SMD LED LTST-C950RKGKT-5A Datasheet - 3.2x2.8x1.9mm - 2.0V - 75mW - Green AlInGaP - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-C950RKGKT-5A, a high-brightness, surface-mount LED lamp. Designed for automated assembly processes, this component is ideal for space-constrained applications requiring reliable and efficient indicator lighting.

1.1 Features

• Compliant with RoHS environmental standards.
• Utilizes an ultra-bright Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor chip for high luminous efficiency.
• Features a dome lens for optimized light output and viewing angle.
• Packaged on 12mm tape wound onto 7-inch diameter reels, compatible with standard automated pick-and-place equipment.
• Conforms to EIA (Electronic Industries Alliance) standard package outlines.
• Designed for compatibility with integrated circuits (I.C. compatible).
• Suitable for use with infrared (IR) reflow soldering processes.

1.2 Applications

This LED is suited for a broad range of electronic equipment, including but not limited to:

• Telecommunication devices (cordless/cellular phones).
• Office automation equipment and notebook computers.
• Network systems and home appliances.
• Indoor signage and display applications.
• Keypad and keyboard backlighting.
• Status and power indicators.
• Micro-displays and symbolic luminaries.

2. Package Dimensions and Mechanical Information

The LTST-C950RKGKT-5A is housed in a standard surface-mount device (SMD) package.

• Lens Color: Water Clear
• Chip/Source Color: AlInGaP Green
• Key Dimensions (Typical): The package measures approximately 3.2mm in length, 2.8mm in width, and 1.9mm in height. All dimensional tolerances are ±0.1mm unless otherwise specified on the detailed mechanical drawing.

3. Ratings and Characteristics

3.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): 75 mW
• Peak Forward Current (IFP): 80 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width)
• Continuous Forward Current (IF): 30 mA DC
• Operating Temperature Range: -30°C to +85°C
• Storage Temperature Range: -40°C to +185°C
• Infrared Reflow Soldering Condition: Withstand 260°C peak temperature for a maximum of 10 seconds.

3.2 Suggested IR Reflow Profile

For lead-free (Pb-free) soldering processes, a recommended reflow profile is provided. Key parameters include a pre-heat zone up to 200°C, a peak temperature not exceeding 260°C, and a time above 260°C limited to 10 seconds maximum. The profile should be characterized for the specific PCB design, solder paste, and oven used.

3.3 Electrical and Optical Characteristics

Typical performance parameters measured at Ta=25°C and a forward current (IF) of 5mA, unless noted.

• Luminous Intensity (Iv): 71.0 - 450.0 mcd (millicandela). The wide range is managed through binning (see Section 4).
• Viewing Angle (2θ½): 25 degrees. This is the full angle at which luminous intensity is half the value on the central axis.
• Peak Emission Wavelength (λP): 574.0 nm (typical).
• Dominant Wavelength (λd): 564.5 - 573.5 nm. This defines the perceived color of the LED and is also binned.
• Spectral Line Half-Width (Δλ): 15.0 nm (typical).
• Forward Voltage (VF): 1.6 - 2.2 V, with a typical value of 2.0V at 5mA.
• Reverse Current (IR): 10 µA (maximum) at a reverse voltage (VR) of 5V.

Measurement Notes: Luminous intensity is measured using a sensor filtered to match the CIE photopic eye-response curve. Caution against Electrostatic Discharge (ESD) is required during handling; proper grounding and ESD-safe practices are mandatory.

4. Bin Rank System

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

4.1 Forward Voltage (VF) Rank

Binned at IF=5mA. Bin codes 1 through 6, with VF ranges from 1.60-1.70V (Bin 1) to 2.10-2.20V (Bin 6). Tolerance per bin is ±0.1V.

4.2 Luminous Intensity (Iv) Rank

Binned at IF=5mA. Bin codes Q, R, S, T, with Iv ranges from 71.0-112.0 mcd (Bin Q) to 280.0-450.0 mcd (Bin T). Tolerance per bin is ±15%.

