LTST-S32F1KT SMD LED Datasheet - Side Looking Full Color Chip - Orange/Green/Blue - 20mA - 75mW - English Technical Document

1. Product Overview

The LTST-S32F1KT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It is particularly suited for space-constrained applications due to its miniature size and specialized configuration. This component is a side-looking, full-color chip LED, integrating multiple semiconductor materials to produce distinct colors from a single package.

1.1 Core Advantages and Target Market

This LED series offers several key advantages for modern electronics manufacturing. It is compliant with RoHS (Restriction of Hazardous Substances) directives, ensuring environmental safety. The package features tin plating for improved solderability and corrosion resistance. It utilizes Ultra Bright InGaN (Indium Gallium Nitride) and AlInGaP (Aluminum Indium Gallium Phosphide) chip technologies, which are known for their high efficiency and brightness. The device is packaged on 8mm tape wound onto 7-inch diameter reels, conforming to EIA (Electronic Industries Alliance) standards, making it fully compatible with high-speed automatic placement equipment commonly used in volume production. Furthermore, it is designed to withstand standard infrared (IR) reflow soldering processes, which is critical for lead-free (Pb-free) assembly lines.

The primary target markets and applications are diverse, reflecting the component's versatility. It is ideal for telecommunications equipment, office automation devices, home appliances, and various industrial equipment. Specific use cases include backlighting for keypads and keyboards, status indicators in consumer and industrial electronics, micro-displays, and signal or symbol luminaires where clear, bright indication is required.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTST-S32F1KT is defined by a comprehensive set of electrical, optical, and thermal parameters measured under standard conditions (Ta=25\u00b0C).

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are not intended for continuous operation.

• Power Dissipation (Pd): 75 mW for the Orange chip, 76 mW for the Green and Blue chips. This parameter indicates the maximum amount of power the LED can dissipate as heat.
• Peak Forward Current (I_F(PEAK)): 80 mA for Orange, 100 mA for Green/Blue. This is the maximum allowable instantaneous current under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): 30 mA for Orange, 20 mA for Green and Blue. This is the recommended maximum continuous forward current for reliable long-term operation.
• Operating Temperature Range: -20\u00b0C to +80\u00b0C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -30\u00b0C to +100\u00b0C.
• Infrared Soldering Condition: Withstands 260\u00b0C for 10 seconds, which aligns with common Pb-free reflow profiles.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters under normal operating conditions (I_F = 20mA, Ta=25\u00b0C).

• Luminous Intensity (I_V): Measured in millicandelas (mcd). The minimum/typical/maximum values are: Orange: 90/-/180 mcd; Green: 140/-/280 mcd; Blue: 45/-/90 mcd. Luminous intensity is measured using a sensor and filter combination that approximates the CIE standard photopic observer (human eye response).
• Viewing Angle (2\u03b8_1/2): Typically 130 degrees. This wide viewing angle is characteristic of side-looking LEDs, providing a broad emission pattern suitable for indicator applications.
• Peak Emission Wavelength (\u03bb_p): The wavelength at which the spectral power distribution is maximum. Typical values: Orange: 612 nm, Green: 520 nm, Blue: 468 nm.
• Dominant Wavelength (\u03bb_d): The single wavelength perceived by the human eye that matches the color of the LED. Ranges: Orange: 598-612 nm (Typ. 605 nm), Green: 518-532 nm (Typ. 525 nm), Blue: 463-477 nm (Typ. 470 nm).
• Spectral Line Half-Width (\u0394\u03bb): The bandwidth of the emitted light at half its maximum intensity. Typical: Orange: 17 nm, Green: 35 nm, Blue: 26 nm. A narrower half-width indicates a more spectrally pure color.
• Forward Voltage (V_F): The voltage drop across the LED when conducting the specified current. Ranges: Orange: 1.8-2.4V, Green: 2.8-3.8V, Blue: 2.8-3.8V. The higher V_F for Green/Blue is typical for InGaN-based LEDs.
• Reverse Current (I_R): Maximum 10 \u00b5A at a reverse voltage (V_R) of 5V. The datasheet explicitly cautions that the device is not designed for reverse operation; this parameter is for IR (Infrared) test purposes only.

3. Binning System Explanation

The LEDs are sorted (binned) based on their measured luminous intensity to ensure consistency within a production lot. The bin code is marked on each packing bag.

3.1 Luminous Intensity Binning

Each color has specific bin codes with defined minimum and maximum luminous intensity values at I_F=20mA. A tolerance of +/-15% is applied within each bin.

