LTW-S115KSDS-5A Dual Color SMD LED Datasheet - Side View - White & Yellow - 5mA - English Technical Document

1. Product Overview

The LTW-S115KSDS-5A is a dual-color, surface-mount device (SMD) light-emitting diode (LED) engineered specifically for side-view illumination applications, most notably as a backlight source for liquid crystal displays (LCDs). It integrates two distinct semiconductor chips within a single EIA-standard package: an InGaN (Indium Gallium Nitride) chip for white light emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for yellow light emission. This configuration allows for flexible lighting solutions from a compact footprint. The device is designed for high-volume assembly, supplied on 8mm tape mounted on 7-inch reels, and is fully compatible with automated pick-and-place equipment and standard infrared (IR) reflow soldering processes.

1.1 Core Advantages

• Dual-Color Source: Combines white and yellow light emission in one package, saving board space and simplifying design for multi-color indication or blended backlighting.
• Side-View Emission: The primary light output is directed parallel to the mounting plane, making it ideal for edge-lighting thin panels like those in LCD modules.
• High Brightness: Utilizes advanced InGaN and AlInGaP chip technologies to deliver high luminous intensity.
• Manufacturing Friendly: Features tin-plated leads for improved solderability and is packaged for compatibility with automated assembly lines.
• Environmental Compliance: The product meets the Restriction of Hazardous Substances (RoHS) directive.

2. Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The following limits must not be exceeded under any conditions, as doing so may cause permanent damage to the device. Ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): White: 35 mW; Yellow: 48 mW. This is the maximum allowable power the LED can dissipate as heat.
• Peak Forward Current (I_FP): White: 50 mA; Yellow: 80 mA. This is the maximum instantaneous current allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): White: 10 mA; Yellow: 20 mA. This is the maximum continuous forward current for reliable operation.
• Operating Temperature Range: -20°C to +80°C.
• Storage Temperature Range: -40°C to +85°C.
• Infrared Soldering Condition: Withstands a peak temperature of 260°C for 10 seconds during reflow soldering.

2.2 Electro-Optical Characteristics

Typical performance parameters are measured at Ta=25°C and a forward current (I_F) of 5 mA, unless otherwise noted.

• Luminous Intensity (I_V): White: Min. 28 mcd, Typ. N/A, Max. 112 mcd. Yellow: Min. 7.1 mcd, Typ. N/A, Max. 71 mcd. This is the perceived brightness of the LED as measured by a photopic (human eye response) sensor.
• Viewing Angle (2θ_1/2): 130 degrees (typical for both colors). This is the full angle at which the luminous intensity drops to half of its peak value.
• Peak Emission Wavelength (λ_P): Yellow: 591 nm (typical). This is the wavelength at which the spectral power distribution of the yellow chip is highest.
• Dominant Wavelength (λ_d): Yellow: 590 nm (typical at I_F=5mA). This is the single wavelength that best represents the perceived color of the yellow LED.
• Spectral Line Half-Width (Δλ): Yellow: 15 nm (typical). This indicates the spectral purity or bandwidth of the emitted yellow light.
• Chromaticity Coordinates (x, y): White: x=0.290, y=0.282 (typical at I_F=5mA). These CIE 1931 coordinates define the color point of the white LED on a chromaticity diagram.
• Forward Voltage (V_F): White: Min. 2.55V, Typ. 2.85V, Max. 3.15V. Yellow: Min. 1.6V, Typ. 2.00V, Max. 2.40V. This is the voltage drop across the LED when conducting the specified forward current.
• Reverse Current (I_R): White: Max. 10 µA; Yellow: Max. 100 µA (at V_R=5V). The device is not designed for reverse bias operation; this parameter is for leakage current testing only.

3. Binning System Explanation

The LEDs are sorted (binned) based on key optical parameters to ensure consistency within a production lot. The bin code is marked on the packaging.

3.1 Luminous Intensity (I_V) Binning

LEDs are classified into bins based on their measured luminous intensity at I_F = 5 mA. The tolerance for each bin is ±15%.

• White Chip Bins: N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd).
• Yellow Chip Bins: K (7.10-11.2 mcd), L (11.2-18.0 mcd), M (18.0-28.0 mcd), N (28.0-45.0 mcd), P (45.0-71.0 mcd).

3.2 Hue (Color) Binning

The white LEDs are further sorted by their chromaticity coordinates (x, y) on the CIE 1931 diagram. Four hue bins are defined (C1, C2, D1, D2), each with specific coordinate boundaries. The tolerance on each hue bin is ±0.01 in both x and y coordinates. This ensures color uniformity, which is critical for backlighting applications where multiple LEDs are used together.

4. Performance Curve Analysis

The datasheet references typical performance curves (though not displayed in the provided text). These curves are essential for design engineers.

• I-V (Current-Voltage) Curve: Shows the relationship between forward current (I_F) and forward voltage (V_F) for both the white and yellow chips. This is crucial for designing the current-limiting circuitry.
• Luminous Intensity vs. Forward Current: Illustrates how the light output (I_V) increases with drive current. It helps determine the optimal operating point for balancing brightness and efficiency/lifetime.
• Luminous Intensity vs. Ambient Temperature: Demonstrates the derating of light output as the junction temperature rises. This is vital for thermal management in the final application.
• Spectral Distribution: For the yellow LED, this curve shows the relative power emitted across different wavelengths, centered around the peak wavelength of ~591 nm.

5. Mechanical and Package Information

5.1 Package Dimensions and Pinout

The device conforms to an EIA standard package outline. Key dimensions include body size and lead spacing. The pin assignment is critical for correct orientation: Pin C1 is assigned to the InGaN White chip, and Pin C2 is assigned to the AlInGaP Yellow chip. A detailed dimensioned drawing (not shown here) specifies all critical package measurements with a typical tolerance of ±0.10 mm.

