SMD LED 42-21A Blue Datasheet - Package 2.0x1.25x1.1mm - Voltage 2.7-3.7V - Power 95mW - English Technical Document

1. Product Overview

The 42-21A is a compact, surface-mount blue LED designed for modern electronic applications requiring high reliability and efficient assembly. Utilizing InGaN chip technology, this component emits blue light with a typical dominant wavelength of 468 nm. Its primary advantage lies in its miniature footprint, which enables significant reductions in PCB size and allows for higher packing densities compared to traditional lead-frame LEDs. This contributes directly to the miniaturization of end-user equipment. The device is supplied on 8mm tape mounted on 7-inch diameter reels, making it fully compatible with automated pick-and-place assembly lines, thereby streamlining high-volume manufacturing processes.

2. Key Features and Compliance

The LED incorporates several features critical for contemporary design and manufacturing:

• Packaged on 8mm tape for 7-inch reels, optimized for automated assembly.
• Compatible with both infrared (IR) and vapor phase reflow soldering processes.
• Constructed as a mono-color (blue) type.
• Manufactured as a Pb-free (lead-free) component.
• The product complies with the RoHS (Restriction of Hazardous Substances) directive.
• Compliance with EU REACH regulations is maintained.
• Classified as Halogen-Free, with bromine (Br) content below 900 ppm, chlorine (Cl) content below 900 ppm, and the combined total of Br+Cl below 1500 ppm.

3. Target Applications

The 42-21A LED is suited for a variety of indicator and backlighting functions, including:

• Backlighting for automotive dashboards and switches.
• Status indicators and keypad backlighting in telecommunication devices such as telephones and fax machines.
• Flat backlighting units for LCD displays, switches, and symbols.
• General-purpose indicator applications.

4. Absolute Maximum Ratings

The following ratings define the limits beyond which permanent damage to the device may occur. All values are specified at an ambient temperature (Ta) of 25°C.

5. Electro-Optical Characteristics

The typical performance parameters are measured at Ta=25°C and a forward current (I_F) of 20 mA. These are the key specifications for design calculations.

Note on Tolerances: Luminous intensity has a tolerance of ±11%, dominant wavelength ±1 nm, and forward voltage ±0.1 V from the typical or binned values.

6. Binning System Explanation

To ensure consistency in production runs, LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific performance windows for their application.

6.1 Luminous Intensity Binning

Bins are defined by a code (V1, V2, W1, W2) specifying a minimum and maximum luminous intensity range measured at I_F=20mA.

6.2 Dominant Wavelength Binning

Wavelength is binned into groups based on the dominant wavelength (λ_d).

6.3 Forward Voltage Binning

Forward voltage (V_F) is categorized into bins numbered 10 through 14, each covering a 0.2V range.

7. Mechanical and Package Information

7.1 Package Dimensions

The 42-21A LED has a compact SMD package. Key dimensions (in millimeters) are as follows, with a general tolerance of ±0.1mm unless otherwise specified:

• Package Length: 2.0 mm
• Package Width: 1.25 mm
• Package Height: 1.1 mm

A detailed dimensioned drawing is provided in the datasheet, showing the body outline, lead positions, and recommended land pattern.

7.2 Polarity Identification

The cathode is clearly marked. On the package, the cathode is typically indicated by a distinctive feature such as a notch, a dot, or a chamfered corner. The corresponding cathode marking is also shown on the recommended solder mask design for the PCB footprint. Correct polarity orientation is crucial for proper circuit function.

8. Soldering and Assembly Guidelines

8.1 Reflow Soldering Profile

The component is rated for lead-free (Pb-free) reflow soldering processes. The maximum recommended peak soldering temperature is 260°C, with the time above 260°C not exceeding 10 seconds. A typical reflow temperature profile should be followed to prevent thermal shock and ensure reliable solder joints. It is critical to avoid applying mechanical stress to the LED body during the heating and cooling phases of reflow.

8.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken. The soldering iron tip temperature should be below 350°C, and contact time with any single terminal should not exceed 3 seconds. A low-power iron (25W or less) is recommended. A cooling interval of at least 2 seconds should be observed between soldering the two terminals to prevent excessive heat buildup.

