Patent Publication Number: US-2023139231-A1

Title: Circuit board with heat dissipation function

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of patent application Ser. No. 17/383,853, filed on Jul. 23, 2021, assigned to the same assignee, which is based on and claims priority to China Patent Application No. 202110758492.0 filed on Jul. 5, 2021, the contents of which are incorporated by reference herein. 
    
    
     FIELD 
     The disclosure relates to printed circuit boards, and more particularly, to a circuit board with improved heat dissipation function and a method for manufacturing the circuit board. 
     BACKGROUND 
     Circuit boards may have electronic components that generate heat during operation. If the heat cannot be dissipated quickly, a safety performance and a service life of the circuit board may be compromised. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. 
         FIG.  1    is a diagrammatic view of an embodiment of a first metal layer according to the present disclosure. 
         FIG.  2    is a diagrammatic view wherein a first adhesive layer and a second adhesive layer are formed on the first metal layer of  FIG.  1   . 
         FIG.  3    is a diagrammatic view wherein a first heat conducting portion and a first heat conducting member are formed on the first metal layer, a first insulating layer is formed on the first adhesive layer, and a fourth insulating layer is formed on the second adhesive layer of  FIG.  2   , to form a first intermediate body. 
         FIG.  4    is a diagrammatic view wherein a first blind hole, a first blind groove, and a through hole are defined in the first intermediate body of  FIG.  3   . 
         FIG.  5    is a diagrammatic view wherein a second heat conducting portion, a second heat conducting member, and a first heat conducting channel are respectively formed in the first blind hole, the first blind groove, and the through hole of  FIG.  4   . 
         FIG.  6    is a diagrammatic view wherein a first copper foil layer and a second copper foil layer are respectively formed on the first insulating layer and the fourth insulating layer of  FIG.  5   . 
         FIG.  7    is a diagrammatic view wherein the first copper foil layer and the second copper foil layer of  FIG.  6    are etched to respectively form a first wiring layer and a fourth wiring layer. 
         FIG.  8    is a diagrammatic view wherein a second insulating layer and a second metal layer are respectively formed on the first wiring layer and the fourth wiring layer of  FIG.  7   . 
         FIG.  9    is a diagrammatic view wherein a second blind hole is defined in the second insulating layer, and a second blind groove and a third blind groove are defined in the second metal layer of  FIG.  8   . 
         FIG.  10    is a diagrammatic view wherein a third heat conducting portion, a third heat conducting member, and a fourth heat conducting member are respectively formed in the second blind hole, the second blind groove, and the third blind groove of  FIG.  9   . 
         FIG.  11    is a diagrammatic view wherein a second wiring layer and a fifth wiring layer are respectively formed on the second insulating layer and the second metal layer of  FIG.  10   . 
         FIG.  12    is a diagrammatic view wherein a third insulating layer is formed on the second wiring layer of  FIG.  11   , to form a second intermediate body. 
         FIG.  13    is a diagrammatic view wherein an opening is defined in the second intermediate body and a second heat conducting channel is formed in the opening of  FIG.  12   . 
         FIG.  14    is a diagrammatic view wherein a third wiring layer is formed on the third insulating layer of  FIG.  13   . 
         FIG.  15    is a diagrammatic view wherein a first solder resist layer and a second solder resist layer are respectively formed on the third wiring layer and the fifth wiring layer of  FIG.  14   . 
         FIG.  16    is a diagrammatic view wherein the first solder resist layer, the third wiring layer, the third insulating layer, and the second wiring layer of  FIG.  15    are cut. 
         FIG.  17    is a diagrammatic view wherein an electronic component is installed in the groove of  FIG.  16   , to form a circuit board. 
     
    
    
     DETAILED DESCRIPTION 
     Implementations of the disclosure will now be described, by way of embodiments only, with reference to the drawings. It should be noted that the embodiments and the features of the present disclosure can be combined without conflict. Specific details are set forth in the following description to make the present disclosure to be fully understood. The embodiments are only some and not all the embodiments of the present disclosure. Based on the embodiments of the present disclosure, other embodiments obtained by a person of ordinary skill in the art without creative efforts shall be within the scope of the present disclosure. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terms used herein in the specification of the present disclosure are only for describing the embodiments, and are not intended to limit the present disclosure. The term “and/or” as used herein includes any combination of one or more related items. 
