SMD LED 42-21/BHC-AUW/1T Specification - Blue - 2.1x2.1x1.2mm - 3.3V - 20mA - English Technical Document

1. Product Overview

The 42-21/BHC-AUW/1T is a compact, surface-mount LED designed for modern electronic applications requiring reliable, low-power indicator or backlighting solutions. This blue LED utilizes InGaN chip technology, encapsulated in a water-clear resin, to deliver consistent performance in a miniature footprint. Its primary advantages include significant space savings on PCBs, high packing density, and suitability for automated assembly processes, making it ideal for high-volume manufacturing.

The component is fully compliant with RoHS, EU REACH, and halogen-free standards, ensuring environmental responsibility and broad market acceptance. Its lightweight construction and small size enable the design of smaller, more portable equipment.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

The device's operational limits are defined to ensure long-term reliability. Exceeding these ratings may cause permanent damage.

• Reverse Voltage (V_R): 5V. A protective circuit is recommended if reverse voltage conditions are possible.
• Continuous Forward Current (I_F): 25mA. The typical operating condition is 20mA.
• Peak Forward Current (I_FP): 100mA (Duty 1/10 @1KHz). Suitable for pulsed operation but not for DC.
• Power Dissipation (P_d): 95mW. This limit considers both electrical and thermal constraints.
• Operating & Storage Temperature: -40°C to +85°C / -40°C to +90°C. This wide range supports industrial applications.
• Electrostatic Discharge (ESD): 150V (HBM). Standard ESD precautions during handling are necessary.
• Soldering Temperature: Reflow: 260°C for 10 sec; Hand: 350°C for 3 sec. Adherence is critical to prevent thermal damage.

2.2 Electro-Optical Characteristics (T_a=25°C)

These parameters define the LED's performance under standard test conditions (I_F=20mA).

• Luminous Intensity (I_v): 450 to 1800 mcd (millicandela). The wide range is managed through a binning system.
• Viewing Angle (2θ_1/2): 30 degrees (typical). This defines the angular spread of emitted light.
• Peak Wavelength (λ_p): 468 nm (typical). The wavelength at which the spectral power is maximum.
• Dominant Wavelength (λ_d): 464.5 to 476.5 nm. This is the perceived color of the light, with a tolerance of ±1nm.
• Spectral Bandwidth (Δλ): 25 nm (typical). The width of the emitted spectrum at half the maximum intensity.
• Forward Voltage (V_F): 2.7V to 3.7V, with a typical value of 3.3V at 20mA.
• Reverse Current (I_R): Maximum 50 µA at V_R=5V.

Critical Design Note: The forward voltage has a range. A current-limiting resistor is absolutely mandatory to prevent thermal runaway and burnout from minor supply voltage fluctuations. The resistor value must be calculated based on the actual supply voltage and the maximum expected V_F to ensure I_F does not exceed 25mA.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins. The 42-21 uses two independent binning systems.

3.1 Luminous Intensity Binning

LEDs are categorized by their measured light output at I_F=20mA. The bin code is marked for identification.

• Bin U: 450 – 715 mcd
• Bin V: 715 – 1120 mcd
• Bin W: 1120 – 1800 mcd

Tolerance: ±11%

3.2 Dominant Wavelength Binning

LEDs are also sorted by their precise shade of blue to maintain color uniformity in an array.

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

Tolerance: ±1nm

Design Implication: For applications requiring matched brightness or color (e.g., multi-LED backlights, status bars), specifying a single bin or requesting tight binning from the supplier is crucial.

4. Mechanical and Packaging Information

4.1 Physical Dimensions

The LED has a compact SMD package. Key dimensions (tolerance ±0.1mm unless noted):

• Package Size: Approximately 2.1mm x 2.1mm.
• Height: Approximately 1.2mm.
• The cathode is identified by a specific marking on the package body.

4.2 Polarity Identification

Correct polarity is essential. The cathode terminal is clearly indicated on the component's body. The recommended PCB land pattern (footprint) should mirror this design to ensure proper alignment during reflow soldering.

4.3 Packaging Specifications

The LEDs are supplied in industry-standard packaging for automated assembly:

• Carrier Tape: 8mm width, on 7-inch diameter reels.
• Quantity per Reel: 1000 pieces.
• Moisture Sensitivity: Packed in a moisture-resistant aluminum bag with desiccant to prevent moisture absorption, which can cause "popcorn" cracking during reflow.

The reel label contains critical information: Product Number (P/N), quantity (QTY), luminous intensity bin (CAT), dominant wavelength bin (HUE), forward voltage rank (REF), and lot number (LOT No).

5. Soldering and Assembly Guidelines

5.1 Reflow Soldering Profile

The component is compatible with infrared and vapor phase reflow processes. A lead-free (Pb-free) soldering profile is required:

• Peak Temperature: 260°C maximum.
• Time Above Liquidus: Recommended 30-60 seconds.
• Preheat: Gradual ramp-up to activate flux and minimize thermal shock.

Critical: Reflow soldering should not be performed more than two times on the same LED assembly.

5.2 Hand Soldering

If manual repair is unavoidable, extreme care must be taken:

• Iron Temperature: Less than 350°C.
• Contact Time: 3 seconds or less per terminal.
• Iron Power: Less than 25W.
• Method: Use a double-head soldering iron to heat both terminals simultaneously and avoid mechanical stress on the solder joints. Confirm LED functionality after any repair.

5.3 Storage and Handling

• Before Opening Bag: Store at ≤30°C and ≤90% RH.
• After Opening Bag (Floor Life): 1 year at ≤30°C and ≤60% RH. Unused parts must be resealed in a moisture-proof bag with fresh desiccant.
• Baking: If the bag is opened beyond the floor life or desiccant is saturated, bake at 60±5°C for 24 hours before reflow to drive out moisture.
• Do not bend or warp the PCB after soldering, as this can stress the LED solder joints and cause failure.

