Patent Publication Number: US-11647587-B2

Title: Power module structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation Application of U.S. patent application Ser. No. 17/168,030 filed on Feb. 4, 2021, and entitled “POWER MODULE STRUCTURE AND ASSEMBLING METHOD THEREOF”, which claims priorities to China Patent Application No. 202010123504.8, filed on Feb. 27, 2020 and China Patent Application No. 202011095568.8, filed on Oct. 14, 2020. The entire contents of the above-mentioned patent applications are incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a power module, and more particularly to a power module structure and an assembling method thereof to reduce the number of reflow soldering processes undergone by the assembled components. 
     BACKGROUND OF THE INVENTION 
     In recent years, an onboard high-power DC/DC power module has been widely used in fields such as telephone communications, data centers, and supercomputers. With the rapid development of fixed-line networks, mobile communications and artificial intelligence, the requirements for the output power and efficiency of the onboard high-power DC/DC power module are getting higher and higher. On the other hand, as communication products tend to miniaturization, the size of the power module has to be further reduced to increase the power density while improving efficiency. 
     In order to significantly reduce the size and the weight of the power module and increase the power density of the power module, the current power module on the market utilizes a planar transformer technology and a double-PCB-welding-assembly technology. The power module includes a power-board assembly and a pin-board assembly. The power-board assembly needs to go through two surface-mounting reflow soldering processes first to mount the power device on the power-board assembly, and then the power-board assembly is assembled with the magnetic component. The upper magnetic core of the magnetic component is attached to a top side of the power-board body, and the lower magnetic core of the magnetic component is bonded therewith, so that the assembly of the power-board assembly and a planar transformer is achieved. After that, the power-board assembly is placed on the pin-board with the components on the pin-board, and then a third reflow soldering process is performed to obtain the power module. In other words, in the conventional power module structure, fine components such as power devices on the power-board assembly need to undergo more than three reflow soldering processes to complete the assembly. Consequently, a long manufacturing time and high cost are required. The risk of damage of the fine components during the manufacturing process is increased. In addition, the power-board assembly, the magnetic component and the pin-board assembly are assembled in sequence, the assembling process has poor modulability, and the height of the overall structure cannot be further reduced to achieve the purpose of increasing the power density. 
     Therefore, there is a need to provide a power module structure and an assembling method thereof to address the above issues encountered by the prior arts. 
     SUMMARY OF THE INVENTION 
     An object of the present disclosure provides a power module structure and an assembling method thereof. A first printed-circuit-board assembly such as a power-board assembly and a second printed-circuit-board assembly such as a pin-board assembly are assembled through at least one conductive connection component and completed by one reflow soldering process, to reduce the number of reflow soldering processes undergone by a fine component such as a power device on the power-board assembly. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. 
     Another objection of the present disclosure provides a power module structure and an assembling method thereof. A first printed-circuit-board assembly such as a power-board assembly and a second printed-circuit-board assembly such as a pin-board assembly are assembled through at least one conductive connection component and completed by one reflow soldering process. A pin board of the pin-board assembly includes at least one hollow slot disposed thereon. The at least one hollow slot spatially corresponds to a magnetic component including an upper magnetic core and a lower magnetic core, and the conductive connection component and the magnetic component are misaligned. Moreover, the projections of the magnetic component and the hollow slot are at least partially overlapped on a plane of the pin board, so as to expose a bottom surface of the lower magnetic core through the hollow slot. Thus, the magnetic component arranged on the power-board assembly is passed through the hollow slot of the pin board after one reflow soldering process, and a tool is used to push the lower magnetic core of the magnetic component through the hollow slot to complete the assembly of the magnetic component fixed to the power-board assembly. It is helpful of increasing the flexibility of the assembly process. In addition, a portion of the lower magnetic core of the magnetic component is received within the hollow slot, so as to reduce the height of the overall structure and achieve the purpose of increasing power density. 