     In the embodiments of the present disclosure, and not as a limitation of the present disclosure, the term “connection” used in the specification and claims of the present disclosure is not limited to physical or mechanical connection, no matter direct connection or indirect connection. The terms of “up”, “down”, “above”, “below”, “left”, “right”, etc., are only used to indicate the relative position relationship. When the absolute position of a described element changes, the relative positions correspondingly changes. 
     A method for manufacturing a circuit board is disclosed in an embodiment. The method is provided by way of example, as there are a variety of ways to carry out the method. The method can begin at step  1 . 
     At step  1 , referring to  FIG.  1   , a first metal layer  10  is provided. 
     In an embodiment, the first metal layer  10  includes a main body  101 , a number of first pillars  102 , and a number of second pillars  103 . The first pillars  102  and the second pillars  103  protrude from two opposite surfaces of the main body  101 . A first slot  11  is defined between the main body  101  and two adjacent first pillars  102 , and a second slot  12  is defined between the main body  101  and two adjacent second pillars  103 . In an embodiment, the first pillars  102  and the second pillars  103  are aligned with each other in a thickness direction of the first metal layer  10 . 
     The first metal layer  10  is made of a thermoelectric separation metal. The thermoelectric separation means that thermal (heat) and electricity are independent from each other, and heat and electric are transmitted in the first metal layer  10  at different positions. In an embodiment, the first metal layer  10  is made of aluminum nitride or potassium nitride. The first metal layer  10  has good heat conductive performance and electric conductive performance. 
     At step  2 , referring to  FIG.  2   , a first adhesive layer  20  and a second adhesive layer  21  are formed in the first slot  11  and the second slot  12 , respectively. 
     A surface of the first adhesive layer  20  away from the main body  101  and a surface of the first pillar  102  away from the main body  101  are substantially flush with each other. A surface of the second adhesive layer  21  away from the main body  101  and a surface of the second pillar  103  away from the main body  101  are substantially flush with each other. 
     At step  3 , referring to  FIG.  3   , copper is electroplated on each of the first pillars  102  and each of the second pillars  103  to form a first heat conducting portion  22  and a first heat conducting member  23 . The first heat conducting portion  22  is in thermal conduction with the first pillar  102 , and the first heat conducting member  23  is in thermal conduction with the second pillar  103 . 
     A first insulating layer  24  is formed on the first adhesive layer  20  having the first heat conducting portion  22 , and a fourth insulating layer  25  is formed on the second adhesive layer  21  having the first heat conducting member  23 . Then, a first intermediate body  30  is obtained. 
     Each of the first insulating layer  24  and the fourth insulating layer  25  can be made of a material selected from epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), Polyimide (PI), polyethylene Terephthalate (PET), polyethylene naphthalate (PEN), and any combination thereof. In an embodiment, the first insulating layer  24  and the fourth insulating layer  25  are both made of polypropylene. 
     At step  4 , referring to  FIG.  4   , a first blind hole  31 , a first blind groove  32 , and a through hole  33  are defined in the first intermediate body  30 . The first blind hole  31  penetrates the first insulating layer  24 , and a bottom of the first blind hole  31  corresponds to the first heat conducting portion  22 . The first blind groove  32  penetrates the fourth insulating layer  25 , and a bottom of the first blind groove  32  corresponds to the first heat conducting member  23 . The through hole  33  sequentially penetrates the first insulating layer  24 , the first adhesive layer  20 , the main body  101 , the second adhesive layer  21 , and the fourth insulating layer  25 . 
     In an embodiment, the first blind hole  31 , the first blind groove  32 , and the through hole  33  may all be formed by laser drilling. 
     At step  5 , referring to  FIG.  5   , a thermoelectric separation metal is filled in the first blind hole  31 , the first blind groove  32 , and the through hole  33  to form a second heat conducting portion  34 , a second heat conducting member  35 , and a first heat conducting channel  36 . 
     The second heat conducting portion  34  is in thermal conduction with the first heat conducting portion  22 . The second heat conducting member  35  is in thermal conduction with the first heat conducting member  23 . The first heat conducting channel  36  is in thermal conduction with the main body  101 . 
     In an embodiment, the thermoelectric separation metal is aluminum nitride or potassium nitride. 
     At step  6 , referring to  FIG.  6   , a first copper foil layer  40  and a second copper foil layer  41  are formed on the first insulating layer  24  and the fourth insulating layer  25 , respectively. 
     At step  7 , referring to  FIG.  7   , the first copper foil layer  40  and the second copper foil layer  41  are etched to form a first wiring layer  42  and a fourth wiring layer  43 , respectively. 
