LTST-S326TBKSKT Dual Color SMD LED Datasheet - Side Looking - Blue & Yellow - 20mA/30mA - English Technical Document

1. Product Overview

This document details the technical specifications for a dual-color, side-looking Surface Mount Device (SMD) Light Emitting Diode (LED). The device integrates two distinct semiconductor chips within a single package: one emitting in the blue spectrum and the other in the yellow spectrum. This configuration is designed for applications requiring compact, multi-indication status lights, backlighting, or decorative lighting where space is at a premium and viewing is from the side of the component.

The core advantages of this product include its compliance with RoHS (Restriction of Hazardous Substances) directives, making it suitable for modern electronic manufacturing. It features a tin-plated lead frame for improved solderability and corrosion resistance. The component is packaged on industry-standard 8mm tape reels, facilitating compatibility with high-speed automated pick-and-place assembly equipment. Furthermore, it is designed to withstand standard infrared (IR) reflow soldering processes, which are prevalent in surface-mount technology (SMT) production lines.

2. Technical Parameters Deep Objective Interpretation

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed and should be avoided for reliable performance.

• Power Dissipation (Pd): The maximum allowable power the LED can dissipate as heat at an ambient temperature (Ta) of 25°C is 76 mW for the blue chip and 75 mW for the yellow chip. Exceeding this limit risks thermal damage.
• Forward Current: The maximum continuous DC forward current (IF) is 20 mA for the blue chip and 30 mA for the yellow chip. A higher peak forward current of 100 mA (blue) and 80 mA (yellow) is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating.
• Thermal Derating: The maximum DC forward current must be reduced linearly above 25°C at a rate of 0.25 mA/°C for the blue chip and 0.4 mA/°C for the yellow chip. This is crucial for high-temperature environment applications.
• Reverse Voltage (VR): The maximum allowable reverse voltage is 5V for both chips. Applying a higher reverse voltage can cause junction breakdown. Note that continuous operation at this reverse voltage is prohibited.
• Temperature Ranges: The device is rated for operation between -20°C and +80°C. Storage should be within -30°C to +100°C.
• Soldering Thermal Limits: The component can withstand wave or IR reflow soldering with a peak temperature of 260°C for up to 5 seconds, and vapor phase soldering at 215°C for up to 3 minutes.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C, IF=20mA) and define the typical performance of the device.

• Luminous Intensity (Iv): This is the measure of the perceived power of light emitted in a specific direction. For both colors, the minimum intensity is 28.0 millicandelas (mcd), typical is 45.0 mcd (blue only specified), and maximum is 180.0 mcd. The actual shipped intensity is determined by the binning system.
• Viewing Angle (2θ1/2): The full viewing angle at which the luminous intensity drops to half of its axial (on-center) value is 130 degrees for both colors, indicating a wide viewing pattern typical for side-looking LEDs.
• Wavelength: The blue chip has a typical peak emission wavelength (λP) of 468 nm and a dominant wavelength (λd) of 470 nm. The yellow chip has a typical peak at 592 nm and dominant at 590 nm. The spectral line half-width (Δλ) is 25 nm for blue and 17 nm for yellow, describing the spectral purity.
• Forward Voltage (VF): The voltage drop across the LED when operating at 20mA is typically 3.4V for blue (max 3.8V) and 2.0V for yellow (max 2.4V). This parameter is critical for driver circuit design and power supply selection.
• Reverse Current (IR): The leakage current when 5V is applied in reverse is a maximum of 10 μA for both chips.
• Capacitance (C): The typical junction capacitance for the yellow chip is 40 pF at 0V bias and 1 MHz measurement frequency.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance bins. This device uses a binning system based on luminous intensity.

For both the blue and yellow chips, the luminous intensity at 20mA is categorized into four bins:

• Bin N: Intensity range from 28.0 mcd to 45.0 mcd.
• Bin P: Intensity range from 45.0 mcd to 71.0 mcd.
• Bin Q: Intensity range from 71.0 mcd to 112.0 mcd.
• Bin R: Intensity range from 112.0 mcd to 180.0 mcd.

