SMD LED LTST-C21TBKT Datasheet - Blue - 20mA - 3.8V - English Technical Document

1. Product Overview

This document details the specifications for a surface-mount device (SMD) Chip LED designed for reverse mounting applications. The component is a blue light-emitting diode utilizing InGaN (Indium Gallium Nitride) technology, encapsulated in a water-clear lens package. It is engineered for compatibility with automated assembly processes, including pick-and-place equipment, and is suitable for standard infrared (IR) and vapor phase reflow soldering. The product adheres to environmental standards, being RoHS compliant and classified as a green product.

The primary application of this LED is in electronic equipment where space-saving and efficient assembly are critical. Its reverse-mount design allows for innovative PCB layouts and lighting solutions. The device is supplied in industry-standard 8mm tape on 7-inch diameter reels, facilitating high-volume manufacturing.

2. Absolute Maximum Ratings

The following table lists the stress limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation: 76 mW
• Peak Forward Current: 100 mA (at 1/10 duty cycle, 0.1ms pulse width)
• Continuous DC Forward Current (IF): 20 mA
• Current Derating: Linear reduction from 25°C at a rate of 0.25 mA/°C
• Reverse Voltage (VR): 5 V (Note: Continuous operation at reverse voltage is not permitted)
• Operating Temperature Range: -55°C to +85°C
• Storage Temperature Range: -55°C to +85°C
• Soldering Temperature Tolerance:
  • Wave Soldering: 260°C for 5 seconds max.
  • Infrared (IR) Reflow: 260°C for 5 seconds max.
  • Vapor Phase Reflow: 215°C for 3 minutes max.

Exceeding these limits, especially the reverse voltage and current ratings, can lead to immediate or latent device failure. The derating curve for forward current is crucial for designs operating at elevated ambient temperatures to ensure long-term reliability.

3. Electrical & Optical Characteristics

The typical performance parameters are measured at Ta=25°C under the specified test conditions. These values define the expected operational behavior of the LED.

3.1 Optical Parameters

• Luminous Intensity (Iv): 45.0 - 280.0 mcd (min - max) at IF = 20 mA. Measured with a sensor/filter approximating the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 70 degrees (typical). Defined as the full angle at which intensity is half the peak axial intensity.
• Peak Emission Wavelength (λ_P): 468 nm (typical). The wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λ_d): 465.0 - 475.0 nm at IF = 20 mA. The single wavelength perceived by the human eye that defines the color, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 25 nm (typical). The spectral width measured at half the maximum intensity (FWHM).

3.2 Electrical Parameters

• Forward Voltage (V_F): 3.0 - 3.8 V (typical - max) at IF = 20 mA.
• Reverse Current (I_R): 100 µA (max) at V_R = 5V.
• Capacitance (C): 40 pF (typical) at V_F=0V, f=1 MHz.

The forward voltage range is important for driver circuit design, especially when multiple LEDs are connected in parallel, to ensure current sharing and uniform brightness.

4. Binning System

To manage production variations, LEDs are sorted into bins based on key performance parameters. This allows designers to select components that meet specific brightness and color consistency requirements for their application.

4.1 Luminous Intensity Binning

Binned at IF = 20 mA. Tolerance within each bin is +/-15%.

• Code P: 45.0 - 71.0 mcd
• Code Q: 71.0 - 112.0 mcd
• Code R: 112.0 - 180.0 mcd
• Code S: 180.0 - 280.0 mcd

4.2 Dominant Wavelength Binning

Binned at IF = 20 mA. Tolerance for each bin is +/- 1 nm.

• Code AC: 465.0 - 470.0 nm
• Code AD: 470.0 - 475.0 nm

Selecting LEDs from a single bin or adjacent bins is critical for applications requiring uniform color and brightness across multiple units, such as in backlighting arrays or status indicator panels.

5. Soldering & Assembly Guidelines

Proper handling and soldering are essential to prevent damage and ensure reliability.

5.1 Reflow Soldering Profiles

The datasheet provides suggested temperature profiles for both standard and lead-free (Pb-free) solder processes. Key parameters include:

• Pre-heat Zone: Gradual ramp to prevent thermal shock.
• Soak Zone: Allows for temperature stabilization across the PCB.
• Reflow Zone: Peak temperature must not exceed 260°C, and the time above 240°C (for Pb-free) should be controlled as per the profile.
• Cooling Zone: Controlled ramp-down to solidify solder joints properly.

For Pb-free processes, it is explicitly noted that SnAgCu solder paste must be used.

5.2 Cleaning

Unspecified chemical cleaners can damage the LED package. If cleaning is necessary post-soldering, it is recommended to:

• Immerse the LED in ethyl alcohol or isopropyl alcohol at normal room temperature.
• Limit immersion time to less than one minute.
• Avoid ultrasonic cleaning unless specifically validated, as it may cause mechanical stress.

5.3 Storage & Handling

• Store in an environment not exceeding 30°C and 70% relative humidity.
• LEDs removed from their original moisture-barrier packaging should be reflow-soldered within one week.
• For longer storage outside the original pack, use a sealed container with desiccant or a nitrogen desiccator.
• Components stored out of bag for more than a week require baking at approximately 60°C for at least 24 hours before assembly to remove absorbed moisture and prevent "popcorning" during reflow.

