SMD LED 27-21 Blue Datasheet - Dimensions 2.7x2.1x1.2mm - Voltage 3.3V - Power 0.095W - English Technical Document

1. Product Overview

The 27-21 SMD LED is a compact, surface-mount device designed for modern electronic applications requiring reliable indicator or backlighting functionality. Its primary advantage lies in its significantly reduced footprint compared to traditional lead-frame LEDs, enabling higher component density on printed circuit boards (PCBs), reduced storage requirements, and ultimately contributing to the miniaturization of end equipment. The lightweight construction further enhances its suitability for space-constrained and portable applications.

This mono-color blue LED is constructed using an InGaN (Indium Gallium Nitride) semiconductor chip, encapsulated in a water-clear resin. It is a Pb-free product compliant with RoHS (Restriction of Hazardous Substances) directives, EU REACH regulations, and halogen-free standards, ensuring environmental safety and broad market acceptance.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Reverse Voltage (V_R): 5V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Continuous Forward Current (I_F): 25 mA. The maximum DC current for reliable operation.
• Peak Forward Current (I_FP): 100 mA. This is permissible only under pulsed conditions (duty cycle 1/10 at 1 kHz) to handle transient surges.
• Power Dissipation (P_d): 95 mW. The maximum power the package can dissipate at an ambient temperature (T_a) of 25°C. Derating is necessary at higher temperatures.
• Electrostatic Discharge (ESD): 150V (Human Body Model). Proper ESD handling procedures are mandatory during assembly and handling.
• Operating Temperature (T_opr): -40°C to +85°C. The ambient temperature range for normal device operation.
• Storage Temperature (T_stg): -40°C to +90°C.
• Soldering Temperature: The device can withstand reflow soldering with a peak temperature of 260°C for up to 10 seconds, or hand soldering at 350°C for up to 3 seconds per terminal.

2.2 Electro-Optical Characteristics

These parameters are measured at T_a=25°C and I_F=20mA, representing typical operating conditions.

• Luminous Intensity (I_v): Ranges from 28.5 mcd (min) to 72.0 mcd (max), with a typical tolerance of ±11%. This defines the perceived brightness of the LED.
• Viewing Angle (2θ_1/2): 130 degrees (typical). This wide angle ensures good visibility from off-axis positions.
• Peak Wavelength (λ_p): 468 nm (typical). The wavelength at which the spectral emission is strongest.
• Dominant Wavelength (λ_d): Ranges from 464.50 nm to 476.50 nm. This defines the perceived color of the light, with a tight tolerance of ±1 nm.
• Spectral Bandwidth (Δλ): 25 nm (typical). The width of the emitted spectrum at half the maximum intensity (FWHM).
• Forward Voltage (V_F): Ranges from 2.70V (min) to 3.70V (max), with a typical value of 3.30V at 20mA. This is critical for designing the current-limiting circuit.
• Reverse Current (I_R): Maximum of 50 µA at V_R=5V. This parameter is for test purposes only; the device should not be operated in reverse bias.

3. Binning System Explanation

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

3.1 Luminous Intensity Binning

LEDs are categorized into four bins (N1, N2, P1, P2) based on their measured luminous intensity at I_F=20mA. This allows designers to select the appropriate brightness grade for their application, ensuring uniform appearance in multi-LED arrays.

• Bin N1: 28.5 – 36.0 mcd
• Bin N2: 36.0 – 45.0 mcd
• Bin P1: 45.0 – 57.0 mcd
• Bin P2: 57.0 – 72.0 mcd

3.2 Dominant Wavelength Binning

LEDs are also binned by dominant wavelength into four codes (A9, A10, A11, A12). This tight control (≈3 nm per bin) is crucial for applications requiring precise color matching.

• Bin A9: 464.5 – 467.5 nm
• Bin A10: 467.5 – 470.5 nm
• Bin A11: 470.5 – 473.5 nm
• Bin A12: 473.5 – 476.5 nm

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet, their implications are critical for design.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The I-V characteristic is exponential. A small increase in forward voltage beyond the typical 3.3V can lead to a large, potentially destructive increase in forward current. This underscores the absolute necessity of using an external current-limiting resistor or constant-current driver in series with the LED.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current within the rated limits. Operating below 20mA will reduce output, while exceeding 25mA risks accelerated degradation and reduced lifespan, even if momentarily within the peak current rating.

4.3 Temperature Dependence

LED performance is temperature-sensitive. As junction temperature increases, forward voltage typically decreases slightly, while luminous intensity can decrease significantly. Adequate thermal management on the PCB is important for maintaining consistent brightness, especially in high-density or enclosed applications.

5. Mechanical & Packaging Information

5.1 Package Dimensions

The 27-21 package has nominal dimensions of 2.7mm (length) x 2.1mm (width) x 1.2mm (height), with a standard tolerance of ±0.1mm unless otherwise specified. The detailed dimension drawing provides critical measurements for PCB land pattern design, including pad size, spacing, and component orientation.

5.2 Polarity Identification

The cathode is typically indicated by a visual marker on the LED package, such as a notch, green dot, or cut corner. Correct polarity must be observed during placement to ensure proper operation.