     In accordance with an aspect of the present disclosure, a power module structure is provided. The power module structure includes a first printed-circuit-board assembly, a second printed-circuit-board assembly and at least one conductive connection component. The first printed-circuit-board assembly includes a first circuit board, at least one power switch and at least one magnetic component. The first circuit board includes a first side, a second side and at least one through hole. The first side and the second side are opposite to each other. The at least one through hole passes through the first side and the second side. The at least one power switch is disposed on the first circuit board. The at least one magnetic component includes a first magnetic core and a second magnetic core disposed on the first side and the second side, respectively, and combined on the first circuit board through the at least one through hole. The second printed-circuit-board assembly includes a second circuit board. The second circuit board includes a third side, a fourth side and at least one hollow slot. The third side and the fourth side are opposite to each other. The third side faces the second side. The at least one hollow slot passes through the third side and the fourth side, and spatially corresponds to the second magnetic core of the at least one magnetic component. The second magnetic core of the at least one magnetic component is exposed through the at least one hollow slot. The conductive connection component is disposed on the second side of the first circuit board and the third side of the second circuit board, and electrically connected to the first printed-circuit-board assembly and the second printed-circuit-board assembly. The at least one conductive connection component and the at least one magnetic component are misaligned to each other. 
     In an embodiment, the at least one conductive connection component is connected between the first printed-circuit-board assembly and the second printed-circuit-board assembly through a reflow soldering process. 
     In an embodiment, a projection area of the at least one hollow slot projected on the third side and a projection area of the second magnetic core of the at least one magnetic component projected on the third side are at least partially overlapped. 
     In an embodiment, a projection area of the at least one hollow slot projected on the third side is greater than 0.2 mm 2 . 
     In an embodiment, the at least one hollow slot includes a stepped structure and has an accommodation region, and the accommodation region is concavely formed from the third side toward the fourth side. A projection area of the accommodation region projected on the third side is greater than a projection area of the second magnetic core of the at least one magnetic component projected on the third side. The second magnetic core of the at least one magnetic component is at least partially accommodated in the accommodation region. 
     In an embodiment, the at least one hollow slot passes through the second printed-circuit-board assembly, and a projection area of the at least one hollow slot projected on the third side is greater than a projection area of the second magnetic core of the at least one magnetic component projected on the third side, and the second magnetic core of the at least one magnetic component is at least partially accommodated in the at least one hollow slot. 
     In an embodiment, the at least one conductive connection component is one selected from the group consisting of a copper block and a pin header. 
     In an embodiment, the at least one conductive connection component is made of a material selected from the group consisting of aluminum, copper and copper alloy. 
     In an embodiment, the at least one magnetic component is a planar transformer. 
     In an embodiment, the second circuit board includes at least one pin disposed on the fourth side and used for external electrical connection. 
     In an embodiment, the at least one pin is one selected from the group consisting of a land grid array pin and a ball grid array pin. 
     In an embodiment, the first printed-circuit-board assembly includes at least one driving chip disposed on the first side or the second side of the first circuit board. 
     In an embodiment, the second printed-circuit-board assembly includes at least one controlling chip disposed on the third side of the second circuit board. 
     In an embodiment, the at least one hollow slot is used for operating a tool to assemble the magnetic component. 
     In an embodiment, the at least one hollow slot has a shape selected from the group consisting of a circle, a rectangle, a square and an ellipse. 
     In accordance with an aspect of the present disclosure, an assembling method of a power module structure is provided. The assembling method includes: (a) providing a first printed-circuit-board assembly including a first circuit board, at least one power switch and at least one magnetic component, wherein the first circuit board includes a first side, a second side and at least one through hole, the first side and the second side are opposite to each other, the at least one through hole passes through the first side and the second side, and the at least one power switch is disposed on the first circuit board, wherein the at least one magnetic component includes a first magnetic core and a second magnetic core; (b) providing a second printed-circuit-board assembly and a conductive connection component, wherein the second printed-circuit-board assembly includes a second circuit board, wherein the second circuit board includes a third side, a fourth side and at least one hollow slot, the third side and the fourth side are opposite to each other, and the at least one hollow slot passes through the third side and the fourth side, wherein the conductive connection component is disposed on the third side; (c) stacking the second printed-circuit-board assembly and the at least one conductive connection component on the second side of the first circuit board, wherein the second side of the first circuit board faces the third side, the second magnetic core of the at least one magnetic component spatially corresponds to the at least one hollow slot, and the second magnetic core of the at least one magnetic component is exposed through the at least one hollow slot; (d) connecting the at least one conductive connection component and the first printed-circuit-board assembly through a reflow soldering process; and (e) pushing against the second magnetic core through the at least one hollow slot, and connecting the first magnetic core and the second magnetic core through the at least one through hole, so that the first magnetic core and the second magnetic core are disposed on the first side and the second side, respectively, and combined on the first circuit board. 
