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FPC (flexible circuit board) broken two major reasons analysis | YMSPCB

Analysis of two major causes of FPC fracture

1. FPC is too short.

2. The material is too hard

It may be better to replace the soft material. 100,000 times of folding is not a problem.

In addition, FPC breaking is a problem in the early stage, which I personally think is not very difficult. The most fatal problem is FPC ringing, excluding the interference of FPC and over-hole. Do you have any good methods for FPC ringing?

There are several common problems with FPC:

Broken LCD does not display and flip out sound;For fracture, most of them are short in design length. In addition, the structural design of the hole gap at the point where the FPC penetrates is not reasonable, which leads to the abnormal sound of the clamshell.

In short, the FPC needs to be repeatedly tried several times before the design is in place. It is better to use transparent shell, or cut the shell open, observe more, and then make design improvements.

Of course, some manufacturers just began to make samples without problems, and then mass production problems, we must see if it is the problem of materials

(I) it can be seen from the first analysis of the fractured FPC pictures that:

1. The fault is the outer electromagnetic shielding layer of FPC

2. As can be seen from the figure, this layer is folded from the back of the product in the swing area, so it is judged that this layer is made separately and then attached to the FPC product

(ii) fracture reason speculation:

1. The shielding layer is solid copper with high hardness, which increases the possibility of fracture during rocking.

2. The shielding layer is attached to the FPC separately, which is not a tight whole with the FPC product. During the rocking process, it will deviate from the original bending direction, which may lead to excessive stress concentration and fracture.

(iii) Suggestions:

1. Wrap tape around the fracture and bind it to FPC to increase its tightness with FPC.

2. Change the copper surface of the shielding layer to mesh to reduce hardness.

Long-term recommendations:

For the shielding layer of FPC swing zone, using the method of making printed or coated conductor, or fitting the conductive cloth specially used for FPC electromagnetic shielding, the problem of shielding breakage will be completely avoided, and the cost will not increase.

The FPC can design a tear line.And DOME has a protective membrane to protect it from moisture and dust.

Change the copper layer of FPC to copper mesh, increase the deflection of FPC, which should be solved, but for binding, it is recommended to do as a last necessity.

As for the fracture of this figure, I personally think it is caused by pulling, that is, the FPC is too short, and the FPC is too porous, which is mainly caused by the mechanism of the rubber shell.We have used silver printing now, which can make FPC thinner, and the effect is good, 100,000 times ok!

This out makes basket empty structure, the reference mobile phone main board bending place.

This is caused by torsion during inversion. The FPC at (right) b-b in the figure should be moved to the center to lengthen the length of torsion deformation and reduce the possibility of fracture.

FPC shield now a lot of useful aluminum foil, clamshell will be better;

FPC design I think is the most important should reduce stress concentration, rounded corners is must as far as possible big, many cases are in FPC fillet fracture, more rounded corners will be improved substantially, had the ends of the shaft do not have apparent stress produced (like about connectors don't stand too close to the people in rotor lead parts, FPC on both ends of the bonding layer can produce a large torsional force);

FPC also has its own torsional force. If the axial length of the over-axis part is longer, it will weaken its own torsional force, but if it is too long, there will be obvious patting sound between layers.

The supplier of FPC is also an important link. There are electrolytic copper and calendered copper on the FPC copper wire.

The length simulation of FPC is very important, and the analysis of failure parts in the later stage should be in place as soon as possible.

In fact, the FPC life is also related to the housing structure.Because of the constant need for movement and the limited space in the housing, the FPC will inevitably come into contact with the hard housing.The flip is less obvious than the canopy.

Quality and price are inseparable.But the FPC's individual value is relatively low, but the original device on the board is not cheap, in addition, if the warranty period is broken, the warranty cost is much higher than the FPC's value.

Images for fpc

Post time: Aug-28-2019
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