A tolerance of +/-15% is applied to the limits of each intensity bin. This system allows designers to select components that meet specific brightness requirements for their application, ensuring visual consistency in end products that use multiple LEDs.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet (e.g., Fig.1, Fig.6), typical curves for such devices provide critical insights:

• I-V (Current-Voltage) Curve: This curve shows the relationship between forward voltage (VF) and forward current (IF). It is non-linear, with a characteristic \"knee\" voltage (around the typical VF) above which current increases rapidly with small voltage increases. This underscores why LEDs must be driven by a current-limited source, not a constant voltage.
• Luminous Intensity vs. Forward Current: Intensity generally increases with current, but the relationship may not be perfectly linear, especially at higher currents where efficiency can drop due to heating.
• Luminous Intensity vs. Ambient Temperature: The light output of an LED decreases as the junction temperature increases. Understanding this derating is essential for applications operating over a wide temperature range.
• Spectral Distribution: The referenced figures would show the relative radiant power versus wavelength, highlighting the peak (λP) and spectral width (Δλ).

5. Mechanical & Packaging Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an EIA standard package outline. The physical dimensions are provided in the datasheet drawings, with all units in millimeters and a general tolerance of ±0.10 mm unless otherwise specified.

Pin Assignment: The dual-color LED has a specific pinout to control each chip independently. For the part number LTST-S326TBKSKT:

• Cathode 1 (C1): Connected to the Yellow AlInGaP chip.
• Cathode 2 (C2): Connected to the Blue InGaN chip.
• The anode is common to both chips.

Correct polarity identification is vital during PCB layout and assembly to ensure proper function.

5.2 Suggested Soldering Pad Dimensions

The datasheet includes a recommended land pattern (solder pad) design for the PCB. Adhering to these dimensions ensures proper solder joint formation, mechanical stability, and thermal relief during the reflow process. Using pads that are too small can lead to weak joints, while pads that are too large may cause tombstoning (component standing up on one end) or solder bridging.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

Two suggested Infrared (IR) reflow profiles are provided: one for standard (tin-lead) solder process and one for lead-free (Pb-free) solder process. The lead-free profile is specifically designed for use with Sn-Ag-Cu (SAC) solder paste. Key parameters in these profiles include:

• Pre-heat/Soak Zone: Gradually raises the temperature to activate flux and minimize thermal shock.
• Reflow Zone: The temperature exceeds the solder melting point to form the joint. The peak temperature must not exceed 260°C, and the time above liquidus (TAL) must be controlled.
• Cooling Zone: Controlled cooling solidifies the solder joints.

6.2 Cleaning

If cleaning is necessary after soldering, 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 or aggressive chemical cleaners can damage the LED package material, leading to discoloration, cracking, or delamination.

6.3 Storage Conditions

For long-term storage, LEDs should be kept in their original moisture-barrier packaging. If removed, they are sensitive to moisture absorption (MSL - Moisture Sensitivity Level). The datasheet recommends that components out of their original packaging be reflowed within one week. For extended storage outside the original bag, they should be stored in a sealed container with desiccant or in a nitrogen ambient. If stored unpackaged for more than a week, a baking process (e.g., 60°C for 24 hours) is recommended before soldering to drive out absorbed moisture and prevent \"popcorning\" damage during reflow.

7. Packaging & Ordering Information

The device is supplied in a tape-and-reel format compatible with automated assembly.

• Tape Width: 8 mm.
• Reel Diameter: 7 inches (178 mm).
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Packing Standard: Complies with ANSI/EIA 481-1-A-1994 specifications. Empty pockets in the tape are sealed with cover tape. The maximum number of consecutive missing components is two.

8. Application Suggestions

8.1 Typical Application Scenarios

This dual-color, side-looking LED is ideal for applications where space is limited and indication needs to be viewed from the edge of a board or assembly. Common uses include:

• Status Indicators: On consumer electronics, networking equipment, or industrial controls, where different colors can signify power (yellow), activity (blue), or fault conditions.
• Backlighting: For edge-lit panels, keypads, or small displays where side emission is an advantage.
• Decorative Lighting: In compact devices where multi-color effects are desired.

8.2 Design Considerations

• Drive Circuit: LEDs are current-driven devices. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, a current-limiting resistor must be placed in series with each LED. Driving multiple LEDs in parallel directly from a voltage source (without individual resistors) is not recommended due to variations in forward voltage (VF) between individual LEDs, which can lead to significant differences in brightness and potential over-current in some devices.
• Thermal Management: While the power dissipation is low, proper PCB layout with adequate copper area can help dissipate heat, especially in high ambient temperature environments or when driving at maximum current. This maintains light output and longevity.
• Electrostatic Discharge (ESD) Protection: LEDs are sensitive to ESD. Handling precautions should include the use of grounded wrist straps, anti-static mats, and ionizers in the assembly area. Equipment and workstations must be properly grounded.

