SMD LED Chip LTST-C171TBKT-5A Datasheet - 0.8mm Height - 2.8V-3.05V Forward Voltage - Blue Color - 76mW Power - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-C171TBKT-5A, a surface-mount device (SMD) light-emitting diode (LED) chip. This product belongs to a family of super-thin, high-brightness blue LEDs designed for modern electronic assembly processes. The primary application of this component is as an indicator light, backlight source, or status display in a wide range of compact electronic devices where space and height are critical constraints.

The core advantage of this LED is its minimal profile, with a height of only 0.80 millimeters. This makes it suitable for applications in ultra-thin consumer electronics, portable devices, and densely packed PCBs. It is manufactured to be compatible with automatic pick-and-place equipment, ensuring high-volume assembly efficiency. The device is also compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product suitable for global markets with strict environmental regulations.

The target market includes manufacturers of office automation equipment, communication devices, household appliances, and various industrial control panels. Its compatibility with infrared (IR) and vapor phase reflow soldering processes aligns it with standard and lead-free (Pb-free) assembly lines used in mass production.

2. Technical Parameter Deep-Dive

This section provides an objective and detailed interpretation of the key technical parameters specified in the datasheet.

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. These are not conditions for normal operation.

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the LED can dissipate as heat at an ambient temperature (Ta) of 25°C. Exceeding this limit risks thermal damage to the semiconductor junction.
• DC Forward Current (IF): 20 mA. This is the maximum continuous forward current recommended for reliable long-term operation.
• Peak Forward Current: 100 mA. This rating applies only under pulsed conditions with a very low duty cycle (1/10) and short pulse width (0.1ms). It is relevant for brief, high-intensity flashes but not for constant illumination.
• Reverse Voltage (VR): 5 V. Applying a reverse bias voltage exceeding this value can cause breakdown and failure of the LED's PN junction.
• Operating Temperature Range: -20°C to +80°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -30°C to +100°C. The device can be stored without degradation within these limits.
• Soldering Temperature Tolerance: The datasheet specifies conditions for wave soldering (260°C for 5 sec), IR reflow (260°C for 5 sec), and vapor phase reflow (215°C for 3 min). These are critical for PCB assembly without damaging the LED package.

2.2 Electrical & Optical Characteristics

These parameters are measured under standard test conditions (Ta=25°C) and define the device's performance.

• Luminous Intensity (Iv): 15.0 mcd (typical) at a forward current (IF) of 5 mA. The minimum guaranteed value is 11.2 mcd. This measures the perceived brightness of the LED to the human eye, using a filter that approximates the CIE photopic response curve.
• Forward Voltage (VF): 2.80 V (typical) with a maximum of 3.05 V at IF=5mA. This is the voltage drop across the LED when conducting current. It is a crucial parameter for designing the current-limiting circuitry.
• Viewing Angle (2θ1/2): 130 degrees (typical). This wide viewing angle indicates the LED emits light over a broad cone, making it suitable for applications where visibility from multiple angles is important.
• Peak Emission Wavelength (λP): 468 nm. This is the wavelength at which the spectral power output is highest.
• Dominant Wavelength (λd): 470.0 nm to 475.0 nm at IF=5mA. This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. It is a more relevant parameter for color specification than peak wavelength.
• Spectral Line Half-Width (Δλ): 25 nm (typical). This measures the bandwidth of the emitted light spectrum at half its maximum intensity. A value of 25 nm is characteristic of a blue InGaN LED.
• Reverse Current (IR): 10 μA (maximum) at VR=5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.

2.3 Thermal Characteristics

The thermal performance is indicated by the derating factor. The DC forward current must be reduced linearly by 0.25 mA for every degree Celsius the ambient temperature rises above 50°C. This is essential for ensuring reliability at elevated operating temperatures. For example, at the maximum operating temperature of 80°C, the maximum allowable continuous current would be: 20 mA - [0.25 mA/°C * (80°C - 50°C)] = 20 mA - 7.5 mA = 12.5 mA.

