Abstract:
A combined wiring board includes a metal frame having multiple opening portions, and multiple wiring boards accommodated in the opening portions in the metal frame, respectively. The opening portions in the metal frame have side walls having holding portions such that the holding portions hold the wiring boards in the opening portions in the metal frame, and the metal frame has slit portions adjacent to the holding portions and connecting portions connecting the slit portions to the opening portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2013-198631, filed Sep. 25, 2013, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a combined wiring board where multiple wiring boards to be reflowed are fixed to a metal frame, and to a method for manufacturing such a combined wiring board. 
         [0004]    2. Description of Background Art 
         [0005]    When mounting an electronic component on a wiring board and conducting other procedures on the wiring board, such procedures may be collectively performed not on one single wiring board but on a combined wiring board where multiple identical wiring boards are accommodated in a wiring-board accommodation kit. JP2011-23657A describes a multipiece wiring-board accommodation kit made up of multiple piece wiring boards and a frame having accommodation holes to accommodate those piece wiring boards. The entire contents of this publication are incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention, a combined wiring board includes a metal frame having multiple opening portions, and multiple wiring boards accommodated in the opening portions in the metal frame, respectively. The opening portions in the metal frame have side walls having holding portions such that the holding portions hold the wiring boards in the opening portions in the metal frame, and the metal frame has slit portions adjacent to the holding portions and connecting portions connecting the slit portions to the opening portions. 
         [0007]    According to another aspect of the present invention, a method for manufacturing a combined wiring board includes preparing multiple wiring boards, preparing a metal frame having multiple opening portions, positioning the wiring boards in the opening portions in the metal frame, respectively, and forming multiple holding portions in side walls of the opening portions in the metal frame by plastic deformation such that the holding portions hold the wiring boards in the opening portions in the metal frame. The metal frame has slit portions adjacent to the holding portions and connecting portions connecting the slit portions to the opening portions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0009]      FIG. 1  is a plan view of a multipiece printed wiring board; 
           [0010]      FIG. 2  is a perspective view of a printed wiring board cut out as an individual piece; 
           [0011]      FIG. 3(A)-3(B)  are perspective views of a printed wiring board under laser processing; 
           [0012]      FIG. 4(A)  is a plan view of a metal frame, and  4 (B) is a plan view of a combined wiring board; 
           [0013]      FIG. 5  is a plan view of a crimp-processed combined wiring board; 
           [0014]      FIG. 6  is an enlarged view of an L-shaped slit and a connecting portion in  FIG. 5 ; 
           [0015]      FIG. 7(A)-7(B)  are enlarged cross-sectional views of part of a combined wiring board; 
           [0016]      FIG. 8  (A)- 8 (B) are cross-sectional views of a crimping tool; 
           [0017]      FIG. 9  is a plan view showing the main body of a printed wiring board separated from the combined wiring board; 
           [0018]      FIG. 10  is a cross-sectional view of a printed wiring board according to a first embodiment; 
           [0019]      FIG. 11  is a cross-sectional view of a printed wiring board with mounted electronic components according to the first embodiment; 
           [0020]      FIG. 12  is an enlarged view of an L-shaped slit and a connecting portion of a combined wiring board according to a second embodiment; and 
           [0021]      FIG. 13  is an enlarged view of an L-shaped slit and a connecting portion of a combined wiring board according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0022]    The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
       First Embodiment 
       [0023]      FIG. 10  is a cross-sectional view of printed wiring board  10  according to a first embodiment before an electronic component is mounted thereon. In printed wiring board  10 , interlayer insulation layers ( 50 A,  50 C,  50 E,  50 G,  50 I) are laminated on the first-surface (F) side of core insulation layer ( 50 M) positioned in the center, and interlayer insulation layers ( 50 B,  50 D,  50 F,  50 H,  50 J) are laminated on the second-surface (S) side. Conductive circuit ( 58 Ma) on first surface (F) of core insulation layer ( 50 M) and conductive circuit ( 58 Mb) on second surface (S) are connected by via conductor ( 60 M). 