     The first wiring layer  42  is in thermal conduction with the second heat conducting portion  34 , so that the heat generated by the first wiring layer  42  can pass through the second heat conducting portion  34  and the first heat conducting portion  22  in sequence to the first metal layer  10 . Since the first metal layer  10  is made of metal, the first metal layer  10  can absorb the heat or dissipate the heat to the outside environment, so that the temperature of the first wiring layer  42  can be decreased. Furthermore, the first heat conducting portion  22  made of copper and the second heat conducting portion  34  made of thermoelectric separation metal are alternately arranged, since copper is lower in cost than the thermoelectric separation metal, the heat dissipation requirements can be meet while reducing the production cost. 
     The fourth wiring layer  43  is in thermal conduction with the second heat conducting member  35 , so that the heat generated by the fourth wiring layer  43  can pass through the second heat conducting member  35  and the first heat conducting member  23  in sequence to the first metal layer  10 . The first metal layer  10  can also absorb the heat or dissipate the heat to the outside environment, so that the temperature of the fourth wiring layer  43  can be decreased. Furthermore, the first heat conducting member  23  made of copper and the second heat conducting member  35  made of thermoelectric separation metal are alternately arranged, since the copper is lower in cost than the thermoelectric separation metal, the heat dissipation requirements can be meet while reducing the production cost. 
     At step  8 , referring to  FIG.  8   , a second insulating layer  50  and a second metal layer  51  are formed on the first wiring layer  42  and the fourth wiring layer  43 , respectively. 
     The second insulating layer  50  can be made of a material the same as the that of the first insulating layer  24 . 
     The second metal layer  51  is in thermal conduction with the fourth wiring layer  43 . In an embodiment, the second metal layer  51  is made of a thermoelectric separation metal. 
     At step  9 , referring to  FIG.  9   , a second blind hole  501  is defined in the second insulating layer  50 . A second blind groove  511  and a third blind groove  512  are defined in the second metal layer  51 . 
     The second blind hole  501  penetrates the second insulating layer  50 , and a bottom of the second blind hole  501  corresponds to the first wiring layer  42 . The second blind hole  501  corresponds to the first blind hole  31 . The second blind groove  511  penetrates the second metal layer  51 , and a bottom of the second blind groove  511  corresponds to the fourth wiring layer  43 . The second blind groove  511  corresponds to the first blind groove  32 . The third blind groove  512  penetrates the second metal layer  51 , and a bottom of the third blind groove  512  corresponds to the fourth wiring layer  43 . The third blind groove  512  and the first blind groove  32  are staggered (misaligned) with each other. 
     At step  10 , referring to  FIG.  10   , copper is electroplated in the second blind hole  501 , the second blind groove  511 , and the third blind groove  512  to form a third heat conducting portion  52 , a third heat conducting member  53 , and a fourth heat conducting member  54 . 
     As shown in  FIG.  10   , the electroplated copper completely infills one second blind holes  501  to form the third heat conducting portion  52 . The electroplated copper is only disposed on the sidewall and the bottom of the second blind hole  501 . As such, the thermoelectric separation metal can further infill the second blind hole  501  having the electroplated copper, so that the electroplated copper and the thermoelectric separation metal in the second blind hole  501  cooperatively form the third heat conducting portion  52 . The third heat conducting portion  52  is in thermal conduction with the first wiring layer  42 . 
     In an embodiment, the third heat conducting member  53  is disposed on the sidewall of the second blind groove  511 . The third heat conducting member  53  is in thermal conduction with the fourth wiring layer  43 . 
     In an embodiment, the fourth heat conducting portion  54  is disposed on the sidewall of the third blind groove  512 . The fourth heat conducting portion  54  is in thermal conduction with the fourth wiring layer  43 . 
     At step  11 , referring to  FIG.  11   , a second wiring layer  60  and a fifth wiring layer  61  are formed on the second insulating layer  50  and the second metal layer  51 , respectively. 
     In an embodiment, a third copper foil layer (not shown) and a fourth copper foil layer (not shown) are formed on the second insulating layer  50  and the second metal layer  51 , respectively. The third copper foil layer and the fourth copper foil layer are then etched to form the second wiring layer  60  and the fifth wiring layer  61 , respectively. 
