Flexible Circuits Extend Lifetime, Safety for Vehicle Batteries

February 03, 2020


The increased electrification of vehicles is a hot and growing technology trend, driven in large part by advances in lithium (Li)-ion cell and battery pack design, as well as in power management. Li-ion battery packs contain an arrangement of cells that can be used for quick, energy-efficient delivery of power to a vehicle. In addition to utilizing Li-ion cells, battery packs are encased in robust packaging to provide maximum safety during a thermal runaway.

Thermal runaway refers to a situation in which an increase in temperature changes a system’s conditions, triggering a further increase in temperature and often leading to a destructive result. In essence, thermal runaway is a process whereby increased temperature releases energy that further increases temperature, and the process can escalate very quickly.

Li-ion battery packs also utilize electronic monitoring systems that can track performance and health of the cells during operation. Battery management systems (BMS) are used to achieve the highest efficiency and therefore the longest possible driving range from the battery pack. A cell connection system, a component of BMS, is used to monitor voltage or charge state and battery temperature during operation. IPC®-certified non-flammable laminate materials provide a proven, reliable option for building energy-efficient battery packs.

This is particularly true when it comes to flexible circuits, which are increasingly being used for applications such as vehicle battery backs. Flexible printed circuits pose a better alternative to wire for moving production of battery packs to production – particularly when converting hybrid electric vehicles (HEVs) to EVs. Li-Ion batteries are replacing lead-acid batteries in EVs and other applications requiring high power because they are well suited for use in “green” environments. Unlike other types of battery technologies, Li-Ion batteries can be completely discharged and recharged hundreds of times with no reduction in performance, and don’t develop a “memory” when only partially charged and discharged.

Because they can be folded, bent and conformed to fit virtually any footprint requirement and create more compact and lightweight devices, flexible circuits are gaining rapid acceptance for applications that demand high reliability and electrical and thermal performance, among other parameters. In manufacturing Li-ion packs for use in EVs, flex circuits can allow more power density by reducing cover height, which also aids in reducing weight and improving throughput. Also, because a flex circuit can be bent 90 degrees and placed on top of the cell or directly on the NTC thermistor, it provides further design options and improves reliability.

Addressing key challenges

Compared to traditional cable systems, flexible printed-circuit connectors with surface mounted sensors allow OEMs to save space and create lightweight battery packs – which, in turn, leads to longer driving range. This arrangement allows the height of individual Li-ion cells to be increased and, therefore, more energy to be stored in each battery pack.

However, there are some key challenges that remain. The height of the wire bundle creates physical limitations; larger battery packs require larger flex circuits, which can be cost-prohibitive; and the process of converting from wire to flex is both time-consuming and costly. Flexible sensors need manufacturing materials that can be seamlessly integrated into a fab’s existing processes, while meeting these stringent demands, and still remain cost-sensitive.

DuPont materials offer optimal solution

EVs require laminates that can withstand high service temperatures for use in power modules and transmission control units. The ability of flexible laminates to meet this requirement expands product design options. As outlined in an earlier post, Flexible Laminate Solutions Target Flexible-Circuit Challenges, DuPont’s Pyralux® family comprises a range of laminates with capabilities that allow fabricators to pick and choose one or more products that best suit their needs. Techniques commonly used in the manufacture of flexible circuits can be used to process Pyralux products.

Used for more than two decades in high-reliability and multilayer flexible circuitry applications, Pyralux AP has become a de facto industry standard for high-performance laminates. The flexible circuit material is a double-sided, copper-clad laminate and an all-polyimide composite of polyimide film bonded to copper foil. With this construction, the material is well-suited for multilayer flex and rigid flex applications requiring advanced material performance, temperature resistance, and high reliability

Pyralux AC flexible circuit materials, also all-polyimide (a composite of polyimide film on copper foil), are single-sided copper-clad laminates. Pyralux AC is ideal for use in single-sided applications such as display drivers, multilayer digital cameras or rigid-flex camcorder circuits that require thin, light and high density circuitry together with chip-on-flex attachment. Techniques commonly used in the manufacture of flexible circuits can be used to process Pyralux AC products.

The right laminate for your needs

As a trusted interconnect materials partner, DuPont has a proven portfolio of laminates useful for just such applications, whether on rigid or flexible substrates, providing both mechanical stability and flexible implementation. Our laminates provide mechanical integrity to flex circuits while allowing designers the freedom to fit circuits into the available footprint. Regardless of your target market, we have a laminate material that will meet your requirements.

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