• Orange: Bin codes Q2 (90.0-112.0 mcd), R1 (112.0-140.0 mcd), R2 (140.0-180.0 mcd).
• Green: Bin codes R2 (140.0-180.0 mcd), S1 (180.0-224.0 mcd), S2 (224.0-280.0 mcd).
• Blue: Bin codes P1 (45.0-56.0 mcd), P2 (56.0-71.0 mcd), Q1 (71.0-90.0 mcd).

This binning allows designers to select LEDs with a known brightness range for their application, aiding in achieving uniform illumination in multi-LED designs.

4. Performance Curve Analysis

The datasheet references typical performance curves which graphically represent the relationship between key parameters. While the specific graphs are not detailed in the text, standard curves for such LEDs would include:

• Relative Luminous Intensity vs. Forward Current (I_V vs. I_F): Shows how light output increases with current, typically in a non-linear fashion, eventually saturating.
• Forward Voltage vs. Forward Current (V_F vs. I_F): Demonstrates the diode's exponential I-V characteristic.
• Relative Luminous Intensity vs. Ambient Temperature (I_V vs. T_a): Illustrates the decrease in light output as junction temperature rises, a critical factor for thermal management.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak and dominant wavelengths and the spectral half-width.

These curves are essential for circuit designers to predict LED behavior under different operating conditions not explicitly covered in the table data.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The LTST-S32F1KT comes in a standard SMD package. All dimensions are in millimeters with a typical tolerance of \u00b10.1 mm unless otherwise noted. The lens color is water clear. The internal chip sources and their corresponding pin assignments are: Pin 1: AlInGaP Orange, Pin 2: InGaN Green, Pin 3: InGaN Blue. Correct polarity identification during assembly is crucial.

5.2 Recommended PCB Attachment Pad and Soldering Direction

The datasheet includes a diagram showing the recommended land pattern (footprint) for the LED on the PCB. Adhering to this pattern ensures proper soldering, alignment, and thermal relief. It also indicates the correct orientation for soldering relative to the tape reel feed direction for automated assembly.

6. Soldering and Assembly Guidelines

6.1 Suggested IR Reflow Profile for Pb-Free Process

A recommended reflow soldering profile is provided for lead-free assembly. Key parameters include a pre-heat zone (150-200\u00b0C), a pre-heat time (maximum 120 seconds), a peak temperature (maximum 260\u00b0C), and a time at peak temperature (maximum 10 seconds). The profile is designed to ensure reliable solder joints without subjecting the LED to excessive thermal stress. The datasheet notes that the optimal profile may vary based on board design, solder paste, and oven characteristics, and recommends following PCB-specific characterization.

6.2 Storage Conditions

Proper storage is vital to maintain solderability. When the moisture-proof barrier bag is sealed, LEDs should be stored at \u2264 30\u00b0C and \u2264 90% RH, with a recommended shelf life of one year. Once the bag is opened, the storage environment should not exceed 30\u00b0C or 60% RH. Components removed from their original packaging should ideally undergo IR reflow within one week (Moisture Sensitivity Level 3, MSL 3). For longer storage outside the original bag, storage in a sealed container with desiccant or in a nitrogen desiccator is advised. LEDs stored out of packaging for more than one week require baking at approximately 60\u00b0C for at least 20 hours 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 normal temperature for less than one minute is acceptable. The use of unspecified chemicals can damage the LED package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178 mm) diameter reels. Standard packing quantity is 3000 pieces per reel. A minimum packing quantity of 500 pieces is available for remainder orders. The packaging conforms to ANSI/EIA-481 specifications. Key dimensional details of the tape pocket and reel are provided to ensure compatibility with automated assembly equipment feeders.

8. Application Suggestions and Design Considerations

8.1 Design Considerations

• Current Limiting: Always use a series current-limiting resistor or a constant-current driver to ensure the forward current (I_F) does not exceed the maximum DC rating (20mA or 30mA depending on color).
• Thermal Management: Although power dissipation is low, ensuring adequate PCB copper area or thermal vias can help manage junction temperature, especially in high ambient temperature environments or when driven at high currents, to maintain luminous output and longevity.
• ESD Protection: The device is sensitive to electrostatic discharge (ESD). Handling procedures should include the use of wrist straps, anti-static mats, and properly grounded equipment. Circuit-level ESD protection may be necessary in sensitive applications.
• Reverse Voltage Protection: The LED is not designed for reverse bias operation. Circuit design should prevent the application of reverse voltage exceeding 5V.

8.2 Typical Application Circuit

A basic driving circuit involves connecting the LED in series with a current-limiting resistor to a DC voltage supply (V_CC). The resistor value can be calculated using Ohm's Law: R = (V_CC - V_F) / I_F, where V_F is the forward voltage of the LED at the desired current I_F. Using the maximum V_F from the datasheet in this calculation ensures the current does not exceed the limit even with part-to-part variation.