4.3 Hue (Dominant Wavelength, λd) Rank

Binned at IF=5mA. Bin codes B, C, D, with λd ranges from 564.5-567.5 nm (Bin B) to 570.5-573.5 nm (Bin D). Tolerance per bin is ±1 nm.

5. Typical Performance Curves Analysis

The datasheet includes graphical representations of key relationships, essential for circuit design and thermal management.

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, typically in a sub-linear manner at higher currents due to heating effects.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the negative temperature coefficient of light output; intensity decreases as junction temperature rises.
• Forward Voltage vs. Forward Current: Illustrates the diode's I-V characteristic, crucial for selecting current-limiting resistor values.
• Wavelength vs. Forward Current: May show a slight shift in peak or dominant wavelength with changing drive current.
• Viewing Angle Pattern: A polar diagram depicting the spatial distribution of light intensity.

6. User Guide for Assembly and Handling

6.1 Cleaning

If cleaning is necessary after soldering, only use specified solvents. Immerse the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute. Avoid unspecified chemicals that may damage the epoxy package.

6.2 Recommended PCB Land Pattern

A suggested solder pad layout is provided to ensure proper mechanical alignment, solder fillet formation, and thermal relief during the reflow process. Adhering to this pattern helps prevent tombstoning and ensures reliable solder joints.

6.3 Tape and Reel Packaging Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178mm) diameter reels. Standard reel quantity is 2000 pieces. Packaging conforms to ANSI/EIA-481 specifications. Key tape dimensions (pocket size, pitch) and reel dimensions (hub diameter, flange diameter) are detailed to ensure compatibility with automated assembly equipment.

7. Cautions and Application Notes

7.1 Application Scope

This LED is designed for standard commercial and industrial electronic equipment. It is not rated for safety-critical or high-reliability applications where failure could risk life or health (e.g., aviation, medical life-support). Consultation with the manufacturer is required for such uses.

7.2 Storage Conditions

• Sealed Package: Store at ≤ 30°C and ≤ 90% Relative Humidity (RH). Use within one year of opening the moisture barrier bag.
• Opened Package: For components removed from the dry pack, the storage environment should not exceed 30°C / 60% RH. It is recommended to complete IR reflow within one week (Moisture Sensitivity Level 3, MSL 3). For longer storage, use a sealed container with desiccant. If stored for over a week, a bake-out at 60°C for at least 20 hours is required before soldering to prevent "popcorning" damage.

7.3 Soldering Guidelines

Detailed soldering parameters are provided for both reflow and hand soldering:

• Reflow Soldering: Pre-heat to 150-200°C (max 120 sec), peak temperature ≤ 260°C, time above 260°C ≤ 10 sec (max two reflow cycles allowed).
• Hand Soldering: Iron tip temperature ≤ 300°C, soldering time ≤ 3 seconds per pad (one time only).

The importance of following JEDEC-based reflow profiles and solder paste manufacturer guidelines is emphasized to ensure joint reliability and avoid thermal damage to the LED.

8. Technical Deep Dive and Design Considerations

8.1 Principle of Operation

The LTST-C950RKGKT-5A is based on an AlInGaP (Aluminium Indium Gallium Phosphide) semiconductor chip. When a forward voltage exceeding its bandgap energy is applied, electrons and holes recombine in the active region, releasing energy in the form of photons. The specific composition of the AlInGaP alloy is engineered to produce light in the green wavelength region (around 574nm). The dome-shaped epoxy lens serves to extract more light from the chip and shape the emission pattern into a 25-degree viewing angle.

8.2 Driving the LED

A constant current source is the ideal method for driving an LED, as it ensures stable light output regardless of minor variations in forward voltage. For simple applications, a current-limiting resistor in series with a voltage supply is common. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - VF_LED) / I_desired. Using the typical VF of 2.0V at 5mA with a 5V supply, R = (5V - 2.0V) / 0.005A = 600Ω. A designer should use the maximum VF from the datasheet (2.2V) for worst-case current calculation to avoid exceeding the absolute maximum current rating.

