Introduction
Flexible Printed Circuits (FPCs) are essential parts within the lithium batteries powering your electric (EV) and hybrid (HEV) cars. Instead of seeing it as Lithium Battery vs FPC, you will see how these technologies work together as a full system. This guide will introduce you to both. You will understand how FPCs are used to build safe and efficient battery packs.
What is Lithium Battery for EV and HEV
A lithium-ion battery is the key source of energy for your electric (EV) and hybrid (HEV) cars. Think of it as a big system that consists of small parts. The entire battery pack would consist of a series of modules, and within one of them would be a series of individual battery cells, including the common 18650 or newer blade-style cells. This multi-level arrangement ensures effective management of the battery’s power and safety.
The brain behind the system is the Battery Management System (BMS), regulating charging and discharging. A Cell Contact System (CCS) provides the BMS with data, but is developed on printed circuit boards to acquire the temperature and voltage of each cell. The circuit boards, such as Flexible Printed Circuits for battery packs, combine important components like connectors, fuses, and busbars, making a compact yet reliable power source for your vehicle.
PCBs Used in Lithium Battery
Your car has a lithium battery with rigid FR4 PCBs and flexible printed circuits (FPCs) in it to work. The primary control unit, the Battery Management System (BMS), often uses a durable FR4 board. In contrast, FPCs are used for the Cell Contact System (CCS) and in the limited space of the battery cover.
This choice of PCB material is critical for performance and design. Though certain CCS solutions use FR4 boards with busbars and metal connections, it is more typical in soft-pack batteries to use an FPC. In such applications, a flexible printed circuit for battery pack designs mounts directly to busbars, saving space and enhancing reliability.
FR4 PCB is used in the BMS
You will usually see a rigid FR4 PCB used for the Battery Management System (BMS Nevertheless, battery pack application in a flexible printed circuit is optimal when dealing with small surfaces like the battery pack cover. The Cell Contact System (CCS) may use either of these types of boards. Although certain designs use FR4 with metal connections, soft-pack batteries tend to use FPCs. Flexible circuits are mounted with busbars to handle power connections effectively.
What is Flexible PCB (FPC)
A flexible printed circuit (FPC) is a circuit board constructed on a series of thin and flexible bases, such as polyimide (PI) and polyester (PET). Its design makes it very lightweight and can be bent or folded to become compact enough to fit in constrained areas. The main advantage of an FPC is that it can offer electrical connections in three dimensions, not possible with a rigid board.
Structure of Flexible PCB
Your FPC is built in layers, beginning with a PI or PET film base, copper traces next, and adhesive to hold them together. For applications where movement is necessary for batteries, rolled annealed (RA) copper is used for its extreme flexibility. A protective coverlay, made of film and adhesive as well, insulates the surface. This design makes FPC material for battery applications both resistant and versatile.
Grounding of Flexible PCB
You frequently must ground an FPC to avoid electrical interference. The connection of the negative power pole of the circuit with a metal enclosure is grounding. The grounding converts the enclosure into a shield and stops interference from affecting the circuit’s functionality. Grounding is common in EV and HEV battery packs to ensure reliability.
Applications of Flexible PCBs in Lithium Battery
In a lithium battery, FPCs perform two key functions. First, FPCs function as pickup lines for the Battery Management System (BMS) on FPC, providing cell voltage and temperature monitoring. Second, the CCS flexible circuit takes care of signal transmission and overcurrent protection. This is the reason why applications of FPC in battery technology are increasingly replacing traditional wiring harnesses in EVs.
Advantages of Using Flexible PCBs in Lithium Battery
Selecting a flexible printed circuit for battery pack designs over traditional wires provides significant benefits. It allows high integration, with components such as fuses and connectors integrated into the circuit. Production can be automated for speed and accuracy. FPCs are also lightweight, flexible for 3D mounting, and safer, due to built-in fuses that avoid short circuits.
How to Make Lithium Battery Pack using Flexible PCB
The process of designing a custom lithium-based battery pack is done in three phases, including locating the battery cells, creating the FPC-based Cell Contact System (CCS), and final automated pack assembly. You begin with the selection of cells and design of the FPC around them. The FPC is then manufactured, built with components, and assembled into the final battery pack.
For the CCS assembly, you can follow our step-by-step process below:
Step 1. Fabricate the Flexible Copper Clad Laminate (FCCL)
You first create the substrate material for your flexible circuit. This is obtained by laminating copper foil, adhesive and polyimide (PI) to create the Flexible Copper Clad Laminate (FCCL). In the meantime, the protective coverlay is also prepared by bonding a PI film to a layer of adhesive.
Step 2. Cut the Laminate to Size
Then, the continuous roll of FCCL is cleaned and prepared thoroughly. It is then precision-cut into separate panels. The panels are cut to your exact flexible printed circuit battery pack design size, ready for circuit imaging in the next stage.