     The second wiring layer  60  is in thermal conduction with the third heat conducting portion  52 , so that the heat generated by the second wiring layer  60  can pass through the third heat conducting portion  52 , the first wiring layer  42 , the second heat conducting portion  34 , and the first heat conducting portion  22  to the first metal layer  10 . The first metal layer  10  can absorb the heat or dissipate the heat to the outside environment, so that the temperature of the second wiring layer  60  can be decreased. Furthermore, the third heat conducting portion  52  made of copper (or made of a mixture of copper and thermoelectric separation metal), the second heat conducting portion  34  made of thermoelectric separation metal, and the first heat conducting portions  22  made of copper are alternately arranged. Since the copper is lower in cost than the thermoelectric separation metal, the heat dissipation requirements can be meet while reducing the production cost. 
     The fifth wiring layer  61  is in thermal conduction with the third heat conducting member  53  and the fourth heat conducting member  54 , so that the heat generated by the fifth wiring layer  61  can pass through the third heat conducting member  53 , the fourth heat conducting portion  54 , the fourth wiring layer  43 , the second heat conducting member  35 , and the first heat conducting member  23  to the first metal layer  10 . The first metal layer  10  can absorb the heat or dissipate the heat to the outside environment, so that the temperature of the fifth wiring layer  61  can be decreased. Furthermore, the third heat conducting member  53  made of copper, the second heat conducting member  35  made of thermoelectric separation metal, and the first heat conducting member  23  made of copper are alternately arranged. Since the copper is lower in cost than the thermoelectric separation metal, the heat dissipation requirements can be meet while reducing the production cost. 
     At step  12 , referring to  FIG.  12   , a third insulating layer  62  is formed on the second wiring layer  60  to obtain a second intermediate body  70 . 
     The third insulating layer  62  may be made of a material the same as that of the first insulating layer  24 . 
     At step  13 , referring to  FIG.  13   , an opening (not shown) is defined in the second intermediate body  70 . Copper is electroplated in the opening to form a second heat conducting channel  71 . 
     The opening penetrates the third insulating layer  62 , the second wiring layer  60  and the second insulating layer  50  in sequence, and a bottom of the opening corresponds to the first wiring layer  42 . The opening is aligned with the through hole  33 . 
     The second heat conducting channel  71  is in thermal conduction with the first wiring layer  42  and the second wiring layer  60 . 
     At step  14 , referring to  FIG.  14   , a third wiring layer  72  is formed on the third insulating layer  62 . 
     The third wiring layer  72  and the second wiring layer  60  are in thermal conduction with the second heat conducting channel  71 , so that the heat generated by the third wiring layer  72  and the second wiring layer  60  can pass through the second heat conducting channel  71 , the first wiring layer  42 , and the first heat conducting channel  36  in sequence to the first metal layer  10 . The first metal layer  10  can absorb the heat or dissipate the heat to the outside environment, so that the temperature of the third wiring layer  72  and the second wiring layer  60  can be decreased. At the same time, the second heat conducting channel  71  made of copper and the first heat conducting channel  36  made of thermoelectric separation metal are alternately arranged. Since the copper is lower in cost than the thermoelectric separation metal, the heat dissipation requirements can be meet while reducing the production cost. 
     At step  15 , referring to  FIG.  15   , a first solder resist layer  80  and a second solder resist layer  81  are formed on the third wiring layer  72  and the fifth wiring layer  61 , respectively. Thus, a circuit substrate  82  is obtained. 
     In an embodiment, the first solder resist layer  80  and the second solder resist layer  81  can be made of a solder resist ink (such as green oil). The first solder resist layer  80  can protect the third wiring layer  72 , and the second solder resist layer  81  can the fifth wiring layer  61 . 
     At step  16 , referring to  FIG.  16   , the first solder resist  80  is cut along a thickness direction of the circuit substrate  82  to obtain a groove  821 . 
     The groove  821  penetrates the first solder resist layer  80 , the third wiring layer  72 , the third insulating layer  62 , and the second wiring layer  60 . The third heat conducting portion  52  is exposed from the groove  821 . In an embodiment, the groove  821  may be cut according to a predetermined cutting depth. 
     At step  17 , referring to  FIG.  17   , an electronic component  90  is installed in the groove  821  to obtain the circuit board  100 . 
     The electronic component  90  is in thermal conduction with the third heat conducting portion  52 , so that the heat generated by the electronic component  90  can pass through the third heat conducting portion  52 , the first wiring layer  42 , the second heat conducting portion  34 , and the first heat conducting portion  22  to the first metal layer  10 . The first metal layer  10  can absorb the heat or dissipate the heat to the outside environment, so that the temperature of the electronic component  90  can be decreased. 
