Patent Publication Number: US-2023156906-A1

Title: Circuit board assembly and method for manufacturing the same

Description:
FIELD 
     The subject matter herein generally relates to circuit boards, and more particularly, to a circuit board assembly and a method for manufacturing the same. 
     BACKGROUND 
     A circuit board is used as a support and a carrier for an electronic component. The electronic component is embedded in the circuit board to reduce the thickness of the electronic product, but it causes heat dissipation problems. Therefore, there is a room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
         FIG.  1    is a cross-sectional view of an embodiment of an inner circuit substrate according to the present disclosure. 
         FIG.  2    is a cross-sectional view showing a heat conducting block placed in a through hole of  FIG.  1   . 
         FIG.  3    is a cross-sectional view showing a first outer circuit substrate and a second outer circuit substrate formed on opposite surfaces of the inner circuit substrate of  FIG.  1   . 
         FIG.  4    is a cross-sectional view showing the first outer circuit substrate and the second outer circuit substrate corresponding to an insulating layer of  FIG.  3    removed to expose the insulating layer. 
         FIG.  5    is a cross-sectional view showing an accommodating groove passing through the first outer circuit substrate of  FIG.  4    and recessed toward the heat conducting block. 
         FIG.  6    is a cross-sectional view showing a thermally conductive filler and a first sub-component accommodated in the accommodating groove of  FIG.  5   . 
         FIG.  7    is a cross-sectional view showing a second sub-component connected to a surface of the first outer circuit substrate of  FIG.  6   . 
         FIG.  8    is a cross-sectional view showing a reinforcing plate formed on a surface of the second outer circuit substrate corresponding to the first sub-component of  FIG.  4    to form a circuit board assembly. 
         FIG.  9    is a cross-sectional view showing of another embodiment of a heat conducting block with a metal layer on its surface placed in a through hole of  FIG.  1   . 
         FIG.  10    is a cross-sectional view showing another embodiment of a circuit board assembly according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. 
     Some embodiments of the present disclosure will be described in detail with reference to the drawings. If no conflict, the following embodiments and features in the embodiments can be combined with each other. 
     A method for manufacturing a circuit board assembly  100  is provided according to an embodiment of the present disclosure. 
     In step  1 , referring to  FIG.  1   , an inner circuit substrate  10  including a through hole  16  is provided. 
     The inner circuit substrate  10  includes an inner dielectric layer  12  and two inner circuit layers  14 . The two inner circuit layers  14  are disposed on opposite surfaces of the inner dielectric layer  12 . In other embodiments, the number of the inner circuit layers  14  can be more, and the multilayer inner circuit layers  14  are electrically connected to each other. 
     The two inner circuit layers  14  can be made of flexible materials such as polyimide, liquid crystal polymer, and modified polyimide. The two inner circuit layers  14  also can be made of hard materials such as polypropylene, and polytetrafluoroethylene. In the embodiment, the inner dielectric layer  12  is made of polypropylene. 
     The through hole  16  penetrates through the inner dielectric layer  12  and the two inner circuit layers  14  along a direction in which the inner dielectric layer  12  and the inner circuit layers  14  are stacked. 
     In some embodiments, the inner circuit substrate  10  can further include an insulating layer  18  disposed on two opposite surfaces of a portion of the inner circuit substrate  10 . 
     In step  2 , referring to  FIG.  2   , a heat conducting block  20  is placed in the through hole  16 . 
     The heat conducting block  20  is made of aluminum nitride. A thermal conductivity of the aluminum nitride is 320 W/(m·K), and an elasticity modulus of aluminum nitride is 320 Gpa. A thermal conductivity of stainless steel is 12.3 W/(m·K), and an elasticity modulus of stainless steel is 190 Gpa. Compared with stainless steel, the aluminum nitride has the characteristics of high thermal conductivity and high rigidity. 
     In some embodiments, the heat conducting block  20  is spaced apart from the sidewall forming the through hole  16 . That is, there is a gap between the heat conducting block  20  and the inner circuit substrate  10 . 
