SMD LED LTST-108KRKT Datasheet - 3.2x2.8x1.9mm - 1.8-2.4V - 72mW - Water Clear AlInGaP Red - English Technical Document

1. Product Overview

This document details the specifications for a compact, surface-mount LED designed for automated printed circuit board assembly. The device is engineered for space-constrained applications across a broad spectrum of electronic equipment. Its miniature footprint and compatibility with standard assembly processes make it a versatile component for modern electronics manufacturing.

1.1 Core Advantages

• Compliant with RoHS environmental standards.
• Packaged on 8mm tape wound onto 7-inch diameter reels, suitable for high-speed automated pick-and-place equipment.
• Features an EIA standard package outline for design consistency.
• IC-compatible logic levels for easy integration with control circuits.
• Designed to withstand infrared reflow soldering processes common in SMT assembly lines.
• Preconditioned to JEDEC Level 3 moisture sensitivity standards, enhancing reliability post-solder.

1.2 Target Applications

The LED is suitable for use as a status indicator, signal luminary, or for front panel backlighting in various sectors including telecommunications, office automation, home appliances, and industrial equipment.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Power Dissipation (Pd): 72 mW. This is the maximum power the package can dissipate as heat at an ambient temperature (Ta) of 25°C. Exceeding this limit risks overheating and reduced lifespan.
• Peak Forward Current (I_FP): 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It allows for brief, high-intensity flashes.
• DC Forward Current (I_F): 30 mA. This is the maximum continuous current recommended for reliable long-term operation.
• Operating Temperature Range: -40°C to +85°C. The device is rated to function within this ambient temperature span.
• Storage Temperature Range: -40°C to +100°C. The device can be stored without applied power within these limits.

2.2 Electro-Optical Characteristics

These parameters are measured at Ta=25°C and an I_F of 20mA, representing typical operating conditions.

• Luminous Intensity (I_V): 112 - 280 mcd (millicandela). The actual output is binned (see Section 4). Measured with a filter approximating the photopic (CIE) eye response.
• Viewing Angle (2θ_1/2): 110 degrees (typical). This wide angle indicates a diffuse, non-focused emission pattern suitable for area illumination or wide visibility indicators.
• Peak Emission Wavelength (λ_p): 639 nm (typical). The wavelength at which the spectral power output is highest.
• Dominant Wavelength (λ_d): 631 nm (typical). The single wavelength perceived by the human eye that defines the color (red). Tolerance is ±1 nm.
• Spectral Line Half-Width (Δλ): 20 nm (typical). The bandwidth of the emitted light, indicating color purity.
• Forward Voltage (V_F): 1.8V (Min), 2.4V (Max) at 20mA. The voltage drop across the LED when conducting. Tolerance is ±0.1V.
• Reverse Current (I_R): 10 µA (Max) at V_R=5V. The device is not designed for reverse bias operation; this parameter is for test purposes only.

3. Binning System Explanation

3.1 Luminous Intensity (I_V) Binning

To ensure consistency in brightness across production lots, LEDs are sorted into intensity bins. The bin code is critical for applications requiring uniform appearance.

Tolerance on each intensity bin is ±11%.

4. Performance Curve Analysis

The datasheet includes typical characteristic curves which are essential for design analysis.

• Relative Luminous Intensity vs. Forward Current: Shows the non-linear relationship between drive current and light output. Output increases with current but may saturate at higher levels.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the negative temperature coefficient of light output. Intensity typically decreases as ambient temperature rises, a critical factor for thermal management.
• Forward Voltage vs. Forward Current: Illustrates the diode's exponential I-V characteristic. The curve helps in selecting appropriate current-limiting resistors and understanding power supply requirements.
• Spectral Distribution: A graph showing the relative radiant power across wavelengths, centered around the peak wavelength of 639 nm with a typical half-width of 20 nm.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD package outline. Key dimensions (in millimeters, tolerance ±0.2mm unless noted) include a body size of approximately 3.2mm x 2.8mm with a height of 1.9mm. The cathode is typically identified by a marking or a chamfered corner on the package.

5.2 Recommended PCB Attachment Pad Layout

A land pattern diagram is provided to ensure proper solder joint formation during reflow. Adhering to this recommended footprint is crucial for mechanical stability, thermal dissipation, and preventing tombstoning.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile (Pb-Free)

A suggested temperature profile compliant with J-STD-020B is provided for lead-free processes. Key parameters include:

• Pre-heat: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: As per the profile curve, typically 60-90 seconds.
• Ramp Rates: Controlled to minimize thermal shock.

