Abstract:
According to one embodiment, there is provided a printed-wiring board in which a composite board is formed to have rigid portions and a bending portion, wherein the bending portion includes linear protrusions each formed with solder resist having a bending resistance property.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-294619, filed Oct. 30, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    One embodiment of the present invention relates to a printed-wiring board in which rigid board portions and a bending portion are formed in a laminated board. 
         [0004]    2. Description of the Related Art 
         [0005]    A technique that allows a portion of a rigid printed-wiring board to have a bending property is one which forms a bending portion between rigid boards by interposing an insulating layer made of a flexible insulating material between the rigid boards and integrating the rigid boards with the insulating layer interposed therebetween. This technique is implemented by using a polyimide-based insulating material, which is used as an FPC base material, as the flexible insulating material. 
         [0006]    However, the polyimide-based material is high in water absorption and therefore subject to variations in shape and electrical characteristic due to moisture absorption. When mounting parts on the board made of the polyimide-based material, a baking process is required prior to mounting of the parts. In addition, the polyimide-based material is expensive. Therefore, the use of the polyimide-based material causes many manufacturing problems. Accordingly, a board manufacturing technique has been devised which allows a rigid board to have a bending property by partially scraping off to reduce the thickness of that portion so that the scraped portion of the rigid board may have the bending property. For example, in a printed-wiring board in which two or more insulating layers are stacked, partially peeling off one of the insulating layers to expose a surface of a second insulating layer at which a thin portion or a bending portion is formed in the printed-wiring board. In this case, however, the surface of the peeled-off portion may have irregularities and stress at the time of bending will be concentrated in the thin portion, causing the bending portion of the wiring board to be damaged. Furthermore, this type of printed-wiring board has confirmed that cracks tends to develop in the bending portion at the boundary between the bending and rigid portions when a torsional stress is applied to the bending portion, for example, in a manufacturing step in which the wiring board is handled. 
         [0007]    As a technique to avoid such cracks caused by forming the thin portion in the printed-wiring board, a prior art technique exists which forms a wiring circuit on one surface of a flexible board and a dummy wiring pattern on its other surface to thereby allow it to have a reasonable bending property. An example of such a technique is described in, for example, JP-A 2005-294639 (KOKAI). 
         [0008]    According to one aspect of the present invention, there is provided a printed-wiring board including a base board having rigid portions and a bending portion wherein on both sides of the bending portion a plurality of linear protrusions each formed of a solder resist so that the linear protrusions constitute a bending resistance portion. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
           [0010]      FIG. 1  is a sectional side view of a printed-wiring board according to an embodiment of the invention, cut along a line I-I and seen in the arrow as shown in  FIG. 2 ; 
           [0011]      FIG. 2  is a plan view of the printed-wiring board shown in  FIG. 1 ; 
           [0012]      FIG. 3  shows an example of the bent state of the printed-wiring board of the embodiment; 
           [0013]      FIG. 4  shows another example of the bent state of the printed-wiring board of the embodiment; 
           [0014]      FIG. 5  is a sectional view of the printed-wiring board of the embodiment at a step for manufacturing the printed-wiring board; 
           [0015]      FIG. 6  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 5 ; 
           [0016]      FIG. 7  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 6 ; 
           [0017]      FIG. 8  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 7 ; 
           [0018]      FIG. 9  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 8 ; 
           [0019]      FIG. 10  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 9 ; 
           [0020]      FIG. 11  is a sectional view of the printed-wiring board of the embodiment at a step subsequent to the step shown in  FIG. 10 ; 
           [0021]      FIG. 12  shows another arrangement of the linear protrusions formed on the bending portion of a printed-wiring board according to another embodiment of the present invention; 
           [0022]      FIG. 13  shows an example of the bent state of the printed-wiring board shown in  FIG. 12 ; and 
           [0023]      FIG. 14  is a sectional side view of an electronic equipment which has a printed-wiring board manufactured according to the present invention and built therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. 