3. Binning System Explanation

To manage natural variations in the semiconductor manufacturing process, LEDs are sorted into performance bins. This allows designers to select components with tightly controlled characteristics for their application.

3.1 Forward Voltage Binning

LEDs are categorized into four bins based on their forward voltage (VF) measured at 5 mA.

• Bin 1: 2.65 V - 2.75 V
• Bin 2: 2.75 V - 2.85 V
• Bin 3: 2.85 V - 2.95 V
• Bin 4: 2.95 V - 3.05 V

Tolerance within each bin is ±0.1 V. Using LEDs from the same voltage bin in a parallel circuit helps achieve more uniform current sharing and brightness.

3.2 Luminous Intensity Binning

LEDs are sorted into six bins based on luminous intensity (Iv) at 5 mA, ranging from L1 (lowest) to N2 (highest).

• L1: 11.2 mcd - 14.0 mcd
• L2: 14.0 mcd - 18.0 mcd
• M1: 18.0 mcd - 22.4 mcd
• M2: 22.4 mcd - 28.0 mcd
• N1: 28.0 mcd - 35.5 mcd
• N2: 35.5 mcd - 45.0 mcd

Tolerance on each intensity bin is ±15%. This binning is critical for applications requiring consistent brightness levels across multiple indicators.

3.3 Dominant Wavelength Binning

For this specific part number, all devices fall into a single dominant wavelength bin: AD, with a range of 470.0 nm to 475.0 nm. The tolerance for this bin is ±1 nm, ensuring a very consistent blue color output.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), their typical behavior can be described based on standard LED physics and the provided parameters.

4.1 Current vs. Voltage (I-V) Characteristic

The I-V curve for a blue InGaN LED like this one is non-linear. Below the forward voltage threshold (approximately 2.6-2.7V), very little current flows. As the voltage approaches and exceeds the typical VF of 2.8V, the current increases rapidly. This is why LEDs must be driven by a current-limited source, not a constant voltage source. The slight variation in VF between individual units (as seen in the binning) is due to minor differences in the semiconductor epitaxial layer and chip processing.

4.2 Luminous Intensity vs. Forward Current

The light output (luminous intensity) is approximately proportional to the forward current over a significant range. However, at very high currents, efficiency drops due to increased heat generation (droop effect). The rated 20 mA DC forward current is chosen as a balance between good brightness and long-term reliability.

4.3 Spectral Distribution

The spectral output curve will show a primary peak around 468 nm (blue). The half-width of 25 nm indicates the spectral purity. There will be no significant secondary peaks in the output of a well-made InGaN blue LED. The dominant wavelength of 470-475 nm places this LED's color in the standard blue region.

4.4 Temperature Dependence

As junction temperature increases, the forward voltage typically decreases slightly (negative temperature coefficient), while the luminous intensity and dominant wavelength may shift. The derating specification directly addresses the need to reduce current at high ambient temperatures to manage the junction temperature and maintain performance and lifetime.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED is an EIA standard package. The key mechanical feature is its super-thin profile with a height (H) of 0.80 mm. All other dimensions (length, width, lead spacing) conform to the standard footprint for this package type, ensuring compatibility with automated assembly equipment and standard PCB land patterns. The lens material is specified as "Water Clear," which is a colorless, transparent epoxy that does not diffuse the light, resulting in a clear, focused beam from the chip.

5.2 Polarity Identification

The datasheet includes a package outline drawing which clearly indicates the cathode and anode terminals. Typically, the cathode is marked by a notch, a green dot, or a shorter lead/tab on the package body. Correct polarity must be observed during PCB assembly, as applying reverse bias can damage the device.