     Referring to  FIG.  17   , the present disclosure further provides an embodiment of a circuit board  100 . The circuit board  100  includes a first metal layer  10 , a first adhesive layer  20 , a second adhesive layer  21 , a first heat conducting portion  22 , a first heat conducting member  23 , a first insulating layer  24 , a fourth insulating layer  25 , a first wiring layer  42 , a fourth wiring layer  43 , a second insulating layer  50 , a second metal layer  51 , a second wiring layer  60 , a fifth wiring layer  61 , a third insulating layer  62 , a third wiring layer  72 , a first solder resist layer  80 , a second solder resist layer  81 , and an electronic component  90 . 
     The first metal layer  10  includes a body  101 , a number of first pillars  102 , and a number of second pillars  103 . The first pillars  102  and the second pillars  103  protrude from two opposite surfaces of the main body  101 . A first slot  11  is defined between the main body  101  and two adjacent first pillars  102 , and a second slot  12  is defined between the main body  101  and two adjacent second pillars  103 . In an embodiment, the first pillars  102  and the second pillars  103  are aligned with each other in a thickness direction of the first metal layer  10 . 
     In an embodiment, the first metal layer  10  is made of a thermoelectric separation metal. In an embodiment, the first metal layer  10  is aluminum nitride or potassium nitride. The first metal layer  10  has good thermal conductivity and certain electrical conductivity. 
     The first adhesive layer  20  and the second adhesive layer  21  are respectively disposed in the first slot  11  and the second slot  12 . 
     The first heat conducting portion  22  and the first heat conducting member  23  are respectively disposed on the first pillar  102  and the second pillar  103 . The first heat conducting portion  22  and the first heat conducting member  23  are both made of copper. The first heat conducting portion  22  is in thermal conduction with the first pillar  102 , and the first heat conducting member  23  is in thermal conduction with the second pillar  103 . 
     The first insulating layer  24  is disposed on the first adhesive layer  20  having the first heat conducting portion  22 . A first blind hole  31  is defined in the first insulating layer  24 . The first blind hole  31  penetrates the first insulating layer  24 , and the bottom of the first blind hole  31  corresponds to the first heat conducting portion  22 . The second heat conducting portion  34  is formed in the first blind hole  31 . The second heat conducting portion  34  is made of the thermoelectric separation metal. The second heat conducting portion  34  is in thermal conduction with the first heat conducting portion  22 . 
     The fourth insulating layer  25  is disposed on the second adhesive layer  21  having the first heat conducting member  23 . The fourth insulating layer  25  defines a first blind groove  32 . The first blind groove  32  penetrates the fourth insulating layer  25 , and the bottom of the first blind groove  32  corresponds to the first heat conducting member  23 . The second heat conducting member  35  is formed in the first blind groove  32 . The second heat conducting member  35  is made of the thermoelectric separation metal. The second heat conducting member  35  is in thermal conduction with the first heat conducting member  23 . 
     The circuit board  100  further defines a through hole  33 . The through hole  33  penetrates the first insulating layer  24 , the first adhesive layer  20 , the main body  101 , the second adhesive layer  21 , and the fourth insulating layer  25  in sequence. The first heat conducting channel  36  is formed in the through hole  33 . The first heat conducting channel  36  is made of the thermoelectric separation metal. The first heat conducting channel  36  is in thermal conduction with the main body  101 . 
     The first wiring layer  42  is disposed on the first insulating layer  24 . The first wiring layer  42  is in thermal conduction with the second heat conducting portion  34 , so that the heat generated by the first wiring layer  42  can pass through the second heat conducting portion  34  and the first heat conducting portion  22  to the first metal layer  10 . 
     The fourth wiring layer  43  is disposed on the fourth insulating layer  25 . The fourth wiring layer  43  is in thermal conduction with the second heat conducting member  35 , so that the heat generated by the fourth wiring layer  43  can pass through the second heat conducting member  35  and the first heat conducting member  23  to the first metal layer  10 . 
     The second insulating layer  50  is disposed on the first wiring layer  42 . A second blind hole  501  is defined in the second insulating layer  50 . The second blind hole  501  penetrates the second insulating layer  50 , and the bottom of the second blind hole  501  corresponds to the first wiring layer  42 . The second blind hole  501  corresponds to the first blind hole  31 . The third heat conducting portion  52  is formed in the second blind hole  501 . The third heat conducting portion  52  is made of copper. 
     The second metal layer  51  is disposed on the fourth wiring layer  43 . The second metal layer  51  is in thermal conduction with the fourth wiring layer  43 . In an embodiment, the second metal layer  51  is made of the thermoelectric separation metal. 
