Recently, our team ran into a painful issue: cracked traces on an FPC. The problem quickly escalated, tying up engineering resources and causing significant losses for the supplier as well. As often happens after a failure, an old debate resurfaced—should FPCs use Rolled & Annealed (RA) copper or Electro-Deposited (ED) copper?
Modern electronic devices keep getting smaller, and that trend has driven the widespread use of Flexible Printed Circuit Boards (FPCs). One interesting thing about FPCs is that in many designs you can actually see the internal traces from the outside, which makes their structure relatively easy to understand.
If we take a single-layer FPC as an example, its structure is quite simple. It usually consists of a copper layer, with insulating cover films on the top and bottom. In some designs, a stiffener is also added to provide extra mechanical support. Because the structure looks simple, many engineers tend to overlook how important the copper foil itself really is.
FPCs (Flexible Printed Circuit Boards) can be categorized by their structure and complexity. Common types include single-layer, double-layer, and multi-layer flexible circuits. There is also a hybrid design called rigid-flex, which combines both flexible and rigid PCBs in the same structure.
At a basic level, FPCs and PCBs are very similar in both function and structure. Whether it’s an FPC or a PCB, both use copper traces on the surface—and sometimes inside the board—to carry electrical signals.
The biggest difference between them lies in the base material.
A traditional PCB uses a glass-fiber–based substrate, which makes the board hard and rigid.
An FPC, on the other hand, is mainly made from polyimide (PI) or Polyester (PET). You can think of it as something closer to thick paper: flat, thin, flexible, and bendable.
Have you ever been in this situation? It’s late at night, you’re working overtime, and suddenly your manager drops a pile of expired components or badly out-of-spec parts on your desk and says, “The customer needs this shipped urgently—just sign a waiver and go home!” Have you ever faced that moment? And after you sign the waiver, if something goes wrong, who actually takes the blame?
Workingbear remembers when he first entered the electronics industry as a junior product or process engineer. The first time colleagues from Quality and Production asked him to “waive” a product, He just froze on the spot. He had no idea what they were talking about—and even got laughed at by the line supervisor.