     In step  3 , referring to  FIG.  3   , a first outer circuit substrate  30  and a second outer circuit substrate  40  are formed on opposite surfaces of the inner circuit substrate  10 , and the first outer circuit substrate  30  and the second outer circuit substrate  40  cover the heat conducting block  20 . 
     The first outer circuit substrate  30  includes a first outer dielectric layer  32  and a first outer circuit layer  34 . The second outer circuit substrate  40  includes a second outer dielectric layer  42  and a second outer circuit layer  44 . The number of each of the first outer dielectric layer  32 , the first outer circuit layer  34 , the second outer dielectric layer  42  and the second outer circuit layer  44  may be one or more. Both the first outer circuit substrate  30  and the second outer circuit substrate  40  are electrically connected to the inner circuit substrate  10 . The first outer dielectric layer  32  and the second outer dielectric layer  42  are connected to the heat conducting block  20 . 
     In some embodiments, during forming the first outer circuit substrate  30  and the second outer circuit substrate  40 , the first outer dielectric layer  32  and the second outer dielectric layer  42  further fill the gap between the heat conducting block  20  and the inner circuit substrate  10 . The first outer dielectric layer  32  or the second outer dielectric layer  42  filled in the gap can fix and buffer the heat conducting block  20 . 
     In some embodiments, during forming the second outer circuit substrate  40 , the method further includes forming a connecting block  46  connecting the heat conducting block  20  and the second outer circuit layer  44 . The connecting block  46  penetrates through the second outer dielectric layer  42 , so as to connect the second outer circuit layer  44  disposed on a surface of the second outer circuit substrate  40  away from the heat conducting block  20  to the heat conducting block  20 . 
     In some embodiments, the first outer circuit substrate  30  and the second outer circuit substrate  40  further cover the insulating layer  18 . 
     In some embodiments, a solder mask  50  is formed on surfaces of the first outer circuit substrate  30  and the second outer circuit substrate  40  facing away from the inner circuit substrate  10  to protect the first outer circuit layer  34  and the second outer circuit layer  44 . 
     In step  4 , referring to  FIG.  4   , the first outer circuit substrate  30  and the second outer circuit substrate  40  corresponding to the insulating layer  18  are removed to expose the insulating layer  18 , thereby forming a flexible region. 
     In some implementations, the step  4  can be omitted. 
     In step  5 , referring to  FIG.  5   , an accommodating groove  60  is formed, which penetrates through the first outer circuit substrate  30  and is recessed toward the heat conducting block  20 . 
     The accommodating groove  60  is formed along the direction in which the first outer circuit substrate  30 , the inner circuit substrate  10 , and the second outer circuit substrate  40  are stacked. During forming the accommodating groove  60 , the first outer circuit substrate  30  is penetrated, and then a portion of the heat conducting block  20  is removed to form the accommodating groove  60 . That is, the accommodating groove  60  penetrates the first outer circuit substrate  30  but does not penetrate the heat conducting block  20 , forming the heat conducting block  20  with a side wall  22  and a bottom wall  24 . 
     In step  6 , referring to  FIGS.  6  and  7   , an electronic component  70  is accommodated in the accommodating groove  60 , and the electronic component  70  is at least partially accommodated in the accommodating groove  60 . 
     The electronic component  70  is electrically connected to the first outer circuit substrate  30 . 
     The electronic component  70  can be an integral structure, or can include at least one first sub-component  72  and at least one second sub-component  74 . 
     In the embodiment, taking the electronic component  70  including a first sub-component  72  and a second sub-component  74  as an example, the electronic component  70  is a lens module, the first sub-component  72  is a chip, and the second sub-component  74  is a lens. In other embodiments, the electronic component  70  is not limited to a lens module. 
     Accommodating the electronic component  70  in the accommodating groove  60  may be carried out as follows. 
     In step  601 : referring to  FIG.  6   , a heat conducting filler  80   a  is filled in the accommodating groove  60 . 
     The heat conducting filler  80   a  can be thermally conductive adhesive, which has both bonding effect and thermally conductive effect. 
     The heat conducting filler  80   a  is filled in the heat conducting block  20 , and the heat conducting filler  80   a  is connected to the side wall  22  and the bottom wall  24 . 