6. Application Notes and Design Considerations

6.1 Typical Applications

• Instrument Panel Backlighting: Illumination for dashboard indicators and switches.
• Telecommunication Devices: Status indicators and keypad backlighting in phones and fax machines.
• LCD Backlighting: Edge or direct backlighting for small monochrome or color LCDs.
• General Indication: Power status, mode indicators, and other user interface elements.

6.2 Circuit Design

The most critical aspect of the drive circuit is the series current-limiting resistor. Its value (R_s) can be calculated using Ohm's Law: R_s = (V_supply - V_F) / I_F.

Example: For a 5V supply and using the maximum V_F of 3.7V to ensure safe current under all conditions at I_F=20mA:
R_s = (5V - 3.7V) / 0.020A = 65 Ohms.
The nearest standard value (e.g., 68 Ohms) would be selected, and the resistor's power rating should be checked: P = I²R = (0.02)² * 68 = 0.0272W. A standard 1/10W (0.1W) resistor is more than sufficient.

6.3 Thermal Management

While the power dissipation is low (95mW max), proper PCB layout aids longevity. Ensure adequate copper area around the LED pads to act as a heat sink, especially if operating at high ambient temperatures or near the maximum current.

6.4 Application Restrictions

This standard commercial-grade LED is not specifically designed or qualified for high-reliability applications where failure could lead to safety risks or significant property damage. This includes, but is not limited to:

• Military, aerospace, or aviation safety systems.
• Automotive safety-critical systems (e.g., brake lights, airbag indicators).
• Medical life-support or diagnostic equipment.

For such applications, components with appropriate automotive, military, or medical qualifications must be sourced. The performance is guaranteed only within the specifications outlined in this document.

7. Technical Comparison and Positioning

The 42-21 package represents a balance between size, performance, and manufacturability. Compared to larger lead-frame LEDs (e.g., 3mm or 5mm through-hole types), it offers a drastic reduction in board space and weight, enabling modern miniaturized designs. Compared to smaller chip-scale packages (CSP), it offers easier handling with standard SMT equipment and provides a molded lens for controlled light distribution (30-degree viewing angle). Its 20mA drive current and 3.3V typical V_F make it directly compatible with common 3.3V and 5V logic supplies with a simple resistor.

8. Frequently Asked Questions (FAQ)

8.1 Why is a current-limiting resistor mandatory?

LEDs are current-driven devices. Their V-I characteristic is exponential. A small increase in voltage beyond the nominal V_F causes a large, potentially destructive increase in current. A series resistor provides a linear, predictable relationship between supply voltage and LED current, ensuring stable and safe operation.

8.2 Can I drive this LED directly from a microcontroller GPIO pin?

Possibly, but with caution. Many GPIO pins can source or sink only 10-25mA. You must check your microcontroller's datasheet. Even if within limits, you still need a series resistor. It is often safer to use the GPIO to control a transistor (BJT or MOSFET) which then drives the LED, isolating the MCU from the LED current load.

8.3 What does "water clear" resin mean?

It means the encapsulating plastic lens is transparent, not diffused or tinted. This allows the true color of the blue InGaN chip to be seen, providing the highest possible light output and a well-defined, narrow viewing angle.

8.4 How do I interpret the bin codes on the reel label?

The "CAT" code (U, V, W) tells you the brightness range. The "HUE" code (e.g., A10) tells you the dominant wavelength range. For consistent appearance in a product, order LEDs from the same CAT and HUE bin. The "REF" code indicates the forward voltage ranking, which can be useful for precise current regulation designs.

9. Practical Design Case Study

Scenario: Designing a compact USB-powered device with four blue status LEDs.

1. Power Source: USB provides 5V.
2. LED Selection: 42-21/BHC-AUW/1T, Bin V for medium brightness, Bin A11 for consistent blue hue.
3. Current Calculation: Target I_F = 18mA (slightly below max for margin). Use max V_F = 3.7V for worst-case.
   R_s = (5V - 3.7V) / 0.018A ≈ 72.2Ω. Use 75Ω standard resistor.
4. Power per LED: P_LED = 3.3V(typ) * 0.018A ≈ 59.4mW. Well within 95mW limit.
5. Total Current: 4 LEDs * 18mA = 72mA. Well within a standard USB port's 500mA capability.
6. PCB Layout: Place LEDs with correct polarity. Use a small ground pour under and around the LED pads for heat dissipation. Ensure the reflow profile matches the recommended 260°C peak.
7. Result: A reliable, consistently bright indicator system with minimal board space and power consumption.

10. Operating Principle and Technology

This LED is based on a semiconductor heterostructure made of Indium Gallium Nitride (InGaN). When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. Their recombination releases energy in the form of photons (light). The specific composition of the InGaN alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, blue (~468 nm). The water-clear epoxy resin encapsulant protects the semiconductor chip, acts as a lens to shape the light output beam (30-degree viewing angle), and provides mechanical stability.

11. Industry Trends

The market for SMD LEDs like the 42-21 continues to be driven by the miniaturization of all electronic devices. There is a constant trend toward higher efficiency (more lumens per watt), which allows for either brighter output at the same current or the same brightness at lower power, extending battery life in portable devices. Additionally, demand for tighter color and brightness binning is increasing as applications like full-color displays and ambient lighting require exceptional uniformity. The underlying InGaN technology for blue LEDs is mature but continues to see incremental improvements in efficiency and reliability. The packaging technology is also evolving, with trends toward even thinner profiles and improved thermal management materials to handle higher power densities in compact spaces.