LTST-S115KETBKT SMD LED Datasheet - Dual Color (Red/Blue) - Side Looking - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a dual-color, side-looking Surface Mount Device (SMD) LED. This component is designed for automated printed circuit board (PCB) assembly and is suitable for applications where space is a critical constraint. The LED integrates two distinct semiconductor chips within a single package: one emitting in the red spectrum and the other in the blue spectrum.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its miniature form factor, compatibility with automated pick-and-place equipment, and suitability for infrared (IR) reflow soldering processes. It is constructed with lead-free (ROHS compliant) materials and features a tin-plated termination for improved solderability. The device utilizes advanced semiconductor materials: AlInGaP for the red emitter and InGaN for the blue emitter, which are known for their high efficiency and brightness.

The target applications span a wide range of consumer and industrial electronics. It is particularly well-suited for status indication, keyboard or keypad backlighting, symbol illumination, and integration into micro-displays within devices such as mobile phones, notebook computers, network equipment, home appliances, and various office automation systems.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operating the LED under conditions exceeding these values is not recommended.

• Power Dissipation (Pd): The maximum allowable power that can be dissipated as heat. The red chip is rated for 62.5 mW, while the blue chip is rated for 76 mW. Exceeding this limit risks thermal degradation.
• Forward Current: Two current limits are specified. The DC Forward Current (IF) is the maximum continuous current: 25 mA for the red chip and 20 mA for the blue chip. The Peak Forward Current is a higher pulsed current (60 mA for red, 100 mA for blue) allowed only under specific conditions (1/10 duty cycle, 0.1 ms pulse width) for brief periods.
• Temperature Ranges: The device is designed to operate within an ambient temperature (Ta) range of -20°C to +80°C. Storage should be within -30°C to +100°C.
• Soldering Condition: The component can withstand a peak infrared reflow soldering temperature of 260°C for a maximum of 10 seconds, which is standard for Pb-free assembly processes.

2.2 Electrical and Optical Characteristics

These parameters are measured at a standard test condition of Ta=25°C and a forward current (IF) of 20 mA, unless otherwise noted. They define the typical performance of the device.

• Luminous Intensity (Iv): This is a measure of the perceived brightness of the light emitted. For the red chip, the intensity ranges from a minimum of 45.0 mcd to a maximum of 180.0 mcd. For the blue chip, the range is from 28.0 mcd to 112.0 mcd. The actual value for a specific unit is determined by its bin rank.
• Viewing Angle (2θ1/2): Defined as the full angle at which the luminous intensity is half of the intensity measured on the central axis. This LED features a very wide viewing angle of 130 degrees for both colors, making it suitable for applications requiring broad visibility.
• Wavelength Parameters: Peak Emission Wavelength (λP) is the wavelength at which the optical output power is greatest (typically 631 nm for red, 468 nm for blue). Dominant Wavelength (λd) is the single wavelength that best represents the perceived color, with specified min/typ/max ranges (e.g., 615-635 nm for red). Spectral Line Half-Width (Δλ) is the width of the spectrum at half the peak power, typically 15 nm for red and 20 nm for blue, indicating the color purity.
• Forward Voltage (VF): The voltage drop across the LED when operating at the specified current. The red chip has a VF range of 1.6V to 2.4V, while the blue chip has a higher range of 2.7V to 3.9V at 20 mA. This difference is due to the different bandgap energies of the AlInGaP and InGaN materials.
• Reverse Current (IR): The maximum leakage current when a reverse voltage (VR) of 5V is applied. It is specified as 10 μA max for both chips. The datasheet explicitly cautions that the device is not designed for reverse operation; this parameter is for test purposes only.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins. This allows designers to select components with tightly controlled characteristics.

3.1 Luminous Intensity (Iv) Binning

The LEDs are grouped based on their measured luminous intensity at 20 mA. Each bin has a minimum and maximum value, with a tolerance of +/-15% within each bin.

• Red Chip Bins: P (45.0-71.0 mcd), Q (71.0-112.0 mcd), R (112.0-180.0 mcd).
• Blue Chip Bins: N (28.0-45.0 mcd), P (45.0-71.0 mcd), Q (71.0-112.0 mcd).

3.2 Hue (Dominant Wavelength) Binning

For the blue chip only, an additional binning is performed based on dominant wavelength to control the shade of blue.

• Blue Chip Wavelength Bins: AC (465-470 nm), AD (470-475 nm). The tolerance for each bin is +/- 1 nm, ensuring very precise color control.

4. Mechanical and Package Information

4.1 Package Dimensions and Pin Assignment

The LED conforms to an EIA standard package outline. All dimensions are in millimeters with a standard tolerance of ±0.1 mm unless otherwise specified. The package is a side-looking type, meaning the primary light emission is from the side of the component, not the top. This is crucial for backlighting applications where light needs to be directed laterally.

