SMD3528 Red LED Datasheet - Size 3.5x2.8mm - Voltage 2.2V - Power 0.144W - English Technical Document

1. Product Overview

The SMD3528 is a surface-mount device (SMD) light-emitting diode (LED) utilizing a single-chip red LED die. Characterized by its compact footprint of 3.5mm x 2.8mm, this component is designed for applications requiring reliable, low-power red illumination. Its primary advantages include a wide 120-degree viewing angle, consistent performance across a specified temperature range, and compatibility with standard surface-mount technology (SMT) assembly processes. The target market encompasses a broad range of consumer electronics, indicator lights, backlighting for small displays, and decorative lighting where space and power efficiency are critical.

2. Technical Parameter Deep Dive

2.1 Electrical Parameters

The electrical characteristics define the operating boundaries and typical performance of the LED. The absolute maximum ratings, measured at a solder point temperature (T_s) of 25°C, establish the limits for safe operation. The maximum continuous forward current (I_F) is 30 mA, while a forward pulse current (I_FP) of up to 40 mA is permissible under specific conditions (pulse width ≤10 ms, duty cycle ≤1/10). The maximum power dissipation (P_D) is rated at 144 mW. The operating and storage temperature range is specified from -40°C to +80°C, with a maximum junction temperature (T_j) of 125°C. For soldering, the LED can withstand a reflow profile with a peak temperature of either 230°C or 260°C for a duration of 10 seconds.

Under typical operating conditions (T_s=25°C, I_F=20mA), the forward voltage (V_F) has a typical value of 2.2V and a maximum of 2.6V. The reverse voltage (V_R) is rated at a minimum of 5V, and the reverse current (I_R) should not exceed 10 µA.

2.2 Optical Parameters

The optical performance is central to the LED's function. The dominant wavelength (λ_d) is specified at 625 nm, placing it in the standard red spectrum. The luminous flux output is categorized into bins, with typical values ranging from 1.5 lm to 2.5 lm at a drive current of 20 mA, depending on the specific bin code (A3, B1, B2). The spatial distribution of light is characterized by a wide viewing angle, with 2θ_1/2 (the full angle at half intensity) specified as 120 degrees.

2.3 Thermal Characteristics

Thermal management is crucial for LED longevity and performance stability. The key parameter is the junction temperature (T_j), which must not exceed 125°C. The thermal path from the LED chip to the solder point and ultimately to the printed circuit board (PCB) must be designed to keep the junction temperature within safe limits during operation, especially when driven at or near the maximum current. The specified operating ambient temperature range of -40°C to +80°C provides guidance for the environmental conditions the device can endure.

3. Binning System Explanation

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

3.1 Wavelength Binning

The dominant wavelength is binned to control the precise shade of red. The provided specification lists two bins: R1 (620-625 nm) and R2 (625-630 nm). This allows designers to select LEDs with a very specific color point for their application, which is vital for applications like full-color displays or signage where color matching is critical. The tolerance for wavelength measurement is inherent in the bin range.

3.2 Luminous Flux Binning

Luminous flux output is categorized to guarantee a minimum level of brightness. The bins are defined by codes A3, B1, and B2, with minimum/typical values of 1/1.5 lm, 1.5/2 lm, and 2/2.5 lm respectively, all measured at 20 mA. A tolerance of ±7% applies to the luminous flux measurement. This binning allows for predictable brightness levels in an array of LEDs.

3.3 Forward Voltage Binning

The forward voltage is binned to aid in circuit design, particularly for current-limiting resistor calculation and power supply design in series-connected strings. The bins are C (1.8-2.0V), D (2.0-2.2V), E (2.2-2.4V), and F (2.4-2.6V), with a measurement tolerance of ±0.08V. Matching V_F bins can help ensure uniform current distribution and brightness in parallel LED configurations.

4. Performance Curve Analysis

4.1 IV Characteristic Curve

The forward voltage versus forward current (V_F-I_F) curve is a fundamental characteristic of any diode, including LEDs. For this SMD3528 red LED, the curve will show the exponential relationship typical of a semiconductor p-n junction. The curve is essential for determining the operating point and for designing the driver circuit. The voltage at the typical operating current of 20mA will fall within the binned V_F range (e.g., ~2.2V for bin D).

4.2 Relative Luminous Flux vs. Forward Current

This curve illustrates how the light output (relative luminous flux) changes with increasing drive current. For LEDs, the output generally increases linearly with current at lower levels but may exhibit saturation or reduced efficiency at higher currents due to thermal and electrical effects. This graph helps designers optimize the drive current for the desired brightness while considering efficacy and lifetime.

4.3 Temperature Dependence

The performance of LEDs is significantly affected by temperature. A key curve shows the relative spectral energy (a proxy for light output and wavelength stability) as a function of junction temperature. For AlInGaP-based red LEDs, the light output typically decreases as temperature increases. This curve is critical for applications operating in varying thermal environments, informing necessary derating or thermal compensation in the drive circuitry.

