Side View Red SMD LED 57-21 Series - Package Dimensions 2.0x1.25x0.7mm - Forward Voltage 1.75-2.35V - Luminous Intensity 45-112mcd - Technical Documentation

1. Product Overview

The 57-21 series represents a family of side-viewing Surface Mount Device (SMD) Light Emitting Diodes (LEDs). This specific document details the red variant, which utilizes an AlGaInP (Aluminum Gallium Indium Phosphide) semiconductor chip to produce brilliant red light. The device is characterized by its compact, low-profile package specifically engineered for applications where space is at a premium and side-emitting illumination is required.

1.1 Core Advantages and Product Positioning

The primary design advantages of this LED series stem from its package architecture. It features a wide viewing angle, typically 120 degrees, which is achieved through an optimized internal reflector design. This makes the component exceptionally suitable for light guide or light pipe applications, where efficient coupling and uniform side illumination are critical. Furthermore, the device operates at low current levels, making it ideal for battery-powered portable electronics and other applications where power consumption is a key concern. The product is manufactured as Pb-free and is compliant with the RoHS (Restriction of Hazardous Substances) directive.

1.2 Target Applications

The combination of a side-view form factor, wide viewing angle, and low power requirement defines its target market. Key application areas include backlighting for full-color Liquid Crystal Displays (LCDs), particularly in slim consumer electronics like mobile phones, tablets, and laptops. It is also suited for status indicators in office automation (OA) equipment and as a modern, efficient replacement for conventional miniature light bulbs in various electronic devices.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified for the device under standard test conditions (Ta=25°C).

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Reverse Voltage (V_R): 5V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Forward Current (I_F): 25 mA DC. The maximum continuous current allowed.
• Peak Forward Current (I_FP): 60 mA. This is permissible only under pulsed conditions (1/10 duty cycle at 1 kHz), useful for multiplexing or brief high-brightness signals.
• Power Dissipation (P_d): 60 mW. The maximum power the package can dissipate as heat.
• Operating & Storage Temperature: -40°C to +85°C and -40°C to +100°C, respectively, indicating suitability for industrial and extended environmental ranges.
• Electrostatic Discharge (ESD): 2000V (Human Body Model). A standard level requiring basic ESD handling precautions during assembly.
• Soldering Temperature: Reflow soldering at 260°C for 10 seconds or hand soldering at 350°C for 3 seconds are specified, defining the thermal profile limits for PCB assembly.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test current of I_F = 10mA and define the device's performance.

• Luminous Intensity (I_v): Ranges from 45 mcd (min) to 112 mcd (max), with a typical tolerance of ±11%. This is the perceived brightness of the red light output.
• Viewing Angle (2θ_1/2): 120 degrees (typical). This is the full angle at which the luminous intensity drops to half of its maximum value, confirming the wide, diffuse emission pattern.
• Dominant Wavelength (λ_d): Between 617.5 nm and 633.5 nm. This defines the perceived color (hue) of the red light. A tolerance of ±1 nm is specified for precise color matching.
• Peak Wavelength (λ_p): Typically 632 nm, indicating the spectral peak of the emitted light, which may differ slightly from the dominant wavelength.
• Spectral Bandwidth (Δλ): Typically 20 nm, describing the width of the emitted spectrum around the peak wavelength.
• Forward Voltage (V_F): Between 1.75V and 2.35V at 10mA, with a tolerance of ±0.1V. This is critical for designing the current-limiting circuitry.
• Reverse Current (I_R): Maximum 10 µA at 5V reverse bias, indicating good junction quality.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. This allows designers to select parts that meet specific requirements for color and brightness.

3.1 Dominant Wavelength Binning

Wavelength bins are grouped under code 'A' and divided into four sub-bins (E4, E5, E6, E7), each covering a 4 nm range from 617.5 nm to 633.5 nm. This allows selection of LEDs with very specific shades of red, crucial for applications requiring consistent color appearance across multiple units.

3.2 Luminous Intensity Binning

Brightness is binned into four groups: P1 (45-57 mcd), P2 (57-72 mcd), Q1 (72-90 mcd), and Q2 (90-112 mcd). This enables selection based on required brightness levels, potentially optimizing power consumption or meeting specific photometric requirements.