     The second metal layer  51  defines a second blind groove  511  and a third blind groove  512 . The second blind groove  511  penetrates the second metal layer  51 , and the bottom of the second blind groove  511  corresponds to the fourth wiring layer  43 . The second blind groove  511  corresponds to the first blind groove  32 . The third blind groove  512  penetrates the second metal layer  51 , and the bottom of the third blind groove  512  corresponds to the fourth wiring layer  43 . The third blind groove  512  and the first blind groove  32  are staggered with each other. The third heat conducting member  53  and the fourth heat conducting portion  54  are respectively formed in the second blind groove  511  and the third blind groove  512 . The third heat conducting member  53  and the fourth heat conducting portion  54  are both made of copper. 
     As shown in  FIG.  17   , the electroplated copper completely infills one second blind holes  501  to form the third heat conducting portion  52 . The electroplated copper is only disposed on the sidewall and the bottom of the second blind hole  501 . As such, the thermoelectric separation metal can further infill the second blind hole  501  having the electroplated copper, so that the electroplated copper and the thermoelectric separation metal in the second blind hole  501  cooperatively form the third heat conducting portion  52 . The third heat conducting portion  52  is in thermal conduction with the first wiring layer  42 . 
     In an embodiment, the third heat conducting member  53  is disposed on the sidewall of the second blind groove  511 . The third heat conducting member  53  is in thermal conduction with the fourth wiring layer  43 . 
     In an embodiment, the fourth heat conducting portion  54  is disposed on the sidewall of the third blind groove  512 . The fourth heat conducting portion  54  is in thermal conduction with the fourth wiring layer  43 . 
     The second wiring layer  60  is disposed on the second insulating layer  50 . The second wiring layer  60  is in thermal conduction with the third heat conducting portion  52 , so that the heat generated by the second wiring layer  60  can pass through the third heat conducting portion  52 , the first wiring layer  42 , the second heat conducting portion  34 , and the first heat conducting portion  22  to the first metal layer  10 . 
     The fifth wiring layer  61  is disposed on the second metal layer  51 . The fifth wiring layer  61  is in thermal conduction with the third heat conducting member  53  and the fourth heat conducting member  54 , so that the heat generated by the fifth wiring layer  61  can pass through the third heat conducting member  53 , the fourth heat conducting portion  54 , the fourth wiring layer  43 , the second heat conducting member  35 , and the first heat conducting member  23  to the first metal layer  10 . 
     The third insulating layer  62  is disposed on the second wiring layer  60 . 
     The circuit board  100  further defines an opening  710 . The opening  710  penetrates the third insulating layer  62 , the second wiring layer  60 , and the second insulating layer  50  in sequence, and the bottom of the opening  710  corresponds to the first wiring layer  42 . The opening  710  corresponds to the through hole  33 . The second heat conducting channel  71  is formed in the opening  710 . The second heat conducting channel  71  is made of copper. The second heat conducting channel  71  is in thermal conduction with the first wiring layer  42  and the second wiring layer  60 . 
     The third wiring layer  72  is formed on the third insulating layer  62 . The third wiring layer  72  and the second wiring layer  60  are in thermal conduction with the second heat conducting channel  71 , so that the heat generated by the third wiring layer  72  and the second wiring layer  60  can pass through the second heat conducting channel  71 , the first wiring layer  42 , and the first heat conducting channel  36  in sequence to the first metal layer  10 . 
     The first solder resist layer  80  and the second solder resist layer  81  are respectively disposed on the third wiring layer  72  and the fifth wiring layer  61 . The first solder resist layer  80  and the second solder resist layer  81  can be made of a solder resist ink. 
     The circuit board  100  also defines a groove  821 . The groove  821  penetrates the first solder resist layer  80 , the third wiring layer  72 , the third insulating layer  62 , and the second wiring layer  60 . The third heat conducting portion  52  is exposed from the groove  821 . The electronic component  90  is disposed in the groove  821 . The electronic component  90  is in thermal conduction with the third heat conducting portion  52 , so that the heat generated by the electronic component  90  can pass through the third heat conducting portion  52 , the first wiring layer  42 , the second heat conducting portion  34 , and the first heat conducting portion  22  to the first metal layer  10 . 
     Although the embodiments of the present disclosure have been shown and described, those having ordinary skill in the art can understand that changes may be made within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will, therefore, be appreciated that the embodiments described above may be modified within the scope of the claims.