         [0024]    In interlayer insulation layer ( 50 A) laminated on the first-surface (F) side of core insulation layer ( 50 M), via conductor ( 60 A) is formed to connect conductive circuit ( 58 A) on interlayer insulation layer ( 50 A) to conductive circuit ( 58 Ma) of core insulation layer ( 50 M). In interlayer insulation layer ( 50 C) laminated on interlayer insulation layer ( 50 A), via conductor ( 60 C) is formed to connect conductive circuit ( 58 C) on interlayer insulation layer ( 50 C) to conductive circuit ( 58 A) on interlayer insulation layer ( 50 A). In interlayer insulation layer ( 50 E) laminated on interlayer insulation layer ( 50 C), via conductor ( 60 E) is formed to connect conductive circuit ( 58 E) on interlayer insulation layer ( 50 E) to conductive circuit ( 58 C) on interlayer insulation layer ( 50 C). In interlayer insulation layer ( 50 G) laminated on interlayer insulation layer ( 50 E), via conductor ( 60 G) is formed to connect conductive circuit ( 58 G) on interlayer insulation layer ( 500 ) to conductive circuit ( 58 E) on interlayer insulation layer ( 50 E). In interlayer insulation layer ( 50 I) laminated on interlayer insulation layer ( 50 G), via conductor ( 60 I) is formed to connect conductive circuit ( 581 ) on interlayer insulation layer ( 50 I) to conductive circuit ( 58 G) on interlayer insulation layer ( 50 G). Solder-resist layer ( 62 F) is formed on interlayer insulation layer ( 50 I), and conductive circuit ( 581 ) exposed from opening ( 64 F) of the solder-resist layer works as pad ( 66 F). 
         [0025]    In interlayer insulation layer ( 50 B) laminated on the second-surface (S) side of core insulation layer ( 50 M), via conductor ( 60 B) is formed to connect conductive circuit ( 58 B) on interlayer insulation layer ( 50 B) to conductive circuit ( 58 Mb) of core insulation layer ( 50 M). In interlayer insulation layer ( 50 D) laminated on interlayer insulation layer ( 50 B), via conductor ( 60 D) is formed to connect conductive circuit ( 58 D) on interlayer insulation layer ( 50 D) to conductive circuit ( 58 B) on interlayer insulation layer ( 50 B). In interlayer insulation layer ( 50 F) laminated on interlayer insulation layer ( 50 D), via conductor ( 60 F) is formed to connect conductive circuit ( 58 F) on interlayer insulation layer ( 50 F) to conductive circuit ( 58 D) on interlayer insulation layer ( 50 D). In interlayer insulation layer ( 50 H) laminated on interlayer insulation layer ( 50 F), via conductor ( 60 H) is formed to connect conductive circuit ( 58 H) on interlayer insulation layer ( 50 H) to conductive circuit ( 58 F) on interlayer insulation layer ( 50 F). In interlayer insulation layer ( 50 J) laminated on interlayer insulation layer ( 50 H), via conductor ( 60 J) is formed to connect conductive circuit ( 58 J) on interlayer insulation layer ( 50 J) to conductive circuit ( 58 H) on interlayer insulation layer ( 50 H). Solder-resist layer ( 62 S) is formed on interlayer insulation layer ( 50 J), and conductive circuit ( 58 J) exposed from opening ( 64 S) of the solder-resist layer works as pad ( 66 S). Through hole  52  is formed penetrating through interlayer insulation layers ( 50 I,  50 G,  50 E,  50 C,  50 A,  50 M,  50 B,  50 D,  50 F,  50 H,  50 J). 
         [0026]      FIG. 11  is a cross-sectional view of printed wiring board  10  with mounted electronic components  11 . On the first-surface (F) side of printed wiring board  10 , electronic component  11  is mounted through solder  68  provided on pad ( 66 F), and on the second-surface (S) side of printed wiring board  10 , electronic component  11  is mounted through solder  68  provided on pad ( 66 S). 
         [0027]      FIG. 1  is a plan view of multipiece printed wiring board ( 10 G) where 8×4 printed wiring boards  10  are manufactured.  FIG. 2  is a perspective view of printed wiring board  10  cut out into an individual piece.  FIG. 10  shows part of the cross section taken at (X1-X1) in  FIG. 2 . As shown in  FIG. 1 , multiple printed wiring boards  10  are manufactured inside frame  20 , which is formed along the periphery of multipiece printed wiring board ( 10 G). As shown in  FIG. 2 , printed wiring board  10  has rectangular main body  12  structured to have short-side sidewalls ( 12 H) and long-side sidewalls ( 12 V). To each of short-side sidewalls ( 12 H) on either side of main body  12 , extension piece  14  is attached to be integrated with main body  12 , extending in a direction along long-side sidewall ( 12 V). Extension pieces ( 14 ,  14 ) are formed to face each other by sandwiching main body  12 , and are each formed to have end wall (edge side) ( 14 H), which is parallel to short-side sidewall ( 12 H) of main body  12 . Width (w2) of extension piece  14  is narrower than width (w1) of main body  12 . Extension piece  14  and main body  12  are connected by bridge portion  19 , which is formed along short-side sidewall ( 12 H) with slits for cutting out the main body (hereinafter referred to as cut-out slits  18 ). A pair of protruding tabs  16  are attached to each extension piece  14  to protrude in a direction perpendicular to the direction in which extension piece  14  extends (in a direction along long-side sidewall ( 12 V)). 
