PCBA LED Not Working After Soldering: How to Prevent Failure

Receiving an assembled PCB only to find that some LEDs do not light up is both frustrating and costly. In most cases, the root cause is not a single error, but a combination of oversights across design, component selection, and manufacturing processes.

At JLCPCB, our objective is to help you achieve first-pass manufacturing success. This guide outlines practical actions you can take during the design and ordering stages to significantly reduce the risk of LED failure—saving both rework time and cost.

1. Design Stage: Building Reliability from the Start

Most LED-related soldering and functional issues originate in the design phase. Pay close attention to the following aspects:

1.1 Verify Polarity and Footprint Compatibility

This is the most common root cause of LED failure.

Ensure that the PCB footprint (pad layout) exactly matches the pin configuration and polarity (anode/cathode) of the selected LED model.

Using a generic “LED” footprint is a frequent hidden risk and often results in reversed polarity or incorrect pad alignment, leading to non-functional LEDs after assembly.

1.2 Evaluate Thermal Management

LEDs are heat-generating devices, especially high-power LEDs, making thermal design critical.

Your PCB layout should provide effective heat dissipation paths, such as:

• Sufficient copper area connected to the LED pads
• Thermal vias conducting heat to internal layers or backside copper planes

Proper thermal management is essential to prevent lumen degradation, intermittent operation, or permanent damage caused by sustained overheating.

2. BOM and Manufacturing Files: Eliminate Ambiguity

Unclear or incomplete documentation often forces assumptions during production. Reduce risk by ensuring clarity in the following areas:

2.1 Specify Accurate Component Part Numbers

In the BOM, always provide the full Manufacturer Part Number (MPN) or the corresponding JLCPCB part number.

Vague descriptions such as “LED, 0805, red” may lead to:

• Components with identical packages but incorrect electrical or optical characteristics, or
• Electrically similar LEDs with incompatible footprints

Either case can directly affect circuit functionality and assembly yield.

2.2 Use the JLCPCB Parts Library Whenever Possible

When creating an SMT order, prioritize selecting LEDs and other components from the JLCPCB parts library.

Library components ensure:

• Verified footprints
• Confirmed process compatibility
• Stable inventory availability

This significantly reduces sourcing and assembly risks.

Important Engineering Note

Regardless of sourcing, always review the official datasheet of every component before ordering.

If a component has special process requirements (e.g., moisture sensitivity requiring pre-baking), be sure to:

• Select the Component Baking service during order placement, or
• Clearly document the requirement in the PCB assembly remarks

This enables our engineering team to apply special handling during review and coordinate confirmation with you, minimizing potential manufacturing and reliability risks.

3. Ordering and Engineering Safeguards

When placing your order with JLCPCB, use the available services to introduce additional quality controls:

3.1 Enable Functional Testing

For boards with multiple LEDs or function-critical indicators, we recommend enabling the Functional Test service.

The standard workflow includes:

1. Customer-Defined Test Method: Provide a clear and executable test procedure, including power supply conditions, current limits, test points, and expected LED illumination patterns or sequences.

2. Feasibility Review and Execution: Our engineering team evaluates the test method. Once approved, functional power-on testing is performed prior to shipment.

3. Customer Confirmation: After testing the first assembled board, a test video is shared for final confirmation.

This collaborative process helps detect major functional or component-related issues before shipment, preventing defects from entering downstream stages.

3.2 Apply Component Baking for Moisture-Sensitive LEDs

Many LEDs—particularly high-density packages or long-stored components—are classified as Moisture-Sensitive Devices (MSDs).

During reflow soldering, absorbed moisture can rapidly vaporize, causing the “popcorn effect”, which may result in:

• Internal microcracks
• Solder voids
• Intermittent LED operation or permanent failure

By selecting the Component Baking service, moisture-sensitive components are pre-baked at 60 °C for 48 hours, effectively removing internal moisture and significantly improving soldering reliability and long-term performance.

Conclusion: First-Time Success Is a Shared Objective

By focusing on robust design, precise documentation, proactive communication, and appropriate testing, you and JLCPCB work together to minimize LED failure risks.

Early investment in design and preparation is the most effective strategy to ensure that the assembled PCBs you receive are fully functional upon delivery.

Ready to place your order with confidence?

Visit jlcpcb.com, upload your design, and experience a reliable, engineering-driven PCB assembly process.