Four layer EM-526 PCB is a kind of multilayer printed circuit board, which has both rigid layer and flexible layer. A typical (four layer) rigid flex printed circuit board has a polyimide core with copper foil on both sides.
For example, from the perspective of production process testing, IC testing is generally divided into chip testing, finished product testing, and inspection testing. Unless otherwise required, chip testing generally only conducts DC testing, and finished product testing can have either AC testing or DC testing. In more cases, both tests are available. The following is about EM-888 PCB related, I hope to help you better understand EM-888 PCB.