         [0025]    An embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. A configuration of the printed-wiring board according to the embodiment of the invention is shown in  FIGS. 1 and 2 . This printed-wiring board shown in  FIGS. 1 and 2  takes, as an example, a structure such that three layers of insulating material are stacked to form a composite or laminated board with four wiring layers so that the printed-wiring board is configured to have two rigid portions  10 A,  10 B and a bending portion  10 C interposed between the rigid portions  10 A and  10 B. 
         [0026]    The printed-wiring board of the embodiment is configured, as shown in  FIG. 1 , such that a composite or laminated board  10 , which is formed with four wiring layers P 1 , P 2 , P 3  and P 4  each formed of a copper or aluminum film and three flexible layers  11 ,  12  and  13  each formed of an insulating material, has two rigid portions  10 A and  10 B and a bending portion  10 C interposed between the rigid portions. 
         [0027]    The rigid portions  10 A and  10 B are formed, as shown in  FIGS. 1 and 2 , by coating the first and second surfaces of the composite board  10  formed by stacking the three flexible insulating boards  11 ,  12  and  13  with layers  20  and  30  of solder resist. 
         [0028]    In the rigid portions  10 A and  10 B, each of the wiring layers P 1  to P 4  is formed, and a through-hole connector (TH) is formed to connect the wiring layers P 1  to P 4 , selectively. In  FIG. 1 , the through-hole connector TH is illustrated only in the rigid portion  10 B and one or more through-hole connectors may be made in the rigid portion  10 A and/or  10 B. In addition, the rigid portions  10 A and  10 B have circuit patterns formed in their respective wiring layers P 1  to P 4  including the first and second surfaces of the composite board  10 . 
         [0029]    The bending portion  10 C is formed by removing (peeling off) wiring layers or copper films P 1  and P 4  from the first and second surfaces of that region of the composite board  10  where the bending portion is to be formed. 
         [0030]    Furthermore, the bending portion  10 C is formed on its first and second surfaces with linear protrusions  21  and  31 , respectively, which are made by partially cutting off the solder resist layers  20  and  30  linearly. In the embodiment shown in  FIG. 1 , six linear protrusions  21  are formed in the solder resist layer  20  on the first surface of the board  10  and six linear protrusions  31  are formed in the solder resist layer  30  on the second surface of the board  10 . The linear protrusions  21  and  31  are arranged at regular intervals on the first and second surfaces of the board  10 , respectively, in such a way that each of the linear protrusions  21  on the first surface is not opposed to each of the linear protrusions  31  on the second surface thereof. Namely, the linear protrusions  21  and  31  are staggered with each other. 
         [0031]    The linear protrusions  21  and  31  are formed when the solder resist layers  20  and  30  are formed on the rigid portions  10 A and  10 B. The linear protrusions  21  and  31  are partially hardened at the bending portion  10 C where the protrusions  21  and  31  are formed. The manufacturing process for forming the linear protrusions  21  and  31  will be described in detail later. 
         [0032]    The linear protrusions  21  and  31  are hardened to form a bending resistance portion to protect the bending portion  10 C from cracks due to application thereto of external torsional stress with respect to the rigid portions  10 A and  10 B. 
         [0033]    Furthermore, the linear protrusions  21  and  31  also acts as a bending direction control means to control the direction of bending when they are arranged parallel to the predetermined bending direction. 
         [0034]    By the linear protrusions  21  and  31 , which constitute the bending resistance portion and the bending direction control means, the bending portion  10 C is made easy to bend in the bending direction but difficult to bend in the torsional direction. Thereby, cracks can be prevented from developing in the bending portion at the time of bending to improve the yield. Furthermore, handling at work can be facilitated to increase the working efficiency. 
         [0035]    If the bending portion  10 C were not formed with the linear protrusions  21  and  31 , it would be easy to bend in the torsional direction when subjected to an external torsional stress and cracks would develop in the edges of the bending portion  10 C when it undergoes a bending stress in the torsional direction as it is without resistance. 
         [0036]    When the linear protrusions  21  and  31  are formed on the bending portion  10 C, they can resist bending stress in the torsional direction and act to prevent bending in the torsional direction. Thereby, cracks can be prevented from developing in the bending portion  10 C at the time of bending, thus improving the yield. 
