Enhancing Safety: PCB Quality Upgrade Strategies for Differentiated Emergency Lighting Products

Based on the key points of PCB manufacturing processes, for products such as emergency lights and exit signs that demand high levels of reliability, safety, and durability, we can propose the following specific product quality improvement recommendations.

The core requirement for these products is that, in emergency situations (such as fire or power failure), they must operate correctly 100% of the time and function stably, while withstanding harsh environmental conditions.

Design Improvements for High Reliability and Safety

DFM and DFR (Reliability Design) Combined

Recommendation: In addition to standard manufacturability checks within DFM analysis, include a dedicated reliability assessment.
Specific Measures:
Increase Copper Trace Width and Spacing: For the power management section responsible for charging the battery and the LED driver section, appropriately widen power and ground traces to reduce temperature rise under high current, thereby enhancing long-term reliability.
Enhance Thermal Design: During PCB design, use thermal simulation software to analyse the distribution of heat-generating components such as the MCU and power MOSFETs. It is recommended to design arrays of thermal vias beneath heat-generating components to transfer heat to the back copper layer. For high-power products, it is advisable to use metal substrates (e.g., aluminium) to significantly improve heat dissipation and extend the lifespan of LED sources and components.
Add Protective Circuits: Reserve or integrate positions on the PCB for transient voltage suppression diodes (TVS), varistors, and other protective elements to enhance the product’s resistance to mains fluctuations and surges.

Material Selection Improvements

Use of High Tg (Glass Transition Temperature) Boards

Recommendation: Mandate the use of FR-4 boards with Tg ≥ 170°C or higher-performance materials.
Rationale: Emergency lights and indicators may be installed on ceilings or in corridors, where ambient temperatures are relatively high. High Tg boards maintain mechanical strength and stability at elevated temperatures, effectively preventing softening, delamination, or warping during long-term use or in cases of overheating (such as in early-stage fires).

Selection of More Durable Surface Finishes

Recommendation: Prefer ENIG (Electroless Nickel Immersion Gold) or hard gold plating for charging contacts or buttons.
Rationale:
ENIG: Provides a flat surface suitable for long-term battery storage, preventing soldering defects due to surface oxidation and withstanding multiple lead-free reflow cycles; it is more wear-resistant than OSP or tin finishes.
Hard Gold Plating: For external test buttons or charging contacts, hard gold treatment withstands tens of thousands of mechanical operations, ensuring reliable contact.

Use of Thick Copper PCBs

Recommendation: Consider using copper thickness of 1 oz (35 μm) or more for power circuit sections.
Rationale: Thicker copper increases current-carrying capacity, reduces resistance and heat generation, and ensures stable operation under prolonged emergency conditions.

Production Process Control Improvements

Strict Implementation of High-Standard Hole Metallisation

Recommendation: Promote horizontal electroplating and monitor copper thickness of hole walls closely.
Rationale: The reliability of through-holes directly affects interlayer connectivity. Ensuring uniform and compliant hole wall copper thickness (e.g., ≥ 25 μm) prevents breakage caused by excessive current or thermal expansion/contraction, which could lead to system failure. This is critical in life safety systems.

Reinforce Soldermask Process

Recommendation: Use high-reliability, high-insulation, yellowing-resistant soldermask ink, and ensure uniform thickness covering all traces.
Rationale:
High Insulation: Prevents tracking or short circuits in humid or dusty environments.
Yellowing Resistance: Maintains panel brightness and appearance over time, avoiding reduced light transmission due to UV exposure or aging.
Good Adhesion: Prevents soldermask peeling under temperature variations, which could expose traces.

Implement More Stringent Burn-in Testing

Recommendation: After PCB assembly, conduct high/low temperature cycle burn-in tests and long-term full-load operation tests.
Specific Measures: Place the product in high (e.g., 60°C) and low (e.g., -10°C) temperature cycles, simulating power failure and emergency lighting scenarios to pre-screen early component failures and soldering defects.

Quality Inspection Improvements

100% Electrical and Functional Testing

Recommendation: Not only should PCBs undergo 100% flying probe testing, but finished products must also undergo 100% functional verification.
Testing Content: Simulate main power failure to test emergency switching time, lighting duration, brightness compliance, and alarm functionality (if applicable).

Incorporate X-ray Inspection (AXI)

Recommendation: Perform AXI sampling or full inspection on key components (e.g., BGA-packaged MCU, QFN power chips).
Rationale: These components have pins underneath, which cannot be checked visually or via AOI for solder defects such as cold joints, bridging, or voids. AXI allows internal inspection of solder joints, ensuring reliability.

PCB Quality Improvement Focus for Emergency Lights/Exit Signs

By carrying out targeted reinforcement and improvement in each of the above-mentioned links, the core quality of emergency lights and exit sign products can be significantly improved, ensuring that they can reliably fulfill their mission of guiding the "life channel" at critical moments.