SMD LED LTW-C171DC-KO Datasheet - White InGaN Chip, Yellow Lens - 30mA, 108mW - English Technical Document

1. Product Overview

The LTW-C171DC-KO is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It is part of a family of miniature LEDs intended for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages and Target Market

This LED offers several key advantages that make it suitable for modern electronics manufacturing. Its primary features include compliance with RoHS (Restriction of Hazardous Substances) directives, ensuring it meets international environmental standards. The device utilizes an ultra-bright InGaN (Indium Gallium Nitride) white chip, which is known for its high efficiency and good color rendering properties. The package is supplied in 8mm tape on 7-inch diameter reels, conforming to EIA (Electronic Industries Alliance) standards, facilitating compatibility with high-speed automated pick-and-place equipment commonly used in volume production. Furthermore, the component is designed to be compatible with infrared (IR) reflow soldering processes, which is the standard for assembling SMD components onto PCBs.

The target applications for this LED are diverse, reflecting its versatility. It is well-suited for telecommunication devices, office automation equipment, home appliances, and various types of industrial equipment. Specific use cases include backlighting for keypads and keyboards, serving as status indicators, integration into microdisplays, and use in signal or symbolic luminary applications where a clear, bright point of light is required.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the electrical, optical, and thermal characteristics specified for the LTW-C171DC-KO LED.

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the limits beyond which permanent damage to the device may occur. These ratings are specified at an ambient temperature (Ta) of 25°C. The maximum power dissipation is 108 milliwatts (mW). The DC forward current should not exceed 30 mA under continuous operation. For pulsed operation, a peak forward current of 100 mA is permissible, but only under specific conditions: a duty cycle of 1/10 and a pulse width of 0.1 milliseconds. Exceeding these current limits can lead to rapid degradation of the LED's internal structure and a significant reduction in its operational lifespan.

The device has an operating temperature range of -20°C to +80°C. This defines the ambient temperature conditions under which the LED is guaranteed to function correctly. The storage temperature range is wider, from -40°C to +85°C, indicating the conditions for non-operational periods. A critical rating for assembly is the infrared soldering condition, which is specified as withstanding 260°C for a maximum of 10 seconds. This parameter is crucial for ensuring the LED survives the reflow soldering process without damage.

2.2 Electrical and Optical Characteristics

The typical operating characteristics are measured at Ta=25°C and a forward current (IF) of 20 mA, which is the standard test condition. The luminous intensity (Iv) for this product has a wide range, from a minimum of 710.0 millicandelas (mcd) to a maximum of 1800.0 mcd. The specific value for a given unit depends on its bin rank (see Section 3). The viewing angle (2θ1/2) is 130 degrees, which is a very wide angle. This means the LED emits light over a broad cone, making it suitable for applications requiring wide-area illumination rather than a focused beam.

The forward voltage (VF) typically ranges from 2.80 volts to 3.40 volts at 20mA. The chromaticity coordinates, which define the color point of the white light in the CIE 1931 color space, are given as x=0.2646 and y=0.2480 under typical conditions. It is important to note the tester specified for these measurements is a CAS140B, and a tolerance of ±0.01 should be applied to the chromaticity coordinates. The reverse current (IR) is specified as a maximum of 10 microamperes at a reverse voltage (VR) of 5V. The datasheet explicitly cautions that this reverse voltage condition is for infrared testing only and that the device is not designed for reverse operation in an actual circuit.

2.3 Thermal Considerations

While not explicitly detailed in a separate thermal characteristics section, the key thermal parameters are embedded in the ratings. The maximum power dissipation of 108 mW is a direct thermal limit. Exceeding this will cause the junction temperature to rise excessively. The operating temperature range of -20°C to +80°C is also a thermal constraint for the environment. Proper PCB layout, including adequate copper area for heat sinking, is essential to maintain the LED junction temperature within safe limits, especially when operating at or near the maximum forward current. High junction temperatures accelerate lumen depreciation and can significantly shorten the LED's lifetime.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into bins based on key parameters. The LTW-C171DC-KO uses a three-dimensional binning system for forward voltage (VF), luminous intensity (Iv), and hue (chromaticity coordinates).

3.1 Forward Voltage (VF) Binning

LEDs are grouped into three voltage bins (D7, D8, D9) at a test current of 20mA. Bin D7 covers VF from 2.8V to 3.0V, D8 from 3.0V to 3.2V, and D9 from 3.2V to 3.4V. A tolerance of ±0.1 volts is applied to each bin. Consistent VF within a batch helps in designing stable current-driving circuits without excessive variation in voltage drop.

