LTST-S225KRTGKT-Q SMD LED Datasheet - Side Looking Dual Color (Red/Green) - English Technical Document

1. Product Overview

This document details the specifications for a compact, side-looking dual-color Surface Mount Device (SMD) LED. This component is engineered for automated printed circuit board (PCB) assembly, making it ideal for applications where space is at a premium. The device integrates two distinct semiconductor chips within a single package: one AlInGaP chip for red emission and one InGaN chip for green emission. This configuration allows for dual-color indication from a single, miniature footprint.

1.1 Features

• Compliant with RoHS (Restriction of Hazardous Substances) directives.
• Dual-color (Red and Green) side-emitting design.
• Terminals feature tin plating for improved solderability.
• Utilizes high-efficiency AlInGaP (for red) and InGaN (for green) chip technology.
• Packaged in 8mm tape on 7-inch diameter reels for automated pick-and-place assembly.
• Standard EIA (Electronic Industries Alliance) compliant package outline.
• Input logic compatible.
• Designed for compatibility with automated placement equipment.
• Suitable for infrared (IR) reflow soldering processes.

1.2 Applications

The component is suitable for a broad range of electronic equipment requiring compact, reliable status indication or backlighting. Typical application areas include:

• Telecommunication devices (e.g., cellular phones, network equipment).
• Office automation equipment and home appliances.
• Industrial control panels and equipment.
• Keypad or keyboard backlighting.
• Status and power indicators.
• Micro-displays and icon illumination.
• Signal and symbolic luminaries.

2. Package Dimensions and Pinout

The LED is housed in a surface-mount package. The specific mechanical drawings defining length, width, height, and pad positions are provided in the datasheet. All dimensions are specified in millimeters (mm) with a standard tolerance of ±0.1 mm unless otherwise noted.

Pin Assignment:

• Pins 1 and 2: Anode and Cathode for the Green (InGaN) LED chip.
• Pins 3 and 4: Anode and Cathode for the Red (AlInGaP) LED chip.

3. Ratings and Characteristics

All specifications are defined at an ambient temperature (Ta) of 25°C unless stated otherwise.

3.1 Absolute Maximum Ratings

Stresses beyond these limits may cause permanent damage to the device.

• Power Dissipation (Pd): Red: 50 mW, Green: 38 mW.
• Peak Forward Current (I_F(peak)): 40 mA for both colors (pulsed at 1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): Red: 20 mA, Green: 10 mA.
• Operating Temperature Range (T_opr): -20°C to +80°C.
• Storage Temperature Range (T_stg): -30°C to +85°C.
• Soldering Temperature: Withstand 260°C for 10 seconds (Pb-free process).

3.2 Electro-Optical Characteristics (at I_F = 5mA)

These are the typical performance parameters under standard test conditions.

• Luminous Intensity (I_V):
  • Red: Minimum 11.2 mcd, Typical -, Maximum 28.0 mcd.
  • Green: Minimum 56.0 mcd, Typical -, Maximum 140.0 mcd.
• Viewing Angle (2θ_1/2): Typically 130 degrees (the angle where intensity is half the on-axis value).
• Peak Wavelength (λ_P): Red: 639.0 nm, Green: 525.0 nm.
• Dominant Wavelength (λ_d):
  • Red: Min 617.0 nm, Max 633.0 nm.
  • Green: Min 520.0 nm, Max 535.0 nm.
• Spectral Bandwidth (Δλ): Red: 20.0 nm, Green: 35.0 nm.
• Forward Voltage (V_F):
  • Red: Min 1.6V, Max 2.3V.
  • Green: Min 2.6V, Max 3.5V.
• Reverse Current (I_R): Maximum 10 µA for both at V_R = 5V (for test purposes only; device is not for reverse operation).

4. Binning System

To ensure color and brightness consistency, the LEDs are sorted into bins based on measured performance.

4.1 Luminous Intensity (Brightness) Binning

• Red: Bins L (11.2-18.0 mcd) and M (18.0-28.0 mcd). Tolerance per bin is ±15%.
• Green: Bins P2 (56.0-71.0 mcd), Q1 (71.0-90.0 mcd), Q2 (90.0-112.0 mcd), R1 (112.0-140.0 mcd). Tolerance per bin is ±15%.

4.2 Hue (Dominant Wavelength) Binning

• Green Only: Bins AP (520-525 nm), AQ (525-530 nm), AR (530-535 nm). Tolerance per bin is ±1 nm.

5. Performance Curves and Graphical Data

The datasheet includes typical characteristic curves to aid in design analysis. These graphical representations help engineers understand device behavior under varying conditions. While specific curve data points are not listed in text, designers should refer to the provided figures for details on:

• The relationship between forward current (I_F) and forward voltage (V_F) for both the red and green chips.
• The relationship between forward current (I_F) and relative luminous intensity for both colors.
• The effect of ambient temperature on relative luminous intensity.
• The spectral power distribution (SPD) curves showing the emission profile of the red and green chips.

6. Assembly and Handling Guide

6.1 Cleaning

If cleaning is necessary after soldering or handling, only use specified solvents. Immerse the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute. Do not use unspecified chemical cleaners as they may damage the package material.

6.2 PCB Pad Layout and Soldering

Recommended land pattern (footprint) dimensions for the PCB pads are provided to ensure proper solder joint formation and mechanical stability. The datasheet includes a diagram showing the optimal orientation for soldering and the recommended pad geometry to facilitate good solder wetting and prevent tombstoning.

