Recently, my company started seeing an increase in field returns caused by open circuits in flexible printed circuits (FPCs) inside the terminal. After digging into several cases, the root cause turned out to be broken copper traces. So what’s going on?
As electronic devices keep getting thinner and more compact, FPCs (flexible printed circuits) are used more and more. In some designs, FPCs even replace traditional PCBs. But no matter how advanced FPC technology becomes, it still needs to connect to a rigid PCB in the end—and most of the time, that interface is a connector. That’s why designing FPCs for manufacturability (DFx) is so important.
Early on, Workingbear thought FPC design was mainly about getting the layout right and choosing the correct stiffener thickness under the gold fingers or edge board contacts—making sure it’s not too thick to fit into the connector or too thin to stay secure.
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.