     In step  602 : referring to  FIG.  6   , the first sub-component  72  is placed in the heat conducting filler  80   a , the heat conducting filler  80   a  covers the periphery of the first sub-component  72 , so that the first sub-component  72  is spaced apart from the heat conducting block  20 . A portion of the first sub-component  72  used for electrical connection is exposed from the heat conducting filler  80   a.    
     The heat conducting filler  80   a  connects the first sub-component  72  and the heat conducting block  20 , so that the heat generated by the first sub-component  72  can be quickly transferred to the heat conducting block  20 . The heat conducting filler  80   a  further plays a buffering role, preventing the first sub-component  72  from being damaged due to rigid contact with the heat conducting block  20 . 
     In some embodiments, a distance between the first sub-component  72  and the heat conducting block  20  can be from 0.1 mm to 0.7 mm. In an embodiment, the distance between the first sub-component  72  and the heat conducting block  20  is 0.3 mm. 
     In step  603 : referring to  FIG.  7   , a second sub-component  74  is connected to a surface of the first outer circuit substrate  30 , and the second sub-component  74  is electrically connected to the first sub-component  72 . 
     In step  7 , referring to  FIG.  8   , a reinforcing plate  90  is formed on a surface of the second outer circuit substrate  40  corresponding to the electronic component  70  and facing away from the electronic component  70 , so as to form the circuit board assembly  100 . 
     The reinforcing plate  90  can be made of stainless steel, red copper, aluminum nitride, graphene, and other materials with high thermal conductivity and high hardness. 
     The reinforcing plate  90  may be connected to the second outer circuit substrate  40  through the heat conducting filler  80   b . The heat conducting filler  80   b  can be a thermally conductive adhesive, which functions as both bonding and thermal conductivity. 
     The step of forming the reinforcing plate  90  is any step after forming the second outer circuit substrate  40 . That is, the step of forming the reinforcing plate  90  may be before the step of forming the accommodating groove  60  or forming the electronic component  70 . 
     In other embodiments, in block  2 , referring to  FIG.  9   , a metal layer  26  is disposed on a surface of the heat conducting block  20 . The metal layer  26  can be made of copper, silver, or the like. The metal layer  26  is substantially parallel to an extending direction of the inner circuit substrate  10 . In step  3 , during forming the first outer circuit substrate  30  and the second outer circuit substrate  40 , the first outer circuit layer  34  and the second outer circuit layer  44  are contact with the metal layer  26 . Referring to  FIG.  10   , the heat generated by the electronic component  70  penetrates through the heat conducting block  20  of the circuit board assembly  100 , and then quickly transfers to the first outer circuit layer  34  and the second outer circuit layer  44  through the metal layer  26 , thereby increasing the rate of heat transfer. In the embodiment, the connecting block  46  is omitted. 
     Referring to  FIG.  8    again, a circuit board assembly  100  is provided according to an embodiment of the present disclosure. The circuit board assembly  100  includes an inner circuit substrate  10 , a first outer circuit substrate  30 , a second outer circuit substrate  40 , an electronic component  70 , a heat conducting block  20 , and a reinforcing plate  90 . 
     The inner circuit substrate  10 , the first outer circuit substrate  30 , and the second outer circuit substrate  40  may be flexible boards, rigid boards or rigid-flex boards. 
     The inner circuit substrate  10  includes an inner dielectric layer  12  and two inner circuit layers  14  stacked with each other. The first outer circuit substrate  30  includes a first outer dielectric layer  32  and a first outer circuit layer  34  stacked with each other. The second outer circuit substrate  40  includes a second outer dielectric layer  42  and a second outer circuit layer  44  stacked with each other. 
     The first outer circuit substrate  30  and the second outer circuit substrate  40  are respectively disposed on opposite surfaces of the inner circuit substrate  10 . The inner circuit substrate  10 , the first outer circuit substrate  30 , and the second outer circuit substrate  40  may be single-layer circuit substrates or multi-layer circuit substrates, respectively. The inner circuit substrate  10 , the first outer circuit substrate  30 , and the second outer circuit substrate  40  are electrically connected to each other. 
