 mcd
- M: 18.00 mcd to 28.00 mcd
- N: 28.00 mcd to 45.00 mcd
A tolerance of ±15% is applied to each intensity bin. The specific combination of voltage and intensity bin codes for a given production lot defines its precise performance characteristics.

4. Mechanical and Packaging Information

4.1 Package Dimensions

The device features an EIA standard package footprint. Key dimensions include a length of 2.8 mm, a width of 1.6 mm, and a critically low height of only 0.35 mm, qualifying it as \"extra thin.\" Detailed dimensional drawings with tolerances (typically ±0.10 mm) are provided in the datasheet for accurate PCB land pattern design.

4.2 Suggested Soldering Pad Layout

A recommended solder pad footprint is included to ensure reliable solder joint formation during reflow soldering. Adhering to these dimensions helps prevent tombstoning (component standing up on one end) and ensures proper wetting and mechanical strength.

4.3 Tape and Reel Packaging

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178 mm) diameter reels. Standard reel quantity is 5,000 pieces. Packaging conforms to ANSI/EIA-481 specifications. Key handling notes include: empty pockets are sealed, a minimum pack quantity of 500 pieces for remnants, and a maximum of two consecutive missing components allowed per reel.

5. Soldering and Assembly Guidelines

5.1 Infrared Reflow Soldering Profile

The component is compatible with lead-free (Pb-free) solder processes. A suggested reflow profile is provided, with critical parameters including a pre-heat zone (120-150°C), a maximum peak temperature of 260°C reached at the solder joints, and a time above liquidus tailored for lead-free alloys. The component must not be exposed to 260°C for more than 10 seconds. This profile ensures reliable solder connections without subjecting the LED package to excessive thermal stress.

5.2 Manual Soldering

If manual soldering with an iron is necessary, it should be performed with the iron tip temperature not exceeding 300°C, and the soldering time limited to a maximum of 3 seconds per pad. Soldering should be performed only once to avoid thermal damage.

5.3 Cleaning

If cleaning after soldering is required, 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. The use of unspecified or aggressive chemicals can damage the plastic lens or package.

5.4 Storage Conditions

For long-term storage, the ambient should not exceed 30°C and 60% relative humidity. Once removed from its original moisture-barrier bag, the device should be IR-reflowed within 672 hours (28 days) to prevent moisture absorption, which can cause \"popcorning\" or delamination during soldering. For storage beyond this period, baking at approximately 60°C for at least 20 hours is recommended before assembly to drive out moisture.

6. Application Suggestions and Design Considerations

6.1 Typical Application Scenarios

This LED is intended for general electronic equipment, including but not limited to office automation devices, communication equipment, and household appliances. Its thin profile makes it ideal for backlighting indicators in slim devices like smartphones, tablets, ultrabooks, and remote controls. It is also suitable for status indicators, panel lighting, and decorative lighting in consumer electronics.

6.2 Drive Circuit Design

An LED is a current-operated device. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, it is strongly recommended to use a current-limiting resistor in series with each LED. Driving LEDs directly from a voltage source without a series resistor (as shown in a non-recommended circuit diagram) can lead to significant brightness variations due to natural differences in the forward voltage (I-V characteristics) between individual LEDs, even from the same bin. The series resistor stabilizes the current flowing through each LED.

6.3 Electrostatic Discharge (ESD) Protection

LEDs are sensitive to electrostatic discharge. ESD can cause latent or catastrophic damage, manifesting as high reverse leakage current, low forward voltage, or failure to illuminate at low currents. To prevent ESD damage:
- Personnel should wear grounded wrist straps or anti-static gloves.
- All workstations, equipment, and tools must be properly grounded.
- Use ionizers to neutralize static charge that may accumulate on the plastic lens.
- Handle devices in controlled ESD-protected areas (EPAs).

7. Technical Comparison and Differentiation

The primary differentiating factor of the LTST-C281KRKT-5A is its 0.35 mm height, which is significantly lower than many standard SMD LEDs (e.g., 0603 or 0805 packages often have heights around 0.8-1.0 mm). This makes it a compelling choice for ultra-thin product designs. The use of AlInGaP technology, compared to older technologies like GaAsP, provides higher luminous efficiency and better performance at elevated temperatures, resulting in brighter and more stable red light output. Its compatibility with automated assembly and standard reflow processes aligns it with modern, cost-effective manufacturing workflows.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λP) is the physical wavelength of the highest intensity point in the light spectrum. Dominant wavelength (λd) is a color science concept representing the perceived color on the CIE chart. For a red LED, they are often close but not identical.

Q: Can I drive this LED at its maximum DC current of 30 mA continuously?
A: While possible, operating at the absolute maximum rating may reduce long-term reliability and luminous output due to heat. For optimal lifetime and stable performance, derating—operating at a current lower than the maximum, such as 20 mA—is a common design practice.

Q: Why is binning important?
A: Binning ensures color and brightness consistency within an application. For example, using LEDs from the same VF and Iv bins on a control panel will prevent visibly different shades of red or brightness levels between adjacent indicators.

Q: Is a heat sink required?
A: Given its low power dissipation (75 mW max) and small size, a dedicated heat sink is typically not required for normal operation within the specified current and temperature limits. However, proper PCB layout to allow some heat dissipation through the copper pads is good practice.

9. Design and Usage Case Study

Scenario: Designing a status indicator for a wearable fitness tracker.
The device has extreme space constraints, with a total PCB thickness budget under 1.0 mm. The LTST-C281KRKT-5A, with its 0.35 mm height, is selected. A drive current of 5 mA is chosen to balance brightness with battery life. An LED from the E3 voltage bin and L intensity bin is specified to ensure consistent performance. The PCB land pattern is designed according to the datasheet's recommended layout. During assembly, the manufacturer follows the provided IR reflow profile for the Pb-free solder paste used. ESD precautions are enforced on the production line. The result is a reliable, uniformly bright red charging/power indicator that meets the mechanical design goals without compromising optical performance.

10. Technology Principle Introduction

The LED is based on a semiconductor heterostructure made of Aluminum Indium Gallium Phosphide (AlInGaP) grown on a substrate. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly correlates to the wavelength (color) of the emitted light—in this case, red (~631-639 nm). The \"water clear\" lens is typically made of an epoxy or silicone material that is molded over the chip. This lens serves to protect the semiconductor die, shape the light output beam (affecting the viewing angle), and enhance light extraction efficiency.

11. Industry Trends and Developments

The trend in SMD LEDs for consumer electronics continues toward miniaturization and higher efficiency. Package heights are decreasing to enable thinner end products. There is also a focus on improving the reliability and performance of LEDs under high-temperature conditions, such as those encountered during reflow soldering and in applications near other heat-generating components. Furthermore, advancements in phosphor technology and chip design are pushing for higher luminous efficacy (more light output per electrical watt) and better color rendering across all LED colors. The move towards standardized packaging and tape-and-reel formats supports fully automated, high-volume manufacturing, reducing assembly costs and improving consistency.