LTST-S115KRKGKT Dual Color SMD LED Datasheet - Side View Package - Red & Green - 20mA - English Technical Document

1. Product Overview

The LTST-S115KRKGKT is a dual-color, side-viewing Surface Mount Device (SMD) LED designed primarily for LCD backlighting applications. It integrates two distinct semiconductor chips within a single package: one emitting red light and the other emitting green light. This configuration allows for the creation of mixed colors and is suitable for status indicators, backlighting, and other applications requiring compact, multi-color illumination from the side of a device.

The device utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) chip technology for both colors, which is known for delivering high luminous efficiency and brightness. The package is water-clear, enhancing light output and color purity. It is supplied on industry-standard 8mm tape on 7-inch reels, making it fully compatible with high-speed automated pick-and-place assembly equipment and infrared (IR) reflow soldering processes.

1.1 Core Features and Advantages

• Dual-Color Chip: Combines red and green AlInGaP LEDs in one compact EIA-standard package.
• Side-Viewing Design: Optimized form factor for edge-lighting LCD panels and other space-constrained side-illumination needs.
• High Brightness: Ultra-bright output from AlInGaP technology.
• RoHS, HF, and Green Product Compliant: Meets environmental and safety regulations.
• Automation Friendly: Packaged on tape and reel for efficient automated assembly.
• Reflow Solder Compatible: Withstands standard IR reflow profiles for lead-free processes.

2. Absolute Maximum Ratings

Stresses beyond these limits may cause permanent damage to the device. These are stress ratings only; functional operation under these conditions is not implied.

3. Electrical & Optical Characteristics

Typical characteristics are measured at an ambient temperature (Ta) of 25°C and a forward current (IF) of 20mA, unless otherwise specified.

3.1 Parameter Definitions

• Luminous Intensity (IV): Measured using a sensor and filter approximating the CIE photopic eye-response curve.
• Dominant Wavelength (λd): The single wavelength perceived by the human eye, derived from the CIE chromaticity diagram. It defines the color of the LED.
• Viewing Angle: The full angle at which the luminous intensity is half of the intensity measured directly on-axis (0°).

4. Binning System

The LEDs are sorted into bins based on luminous intensity and dominant wavelength (for green) to ensure color and brightness consistency within a production batch.

4.1 Luminous Intensity Binning

Red Chip (@20mA):

Tolerance on each intensity bin is ±15%.

Green Chip (@20mA):

Tolerance on each intensity bin is ±15%.

4.2 Dominant Wavelength Binning (Green Chip Only)

Tolerance for each dominant wavelength bin is ±1 nm.

5. Mechanical & Package Information

The device conforms to EIA standard package dimensions for side-view LEDs. Detailed mechanical drawings are provided in the datasheet, including body dimensions, lead spacing, and recommended PCB land pattern (solder pad) design. The pin assignment is clearly marked: Cathode 1 (C1) is for the Green chip, and Cathode 2 (C2) is for the Red chip. The common anode is not explicitly labeled in the provided snippet but is standard for this package type. Engineers must consult the full dimensional drawing for accurate placement and footprint design.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared (IR) reflow profile for lead-free (Pb-free) solder processes is provided. Key parameters include:

• Pre-heat: 150-200°C for a maximum of 120 seconds.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus: The device should be exposed to the peak temperature for a maximum of 10 seconds. Reflow should be performed a maximum of two times.

The profile is based on JEDEC standards to ensure reliable solder joints without damaging the LED package. It is critical to characterize the profile for the specific PCB design, solder paste, and oven used in production.

6.2 Hand Soldering

If hand soldering is necessary, use a soldering iron with a temperature not exceeding 300°C. The soldering time should be limited to a maximum of 3 seconds per joint, and it should be performed only once.

6.3 Cleaning

Do not use unspecified chemical cleaners. If cleaning is required after soldering, immerse the LEDs in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute.

7. Storage & Handling

• Sealed Package: Store at ≤30°C and ≤90% Relative Humidity (RH). Use within one year of opening the moisture barrier bag.
• Opened Package: Store at ≤30°C and ≤60% RH. It is recommended to complete IR reflow within one week of removal from the sealed package.
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen ambient. LEDs stored out of original packaging for more than one week should be baked at approximately 60°C for at least 20 hours before assembly to remove moisture and prevent \"popcorning\" during reflow.