6. Mechanical & Packaging Information

6.1 Package Dimensions & Polarity

The LED is housed in a standard EIA package. The detailed mechanical drawing (implied in the datasheet) would show key dimensions including length, width, height, and the cathode/anode pad identification. The "reverse mount" feature typically implies a specific pad layout or lens orientation designed for mounting on the opposite side of the PCB relative to standard LEDs. The suggested soldering pad layout is provided to ensure proper solder joint formation and mechanical stability.

6.2 Tape and Reel Specifications

The component is supplied in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels.

• Pieces per Reel: 3000
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Cover Tape: Empty component pockets are sealed with top cover tape.
• Missing Components: A maximum of two consecutive missing LEDs is allowed per reel specification.
• The packaging conforms to ANSI/EIA-481-1-A-1994 standards for handling and shipping.

7. Application Notes & Design Considerations

7.1 Drive Circuit Design

LEDs are current-operated devices. Their brightness is primarily a function of forward current (IF), not voltage.

• Recommended Circuit (Model A): A current-limiting resistor should be placed in series with each LED, even when multiple LEDs are connected in parallel to a voltage source. This resistor (R_limit) is calculated using Ohm's Law: R_limit = (V_supply - V_F) / I_F. This ensures consistent current through each LED, compensating for natural variations in forward voltage (V_F) from device to device, which leads to uniform brightness.
• Non-Recommended Circuit (Model B): Directly connecting multiple LEDs in parallel without individual series resistors is discouraged. Small differences in the I-V characteristics of each LED can cause significant current imbalance, where one LED may draw much more current than others, leading to uneven brightness and potential overstress of the highest-current device.

7.2 Electrostatic Discharge (ESD) Protection

This LED is susceptible to damage from electrostatic discharge. Precautions must be taken during handling and assembly:

• Operators must wear grounded wrist straps or anti-static gloves.
• All workstations, tools, and machinery must be properly grounded.
• Use ionizers to neutralize static charge that may accumulate on the plastic lens due to friction during handling.
• Store and transport LEDs in conductive or anti-static containers.

7.3 Thermal Management

While the power dissipation is relatively low (76 mW max), effective thermal management is still important for longevity, especially at high ambient temperatures or high drive currents. The derating specification of 0.25 mA/°C above 25°C must be factored into the design. Ensuring adequate copper area around the LED pads on the PCB helps dissipate heat and maintain lower junction temperature, which preserves luminous output and extends operational life.

8. Typical Performance Curves Analysis

The datasheet references typical characteristic curves (e.g., relative luminous intensity vs. forward current, forward voltage vs. temperature, spectral distribution). While the specific graphs are not rendered in the provided text, their implications are standard:

• I_V vs. I_F Curve: Shows that luminous intensity increases with forward current but may become sub-linear at higher currents due to efficiency droop and increased heat.
• V_F vs. Temperature Curve: Demonstrates that the forward voltage has a negative temperature coefficient (decreases as junction temperature increases). This is a critical factor for constant-current drivers.
• Spectral Distribution Curve: Illustrates the narrow emission band centered around the peak wavelength (468 nm), which is characteristic of InGaN blue LEDs.

9. Reliability & Application Scope

The device is intended for use in ordinary electronic equipment such as office automation devices, communication equipment, and household appliances. For applications requiring exceptional reliability where failure could risk life or health (e.g., aviation, medical devices, critical safety systems), a specific technical consultation with the component manufacturer is mandatory prior to design-in. The specified operating and storage temperature ranges (-55°C to +85°C) indicate robustness suitable for a wide array of commercial and industrial environments.

10. Technical Comparison & Trends

Reverse Mount Advantage: This design allows the LED to be mounted on the opposite side of the PCB from the viewer, with light emitted through a hole or aperture in the board. This enables sleek, flat-panel designs where the light source is hidden, providing only the emitted light without visible components. It contrasts with traditional top-mount LEDs where the package is visible on the surface.

InGaN Technology: The use of Indium Gallium Nitride semiconductor material is standard for high-efficiency blue (and green) LEDs. It offers good luminous efficacy and stability. The evolution in this field focuses on increasing efficiency (lumens per watt), improving color consistency (tighter binning), and enhancing reliability under high-temperature and high-current operating conditions, often driven by demands from general lighting and automotive applications.

11. Frequently Asked Questions (FAQ)

Q1: Can I drive this LED at 30 mA for higher brightness?

A1: No. The absolute maximum continuous DC forward current is 20 mA. Exceeding this rating will reduce lifespan and may cause immediate failure. For higher brightness, select an LED bin with higher luminous intensity or a different LED model rated for higher current.

Q2: What is the difference between peak wavelength and dominant wavelength?

A2: Peak wavelength (λ_P) is the physical wavelength where the LED emits the most optical power. Dominant wavelength (λ_d) is a calculated value based on human color perception (CIE chart) that defines the perceived color. For monochromatic LEDs like this blue one, they are typically close, but λ_d is the relevant parameter for color matching.

Q3: Why is a series resistor necessary for each parallel LED?

A3: Due to manufacturing tolerances, the forward voltage (V_F) of LEDs varies slightly. Without a series resistor to limit current, LEDs with a lower V_F will draw disproportionately more current in a parallel configuration, leading to brightness mismatch and potential overcurrent failure. The resistor acts as a simple, stabilizing ballast.

Q4: How do I interpret the bin codes when ordering?

A4: You must specify both the Intensity Bin Code (e.g., "S" for highest brightness) and the Wavelength Bin Code (e.g., "AC" for 465-470 nm). A full order code would specify something like LTST-C21TBKT-S-AC to get devices from those specific bins, ensuring brightness and color consistency in your production run.