5.3 Tape and Reel Packaging

The device is supplied in 8mm carrier tape on 7-inch diameter reels, compatible with standard automated pick-and-place equipment. Each reel contains 3000 pieces. The packaging includes moisture-resistant materials: an aluminum moisture-proof bag with a desiccant and a humidity indicator card to protect the LEDs from ambient moisture during storage and transport.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A lead-free (Pb-free) reflow profile is specified. Key parameters include: a pre-heating stage between 150-200°C for 60-120 seconds; time above liquidus (217°C) of 60-150 seconds; a peak temperature not exceeding 260°C for a maximum of 10 seconds; and controlled ramp-up and cool-down rates to minimize thermal shock. Reflow should not be performed more than two times.

6.2 Hand Soldering

If hand soldering is necessary, extreme care is required. Use a soldering iron with a tip temperature below 350°C, apply heat to each terminal for no more than 3 seconds, and allow a cooling interval of at least 2 seconds between terminals. The iron power should be 25W or less to prevent localized overheating.

6.3 Moisture Sensitivity and Storage

The LEDs are moisture-sensitive. The sealed moisture-proof bag should not be opened until immediately before use. After opening, unused LEDs must be stored in an environment of 30°C or less and 60% relative humidity or less. The "floor life" after bag opening is 168 hours (7 days). If this time is exceeded or the desiccant indicates saturation, a baking treatment at 60°C ±5°C for 24 hours is required before use.

7. Application Suggestions

7.1 Typical Application Scenarios

• Backlighting: Ideal for dashboard indicators, switch illumination, and symbol backlighting due to its compact size and consistent blue output.
• Telecommunication Equipment: Serves as status indicators or keypad backlights in devices like telephones and fax machines.
• LCD Flat Backlighting: Can be used in arrays for small, low-power LCD displays.
• General Indicator Use: Suitable for power status, mode indication, and other signaling functions in consumer and industrial electronics.

7.2 Design Considerations

• Current Limiting: Always use a series resistor calculated based on the supply voltage (V_CC), the LED's forward voltage (V_F), and the desired forward current (I_F). Formula: R = (V_CC - V_F) / I_F. Use the maximum V_F from the datasheet for a conservative design.
• Thermal Management: Ensure the PCB has adequate copper area connected to the LED pads to act as a heat sink, particularly when operating at or near the maximum current rating.
• ESD Protection: Implement ESD protection measures on sensitive input lines if the LED is user-accessible.

8. Technical Comparison & Differentiation

The 27-21 SMD LED offers several key advantages in its class. Its 2.7x2.1mm footprint is smaller than many traditional 3mm or 5mm through-hole LEDs, saving significant board space. The wide 130° viewing angle provides better off-axis visibility compared to narrower-angle LEDs. The use of InGaN technology yields a bright, saturated blue color with high efficiency. Furthermore, its compliance with RoHS, REACH, and halogen-free standards makes it a future-proof choice for global markets with stringent environmental regulations. The detailed binning system provides designers with the predictability needed for high-volume production requiring visual consistency.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 Why is a current-limiting resistor mandatory?

The LED's I-V characteristic is non-linear. Without a resistor, a small increase in supply voltage causes a large, uncontrolled surge in current, rapidly exceeding the Absolute Maximum Rating of 25mA and leading to immediate failure. The resistor sets a stable operating point.

9.2 Can I drive this LED with a 5V supply?

Yes, but you must use a series resistor. For example, with a 5V supply (V_CC=5V), a typical V_F of 3.3V, and a target I_F of 20mA, the resistor value would be R = (5V - 3.3V) / 0.020A = 85 Ohms. A standard 82 or 100 Ohm resistor would be appropriate, with power rating P = I²R = (0.02)² * 85 = 0.034W, so a 1/8W or 1/10W resistor is sufficient.

9.3 What is the difference between Peak and Dominant Wavelength?

Peak Wavelength (λ_p) is the physical wavelength where the spectral output is highest. Dominant Wavelength (λ_d) is a calculated value that corresponds to the perceived color by the human eye, factoring in the entire emission spectrum and the eye's sensitivity. For monochromatic LEDs like this blue one, they are often close, but λ_d is more relevant for color specification.

9.4 Why is there a strict "floor life" after opening the bag?

SMD LEDs can absorb moisture from the atmosphere through their plastic packaging. During the high-temperature reflow soldering process, this trapped moisture can rapidly expand, causing internal delamination or "popcorning," which cracks the package and destroys the device. The floor life and baking procedures manage this moisture content.

10. Operational Principles

This LED is a semiconductor photonic device. When a forward voltage exceeding its junction potential (approximately 3.3V) is applied, electrons and holes are injected into the active region of the InGaN chip. These charge carriers recombine, releasing energy in the form of photons (light). The specific composition of the InGaN alloy determines the bandgap energy, which directly dictates the wavelength (color) of the emitted light—in this case, blue at around 468 nm. The water-clear resin encapsulation protects the chip and acts as a lens, shaping the emitted light into the specified 130-degree viewing angle.

11. Industry Trends & Context

The 27-21 package represents a mature and widely adopted form factor in the SMD LED market, balancing size, performance, and manufacturability. The industry continues to drive towards even smaller packages (e.g., 2016, 1608) for ultra-miniaturization, and higher-power packages for illumination. Key trends influencing components like this include: increased demand for high-color-accuracy and consistent binning for display applications; the integration of onboard ICs for smart LEDs; and a relentless focus on improving luminous efficacy (lumens per watt) and reliability. Furthermore, environmental compliance (RoHS, halogen-free) has transitioned from a differentiator to a baseline requirement for most electronic components in global supply chains.