Abstract:
A combined circuit board including a flexible circuit board (FCB), a rigid circuit board (RCB), and first and second conductive vias (CVs) is provided. The FCB includes a flexible dielectric layer (DL) and a circuit layer (CL) disposed thereon. The RCB includes a rigid DL and a CL including a main circuit (MC) and an out connection interface circuit (OCIC). The rigid DL is disposed on the FCB and includes first and second rigid dielectric portions (RDPs) apart from each other by a distance such that part of the FCB is exposed outside. The MC and the OCIC are disposed on the first and the second RDPs, respectively. The first CV disposed in the second RDP electrically connects a contact of the OCIC and the CL of the FCB. The second CV disposed in the first RDP electrically connects the MC and the CL of the FCB.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims the benefit of priority from Taiwan Patent Application 102119669 filed on Jun. 3, 2013, which is incorporated herein by reference and assigned to the assignee hereof. 
       FIELD OF THE INVENTION 
       [0002]    The present invention is related to a circuit board and a method of manufacturing the same and in particular, to a combined circuit board and a method of manufacturing the same. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    In general, a conventional circuit board for carrying and electrically connecting a plurality of electronic components substantially comprises circuit layers and dielectric layers that are stacked alternately. Each of the circuit layers are defined and formed by performing a patterning process on a conductive layer. Each of the dielectric layers is disposed between adjacent ones of the circuit layers in order to space apart the adjacent circuit layers. In addition, each of the stacked circuit layers may be electrically connected to another by a conductive via. Furthermore, various electronic components (such as active components or passive components) can be disposed on a surface of the circuit board, and electrical signal propagation is achieved by means of an internal circuit of the circuit board. 
         [0004]    Due to miniaturization of any of electronic products, the application of circuit boards rapidly increases; for example, circuit boards can be applied in clam type mobile phones and notebook computers. Accordingly, the development of combing a rigid circuit board and a flexible circuit board to form a combined circuit board is required. 
         [0005]      FIG. 1  is a schematically illustrated cross-sectional view of a conventional combined circuit board. Referring to  FIG. 1 , the conventional combined circuit board  100  comprises a flexible circuit board  110 , a rigid circuit board  120 , a rigid dielectric layer  130 , a plurality of conductive vias  140 , and a reinforcing plate  150 . The flexible circuit board  110  comprises a flexible dielectric layer  112  and a circuit layer  114 . The circuit layer  114  is disposed on a surface  112   a  of the flexible dielectric layer  112 . The circuit layer  114  comprises a plurality of golden finger contacts  114   a  and only one contact  114   a  is schematically shown in  FIG. 1 . The reinforcing plate  150  is disposed on another surface  112   b  of the flexible dielectric layer  112  and corresponds in position to the golden finger contacts  114   a.    
         [0006]    The rigid circuit board  120  comprises a rigid dielectric layer  122  and a circuit layer  124 . The rigid dielectric layer  122  is disposed on the surface  112   a  of the flexible dielectric layer  112  and the circuit layer  124  is disposed on the rigid dielectric layer  122  such that the rigid dielectric layer  122  is located between the flexible circuit board  110  and the circuit layer  124 . The circuit layer  124  comprises a plurality of pads  124   a.  The conductive vias  140  are disposed in the rigid dielectric layer  122  and electrically connect the pads  124   a  and the golden finger contacts  114   a.  The rigid dielectric layer  130  is disposed on the surface  112   b  of the flexible dielectric layer  112  and corresponds in position to the rigid dielectric layer  122 . Moreover, a chip (not shown) may be disposed on the rigid dielectric layer  122  and electrically connected to the pads  124   a  by means of wire bonding technology so as to be electrically connected to the golden finger contacts  114   a.    
         [0007]    The combined circuit board  100  has a thickness T 1  in the vicinity of the golden finger contacts  114   a  and the thickness T 1  can be 0.2 mm to meet the current industrial requirements. However, based on the limitation caused by the physical properties of the materials which are usually selected by the current industry for the rigid dielectric layers  122  and  130 , a maximum thickness T 2  of the combined circuit board  100 , i.e., the thickness in the vicinity of the rigid dielectric layers  122  and  130 , must be at least 0.3 mm. Hence, the conventional combined circuit board  100  cannot be further thinned. 
