BACKGROUND OF THE INVENTION 0001 1. Field of the Invention 0002 The present invention is related to a manufacturing method for a flexible PCB (Printed Circuit Board), and more particularly to a flexible PCB formed with single backing double exposed foil. 0003 2. Description of Related Art 0004 Referring to FIG. 3, a conventional manufacturing method for a flexible printed circuit board with single backing double exposed foil is illustrated. A polyimide backing (70) is first plated with a copper layer (71) at a first surface thereof, as shown in FIG. 3A. A first sensitive layer (72) is provided on the copper layer (71), as shown in FIG. 3B. A first circuit pattern is printed on the first sensitive layer (72) by shooting, exposing and developing, as shown in FIG. 3C. The unwanted sensitive material is removed and the first circuit pattern is then formed on the first sensitive layer (72), as shown in FIG. 3D. According to the circuit pattern on the first sensitive layer (72), the unwanted copper is removed by etching, as shown in FIG. 3E. Afterwards, the first sensitive layer (72) is removed and the copper circuit (710) is formed at the first surface of the backing (70), as shown in FIG. 3F. 0005 A second sensitive layer (73) is provided on a second surface of the backing (70), as shown in FIG. 3G. A second circuit pattern is printed on the second sensitive layer (73) by shooting, exposing and developing, as shown in FIG. 3H. The unwanted sensitive material is removed and the second circuit pattern is then formed on the first sensitive layer (73), as shown in FIG. 3I. According to the second circuit pattern on the second sensitive layer (73), the unwanted polyimide is removed by etching, as shown in FIG. 3J. Finally, the second sensitive layer (73) is removed and the copper circuit (710) is exposed from the backing (70) to form the second circuit pattern, as shown in FIG. 3K. 0006 In this process, there are two procedures of optical lithography to respectively form the circuit patterns on the both surfaces of the backing. The optical lithography need use poisonous chemical preparation in processing and will produce a lot of poisonous waste water, which is very harmful to environment. 0007 Therefore, the invention provides an improved manufacturing method for a flexible PCB to mitigate and/or obviate the aforementioned problems.

SUMMARY OF THE INVENTION 0008 The main objective of the invention is to provide a manufacturing method for a flexible PCB which is advantageous to environment protection. 0009 Another objective of the invention is to provide a manufacturing method for a flexible PCB which is simplified. 0010 Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 0011 FIG. 1 is a diagram of a process for manufacturing a flexible PCB in accordance with the invention; 0012 FIG. 2 is a schematic view showing the process for manufacturing the flexible PCB in accordance with the invention; and 0013 FIG. 3 is a schematic view showing a conventional manufacturing method for the flexible PCB.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 0014 Referring to FIG. 1, a manufacturing method for a flexible PCB in accordance with the invention includes steps: 0015 Forming a copper circuit on a first surface of a polyimide backing; 0016 Removing unwanted polyimide by a laser processing to expose the copper circuit on a second surface of the backing; 0017 Removing polyimide leavings generated by the laser processing; and 0018 Making a surface treatment to the copper circuit exposed at the second surface of the backing. 0019 FIG. 2 shows a preferred embodiment according to the present invention. As shown in FIG. 2A, a copper layer (11) is formed on a polyimide backing (10). The backing (10) with the copper layer (11) has a double layers type and a triple layers type. In the former, the copper layer (11) is directly plated on a first surface of the backing (10), and in the latter, a layer of adhesive is provided between the copper layer and the backing (10). In this embodiment, the backing (10) with the copper layer (11) is the double layers type. 0020 By a conventional procedure of optical lithography, a copper circuit (110) is formed on the first surface of the backing (10), as shown in FIG. 2B. The procedure of optical lithography includes following steps: 0021 Covering the copper layer (11) with a sensitive layer (not shown or numbered); 0022 Printing a first circuit pattern on the sensitive layer and removing unwanted sensitive material; and 0023 Removing unwanted copper by etching according to the circuit pattern and removing the sensitive layer. 0024 Thereafter, by a laser processing, the unwanted polyimide (10) is removed to define windows (111) on the backing (10) and the copper circuit (110) is exposed from these windows (111) to form a second circuit pattern on a second surface of the backing (10), as shown in FIG. 2C. 0025 In the laser processing, the second circuit pattern is drawn in a computer by a CAD software such as AutoCAD and translated to machining information inputting a laser machine. According to these machining information, the laser machine can remove unwanted polyimide to define the windows (111) as the second circuit pattern. The laser source can be CO2, YAG, or UV, etc. 0026 Certainly, the copper circuit (110) on the first surface of the backing (10) also can be manufactured by the laser processing to remove unwanted copper. 0027 When the laser source is CO2, the backing (10) will have polyimide leavings (not numbered) in the windows (111) thereof, as shown in FIG. 2D. Thus, the backing (10) must be put in a cleaning solvent, of which a PH value is above 12, preferable 13 to 14, to remove these leavings. The cleaning solvent can be potassium permanganate, natrium permanganate, or alkaline solution. The preferable temperature of the cleaning solvent is above 75 C. 0028 Afterwards, the PCB is put in a treating solvent to make a surface treatment for the copper circuit exposed on the second surface thereof. The treating solvent can be sulfuric acid, hydrogen peroxide, diluted sulfuric acid, or micro etchant. 0029 From the above description, it is noted that the invention has the following advantages: 0030 1. The manufacturing process is simple because the second surface of backing is machined by laser. 0031 2. Because there is only one or no procedure of optical lithography in the manufacturing process, poisonous waste water is reduced greatly and it is very advantageous to environment protection. 0032 It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.