Flexible printed circuit board. The number of circuits in one FPC can exceed 100, but it only occupies the thickness of 0.2mm Although it is more expensive than flat cable, it is widely used in smart products with compact volume. Especially mobile phones, smart bracelets and other scenes.
Today, the most important thing for everyone is to talk about the golden finger design skills of soldered FPC.
How about the quality of the hardware, the design accounts for more than half.
FPC welding can save two board-to-board connectors or one Zif connector, saving 1-2 yuan dollars in cost.
Therefore, in many low-end products, the soldered FPC is selected. (Hand-made welding is faster than equipment pasting. )
If the real FPC is well designed, it is not only more cost-effective than the connector, but also stronger than the connector: welding is undoubtedly more solid than fastening.
The defect is that the relative connector in the welding area is larger and the maintenance is more complicated.
Although only one layer of solder layer can be matched with the gold finger, the gold finger of FPC can’t be only one layer.
FPC is a nonmetallic plate, and its heat conduction is relatively slow. If there is only one layer of gold fingers, the heat transfer of the soldering iron can’t be achieved by hand, so there is no way to weld it.
Similarly, the tin holes punched in the welding layer are also used to conduct heat and allow the molten solder wire to flow between the upper and lower layers.
At the beginning, the technical engineer only dried the double-sided pads. However, in the case of commodity manufacturing, FPC is often short-circuited.
After that, it was found that the quality of FPC manufacturers was not very good, but the in-situ stress was too large and it was very easy to break, so it must be improved according to the design method.
Finally, everyone invented the method of “two-sided wiring+additional via”, and finally solved this problem. No matter how you fold it, FPC is not easy to break.
Cause of destruction: FPC can be bent, which is basically created in the copper berth. After FPC welding, the welding surface cannot be pulled. Once pulled up, the supporting points are concentrated on the edge of the welding surface, and the edge will be torn off.
After changing to two-sided routing, the problem of bottom edge breakage is not actually solved. However, due to the double-layered routing, it is not easy to cause data signal short circuit because one layer is broken and another layer is broken.