SMD LED LTST-C230KRKT Datasheet - Reverse Mount Chip - Red Color - 20mA Forward Current - 2.4V Forward Voltage - English Technical Document

1. Product Overview

This document details the technical specifications for a high-brightness, reverse mount chip-type SMD LED. The device utilizes an advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, which is known for producing high luminous efficiency and excellent color purity, particularly in the red spectrum. The primary design feature is its reverse mount configuration, making it suitable for applications where the LED is mounted on the opposite side of the PCB relative to the light emission direction. This package is compliant with EIA standards, designed for compatibility with automated pick-and-place equipment, and is qualified for use in lead-free infrared reflow soldering processes. It is supplied on industry-standard 8mm tape mounted on 7-inch reels for high-volume manufacturing efficiency.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (Ta) of 25°C. The maximum continuous power dissipation is 75 mW. The DC forward current should not exceed 30 mA under normal operating conditions. For pulsed operation, a peak forward current of 80 mA is permissible under a strict 1/10 duty cycle with a pulse width of 0.1ms. The device can withstand a reverse voltage of up to 5 V. The operational temperature range is from -30°C to +85°C, while the storage temperature range is slightly wider, from -40°C to +85°C. The device is rated to survive infrared reflow soldering at a peak temperature of 260°C for a duration of 10 seconds, which aligns with common lead-free assembly profiles.

2.2 Electro-Optical Characteristics

The key performance parameters are measured at Ta=25°C with a forward current (IF) of 20 mA, which is the standard test condition. The luminous intensity (Iv) has a typical value of 54.0 millicandelas (mcd) with a minimum specified value of 18.0 mcd. This intensity is measured using a sensor and filter combination that approximates the photopic (CIE) human eye response curve. The device features a very wide viewing angle (2θ1/2) of 130 degrees, defined as the full angle at which the luminous intensity drops to half of its axial (on-axis) value. The peak emission wavelength (λP) is typically 639 nanometers (nm), while the dominant wavelength (λd), which perceptually defines the color, is typically 631 nm. The spectral line half-width (Δλ) is 20 nm, indicating a relatively narrow spectral bandwidth characteristic of AlInGaP technology. The forward voltage (VF) typically measures 2.4 V with a maximum of 2.4 V at 20 mA. The reverse current (IR) is limited to a maximum of 10 μA when a 5 V reverse bias is applied.

3. Binning System Explanation

To ensure consistency in brightness across production batches, the LEDs are sorted into intensity bins. The binning is based on the luminous intensity measured at 20 mA. The provided bin code list includes several categories: Bin M (18.0-28.0 mcd), Bin N (28.0-45.0 mcd), Bin P (45.0-71.0 mcd), Bin Q (71.0-112.0 mcd), and Bin R (112.0-180.0 mcd). A tolerance of +/-15% is applied to the intensity within each bin. This system allows designers to select the appropriate brightness grade for their application, ensuring visual uniformity in products using multiple LEDs.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1 for spectral distribution, Fig.5 for viewing angle pattern), their data points are not provided in the text. Typically, such curves would illustrate the relationship between forward current and luminous intensity (showing a near-linear increase until saturation), the effect of ambient temperature on luminous intensity (showing a decrease with rising temperature), and the detailed spectral power distribution peaking around 639 nm. These curves are crucial for understanding the device's behavior under non-standard operating conditions and for precise optical system design.

5. Mechanical and Package Information

The device conforms to a standard EIA package outline. Detailed package dimensions are provided in the datasheet drawings, including length, width, height, and electrode pad sizes, all specified in millimeters with a typical tolerance of ±0.10 mm. The "reverse mount" designation is critical for PCB layout; the component must be oriented correctly so that light emits through the board. The datasheet includes suggested soldering pad dimensions to ensure a reliable solder joint and proper alignment during the reflow process. Polarity is indicated by the package marking or pad design.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared reflow profile for lead-free processes is provided. Key parameters include a pre-heat zone temperature between 150°C and 200°C, a pre-heat time up to 120 seconds maximum, a peak body temperature not exceeding 260°C, and a time above 260°C limited to a maximum of 10 seconds. It is recommended that the profile adheres to JEDEC standards and is characterized for the specific PCB design, solder paste, and oven used in production.

6.2 Handling and Storage

The LED is sensitive to Electrostatic Discharge (ESD). Proper ESD precautions, such as using grounded wrist straps and anti-static workstations, are mandatory during handling. For storage, if the original moisture-proof bag with desiccant is unopened, the device should be stored at ≤30°C and ≤90% Relative Humidity (RH) and used within one year. Once the bag is opened, the storage environment should not exceed 30°C and 60% RH. Components exposed to ambient conditions for more than 672 hours (28 days, MSL 2a) should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. The use of unspecified or aggressive chemical cleaners can damage the LED package material.