         [0008]    Moreover, the process of manufacturing the conventional combined circuit board  100  is complicated. During the manufacturing process of the combined circuit board  100 , the golden finger contacts  114   a  are preformed on the surface  112   a  of the flexible dielectric layer  112 , and thus the flexible circuit board  110  is finished in advance. Afterward, the manufacturing process involves laminating a rigid substrate, the flexible circuit board  110  and the rigid dielectric layer  130 , wherein the rigid substrate comprises the rigid dielectric layer  122  and a conductive layer disposed on the rigid dielectric layer  122  and usually a copper layer on a whole surface of the rigid dielectric layer  122 . Afterward, the manufacturing process involves patterning the conductive layer to form the circuit layer  124  and performing drilling and electroplating steps to form the conductive vias  140 . In doing so, the production of the conventional combined circuit board  100  is finalized. However, in the steps of lamination, patterning the conductive layer, and forming the conductive vias  140 , the golden finger contacts  114   a  must be properly protected to be prevented from being damaged in the aforesaid steps. Moreover, when the golden finger contacts  114   a  are being formed, it is necessary to dispose the reinforcing plate  150  which corresponds in position to the golden finger contacts  114   a  to be formed. As a result, the process of manufacturing the conventional combined circuit board  100  is complicated. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a combined circuit board for which the process of manufacturing is relatively simple. 
         [0010]    The present invention provides a combined circuit board of which the thickness can be thinner. 
         [0011]    The present invention provides a method of manufacturing a combined circuit board, wherein the manufacturing process of the combined circuit board is relatively simple. 
         [0012]    The present invention provides a method of manufacturing a combined circuit board, wherein the combined circuit board produced has a thinner thickness. 
         [0013]    In an embodiment of the present invention, a combined circuit board comprising a flexible circuit board, a first rigid circuit board, at least one first conductive via and at least one second conductive via is provided. The flexible circuit board comprises a flexible dielectric layer and a first circuit layer disposed on the flexible dielectric layer. The first rigid circuit board comprises a first rigid dielectric layer and a second circuit layer. The first rigid dielectric layer is disposed on the flexible circuit board and comprises a first rigid dielectric portion and a second rigid dielectric portion spaced apart from the first rigid dielectric portion by a distance to expose a portion of the flexible circuit board. The second circuit layer comprises a main circuit and an out connection interface circuit. The main circuit is disposed on the first rigid dielectric portion, and the out connection interface circuit is disposed on the second rigid dielectric portion and comprises at least one contact. The at least one first conductive via is disposed in the second rigid dielectric portion and electrically connects the at least one contact and the first circuit layer. The at least one second conductive via is disposed in the first rigid dielectric portion and electrically connects the main circuit and the first circuit layer. 
         [0014]    In an embodiment of the present invention, the first rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard. 
         [0015]    In an embodiment of the present invention, the flexible circuit board further comprises a third circuit layer disposed on the flexible dielectric layer. The first circuit layer and the third circuit layer are disposed on two opposite sides of the flexible dielectric layer, respectively. The combined circuit board further comprises a second rigid circuit board comprising a second rigid dielectric layer and a fourth circuit layer. The second rigid dielectric layer is disposed on the flexible circuit board, and the fourth circuit layer is disposed on the second rigid dielectric layer. The second rigid dielectric layer comprises a third rigid dielectric portion and a fourth rigid dielectric portion. The third rigid dielectric portion and the fourth rigid dielectric portion correspond in position to the first rigid dielectric portion and the second rigid dielectric portion, respectively. The second rigid circuit board and the first rigid circuit board are disposed on two opposite sides of the flexible circuit board, respectively. 
         [0016]    In an embodiment of the present invention, the first rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard, and the second rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard. The combined circuit board has a maximum thickness which is not larger than 0.2 mm. 
         [0017]    In an embodiment of the present invention, the at least one contact is a golden finger contact. 
         [0018]    In an embodiment of the present invention, a method of manufacturing a combined circuit board comprising the following steps is provided. First, a flexible circuit board comprising a flexible dielectric layer and a first circuit layer disposed on the flexible dielectric layer is provided. Next, a first rigid substrate comprising a first rigid dielectric layer and a first conductive layer disposed on the first rigid dielectric layer is provided. Next, the flexible circuit board and the first rigid substrate is laminated such that the first rigid dielectric layer is located between the first conductive layer and the flexible circuit board. Next, the first conductive layer is patterned to form a second circuit layer, wherein the first rigid dielectric layer and the second circuit layer together form a first rigid circuit board. 