         [0028]    In the first embodiment, when printed wiring board  10  is cut out from multipiece wiring board ( 10 G), a laser is used to cut along the outline of printed wiring board  10  as shown in  FIG. 3(A)  and an individual piece is cut out as shown in  FIG. 3(B) . Prior to cutting along the outline of printed wiring board  10 , cut-out slits  18  are formed by a laser. 
         [0029]      FIG. 4(A)  is a plan view of metal frame ( 30 G) made of aluminum. Metal frame ( 30 G) has three accommodation openings  30 , each for accommodating printed wiring board  10 , and alignment holes  38  are formed at the four corners of the frame. On the periphery of opening  30 , L-shaped slits  44  and connecting portions  45  are formed to adjust stress. 
         [0030]      FIG. 4(B)  shows a state where printed wiring boards  10  are fixed into all the accommodation openings  30  of metal frame ( 30 G).  FIG. 7(A)  shows a cross-sectional view showing part of printed wiring board  10  taken at (X2-X2) in  FIG. 4(B) . Metal frame ( 30 G) is set to have a thickness (t1) of 750 μm, and printed wiring board  10  is set to have a thickness (t2) of 780 μm. Namely, the thickness of metal frame ( 30 G) is less than that of printed wiring board  10 . In addition, printed wiring board  10  is fixed to metal frame ( 30 G) so that its center plane (C2) in a thickness direction corresponds to center plane (C1) of metal frame ( 30 G) in the thickness direction. Therefore, metal frame ( 30 G) is recessed from upper surface (first surface) (F) of printed wiring board  10 , and metal frame ( 30 G) is recessed from lower surface (second surface) (S) of printed wiring board  10 . Accordingly, when electronic components are mounted on printed wiring boards  10 , metal frame ( 30 G) will not interfere with the mounting procedure. 
         [0031]    The coefficient of thermal expansion along a main surface of metal frame ( 30 G) made of aluminum is 23 ppm/° C., and the coefficient of thermal expansion along a main surface of printed wiring board  10  made of resin is 16 ppm/° C. The thermal expansion coefficient of metal frame ( 30 G) is higher than that of printed wiring board  10 . The thickness of metal frame ( 30 G) is set to be less than that of printed wiring board  10  so that warping caused by a difference in thermal expansion coefficients is suppressed in printed wiring board  10 . Aluminum is used as the material for the metal frame in the first embodiment, but copper, stainless steel or the like may also be used as long as its thermal expansion coefficient is higher than that of printed wiring boards  10 . 
         [0032]      FIG. 5  shows a state where printed wiring board  10  is fixed to accommodation opening  30  of metal frame ( 30 G). Accommodation opening  30  has long-side sidewall ( 30 V) facing long-side sidewall ( 12 V) of main body  12 , short-side sidewall ( 30 H) facing short-side sidewall ( 12 H) of main body  12 , extension-side sidewall ( 30 Vv) facing extension-side sidewall ( 14 V) of extension piece  14 , and recess ( 30 D) facing end wall ( 14 H) of extension piece  14 , and U-shaped portion ( 30 U) making surface contact with protruding tab  16  by abutting partially the sidewall of the protruding tab. A predetermined clearance is provided between long-side sidewall ( 12 V) of main body  12  and long-side sidewall ( 30 V), and between extension-side sidewall ( 14 V) of extension piece  14  and extension-side sidewall ( 30 Vv). In addition, a predetermined clearance is formed by the rest of U-shaped portion ( 30 U) where no surface contact is made with the sidewall of protruding tab  16  (see  FIG. 6 ). Since printed wiring board  10  expands more in a long-side direction (in a direction along long-side sidewall ( 12 V)), a space greater than the above predetermined clearance is provided between end wall ( 14 H) of extension piece  14  and recess ( 30 D). Accordingly, interference is prevented between recess ( 30 D) and end wall ( 14 H), and stress on end wall ( 14 H) is suppressed when printed wiring board  10  undergoes thermal deformation. 