3.2 Luminous Intensity (Iv) Binning

The luminous output is categorized into four bins: V1 (710-900 mcd), V2 (900-1120 mcd), W1 (1120-1400 mcd), and W2 (1400-1800 mcd). A tolerance of ±15% is noted for each intensity bin. This binning allows designers to select LEDs appropriate for the required brightness level of their application, ensuring uniformity in multi-LED arrays.

3.3 Hue (Chromaticity) Binning

This is the most complex binning, defining the color point of the white light on the CIE 1931 diagram. Multiple bins are defined (C1, C2, C3, C4, C6, C7, C8, C9, C10), each representing a small quadrilateral area on the chromaticity chart with specific x and y coordinate boundaries. A tolerance of ±0.01 is applied to each hue bin. This tight control is crucial for applications where color consistency is important, such as in backlighting or status indicators where multiple LEDs must match.

4. Performance Curve Analysis

The datasheet references typical performance curves, which are graphical representations of how key parameters change under different conditions. While the specific graphs are not fully detailed in the provided text, standard curves for such LEDs would typically include:

Relative Luminous Intensity vs. Forward Current: This curve shows how the light output increases with increasing forward current. It is generally linear at lower currents but may saturate or roll off at higher currents due to thermal and efficiency effects. Operating at the recommended 20mA ensures a good balance between brightness and longevity.

Forward Voltage vs. Forward Current: This is the diode's I-V characteristic. It shows the exponential relationship, indicating the voltage required to achieve a certain current. The curve shifts with temperature.

Relative Luminous Intensity vs. Ambient Temperature: This critical curve demonstrates the thermal quenching effect. As the ambient (and thus junction) temperature rises, the luminous output of the LED typically decreases. The slope of this curve is a key indicator of the LED's thermal performance. Understanding this helps in designing for environments with high operating temperatures.

Spectral Power Distribution: While not explicitly mentioned, a white LED's spectrum would show a blue peak from the InGaN chip and a broader yellow emission from the phosphor coating (which in this case results in a yellow lens appearance). The exact coordinates in the hue bin define the precise color point of this combined spectrum.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity

The LED has a standard SMD package footprint. The lens color is yellow, while the light source (chip) color is white (InGaN). All dimensions on the mechanical drawing are in millimeters, with a standard tolerance of ±0.1 mm unless otherwise noted. The polarity is typically indicated by a marking on the package or by an asymmetric feature in the pad design. The datasheet includes a diagram for the recommended PCB attachment pad layout, which is essential for ensuring proper soldering, thermal management, and alignment during the reflow process.

5.2 Tape and Reel Packaging

The LEDs are supplied in industry-standard embossed carrier tape that is 8mm wide. This tape is wound onto 7-inch (approximately 178mm) diameter reels. Each reel contains 3000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces is specified for remainder lots. The packaging follows ANSI/EIA 481 specifications. Key notes include that empty component pockets are sealed with a top cover tape, and a maximum of two consecutive missing lamps is allowed per the standard. This packaging is optimized for automated assembly machines.

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile

For lead-free (Pb-free) soldering processes, a specific reflow profile is suggested. The peak temperature should not exceed 260°C, and the time at or above this peak temperature should be limited to a maximum of 10 seconds. A pre-heat stage is also recommended. The datasheet emphasizes that the optimal profile can vary based on the specific PCB design, solder paste, oven, and other components, so board-specific characterization is advised.

6.2 Manual Soldering

If manual soldering with an iron is necessary, the temperature should be kept at a maximum of 300°C, and the soldering time should not exceed 3 seconds. This should be performed only once to avoid thermal stress.

6.3 Cleaning

If cleaning after soldering is required, only specified chemicals should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. The use of unspecified chemicals could damage the plastic package or lens.

6.4 Storage and Handling

ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). It is recommended to use a wrist strap or anti-static gloves when handling them. All equipment and workstations must be properly grounded.

Moisture Sensitivity: The LEDs are packaged in a moisture-proof bag with desiccants. While sealed, they should be stored at ≤30°C and ≤90% relative humidity (RH) and used within one year. Once the original bag is opened, the storage environment should not exceed 30°C and 60% RH. Components removed from their original packaging should undergo IR reflow soldering within 672 hours (28 days, corresponding to Moisture Sensitivity Level 2a). For longer storage outside the original bag, they should be kept in a sealed container with desiccant. If stored for more than 672 hours, a bake-out at approximately 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

The LED must be driven by a current-limiting circuit, not a voltage source. A simple series resistor is the most common method for low-current applications. The resistor value is calculated as R = (Vsupply - VF) / IF, where VF is the forward voltage of the specific LED bin. For example, with a 5V supply and a VF of 3.0V (Bin D7) at 20mA, R = (5 - 3.0) / 0.02 = 100 Ohms. For applications requiring constant brightness or operation over a wide temperature range, a constant current driver is recommended.