4.4 Spectral Distribution

The spectral energy distribution curve plots the intensity of light emitted across different wavelengths. For a monochromatic red LED, this curve will show a single, dominant peak centered around the binned wavelength (e.g., 625 nm). The width of this peak (full width at half maximum, or FWHM) determines the color purity. A narrower peak indicates a more saturated, pure color.

5. Mechanical & Packaging Information

5.1 Dimensions and Outline Drawing

The LED package conforms to the industry-standard 3528 footprint, with nominal dimensions of 3.5mm in length and 2.8mm in width. The exact dimensional drawing provides critical measurements including package height, lens dimensions, and lead (pad) spacing. Tolerances are specified: dimensions noted as .X have a tolerance of ±0.10mm, while .XX dimensions have a tighter tolerance of ±0.05mm.

5.2 Recommended Pad Layout & Stencil Design

A recommended land pattern (footprint) for PCB design is provided to ensure proper soldering and mechanical stability. This includes the size, shape, and spacing of the copper pads. A corresponding stencil design (solder paste mask) is also suggested to control the volume of solder paste deposited during assembly, which is crucial for achieving reliable solder joints without causing shorts or tombstoning.

5.3 Polarity Identification

The cathode (negative terminal) is typically identified by a visual marker on the LED package, such as a green dot, a notch, or a chamfered corner. The datasheet should clearly indicate this marking scheme. Correct polarity must be observed during placement on the PCB to ensure the device functions.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Parameters

The component is suitable for infrared (IR) or convection reflow soldering processes. The maximum permissible solder temperature is specified as 230°C or 260°C, measured at the LED leads, for a maximum duration of 10 seconds. A standard lead-free (SAC305) reflow profile with a preheat, soak, reflow, and cooling phase should be followed, ensuring the peak temperature and time above liquidus (TAL) do not exceed the LED's ratings.

6.2 Handling and Storage Precautions

LEDs are sensitive to electrostatic discharge (ESD). They should be handled in an ESD-protected environment using grounded wrist straps and conductive work surfaces. The devices should be stored in their original moisture-barrier bags with desiccant, in conditions not exceeding the specified storage temperature range (-40°C to +80°C) and at low humidity to prevent moisture absorption, which can cause "popcorning" during reflow.

6.3 Cleaning

If cleaning is required after soldering, use approved solvents that are compatible with the LED's epoxy lens and plastic package. Avoid ultrasonic cleaning, as the high-frequency vibrations can damage the internal wire bonds or the die attach. Always verify chemical compatibility before proceeding with any cleaning process.

7. Packaging & Ordering Information

7.1 Tape and Reel Packaging

The SMD3528 LEDs are supplied in standard embossed carrier tape on reels, suitable for automated pick-and-place machines. The carrier tape dimensions (pocket size, pitch) are specified to ensure compatibility with feeders. The cover tape peel strength is defined as 0.1 to 0.7 Newtons when peeled at a 10-degree angle, ensuring it is secure during shipping but easy for the machine to remove.

7.2 Model Numbering Rule

The product model follows a structured naming convention: T [Shape Code] [Chip Count] [Lens Code] [Internal Code] - [Luminous Flux Code] [Color Code]. For example, T3200SRA decodes as: Shape 32 (3528), Chip Count S (single, small power), Lens Code 00 (no lens), Internal Code, Luminous Flux Code, and Color A (Red). Other color codes include Y (Yellow), B (Blue), G (Green), etc. This system allows precise identification of all key attributes.

8. Application Suggestions

8.1 Typical Application Scenarios

The SMD3528 red LED is well-suited for numerous applications: Status and indicator lights on consumer electronics (TVs, routers, chargers). Backlighting for small LCD displays, keypads, or panels. Decorative and accent lighting in appliances, automotive interiors, or architectural features. Signalization and emergency lighting where a distinct red color is required.

8.2 Design Considerations

Current Limiting: Always use a series current-limiting resistor or a constant-current driver. The resistor value is calculated using R = (V_supply - V_F) / I_F. Use the maximum V_F from the bin to ensure current does not exceed limits even with a low-V_F device.
Thermal Management: For continuous operation at high currents or in high ambient temperatures, ensure adequate PCB copper area or heatsinking to dissipate heat and keep the junction temperature low.
Optical Design: Consider the 120-degree viewing angle when designing light guides, lenses, or diffusers to achieve the desired illumination pattern.

9. Technical Comparison

Compared to through-hole red LEDs, the SMD3528 offers significant advantages for modern electronics: a much smaller footprint, lower profile for slim devices, suitability for high-speed automated assembly, and often better thermal performance due to direct soldering to the PCB. Within the SMD red LED family, the 3528 package is a common, cost-effective choice. Compared to newer, higher-efficacy LED packages (e.g., 2835), the 3528 may have slightly lower luminous efficacy but remains highly competitive in standard brightness applications due to its widespread availability and proven reliability.

