What Are Rigid-Flex PCBs for Batteries?

Rigid-Flex PCBs for batteries combine rigid boards and flexible circuits to create compact, lightweight, and durable power delivery systems. They’re perfect for wearable devices, electric vehicles, and medical equipment, where space-saving and reliability are critical.

What you’ll learn in this article:
You’ll learn what rigid-flex PCBs are and how they work in battery systems. You’ll discover their benefits like space efficiency and vibration resistance. You’ll also understand where they are best used and why.

Excerpt of What Are Rigid-Flex PCBs for Batteries?

Rigid-Flex PCBs blend the best of both worlds: the durability of rigid boards and the flexibility of flex circuits. When it comes to battery integration, these hybrid boards offer streamlined connectivity, reduced wiring, and improved reliability. They’re especially useful in applications where movement, limited space, or odd shapes are factors — like wearable electronics or medical implants. These boards also reduce the risk of connection failures by eliminating bulky connectors and minimizing mechanical stress.

Key Benefits of Rigid-Flex PCBs for Battery Applications

• Compact design fits batteries into tight or oddly shaped enclosures
• Fewer connectors reduce points of failure and assembly complexity
• Enhanced durability withstands shock, vibration, and repeated bending
• Improved performance through reduced parasitic resistance and better signal paths
• Perfect for portable tech like wearables, medical devices, and drones

As the EV revolution continues to take shape, compact battery designs are at the forefront of the changes required to make these cars better and sleeker. Traditional battery designs take up a lot of space under the floor, resulting in a smaller passenger and cargo space compared to ICE vehicles (not considering the hood). Different car manufacturers are solving this problem in their own ways, but one of the methods involves using flexible or rigid-flex PCBs in the battery pack. Let’s look at the importance of these PCBs in battery packs and why switching to flexible or rigid-flex is a game changer.

A rigid-flex PCB

Importance of PCBs in Battery Packs

Battery packs are no longer just passive devices. PCBs bring an element of smartness in them, serving as the brain that runs the entire charging and discharging process to ensure efficient use of the battery chemistry, safety, and durability. Here are the key functions of battery PCBs, which are essentially a combination of the battery management system (BMS) and cell contact system (CCS).

Charging Management

Each battery chemistry has its distinct charging profile or curve that should be followed to prolong the lifespan and performance of the cells, while also preventing explosions. This is more critical in lithium batteries because they are costly and can be fatal if they catch fire.

Enhancing Efficiency

The battery management system that runs on these PCBs has various algorithms that optimize the charging process and power distribution, while also maximizing the driving range. This function also requires hardware like balancing resistors to equalize charging and discharging.

A battery management system PCB

Safety Management

Battery management systems also safeguard the battery from short-circuiting, over-charging, and over-discharging, which helps to protect the battery cells from overheating, exploding, catching fire, internal damage, or damaging externally connected components.

Battery Monitoring

Continuous monitoring is critical in lithium battery packs, and the PCBs keep tabs on them, providing real-time data about the voltage level, current level, temperature, SOH (State of Health), SOC (State of Charge), internal resistance, and coolant flow. If any of these parameters goes outside the set limits, the BMS raises a red flag and alerts the user.

Communication

The BMS is not an isolated system. It communicates with other control systems or ECUs in the vehicle to enable remote monitoring, troubleshooting, and diagnostics, while also controlling charging and discharging. It can also provide data to external systems for data logging and analysis.

Components on the BMS and CCS PCBs

The BMS and CCS PCBs handle these functions using the following components.

Chip

The chip or control IC is the actual brain behind the operations, but it needs the PCB to house all the required peripheral components in a tightly packed circuit. This part handles the safety protocol, voltage, and current management.

Generic BMS PCBs with several components assembled on board

Balancing Resistors

As stated earlier, these components equalize charging and discharging across the cells in the battery pack.

MOSFETs

MOSFETs are electronic switches that control the flow of power in the battery for protection purposes, such as to prevent overcharging and over-discharging.

Temperature Sensors

These collect data about the battery cell temperature in real-time for analysis by the chip.

Connectors

Connectors link the PCB to the charger, battery cells, and other systems in the vehicle.

Fuses

Fuses protect the battery pack from short circuits and overcurrents.

Benefits of Using Rigid-Flex PCBs for Batteries

Flexibility

The flexible part in rigid-flex and flexible PCBs (especially CCS) makes it possible to design and fit the batteries into unconventional spaces in the vehicle. This results in better use of space under the floor, which enables car manufacturers to make sleeker cars that are more ergonomic while having long-range batteries.

A Nissan Leaf’s battery pack

Resilience and Durability

The flex part in the rigid-flex design also provides durability and resilience. Here’s how. The BMS and CCS are able to withstand mechanical stress and vibrations better, which ensures a long service life.

Superior Performance

Flexible PCBs usually require polyimide as the substrate material, which provides better electrical insulation and thermal stability than FR4. As such, the PCB experiences reduced signal interference and is less susceptible to heat damage, which results in better battery performance. Flexible PCBs also enable easy optimization of the electrical routing, which can reduce the electrical pathways in the circuit and minimize resistance.

Easy Integration with Components

It is easy to integrate sensors, chips, and connectors into a flex PCB to form a single cohesive unit during product design. Such integrated designs simplify the assembly process and reduce the number of external connections for the circuit, which cuts the PCB manufacturing service costs. On top of that, this integration minimizes the potential failure points in the circuit, making the battery pack more reliable.

Environmentally Friendly Manufacturing

Fabricating flex PCBs is more environmentally friendly than rigid circuit boards because the thin and more flexible material is made using cleaner manufacturing techniques. These techniques reduce material wastage and energy consumption, making the overall EV production process more sustainable.

Conclusion

PCBs are critical in EV battery pack architectures, and incorporating flexible materials and circuits in them makes these power sources lighter, compact, resilient, durable, and easier to integrate with other components while providing better battery performance.

But to get these benefits, you have to get the PCB made and assembled using a knowledgeable, capable, and reputable manufacturer. OurPCB fits this description as the company has been in this business for almost two decades, partnering with car manufacturers like Great Wall Motors during this time.

So if you would like to get the next generation of battery packs for your EVs to have the benefits described above, partner with contract manufacturers like OurPCB to get the project developed in a short lead time and at reasonable costs. Reach out to them to learn more about their flex and rigid-flex manufacturing capabilities.