8. Packaging & Ordering

The LTST-S115KRKGKT is supplied in standard packaging:

• Tape: 8mm wide embossed carrier tape.
• Reel: 7-inch (178mm) diameter reel.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• The packaging complies with ANSI/EIA-481-1-A-1994 specifications. Empty pockets are sealed with cover tape.

9. Application Notes & Design Considerations

9.1 Drive Method

LEDs are current-operated devices. To ensure stable light output and long lifetime, they must be driven by a constant current source, not a constant voltage source. A current-limiting resistor is essential when driving from a voltage source. The recommended DC forward current (IF) is 20mA for normal operation, with an absolute maximum of 30mA. Pulsing at higher currents (up to 80mA peak) is possible with a low duty cycle (1/10) to achieve higher instantaneous brightness.

9.2 Thermal Management

While the power dissipation is relatively low (75mW per chip), proper PCB layout is important. Ensure adequate copper area around the solder pads to act as a heat sink, especially if operating at high ambient temperatures or near maximum current. This helps maintain LED performance and longevity.

9.3 Polarity and Circuit Design

Pay close attention to the pin assignment (C1: Green, C2: Red). The two chips share a common anode. Independent control of the red and green colors requires separate current-limiting circuits for each cathode. This allows for individual color activation or PWM dimming to create color mixing effects (e.g., yellow when both are on).

9.4 Application Scope

This LED is designed for ordinary electronic equipment such as office equipment, communication devices, and household appliances. It is not recommended for safety-critical applications (e.g., aviation, medical life-support, transportation control) without prior consultation and qualification, as failure could jeopardize life or health.

10. Technical Deep Dive & Analysis

10.1 AlInGaP Technology

The use of AlInGaP for both red and green chips is a significant feature. AlInGaP is a direct-bandgap semiconductor material known for its high internal quantum efficiency, especially in the red-to-amber spectrum. Its application in green LEDs, while less common than InGaN for pure green, can offer advantages in certain wavelength ranges and temperature stability. The typical forward voltage of 2.0V for both colors is relatively low compared to some blue/white InGaN LEDs, which can simplify power supply design.

10.2 Optical Performance

The wide viewing angle of 130 degrees is ideal for backlighting applications where even side illumination is required. The luminous intensity bins provide a wide range of brightness options, allowing designers to select the appropriate bin for their specific luminance requirements. The tight wavelength binning for the green chip (D and E bins) is crucial for applications where consistent color appearance is important, especially when mixing with other colors.

10.3 Reliability and Manufacturing

The compatibility with IR reflow soldering and automatic placement is critical for modern, high-volume electronics manufacturing. The specified soldering profile and storage conditions are designed to prevent thermal and moisture-induced stress, which are common failure mechanisms for plastic-encapsulated SMD components. Adherence to these guidelines is essential for achieving high yield and long-term reliability in the field.

11. Frequently Asked Questions (FAQ)

Q: Can I drive the red and green chips simultaneously at 20mA each?
A: Yes, but you must consider the total power dissipation. At 20mA and a typical Vf of 2.0V, each chip dissipates 40mW, totaling 80mW. This is within the absolute maximum rating of 75mW per chip, but close to the limit. Ensure adequate PCB cooling if operating continuously at this level, especially in high ambient temperatures.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λP) is the wavelength at the highest point in the LED's emission spectrum. Dominant wavelength (λd) is the single wavelength perceived by the human eye, calculated from the color coordinates on the CIE chart. λd is more relevant for color specification in visual applications.

Q: How do I create yellow light with this LED?
A: Yellow is perceived when red and green light are mixed. By turning on both the red and green chips simultaneously and adjusting their relative intensities (e.g., through PWM dimming or different series resistors), you can achieve various shades of yellow, including amber.

Q: Is a reverse protection diode necessary?
A: While the LED can withstand a reverse voltage of up to 5V, it is not designed for continuous reverse bias. In circuits where reverse voltage transients are possible (e.g., inductive loads, hot-plugging), implementing external reverse polarity protection is a prudent design practice to enhance reliability.