Flex circuits are regularly used in high current/power applications. Some application examples of designs produced at PFC include bus bars, backplanes, and power distribution cables. Most of the high current applications PFC develops are to replace wire harnesses.
The benefit of using flex circuit replacing a wire harness includes:
- Decreased assembly time
- Reduced materials and part numbers
- Increased reliability – reduction of assembly errors
- Decreased space, increased air flow
- Improved thermal characteristics
- Increase interconnect options
IPC has come out with a new specification on current carrying capabilities for PCBs and flex circuits in 2010: IPC 2152. This new specification takes the place of IPC 2221 which was developed in 1955!
IPC 2152 contains information that can be used to develop current-carrying capacity guidelines for individual designs. Through the use of computer modeling and information within IPC 2152 and its appendix, current carrying capacity design guidelines can be optimized for any variation in printed circuit technology. Until the publication of IPC 2152, this was not possible with the available public information.
If you are designing a high current flex, PFC urges you to obtain IPC 2152. You can purchase the publication from the IPC online store.
Temperature rise and material CTEs (thermal expansion)
The biggest design consideration for high current flex circuit applications is temperature rise and material thermal expansion. Below is a list of relevant material expansion characteristics.
Copper 18 ppm/deg C
Polyimide 25 ppm/ deg C (x,y) and 100 ppm/ deg C (z)
Acrylic adhesive (<tg 40C) – 100 ppm/ deg C (x,y,z)
Acrylic adhesive (>tg 40C) – 400 ppm/ deg C (x,y,z)
Polyimide adhesive ( <tg 170C) – 150 ppm/ deg C (x,y)
The thicker the copper, the more current a flex circuit can carry.
PFC has the ability to provide flex circuits utilizing up to 560 micron thick copper for power applications. Available copper weights for power applications in microns include:
Contact PFC to assist with your high current circuit design.