         [0019]    Next, a plurality of conductive vias in the first rigid dielectric layer are formed, wherein each of the conductive vias electrically connects the second circuit layer and the first circuit layer. Afterwards, a portion of the first rigid circuit board is removed to expose a portion of the flexible circuit board. The first rigid dielectric layer is divided into a first rigid dielectric portion and a second rigid dielectric portion spaced apart from the first rigid dielectric portion by a distance. The second circuit layer is divided into a main circuit and an out connection interface circuit. The conductive vias are divided into at least one first conductive via and at least one second conductive via. The main circuit is disposed on the first rigid dielectric portion, and the out connection interface circuit is disposed on the second rigid dielectric portion and comprises at least one contact. The at least one first conductive via is disposed in the second rigid dielectric portion and electrically connects the at least one contact and the first circuit layer. The at least one second conductive via is disposed in the first rigid dielectric portion and electrically connects the main circuit and the first circuit layer. 
         [0020]    In an embodiment of the present invention, the first rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard. 
         [0021]    In an embodiment of the present invention, the flexible circuit board further comprises a third circuit layer disposed on the flexible dielectric layer. The first circuit layer and the third circuit layer are disposed on two opposite sides of the flexible dielectric layer, respectively. The method of manufacturing the combined circuit further comprises the following steps. A second rigid substrate comprising a second rigid dielectric layer and a second conductive layer disposed on the second rigid dielectric layer is provided. Next, the flexible circuit board and the second rigid substrate is laminated such that the second rigid dielectric layer is located between the second conductive layer and the flexible circuit board. The second rigid substrate and the first rigid substrate are disposed on two opposite sides of the flexible circuit board, respectively. Next, the second conductive layer is patterned to form a fourth circuit layer. The second rigid dielectric layer and the fourth circuit layer together form a second rigid circuit board. Next, a portion of the second rigid circuit board is removed to expose another portion of the flexible circuit board. The second rigid dielectric layer is divided into a third rigid dielectric portion and a fourth rigid dielectric portion. The third rigid dielectric portion and the fourth rigid dielectric portion correspond in position to the first rigid dielectric portion and the second rigid dielectric portion, respectively. 
         [0022]    In an embodiment of the present invention, the first rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard, and the second rigid dielectric layer comprises an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard. The combined circuit board has a maximum thickness which is not larger than 0.2 mm. 
         [0023]    In an embodiment of the present invention, the at least one contact is a golden finger contact. 
         [0024]    During the manufacturing process of the combined circuit board of the embodiment of the present invention, the contact of the rigid circuit board comprising the out connection interface circuit is formed on the rigid dielectric layer of the rigid circuit board at the step of patterning the conductive layer. In this embodiment of the present invention, the contact is not formed yet during the laminating step and is being formed during the patterning step. Hence, compared to the conventional art, the contact of the embodiment of the present invention does not require additional protection during the two steps and the reinforcing plate is not required while the contact is being formed. Accordingly, the method of manufacturing the combined circuit board of the embodiment of the present invention is relatively simple. In addition, because the rigid dielectric layer comprises the epoxy resin and the glass fabric which meets the style 1017 of the IPC standard, compared to the conventional art, the thickness of the rigid dielectric layer can be reduced and the structural strength requirements for the rigid dielectric layer can be still meet such that the maximum thickness of the combined circuit board of this embodiment of the present invention can be effectively reduced and therefore, the combined circuit board can be thinner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a schematically illustrated cross-sectional view of a conventional combined circuit board. 
           [0026]      FIG. 2  is a schematically illustrated cross-sectional view of a combined circuit board according to an embodiment of the present invention. 
           [0027]      FIG. 3A  through  FIG. 3F  are schematic views illustrating a method of manufacturing a combined circuit board according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0028]      FIG. 2  is a schematically illustrated cross-sectional view of a combined circuit board according to an embodiment of the present invention. Referring to  FIG. 2 , the combined circuit board  200  of the embodiment comprises a flexible circuit board  210 , a plurality of rigid circuit boards  220  and  230 , and a plurality of conductive vias  240  and  250 . The flexible circuit board  210  comprises a flexible dielectric layer  212  and two circuit layers  214  and  216 . The circuit layers  214  and  216  are disposed on two opposite sides of the flexible dielectric layer  212 , respectively. The flexible dielectric layer  212  comprises polyimide (PI) or epoxy resin, for example. 
