PCB Tech - ​Integration of inspection items for rigid-flex boards

What are the inspection items for rigid-flex circuit boards?

There are many inspection items for the rigid-flex circuit board, because the rigid circuit board PCB only serves as an electrical connection, and the flexible circuit board FPC not only has the same function as the rigid circuit board PCB, but also has the ability to fold and bend. Function, so this mechanical performance must also be checked to ensure quality.

At present, more than 100% inspections are performed on flexible printed circuit boards FPC. Of course, in addition to the FPC disconnection and short circuit must be checked and there are inspection equipment, there are also many other items for visual inspection. Generally, lines can be inspected manually or with a magnifying glass of 2 to 3 times, but high-power microscopes should be used to inspect high-density lines. Lines with a size of about 100μm should be inspected with a magnifying glass of 5-10 times, lines with a size of 50-100μm should be inspected with a magnifying glass of 10-20 times, and lines below 50μm should be inspected with a stereo microscope with a magnification of 20 times or more. It is not that the higher the magnification of the microscope, the better.

To be able to perform inspections efficiently, a wide field of view is also very important. Although it is a high magnification, the inspection efficiency cannot be improved without the electronic image magnification function.

Using automatic optical inspection instrument (AOI, Automatic Optical Inspection) to inspect the defects of flexible printed circuit board is still only a part of mass production. The automatic optical inspector has been used in the tape reel process, but the automatic optical inspector can only inspect the defects of the circuit and can only partially replace the inspector. Moreover, the flexible circuit is different from the usual digital circuit, and the conventional automatic optical inspector cannot be used., Must also attach a special program. It is difficult to adapt to the rapid development of miniaturized circuits.

With the high density of circuits, the magnification of the microscope used will increase accordingly, and the inspection time per unit area will also be extended. The proportion of man-hours required for the inspection of flexible printed boards is not small. With the further development of circuit density, this The proportion will increase further. If the defect rate drops, the inspection speed will increase, but the density of the circuit continues to move forward. From the inspection standpoint, the pass rate of the precision pattern circuit will not increase significantly.

All inspection items of rigid-flex circuit boards are not carried out in the final process, especially the defects of the circuit and coverage are better to be inspected in the process. The reality is that the inspection in the process cannot completely replace the final inspection, but it still has a certain effect on improving the efficiency of the entire production.