LTST-C235KGKRKT Dual-Color SMD LED Datasheet - Reverse Mount - Green/Red - 20mA - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a dual-color, reverse mount, surface-mount device (SMD) LED. The component integrates two distinct AlInGaP semiconductor chips within a single package, emitting green and red light. It is designed for automated assembly processes and is compliant with RoHS environmental standards.

The primary application of this LED is in backlighting, status indicators, and decorative lighting where space is constrained and a dual-color indication is required from a single component footprint. Its reverse mount configuration allows for light emission through the PCB, enabling innovative and space-saving design solutions.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device must not be operated beyond these limits to prevent permanent damage.

• Power Dissipation (Pd): 75 mW per color (Green/Red). This defines the maximum power the LED can dissipate as heat.
• Peak Forward Current (I_FP): 80 mA (pulsed, 1/10 duty cycle, 0.1ms pulse width). For brief current surges.
• Continuous Forward Current (I_F): 30 mA DC. The standard operating current for reliable long-term performance.
• Reverse Voltage (V_R): 5 V. Exceeding this can cause junction breakdown.
• Operating Temperature (T_opr): -30°C to +85°C. The ambient temperature range for normal operation.
• Storage Temperature (T_stg): -40°C to +85°C.
• Soldering Temperature: Withstands 260°C for 10 seconds, compatible with lead-free (Pb-free) reflow processes.

2.2 Electro-Optical Characteristics @ T_a=25°C, I_F=20mA

These parameters define the performance under typical operating conditions.

• Luminous Intensity (I_V):
  • Green: Typical 35.0 mcd (Min. 18.0 mcd)
  • Red: Typical 45.0 mcd (Min. 18.0 mcd)
  • Measured using a sensor filtered to the CIE photopic eye response curve.
• Viewing Angle (2θ_1/2): 130 degrees (typical for both colors). This wide angle provides a broad emission pattern suitable for area illumination.
• Peak Wavelength (λ_P):
  • Green: 574 nm (typical)
  • Red: 639 nm (typical)
• Dominant Wavelength (λ_d):
  • Green: 571 nm (typical)
  • Red: 631 nm (typical)
  • This is the single wavelength perceived by the human eye, derived from the CIE chromaticity diagram.
• Spectral Bandwidth (Δλ):
  • Green: 15 nm (typical)
  • Red: 20 nm (typical)
• Forward Voltage (V_F):
  • Typical: 2.0 V for both colors.
  • Maximum: 2.4 V for both colors.
  • A low V_F contributes to higher efficiency.
• Reverse Current (I_R): Maximum 10 µA at V_R=5V.

ESD Caution: The LED is sensitive to electrostatic discharge (ESD). Proper handling with grounded wrist straps, anti-static mats, and equipment is mandatory to prevent latent or catastrophic failure.

3. Binning System Explanation

The LEDs are sorted (binned) based on key optical parameters to ensure consistency within a production batch.

3.1 Luminous Intensity Binning

Bins are defined by minimum and maximum luminous intensity values at 20mA. Tolerance within each bin is +/-15%.

• Code M: 18.0 – 28.0 mcd
• Code N: 28.0 – 45.0 mcd
• Code P: 45.0 – 71.0 mcd
• Code Q: 71.0 – 112.0 mcd

This applies separately to both the Green and Red chips.

3.2 Dominant Wavelength Binning (Green only in this datasheet)

For the green emitter, bins ensure color consistency. Tolerance is +/-1 nm.

• Code C: 567.5 – 570.5 nm
• Code D: 570.5 – 573.5 nm
• Code E: 573.5 – 576.5 nm

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (e.g., Fig.1, Fig.6), their implications are critical for design.

• Relative Luminous Intensity vs. Forward Current: The light output is approximately linear with current up to the maximum rated DC current. Driving above I_F increases output but reduces efficiency and lifespan due to heat.
• Forward Voltage vs. Forward Current: Exhibits the standard diode exponential relationship. The typical V_F of 2.0V at 20mA is a key parameter for driver design (e.g., current-limiting resistor calculation).
• Relative Luminous Intensity vs. Ambient Temperature: For AlInGaP LEDs, light output typically decreases as temperature increases. This derating must be considered for applications operating at high ambient temperatures.
• Spectral Distribution: The graphs show the narrow emission peaks characteristic of AlInGaP technology, centered around 574nm (green) and 639nm (red). The 15-20nm bandwidth indicates good color purity.
• Viewing Angle Pattern: The 130-degree viewing angle with a near-Lambertian distribution ensures uniform brightness over a wide area when viewed off-axis.