8.3 Rework and Repair

Rework after the initial soldering is strongly discouraged. If absolutely unavoidable, a specialized double-head soldering iron should be used to simultaneously heat both terminals, allowing for removal without applying torsional stress to the package. The potential for damaging the LED's internal wire bonds or degrading its optical performance during rework is high, and pre-testing the rework procedure is advised.

9. Storage and Handling Precautions

9.1 Moisture Sensitivity

The LEDs are packaged in a moisture-resistant barrier bag with desiccant to prevent absorption of atmospheric moisture, which can cause "popcorning" (package cracking) during reflow. Key storage rules:

• Before Opening: Store at ≤30°C and ≤90% Relative Humidity (RH).
• After Opening: The "floor life" (time exposed to ambient factory conditions) is 1 year when stored at ≤30°C and ≤60% RH.
• Rebagging: Unused devices should be resealed in a moisture-proof bag with fresh desiccant.
• Baking: If the desiccant indicator shows saturation or the floor life is exceeded, a bake at 60±5°C for 24 hours is required before reflow to drive out moisture.

9.2 Electrostatic Discharge (ESD) Protection

With an ESD rating of 150V (HBM), this device is sensitive to electrostatic discharge. Standard ESD handling procedures must be followed during all assembly and handling stages, including the use of grounded workstations, wrist straps, and conductive containers.

10. Packaging and Ordering Information

10.1 Tape and Reel Specifications

The product is supplied in embossed carrier tape with dimensions tailored for the 42-21A package. The tape is wound onto a standard 7-inch (178mm) diameter reel. Each reel contains 1000 pieces of the LED. Detailed drawings for the carrier tape pocket dimensions, pitch, and reel hub/flange dimensions are provided to ensure compatibility with automated assembly equipment feeders.

10.2 Label Information

The reel and outer bag include labels with critical information for traceability and correct application:

• CPN: Customer's Part Number (if assigned).
• P/N: Manufacturer's Product Number (e.g., 42-21A/BHC-ZV1W2N/1T).
• QTY: Packing Quantity (e.g., 1000 pcs).
• CAT: Luminous Intensity Rank (e.g., W2).
• HUE: Chromaticity/Dominant Wavelength Rank (e.g., Z).
• REF: Forward Voltage Rank (e.g., N12).
• LOT No: Manufacturing Lot Number for traceability.

11. Application Design Considerations

11.1 Current Limiting

This is a critical design rule. An LED is a current-driven device. A series current-limiting resistor must be used in the circuit. The forward voltage (V_F) has a range (2.7V to 3.7V) and a negative temperature coefficient. Connecting the LED directly to a voltage source, even one nominally within the V_F range, can lead to a runaway current condition due to minor variations, resulting in immediate failure (burn-out). The resistor value should be calculated based on the supply voltage, the maximum expected V_F from the bin, and the desired forward current (I_F), which must not exceed 25 mA continuous.

11.2 Thermal Management

While the power dissipation is low (95 mW max), proper thermal design on the PCB is still important for long-term reliability, especially when operating at high ambient temperatures or at the maximum current. Ensuring adequate copper area around the LED pads helps dissipate heat and maintains stable optical output and lifespan.

11.3 Optical Design

The 20-degree viewing angle (2θ_1/2) indicates a relatively focused beam. This makes the 42-21A suitable for applications requiring directed illumination or a bright, concentrated spot. For wider area illumination, secondary optics (e.g., light guides, diffusers) would be necessary. Designers should account for the binning ranges of luminous intensity and wavelength to ensure consistent brightness and color appearance across multiple units in an array or display.

12. Technical Comparison and Differentiation

The 42-21A represents a specific class of miniature, reflector-type SMD LEDs. Its key differentiators include its very small 2.0x1.25mm footprint, which is smaller than many common "chip" LEDs, allowing for higher density layouts. The integrated reflector cup provides a controlled, 20-degree viewing angle without the need for an external lens, simplifying optical design. The comprehensive binning system for intensity, wavelength, and voltage offers designers the ability to specify tight performance windows for applications requiring high uniformity, such as backlighting arrays. Its compliance with Halogen-Free and other environmental standards makes it suitable for products targeting global markets with strict regulatory requirements.