Step 3. Generate the Flexible PCB Circuit
This is where your circuit design is brought to reality. The cut FCCL panel is subjected to a pattern of a circuit and then etched, and the excess copper is stripped out, leaving only the traces desired. The panel is then scrubbed, cleaned, and dried in preparation for the following manufacturing processes.
Step 4. Apply a Surface Finish
To protect the exposed copper and provide reliable contacts, you apply a surface finish. Flexible PCBs are typically offered with Organic Solderability Preservative (OSP) or Immersion Gold (ENIG). It keeps the surface oxidation-free and provides an ideal soldering surface for components later on.
Step 5. Perform an Automated Optical Inspection (AOI)
Quality control is important after creating the circuit. An Automated Optical Inspection (AOI) machine inspects the board, cross-referencing it with the original design data. This test detects any likely defects, such as shorts or open circuits, which ensures the integrity of your high-current FPC design before proceeding.
Step 6. Cut and Attach the FPC Coverlay
You now add the protective insulating layer. The FPC coverlay material is cut to the precise shape you need for your FPC automatically. It is drilled and aligned accurately before being attached to the circuit board, so that it covers the copper traces while leaving connection pads exposed.
Step 7. Laminate the Flexible PCB
To create a permanent bond, the flexible PCB with its recently attached coverlay undergoes thermal lamination. Pressure and heat are used to firmly fuse the layers. This process causes the coverlay and the circuit layers to produce a single, reliable, and durable flexible circuit board.
Step 8. Print the Silkscreen
For easier identification during assembly and testing, you add a silkscreen layer on the FPC’s surface. This layer commonly includes component designators, part numbers, and other helpful marks. It adds important visual information without affecting the circuit’s electrical performance.
Step 9. Conduct Final Electrical Testing
Before adding components, you perform a final electrical test. A specialized jig holds the flexible PCB in place while an AOI system tests each circuit path for continuity and isolation. This second testing serves to ensure the bare board is clear of any electrical defects.
Step 10. Flexible PCB Assembly
Here, your bare FPC is now an assembled electronic product. Through the use of a stainless steel jig to support the FPC in a flat position, components such as connectors, NTC resistors, and fuses are soldered onto the board through the method of Surface Mount Technology (SMT). The board is then subjected to a reflow oven in order to solder surface-mount components (e.g., connectors, NTC resistors) onto the FPC.
Step 11. Flexible PCBA Testing
After assembly, the flexible PCBA is subjected to rigorous testing to ensure it meets its quality and performance standards. This can involve tension and bend tests, voltage and resistance tests, and environmental testing. This will ensure that the board will function correctly within the battery pack.
Step 12. Assemble the Cell Contact System (CCS)
Finally, you produce the complete CCS module. The FPC assembly that has been tested is laminated with the pre-soldered busbars and insulating black films. This forms a single, integrated module in which the fuse is safely embedded and ready for automatic assembly onto the battery cells.
MV Flex Circuit: Your One-Stop FPC and CCS Assembly Manufacturer for Lithium Battery
MV Flex Circuit is your dedicated, one-stop manufacturing company for FPCs and Cell Contact System (CCS) modules used in lithium batteries. We offer end-to-end, A-to-Z fabrication and assembly service from our ISO-certified factories. You can rely on us to handle the whole production process, from producing the base laminate and FPC to assembling and testing the CCS module.
When you partner with us, you are assured of on-time and guaranteed quality. We use a very efficient roll-to-roll process and can produce FPCs up to 1.8 meters in length for mass production. Our extensive experience enables us to offer professional manufacturing assistance for your custom battery pack with FPC projects.
If you need a reliable manufacturer for your lithium batteries and CCS modules, we are here to assist you. Simply send your Gerber and BOM files to sales@flexiblepcbboard.com and get a free quote!
FAQs
What Is the Biggest Problem with Lithium Batteries?
The most serious issue is a safety hazard referred to as thermal runaway. When a battery is broken, it can initiate an unstoppable chemical reaction in which it quickly overheats, emits poisonous gases, and has the potential to explode or catch fire.
What is FPC in Battery?
An FPC is a printed circuit that is flexible, used to connect and protect the battery cells. It replaces bulky wires, conserves space, and usually contains protective circuitry, making it ideal for small devices such as smartphones and FPC for wearable electronics battery applications.
Conclusion
This guide explained how FPCs play a critical role in connecting and monitoring the cells within a lithium battery’s complex pack, module, and cell structure. The comparison of Lithium Battery vs FPC shows they are not separate options but a necessary partnership for modern EV technology. When you need a one-stop manufacturer for your custom FPC and CCS modules, you can count on MV Flex Circuit to provide you with quality work.