         [0029]    The rigid circuit boards  220  and  230  are disposed on two opposite sides of the flexible circuit board  210 , respectively. The rigid circuit board  220  comprises a rigid dielectric layer  222  and a circuit layer  224 . The rigid dielectric layer  222  is disposed on the flexible circuit board  210  and the circuit layer  224  is disposed on the rigid dielectric layer  222  such that the rigid dielectric layer  222  is disposed between the flexible circuit board  210  and the circuit layer  224 . The rigid dielectric layer  222  comprises two rigid dielectric portions  222   a  and  222   b.  The rigid dielectric portion  222   a  and the rigid dielectric portion  222   b  are spaced apart from each other by a distance D 1  such that a portion of the flexible circuit board  210  is exposed. The circuit layer  224  comprises a main circuit  224   a  and an out connection interface circuit  224   b.  The main circuit  224   a  is disposed on the rigid dielectric portion  222   a.  The main circuit  224   a  comprises at least one pad P 1  and a plurality of the pads P 1  are schematically shown in  FIG. 2 . The out connection interface circuit  224   b  is disposed on the rigid dielectric portion  222   b.  The out connection interface circuit  224   b  comprises a plurality of contacts C 1  and only one contact C 1  is schematically shown in  FIG. 2 . Each of the contacts C 1  is a golden finger contact, for example. 
         [0030]    A plurality of conductive vias  240  are disposed in the rigid dielectric portion  222   b  (only one conductive via  240  is schematically shown in  FIG. 2 ), and each of the conductive vias  240  electrically connects one of the contacts C 1  and the circuit layer  214 . Moreover, the conductive vias  250  are disposed in the rigid dielectric portion  222   a,  and each of the conductive vias  250  electrically connects one of the pads P 1  of the main circuit  224   a  and the circuit layer  214 . In other words, each of the pads P 1  of the main circuit  224   a  is electrically connected to one of the contacts C 1  through one of the conductive vias  250 , the circuit layer  214  and one of the conductive vias  240 . Moreover, a chip (not shown) may be disposed on the rigid dielectric portion  222   a  of the rigid dielectric layer  222  and electrically connected to the pads P 1  by means of wire bonding technology so as to be electrically connected to the contacts C 1 . 
         [0031]    In this embodiment, the rigid circuit board  230  comprises a rigid dielectric layer  232  and a circuit layer  234 . The rigid dielectric layer  232  is disposed on the flexible circuit board  210  and the circuit layer  234  is disposed on the rigid dielectric layer  232  such that the rigid dielectric layer  232  is disposed between the flexible circuit board  210  and the circuit layer  234 . The rigid dielectric layer  232  comprises two rigid dielectric portions  232   a  and  232   b.  The rigid dielectric portions  232   a  and  232   b  of the rigid dielectric layer  232  correspond in position to the rigid dielectric portions  222   a  and  222   b  of the rigid dielectric layer  222 , respectively. 
         [0032]    Each of the rigid dielectric layers  222  and  232  is made of an epoxy resin and a glass fabric which meets the style 1017 of the IPC standard. That is to say, each of the rigid dielectric layers  222  and  232  comprises the epoxy resin and a plurality of fiberglass included in the glass fabric which meets the style 1017 of the IPC standard. The rigidity of each of the rigid dielectric layers  222  and  232  comprising the fiberglass and resin is relatively high. Moreover, the glass fabric which meets the style 1017 of the IPC standard has a thickness of about 10 μm and contains the fiberglass each of which has a diameter of about 4 μm. Because each of the rigid dielectric layers  222  and  232  comprises the epoxy resin and the glass fabric which meets the style 1017 of the IPC standard, compared to the conventional art, the thickness of each of the rigid dielectric layers  222  and  232  can be reduced and the structural strength requirements for them can be still meet such that the maximum thickness T 3  of the combined circuit board  200  of this embodiment can be effectively reduced to 0.2 mm or even less and therefore, the combined circuit board  200  can be thinner. 
         [0033]    In another embodiment, the rigid circuit boards  230  and the circuit layer  216  of the flexible circuit board  210  can be omitted in the combined circuit board  200 , but the above mentioned is not depicted in any drawing. 
         [0034]    A method of manufacturing the combined circuit board  200  according to this embodiment of the present invention is described below.  FIG. 3A  through  FIG. 3F  are schematic views illustrating a method of manufacturing a combined circuit board according to an embodiment of the present invention. First, referring to  FIG. 3A , a flexible circuit board  210  which comprises a flexible dielectric layer  212  and two circuit layers  214  and  216  is provided. Afterward, referring to  FIG. 3B , two rigid substrates  202  and  204  are provided. The rigid substrate  202  comprises the rigid dielectric layer  222  and a conductive layer  224 ′ disposed on the rigid dielectric layer  222 . The rigid substrate  204  comprises the rigid dielectric layer  232  and a conductive layer  234 ′ disposed on the rigid dielectric layer  232 . Afterward, referring to  FIG. 3C , the flexible circuit board  210  and the rigid substrates  202  and  204  are laminated together such that the rigid substrates  202  and  204  are disposed on the two opposite sides of the flexible circuit board  210 , respectively. The rigid dielectric layer  222  is disposed between the conductive layer  224 ′ and the flexible circuit board  210 . The rigid dielectric layer  232  is disposed between the conductive layer  234 ′ and the flexible circuit board  210 . 