         [0033]    First crimped portion ( 36   a ) is formed at the base of U-shaped portion ( 30 U) of opening  30 , which is at the border between U-shaped portion ( 30 U) and recess ( 30 D). Second crimped portion ( 36   b ) is formed at the border of U-shaped portion ( 30 U) and extension-side sidewall ( 30 Vv). First crimped portion ( 36   a ) and second crimped portion ( 36   b ) cause the sidewall of U-shaped portion ( 30 U) to be bonded to the sidewall of protruding tab  16  as they abut each other when plastic deformation occurs. Accordingly, printed wiring board  10  is held in place by metal frame ( 30 G). Except for protruding tab  16  bonded by first crimped portion ( 36   a ) and second crimped portion ( 36   b ) (holding portion), sidewalls of printed wiring board  10  do not make contact with sidewalls of opening  30 . The distance from the center of printed wiring board  10  to first crimped portion ( 36   a ) is greater than the distance from the center to second crimped portion ( 36   b ). 
         [0034]      FIG. 6  is an enlarged view of L-shaped slit  44  and connecting portion  45 . Slit  44  is formed in an L-shape in the vicinity of the holding portion of printed wiring board  10  to surround the holding portion, and has first straight portion ( 44 V) formed along a long side of printed wiring board  10 , second straight portion ( 44 H) formed to be perpendicular to first straight portion ( 44 V), and third straight portion ( 44 C) connecting first straight portion ( 44 V) and second straight portion ( 44 H). The angle made by an extended line from first straight portion ( 44 V) and third straight portion ( 44 C) is approximately 45 degrees, and the angle made by an extended line from second straight portion ( 44 H) and third straight portion ( 44 C) is approximately 45 degrees. Length (Y1) (length of L-shaped slit in a direction Y) obtained by adding the length of first straight portion ( 44 V) and the length of a component of third straight portion ( 44 C) extended in a direction along the first straight portion is 18 mm. Length (X1) (length of L-shaped slit in a direction X) obtained by adding the length of second straight portion ( 44 H) and the length of a component of third straight portion ( 44 C) extended in a direction along the second straight portion is 18 mm. The length of first straight portion ( 44 V) is equal to the length of second straight portion ( 44 H). 
         [0035]    Connecting portion  45  is a portion connecting from an intermediate point of first straight portion ( 44 V) to opening  30 . Thus, printed wiring board  10  is accommodated in opening  30  of metal frame ( 30 G) while its four corners at protruding tabs  16  are each held by a portion of metal frame ( 30 G) structured to be surrounded by opening  30 , L-shaped slit  44  and connecting portion  45  (hereinafter also referred to as holding portion  46 ). Here, width (w3) of first straight portion ( 44 V) is 3 mm, for example, and width (w4) of connecting portion  45  is 1 mm, for example, which is smaller than width (w3) of first straight portion ( 44 V). 
         [0036]      FIG. 8(A)  is a cross-sectional view of crimping tool  300  to conduct crimping on printed wiring board  10 . Crimping tool  300  has lower die  210  and upper die  310 . Lower die  210  has base portion  211  and support plate  218 . Support plate  218  is supported to be vertically movable with respect to base portion  211 . Punches  216  for crimping are provided for base portion  211 , and penetrating holes ( 218   h ) for punches  216  to pass through are formed in support plate  218 . In the central portion of support plate  218 , recessed portion ( 218   d ) is formed so as not to exert force on printed wiring board  10  during crimping. Metal frame ( 30 G) is placed on support plate  218  in such a way that printed wiring board  10  is positioned on recessed portion ( 218   d ) with a predetermined space between them. 
         [0037]    Upper die  310  has base portion  311  and support plate  318 . Support plate  318  is supported to be vertically movable with respect to base portion  311 . Punches  316  for crimping are provided for base portion  311 , and penetrating holes ( 318   h ) for punches  316  to pass through are formed in support plate  318 . Recessed portion ( 318   d ) is formed in the center of support plate  318  so that no force is exerted on printed wiring board  10  during crimping. 