7. Packaging and Ordering Information

The product is supplied in a tape-and-reel format compatible with automated assembly equipment. The tape width is 8mm. The reels have a 7-inch diameter and typically contain 3000 pieces per full reel. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies for remainder lots. The packaging follows ANSI/EIA-481 specifications. The tape is sealed with a cover tape over empty pockets, and the maximum allowable number of consecutive missing components in the tape is two.

8. Application Recommendations

8.1 Typical Application Scenarios

This reverse mount LED is ideal for backlighting applications where a thin profile is required, such as in membrane switches, front panel indicators, and LCD backlights where the LED is mounted on the rear of the PCB. Its wide viewing angle makes it suitable for area illumination or status indicators that need to be visible from a broad range of angles. The high brightness and stable red color also make it applicable in automotive interior lighting, consumer electronics status lights, and industrial equipment indicators.

8.2 Design Considerations

Drive Method: LEDs are current-driven devices. To ensure consistent brightness and color, and to prevent thermal runaway, they must be driven by a constant current source or through a current-limiting resistor. The datasheet parameters are based on 20mA; driving at different currents will affect intensity, voltage, and lifetime.
Thermal Management: Although power dissipation is low, maintaining the junction temperature within limits is crucial for long-term reliability. Ensure adequate PCB copper area or thermal vias if operating at high ambient temperatures or near maximum current.
Optical Design: The wide 130-degree viewing angle provides a diffuse light pattern. For more focused light, external lenses or light guides may be necessary. The reverse mount design requires a properly sized aperture in the PCB or front panel for light emission.

9. Technical Comparison and Differentiation

Compared to traditional through-hole LEDs or standard top-emitting SMD LEDs, this device's key differentiator is its reverse mount capability, enabling unique mechanical integration. The use of AlInGaP technology offers advantages over older GaAsP or GaP LEDs, including significantly higher luminous efficiency (more light output per unit of electrical power), better temperature stability of color and output, and superior long-term reliability. The combination of high brightness, wide viewing angle, and compatibility with automated, high-temperature reflow processes makes it a modern, cost-effective solution for mass-produced electronic assemblies.

10. Frequently Asked Questions (FAQ)

Q: What does "reverse mount" mean?
A: It means the LED is designed to be soldered onto the PCB with its light-emitting surface facing down towards the board. Light exits through an aperture in the PCB or is reflected, allowing for a very low-profile installation.

Q: Can I drive this LED directly from a 3.3V or 5V logic output?
A: Not directly without a series resistor. The typical forward voltage is 2.4V at 20mA. A current-limiting resistor must be calculated based on the supply voltage (Vsupply), the LED forward voltage (Vf), and the desired current (If): R = (Vsupply - Vf) / If. For example, with a 5V supply: R = (5V - 2.4V) / 0.020A = 130 Ohms (use nearest standard value).

Q: How do I interpret the bin code?
A: The bin code (e.g., N, P, Q) on the reel label indicates the guaranteed minimum and maximum luminous intensity range for the LEDs on that reel. Selecting a higher bin code (like Q or R) ensures brighter LEDs but may come at a higher cost.

Q: Is baking always required before soldering?
A: Baking is required if the components have been exposed to ambient conditions (outside their dry bag) for longer than the specified floor life, which is 672 hours (28 days) for MSL 2a. This prevents moisture-induced package cracking during the high-temperature reflow soldering process.

11. Practical Design and Usage Case

Case: Designing a Low-Profile Status Indicator Panel
A designer is creating a control panel with multiple status indicators. Space behind the front panel is extremely limited. By using the reverse mount LED, they can place the LEDs on the backside of the main control PCB. The PCB has precisely drilled holes at each indicator location. When assembled, the LED light shines up through these holes, illuminating translucent icons on the front panel. This eliminates the need for separate LED holders or light pipes, reducing part count, assembly time, and overall thickness of the product. The designer uses a constant current driver IC to power all LEDs, ensuring uniform brightness regardless of slight forward voltage variations. They specify Bin P or Q LEDs to guarantee sufficient brightness even when diffused through the panel icon.

12. Technology Principle Introduction

The LED is based on AlInGaP semiconductor material grown on a substrate. When a forward voltage is applied across the P-N junction, electrons and holes are injected into the active region where they recombine. This recombination process releases energy in the form of photons (light). The specific composition of the Aluminum, Indium, Gallium, and Phosphide atoms in the crystal lattice determines the bandgap energy, which directly dictates the wavelength (color) of the emitted light—in this case, red around 631-639 nm. The chip is then encapsulated in a plastic package that serves to protect the semiconductor die, provide mechanical stability, and often includes a lens to shape the light output pattern, resulting in the wide 130-degree viewing angle.

13. Technology Development Trends

The general trend in LED technology is toward higher efficiency (more lumens per watt), increased power density, improved color rendering, and greater reliability. For indicator-type LEDs like this one, miniaturization continues while maintaining or increasing light output. There is also a strong focus on broadening the range of available colors and improving color consistency (tighter binning). Packaging technology advances aim for better thermal performance to support higher drive currents and for enhanced compatibility with harsh environmental conditions and demanding assembly processes like double-sided reflow soldering.