The requirements for printed circuit boards in automotive electronic systems  (6) Safety & Monitoring Systems

Introduction

Safety and monitoring systems form the protective backbone of electric vehicles (EVs), directly safeguarding passengers and enhancing vehicle security. These critical systems include Airbag Control Units (ACU), Tire Pressure Monitoring Systems (TPMS), collision sensors, and occupant detection units, all of which rely on instantaneous responsiveness and unwavering reliability. In safety-critical applications, even minor PCB failures can have catastrophic consequences, making PCB design and manufacturing standards exceptionally stringent. This article explores the specialized PCB requirements, manufacturing challenges, and emerging trends in EV safety and monitoring systems, highlighting their role in ensuring safe driving experiences.

System Overview

EV safety and monitoring systems encompass a range of modules, each engineered to detect hazards and trigger protective responses:

• Airbag Control Unit (ACU): Acts as the central hub for collision response, processing data from accelerometers and impact sensors to deploy airbags within milliseconds of a collision.
• Tire Pressure Monitoring System (TPMS): Continuously monitors tire pressure and temperature, alerting drivers to leaks or over-inflation to prevent blowouts and improve fuel efficiency.
• Collision Sensors: Deployed across the vehicle (front, rear, and sides) to detect impacts or potential collisions, triggering safety measures like seatbelt pre-tensioning or emergency braking.
• Occupant Detection Units: Use weight sensors and capacitive technology to detect passenger presence and position, optimizing airbag deployment force and preventing unnecessary activation.
• Smart Door Locks: Integrate with vehicle security systems to prevent unauthorized access, using RFID or biometric sensors for enhanced protection.

PCB Design Requirements

Safety and monitoring system PCBs must meet exacting design criteria to ensure fail-safe operation:

1. Extreme Reliability

Instantaneous responsiveness is non-negotiable in safety systems, demanding PCBs designed for zero latency:

• Millisecond-level response: ACUs require PCBs with minimal signal propagation delays, ensuring airbag deployment within 20–30 milliseconds of impact.
• Redundant critical paths: Duplicate traces and components for vital circuits (e.g., collision sensor inputs) prevent single-point failures from disabling the system.

2. Miniaturization

Space constraints in mounting locations (e.g., wheel wells for TPMS, door panels for sensors) drive the need for compact designs:

• Rigid-flex PCBs: TPMS and in-cabin sensors use rigid-flex substrates to conform to tight spaces, combining rigid sections for component mounting with flexible sections for vibration resistance.
• High-density layouts: Miniaturized components (e.g., 01005 packages) and fine-pitch routing enable complex functionality in 巴掌大小的 PCBs.

3. Low Power Consumption

Many monitoring systems (e.g., TPMS) rely on batteries, requiring PCBs optimized for energy efficiency:

• Low-power component integration: Selection of microcontrollers and sensors with ultra-low standby current to extend battery life (typically 5–7 years for TPMS).
• Power management circuits: Efficient voltage regulators and sleep-mode functionality minimize energy drain during idle periods.

Table 1: Safety Modules & PCB Requirements

Module	PCB Type	Reliability Focus
ACU	6–8 layer	Functional safety
TPMS	Rigid-Flex	Miniaturization, low power
Collision Sensor	4–6 layer	Shock resistance

Manufacturing Challenges

Producing PCBs for safety systems involves unique technical hurdles, driven by the need for reliability:

• Rigid-Flex Reliability: Flexible sections must withstand >10,000 flex cycles without trace cracking or conductor fatigue, requiring precise material selection (e.g., polyimide substrates) and controlled lamination processes.
• Miniaturized Component Assembly: Soldering 01005 packages (0.4mm × 0.2mm) demands advanced SMT equipment with ±25μm placement accuracy to avoid bridging or cold joints.
• Compliance Testing: PCBs must pass rigorous certification standards, including AEC-Q200 (for passive components) and ISO 26262 (functional safety), involving thermal cycling, humidity testing, and vibration stress screening.

Table 2: PCB Reliability Standards for Safety Systems

Standard	Requirement	Application
AEC-Q200	Passive component reliability	TPMS, sensors
ISO 26262	Functional safety (ASIL)	ACU
IPC-6012DA	Automotive addendum for PCB	All safety PCBs

Future Trends

Advancements in safety technology are driving evolution in PCB design for monitoring systems:

• Sensor Fusion: Integrating data from multiple sensors (e.g., cameras, radar, and ultrasonic) onto a single PCB to improve hazard detection accuracy, requiring high-speed data buses and advanced signal processing.
• Wireless Safety Systems: Eliminating wired connections in TPMS and collision sensors through integration with V2X (Vehicle-to-Everything) communication modules, demanding optimized RF performance and low-power wireless protocols.
• Ultra-Reliable Materials: Adoption of high Tg (≥180°C) laminates with low moisture absorption to enhance durability in harsh environments, reducing long-term failure risks.

Table 3: PCB Design Parameters for Safety Modules

Parameter	Typical Value
Flex Cycles	> 10,000
Line Width	75 μm
Reliability Level	ASIL-C/D

Conclusion

Safety and monitoring systems represent the highest standard for PCB reliability in EVs, requiring designs that prioritize instantaneous response, miniaturization, and compliance with stringent automotive standards. From rigid-flex PCBs enabling compact TPMS modules to redundant circuits ensuring ACU functionality, these boards are critical to passenger protection. As EV safety technology advances, future PCBs will integrate sensor fusion, wireless connectivity, and advanced materials, further enhancing their role as the foundation of automotive safety. Manufacturers that master these technologies will continue to set the benchmark for safe electric mobility.