6.3 Packaging: Tape and Reel

The components are supplied in an 8mm wide embossed carrier tape wound onto a standard 7-inch (178mm) diameter reel. This packaging is compliant with ANSI/EIA-481 specifications. Key details include:

• Pocket pitch and dimensions for component housing.
• Reel hub diameter, flange diameter, and width.
• Standard quantity: 4000 pieces per full reel.
• Minimum order quantity for remnants: 500 pieces.
• A maximum of two consecutive empty pockets is allowed.

7. Important Cautions and Usage Notes

7.1 Application Scope

This LED is designed for standard commercial and industrial electronic equipment. It is not intended for use in safety-critical or high-reliability applications where failure could directly threaten life or health (e.g., aviation, medical life-support, transportation control). For such applications, consultation with the manufacturer is required.

7.2 Storage Conditions

Proper storage is critical to maintain solderability and performance.

• Sealed Package: Store at ≤ 30°C and ≤ 90% Relative Humidity (RH). Use within one year from date code.
• Opened Package: Components are moisture sensitive (MSL 3). Store at ≤ 30°C and ≤ 60% RH. It is recommended to complete IR reflow soldering within one week of opening the moisture barrier bag. For storage beyond one week, bake at 60°C for at least 20 hours before soldering, or store in a sealed container with desiccant or in a nitrogen atmosphere.

7.3 Soldering Recommendations

Adhere to the following conditions to prevent thermal damage:

• Reflow Soldering (Recommended):
  • Pre-heat: 150-200°C for a maximum of 120 seconds.
  • Peak Temperature: Maximum 260°C.
  • Time above 260°C: Maximum 10 seconds. Reflow should be performed a maximum of two times.
• Hand Soldering (Iron):
  • Iron Tip Temperature: Maximum 300°C.
  • Soldering Time: Maximum 3 seconds per joint. Limit to one soldering cycle.

Note on Reflow Profiles: The optimal temperature profile depends on the specific PCB design, components, solder paste, and oven. The profile should be characterized for the specific assembly. The datasheet references a sample profile based on JEDEC standards.

7.4 Electrostatic Discharge (ESD) Sensitivity

LEDs are susceptible to damage from electrostatic discharge (ESD) and electrical surges. Always follow proper ESD control procedures during handling and assembly:

• Use a grounded wrist strap or anti-static gloves.
• Ensure all workstations, equipment, and tools are properly grounded.
• Handle devices in an ESD-protected area.

8. Design Considerations and Application Notes

8.1 Current Limiting

Always operate the LED with a series current-limiting resistor or a constant-current driver. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet for a conservative design to ensure the current does not exceed the desired I_F. Do not exceed the Absolute Maximum Ratings for DC or pulsed current.

8.2 Thermal Management

While the package is small, power dissipation (up to 50 mW for red, 38 mfor green) generates heat. For continuous operation at or near maximum current, ensure adequate PCB copper area around the solder pads to act as a heat sink. This helps maintain lower junction temperature, which preserves luminous output and long-term reliability.

8.3 Optical Design

The side-looking (120-degree typical viewing angle) design emits light parallel to the PCB plane. This is ideal for edge-lighting light guides, illuminating side-firing icons, or status indicators viewed from the side of a device. Consider the angular intensity distribution when designing light pipes or lenses to achieve the desired illumination pattern.

8.4 Dual-Color Driving

The red and green chips are electrically independent. They can be driven separately to show red, green, or through rapid switching, an apparent amber/yellow color. For mixed-color applications, a microcontroller with PWM (Pulse Width Modulation) outputs is commonly used to control intensity and color blending.

9. Technical Comparison and Differentiation

This dual-color, side-looking SMD LED offers specific advantages in space-constrained designs:

• Space Efficiency: A single component provides two distinct colors, reducing part count and PCB footprint compared to using two separate single-color LEDs.
• Automation Friendly: The tape-and-reel packaging and standard SMD footprint are optimized for high-speed, automated assembly lines, lowering manufacturing cost.
• Material Technology: The use of AlInGaP for red offers high efficiency and good temperature stability, while InGaN for green provides bright output in the visible spectrum.
• Side Emission: Unlike top-emitting LEDs, this package directs light laterally, which is a critical feature for specific backlighting and indicator applications where vertical space or a specific viewing angle is required.

10. Frequently Asked Questions (FAQs)

Q1: What is the difference between peak wavelength and dominant wavelength?
A1: Peak wavelength (λ_P) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λ_d) is the single wavelength of monochromatic light that, when combined with a specified white reference, matches the perceived color of the LED. λ_d is more closely related to the human perception of color.

Q2: Can I drive the red and green chips simultaneously at their maximum DC current?
A2: No. The Absolute Maximum Ratings specify power dissipation limits for each chip individually (Red: 50 mW, Green: 38 mW). Driving both at max current (Red 20mA @ ~2.3V = 46 mW, Green 10mA @ ~3.5V = 35 mW) would likely exceed the package's total thermal dissipation capability if sustained, potentially leading to overheating and reduced lifetime. Derate currents or implement thermal management for dual-operation at high power.

Q3: Why is the storage humidity requirement stricter after the bag is opened?
A3: The sealed bag contains desiccant and is a moisture barrier. Once opened, the SMD package can absorb moisture from the air. During reflow soldering, this trapped moisture can rapidly expand ("popcorn effect"), causing internal delamination or cracking of the package. The MSL 3 rating dictates the "floor life" and baking requirements to prevent this.

Q4: How do I interpret the binning codes when ordering?
A4: The part number typically includes bin codes for luminous intensity and sometimes wavelength. You must specify your required brightness (e.g., Green in R1 bin for highest output) and color (e.g., Green in AP bin for a specific green hue) to ensure you receive components that meet your application's consistency requirements for brightness and color appearance.