5.3 Suggested Soldering Pad Layout

A recommended land pattern (solder pad dimensions and spacing) is provided to ensure proper solder joint formation, mechanical stability, and thermal relief during the reflow process. Following this guideline is essential for achieving high assembly yield and reliability.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles: one for normal (tin-lead) solder process and one for Pb-free process. The key parameters are:

• Pre-heat: A gradual ramp to activate the flux and minimize thermal shock.
• Soak/Pre-heat Time: Maximum of 120 seconds to prevent excessive oxidation.
• Peak Temperature: Maximum of 260°C. The LED can withstand this temperature for a very limited time.
• Time Above Liquidus (TAL): For Pb-free process, the profile must ensure the solder paste is molten for the correct duration to form a reliable joint, typically referenced between specific temperature lines (e.g., 217°C for SnAgCu).

Adherence to these profiles is critical. Excessive time or temperature during reflow can damage the LED's epoxy lens, degrade the semiconductor chip, or weaken the internal wire bonds.

6.2 Storage Conditions

LEDs are moisture-sensitive devices. If removed from their original moisture-barrier packaging, they must be used within 672 hours (28 days) or be baked before soldering to remove absorbed moisture. Extended storage out of the original bag requires a controlled environment: a sealed container with desiccant or a nitrogen-filled desiccator. Failure to follow these procedures can lead to "popcorning" during reflow, where internal vapor pressure cracks the package.

6.3 Cleaning

If post-solder cleaning is necessary, only specified solvents should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Harsh or unspecified chemicals can cloud, crack, or otherwise damage the LED's epoxy lens.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in industry-standard embossed carrier tape on 7-inch (178 mm) diameter reels. This packaging is compatible with high-speed automated placement machines.

• Pieces per Reel: 3000 units.
• Minimum Packing Quantity: 500 pieces for remainder quantities.
• Cover Tape: Empty component pockets are sealed with a top cover tape.
• Missing Lamps: The maximum number of consecutive missing components in the tape is two, as per quality standards.
• Standard: Packaging conforms to ANSI/EIA 481-1-A-1994 specifications.

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Power-on, standby, charging, or error lights in consumer electronics, appliances, and networking equipment.
• Backlighting: For small LCD displays, keypads, or membrane switches in thin devices.
• Panel Lighting: Illumination for instrument clusters, control panels, and industrial HMI devices.
• Decorative Lighting: Accent lighting in compact spaces where a thin form factor is paramount.

8.2 Circuit Design Considerations

Critical: LEDs are current-driven devices. The most important design rule is to control the forward current.

• Current Limiting Resistor (Circuit Model A): When connecting multiple LEDs in parallel, a separate current-limiting resistor must be used in series with each LED. This is because the forward voltage (VF) can vary slightly from one LED to another (as defined by the binning). Without individual resistors, LEDs with a lower VF will draw disproportionately more current, leading to uneven brightness and potential overstress of those units. The resistor value is calculated using Ohm's Law: R = (Vsupply - VF_LED) / Idesired.
• Parallel Connection without Resistors (Circuit Model B): This configuration is not recommended as it leads to non-uniform brightness and unreliable operation due to the natural variance in I-V characteristics.
• Series Connection: Connecting LEDs in series ensures they all pass the same current. A single current-limiting resistor can be used for the entire series string. The supply voltage must be high enough to overcome the sum of all forward voltages in the string.

8.3 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. Precautions must be taken during handling and assembly:

• Operators should wear grounded wrist straps or anti-static gloves.
• All workstations, tools, and equipment must be properly grounded.
• Store and transport LEDs in ESD-safe packaging.

9. Technical Comparison & Differentiation

The primary differentiating factors of this LED compared to generic or older blue LED chips are:

• Ultra-Low Profile (0.8mm H): Enables design of thinner end products, a key requirement in modern smartphones, tablets, and ultrabooks.
• Standardized EIA Package: Guarantees compatibility with automated assembly lines and existing PCB library footprints, reducing design time and risk.
• Dual Soldering Process Compatibility: Certified for both standard (SnPb) and lead-free (SnAgCu) reflow processes, future-proofing designs for global environmental regulations.
• Comprehensive Binning: Offers designers the ability to select components with tightly controlled brightness (Iv) and forward voltage (VF), leading to more consistent performance in mass-produced goods.
• High-Brightness Options: The availability of bins up to N2 (45.0 mcd) provides flexibility for applications requiring higher visibility.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive this LED directly from a 3.3V or 5V logic supply?

