Abstract:
A printed circuit board substrate includes an insulation matrix and a waterproof layer. The insulation matrix includes a first surface and a second surface at an opposite side thereof to the first surface. The waterproof layer is formed in the insulation matrix and is arranged between the first surface and the second surface for blocking water from passing therethrough in a thicknesswise direction of the insulation matrix.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to flexible printed circuit boards (PCBs) and, particularly, to a printed circuit board substrate and a printed circuit board having the same. 
         [0003]    2. Description of Related Art 
         [0004]    Nowadays, flexible printed circuit boards (FPCBS) are widely used in portable electronic devices such as mobile phones, digital cameras, and personal digital assistants (PDAS). In some electronic devices, certain parts are movable relative to a main body. In these electronic devices, FPCBS can maintain an electrical connection between the main body and the movable parts due to their flexibility. 
         [0005]    FPCBS can be manufactured by at least a base film using a wetting process, such as cleaning, developing, etching, electro-plating, etc. The base film includes an insulation film and a copper film. For example, a process for manufacturing electrical traces of the FPCB includes the following steps. Firstly, the base film is cleaned in a cleaning solution to remove surface oils of the copper film. Secondly, a photo-resist layer is formed on the surface of the copper film. Thirdly, the photo-resist layer is exposed to a light beam using a mask having a predetermined pattern. Thus, one portion of photo-resist layer is covered by the mask, and the other portion of photo-resist layer is not covered and irradiated by the light beam. When the photo-resist layer is made of a positive photo-resist, the uncovered photo-resist layer (i.e. the exposed photo-resist layer) is changed to be soluble in a developing agent. Fourthly, the base film having the photo-resist layer is developed in the developing agent. During the developing process, the exposed photo-resist layer is dissolved in the developing agent, and the residual photo-resist layer forms a patterned photo-resist layer. Thus, one portion of the copper film is covered by the pattered photo-resist layer, and the other portion of the copper film is exposed to the outside. Fifthly, the base film having the patterned photo-resist layer is arranged in an etching solution, and the copper film not covered by the photo-resist layer is dissolved by the etching solution. As a result, the residual copper film covered by the photo-resist layer forms a copper trace. Finally, the photo-resist layer covering the copper trace is eliminated, thereby obtaining the desired electrical traces of the FPCB. 
         [0006]    In the process mentioned above, the base film is exposed in liquid solutions (e.g., the cleaning solution, the developing agent, the etching solution) repeatedly, and the liquid solution may inevitably penetrate into the base film. Thus, an original characteristic of the base film may be changed, thereby affecting the quality of the FPCB manufactured by such base film. Furthermore, when the copper film is made into copper traces, molecules (e.g., water molecules) or other ions of the liquid solution may migrate from the insulation film to the copper traces to react with the copper traces. That is, an ion migration phenomena has happened between the insulation film and the copper traces. As a result, a quality of the copper traces may be affected, e.g., causing an open circuit phenomena or a short circuit phenomena. 
         [0007]    What is need, therefore, is PCB substrate which can resist/avoid the happening of the ion migration phenomena. What is also need is a PCB having the PCB substrate. 
       SUMMARY OF THE INVENTION 
       [0008]    An embodiment of printed circuit board substrate includes an insulation matrix and a waterproof layer. The insulation matrix includes a first surface and a second surface at an opposite side thereof to the first surface. The waterproof layer is formed in the insulation matrix and is arranged between the first surface and the second surface for blocking water from passing therethrough in a thicknesswise direction of the insulation matrix. 
         [0009]    Advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0011]      FIG. 1  is a schematic view of an insulation film, in accordance with a present first embodiment. 
           [0012]      FIG. 2  is a schematic view of a base film, in accordance with a present second embodiment. 
           [0013]      FIG. 3  is a schematic view of a base film, in accordance with a present third embodiment. 
           [0014]      FIG. 4  is a schematic view of a base film, in accordance with a present fourth embodiment. 
           [0015]      FIG. 5  is a schematic view of a flexible printed circuit board, in accordance with a present fifth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Embodiments will now be described in detail below and with reference to the drawings. 
