3535 Ceramic LED Handling Guide - Size 3.5x3.5mm - Voltage Varies - Power Varies - English Technical Document

1. Product Overview

The 3535 ceramic LED series represents a high-performance surface-mount device (SMD) package designed for demanding lighting applications. Characterized by its 3.5mm x 3.5mm footprint and ceramic substrate, this package offers superior thermal management, mechanical stability, and reliability compared to traditional plastic packages. The ceramic construction provides excellent heat dissipation, which is critical for maintaining LED performance and longevity, especially in high-power or high-density array configurations. These LEDs are suitable for a wide range of applications including automotive lighting, general illumination, backlighting, and specialty lighting where consistent color output and long-term reliability are paramount.

2. Handling and Manual Operation Precautions

Proper handling is essential to prevent physical damage to the LED, particularly the sensitive optical lens.

2.1 Manual Operation Guidelines

Manual handling should be minimized in production. When necessary, always use tweezers, preferably rubber-tipped, to pick up the LED. The tweezers must grip the ceramic body of the LED package. It is strictly forbidden to touch, press, or apply any mechanical force to the silicone lens. Contact with the lens can cause contamination, scratches, or deformation, which will severely degrade optical performance, light output, and color uniformity. Applying pressure can lead to internal delamination or cracking, resulting in immediate failure.

3. Moisture Sensitivity and Baking Procedures

The 3535 ceramic LED package is classified as moisture-sensitive according to the IPC/JEDEC J-STD-020C standard. Absorbed moisture can vaporize during the high-temperature reflow soldering process, causing internal pressure build-up and potential catastrophic failure (e.g., \"popcorning\").

3.1 Storage Conditions

As received in their original sealed moisture barrier bag (MBB) with desiccant, LEDs should be stored at temperatures below 30°C and relative humidity (RH) below 85%. Upon opening the MBB, the internal humidity indicator card must be checked immediately. If the indicator shows that the safe exposure level has not been exceeded, and the components will be used within the specified floor life, baking may not be required.

3.2 Conditions Requiring Baking

Baking is mandatory for LEDs that meet the following criteria: 1) They have been removed from their original sealed packaging. 2) They have been exposed to ambient conditions (outside a dry storage cabinet) for more than 12 hours. 3) The humidity indicator card shows the allowable exposure limit has been exceeded.

3.3 Baking Method

The recommended baking procedure is as follows: Bake the LEDs, preferably still on their original reel, in a circulating air oven at 60°C (±5°C) for 24 hours. The temperature must not exceed 60°C to avoid damaging the reel or the LED's internal materials. After baking, the LEDs must be reflow soldered within one hour or immediately placed into a dry storage environment with less than 20% RH.

4. Storage Guidelines

Correct storage is vital for preserving LED quality and solderability.

4.1 Unopened Packaging

Store sealed moisture barrier bags at 5°C to 30°C with RH below 85%.

4.2 Opened Packaging

After opening, store components at 5°C to 30°C with RH below 60%. For optimal protection, store opened reels or trays in a sealed container with fresh desiccant or in a nitrogen-purged dry cabinet. The recommended \"floor life\" after bag opening is 12 hours under these conditions.

5. Electrostatic Discharge (ESD) Protection

LEDs are semiconductor devices and are highly susceptible to damage from electrostatic discharge (ESD). White, blue, green, and purple LEDs are particularly sensitive due to their wider bandgap materials.

5.1 ESD Damage Mechanisms

ESD can cause two primary types of damage: 1) Latent Damage: A partial discharge may cause localized heating, degrading the LED's internal structure. This results in increased leakage current, reduced luminous output, color shift (in white LEDs), and shortened lifespan, though the LED may still function. 2) Catastrophic Failure: A strong discharge can completely rupture the semiconductor junction, causing immediate and permanent failure (dead LED).

5.2 ESD Control Measures

A comprehensive ESD control program must be implemented in all areas where LEDs are handled, including production, testing, and packaging. Key measures include: Establishing an Electrostatic Protected Area (EPA) with grounded conductive flooring. Using grounded anti-static workstations and ensuring all production equipment is properly grounded. Requiring all personnel to wear anti-static garments, wrist straps, and/or heel straps. Using ionizers to neutralize static charges on non-conductive materials. Employing grounded soldering irons. Using conductive or dissipative materials for trays, tubes, and packaging.

6. Application Circuit Design

Proper electrical design is crucial for stable operation and long LED life.

6.1 Driving Methodology

Constant Current (CC) drivers are strongly recommended over Constant Voltage (CV) drivers. LEDs are current-operated devices; their forward voltage (Vf) has a negative temperature coefficient and can vary from unit to unit. A CC driver ensures a stable current flows through the LED regardless of Vf variations, providing consistent brightness and preventing thermal runaway.

6.2 Current Limiting Resistors

When multiple LED strings are connected in parallel to a CC driver or when using a CV source, a current-limiting resistor must be placed in series with each individual LED string. This resistor compensates for minor Vf differences between strings, ensuring current sharing and preventing one string from drawing excessive current. The resistor value is calculated based on the driver voltage, the total Vf of the string, and the desired operating current (R = (Vsource - Vf_string) / I_LED).