The pin assignment is clearly defined: Cathode 1 (C1) is connected to the blue chip's anode (common anode configuration is implied, but the datasheet specifies pin assignment for the chips). Cathode 2 (C2) is connected to the red chip. Correct polarity must be observed during assembly.

4.2 Recommended PCB Attachment Pad and Soldering Direction

The datasheet includes a diagram showing the recommended copper pad layout on the PCB. Following this layout is essential for achieving a reliable solder joint, proper alignment, and effective heat dissipation during the reflow process. The diagram also indicates the correct orientation of the LED on the tape relative to the PCB for automated assembly.

5. Soldering and Assembly Guidelines

5.1 IR Reflow Soldering Parameters

For lead-free (Pb-free) soldering processes, a specific thermal profile is recommended. The key parameters include a pre-heat zone (150-200°C), a maximum pre-heat time of 120 seconds, a peak body temperature not exceeding 260°C, and a time at this peak temperature limited to 10 seconds maximum. The LED should not be subjected to more than two reflow cycles under these conditions.

5.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken. The soldering iron tip temperature should not exceed 300°C, and the contact time with the LED terminal should be limited to a maximum of 3 seconds. Hand soldering should be performed only once per device.

5.3 Cleaning

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

6. Storage and Handling Cautions

6.1 Storage Conditions

Proper storage is critical to maintain solderability and prevent moisture-induced damage (popcorning) during reflow.

• Sealed Package: LEDs in their original moisture-proof bag with desiccant should be stored at ≤30°C and ≤90% Relative Humidity (RH). The shelf life under these conditions is one year.
• Opened Package: Once the moisture barrier bag is opened, the storage environment must be more controlled: ≤30°C and ≤60% RH. Components removed from the sealed bag should be reflow-soldered within one week.
• Extended Storage (Opened): For storage beyond one week, LEDs should be placed in a sealed container with desiccant or in a nitrogen-purged desiccator. If stored open for more than a week, a bake-out at approximately 60°C for at least 20 hours is mandatory before the soldering process to drive off absorbed moisture.

6.2 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge and voltage surges. Proper ESD precautions must be observed during handling and assembly. This includes the use of grounded wrist straps, anti-static gloves, and ensuring all equipment and workstations are properly grounded.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied packaged for automated assembly. They are mounted on 8mm wide embossed carrier tape. This 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.

7.2 Reel Dimensions and Features

Detailed mechanical drawings for the reel and tape are provided. Key features include: empty component pockets on the tape are sealed with a top cover tape to protect components, and the maximum allowable number of consecutive missing components on a reel is two, ensuring supply consistency for pick-and-place machines.

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

When designing a drive circuit, the different forward voltage (VF) requirements of the red and blue chips must be accounted for. A simple series resistor for each color channel is the most common method to limit current. The resistor value (R) is calculated using the formula: R = (Vcc - VF_LED) / I_F, where Vcc is the supply voltage, VF_LED is the forward voltage of the specific chip (use max value from datasheet for a conservative design), and I_F is the desired forward current (not to exceed the DC rating). Due to the voltage difference, the resistor value for the blue channel will typically be different from that of the red channel, even if the same current is desired.

8.2 Thermal Management

Although power dissipation is low, proper thermal design on the PCB contributes to long-term reliability. Ensuring the recommended solder pad layout is used helps dissipate heat from the LED junction into the PCB. Operating the LED at or near its maximum current rating in a high ambient temperature environment should be avoided, as this pushes the junction temperature towards its limit.

8.3 Optical Design

The side-looking emission profile is ideal for applications where light needs to be coupled into a light guide, edge-lit a panel, or indicate status from the side of a device. Designers should consider the 130-degree viewing angle when designing light pipes or apertures to ensure the desired illumination pattern is achieved.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the red and blue chips simultaneously at their full DC current (25mA and 20mA)?

A: The datasheet provides ratings per chip. The power dissipation and thermal limits must be considered for the combined heat generated. It is generally safe if the total power (Vf_red * 25mA + Vf_blue * 20mA) is within the package's overall thermal dissipation capability, but simultaneous operation at absolute max ratings should be evaluated carefully, especially at high ambient temperatures.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?

A> Peak Wavelength (λP) is a physical measurement of the spectrum's highest point. Dominant Wavelength (λd) is a calculated value from colorimetry that best matches the human eye's perception of the color. λd is more relevant for applications where specific color appearance is critical.

Q: The reverse current is specified at 5V. Can I use this LED in an AC circuit or with reverse polarity protection?

A: No. The datasheet explicitly states the device is not designed for reverse operation. The 5V test is for quality verification only. Applying a continuous reverse voltage, even below 5V, is not recommended and may damage the LED. External protection, such as a diode in parallel, would be required for AC or bipolar drive.

Q: How do I select the appropriate bin for my application?

A: Choose the luminous intensity (Iv) bin based on your required brightness level and the need for consistency between units. For the blue LED, also select the wavelength (hue) bin if color consistency is paramount. Using a tighter bin (e.g., Q for intensity) may increase cost but ensures more uniform performance across your production.