     The heat conducting block  20  penetrates through the inner circuit substrate  10 . The first outer circuit substrate  30  and the second outer circuit substrate  40  cover the heat conducting block  20 . The heat conducting block  20  is connected to the inner circuit substrate  10  through the first outer dielectric layer  32  or the second outer dielectric layer  42 , which can prevent rigid contact between the heat conducting block  20  and the two inner circuit layers  14 . 
     An accommodating groove  60  with an opening  62  towards the first outer circuit substrate  30  is defined on the heat conducting block  20 . The heat conduction block includes a side wall  22  and a bottom wall  24 , and the side wall  22  surrounds the bottom wall  24 . At least portion of the electronic component  70  is accommodated in the accommodation groove  60  formed by the side wall  22  and the bottom wall  24 . 
     In some embodiments, the electronic component  70  includes a first sub-component  72  and a second sub-component  74 . The first sub-component  72  is accommodated in the accommodating groove  60 , and the second sub-component  74  is disposed on a surface of the first outer circuit substrate  30  and is electrically connected to the first sub-component  72 . In the embodiment, the first sub-component  72  is a chip, and the second sub-component  74  is a lens. 
     In some embodiments, a heat conducting filler  80   a  is further filled between the first sub-component  72  and the heat conducting block  20 . Multiple surfaces of the first sub-component  72  are contact with the heat conducting filler  80   a , and the heat conducting filler  80   a  is contact with the heat conducting block  20  with a large contact area. The heat conducting filler  80   a  can quickly transfer the heat generated by the first sub-component  72  to the heat conducting block  20 . In addition, due to the high rigidity of the heat conducting block  20 , the heat conducting filler  80   a  can prevent the first sub-component  72  from being damaged due to rigid contact with the heat conducting filler  80   a . The rigidity of the heat conducting block  20  is sufficient to support the first sub-component  72  and prevent the first sub-component  72  from being deformed and damaged. 
     In some embodiments, the circuit board assembly  100  further includes a solder mask  50  disposed on surfaces of the first outer circuit substrate  30  and the second outer circuit substrate  40  away from the inner circuit substrate  10 . 
     The reinforcing plate  90  is disposed on a surface of the second outer circuit substrate  40  corresponding to the electronic component  70  and facing away from the electronic component  70 . The reinforcing plate  90  can be connected to the second outer circuit substrate  40  through a heat conducting filler  80   b.    
     In some embodiments, the second outer circuit substrate  40  is also connected to the heat conducting block  20  through a connecting block  46 . The second outer circuit substrate  40  includes a second outer dielectric layer  42  and a second outer circuit layer  44  stacked with each other. The connecting block  46  penetrates through the second outer dielectric layer  42  and connects the second outer circuit layer  44  and the heat conducting block  20 . 
     Further, the connecting block  46  is connected to the second outer circuit layer  44  disposed on the second outer circuit substrate  40  away from the heat conducting block  20 , so as to quickly transfer the heat generated by the electronic component  70  to the outside of the circuit board assembly  100 . 
     Referring to  FIG.  10    again, in some embodiments, a surface of the heat conducting block  20  facing the first outer circuit substrate  30  and a surface facing the second outer circuit substrate  40  are both provided with a metal layer  26 . The metal layer  26  is directly connected to the first outer circuit layer  34  and the second outer circuit layer  44  to conduct heat quickly. 
     The circuit board assembly  100  provided by the present disclosure, a portion of the electronic component  70  is embedded in the first outer circuit substrate  30  and the inner circuit substrate  10 , which can effectively reduce the volume of the circuit board assembly  100 . By accommodating the electronic component  70  in the heat conducting block  20  which made of aluminum nitride, due to the high heat conduction efficiency and high rigidity of aluminum nitride, the electronic component  70  and the heat conducting block  20  have multiple contact surfaces (including the side wall  22  and the bottom wall  24 ), which effectively improves the heat dissipation efficiency of the circuit board assembly  100 . In addition, the cooperation of the aluminum nitride heat conducting block  20  and the reinforcing plate  90  can reinforce the circuit board assembly  100 . 
     It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.