5. Mechanical & Packaging Information

5.1 Package Dimensions & Pin Assignment

The LED conforms to an industry-standard SMD package outline (EIA standard). Key dimensional tolerances are ±0.10mm.

• Pin Assignment:
  • Pins 1 & 2: Anode/Cathode for the Green chip.
  • Pins 3 & 4: Anode/Cathode for the Red chip.
• Lens: Water Clear. This provides the widest possible viewing angle and does not tint the emitted light.

5.2 Recommended Solder Pad Layout

A land pattern diagram is provided to ensure proper solder joint formation, reliable electrical connection, and mechanical stability during reflow. Adhering to this pattern prevents tombstoning and ensures correct alignment.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared (IR) reflow profile is provided, compliant with JEDEC standards for lead-free assembly.

• Preheat: 150-200°C for up to 120 seconds to slowly ramp temperature and activate flux.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: The profile ensures the solder paste is molten for the correct duration to form reliable joints without thermal damage to the LED package. The component can withstand 260°C for 10 seconds.

Note: The optimal profile depends on the specific PCB design, solder paste, and oven. Board-level characterization is recommended.

6.2 Hand Soldering

If necessary, hand soldering is possible with strict limits:

• Iron Temperature: Max 300°C.
• Contact Time: Max 3 seconds per joint.
• Attempts: One time only. Repeated heating can damage the package or wire bonds.

6.3 Cleaning

Only specified cleaners should be used:

• Recommended: Ethyl alcohol or isopropyl alcohol at room temperature.
• Immersion Time: Less than one minute.
• Avoid: Unspecified chemical solvents which may damage the epoxy lens or package.

6.4 Storage & Handling

• Sealed Bag (with desiccant): Store at ≤30°C and ≤90% RH. Use within one year of bag opening.
• After Bag Opening: Store at ≤30°C and ≤60% RH. For best results, complete IR reflow within one week.
• Extended Storage (Opened): Store in a sealed container with desiccant or in a nitrogen desiccator.
• Baking: If stored out of the original bag for more than a week, bake at 60°C for at least 20 hours before soldering to remove moisture and prevent "popcorning" during reflow.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The device is supplied for automated pick-and-place assembly.

• Carrier Tape Width: 8 mm.
• Reel Diameter: 7 inches.
• Quantity per Reel: 3000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Pocket Sealing: Top cover tape seals empty pockets.
• Missing Lamps: Maximum of two consecutive missing components allowed, per industry standards (ANSI/EIA 481-1-A-1994).

8. Application Suggestions

8.1 Typical Application Scenarios

• Consumer Electronics: Dual-status indicators on routers, chargers, or audio equipment (e.g., green for power/ready, red for charging/error).
• Automotive Interior Lighting: Low-power accent or indicator lighting, leveraging the wide viewing angle.
• Industrial Control Panels: Multi-state machine status indicators.
• Portable Devices: Space-constrained devices requiring two-color feedback.
• Reverse-Mount Applications: Backlighting panels or logos where the LED is mounted on the opposite side of the PCB, with light piped through a hole or translucent material.

8.2 Design Considerations

• Current Driving: Always use a constant current driver or a current-limiting resistor in series with each LED chip. Calculate resistor value using R = (V_supply - V_F) / I_F.
• Thermal Management: While power dissipation is low, ensure the PCB provides adequate thermal relief, especially if driving at or near the maximum current, to maintain LED lifetime and color stability.
• ESD Protection: Incorporate ESD protection diodes on signal lines connected to the LED anodes if they are exposed to user interfaces.
• Mixing Colors: By controlling the current to each chip independently, intermediate colors (e.g., yellow, orange) can be created through additive color mixing.

