Reverse Mount Chip LED LTST-C21KFKT Datasheet - Orange - 20mA - 2.4V - English Technical Document

1. Product Overview

This document details the specifications for a high-brightness, reverse-mount chip LED utilizing an AlInGaP semiconductor material, emitting orange light. Designed for surface-mount technology (SMT), it is packaged in 8mm tape on 7-inch diameter reels, making it compatible with automated pick-and-place assembly systems. The device is compliant with RoHS directives and is classified as a green product.

1.1 Core Advantages

• High Brightness: Features an ultra-bright AlInGaP chip, offering superior luminous intensity.
• Reverse Mount Design: The package is specifically designed for mounting where the light-emitting surface faces the PCB, enabling unique design applications.
• Automation Friendly: EIA standard package ensures compatibility with automatic placement equipment.
• Robust Soldering: Compatible with both infrared (IR) and vapor phase reflow soldering processes.
• IC Compatibility: Can be driven directly by integrated circuit outputs with appropriate current limiting.

1.2 Target Applications

This LED is suitable for a wide range of applications requiring a compact, bright orange indicator. Typical uses include status indicators on consumer electronics, backlighting for switches and panels, automotive interior lighting, and various instrumentation displays. Its reverse-mount capability is particularly useful for applications where the LED is mounted on the opposite side of the PCB from the viewing direction.

2. Technical Parameter Analysis

2.1 Absolute Maximum Ratings

Stresses beyond these limits may cause permanent damage to the device. All values are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 75 mW
• Peak Forward Current (I_F(peak)): 80 mA (at 1/10 duty cycle, 0.1ms pulse width)
• Continuous Forward Current (I_F): 30 mA DC
• Current Derating: Linear derating from 50°C at a rate of 0.4 mA/°C.
• Reverse Voltage (V_R): 5 V
• Operating Temperature Range (T_opr): -55°C to +85°C
• Storage Temperature Range (T_stg): -55°C to +85°C
• Soldering Temperature: Withstands 260°C for 5 seconds (IR/Wave) or 215°C for 3 minutes (Vapor Phase).

2.2 Electro-Optical Characteristics

Typical performance parameters measured at Ta=25°C and a forward current (I_F) of 20mA, unless otherwise noted.

• Luminous Intensity (I_V): 180 mcd (Typical). Measured with a sensor/filter approximating the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 70 degrees. Defined as the full angle where intensity drops to half its axial value.
• Peak Wavelength (λ_P): 611 nm (Typical). The point of maximum spectral power.
• Dominant Wavelength (λ_d): 605 nm (Typical). The single wavelength describing the perceived color, derived from the CIE chromaticity diagram.
• Spectral Bandwidth (Δλ): 17 nm (Typical). The full width at half maximum (FWHM) of the emission spectrum.
• Forward Voltage (V_F): 2.4 V (Typical), with a maximum of 2.4V at I_F=20mA.
• Reverse Current (I_R): 10 µA (Maximum) at V_R=5V.
• Capacitance (C): 40 pF (Typical) measured at V_F=0V, f=1MHz.

3. Binning System Explanation

The luminous intensity of the LEDs is sorted into bins to ensure consistency within a production lot. The bin code is part of the full part number selection.

3.1 Luminous Intensity Binning

Intensity is measured at the standard test condition of I_F = 20mA. The tolerance within each bin is +/-15%.

• Bin Q: 71.0 mcd (Min) to 112.0 mcd (Max)
• Bin R: 112.0 mcd (Min) to 180.0 mcd (Max)
• Bin S: 180.0 mcd (Min) to 280.0 mcd (Max)
• Bin T: 280.0 mcd (Min) to 450.0 mcd (Max)

This binning allows designers to select the appropriate brightness grade for their application, balancing cost and performance.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), the following analysis is based on the provided tabular data and standard LED physics.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The typical forward voltage of 2.4V at 20mA indicates this is a standard AlInGaP LED. The I-V relationship is exponential, characteristic of a semiconductor diode. Operating significantly above the recommended current will cause a rapid increase in junction temperature and accelerated degradation.

4.2 Temperature Dependence

The specified current derating of 0.4 mA/°C above 50°C is critical for reliability. As junction temperature increases, the maximum allowable continuous current decreases linearly to prevent thermal runaway. The luminous intensity and forward voltage will also decrease with increasing temperature, which is typical for LEDs.

4.3 Spectral Characteristics

With a peak wavelength of 611 nm and a dominant wavelength of 605 nm, the LED emits in the orange region of the visible spectrum. The relatively narrow spectral bandwidth of 17 nm results in a saturated, pure orange color. The difference between peak and dominant wavelength is due to the shape of the human eye's photopic response curve.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity

The LED conforms to an EIA standard chip LED footprint. Detailed dimensioned drawings are provided in the datasheet for the component itself. The reverse-mount design means the primary light-emitting surface is intended to be mounted facing the printed circuit board. Polarity is indicated by the package marking or internal die structure; correct orientation is essential for operation.

5.2 Recommended Solder Pad Layout

A suggested land pattern (solder pad geometry) is provided to ensure reliable solder joint formation during reflow. Adhering to these recommendations helps prevent tombstoning (component standing on end) and ensures proper alignment and thermal relief.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles: one for standard SnPb solder and one for Pb-free (e.g., SnAgCu) solder processes.

• Pb-Free Process: Requires a higher peak temperature, typically up to 260°C, sustained for a maximum of 5 seconds. The time above liquidus (TAL) and ramp rates are critical to avoid thermal shock.
• Precautions: The component must not be subjected to wave or hand soldering after the initial reflow process, as the plastic package may not withstand a second high-temperature exposure.