         [0035]    Afterward, referring to  FIG. 3D , the conductive layers  224 ′ and  234 ′ is patterned to form the circuit layers  224  and  234 . The patterning step includes related procedures containing photoresist coating, photolithography (exposure and development), and etching. At this time, the rigid dielectric layer  222  and the circuit layer  224  together form the rigid circuit board  220 , and the rigid dielectric layer  232  and the circuit layer  234  together form the rigid circuit board  230 . Afterward, referring to  FIG. 3E , a plurality of conductive vias V 1  are formed in the rigid dielectric layer  222  by means of machinery drilling or laser drilling and electroplating. Each of the conductive vias V 1  electrically connects the second circuit layer  224  and the first circuit layer  214 . 
         [0036]    Afterward, referring to  FIG. 3F , a portion of the rigid circuit board  220  and a portion of the rigid circuit board  230  are removed such that a portion of the flexible circuit board  210  is exposed, i.e., a portion of each of the two opposite sides of the flexible circuit board  210  is exposed. At this time, the combined circuit board  200  of this embodiment is finished. 
         [0037]    After the step depicted in  FIG. 3F , the rigid dielectric layer  222  is divided into a rigid dielectric portion  222   a  and a rigid dielectric portion  222   b  which are spaced apart from each other by the distance D 1 . The circuit layer  224  is divided into the main circuit  224   a  disposed on the rigid dielectric portion  222   a  and the out connection interface circuit  224   b  disposed on the rigid dielectric portion  222   b.  The conductive vias V 1  are divided into the conductive vias  240  disposed in the rigid dielectric portion  222   b  and the conductive vias  250  disposed in the rigid dielectric portion  222   a.  Each of the conductive vias  240  electrically connects one of the contacts C 1  of the out connection interface circuit  224   b  and the circuit layer  214 . Each of the conductive vias  250  electrically connects one of the pads P 1  of the main circuit  224   a  and the circuit layer  214 . Moreover, the rigid dielectric layer  232  is divided into the rigid dielectric portions  232   a  and  232   b  which are spaced apart from each other. The rigid dielectric portions  232   a  and  232   b  correspond in position to the rigid dielectric portions  222   a  and  222   b,  respectively. 
         [0038]    In this embodiment, the contacts C 1  of the out connection interface circuit  224   b  of the circuit layer  224  are formed on the rigid dielectric layer  222  of the rigid circuit board  220  at the step of patterning the conductive layer  224 .′ In this embodiment, the contacts C 1  are not formed yet during the laminating step and are being formed during the patterning step. Hence, compared to the conventional art, the contacts C 1  of the present embodiment do not require additional protection during the two steps and the reinforcing plate  150  (see  FIG. 1 ) is not required while the contacts C 1  are being formed. Accordingly, compared to the conventional art, the method of manufacturing the combined circuit board  200  of the present embodiment is relatively simple. 
         [0039]    Based on the above mentioned, the combined circuit board has one of the following advantages or another advantage. 
         [0040]    During the manufacturing process of the combined circuit board of the embodiment of the present invention, the contact of the rigid circuit board comprising the out connection interface circuit is formed on the rigid dielectric layer of the rigid circuit board at the step of patterning the conductive layer. In this embodiment of the present invention, the contact is not formed yet during the laminating step and is being formed during the patterning step. Hence, compared to the conventional art, the contact of the embodiment of the present invention does not require additional protection during the two steps and the reinforcing plate is not required while the contact is being formed. Accordingly, the method of manufacturing the combined circuit board of the embodiment of the present invention is relatively simple. 
         [0041]    Because the rigid dielectric layer comprises the epoxy resin and the glass fabric which meets the style 1017 of the IPC standard, compared to the conventional art, the thickness of the rigid dielectric layer can be reduced and the structural strength requirements for the rigid dielectric layer can be still meet such that the maximum thickness of the combined circuit board of this embodiment of the present invention can be effectively reduced and therefore, the combined circuit board can be thinner.