         [0037]    Moreover, by arranging the linear protrusions  21  and  31  parallel to the predetermined direction of bending, the bending portion  10 C is made to resist bending in a direction different from the predetermined bending direction but can be bent without resistance in the predetermined bending direction. In this case, the bending portion  10 C can be bent at even angles of bending so that bending is not biased (bending is not concentrated on a particular part of the bending portion). Thereby, handing at work can be facilitated to increase the working efficiency. 
         [0038]      FIGS. 3 and 4  show examples of bent states of the bending portion  10 C. 
         [0039]      FIG. 3  shows the bent state of the bending portion  10 C when the rigid portions  10 A and  10 B are mounted in parallel with each other with a difference in level L therebetween. In such a case, the bending portion  10 C tends to undergo external stress in the torsional direction at the time of mounting. Therefore, when the bending portion  10 C is not formed with the linear protrusions  21  and  31 , the external stress is directly applied to the edges of the bending portion  10 C, making cracks easy to develop in the bending portion  10 C. In this embodiment, however, the bending portion  10 C is formed with the linear protrusions  21  and  31 , and accordingly, the linear protrusions  21  and  31  can resist bending stress in the torsional direction and act to prevent bending in the torsional direction. Moreover, since the linear protrusions  21  and  31  are arranged evenly and in parallel to the predetermined direction of bending, the bending portion  10 C can be bent without resistance in the predetermined bending direction and moreover at even angles of bending. 
         [0040]      FIG. 4  shows another bent state of the bending portion  10 C when it is bent into the shape of the letter U. In such a case, as in the case shown in  FIG. 3 , the linear protrusions  21  and  31  act to prevent the bending portion  10 C from bending in the torsional direction and the bending portion  10 C can be bent in the bending direction without resistance at even angles of bending. 
         [0041]    The manufacturing steps of the above-mentioned printed-wiring board of the embodiment are shown in  FIG. 5  to  FIG. 11 . 
         [0042]    In step  1  shown in  FIG. 5 , the flexible board  11  is processed which forms the core insulation material layer as an inner layer of the composite board  10  shown in  FIG. 1 . For example, a prepreg material layer with flexibility is prepared and on both sides thereof are formed electro-conducting layers  11 P of copper film to thereby fabricate the flexible board  11 . 
         [0043]    In step  2  shown in  FIG. 6 , the conducting layers  11   p  formed on the sides of the flexible board  11  are etched to form wiring layers P 2  and P 3  of circuit patterns as inner-layer circuit patterns. 
         [0044]    In step  3  shown in  FIG. 7 , the insulation flexible boards  12  and  13  are stacked to the first and second surfaces of the flexible board  11  formed with the wiring layers P 2  and P 3  to form the top and bottom layers of the composite board  10 . For example, the flexible boards  12  and  13  are each formed of an RCC (resin coated copper foil) material with copper films  12 P and  13 P but with no glass fiber. Thereby, the flexible boards  12  and  13  are stacked on top and bottom surface of the board  11  with conducting layers  12   p  and  13   p,  respectively. 
         [0045]    In step  4  shown in  FIG. 8 , the stacked flexible boards  11 ,  12  and  13  are drilled to form a through-hole h or a via hole. 
         [0046]    In step  5  shown in  FIG. 9 , the drilled inner wall portion of the hole h is plated with copper, for example, to form the through-hole (TH) connector C for connecting the given portions of the wiring layers  12 P, P 2 , P 3  and  13 P together. A via (not shown) may be formed in the similar manner in the board  10 . 
         [0047]    In step  6  shown in  FIG. 10 , the surfaces of the stacked flexible boards  11  and  13  are subjected to an etching process. This etching process entirely removes the conductive wiring layers  12   p  and  13   p  in a region of the composite board  10  where the bending portion  10 C is to be formed. 