Note: The actual profile must be characterized for the specific PCB assembly, considering board thickness, component density, and solder paste specifications.

6.2 Hand Soldering

If necessary, hand soldering with a soldering iron is permissible with strict limits: iron tip temperature not exceeding 300°C and soldering time limited to a maximum of 3 seconds per joint, for one time only.

6.3 Storage Conditions

• Sealed Package: Store at ≤ 30°C and ≤ 70% Relative Humidity. Use within one year of opening the moisture barrier bag.
• Opened Package: For components removed from the sealed bag, the ambient should not exceed 30°C / 60% RH. It is recommended to complete IR reflow within 168 hours (1 week).
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen desiccator. If exposed for >168 hours, a bake at 60°C for at least 48 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.4 Cleaning

If cleaning after soldering is necessary, use only alcohol-based solvents like isopropyl alcohol or ethyl alcohol. Immerse at normal temperature for less than one minute. Avoid unspecified chemical cleaners which may damage the epoxy lens.

7. Application Suggestions

7.1 Drive Circuit Design

LEDs are current-driven devices. To ensure uniform brightness and prevent current hogging, a series current-limiting resistor must be used for each LED, even when multiple LEDs are connected in parallel to the same voltage rail. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F, where V_F is the forward voltage of the LED at the desired current I_F.

7.2 Thermal Considerations

While the power dissipation is low (72mW max), maintaining the junction temperature within limits is vital for longevity and stable light output. Ensure adequate PCB copper area or thermal vias under the device's thermal pad (if applicable) to conduct heat away, especially in high ambient temperature environments or when operating near maximum current.

7.3 Optical Design

The 110-degree viewing angle provides wide, diffuse light. For applications requiring a more directed beam, external lenses or light guides may be necessary. The water-clear lens with a red AlInGaP chip offers good color saturation.

8. Technical Comparison and Differentiation

Compared to older technologies like GaAsP, this AlInGaP (Aluminum Indium Gallium Phosphide) LED offers significantly higher luminous efficiency, resulting in brighter output at the same drive current. The wide viewing angle is a characteristic of the package and lens design, differing from narrow-angle \"straw hat\" LEDs. Its compatibility with IR reflow and tape-and-reel packaging differentiates it from through-hole LEDs, catering specifically to automated, high-volume SMT production.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 Can I drive this LED at 30mA continuously?

Yes, 30mA is the maximum recommended DC forward current. For optimal lifetime and reliability, operating at a lower current, such as 20mA (the test condition), is advisable if the application's brightness requirements allow it.

9.2 Why is there a peak current rating of 80mA if the DC max is only 30mA?

The 80mA rating is for very short pulses (0.1ms width) at a low duty cycle (10%). This allows the LED junction to cool between pulses, preventing thermal overload. It is useful for multiplexing schemes or creating very bright strobe effects, but not for constant illumination.

9.3 What does \"JEDEC Level 3\" preconditioning mean?

It means the component has been classified to have a \"floor life\" of 168 hours (7 days) at factory conditions (<30°C/60%RH) after the moisture barrier bag is opened, before it requires baking prior to reflow soldering. This information is critical for production planning to avoid moisture-induced defects.

10. Practical Use Case

Scenario: Designing a status indicator panel for a network router. Multiple LTST-108KRKT LEDs (e.g., for Power, LAN, WAN, Wi-Fi status) are to be used. To ensure uniform brightness, specify LEDs from the same intensity bin (e.g., all R2 or S1) during procurement. Design the PCB with the recommended pad layout. Use a 5V supply rail. Calculate the series resistor for each LED: Assuming a typical V_F of 2.1V and a target I_F of 20mA, R = (5V - 2.1V) / 0.02A = 145 Ohms. A standard 150 Ohm resistor would be suitable. Follow the reflow profile guidelines during assembly. This approach guarantees consistent, reliable visual indicators.

11. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons and holes recombine in the active region (composed of AlInGaP in this case). The energy released during this recombination is emitted as photons (light). The specific material composition (AlInGaP) determines the bandgap energy, which defines the wavelength (color) of the emitted light, in this case, red. The epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output pattern.

12. Technology Trends

The general trend in LED technology continues towards higher efficiency (more lumens per watt), improved color rendering, and higher reliability. For indicator-type SMD LEDs, the focus includes further miniaturization (smaller packages like 0201 or 01005), lower operating voltages to align with modern IC voltages, and enhanced compatibility with lead-free, high-temperature soldering processes. Integration with onboard control circuits (like built-in current regulators or drivers) in multi-chip packages is also an area of development for more advanced applications.