         [0017]    Referring to  FIG. 1 , an insulation film  10 , in accordance with a first preferred embodiment, is shown. The insulation film  10  is used as a printed circuit board substrate and includes an insulation matrix  11 , and a waterproof layer  20  formed in the insulation matrix  11 . The insulation matrix  11  includes a first surface  12  and a second surface  14  on opposite sides of the insulation matrix  11 . At least one waterproof layer  20  is formed between the first surface  12  and the second surface  14  to separate/divide the first surface  12  and the second surface  14  from each other along a thickness (height) of the insulation matrix  11 , thereby preventing molecules or ions migrating/seeping/leaking between the first surface  12  and the second surface  14 . In other words, the waterproof layer  20  is provided to avoid an ion migration phenomena happening between the first surface  12  and the second surface  14 . In order to realize the separation/division the first surface  12  and the second surface  14 , a projection area of the waterproof layer  20  along the thickness of the insulation matrix  11  is equal to a vertical sectional area of the insulation matrix  11 , where the waterproof layer  20  is located. 
         [0018]    The waterproof layer  20  is made of waterproof materials such as an aluminum foil. When used as the waterproof layer  20 , the aluminum foil has many advantages, such as excellent waterproof characteristics, light weight, non-magnetic, low oxidation activity, corrosion resistance, and so on. Therefore, the waterproof layer  20  made of aluminum foil is adopted in the insulation matrix  11  to add the corresponding advantages of the aluminum foil to the waterproof  20 . 
         [0019]    The insulation film  10  can be used to manufacture either rigid or flexible PCBS. Generally, the PCBS are composed of at least one base film. The base film includes an insulation film and a copper film formed on at least one surface of the insulation film. A thickness of the insulation film is in a range from about 7 mils to about 8 mils (1 mil equals to about 25.4 micrometers), and the thickness of the waterproof layer  20  have a thickness in a range from about 3 micrometers to about 25 micrometers. It is to be understood that any potential variances in the thickness of the waterproof layer  20  are considered to be within the scope of the present insulation film  10 , so long as the waterproof layer  20  prevents the ion migration phenomenon from happening between the first surface  12  and the second surface  14 . 
         [0020]    The insulation matrix  11  can be made of a resin or a prepreg. The resin includes phenolic resin, epoxy resin, polytetrafluoroethylene (PTFE) resin, polymide resin, and so on. The prepreg is a semi-hardened composite sheet made of a fiberglass cloth and one of the above resins. The fiberglass cloth is soaked in one of the resins, e.g., epoxy resin, and is dried, thereby yielding an epoxy prepreg. 
         [0021]    The insulation film  10  of the present embodiment is manufactured using a laminating method. First, one waterproof layer  20  and two insulation matrixes  11  are provided. Second, the waterproof layer  20  is clamped between the two insulation matrixes  11 . Finally, the two insulation matrixes  11  with the waterproof layer  20  clamped therebetween are laminated by a laminating device, thereby yielding a desired insulation film  10 . In the present embodiment, the two insulation matrixes  11  are two fiberglass cloths, and the waterproof layer  20  is an aluminum foil. Moreover, two or more of the waterproof layer  20  can be configured between two insulation matrixes  11  correspondingly to manufacture various insulation films  10 . 
         [0022]    In other preferred embodiments, the insulation films  10  may have a multi-layered configuration composed of a number of waterproof layers  20  and a number of matrixes  11  laminated in an alternating manner correspondingly. In the multi-layered configuration, the insulation matrix  11  may be resin, prepreg, or the combination thereof. For example, the insulation film  10  includes three insulation matrixes  11  and two waterproof layers  20  clamped between adjacent two insulation matrixes  11  correspondingly. In the three insulation matrixes  11 , one of the three insulation matrixes  11  is epoxy prepreg, while the remained of the three insulation matrixes  11  are epoxy resins. It is to be understood that any potential variances in the configuration of the insulation matrix  11  are considered to be within the scope of the insulation film  10 , as long as at least one waterproof layer  20  is provided in the insulation film  10  to prevent the ion migration phenomenon from happening between the first surface  12  and the second surface  14 . 
