LTST-S327TBKSKT Dual Color SMD LED Datasheet - Blue & Yellow - 20mA/30mA - 76mW/75mW - English Technical Document

1. Product Overview

This document details the specifications for a compact, surface-mount dual-color LED component. The device integrates two distinct semiconductor chips within a single package: one emitting blue light and the other emitting yellow light. This configuration is designed for applications requiring multiple status indications or color mixing in a minimal footprint.

1.1 Core Advantages and Target Market

The primary advantage of this component is its space-saving design, combining two light sources. It is constructed using advanced semiconductor materials: InGaN for the blue emitter and AlInGaP for the yellow emitter, which are known for their high efficiency and brightness. The package is fully compliant with RoHS directives and is finished with a tin plating for improved solderability. It is supplied on industry-standard 8mm tape mounted on 7-inch reels, making it fully compatible with high-speed automated pick-and-place assembly systems and infrared reflow soldering processes. Its typical applications span telecommunications equipment, office automation devices, home appliances, industrial control panels, keyboard backlighting, status indicators, and various signaling applications.

2. Technical Parameters: In-Depth Objective Interpretation

The following section provides a detailed analysis of the device's electrical, optical, and thermal characteristics based on the provided data.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed. For the blue chip: Maximum power dissipation is 76 mW, peak forward current (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width) is 100 mA, and the maximum continuous DC forward current is 20 mA. For the yellow chip: Maximum power dissipation is 75 mW, peak forward current is 80 mA, and the maximum continuous DC forward current is 30 mA. The device is rated for an operating temperature range of -20°C to +80°C and a storage temperature range of -30°C to +100°C. The maximum allowable infrared soldering temperature is 260°C for a duration not exceeding 10 seconds.

2.2 Electrical and Optical Characteristics

These parameters are specified at an ambient temperature (Ta) of 25°C and represent typical operating conditions. Luminous intensity (Iv) for both colors ranges from a minimum of 28.0 mcd to a maximum of 180.0 mcd when driven at their respective recommended DC forward current (20mA for blue, 20mA for yellow test condition). The viewing angle (2θ1/2) is 130 degrees for both emitters, indicating a very wide beam pattern. The peak emission wavelength (λP) is approximately 468 nm for blue and 592 nm for yellow. The dominant wavelength (λd), which defines the perceived color, is typically 470 nm for blue and 590 nm for yellow. The spectral line half-width (Δλ) is 25 nm for blue and 17 nm for yellow, describing the spectral purity. The forward voltage (Vf) at 20mA is typically 3.4V for the blue chip (range 3.4V to 3.8V) and 2.0V for the yellow chip (range 2.0V to 2.4V). The maximum reverse current (Ir) at 5V is 10 μA for both.

3. Binning System Explanation

To ensure consistency in brightness, the LEDs are sorted into bins based on their measured luminous intensity.

3.1 Luminous Intensity Binning

Both the blue and yellow chips use an identical binning structure defined by codes N, P, Q, and R. Each bin has a specified minimum and maximum luminous intensity value measured in millicandelas (mcd) at the standard test current of 20mA. Bin N covers 28.0 to 45.0 mcd, Bin P covers 45.0 to 71.0 mcd, Bin Q covers 71.0 to 112.0 mcd, and Bin R covers 112.0 to 180.0 mcd. A tolerance of +/-15% is applied to the limits of each bin. This system allows designers to select components with predictable brightness levels for their application.

4. Performance Curve Analysis

While specific graphical data is referenced in the document (e.g., Figure 1 for spectral measurement, Figure 5 for viewing angle), typical performance trends can be inferred from the parameters. The forward voltage (Vf) will have a negative temperature coefficient, meaning it decreases slightly as the junction temperature increases. The luminous intensity will also decrease with increasing junction temperature, a characteristic common to all LEDs. The relationship between forward current (If) and luminous intensity (Iv) is generally linear within the recommended operating range. The spectral characteristics (peak wavelength, dominant wavelength) may experience a slight shift with changes in drive current and temperature.

5. Mechanical and Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an industry-standard SMD package outline. Detailed dimensional drawings with all critical measurements in millimeters are provided in the source document, with a general tolerance of ±0.1 mm. The lens is water clear. The pin assignment is clearly defined: Pin A1 is the anode for the InGaN Blue chip, and Pin A2 is the anode for the AlInGaP Yellow chip. The cathodes are presumably common, though the exact internal connection should be verified in the package diagram. Correct polarity identification during assembly is crucial.