         [0048]    Then, in step  7  shown in  FIG. 11 , solder resist layers  20  and  30  are coated onto the whole top and bottom surfaces of the board  10 . Then, the solder resist layers applied to those regions of the surfaces of the composite board where the rigid portions  10 A and  10 B are to be formed remained, and those regions of the solder resist layers  20  and  30  applied to the top and bottom surfaces of the bent portion  10 C are subjected to be etched partially to form the linear protrusions  21  and  31  using a known lithography method, for example. In the etching process, the solder resist is hardened by a known hardening method such as that using a violet ray while applying heat thereto. 
         [0049]    Thus, the printed-wiring board shown in  FIG. 1  is manufactured which has the rigid portions  10 A and  10 B coated with the solder resist layers  20  and  30  and the bending portion  10 C formed with the linear protrusions  21  and  31 . 
         [0050]    In the above embodiment, the bending portion  10 C is formed with the linear protrusions  21  and  31  parallel to the direction of its width between the rigid portions  10 A and  10 B, so that the rigid portions  10 A and  10 B may be overlapped when the bent portion  10 C is bent in the letter U as shown in  FIG. 4 . As shown in  FIGS. 12 and 13 , however, in another embodiment of the present invention, the linear protrusions may be formed at a predetermined angle θ of inclination with respect to the direction of width of the bending portion  10 C. By so doing, the bending portion  10 C can be easily bent into the shape of the letter U at the given angle θ of inclination, so that the rigid portions  10 A and  10 B are bent in the given direction as shown in  FIG. 13 . In the case of the embodiment of  FIGS. 12 and 13 , if the bent portion  10 C is bent in a state as shown in the case of  FIG. 4 , a tortional stress will be applied to the bent portion  10 C. When the board  10  shown in the embodiment of  FIG. 12  is bent in the similar manner as in the case of the bent state shown in  FIG. 3 , the rigid portions  10 A and  10 B may be positioned at the different level L while the rigid portions  10 A and  10 B are offset in the width direction of the bent portion  10 C. 
         [0051]    In such an example of bending, as in the example shown in  FIG. 4 , the bending portion  10 C can be structured such that it is easy to bend in the predetermined bending direction at the given angle θb but difficult to bend in the width direction of the bent portion  10 C due to the tortional resistance function of the linear protrusions  21  and  31  inclined by θ as shown in  FIG. 12 . That is, the linear protrusions  21  and  31  act to prevent the bending portion  10 C from bending in the torsional direction, and the bending portion  10 C can be bent in the bending direction without resistance at even angles of bending in the similar manner as in the case of  FIGS. 1 and 2 . 
         [0052]      FIG. 14  shows the configuration of electronic equipment in which the printed-wiring board  50  prepared in the similar manner as the embodiments according to the present invention is mounted. Here, the printed-wiring board  50  may be manufactured in accordance with the manufacturing steps shown in  FIGS. 5 through 11  and is applicable to a small-sized portable computer or the like. 
         [0053]    In  FIG. 14 , a display unit casing  3  is swingably mounted to the main body  2  of the portable computer  1  by a hinge mechanism  3   h.  The main body  2  is equipped with operation units, such as a pointing device, a keyboard  4 , etc. The display unit casing  3  has a display device  5 , such as an LCD, built in. 
         [0054]    In addition, the main body  2  is equipped with a printed circuit board (mother board) which has various control circuits M 1 , M 2  and M 3  for controlling, for example, the keyboard  4  and the display device  5  mounted on the printed-wiring board  50  which has rigid portions  50 A and  50 B coated with solder resist layers  20  and  30  and a bending portion  50 C with linear protrusions  51  and  52  of solder resist, manufactured in accordance with the manufacturing steps shown in  FIGS. 5 through 11 . 
         [0055]    The printed-wiring board  50  is structured such that the bending portion  50 C is easy to bend in the bending direction but difficult to bend in the torsional direction owing to the bending resistance portion and bending direction control means based on the linear protrusions  51  and  52 . Thereby, the bending portion  50 C can be bent easily without developing cracks therein, thus improving the yield. In addition, the bending portion  50 C can be bent at even angles of bending with no bending concentrated only on a particular part. This allows handling at work to be facilitated and working efficiency to be improved. 
         [0056]    While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.