In a method for fabricating a multi-layered printed circuit board without via holes in accordance with the present invention, a plurality of layers of printed circuit board are stacked layer by layer, and then a plurality of pads pre-formed at edges of each printed circuit board are electrically connected together, thereby achieving electric connection of circuits on different layers of the multi-layered printed circuit board.
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Next, the pads 14 extended to the edge (or side surface) of the printed circuit boards 10 on various layers are electrically connected 16, thereby connecting the circuits 12 on various layers together. The multiple layers of the printed circuit boards 10 mentioned above may be fixed by any conventional methods, such as stapling, riveting, bonding, binding, or any conventional lamination techniques. The electric connection method mentioned above does not have any particular limitation in the present invention. It can be soldering or electroplating.
In order for easily alignment and connection of the pads 14 therebetween on various layers of the printed circuit boards 10, the width of the pads 14 can be broadened, that is, the width of the pads 14 is greater than that of conductive traces of the circuits 12.
When the multiple layers of the printed circuit boards 10 are stacked, in order to make it easy to meet the alignment demand of the electric connection, such as soldering or electroplating, a plurality of aligning holes 18 are provided on the printed circuit boards 10, as shown in
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The conventional substrate of the printed circuit board 10 is a dielectric layer. Therefore, as the conventional multiple layers of the printed circuit boards 10 are stacked by the method according to the present invention, the dielectric layers isolate the circuits 12 on various layers of the printed circuit boards 10. As the circuits 12 on various printed circuit boards 10 are to be electrically connected by the method in accordance with the present invention, the pads 14 extended to the edges of the printed circuit boards 10 are soldered together by a bridge 20, as shown in
A printed circuit board applicable to the present invention is a thin-film printed circuit board, which is conventionally known as a flexible printed circuit board. However, a rigid thin-film printed circuit board can also utilize the method according to the present invention. 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 boards. Additionally, the copper foil layer for the circuits on the printed circuit boards applicable to the present invention may be fabricated with but not limited to electric deposited copper foil, roll annealed copper foil, or heat-treated electrolytic copper foil. Roll annealed copper foil is preferred if the flexibility of the printed circuit board is of concern. The thickness of the aforementioned copper foil 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.