     In an embodiment, the step (a) further includes a step of (a0) disposing the at least one power switch on the first circuit board through through a reflow soldering process, and the step (b) further includes a step of (b0) disposing the at least one conductive connection component on the third side through a reflow soldering process. 
     In an embodiment, the step (c) further includes a step of (c1) pre-placing the second magnetic core between the first circuit board and the second circuit board. 
     In an embodiment, the at least one hollow slot passes through the second circuit board, and a projection area of the at least one hollow slot projected on the third side and a projection area of the second magnetic core of the at least one magnetic component projected on the third side are at least partially overlapped. 
     In an embodiment, a projection area of the at least one hollow slot projected on the third side is greater than 0.2 mm 2 . 
     In an embodiment, the at least one hollow slot includes a stepped structure and has an accommodation region, and the accommodation region is concavely formed from the third side toward the fourth side, wherein a projection area of the accommodation region projected on the third side is greater than a projection area of the second magnetic core of the at least one magnetic component projected on the third side, and the second magnetic core of the at least one magnetic component is at least partially accommodated in the accommodation region. 
     In an embodiment, the at least one conductive connection component is one selected from the group consisting of a copper block and a pin header. 
     In an embodiment, the at least one magnetic component is a planar transformer. 
     In an embodiment, the at least one hollow slot has a shape selected from the group consisting of a circle, a rectangle, a square and an ellipse. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an exploded view illustrating a power module structure according to a first embodiment of the present disclosure; 
         FIG.  2    is an exploded view illustrating the power module structure according to the first embodiment of the present disclosure and taken from another perspective; 
         FIG.  3    is a perspective view illustrating the power module structure according to the first embodiment of the present disclosure; 
         FIG.  4    is a perspective view illustrating the power module structure according to the first embodiment of the present disclosure and taken from another perspective; 
         FIG.  5    is an exploded view illustrating a power module structure according to a second embodiment of the present disclosure; 
         FIG.  6    is an exploded view illustrating the power module structure according to the second embodiment of the present disclosure and taken from another perspective; 
         FIG.  7    is a perspective view illustrating the power module structure according to the second embodiment of the present disclosure; 
         FIG.  8    is a perspective view illustrating the power module structure according to the second embodiment of the present disclosure and taken from another perspective; 
         FIG.  9    is an exploded view illustrating a power module structure according to a third embodiment of the present disclosure; 
         FIG.  10    is an exploded view illustrating the power module structure according to the third embodiment of the present disclosure and taken from another perspective; 
         FIG.  11    is a perspective view illustrating the power module structure according to the third embodiment of the present disclosure; 
         FIG.  12    is a perspective view illustrating the power module structure according to the third embodiment of the present disclosure and taken from another perspective; and 
         FIG.  13    is a flow chart showing an assembling method of a power module structure according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
       FIG.  1    and  FIG.  2    are exploded views illustrating a power module structure according to a first embodiment of the present disclosure.  FIG.  3    and  FIG.  4    are perspective views illustrating the power module structure according to the first embodiment of the present disclosure. In the embodiment, the power module structure  1  includes a first printed-circuit-board assembly  2 , a second printed-circuit-board assembly  3  and at least one conductive connection component  50 . Preferably but not exclusively, the first printed-circuit-board assembly  2  is a power-board assembly and the second printed-circuit-board assembly  3  is a pin-board assembly. Preferably but not exclusively, the at least one conductive connection component  50  is a copper block or a pin header. The first printed-circuit-board assembly  2 , the second printed-circuit-board assembly  3  and the at least one conductive connection component  50  are assembled through one reflow soldering process. 
