PCB Tech - Check the FPC defective product open circuit position

When analyzing this kind of soft line breakage, which is also difficult to detect with the naked eye or microscope, the segmented elimination method is usually adopted.

When we encounter the problem of open/disconnected FPC (soft board), the easiest way is to check the problem of trace breakage under the microscope, because FPC is usually a single-layer board, and it is a three-layer board. Most of the lines can be seen through optical instruments. However, Shenzhen Grace Jie has encountered many cases. The line break can not be detected under the microscope, but the gold finger is directly measured with a three-meter electric meter. However, it is possible to measure the open circuit, or the ups and downs of contact.

In fact, there is no need to fuss over such a result, because FPC is called "soft board" because it is soft and can be bent. This is also the advantage and disadvantage of FPC. The disadvantage is that it can be bent because it may cause copper foil. The copper trace is broken.

Although copper foil is soft, repeated bending or reciprocating motion or impact is still very likely to cause it to break. If it is visible to the naked eye, it is easy to solve, because just observe the location of the break. In general, the cause of the fracture can be known, and countermeasures can be taken.

The more difficult thing is that the open/disconnected circuit can be measured from the gold finger at the end, but the location of the copper foil break can not be found. If the location is not found, it is difficult to confirm what caused the FPC break.

1. First observe the problematic circuit with a microscope, and first find the suspicious broken position and mark it.

2. If the microscope can't find any suspicious fracture location, you can also divide the line into several small sections.

3. At the two ends of the line where the line may be broken, or at the segmented position, carefully cut the cover film of the soft board with a blade. It is best to take a new utility knife or engraving knife, and then Place the blade on the outer protective film and move it left and right to scrape the cover film and expose the copper foil circuit underneath. In this way, you can use a three-purpose meter to measure the line. Then step by step to eliminate the location that may be broken, and finally you can find the exact location of the break of the copper foil circuit.

4. If you are worried that this method may break the copper foil circuit, you can also try to cut the place where there is no copper foil next to the copper foil circuit, and then try to peel off the cover film to achieve the same purpose .

(This method needs to be very careful and dexterous, I believe that capable PCBA engineers should be able to do it)

If you are worried that this method may break the copper foil circuit, you can also try to cut the place where there is no copper foil next to the copper foil circuit, and then try to peel off the cover film to achieve the same purpose.

Once you find the exact location of the copper foil circuit breakage, if you still cannot observe the fracture, try to bend the soft board at that location under a microscope, so that you can highlight and enlarge the opening of the broken copper foil.

5. Once you find the exact location of the breakage of the FPC copper foil circuit, if you still cannot observe the fracture, try to bend the soft board at that location under a microscope, so that you can highlight and enlarge the opening of the broken copper foil.