FPC, flexible circuit board. The number of FPC circuits can exceed 100, but only occupies a thickness of 0.2mm. Although more expensive than wiring, it is widely used in compact smart hardware. Especially mobile phones, smart watches and other scenarios.

Soldered FPC golden finger design tips.

Hardware product quality don't do well, design accounted for more than half!

Benefits of welding FPC

FPC welding can save 2 board-to-board connectors or 1 Zif connector, saving 1-2 yuan of cost.

So in many low-end products, the use of welding FPC. (manual welding, faster than machine mounting.)

Soldered FPC, if designed well, is not only cheaper than the connector, it is also more robust: soldered than buttoned.

The disadvantage is that the welding area is larger than the connector and maintenance is more complex.

Double goldfinger + through tin hole

Although the gold finger corresponds to only one layer of pad, FPC's gold finger cannot be made into only one layer.

FPC is a non-metallic substrate with slow heat transfer. If there is only a layer of golden fingers, manual welding when the heat transfer iron cannot pass, it is difficult to weld.

Similarly, holes in the solder pads are made to transfer heat and allow molten solder to flow between the upper and lower layers.

Double-sided threading + extra holes

In the early days of engineering, they only made two-sided pads. However, FPC is often broken when the product is manufactured.

Later, it was found that FPC manufacturers were not to blame for the poor quality, but the stress was too large and easy to fracture, which must be improved through design methods.

Finally, we invented the method of "double-sided threading + extra holes", which finally solved this problem. No matter how you fold it, the FPC will not break.

Cause of damage: FPC can be bent, is based on the copper foil as a whole is stretched. After FPC welding, the welding surface cannot be stretched. Once pulled, the force is concentrated on the edge of the welded face, and the edge is broken.

After changing to double-layer wiring, the problem of bottom surface fracture has not been solved. However, because of the two layers of wiring, one layer is broken and one layer is left, the signal circuit will not be broken.