         [0023]    Referring to  FIG. 2 , a base film  100  for manufacturing flexible printed circuit board (FPCB), in accordance with a second embodiment, is shown. The base film  100  is used as a printed circuit board substrate and includes an insulation film  110 , an electrically conductive layer  120  formed on at least one surface of the insulation film  110 , and at least one waterproof layer  130 . The insulation film  110  includes a first surface  111  and a second surface  112  on opposite sides of the insulation film  110 . The electrically conductive layer  120  is formed on the first surface  111 . The waterproof layer  130  is formed between the first surface  111  and the second surface  112  to separate/divide the first surface  111  and the second surface  112  from each other along a thickness (height) of the insulation film  110 , thereby preventing molecules or other ions from migrating/seeping/leaking between the first surface  111  and the second surface  112 . In order to achieve this separation/division, a projection area of the waterproof layer  130  along the thickness (height) of the insulation film  110  is equal to a vertical sectional area of the insulation film  110 , where the waterproof layer  130  is positioned. When wetting processes such as clearing, etching, electro-plating and so on, is performed on the base film  100 , the waterproof layer  130  prevents molecules or other ions migrating from the second surface  112  to the first surface  111  and further reacting with the electrically conductive layer  120 . As a result, a natural characteristic of the electrically conductive layer  120  cannot be affected or changed. Especially, when the electrically conductive layer  120  is made into electrical traces, the electrical traces cannot be affected (e.g., cannot causing an open circuit phenomena or a short circuit phenomena). 
         [0024]    In the present embodiment, the insulation film  110  is a rectangular sheet, and the waterproof layer  130  is a flat aluminum foil. The waterproof layer  130  is parallel to the first surface  111  and the second surface  112 , and is arranged between the first surface  111  and the second surface  112 . In the present embodiment, the projection area of the waterproof layer  130  along the thickness (height) of the insulation film  110  is equal to a surface area of the waterproof layer  130 . Therefore, the surface area of the waterproof layer  130  is identical with that of either the first surface  111  or the second surface  112 . Thus, the waterproof layer  130  separates/divides the first surface  111  and the second surface  112  along the thickness (height) of the insulation film  110 . It is to be understood that any potential variances in the shape of the waterproof layer  130  are considered to be within the scope of the present base film  100 , as long as the projection area of the waterproof layer  130  along the thickness of the insulation film  110  is equal to a vertical sectional area of the insulation film  110 , where the waterproof layer  130  is located. 
         [0025]    A thickness of the waterproof layer  130  is determined by the thickness of the insulation  110 . In the present embodiment, the thickness of the insulation film  110  is in a range from about 7 mils to about 8 mils (1 mil is about 25.4 micrometers). So the thickness of the waterproof layer  130  is in a range from about 3 micrometers to about 25 micrometers. Certainly, any potential variances in the thickness of the waterproof layer  130  are considered to be within the scope of the present base film  100 , as long as the waterproof layer  130  can provide the waterproof function between the opposite surfaces of the insulation film  110 . For example, in some base films, the thickness of the waterproof layer  130  can be larger than 25 micrometers or less than 3 micrometers. 
         [0026]    The insulation film  110  can be made of a resin, a prepreg or a combination thereof. In the present embodiment, the insulation film  110  is made of prepreg, the electrically conductive layer  120  is a copper foil, and the waterproof layer  130  is an aluminum foil. 
         [0027]    A method for manufacturing the base film  100  includes the following steps. Firstly, two prepreg sheets, a waterproof layer  130  and one electrically conductive layer  120  are provided. Secondly, the waterproof layer  130  is clamped between two prepreg sheets. Thirdly, two prepreg sheets with the waterproof layer  130  clamped therebetween are laminated by a laminating device, thereby yielding the desired insulation film  110  having the waterproof layer  130 . Finally, the electrically conductive layer  120  is laminated on one surface of the insulation film  110  to obtain the desired base film  100 . Certainly, two prepreg sheets, one waterproof layer  130  and one electrically conductive layer  120  can be laminated all at once to form the base film  100 . 
