SMD LED LTST-C950KSKT Datasheet - Yellow AlInGaP - 25mA - 62.5mW - English Technical Document

1. Product Overview

The LTST-C950KSKT is a high-brightness, surface-mount LED designed for modern electronic applications requiring reliable, compact, and efficient light sources. Utilizing an advanced AlInGaP (Aluminum Indium Gallium Phosphide) chip technology, this LED delivers superior luminous intensity in a miniature package. Its primary design goal is to facilitate automated assembly processes while providing consistent performance in space-constrained environments.

1.1 Core Advantages

The key advantages of this component stem from its material and construction. The AlInGaP semiconductor material is known for its high efficiency and excellent color purity in the yellow-orange-red spectrum. The dome lens design enhances light extraction and viewing angle. Furthermore, the device is fully compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. Its compatibility with infrared (IR) reflow soldering processes aligns with modern, lead-free (Pb-free) PCB assembly lines, ensuring high-volume manufacturability.

1.2 Target Market and Applications

This LED is engineered for a broad range of consumer and industrial electronics. Its primary target markets include telecommunications (e.g., cellular and cordless phones), computing (notebook computers, keyboards), network systems, home appliances, and indoor signage. Specific applications leverage its brightness and compact form factor for keypad/ keyboard backlighting, status indication, micro-displays, and various signal or symbol luminaires.

2. Technical Parameters: In-Depth Objective Interpretation

Understanding the electrical and optical characteristics is crucial for proper circuit design and performance prediction.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. The device can dissipate a maximum of 62.5mW of power. The continuous DC forward current is rated at 25mA, while a higher peak forward current of 60mA is permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The maximum reverse voltage is 5V. The operating and storage temperature ranges are -30°C to +85°C and -40°C to +85°C, respectively. Exceeding these limits, especially current and temperature, can degrade the LED's lifetime and luminous output.

2.2 Electrical and Optical Characteristics

Measured at a standard junction temperature of 25°C and a forward current (IF) of 20mA, the typical performance parameters are defined. The luminous intensity (Iv) has a wide range from a minimum of 1120 millicandelas (mcd) to a maximum of 4500 mcd, with typical values expected within this binning range. The viewing angle (2θ1/2), where intensity is half the on-axis value, is 25 degrees, indicating a relatively focused beam. The peak emission wavelength (λP) is 588 nm, placing it firmly in the yellow spectrum. The dominant wavelength (λd) ranges from 584.5 nm to 597.0 nm depending on the bin. The forward voltage (VF) typically falls between 1.8V and 2.4V at 20mA, which is important for driver design. The reverse current (IR) is specified at a maximum of 10 μA when a 5V reverse bias is applied.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters.

3.1 Forward Voltage (VF) Binning

LEDs are categorized into three voltage bins (D2, D3, D4) with ranges of 1.8-2.0V, 2.0-2.2V, and 2.2-2.4V respectively, measured at 20mA. A tolerance of ±0.1V is applied to each bin. This allows designers to select LEDs with tighter voltage matching for applications where current regulation is critical.

3.2 Luminous Intensity (IV) Binning

The brightness is sorted into three bins: W (1120-1800 mcd), X (1800-2800 mcd), and Y (2800-4500 mcd), all at 20mA. A tolerance of ±15% is applied per bin. This binning is essential for applications requiring uniform brightness across multiple indicators.

3.3 Hue (Dominant Wavelength) Binning

The color hue is precisely controlled through five wavelength bins: H (584.5-587.0 nm), J (587.0-589.5 nm), K (589.5-592.0 nm), L (592.0-594.5 nm), and M (594.5-597.0 nm), with a ±1 nm tolerance. This ensures minimal color variation between different units in a single production batch or application.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet, their implications are standard. The forward current vs. forward voltage (I-V) curve shows the exponential relationship typical of diodes. The luminous intensity vs. forward current curve demonstrates how output increases with current, but designers must stay within absolute maximum ratings. The spectral distribution curve centers around 588 nm with a typical half-width (Δλ) of 15 nm, confirming a pure yellow color. Performance will vary with ambient temperature; luminous intensity generally decreases as temperature increases.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD package outline. Critical dimensions include the body size, lead spacing, and overall height. All dimensions are provided in millimeters with a standard tolerance of ±0.1mm unless otherwise noted. The lens is water clear, and the source color is yellow from the AlInGaP chip.

5.2 Polarity Identification and Pad Design

The component has anode and cathode markings. A recommended PCB land pattern (footprint) is provided to ensure proper solder joint formation, mechanical stability, and thermal management during and after the soldering process. Adhering to this design is critical for reliable assembly.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Conditions

For lead-free (Pb-free) processes, a peak reflow temperature of 260°C is specified, with the component body at this temperature for a maximum of 10 seconds. A pre-heat stage is recommended. The profile should follow JEDEC standards to prevent thermal shock and ensure reliable solder joints without damaging the LED's internal structure or epoxy lens.