         [0038]      FIG. 8(B)  is a view showing a state where upper die  310  is pressed against lower die  210 , punches  316  of upper die  310  are pressed against the upper surface of metal frame ( 30 G), and punches  216  of lower die  210  are pressed against the lower surface of metal frame ( 30 G). In each of three accommodation openings  30  of metal frame ( 30 G) shown in  FIG. 4(B) , first crimped portion ( 36   a ) and second crimped portion ( 36   b ) are formed simultaneously as shown in  FIG. 5 . Accordingly, combined wiring board  100  ready for reflow is completed where each printed wiring board  10  is held in place by metal frame ( 30 G). Since outward stress is exerted on printed wiring board  10  when a greater degree of deformation is caused on second crimped portion ( 36   b ) positioned closer to the center as mentioned above, the degree of deformation on second crimped portion ( 36   b ) during crimping is greater than that on first crimped portion ( 36   a ). 
         [0039]    In a combined wiring board of the first embodiment, since crimped portions ( 36   a ,  36   b ) are formed simultaneously in each of three accommodation openings  30 , accurate alignment of printed wiring boards  10  is achieved with respect to metal frame ( 30 G). Here, compared with a combined wiring board where an adhesive agent or the like is used for fixing printed wiring boards  10  to the frame, crimping is conducted simultaneously on all printed wiring boards  10 . Thus, alignment with metal frame ( 30 G) is accurate, and positional shifting among printed wiring boards is minimized. Moreover, compared with an alignment method using an adhesive agent, since the steps for filling and curing the adhesive agent are not required, there are fewer manufacturing steps. Thus, productivity is enhanced and the cost of fixing printed wiring boards  10  to metal frame ( 30 G) is reduced. 
         [0040]    When printed wiring board  10  is fixed into accommodation opening  30  of metal frame ( 30 G) shown in  FIG. 5 , solder is printed, an electronic component is placed, and reflow is conducted in a reflow oven for the purpose of mounting the electronic component. Since a reflow temperature of almost 200° C. exceeds the glass transition temperature (Tg) of the resin in printed wiring board  10 , warping tends to occur in printed wiring board  10  because of the weight of the mounted electronic component and residual stress in the wiring board. In printed wiring board  10  fixed to metal frame ( 30 G) of the first embodiment, stress toward the center, along with stress caused by the weight of electronic component  11 , is generated as shown in  FIG. 7(B) . However, since the coefficient of thermal expansion along a main surface of metal frame ( 30 G) is higher than that of printed wiring board  10  as described above, expansion of metal frame ( 30 G) in a planar direction is greater than that of printed wiring board  10 . Thus, on printed wiring board  10  fixed into accommodation opening  30 , stress (F1) toward the periphery is exerted so as to cancel out the stress toward the center of printed wiring board  10 . Accordingly, warping is unlikely to occur in the printed wiring board during the reflow process. 
         [0041]    In the combined wiring board related to the present invention, printed wiring board  10  accommodated in opening  30  is held in place by holding portion  46  of metal frame ( 30 G), which is surrounded by opening  30 , slit  44  and connecting portion  45 . Thus, stress exerted through the holding portion of metal frame ( 30 G) is dispersed to slit  44  and connecting portion  45 , and stress is less likely to propagate further. Accordingly, when a difference in the thermal expansion coefficients of printed wiring board  10  and metal frame ( 30 G) causes a difference in the degrees of thermal deformation during a reflow process, stress generated by the difference in thermal deformation is less likely to affect printed wiring board  10  and metal frame ( 30 G) because slit  44  and connecting portion  45  suppress the propagation of stress. In the present embodiment, stress caused by thermal expansion can be limited in a tensile direction. Therefore, warping caused by thermal deformation during a reflow process is suppressed in printed wiring board  10  and metal frame ( 30 G). 
         [0042]    Because of elastic deformation of holding portion  46 , stress exerted through holding portions connected to metal frame ( 30 G) is more likely to be dispersed. Since printed wiring board  10  is fixed to metal frame ( 30 G) while elasticity is retained between them, when a difference in the thermal expansion coefficients of printed wiring board  10  and metal frame ( 30 G) causes a difference in the degrees of thermal deformation during a reflow process, stress generated by the difference in thermal deformation is less likely to affect printed wiring board  10  and metal frame ( 30 G) because holding portion  46  makes elastic deformation. Accordingly, warping caused by thermal deformation during a reflow process is suppressed in printed wiring board  10  and metal frame ( 30 G). 