10. Frequently Asked Questions (FAQ)

Q: What is the difference between the luminous flux bins A3, B1, and B2?
A: These bins represent different minimum and typical brightness levels at 20mA. A3 is the lowest (1.0 lm min, 1.5 lm typ), B1 is medium (1.5 lm min, 2.0 lm typ), and B2 is the highest (2.0 lm min, 2.5 lm typ). Selection depends on the required brightness for your application.

Q: Can I drive this LED at 30mA continuously?
A: Yes, 30mA is the absolute maximum continuous forward current rating. However, for optimal longevity and reliability, it is often advisable to operate below the maximum, perhaps at 20-25mA, unless the application requires maximum brightness and the thermal design is robust.

Q: How do I identify the cathode on the LED?
A: The datasheet's outline drawing should indicate the polarity marking. Typically, for a 3528 package, the cathode is marked by a green dot or a small notch/chamfer on one corner of the plastic body.

Q: Is a lens used in this LED?
A: According to the model number decoding and the lens code "00" in the naming rule, this specific variant (T3200SRA) does not have an additional primary lens (it uses the standard epoxy dome). Other variants with lens code "01" would incorporate a lens for beam shaping.

11. Practical Use Case

Scenario: Designing a status indicator panel for a network switch. The panel requires ten red LEDs to indicate port activity/link status. The designer selects the SMD3528 LED in bin R2 (625-630nm) for a vibrant red and bin B1 (1.5/2.0 lm) for consistent, visible brightness. A 3.3V supply rail is available on the PCB. Using the maximum V_F of 2.6V (from bin F, assuming worst-case selection) and a target I_F of 20mA, the current-limiting resistor is calculated: R = (3.3V - 2.6V) / 0.020A = 35 Ohms. A standard 33 Ohm resistor is chosen, resulting in a slightly higher current of ~21.2mA (using typical V_F of 2.2V), which is within safe limits. The LEDs are placed on the PCB with the recommended pad layout. A simple microcontroller GPIO pin, configured as an open-drain output with a pull-up resistor to 3.3V, can sink current through each LED to turn it on. The wide 120-degree viewing angle ensures the status is visible from various angles.

12. Operating Principle

Light-emitting diodes are semiconductor devices that convert electrical energy directly into light through a process called electroluminescence. The core of a red LED like the SMD3528 is a chip made from aluminum indium gallium phosphide (AlInGaP) materials. When a forward voltage is applied across the p-n junction of this semiconductor, electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, they release energy in the form of photons (light particles). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap that corresponds to photons in the red to yellow-orange part of the visible spectrum. The epoxy package encapsulates the chip, protects it from the environment, and often acts as a lens to shape the light output.

13. Reliability Test Standards

The datasheet references several industry-standard tests to validate the LED's reliability under various stress conditions. These tests simulate years of operation or harsh environments in an accelerated timeframe.

13.1 Life Tests

Room Temperature Operating Life (RTOL): LEDs are operated at maximum current at room temperature for 1008 hours. Failure criteria include V_F shift >200mV, luminous flux drop >25% (for AlInGaP red LEDs), leakage current >10µA, or catastrophic failure.
High-Temperature Operating Life (HTOL): Similar to RTOL but conducted at 85°C ambient temperature, accelerating thermal aging.
Low-Temperature Operating Life (LTOL): Conducted at -40°C to test performance under extreme cold.

13.2 Environmental Stress Tests

High Temperature High Humidity Operating Life (H3TRB): Tests at 60°C/90% RH with bias applied for 1008 hours, assessing resistance to moisture-induced degradation.
Temperature Humidity Bias (THB) Cycling: Subjects LEDs to cycling between -20°C, 0°C, 25°C, and 60°C at 60% RH for 20 cycles.
Thermal Shock: Rapidly cycles between -40°C and 125°C for 100 cycles (15 min dwell, <60 sec transfer). Post-test, the LED must still function.

14. Development Trends

The LED industry continuously evolves towards higher efficiency, smaller size, and greater reliability. For packages like the SMD3528, trends include: Increased Luminous Efficacy: Ongoing improvements in chip design, epitaxial growth, and phosphor technology (for white LEDs) allow newer generations of the same package size to produce more light per watt of electrical input. Enhanced Color Consistency: Tighter binning tolerances for wavelength, flux, and V_F are becoming standard, driven by demand from high-end display and lighting applications. Improved Thermal Performance: Advances in package materials (e.g., high-thermal-conductivity plastics, ceramic substrates) and die-attach techniques help lower thermal resistance, allowing higher drive currents or improved lifetime. Miniaturization: While 3528 remains popular, even smaller packages like 2020, 1515, and 1010 are being developed for ultra-compact devices, though often with trade-offs in light output and thermal handling. Smart Integration: The broader trend includes integrating control circuitry, sensors, or multiple color chips (RGB) into a single package, moving beyond simple discrete emitters.