Method for fabricating multi-layered flexible printed circuit board without via holes

Abstract

A method for fabricating a multi-layered flexible printed circuit board without via holes is disclosed herein, which includes the steps of: providing a flexible printed circuit board formed with a circuit thereon in advance; and fan-folding or rolling the flexible printed circuit board to build up a plurality of layers in order to obtain the multi-layered flexible printed circuit board without via holes; thereby being capable of solving the problems resulting from the via holes formed on a conventional flexible printed circuit board.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of a flexible printed circuit board in accordance with the present invention.

FIG. 2 is a perspective schematic view showing a method of folding the flexible printed circuit board of FIG. 1.

FIG. 3 is a perspective schematic view of a fan-folded-type multi-layered flexible printed circuit board in accordance with an embodiment of the present invention.

FIG. 4 is a perspective schematic view showing another method of folding the flexible printed circuit board of FIG. 1.

FIG. 5 is a perspective schematic view of a rolled-type multi-layered flexible printed circuit board in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a method for fabricating a multi-layered printed circuit board without via holes in accordance with the present invention, a flexible printed circuit board is fan-folded repeatedly to build up a plurality of layers in order to accommodate a large amount of conductive traces within a small space inside an electronic product.

Please to refer to FIGS. 1-3, which show a method for fabricating a multi-layered printed circuit board in accordance with an embodiment of the present invention. Also referring to FIG. 1, first, a flexible printed circuit board 10 with a required circuit 12 formed on a single side of the board in advance is provided. The wiring of the circuit 12 may be obtained using prior techniques. The circuit 12 is formed on each area 16 of the flexible printed circuit board 10. After the flexible printed circuit board 10 is folded, each area 16 is configured to be one layer of the multi-layered flexible printed circuit board 10. In addition, each conductive trace of the circuit 12 is electrically connected to a pad 14, and the pad 14 is located on an outer surface of the flexible printed circuit board 10 after it is folded, for connection with an external component.

Before the flexible printed circuit board 10 is folded, the circuit 12 has to be protected and insulated with coverlay or solder mask with the pad 14 left bare. Then the flexible printed circuit board 10 is fan-folded repeatedly (see FIG. 2) to build up a plurality of layers like a sandwich structure (see FIG. 3).

The aforementioned built multiple layers of the printed circuit board 10 may be fixed by any conventional methods, such as stapling, riveting, adhesion, binding, or other conventional lamination techniques.

With reference to FIG. 4, which is a second embodiment of the method in accordance with the present invention, the flexible printed circuit board 10 is rolled up to build up a plurality of layers like an egg roll structure (see FIG. 4), and then is pressed for fixation (see FIG. 5).

A substrate applicable to the present invention is a single-sided thin-film flexible printed circuit board. There is no limitation to the type of the flexible printed circuit board. It may be a two-layer flexible copper clad laminate (FCCL) formed with polyimide film and copper foil, a three-layer FCCL formed with polyimide film, adhesive, and copper foil, or other flexible printed circuit board.

The electrically conductive layer for the circuit on the printed circuit board applicable to the present invention may be fabricated with but not limited to copper foil, electric deposited copper foil, roll annealed copper foil, heat-treated electrolytic copper foil, or electrically conductive aluminum foil. Roll annealed copper foil or aluminum foil are preferred if the flexibility of the printed circuit board is of concern. The thickness of the aforementioned electrically conductive layer may be fabricated according to the requirements, and is not specifically limited in the present invention.

Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.

Claims

1. A method for fabricating a multi-layered flexible printed circuit board without via holes, comprising the steps of: (1) providing a flexible printed circuit board formed with a circuit thereon in advance, said circuit being formed on a single side of said flexible printed circuit board; and(2) fan-folding or rolling said flexible printed circuit board to build up a plurality of layers, wherein said circuit is electrically connected with pads, said pads located on an outer surface of said flexible printed circuit board after folded or rolled, for connection with an external component.

2. The method as claimed in claim 1, wherein a surface of said flexible printed circuit board where said circuit is formed, is covered with an insulating layer, with said pads left bare.

3. The method as claimed in claim 2, wherein said insulating layer is one of coverlay and solder mask.

4. The method as claimed in claim 1, further the step of fixing said fan-folded or rolled flexible printed circuit board after said step (2).

5. The method as claimed in claim 1, wherein said flexible printed circuit board is a single-sided thin-film flexible printed circuit board.

6. The method as claimed in claim 1, wherein an electrically conductive layer served as said circuit on said printed circuit board is made of the material selected from the group consisting of electric deposited copper foil, roll annealed copper foil, heat-treated electrolytic copper foil, and electrically conductive aluminum foil.