5.2 Suggested Solder Pad Layout and Polarity

A recommended land pattern (solder pad design) for the printed circuit board (PCB) is provided to ensure reliable solder joint formation and proper alignment during reflow. The datasheet also indicates the suggested soldering direction relative to the tape reel feed to optimize the process.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The LED is compatible with infrared (IR) reflow soldering. A specific soldering profile is recommended, with a peak temperature of 260°C held for 10 seconds. The datasheet emphasizes that profiles with peak temperatures below 245°C may be insufficient for reliable soldering, especially without the benefit of the component's tin plating. A detailed time-temperature graph typically shows preheat, soak, reflow, and cooling zones.

6.2 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. The use of unspecified chemicals may damage the LED package.

6.3 Storage and Handling

• Electrostatic Discharge (ESD): The LED is sensitive to ESD. Handling procedures should include the use of wrist straps, anti-static gloves, and properly grounded equipment.
• Moisture Sensitivity: As a surface-mount device, it is sensitive to moisture absorption. Unopened, moisture-proof bags with desiccant have a shelf life of one year when stored at ≤ 30°C and ≤ 90% RH. Once opened, LEDs should be used within one week or stored in a dry environment (≤ 30°C / ≤ 60% RH). Components stored out of their original packaging for more than a week require baking (e.g., 60°C for 20 hours) before soldering to prevent \"popcorning\" during reflow.

7. Packaging and Ordering

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape (8mm width) with a protective cover tape, wound onto 7-inch (178 mm) diameter reels. Standard reel quantity is 3000 pieces. A minimum packing quantity of 500 pieces is available for remainder orders. The packaging conforms to ANSI/EIA-481 standards.

7.2 Part Number Structure

The part number LTW-S115KSDS-5A contains coded information about the product family, color, package, and likely performance bin (though the exact decoding is model-specific).

8. Application Notes and Design Considerations

8.1 Typical Application Scenarios

• LCD Backlighting: The primary application, providing edge-lighting for small to medium-sized LCD panels in consumer electronics, industrial displays, and automotive clusters.
• Status Indication: The dual-color capability allows for multi-state indication (e.g., white for \"on,\" yellow for \"standby/alert,\" or both for a third state).
• Decorative Lighting: Can be used in compact spaces where side emission and color mixing are required.

8.2 Design Considerations

• Current Driving: Always use a constant current driver or a current-limiting resistor in series with the LED. The forward voltage varies, so driving by voltage is not recommended. Do not exceed the maximum DC forward current (10mA for white, 20mA for yellow).
• Thermal Management: Although power dissipation is low, ensuring adequate PCB copper area or thermal vias helps maintain a lower junction temperature, which preserves luminous output and extends operational lifetime.
• Optical Design: The 130-degree viewing angle provides a wide emission pattern. For backlighting, light guides and diffusers are typically used to distribute the light evenly across the display area.
• Circuit Protection: Consider implementing reverse polarity protection if there is a risk of incorrect installation, as the LED is not designed for reverse bias operation.

9. Technical Comparison and Differentiation

Compared to single-color side-view LEDs, the LTW-S115KSDS-5A offers significant space savings and design flexibility by integrating two colors. Its use of AlInGaP for yellow provides high efficiency and good color saturation for that wavelength. The combination of InGaN for white and AlInGaP for yellow in one package represents a solution tailored for applications requiring distinct, reliable color sources from a minimal footprint, differentiating it from simpler monochromatic alternatives or larger discrete solutions.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive the white and yellow chips independently?

Yes. The two chips have separate anode/cathode connections (Pins C1 and C2). They must be driven by separate current-limiting circuits to control each color independently.

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

Peak wavelength (λ_P) is the physical wavelength where the emission spectrum is strongest. Dominant wavelength (λ_d) is a calculated value that represents the perceived color as a single wavelength on the CIE diagram. For monochromatic LEDs like the yellow one here, they are often very close.

10.3 Why is a baking process required before soldering if the bag has been opened?

SMD plastic packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can rapidly vaporize, creating internal pressure that may crack the package or delaminate internal interfaces—a failure known as \"popcorning.\" Baking removes this absorbed moisture.

11. Practical Design Case Study

Consider designing a backlight for a small industrial instrument display. The design requires both a bright white backlight for normal operation and a distinct yellow indicator for alarm conditions. Using the LTW-S115KSDS-5A, the designer can place a single component at the edge of the light guide. The white chip is driven at 5mA via a constant current circuit for the main backlight. The yellow chip is connected to a separate driver circuit controlled by the instrument's alarm logic. This approach simplifies the mechanical design (one component instead of two), reduces the PCB footprint, and ensures perfect alignment of the two light sources relative to the light guide.

12. Operating Principle

Light emission in LEDs is based on electroluminescence in a semiconductor p-n junction. 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 color (wavelength) of the emitted light is determined by the bandgap energy of the semiconductor material. The InGaN chip has a wider bandgap, enabling the emission of shorter-wavelength light (blue), which is partially converted to a broader spectrum (appearing white) by a phosphor coating inside the package. The AlInGaP chip has a narrower bandgap, engineered to emit photons directly in the yellow/orange/red part of the spectrum, resulting in the pure yellow light observed.

13. Technology Trends

The LED industry continues to evolve towards higher efficiency (more lumens per watt), improved color rendering (especially for white LEDs), and greater miniaturization. For side-view and backlight applications, trends include even thinner packages, higher brightness density, and the integration of more complex multi-chip arrays (RGB, RGBW) into single packages for dynamic color control. Furthermore, advancements in packaging materials and phosphor technology aim to enhance reliability, thermal performance, and color consistency over temperature and lifetime.