         [0043]      FIG. 9  shows metal frame ( 30 G) after bridge portion  19  between cut-out slits  18  is cut and main body  12  of printed wiring board  10  is separated. Extension piece  14  of printed wiring board  10  remains on the metal-frame ( 30 G) side. In the first embodiment, since cut-out slits  18  are formed in advance, it is easier to separate main body  12  of printed wiring board  10 . 
       Second Embodiment 
       [0044]      FIG. 12  is an enlarged view showing L-shaped slit  44  and connecting portion ( 45   a ) of combined wiring board ( 100   a ) according to a second embodiment. In metal frame ( 30 Ga) of combined wiring board ( 100   a ) of the second embodiment, connecting portion ( 45   a ) is formed at a position farther from second straight portion ( 44 H) so that opening  30  and an edge of first straight portion ( 44 V) are connected and the space is enlarged between opening  30  and main body  12  or extension piece  14 . Accordingly, printed wiring board  10  is accommodated in opening  30  of metal frame ( 30 Ga) while its four corners at protruding tabs  16  are each held by holding portion ( 46   a ) of metal frame ( 30 Ga), which is surrounded by opening  30 , L-shaped slit  44  and connecting portion ( 45   a ). 
         [0045]    As described, even if connecting portion ( 45   a ) is positioned to enlarge the space between opening  30  and main body  12  or extension piece  14 , printed wiring board  10  accommodated in opening  30  is held by holding portion ( 46   a ). Thus, stress exerted through the holding portion in metal frame ( 30 Ga) is dispersed by slit  44  and connecting portion ( 45   a ), and is less likely to propagate further. Accordingly, warping caused by thermal deformation is suppressed from occurring in printed wiring board  10  and metal frame ( 30 Ga). 
       Third Embodiment 
       [0046]      FIG. 13  is an enlarged view showing L-shaped slit  44  and connecting portion ( 45   b ) of combined wiring board ( 100   b ) according to a third embodiment. In metal frame ( 30 Gb) of combined wiring board ( 100   b ) in the third embodiment, connecting portion ( 45   b ) is formed to connect opening  30  and an edge of first straight portion ( 44 V), which is farther from second straight portion ( 44 H). Accordingly, printed wiring board  10  is accommodated in opening  30  of metal frame ( 30 G) while its four corners at protruding tabs  16  are each held by holding portion ( 46   b ) of metal frame ( 30 Gb), surrounded by opening  30 , L-shaped slit  44  and connecting portion ( 45   b ). 
         [0047]    Printed wiring board  10  accommodated in opening  30  is held by holding portion ( 46   b ) by the above structure as well. Accordingly, stress exerted through the holding portion connected to metal frame ( 30 Gb) is dispersed by slit  44  and connecting portion ( 45   b ), and warping caused by thermal deformation is suppressed from occurring in printed wiring board  10  and metal frame ( 30 Gb). 
         [0048]    In the first through third embodiments, metal frames ( 30 G,  30 Ga,  30 Gb) are each preferred to have higher rigidity at reflow temperatures than printed wiring board  10 . 
         [0049]    When the temperature of heat applied to a wiring board during a solder reflow process for mounting an electronic component exceeds the glass transition temperature (Tg) of the material in the wiring board, warping occurs in the wiring board due to the weight of the mounted electronic component and residual stress in the wiring board. 
         [0050]    A combined wiring board according to an embodiment of the present invention and its manufacturing method according to an embodiment of the present invention suppress warping of a wiring board and of a metal frame caused by thermal deformation. 
         [0051]    A combined wiring board according to an embodiment of the present application has wiring boards and a metal frame that has openings to accommodate wiring boards and surrounds the wiring boards. In an opening into which a wiring board is accommodated, multiple portions of the wiring board are held by part of the sidewall of the opening. In the metal frame, a slit is formed near the portion that holds the wiring board, and a connecting portion is also formed to connect the slit and the opening. 
         [0052]    In a combined wiring board according to an embodiment of the present application, a wiring board accommodated in an opening is held in place by a portion of the metal frame that is surrounded by the opening, a slit and a connecting portion (hereinafter may also be referred to as a holding portion). Thus, stress exerted through the holding portion of the metal frame is dispersed by the slit, and is less likely to propagate further. Accordingly, when a difference in the thermal expansion coefficients of a wiring board and the metal frame causes a difference in the degrees of thermal deformation, stress generated by the difference in thermal deformation is less likely to affect the wiring board and the metal frame because the propagation of the stress is suppressed by the slit. Thus, warping caused by thermal deformation is reduced in the wiring board and metal frame. 
         [0053]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.