3.3 Forward Voltage Binning

Forward voltage is grouped under code 'B' with three bins: 0 (1.75-1.95V), 1 (1.95-2.15V), and 2 (2.15-2.35V). Knowledge of the V_F bin can be important for designing efficient driver circuits, especially in battery-operated devices, to minimize voltage drop and power loss.

4. Performance Curve Analysis

The datasheet includes several characteristic curves that provide deeper insight into device behavior under varying conditions.

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

This curve shows the exponential relationship between current and voltage for a semiconductor diode. For this LED, at 25°C, the voltage rises from approximately 1.6V at very low currents to around 2.8V at 40mA. The curve is essential for determining the operating point and designing an appropriate current-limiting resistor or constant-current driver.

4.2 Relative Luminous Intensity vs. Forward Current

This graph demonstrates that light output increases with current but not linearly. It tends to saturate at higher currents. Furthermore, it shows the effect of pulsed operation (1/10 duty cycle), where higher peak currents can be used to achieve momentary higher brightness without exceeding the average power dissipation limits.

4.3 Forward Current Derating Curve

This is a critical thermal management graph. It shows the maximum allowable continuous forward current as a function of the ambient temperature (T_a). As temperature increases, the maximum current must be reduced to prevent overheating. For example, at 85°C, the maximum continuous current is significantly lower than the 25mA rating at 25°C.

4.4 Spectrum Distribution

The spectral plot confirms the monochromatic nature of the LED, showing a single peak around 632 nm with a typical bandwidth of 20 nm. There is minimal emission in other parts of the visible spectrum, which is characteristic of a high-purity red AlGaInP LED.

4.5 Radiation Pattern (Polar Diagram)

This diagram visually represents the 120-degree viewing angle. The intensity is plotted on a polar graph, showing a broad, Lambertian-like emission pattern where intensity is highest at 0 degrees (perpendicular to the chip) and decreases smoothly to 50% at ±60 degrees from the center.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Footprint

The device has a compact side-view SMD package. Key dimensions include a body length of approximately 2.0 mm, a width of 1.25 mm, and a height of 0.7 mm. Detailed mechanical drawings specify all critical dimensions, including pad locations and tolerances (typically ±0.1mm), which are essential for PCB layout and ensuring proper soldering and alignment.

5.2 Polarity Identification

The cathode is typically identified by a marked corner or a notch on the package. Correct polarity must be observed during placement to ensure proper operation.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

The component is rated for lead-free reflow soldering processes with a peak temperature of 260°C for up to 10 seconds. This aligns with standard IPC/JEDEC J-STD-020 profiles. Hand soldering with an iron is also permissible at 350°C for a maximum of 3 seconds per lead, requiring careful technique to avoid thermal damage.

6.2 Moisture Sensitivity and Storage

The LEDs are packaged in moisture-resistant barrier bags with desiccant to prevent moisture absorption, which can cause \"popcorning\" (package cracking) during reflow. Once the sealed bag is opened, the components should be used within a specified time frame (not explicitly stated but implied by the packaging) or baked according to standard MSL (Moisture Sensitivity Level) procedures before soldering.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

For automated assembly, the components are supplied on embossed carrier tape wound onto reels. The tape width, pocket spacing, and reel dimensions are specified to be compatible with standard SMD pick-and-place equipment. Each reel contains 500 pieces.

7.2 Label Explanation and Part Numbering

The reel label contains critical information for traceability and correct application: Part Number (PN), Customer Part Number (CPN), quantity (QTY), lot number (LOT NO), and the specific performance bins for Luminous Intensity (CAT), Dominant Wavelength (HUE), and Forward Voltage (REF). The part number 57-21/R6C-AP1Q2B/BF likely encodes the series, color, and specific bin codes.

8. Reliability and Qualification Testing

The product undergoes a suite of reliability tests conducted with a 90% confidence level and a Lot Tolerance Percent Defective (LTPD) of 10%. Key tests include:

• Reflow Soldering: Verifies survivability through the assembly thermal profile.
• Temperature Cycling & Thermal Shock: Tests robustness against thermal expansion stresses from -40°C to +100°C.
• High/Low Temperature Storage: Assesses long-term stability under extreme non-operating conditions.
• DC Operating Life: A 1000-hour life test at 20mA to evaluate performance degradation over time.
• High Temperature/Humidity (85°C/85% RH): Tests resistance to damp heat, which can cause corrosion or other failures.

