Properties of Flex-Rigid PCBs in the Automotive Industry
Modern automotive systems contain more than 250 electronic control units, which are distributed in various parts of the vehicle, from the engine compartment to the dashboard. These systems must meet strict reliability requirements as they are exposed to extreme conditions such as vibrations, temperature changes, and high humidity.
Flex-rigid PCBs have been used in the automotive industry for over 15 years as a solution to enhance system reliability by reducing the number of connectors and solder joints. This article focuses on the advantages of their application, types, and design specifications.
Advantages of Flex-Rigid PCBs in the Automotive Industry
- Increased Quality and Reliability
By reducing the number of connectors and solder joints, potential risks of electrical failure are minimized. This increases the overall reliability of automotive control systems. - Cost Reduction through Manufacturing Step Reduction
By eliminating the soldering of cable connections and connectors, production and assembly costs are reduced. - Simplified Maintenance
Flex-rigid PCBs combine rigid and flexible parts, allowing for compact and precise integration into small spaces, while eliminating the need for complex management and maintenance. - Greater Flexibility in Design and Assembly
Designers can focus on the layout of the rigid parts of the PCB, and the flexible parts can serve only for interconnection, simplifying both assembly and design.
Table: Main Design Requirements for Automotive PCBs
| Factor | Requirement |
| Temperature Resistance | -40°C to 150°C |
| Vibration Resistance | Resistance to long-term vibrations |
| Chemical Resistance | Resistance to oils, liquids, and corrosive substances |
| Electrical Stability | Minimal interference and high insulation strength |
| Long Lifespan | Resistance to mechanical wear and material fatigue |
Types of Flex-Rigid PCBs
- Semi-flexible PCBs: Made from thin FR-4 material, suitable for applications with low flexibility requirements and lower manufacturing costs.
- Multi-flexible PCBs: Made from polyimide material, suitable for applications with high dynamic flexibility requirements.
Multi-flexible PCBs consist of a hybrid structure where rigid and flexible substrates are connected using electroplated vias. The flexible part consists of a copper foil on a polyimide substrate, ensuring high mechanical stress resistance.
When adhesives with a high coefficient of thermal expansion (CTE) are used in multilayer PCBs, mechanical damage to the vias can occur during thermal shock or stress tests. Therefore, it is important to minimize the use of flexible materials in rigid sections, especially near the vias.
Reliability Requirements for PCBs in Various Vehicle Parts
- Quality Assurance Requirements
Automotive PCB manufacturers must comply with standards such as ISO9001, QS9000, or the latest version of ISO/TS16949 to prevent defects and minimize production errors. - Thermal Circulation and Environmental Resistance
Automotive PCBs must pass strict thermal resistance tests:
| Level | Temperature Range | Number of Cycles | Application |
| 0 | 85°C ± 2°C | 500 | Vehicle interior |
| 1 | -40°C to 85°C | 500 | Protected areas (not exposed to weather) |
| 2 | -40°C to 105°C | 1000 | Engine compartment |
| 3 | -40°C to 125°C | 1000 | Near the engine |
| 4 | -40°C to 150°C | 1000 | Directly on or near the engine |
Use of Different Types of PCBs in the Automotive Industry
| Vehicle Equipment | Types of PCBs |
| Speedometer, Air Conditioning | Single-sided/Double-sided PCBs, Flexible PCBs |
| Car Radio, Monitor | Double-sided PCBs, Multilayer PCBs, Flexible PCBs |
| Engine System | Metal core PCBs, Rigid-flex PCBs |
| Navigation Device | Embedded PCBs |
Flex-Rigid PCBs
Flex-rigid PCBs represent a key component in modern automotive systems due to their high reliability, compactness, and reduction in production costs. When designing and manufacturing them, strict quality and temperature resistance requirements must be met. The implementation of these components allows automotive manufacturers to improve the performance of their electronic systems and ensure their long lifespan.
The idea of increasing the use of Flex-Rigid PCBs in the automotive industry is absolutely correct. Flexible PCBs offer advantages such as flexibility, compactness, and space-saving, which are critical for integrating modern technologies into automotive electronics, especially with the increasing complexity of advanced safety systems, electric vehicles, and autonomous vehicles.
They enable manufacturers to design more efficient and compact circuits that fit easily into small spaces, such as sensors, control units, or other important automotive components.
In addition to integrating safety systems, the trend of focusing on sustainability is becoming more important. Flexible PCBs require fewer raw materials and less energy during manufacturing, which contributes to a reduction in the overall environmental impact. As the automotive industry continues to transition to eco-friendly technologies, this is a significant advantage.