No, not directly. You must use a series current-limiting resistor. For example, with a 3.3V supply and a target current of 5mA, using a typical VF of 2.8V: R = (3.3V - 2.8V) / 0.005A = 100 Ohms. Without the resistor, the LED would attempt to draw excessive current, limited only by the power supply and the LED's internal resistance, likely destroying it.

10.2 Why is there a peak current rating (100mA) much higher than the DC rating (20mA)?

The peak current rating is for very short pulses (0.1ms) at a low duty cycle (10%). Under these conditions, the semiconductor junction does not have time to heat up significantly. For continuous operation (DC), heat buildup is the limiting factor, hence the lower 20mA rating to ensure long-term reliability and prevent thermal runaway.

10.3 What is the difference between Peak Wavelength and Dominant Wavelength?

Peak Wavelength (λP) is the literal highest point on the spectral output curve (468 nm). Dominant Wavelength (λd) is a calculated value (470-475 nm) that corresponds to the perceived color by the human eye on the CIE chromaticity diagram. For specifying color in applications, the dominant wavelength is the more relevant parameter.

10.4 The LED worked after soldering but failed later. What could be the cause?

Common causes include: ESD damage during handling, thermal overstress during soldering (exceeding time/temperature profile), incorrect polarity on the PCB, driving with excessive current due to a missing or miscalculated current-limiting resistor, or moisture-induced damage (popcorning) from improper storage of moisture-sensitive devices.

11. Practical Design Case Study

Scenario: Designing a control panel with four blue status indicators. The panel is powered by a 5V rail. Uniform brightness is critical for aesthetics.

1. LED Selection: Choose LEDs from the same luminous intensity bin (e.g., all from M1 bin: 18.0-22.4 mcd) and the same forward voltage bin (e.g., all from Bin 2: 2.75-2.85V) to minimize inherent variation.
2. Circuit Design: Use Circuit Model A. Place each LED in parallel with its own series resistor. For a target current of 5mA and a conservative VF of 2.85V (max of Bin 2), calculate R = (5V - 2.85V) / 0.005A = 430 Ohms. The nearest standard value is 430Ω or 470Ω.
3. PCB Layout: Follow the suggested soldering pad dimensions from the datasheet. Ensure correct polarity alignment based on the package marking.
4. Assembly: Use the recommended Pb-free reflow profile. Ensure LEDs are used within 672 hours of opening the moisture-barrier bag or are properly baked.
5. Result: Four indicators with consistent brightness and color, reliable long-term operation, and high manufacturing yield.

12. Operating Principle

The LTST-C171TBKT-5A is a semiconductor device based on Indium Gallium Nitride (InGaN) material. When a forward bias voltage exceeding the junction's built-in potential 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 InGaN alloy in the active layer determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light. For this device, the bandgap is engineered to produce photons in the blue spectrum (~470 nm). The clear epoxy lens encapsulates and protects the semiconductor chip, provides mechanical stability, and shapes the light output beam.

13. Technology Trends

The development of SMD LEDs like this one follows several clear industry trends:

• Miniaturization: Continuous reduction in package size (footprint and height) to enable thinner and more compact electronic products.
• Increased Efficiency: Ongoing improvements in internal quantum efficiency (IQE) and light extraction efficiency to deliver higher luminous intensity at the same or lower drive currents, improving battery life in portable devices.
• Standardization & Automation: Adherence to standardized package outlines and tape-and-reel formats to streamline high-volume, automated manufacturing processes globally.
• Environmental Compliance: Elimination of hazardous substances (RoHS, REACH) and compatibility with lead-free (Pb-free) assembly processes are now standard requirements.
• Color Consistency: Tighter binning tolerances for luminous intensity, forward voltage, and chromaticity coordinates are demanded for applications where visual uniformity is paramount, such as in displays and signage.