         [0028]    Referring to  FIG. 3 , a base film  200  for manufacturing FPCB, in accordance with a third embodiment, is shown. The base film  200  includes an insulation film  210 , a copper layer  220  formed on one surface of the insulation film  210 , and a waterproof layer  230  formed in the insulation film  210 . The insulation film  210  is a rectangular sheet and includes a first surface  211  and a second surface  212  opposite to the first surface  211 . The waterproof layer  230  is a flat sheet of aluminum foil and is slant across in between (e.g., oblique to) the first surface  211  and the second surface  212 . A projection area of the waterproof  230  along a horizontal parallel to the first and second surfaces  211  and  212  is equal to the area of either the first surface  211  or the second surface  212 . Thus, the waterproof layer  230  partitions the first surface  211  and the second surface  212  along the thickness of the insulation film  210 . 
         [0029]    Referring to  FIG. 4 , a base film  300  for manufacturing FPCB, in accordance with a fourth embodiment, is shown. The base film  300  includes an insulation film  310 , a copper layer  320  formed on one surface of the insulation film  310 , and a waterproof layer  330  formed in the insulation film  310 . The insulation film  310  is a rectangular sheet and includes a first surface  311  and a second surface  312  opposite to the first surface  311 . The waterproof layer  330  is a wave-shaped aluminum foil and is arranged between the first surface  311  and the second surface  312 . As a whole, the waterproof layer  330  is parallel to the first and second surfaces  311 ,  312 . A projection area of the waterproof  330  along a horizontal parallel to the first and second surfaces  311 ,  312  is equal to the area of either the first surface  311  or the second surface  312 . Thus, the waterproof layer  330  separates/divides the first surface  311  and the second surface  312  along the thickness of the insulation film  310 . 
         [0030]    Referring to  FIG. 5 , a FPCB  400 , in accordance with a fifth embodiment, is shown. The FPCB  400  can be manufactured by at least one of the above-mentioned base film. In the present embodiment, the FPCB  400  is manufactured by laminating one double-sided FPCB and one single-sided FPCB. In detail, the FPCB  400  includes a first FPCB  410  (i.e., a double-sided FPCB), a second FPCB  420  (i.e., a single-sided FPCB), and an adhesive layer  430  for adhering the first FPCB  410  and the second FPCB  420  together. 
         [0031]    The first FPCB  410  includes a first insulation film  411 , two first traces  412 , and a first waterproof layer  413 . The first insulation film  411  is a rectangular sheet and includes a first surface  411   a  and a second surface  411   b  on opposite sides of the first insulation film  411 . The waterproof layer  413  is arranged between the first surface  411   a  and the second surface  411   b . The waterproof layer  413  is a flat aluminum foil and is parallel to the first surface  411   a  and the second surface  411   b . Two first traces  412  are separately formed on the first surface  411   a  and the second surface  411   b.    
         [0032]    The second FPCB  420  includes a second insulation film  421 , a second trace  422 , and a second waterproof layer  423 . The second insulation film  421  is a rectangular sheet and includes a third surface  421   a  and a fourth surface  421   b  on opposite sides of the second insulation film  421 . The waterproof layer  433  is arranged between the third surface  421   a  and the fourth surface  421   b . The waterproof layer  423  is wave-shaped and is parallel to the third surface  421   a  and the fourth surface  421   b , as a whole. The second trace  422  is formed on the second surface  421   b  of the second insulation film  421 . 
         [0033]    The insulation films and the base films can be used in rigid printed circuit boards, flexible printed circuit boards, or rigid-flexible printed circuit boards. In those printed circuit boards, the insulation film thereof includes the waterproof layer. During the wetting processes (e.g., clearing, etching, electro-plating and so on) for manufacturing those printed circuit boards, the waterproof layer prevents molecules (e.g., water molecules) or other ions from migrating opposite surfaces of the insulation film and reacting with the electrically conductive layer or traces. Thus, a stability of the manufacturing process can be improved, and the printed circuit boards with excellent water-resistance characteristic have been obtained. 
         [0034]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.