6.2 Storage and Handling

• Storage Conditions: Recommended storage is below 30°C and 70% relative humidity. Components removed from their moisture-barrier bag should be used within one week.
• Baking: If exposed to ambient conditions for more than a week, a bake at 60°C for 24 hours is recommended before soldering to remove absorbed moisture and prevent "popcorning" during reflow.
• Cleaning: If post-solder cleaning is necessary, only use specified solvents like isopropyl alcohol or ethyl alcohol at room temperature for less than one minute. Harsh or unspecified chemicals can damage the plastic lens and package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape, sealed with cover tape, and wound on 7-inch (178mm) diameter reels.

• Pocket Pitch: 8mm.
• Quantity per Reel: 3000 pieces (standard full reel).
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Packaging Standard: Complies with ANSI/EIA-481-1-A.
• Missing Components: A maximum of two consecutive empty pockets is allowed per specification.

8. Application Notes and Design Considerations

8.1 Drive Circuit Design

LEDs are current-driven devices. For stable and uniform operation:

• Constant Current Drive: The recommended method is to use a series current-limiting resistor for each LED, as shown in "Circuit A" in the datasheet. This compensates for the natural variation in forward voltage (V_F) from one LED to another.
• Avoid Direct Parallel Connection: Connecting multiple LEDs directly in parallel ("Circuit B") is not recommended. The LED with the lowest V_F will draw more current, potentially over-stressing it while leaving the others dimmer, leading to uneven brightness and reduced reliability.
• Current Calculation: The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Using the typical V_F of 2.4V and a desired I_F of 20mA with a 5V supply gives R = (5 - 2.4) / 0.02 = 130 Ω. The resistor power rating should be I_F² * R.

8.2 Electrostatic Discharge (ESD) Protection

This LED is susceptible to damage from electrostatic discharge. Mandatory precautions include:

• Operators must wear grounded wrist straps or anti-static gloves.
• All workstations, tools, and equipment must be properly grounded.
• Use ionizers to neutralize static charge that can build up on the plastic lens during handling.
• ESD-damaged LEDs may exhibit high leakage current, reduced light output, or complete failure.

8.3 Thermal Management

Although a small device, power dissipation (up to 75mW) must be considered. Ensure the PCB provides adequate thermal relief, especially if operating near the maximum current or in high ambient temperatures. The copper pads and traces act as a heat sink. The derating curve must be followed for applications above 50°C ambient.

9. Technical Comparison and Differentiation

Compared to standard top-emitting chip LEDs, this reverse-mount variant offers a key mechanical advantage for specific PCB layouts where the indicator needs to be viewed from the side opposite the component placement. The use of AlInGaP technology provides higher efficiency and brighter orange/red emission compared to older technologies like GaAsP, resulting in better visibility at lower currents.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive this LED without a current-limiting resistor?

No. Connecting an LED directly to a voltage source is a common cause of immediate failure. The forward voltage is not a fixed threshold but a characteristic of the current flowing through it. Without a resistor to limit current, the LED will draw excessive current, leading to rapid overheating and destruction.

10.2 Why is there a difference between Peak and Dominant Wavelength?

Peak wavelength (λ_P) is the physical point of maximum energy output from the LED chip. Dominant wavelength (λ_d) is a calculated value based on how the human eye perceives the color of that spectrum. It represents the single wavelength of a pure spectral color that would appear to have the same hue. For orange/red LEDs, the dominant wavelength is often slightly shorter than the peak wavelength due to the eye's sensitivity curve.

10.3 What does "Reverse Mount" mean for PCB design?

It means the LED is mounted with its primary light-emitting surface facing downwards towards the PCB. The light exits through the substrate or is reflected. This requires a corresponding aperture or light pipe in the PCB or enclosure to allow the light to be seen from the opposite side. The solder pads and footprint are standard, but the optical path must be designed accordingly.

11. Practical Application Example

11.1 Front Panel Status Indicator with PCB-Back Mounting

Consider a consumer audio amplifier with a brushed aluminum front panel. Designers want a small, discreet orange power indicator. Instead of mounting an LED on the front of the control PCB behind a hole in the panel, they can use this reverse-mount LED. The LED is soldered onto the back of the control PCB. A small, precisely drilled hole in the PCB allows the light from the reverse-mounted LED to pass through. The front panel has a corresponding tiny aperture or uses a translucent insignia. This creates a sleek, flush indicator with no visible component protrusion, simplifying assembly and improving aesthetics.

12. Operating Principle

This LED is based on Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology. When a forward voltage exceeding the diode's junction potential is applied, electrons and holes are injected into the active region from the n-type and p-type materials, respectively. These charge carriers recombine radiatively, releasing energy in the form of photons. The specific composition of the AlInGaP alloy determines the bandgap energy, which directly corresponds to the wavelength (color) of the emitted light—in this case, orange (~605-611 nm). The chip is encapsulated in a water-clear epoxy lens that protects the semiconductor die and shapes the light output beam (70-degree viewing angle).

13. Technology Trends

The general trend in indicator LEDs is towards higher efficiency (more lumens per watt), which allows for equivalent brightness at lower drive currents, reducing power consumption and thermal load. There is also a move towards tighter binning tolerances for both color and intensity to ensure consistency in applications using multiple LEDs, such as full-color displays or backlighting arrays. Packaging continues to evolve for better thermal performance and compatibility with lead-free, high-temperature soldering processes. Reverse-mount and side-view packages are becoming more common as electronic devices become thinner and industrial design demands more integrated lighting solutions.