6.3 Polarity and Connection Sequence

LEDs are diodes and must be connected with correct polarity (anode to positive, cathode to negative). During final assembly, first verify the polarity of the LED array and the driver output. Connect the driver's output to the LED array first. Only then should the driver's input be connected to the mains or DC power source. This sequence prevents voltage transients or incorrect connections from damaging the LEDs.

7. Reflow Soldering Characteristics

The 3535 ceramic package is designed for compatibility with standard surface-mount technology (SMT) reflow processes.

7.1 Lead-Free (Pb-Free) Solder Profile

The recommended reflow profile for lead-free solder (e.g., SAC305) is critical. The profile typically consists of: Preheat: A gradual ramp-up (1-3°C/second) to activate the flux. Soak/Dwell: A plateau between 150-200°C for 60-120 seconds to allow the board and components to thermally equalize and for the flux to fully clean the solder pads. Reflow: A rapid rise to the peak temperature. The peak solder joint temperature must reach 245-250°C. The time above liquidus (TAL), typically 217°C for SAC305, should be maintained for 45-75 seconds. Cooling: A controlled cool-down rate of -6°C/second maximum to ensure proper solder joint formation and minimize thermal stress.

7.2 Leaded (SnPb) Solder Profile

For tin-lead solder, the peak temperature is lower. The peak solder joint temperature should be 215-230°C, with time above liquidus (183°C) maintained for 60-90 seconds. The same careful control over preheat, soak, and cooling rates applies.

7.3 Critical Considerations

Do not exceed the maximum recommended peak temperature or TAL, as this can damage the LED's internal die, wire bonds, or phosphor. Ensure the reflow oven is properly calibrated and profiled for the specific PCB thickness, component density, and solder paste used.

8. Cleaning of Assembled Boards

Post-reflow cleaning may be necessary to remove flux residues, which can be corrosive or cause electrical leakage over time.

8.1 Cleaning Agent Compatibility

It is essential to verify the chemical compatibility of any cleaning agent with the LED's silicone lens and package materials. Harsh solvents can cause the lens to swell, crack, or become cloudy. Recommended cleaning agents are typically mild, alcohol-based, or aqueous solutions designed for electronics. Always consult the LED manufacturer's specifications and perform tests on sample boards before full-scale cleaning.

8.2 Cleaning Process

Use gentle cleaning methods such as ultrasonic cleaning with caution, as excessive power or frequency can damage the LED. Preferred methods include spray washing or immersion with gentle agitation. Ensure boards are thoroughly dried after cleaning to prevent moisture entrapment.

9. Storage and Handling of Assembled Semi-Finished Products

PCBs with LEDs soldered onto them (semi-finished products) also require careful handling.

Avoid stacking boards directly on top of each other in a way that applies pressure to the LED lenses. Use spacers or dedicated storage racks. Store assembled boards in a clean, dry, and ESD-safe environment. If storage is prolonged, consider using moisture barrier bags with desiccant, especially if the boards will undergo a second reflow process (for double-sided assembly). Handle boards by their edges to avoid contaminating or stressing components.

10. Thermal Management Technology

Effective heat sinking is the single most important factor for LED performance and reliability. While the ceramic package offers good thermal conductivity, the heat must be efficiently transferred away from the package.

10.1 PCB Design for Thermal Management

The PCB acts as the primary heat sink. Use a metal-core PCB (MCPCB) or a standard FR4 board with extensive thermal vias under the LED footprint. The thermal pad of the LED must be soldered to a corresponding copper pad on the PCB. This pad should be as large as possible and connected to internal ground planes or external heat sinks through multiple thermal vias. The vias should be filled or capped with solder to improve thermal conduction.

10.2 System-Level Thermal Design

Calculate the total thermal resistance from the LED junction to the ambient air (Rth_j-a). This includes the junction-to-case (Rth_j-c, provided in datasheet), case-to-board (solder interface), board-to-heatsink, and heatsink-to-ambient resistances. The maximum allowable junction temperature (Tj_max, typically 125-150°C) must not be exceeded under worst-case operating conditions. Use the formula: Tj = Ta + (Power_dissipated * Rth_j-a). Power_dissipated is approximately (Vf * If) minus the radiant optical power. Proper design ensures Tj remains well below Tj_max, maximizing light output and lifespan.

11. Other Important Considerations

11.1 Optical Considerations

Maintain a clean optical path. Any contamination on the lens or secondary optics will reduce light output. The viewing angle and spatial radiation pattern are fixed by the primary lens design; secondary optics must be chosen accordingly.

11.2 Electrical Testing

When performing in-circuit testing (ICT) or functional testing, ensure test probes do not contact or scratch the LED lens. Test voltages and currents must be within the LED's absolute maximum ratings to avoid electrical overstress (EOS).

11.3 Long-Term Reliability

Adherence to all handling, soldering, and thermal guidelines directly impacts the LED's long-term reliability, including lumen maintenance (L70/L90 lifetime) and color stability. Failure to follow these procedures can lead to premature degradation and field failures.