7.2 PCB Layout and Thermal Management

Follow the recommended pad layout from the datasheet to ensure proper solder fillet formation. To aid heat dissipation, connect the thermal pad (if applicable) or the cathode/anode pads to a larger area of copper on the PCB. This copper acts as a heat sink, helping to keep the junction temperature low and maintain light output and longevity.

7.3 Optical Design

The 130-degree viewing angle provides very wide emission. For applications needing more directed light, secondary optics such as lenses or light pipes may be used. The yellow lens will filter the emitted white light, resulting in a final output color that is yellowish-white.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED with 30mA continuously?

A: Yes, 30mA is the maximum continuous DC forward current rating. However, for optimal lifetime and reliability, operating at or below the typical 20mA is recommended unless the higher brightness is essential and thermal management is excellent.

Q: What is the difference between the Iv bins V1, V2, W1, W2?

A: These represent different guaranteed minimum levels of luminous intensity. W2 is the brightest bin (1400-1800 mcd), while V1 is the dimmest (710-900 mcd). Select the bin based on the brightness requirement of your application.

Q: How do I interpret the hue bin codes like C2 or C7?

A: Each code corresponds to a specific small region on the CIE color chart. Bins closer together represent very similar shades of white. For consistent color in an array, specify and use LEDs from the same hue bin.

Q: The datasheet mentions a 260°C reflow. Is this the actual solder melting point?

A: No, 260°C is the maximum temperature the LED package can withstand for 10 seconds. The solder paste will have its own melting profile (e.g., melting around 217-220°C for typical lead-free solder). The reflow oven profile must bring the solder to melt while ensuring the LED body temperature does not exceed its 260°C limit.

9. Practical Design and Usage Case

Case: Designing a Status Indicator Panel for Industrial Equipment

An engineer is designing a control panel that requires 10 uniform white status indicators. The panel will be in an environment with ambient temperatures up to 50°C.

Design Steps:

1. Brightness Selection: Choose an Iv bin (e.g., W1: 1120-1400 mcd) that provides sufficient visibility under the expected lighting conditions.

2. Color Consistency: Specify a single Hue bin (e.g., C7) for all 10 LEDs to ensure they all appear the same shade of white.

3. Circuit Design: Use a 5V rail. Assuming a VF bin of D8 (3.0-3.2V), design for the worst-case (min VF=3.0V) to ensure current doesn't exceed limits. R = (5V - 3.0V) / 0.02A = 100Ω. A 100Ω, 1/8W resistor in series with each LED is suitable.

4. Thermal Management: Given the 50°C ambient, ensure the PCB has adequate copper pours connected to the LED pads to dissipate the ~40mW of heat per LED ( (5V-3.1V)*0.02A ).

5. Assembly: Ensure the manufacturing house uses the recommended reflow profile and that the LEDs are baked if the moisture exposure time exceeds 672 hours.

10. Technical Principle Introduction

The LTW-C171DC-KO is based on a semiconductor light-emitting diode principle. The core is an InGaN chip that emits light in the blue spectrum when electrical current passes through its P-N junction (electroluminescence). This blue light is then partially converted to longer wavelengths (yellow, red) by a phosphor coating applied over the chip. The mixture of the remaining blue light and the phosphor-converted yellow/red light results in the perception of white light. The specific composition and thickness of the phosphor layer determine the exact chromaticity coordinates (hue). The yellow-tinted lens further modifies the final output color. The wide viewing angle is a result of the package geometry and the lens design, which scatters the light from the chip over a broad solid angle.

11. Technology Trends

The use of InGaN technology for white LEDs represents a mature and highly optimized approach. Ongoing trends in the industry include:

Increased Efficiency (lm/W): Continuous improvements in chip design, phosphor efficiency, and package architecture drive higher luminous efficacy, allowing more light output for the same electrical input power.

Improved Color Rendering and Consistency: Advances in phosphor technology and tighter binning processes lead to LEDs with better color quality (higher CRI - Color Rendering Index) and more consistent color from batch to batch.

Miniaturization: The drive for smaller devices continues, leading to even more compact SMD LED packages for ultra-space-constrained applications.

Enhanced Reliability and Lifetime: Improvements in materials (e.g., more stable plastics, better phosphors) and thermal management designs are extending the operational lifetime of LEDs, making them suitable for more demanding applications.