9. Technical Comparison & Differentiation

This device offers specific advantages in its niche:

• vs. Single-Color LEDs: Reduces component count, PCB footprint, and assembly cost by providing two colors in one package.
• vs. RGB LEDs: Offers a simpler, often more cost-effective solution when only green and red are required, without the complexity of a blue chip and phosphor or three separate drivers.
• Reverse Mount Capability: A key differentiator enabling unique optical designs not possible with standard top-emitting LEDs.
• AlInGaP Technology: Provides high efficiency and excellent color purity (narrow spectrum) for green and red, compared to older technologies.
• Wide Viewing Angle (130°): Offers better off-axis visibility than LEDs with narrower viewing angles, ideal for panel indicators.

10. Frequently Asked Questions (FAQ)

Q1: Can I drive both the green and red chips simultaneously at 30mA each?
A1: No. The absolute maximum power dissipation is 75 mW per chip. At 30mA and a typical V_F of 2.0V, power per chip is 60 mW (P=IV). Driving both simultaneously at full current results in 120 mW total dissipation, which may exceed the package's ability to shed heat, especially at high ambient temperatures. Derating or pulsed operation is advised for dual-color simultaneous use.

Q2: What is the difference between peak wavelength and dominant wavelength?
A2: Peak wavelength (λ_P) is the physical wavelength at which the spectral power output is highest. Dominant wavelength (λ_d) is a calculated value from the CIE color chart that represents the single perceived color of the light. For monochromatic LEDs like these, they are very close, but λ_d is more relevant for color specification.

Q3: How do I interpret the bin codes when ordering?
A3: Specify the required bin codes for luminous intensity (e.g., Code N) and dominant wavelength (e.g., Code D for green) to ensure you receive LEDs with consistent brightness and color. If not specified, you may receive any bin within the product's range.

Q4: Is a heat sink required?
A4: For continuous operation at the maximum DC current (30mA) in a high ambient temperature environment, thermal management via the PCB (copper pours, thermal vias) is important. A separate heat sink is typically not required for this low-power SMD device if the PCB is designed appropriately.

11. Design-in Case Study

Scenario: Designing a compact IoT sensor node with a multi-status indicator.
Challenge: Limited PCB space, need for clear "Power/Network/Error" states.
Solution: Use the dual-color LED.
Implementation:

• Green Only (20mA): Device powered on and operating normally.
• Red Only (20mA): Error condition (e.g., sensor fault).
• Green & Red Simultaneously (e.g., 10mA each to stay within thermal limits): Network activity/blinking pattern.

This single component provides three distinct visual states, saving space and simplifying the bill of materials compared to using two separate LEDs.

12. Technology Principle Introduction

This LED utilizes Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material for both light-emitting chips. AlInGaP is a direct bandgap semiconductor where electron-hole recombination releases energy in the form of photons (light). The specific wavelength of light (color) is determined by the bandgap energy of the material, which is engineered by precisely controlling the ratios of Aluminum, Indium, Gallium, and Phosphorus during crystal growth. The green chip has a wider bandgap (~2.16 eV for 574nm) than the red chip (~1.94 eV for 639nm). The chips are wire-bonded inside a reflective epoxy package with a clear lens that shapes the light output. The reverse mount design means the primary light-emitting surface of the chip is oriented towards the PCB, requiring a via or aperture in the board for the light to escape.

13. Technology Trends

The development of SMD LEDs like this one follows several industry trends:

• Miniaturization & Integration: Combining multiple functions (two colors) into a single package saves board space, a constant driver in electronics.
• Higher Efficiency: Ongoing improvements in AlInGaP epitaxial growth and chip design lead to higher luminous efficacy (more light output per electrical watt).
• Robustness for Automation: Packages are designed to withstand higher reflow temperatures (for Pb-free soldering) and the mechanical stresses of tape-and-reel handling and placement.
• Expanded Color Gamut: While this LED uses discrete green and red, there is a trend towards multi-chip packages (RGB, RGBW) and advanced phosphor-converted LEDs to achieve a wider range of colors and higher color rendering indices for lighting applications.
• Improved Thermal Performance: New package materials and designs better manage heat, allowing for higher drive currents and greater light output from a small footprint.