Flexible printed circuit board with contoured conductive lines

An exemplary flexible printed circuit board (2) includes a wiring layer (21). The wiring layer includes a number of conductive lines (211). Each of the conductive lines includes a finger (213), a line portion (212) and a junction portion (214) between the finger and the line portion. A width of the finger is greater than a width of the line portion, a width of the junction portion gradually changes from the width of the line portion to the width of the finger. The flexible printed circuit board has high reliability.

FIELD OF THE INVENTION

The present invention relates to flexible printed circuit boards, and particularly to a flexible printed circuit board having high reliability for connecting electrical circuits.

GENERAL BACKGROUND

Many electronic appliances such as liquid crystal display monitors need flexible printed circuit (FPC) boards to connect various electronic circuits together. FPC boards are necessary components in many electronic devices having folding portions.

Referring toFIG. 4, a typical FPC board1includes a wiring layer11, an insulating layer12, and a reinforcing layer13. The insulating layer12covers most of the wiring layer11to protect the wiring layer11from being exposed to air. The reinforcing layer13covers part of the insulating layer12to reinforce the mechanical strength of the FPC board1. The wiring layer11includes a plurality of conductive lines111. The conductive lines111are separate from each other, and are generally parallel to each other. Each of the conductive lines111includes a line portion112and a finger113. The fingers113connect with external circuits or chips. In order to ensure mechanical and electrical contact when the fingers113are connected to an external circuit or chip, a width of each finger113is greater than a width of the corresponding line portion112.

Referring toFIG. 5, because the width of the finger113is greater than the width of the line portion112, a junction portion (not labeled) between the finger113and the line portion112forms sharp right angles. That is, the width of the line portion112at one side of the junction portion is much less than the width of the finger113at the other side of the junction portion. Thus when the FPC board1is bent or the conductive lines111are subjected to other stress, the conductive lines111are liable to fracture or even break at the junction portions. Therefore the reliability of the FPC board1may be unsatisfactory.

Referring toFIG. 6, a strength of the material of the reinforcing layer13is greater than a strength of the material of the insulating layer12and a strength of the material of the wiring layer11. In addition, a thickness of the FPC board1is nonuniform. For these reasons, tension force at a transverse edge portion of the reinforcing layer13at a middle portion of the FPC board1is great. Thus the conductive lines111are liable to fracture or break at the edge portion when the FPC board1is bent. This is another reason why the reliability of the FPC board1may be unsatisfactory.

What is needed, therefore, is an FPC board that can overcome the above-described deficiencies.

SUMMARY

In one preferred embodiment, an FPC board includes a wiring layer including a plurality of conductive lines, each of the conductive lines including a finger, a line portion, and a junction portion between the finger and the line portion, a width of the finger being greater than a width of the line portion, a width of the junction portion gradually changing from the width of the line portion to the width of the finger.

Other novel features and advantages of the present FPC board will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawing figures to describe various embodiments of the present invention in detail.

Referring toFIG. 1, an FPC board2according to an exemplary embodiment of the present invention is shown. The FPC board2includes a wiring layer21, an insulating layer22, and a reinforcing layer23. The insulating layer22covers most of the wiring layer21to protect the wiring layer21from being exposed to air. The reinforcing layer23covers part of the insulating layer22to reinforce the mechanical strength of the FPC board2. The wiring layer21includes a base substrate (not labeled), and a plurality of conductive lines211on the base substrate. The conductive lines211are generally separated from each other, and are parallel to each other. Each of the conductive lines211includes a finger213, a line portion212, and a junction portion214between the finger213and the line portion212. The fingers213of the conductive lines211are configured to connect to external circuits or chips (not shown). That is, the fingers213function as connection pads. The line portion212of each conductive line211connects with the finger213via the junction portion214. In order to ensure mechanical and electrical contact when the fingers213are connected to an external circuit or chip, a width of each finger213is greater than a width of the corresponding line portion212. The line portions212of the conductive lines211are made from copper foil. The fingers213are made from gilded copper. The base substrate is made from polyimide (PI), polyethylene terephthalate (PET), polyester, or polytetrafluoroethylene (PTFE). A thickness of the base substrate is in the range from 10 microns (μm) to 100 μm. The insulating layer22can be made from polyimide (PI). The reinforcing layer23can be made from aluminum (Al).

Referring toFIG. 2, part of one of the conductive lines211is shown. A width of a bottom end of the junction portion214is equal to a width of the line portion212, and a width of a top end of the junction portion214is equal to the width of the finger213. Two opposite edges of the junction portion214are smooth curves or a combination of smooth curves and straight lines. In the illustrated embodiment, each of the opposite edges of the junction portion214has a gently curving, generally S-shaped configuration. For example, each opposite edge can include two arcuate bends arranged end-to-end, with the arc of each arcuate bend being one-quarter of a same circle. Thus, a width of the conductive line211changes gradually at the junction portion214. Because there is no sudden change in width between the finger213and the line portion212, the conductive line211is less liable to fracture or break when the FPC board2is bent or folded. Compared to a conventional FPC board, the FPC board2has improved reliability.

Referring toFIG. 3, the reinforcing layer23covers part of the insulating layer22. A strength of the material of the reinforcing layer23is greater than a strength of the material of the insulating layer22and a strength of the material of the base substrate of the wiring layer21. A transverse edge portion (not labeled) of the reinforcing layer23at a middle portion of the FPC board2has a shape of a wedge. That is, a thickness of the FPC board2changes gradually at the edge portion of the reinforcing layer23. Because there is no sudden change in thickness of the middle portion of the FPB board2, a tension force at the edge portion of the reinforcing layer23is reduced. Therefore the conductive lines211of the FPC board2are less liable to fracture or break at the edge portion of the reinforcing layer23. Thus, the reliability of the FPC board2is further improved.