9. Application Suggestions and Design Considerations

9.1 Typical Application Circuits

The most common drive method is a simple series resistor. The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Using the maximum V_F (2.35V) for calculation ensures the current does not exceed the desired level even with part-to-part variation. For example, with a 5V supply and a target I_F of 10mA: R = (5V - 2.35V) / 0.01A = 265 Ω. A standard 270 Ω resistor would be suitable. For applications requiring stable brightness or operation from a variable voltage source (like a battery), a constant-current driver is recommended.

9.2 Design for Light Pipe Coupling

The wide viewing angle and package design are optimized for light pipes. For best results, the LED should be positioned as close as possible to the entrance of the light guide. The material and finish of the light pipe (e.g., acrylic, polycarbonate) and any bends or features will affect the final light output uniformity and efficiency. Optical simulation or prototyping is often necessary for complex designs.

9.3 Thermal Management Considerations

While the power dissipation is low, continuous operation at high ambient temperatures or high currents requires attention. The derating curve must be followed. Ensuring adequate copper area around the PCB pads helps dissipate heat and maintain LED performance and longevity.

10. Technical Comparison and Differentiation

The key differentiators of this side-view LED series are its specific combination of attributes: the side-emitting form factor, the very wide 120-degree viewing angle facilitated by the integrated reflector, and the use of AlGaInP technology for high-efficiency red light. Compared to top-view LEDs, it provides illumination parallel to the PCB plane, which is essential for edge-lighting displays. Compared to other side-view LEDs, its optimized internal reflector aims for higher coupling efficiency into light guides. The low forward voltage of the AlGaInP chip also contributes to higher overall electrical efficiency compared to some older technologies.

11. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED at 20mA continuously?
A: Yes, the Absolute Maximum Rating for continuous forward current is 25mA, so 20mA is within the safe operating area, provided the ambient temperature is within limits (refer to the derating curve).

Q: Why is there such a wide range in Luminous Intensity (45-112 mcd)?
A: This is the full production spread. Through the binning system (P1, P2, Q1, Q2), manufacturers and customers can select parts within a much tighter brightness range to ensure consistency in their final product.

Q: What is the difference between Dominant and Peak Wavelength?
A: Peak Wavelength (λ_p) is the single point of highest spectral power. Dominant Wavelength (λ_d) is a calculated value that best represents the perceived color by the human eye, taking the entire emission spectrum and the eye's sensitivity into account. λ_d is more relevant for color specification.

Q: Is a current-limiting resistor always necessary?
A: Yes. An LED is a current-driven device. Its forward voltage is relatively constant, but current can increase rapidly with small voltage increases. A resistor or active constant-current circuit is essential to prevent thermal runaway and destruction of the LED.

12. Practical Use Case Example

Scenario: Designing a status indicator for a portable medical device.
The device requires a red \"standby/charging\" indicator visible from the side. A 57-21 series LED in the Q1 brightness bin (72-90 mcd) is selected for adequate visibility. The device is powered by a 3.3V regulated supply. Targeting a conservative I_F of 8mA for long battery life and using the max V_F of 2.35V for a worst-case calculation: R = (3.3V - 2.35V) / 0.008A = 118.75 Ω. A 120 Ω resistor is chosen. The LED is placed on the edge of the PCB, aligned with a molded acrylic light pipe that directs the light to a small window on the device casing. The wide viewing angle ensures the indicator is visible even when the device is viewed from an oblique angle.

13. Operational Principle Introduction

Light emission in this LED is based on electroluminescence in a semiconductor p-n junction made of AlGaInP. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region where they recombine. The energy released during this recombination is emitted as photons (light). The specific composition of the AlGaInP alloy determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light, in this case, in the red spectrum (~632 nm). The internal reflector and clear epoxy lens shape the light output into the desired wide-angle pattern.

14. Technology Trends and Context

Side-view SMD LEDs like the 57-21 series represent a mature and optimized solution for space-constrained backlighting and indication. The trend in this segment continues towards even smaller package sizes (e.g., 1.0mm height or less), higher efficiency (more lumens per watt), and improved color consistency through tighter binning. Furthermore, there is integration with other components, such as LEDs with built-in current-limiting resistors or IC drivers. While newer technologies like Micro-LEDs and advanced OLEDs are emerging for direct-display applications, the simplicity, reliability, and cost-effectiveness of discrete side-view LEDs ensure their continued relevance in secondary illumination and status indication roles for the foreseeable future.