5.2 Recommended PCB Pad Layout and Soldering Direction

The datasheet includes a recommended footprint for the printed circuit board (PCB) attachment pads. Adhering to this design is critical for achieving reliable solder joints, proper alignment, and effective heat dissipation during the reflow process. It also indicates the preferred orientation of the component on the tape relative to the soldering direction to ensure stable placement.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Conditions

For lead-free (Pb-free) assembly processes, a specific infrared (IR) reflow profile is recommended. This profile is designed to be compliant with JEDEC standards. Key parameters include a pre-heat stage in the range of 150–200°C, a maximum pre-heat time of 120 seconds, a peak body temperature not exceeding 260°C, and a time above this peak temperature limited to a maximum of 10 seconds. The component should not be subjected to more than two reflow cycles under these conditions. It is emphasized that the optimal profile depends on the specific PCB design, solder paste, and oven used, so process characterization is advised.

6.2 Storage and Handling

The LEDs are moisture-sensitive (MSL3). When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤30°C and ≤90% RH and used within one year. Once the bag is opened, the storage environment must not exceed 30°C and 60% RH. Components removed from their original packaging should be subjected to IR reflow within one week. For storage beyond one week outside the original bag, they must be stored in a sealed container with desiccant or in a nitrogen atmosphere. If stored open for more than a week, a bake-out at approximately 60°C for at least 20 hours is required before soldering. Proper ESD (Electrostatic Discharge) precautions, such as using grounded wrist straps and equipment, are mandatory as the device can be damaged by static electricity.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Unspecified chemicals may damage the package material. The recommended method is to immerse the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute.

7. Packaging and Ordering Information

The components are supplied on embossed carrier tape with a protective cover tape. The tape width is 8 mm. The tape is wound onto standard 7-inch (178 mm) diameter reels. Each full reel contains 3000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies for remainder lots. The packaging conforms to ANSI/EIA-481 specifications.

8. Application Suggestions

8.1 Typical Application Scenarios

This dual-color LED is ideal for applications where board space is at a premium but multiple visual states are required. Examples include: dual-status indicators (e.g., power on/standby, network connected/active, charge status), backlighting for keypads with color-coded functions, and small-scale informational displays in consumer electronics, telecom gear, and industrial human-machine interfaces (HMIs).

8.2 Design Considerations

Designers must account for the different forward voltage (Vf) and current ratings of the two chips. Separate current-limiting resistors will be required for each anode (A1 and A2) to ensure proper operation and prevent over-current damage. The wide 130-degree viewing angle makes it suitable for applications where the indicator needs to be visible from a broad range of positions. Thermal management should be considered, especially if operating near maximum current ratings or in elevated ambient temperatures, as heat will reduce light output and lifespan.

9. Technical Comparison and Differentiation

The key differentiating factor of this component is the integration of two high-performance, chemically distinct LED chips (InGaN blue and AlInGaP yellow) in one miniature SMD package. This offers a more compact and potentially more reliable solution compared to using two separate single-color LEDs. The use of AlInGaP for yellow typically offers higher efficiency and better temperature stability compared to some other yellow-emitting technologies like phosphor-converted LEDs.

10. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive the blue and yellow LEDs simultaneously at their maximum DC current?

A: It is not recommended to drive both at their absolute maximum DC current (20mA blue + 30mA yellow = 50mA total) continuously without careful thermal analysis, as the combined power dissipation may exceed the package's ability to shed heat, leading to accelerated degradation.

Q: Why is the forward voltage different for the two colors?

A: The forward voltage is a fundamental property of the semiconductor material's bandgap. InGaN (blue) has a wider bandgap than AlInGaP (yellow), which results in a higher forward voltage requirement.

Q: What does the \"Peak Emission Wavelength\" vs. \"Dominant Wavelength\" mean?

A: The peak wavelength is the wavelength at which the spectral power output is highest. The dominant wavelength is the single wavelength of monochromatic light that would appear to have the same color to the human eye. They are often close but not identical, especially for LEDs with broader spectra.

11. Practical Design and Usage Case

Consider a portable device with a single indicator cutout. By using this dual-color LED, the design can show three distinct states: Off (both chips off), State A (Blue on, e.g., \"Bluetooth enabled\"), State B (Yellow on, e.g., \"Battery charging\"), and potentially State C (Both on, creating a greenish hue, e.g., \"Fully charged and connected\"). This maximizes functionality per unit of board area and simplifies the mechanical design compared to fitting two separate LEDs.

12. Operating Principle Introduction

Light emission in an LED is based on electroluminescence. When a forward voltage is applied across the p-n junction of a semiconductor chip, electrons and holes are injected into the junction region. When these charge carriers recombine, they release energy. In a direct bandgap semiconductor like InGaN or AlInGaP, this energy is released primarily as photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. The InGaN chip emits in the blue spectrum, while the AlInGaP chip emits in the yellow/amber spectrum.

13. Technology Trends

The trend in indicator LEDs continues towards higher efficiency (more light output per electrical watt), smaller package sizes, and greater integration. Dual- and multi-color packages in ultra-miniature footprints are becoming more common to support increasingly dense electronic assemblies. There is also a focus on improving color consistency and stability over temperature and lifetime. The underlying materials, like InGaN, continue to see improvements in performance and cost-effectiveness, expanding their use beyond blue/green into broader spectral ranges.