6.2 Manual Soldering

If manual soldering with an iron is necessary, the tip temperature should not exceed 300°C, and contact time should be limited to a maximum of 3 seconds per pad. This should be performed only once to avoid thermal damage.

6.3 Storage and Handling

The LEDs are moisture-sensitive (MSL 3). When stored in their original sealed moisture-proof bag with desiccant, they have a shelf life of one year under conditions of ≤30°C and ≤90% RH. Once the bag is opened, they should be used within one week. For longer storage after opening, they must be kept in a dry environment (≤30°C, ≤60% RH, preferably in a sealed container with desiccant). If exposed beyond one week, a bake-out at approximately 60°C for at least 20 hours is required before soldering to prevent \"popcorning\" during reflow.

6.4 Cleaning

If cleaning is required after soldering, only specified alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol should be used. Unspecified chemicals may damage the LED package or lens.

7. Packaging and Ordering Information

The LEDs are supplied on 8mm wide embossed carrier tape, wound onto 7-inch (178mm) diameter reels. Each reel contains 2000 pieces. For quantities less than a full reel, a minimum pack quantity of 500 pieces is available. The packaging follows ANSI/EIA-481 standards. The part number LTST-C950KSKT uniquely identifies this specific yellow AlInGaP SMD LED variant.

8. Application Recommendations

8.1 Typical Application Circuits

The LED must be driven with a current-limiting mechanism. A simple series resistor is sufficient for many applications, calculated as R = (Vsupply - VF) / IF, where VF is the forward voltage from the datasheet (use max value for worst-case resistor power calculation). For constant brightness across temperature or supply voltage variations, a constant current driver is recommended. The reverse voltage rating of 5V is low, so care must be taken in circuit design to avoid accidental reverse bias.

8.2 Design Considerations

Thermal Management: Although power dissipation is low, maintaining a low junction temperature is key to long-term reliability and stable light output. Ensure adequate PCB copper area or thermal vias for heat sinking if operating at high ambient temperatures or near maximum current.
ESD Protection: The device is sensitive to electrostatic discharge (ESD). Proper ESD controls (wrist straps, grounded workstations) must be used during handling. Incorporating ESD protection diodes on the PCB may be necessary in sensitive environments.
Optical Design: The 25-degree viewing angle provides a focused beam. For wider illumination, secondary optics like light guides or diffusers may be required.

9. Technical Comparison and Differentiation

Compared to traditional GaP (Gallium Phosphide) yellow LEDs, AlInGaP technology offers significantly higher luminous efficiency, resulting in much brighter output for the same drive current. The dome lens package provides better light extraction and a more consistent viewing angle than flat or truncated designs. Its compatibility with high-temperature IR reflow soldering differentiates it from older LED packages that could only withstand wave soldering or manual processes, making it ideal for modern SMT assembly lines.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λP) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is the single wavelength perceived by the human eye that matches the color of the LED, calculated from the CIE chromaticity diagram. λd is often more relevant for color specification.

Q: Can I drive this LED at 30mA for more brightness?
A: No. The absolute maximum continuous forward current is 25mA. Exceeding this rating will reduce the LED's lifespan and may cause catastrophic failure. For higher brightness, select an LED from a higher luminous intensity bin (Y bin) or a product rated for higher current.

Q: Why is the storage condition after opening so strict?
A> The epoxy packaging material can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that may crack the package (\"popcorning\"). The specified storage conditions and bake-out procedures prevent this failure mode.

11. Practical Application Case Study

Scenario: Backlighting for a Membrane Keypad. A designer needs to evenly illuminate 12 keys on a handheld medical device. They select the LTST-C950KSKT in the Y brightness bin and J wavelength bin for consistent color. One LED is placed under each key. A constant current driver circuit is designed to provide 20mA to each LED, arranged in parallel strings with individual current-setting resistors to account for minor VF variations. The 25-degree viewing angle is sufficient to light each key without excessive spillover. The design accounts for the MSL 3 rating by scheduling board assembly immediately after the reel is opened and specifying a bake if delays occur.

12. Operating Principle Introduction

Light emission in this LED is based on electroluminescence in a semiconductor p-n junction made of AlInGaP materials. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). 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, yellow (~588 nm). The dome-shaped epoxy lens serves to protect the semiconductor chip and efficiently extract the generated light from the high-refractive-index semiconductor material into the air.

13. Technology Trends

The general trend in SMD LEDs is toward higher efficiency (more lumens per watt), improved color rendering, and increased power density in smaller packages. AlInGaP technology represents a mature and highly efficient solution for the red-orange-yellow-green spectrum. Ongoing research focuses on further efficiency gains through improved epitaxial growth techniques and advanced package designs for better thermal management and light extraction. The integration of LEDs with onboard drivers or control circuitry (\"smart LEDs\") is also a growing trend, though this particular component remains a discrete, standard-brightness optoelectronic device.