13. Frequently Asked Questions (FAQs)

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

Peak Wavelength (λ_p): The single wavelength at which the optical output power of the LED is at its maximum. It's the highest point on the spectral distribution curve.
Dominant Wavelength (λ_d): The single wavelength of monochromatic light that matches the perceived color of the LED's output to the human eye. It is calculated from the chromaticity coordinates and is often more relevant for color-based applications. For this blue LED, the typical values are very close (468 nm peak vs. binned 465-475 nm dominant).

13.2 Can I drive this LED with a constant voltage source?

No. As emphasized in the design considerations, LEDs require current regulation. A constant voltage source, even set to the typical V_F, does not account for unit-to-unit variation (binning), temperature effects (V_F decreases as temperature rises), or power supply tolerances. This will almost certainly lead to overcurrent and device failure. Always use a series resistor or a dedicated constant-current LED driver circuit.

13.3 How many times can I reflow solder this component?

The datasheet specifies that reflow soldering should not be performed more than two times. Each reflow cycle subjects the component to thermal stress, which can degrade internal materials, weaken wire bonds, or compromise the moisture resistance of the package. If a board requires rework, it is preferable to replace the LED rather than subject it to a third reflow cycle.

13.4 Is this LED suitable for automotive or medical applications?

The datasheet includes an Application Restrictions section stating that high-reliability applications such as automotive safety/security systems, medical equipment, military, and aerospace may require a different, more rigorously qualified product. The standard 42-21A is intended for commercial and industrial applications. For safety-critical uses, consult the manufacturer for products specifically designed and tested to meet the relevant industry standards (e.g., AEC-Q101 for automotive).

14. Practical Application Example

Scenario: Designing a status indicator panel with 10 uniform blue LEDs.

1. Circuit Design: A 5V supply is available. Using the maximum V_F from bin N14 (3.7V) and a target I_F of 20 mA, calculate the series resistor: R = (V_supply - V_F) / I_F = (5V - 3.7V) / 0.020A = 65 Ohms. The nearest standard value of 68 Ohms would result in I_F ≈ 19.1 mA, which is safe and within spec. One resistor is needed per LED.
2. Component Selection: To ensure visual uniformity, specify tight bins. For example, order all LEDs from luminous intensity bin W1 (1120-1420 mcd) and dominant wavelength bin Z/X (465-470 nm). This minimizes brightness and color variation across the panel.
3. PCB Layout: Place the LEDs on a 0.1" grid. Use the recommended land pattern from the datasheet. Include a small thermal relief pad connected to a ground plane for heat dissipation. Clearly mark the cathode orientation on the silkscreen.
4. Assembly: Keep reels in sealed bags until ready for use. Follow the 260°C peak reflow profile. After assembly, avoid flexing the PCB near the LEDs.

15. Operating Principle

The 42-21A LED is based on a semiconductor chip made from Indium Gallium Nitride (InGaN). When a forward voltage exceeding the diode's turn-on threshold is applied, electrons and holes are injected into the active region of the semiconductor. These charge carriers recombine, releasing energy in the form of photons (light). The specific composition of the InGaN alloy determines the bandgap energy, which in turn defines the wavelength (color) of the emitted light—in this case, blue. The light is emitted from the chip and is directed by an integrated reflector cup within the package to achieve the specified 20-degree viewing angle. The epoxy resin encapsulant protects the chip and wire bonds while also acting as a primary lens.

16. Technology Trends

SMD LEDs like the 42-21A are part of a continuous trend toward miniaturization, increased efficiency, and enhanced reliability in solid-state lighting. Advances in epitaxial growth techniques for InGaN materials have steadily improved internal quantum efficiency, allowing for higher luminous output from smaller chips. Packaging technology has evolved to provide better thermal paths (e.g., exposed thermal pads) and more precise optical control. Furthermore, industry-wide drivers include the push for higher levels of environmental compliance (beyond RoHS to Halogen-Free, lower carbon footprint) and the integration of smart features, though the latter is more relevant for higher-power or addressable LED packages. The demand for consistent performance, enabled by sophisticated binning systems as seen with this component, remains critical for applications in consumer electronics, displays, and automotive interiors where visual quality is paramount.