9. Technical Comparison and Differentiation

The LTST-S32F1KT differentiates itself through its side-looking form factor and integration of three distinct color chips (Orange/AlInGaP, Green/InGaN, Blue/InGaN) in one package. Compared to top-emitting LEDs, side-looking types are better suited for applications where light needs to be directed parallel to the PCB surface, such as edge-lit panels or light guides. The use of both AlInGaP and InGaN technologies allows it to cover a broad range of colors with high efficiency; AlInGaP is particularly efficient in the red-orange-yellow spectrum, while InGaN dominates the green-blue spectrum. Its compatibility with automated placement and standard IR reflow makes it a cost-effective choice for high-volume manufacturing.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the Green and Blue LEDs at 30mA like the Orange one?

A: No. The Absolute Maximum Ratings specify a DC Forward Current of 20mA for the Green and Blue chips. Exceeding this rating can lead to accelerated degradation, reduced lifetime, or immediate failure. Always adhere to the specified limits for each color.

Q: What does \"I.C. Compatible\" mean?

A: This indicates that the LED's input characteristics (primarily its forward voltage and current requirements) are compatible with direct driving from standard digital integrated circuit (IC) outputs, such as microcontrollers or logic gates, often without the need for additional buffering or driving transistors, simplifying circuit design.

Q: Why is the storage condition different once the bag is opened?

A: The original packaging is a moisture barrier bag with desiccant. Once opened, the LEDs are exposed to ambient humidity and can absorb moisture. If subjected to high-temperature reflow soldering too quickly after moisture absorption, the rapid vaporization of this moisture can cause internal delamination or cracking (\"popcorning\"). The stricter storage conditions and baking requirements mitigate this risk.

Q: How do I interpret the luminous intensity bin code?

A> The bin code (e.g., R2, S1, P1) printed on the bag corresponds to a predefined range of luminous intensity. When ordering or designing, you can specify a bin code to ensure all LEDs in your batch have a similar brightness, which is critical for achieving uniform appearance in multi-LED arrays or indicators.

11. Practical Use Case Example

Scenario: Designing a multi-status indicator for a network router. The device needs distinct, bright indicators for Power (Orange), Network Activity (Green), and System Error (Blue). Using the LTST-S32F1KT allows all three indicators to be placed as a single compact component on the PCB. The designer would:

1. Create a footprint matching the recommended land pattern.

2. Design three separate driver circuits (e.g., from a microcontroller's GPIO pins), each with a current-limiting resistor calculated for the specific LED color's V_F range (e.g., 3.3V supply, target I_F=15mA, using max V_F for safety).

3. Specify a tight luminous intensity bin (e.g., S1 for Green) during procurement to ensure all router units have consistently bright indicators.

4. Follow the recommended reflow profile during PCB assembly to ensure reliable soldering.

12. Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon is called electroluminescence. In the LTST-S32F1KT:

- The AlInGaP (Aluminum Indium Gallium Phosphide) chip emits light in the orange/red part of the spectrum. The specific color (wavelength) is determined by the precise ratios of the constituent elements in the semiconductor crystal.

- The InGaN (Indium Gallium Nitride) chips emit light in the green and blue parts of the spectrum. Again, the indium/gallium ratio tunes the bandgap and thus the emitted wavelength.

When forward voltage is applied, electrons and holes recombine in the active region of the semiconductor, releasing energy in the form of photons (light). The side-looking package incorporates optics (the water-clear lens) to shape the emitted light into a wide, 130-degree viewing angle pattern suitable for indicator applications.

13. Development Trends

The field of SMD LEDs continues to evolve. General trends observable in components like the LTST-S32F1KT and its successors include:

- Increased Efficiency and Luminous Output: Ongoing improvements in epitaxial growth and chip design yield more light output (lumens or mcd) per unit of electrical input power (mW), reducing energy consumption and thermal load.

- Miniaturization: The drive for smaller devices continues, enabling even denser packaging on PCBs for applications like mini-LED backlighting.

- Enhanced Color Consistency and Binning: Tighter manufacturing controls and more sophisticated binning strategies (including chromaticity coordinates x,y in addition to intensity) allow for better color matching in applications requiring high uniformity.

- Integration and Smart Features: There is a trend towards integrating control electronics (like constant-current drivers or pulse-width modulation controllers) directly with the LED chip or within the package, creating \"smart LED\" modules that simplify system design.

- Expanded Color Gamut and New Materials: Research into materials like perovskite quantum dots or micro-LEDs aims to provide wider color gamuts and new form factors for advanced display and lighting applications.