9. Technical Comparison & Differentiation

The key differentiating features of this component are its dual-color capability in a single side-looking SMD package and its specific performance ratings. Compared to single-color LEDs, it saves board space and simplifies assembly for bi-color indication. The side-looking form factor differentiates it from top-emitting LEDs, making it suitable for specific mechanical designs. Its compatibility with automated placement and standard reflow profiles aligns it with modern, high-volume manufacturing processes. The detailed binning system provides a level of brightness consistency that may be superior to unbinned or broadly binned generic components.

10. Frequently Asked Questions (Based on Technical Parameters)

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

A: Not necessarily. The Absolute Maximum Ratings specify power dissipation per chip. Driving both at 20mA (blue) and 30mA (yellow) simultaneously results in a total power dissipation that must be checked against thermal limits, especially considering the shared package. Derating at elevated ambient temperatures must be applied.

Q: Why is a series resistor necessary for each LED, even in a parallel array?

A: The forward voltage (VF) of LEDs has a manufacturing tolerance. Without individual resistors, LEDs with a slightly lower VF will draw disproportionately more current, becoming brighter and potentially overheating, while those with a higher VF will be dim. The resistor acts as a simple, effective current regulator for each LED.

Q: What does \"side looking\" mean for the viewing angle?

A: A \"side looking\" LED emits light primarily from the side of the package, perpendicular to the mounting plane. The 130-degree viewing angle is measured from this primary emission axis. This is in contrast to a \"top looking\" LED which emits light upwards from the top of the package.

Q: How do I interpret the bin code for ordering?

A: The bin code (N, P, Q, R) specifies the guaranteed minimum and maximum luminous intensity range for the LEDs in that batch. Designers should select a bin that meets their minimum brightness requirement while considering cost, as higher bins (e.g., R) with higher brightness may be more expensive.

11. Practical Use Case Example

Scenario: Dual-Status Indicator for a Portable Device

A designer is creating a compact handheld sensor. They need a single, small indicator to show both \"Standby\" and \"Active/Transmitting\" states. They choose this dual-color LED.

Implementation: The LED is placed at the edge of the main PCB, with its emitting side facing a small light pipe that directs light to the device's exterior. The microcontroller's GPIO pins drive the cathodes (C1 for Yellow, C2 for Blue) through individual current-limiting resistors (calculated based on the supply voltage and desired 20mA current). The common anode is connected to the positive supply. Firmware lights the yellow LED for Standby and the blue LED for Active mode. The side-looking nature of the LED allows it to couple efficiently into the side-entry light pipe, creating a clean, professional indicator in a very constrained space.

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. When a voltage is applied in the forward direction, electrons from the n-type semiconductor material recombine with holes from the p-type material within the active region of the chip. This recombination releases energy in the form of photons (light particles). The specific wavelength (color) of the emitted light is determined by the energy bandgap of the semiconductor materials used. The blue LED chip is typically made from Indium Gallium Nitride (InGaN), which has a wider bandgap suitable for shorter wavelengths (blue light). The yellow LED chip is typically made from Aluminium Indium Gallium Phosphide (AlInGaP), which has a bandgap corresponding to longer wavelengths (yellow/red light). Packaging the two chips together with a common anode allows independent control of each color from a single 3-pad SMD component.

13. Development Trends

The field of SMD LEDs continues to evolve. General trends observable in the industry, which provide context for components like this one, include:

• Increased Efficiency and Luminous Efficacy: Ongoing material science and chip design improvements yield more light output (lumens) per unit of electrical input power (watts).
• Miniaturization: Packages continue to shrink (e.g., from 0603 to 0402 to 0201 metric sizes) while maintaining or improving performance, enabling denser electronics.
• Higher Reliability and Longer Lifetimes: Improvements in packaging materials, die attach methods, and phosphor technology (for white LEDs) enhance longevity and stability over temperature and time.
• Advanced Color Mixing and Control: Beyond dual-color, RGB (Red, Green, Blue) and RGBW (RGB + White) LEDs in single packages are common, often with integrated drivers for sophisticated color and dimming control.
• Integration: Trends include LEDs with built-in current-limiting resistors, Zener diodes for ESD protection, or even full IC drivers in the package, simplifying circuit design.

This dual-color side-looking LED represents a well-established, reliable solution for specific spatial and indication requirements within this broader technological landscape.