Abstract:
A method for cutting a printed circuit board includes providing a printed circuit board including a cutting region having a plurality of metal conducting wires, disposing a patterned first protection layer on the printed circuit board surface and exposing the metal conducting wires in the cutting region, forming a conducting layer on a surface of the metal conducting wires, disposing a second protection layer on the cutting region, performing a cutting process in the cutting region, and removing the second protection layer.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for cutting a printed circuit board, and more particularly, to a cutting method capable of reducing burrs in metal conducting wires and increasing the quality of printed circuit boards. 
   2. Description of the Prior Art 
   The window ball-grid-array (WBGA) package is a novel chip package technology. Connecting wires, which are drawn from a die, of a WBGA packaged memory pass through a window of a load board and connect with contact pads on the load board. Therefore, the connecting wires between the die and the load board are shortest of all of ball-grid-array (BGA) package technologies in existence such that the transmission speed is quicker and the inductance and the noise interference are smaller. For this reason, WBGA packaged memories are more suitable to be applied in a high frequency and high speed operation environment, and because of the short connecting wires WBGA packaged memories have lower power consumption and generate less heat. For instance, memories adopting the WBGA package technology have two to three times more memory capacity than other memories, which have the same size, and have better electric and heat conducting characteristics, so they are widely applied in portable products, for example, desktops and so forth. 
   A load board of a WBGA packaged memory is fabricated by using printed circuit board compatible processes, and windows of the load board and finished product separations are performed by utilizing cutting mills.  FIG. 1  to  FIG. 4  are schematic diagrams for illustrating a method for forming a window  26  by cutting a load board  10  of a WBGA packaged memory according to the prior art. As shown in  FIG. 1 , a substrate  12  is provided after an internal circuit process of the substrate  12  is finished. A plurality of metal conducting wires  14 ,  16 ,  18 ,  20 , and  22  consisting of copper are formed on an upper and a lower surface of the substrate  12 . 
   As shown in  FIG. 2 , a solder-resist ink layer  23  covers a portion of the metal conducting wires  14 ,  16 ,  18 ,  20 , and  22 . An exposure and development process are performed to increase an adhesive force between the solder-resist ink layer  23  and the metal conducting wires  14 ,  16 ,  18 ,  20 , and  22  by light polymerization. As shown in  FIG. 3 , a conducting layer  24  is plated on the metal conducting wires  14 ,  16 ,  18 ,  20 , and  22 , which are not covered by the solder-resist ink layer  23 . The conducting layer  24  consists of nickel (Ni) or gold (Au). As shown in  FIG. 4 , a cutting process is performed to form a window  26  by utilizing mill cutting on the substrate  12 . The window  26  of a load board  10  of a WBGA packaged memory is finished. 
   According to the prior art, when a mill is used to cut the load board  10  of the WBGA packaged memory directly to form the window  26 , burrs often result in edges where the metal conducting wires  14 ,  16 , and  18  are cut, influencing the quality of the load board  10 . In the past, the burrs are removed by laborers, hence manual labor is required and the quantity of output is influenced. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of the present invention to provide a method for cutting a printed circuit board to prevent metal conducting wires from having burrs and to increase the quality of the printed circuit board. 
   According to the objective of the present invention, the present invention provides a method for cutting a printed circuit board, which includes providing a printed circuit board including a cutting region having a plurality of metal conducting wires, disposing a patterned first protection layer on the printed circuit board surface and exposing the metal conducting wires in the cutting region, forming a conducting layer on a surface of the metal conducting wires, disposing a second protection layer on the cutting region, performing a cutting process in the cutting region, and removing the second protection layer. 
   Since the present invention utilizes the second protection layer to cover the cutting region and press against the metal conducting wires, burrs will be prevented while cutting. Furthermore, the second protection layer can be removed easily after the cutting process is finished. Therefore, the present invention is capable of increasing the quality of printed circuit boards, saving manual labor for removing burrs, and reducing the production cost. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  to  FIG. 4  are schematic diagrams for illustrating a method for forming a window by cutting into a load board of a WBGA packaged memory according to the prior art. 
       FIG. 5  to  FIG. 10  are schematic diagrams for illustrating a method for cutting a printed circuit board according to the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 5  to  FIG. 10 .  FIG. 5  to  FIG. 10  are schematic diagrams for illustrating a method for cutting a printed circuit board according to the present invention. As shown in  FIG. 5 , a printed circuit board  30  is provided. The printed circuit board  30 , which is a multi-layer printed circuit board having undergone an internal circuit process, includes a substrate  32  and a plurality of metal conducting wires  34 ,  36 ,  38 ,  40 , and  42  disposed on the substrate  32  surfaces. The substrate  32  can be fabricated by using a copper clad laminate (CCL) or an insulating substrate without an additional copper clad layer. For convenience of illustration, the present embodiment only displays the five metal conducting wires  34 ,  36 ,  38 ,  40 , and  42  that are fabricated by a photolithography and etching process or a plating, photolithography, and etching process. The metal conducting wires  34 ,  36 ,  38 ,  40 , and  42  are made of copper. 