8.3 Thermal Management

Although a small device, thermal management is critical for longevity and performance. The 75mW maximum power dissipation limit must be respected. Operating at high currents or in high ambient temperatures increases the junction temperature, which leads to reduced light output (as seen in the performance curves), accelerated lumen depreciation, and potentially shortened lifespan. Ensuring adequate copper area on the PCB under and around the LED's thermal pad (if applicable) or solder pads helps dissipate heat.

8.4 Optical Design Considerations

The 25-degree viewing angle makes this LED suitable for directed indicator applications. For backlighting a panel or creating a more diffuse glow, secondary optics like light guides or diffuser films would be necessary. The water-clear lens produces a narrow, intense beam, whereas a diffused lens would create a wider, softer emission pattern.

8.5 Comparison and Selection

When selecting an LED, engineers compare key parameters: Brightness (Iv), Color (Wavelength, CIE coordinates), Viewing Angle, Forward Voltage, and Package Size. The AlInGaP technology in this LED offers high efficiency and good stability in the green/yellow color range compared to older technologies. The binning system allows for precise selection for applications requiring tight color or brightness matching across multiple units.

8.6 Typical User Questions Answered

Q: Can I drive this LED at 20mA continuously?

A: Yes, the absolute maximum continuous current is 30mA. Operating at 20mA is within specification, but you must ensure the power dissipation (VF * IF) does not exceed 75mW. At 20mA and a typical VF of 2.0V, power is 40mW, which is acceptable.

Q: Why is there such a wide range in Luminous Intensity (71-450 mcd)?

A: This is the total possible spread across all production. For a specific order, you would select a bin (e.g., Bin T: 280-450 mcd) to get a much tighter, predictable range of brightness.

Q: How do I interpret the "Peak" vs "Dominant" wavelength?

A: The Peak Wavelength (λP=574nm) is the single wavelength where the emission spectrum is strongest. The Dominant Wavelength (λd=564.5-573.5nm) is calculated from the CIE color chart and represents the perceived color. λd is more relevant for color specification in human-centric applications.

8.7 Application Case Study: Status Indicator Panel

Consider designing a status indicator panel for a network router with four identical green LEDs. To ensure uniform appearance:

1. Binning: Specify the same Hue bin (e.g., Bin C: 567.5-570.5nm) and Luminous Intensity bin (e.g., Bin S: 180-280 mcd) for all four LEDs. This guarantees nearly identical color and brightness.
2. Circuit Design: Use a common 5V rail. Calculate the current-limiting resistor for 5mA drive using the maximum VF (2.2V) to ensure brightness consistency even if individual VF varies: R = (5V - 2.2V) / 0.005A = 560Ω. Use 1% tolerance resistors.
3. PCB Layout: Follow the recommended land pattern. Include a small copper pour connected to the cathode pad to aid heat dissipation, especially if the PCB is enclosed.
4. Assembly: Follow the MSL3 guidelines. If the reel is opened, plan to solder all LEDs within one week or store them properly with desiccant.

8.8 Technology Trends

AlInGaP LEDs represent a mature and highly efficient technology for the amber-to-red color spectrum, with green being at the shorter-wavelength limit of its capability. Ongoing development in the LED industry focuses on increasing efficiency (lumens per watt), improving color rendering, and reducing costs. For pure green and blue colors, InGaN (Indium Gallium Nitride) technology is dominant and continues to see rapid efficiency gains. The trend in packaging is towards smaller footprints, higher power density, and improved thermal paths (e.g., flip-chip designs) to manage the heat from ever-brighter chips. This particular SMD LED utilizes a well-established package technology optimized for reliability and automated assembly in high-volume consumer and industrial electronics.