PCB News - FPC trace broken

FPC trace broken

Recently, it has been discovered that some flexible circuit boards(FPC) have poor feedback about traces. In order to be lighter and thinner, we abandoned 1/2 ounce (oz) a few years ago and started to switch to 1/3 ounce copper. However, the thinner the copper foil, the weaker its ability to withstand bending, even if rolled copper is used.

In fact, when these defective products were sent back, they were measured with a three-meter electric meter to show that there was an open circuit, but at the beginning, I couldn’t find out where the failed soft boards were broken. In the end, it was the supplier. Great, they bend the FPC little by little, of course, not a dead bend, but forced the FPC to bend, and then checked under a microscope, and finally found the copper foil line break. In other words, although these lines have been broken, it is generally impossible to see the broken place even with a microscope when lying flat.

Now that the copper foil circuit is found to be broken, and the place where the copper foil circuit is broken is not a dead-bending position during our use, and there is no trace of bending during the assembly process, it is obvious that it is already there when the FPC comes in. There was a problem, and it slowly became apparent after using it for a while.

Send the bad FPC back to the original FPC factory for analysis. The other party should be very serious. Because we told the other party that all the bad products in the market must be absorbed by the other party, so the supplier is very nervous and actively looking for FPC. The factory traces the possible causes.

After several weeks of hard work, the other party replied that the real reason for the FPC fracture was that there was a gap between the copper foil circuit and the PI layer, so that the copper foil did not have enough support, and the fracture occurred after several stresses. This argument should be established, but the gap should be difficult to avoid, and the rolled copper should have enough ductility to withstand such a gap.

At present, I personally accept this conclusion but doubt it, because if the wrong copper electroplating is used, it will be a batch problem, rather than such a sporadic case. So it should be some single reason that caused the FPC line to break, but the gap is again There is no way to avoid it.

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