   Please refer to  FIG. 6 . A first protection layer  44  is disposed on (i.e. coated onto) a portion of the lower and the upper surfaces of the printed circuit board  30  and disposed on a portion of the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42  to form a cutting region  46 . The cutting region  46  includes the metal conducting wires  34 ,  36 , and  38 . The first protection layer  44  is selected from a group consisting of dry film, wet film, B-stage epoxy, and ultraviolet adhesive tape and is disposed onto the printed circuit board  30  surfaces by screen-printing, sticking, laminating, or other process. In the present embodiment, the first protection layer  44  is a wet film comprising a solder-resist ink layer and coated onto the printed circuit board  30  surfaces by screen-printing to cover a portion of the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42 . An exposure and development process is performed to increase an adhesive force between the first protection layer  44  and the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42  by light polymerization, and then the first protection layer  44  indeed presses against and covers the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42 . 
   As shown in  FIG. 7 , a conducting layer  48 , for example, comprising nickel (Ni) or gold (Au) is plated on the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42 , which are not covered by the first protection layer  44  to enhance the corrosive resistance and increase the electric conductivity of the metal conducting wires  34 ,  36 ,  38 ,  40 , and  42 . 
   Please refer to  FIG. 8 . A second protection layer  50  is formed on the upper surface of the printed circuit board  30 . The second protection layer  50  is disposed on the cutting region  46  completely coating it, and covers the metal conducting wire  34 ,  36 , and  38 , which will be cut. The second protection layer  50  is selected from the group consisting of dry film, wet film, B-stage epoxy, and ultraviolet adhesive tape and is disposed on the cutting region  46  by screen-printing, sticking, laminating, or other process. In the present embodiment, the second protection layer  50  is a wet film comprising a solder-resist ink layer and coated onto the cutting region  46  or a vicinity of the cutting region  46  by screen-printing to cover the exposed metal conducting wires  34 ,  36 , and  38 . An exposure and development process is performed to increase an adhesive force between the second protection layer  50  and the metal conducting wires  34 ,  36 ,  38 ,  40  and  42  by light polymerization, and then the second protection layer  50  indeed presses against and covers the metal conducting wires  34 ,  36 , and  38  to prevent the metal conducting wires  34 ,  36 , and  38  from being damaged during follow-up cutting. 
   As shown in  FIG. 9 , a cutting process is performed in the cutting region  46  to cut off at least one of the metal conducting wires  34 ,  36 , and  38  and separate the region of the printed circuit board  30  which is not covered by the first protection layer  44  and is electrically connected by the metal conducting wires  34 ,  36 , and  38 . According to the requirements of specific products, the printed circuit board  30  is separated to form two printed circuit boards or is cut to form a window in the printed circuit board  30 . In the present embodiment, a window  52  is formed in the printed circuit board  30  by cutting, and the window  52  is a window of a load board of a WBGA packaged memory. The cutting process could be performed by a mill, a punch, or a blade according to the prior art. In the present embodiment, a mill is used for cutting. In the cutting process, since the second protection layer  50  indeed presses and covers the metal conducting wires  34 ,  36 , and  38 , portions of the metal conducting wires  34 ,  36 , and  38  that are not cut are protected properly and the mill does not pull, drag, or damage the metal conducting wires  34 ,  36 , and  38  to induce burrs. 
   Please refer to  FIG. 10 . The protection layer  50  is removed by an etching or a stripping process to complete manufacturing a window  52  of the load board of the WBGA packaged memory. The metal conducting wires  34 ,  36 , and  38  are contact pads of the load board of the WBGA packaged memory. In the present embodiment, since the second protection layer  50  is a solder-resist ink layer, which is hardened by light polymerization, it is easily striped by a prior art method to save manual labor in removing burrs, increase the yield, and reduce the production cost. Furthermore, since the second protection layer  50  can be removed, an appearance of a product made according to the present invention is not different from an appearance of a product made according to the prior art. It is noted that the second protection layer  50  can be completely removed or partially removed depending on the requirements of different products. The second protection layer  50  can be completely removed if the end user wants to preserve the inherent appearance of the product, or it can be partially removed if the end user does not care about the inherent appearance of the product but wants an additional protection layer to protect the contact pads. In the case that the second protection layer is partially removed, the removal exposes a portion of the contact pads, which will be bonded. 
   Compared to the prior art, since the present invention utilizes the second protection layer to cover the cutting region and press the metal conducting wires, burrs will be prevented while cutting. Furthermore, the second protection layer can be removed easily after the cutting process is finished. Therefore, the present invention is capable of increasing the quality of printed circuit boards, reducing manual labor in removing burrs, and reducing the production cost. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.