     In the embodiment, the first printed-circuit-board assembly  2  includes a first circuit board  10 , at least one power switch  20  and at least one magnetic component  30 . The first circuit board  10  includes a first side  11 , a second side  12  and at least one through hole  13 . The at least one through hole  13  passes through the first side  11  and the second side  12 . The at least one power switch  20  is disposed on the first circuit board  10 . Preferably but not exclusively, in the embodiment, the first printed-circuit-board assembly  2  further includes a plurality of power switch  20  disposed on the first side  11  and the second side  12  of the first circuit board  10 . Preferably but not exclusively, in other embodiments, the at least one power switch  20  is disposed on the first side  11  or the second side  12  of the first circuit board  10 . The present disclosure is not limited thereto. 
     In the embodiment, the at least one magnetic component  30  includes a first magnetic core  31  and a second magnetic core  32 . Preferably but not exclusively, the first magnetic core  31  and the second magnetic core  32  are an upper magnetic core and a lower magnetic core cooperated with each other, disposed on the first side  11  and the second side  12  of the first circuit board  10 , respectively, and combined on the first circuit board  10  through the at least one through hole  13 . Preferably but not exclusively, the magnetic component  30  is a planar transformer, further includes a planar winding (not shown) disposed on the first circuit board  10 . The planar winding, the first magnetic core  31  and the second magnetic core  32  are cooperated to form the planar transformer. In other embodiments, when a magnetic leg  33  of the first magnetic core  31  and a magnetic leg  34  of the second magnetic core  32  are connected by passing through the at least one through hole  13 , at least one air gap (not shown) is formed therebetween according to the practical requirements. In that, the performance of the at least one magnetic component  30  is modulated. Certainly, the present disclosure is not limited thereto. 
     In the embodiment, the second printed-circuit-board assembly  3  includes a second circuit board  40 . The second circuit board  40  includes a third side  41 , a fourth side  42  and at least one hollow slot  43 . The third side  41  of the second circuit board  40  faces the second side  12  of the first circuit board  10 . In the embodiment, the at least one hollow slot  43  passes through the third side  41  and the fourth side  42 , and spatially corresponds to the second magnetic core  32  of the at least one magnetic component  30 . Furthermore, the second magnetic core  32  of the at least one magnetic component  30  is exposed through the at least one hollow slot  43 . Preferably but not exclusively, the at least one hollow slot  43  has a shape selected from the group consisting of a circle, a rectangle, a square and an ellipse. The present disclosure is not limited thereto. 
     In the embodiment, the conductive connection component  50  is disposed between the second side  12  of the first circuit board  10  and the third side  41  of the second circuit board  40 , and electrically connected between the first printed-circuit-board assembly  2  and the second printed-circuit-board assembly  3 . Moreover, the at least one conductive connection component  50  and the at least one magnetic component  30  are misaligned to each other. Thereby, the first printed-circuit-board assembly  2  such as a power-board assembly and the second printed-circuit-board assembly  3  such as a pin-board assembly are assembled through the at least one conductive connection component  50  and completed by one reflow soldering process, to reduce the number of reflow soldering processes undergone by the fine component such as the at least one power switch  20  on the first printed-circuit-board assembly  2 . Thus, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. 
     Notably, in the embodiment, the at least one power switch  20  of the first printed-circuit-board assembly  2  is preset on the first circuit board  10  by one reflow soldering process. Thereafter, when the first printed-circuit-board assembly  2  and the second printed-circuit-board assembly  3  are connected through the at least one conductive connection component  50  by another reflow soldering process, the at least one power switch  20  of the first printed-circuit-board assembly  2  undergoes twice reflow soldering processes. On the other hand, a projection area of the at least one magnetic component  30  projected on the third side  41  of the second circuit board  40  and a projection area of the at least one hollow slot  43  projected on the third side  41  of the second circuit board  40  are at least partially overlapped. Furthermore, the bottom of the second magnetic core  32  is exposed through the at least one hollow slot  43 . Preferably but not exclusively, the projection area of the at least one hollow slot  43  projected on the third side  41  is greater than 0.2 mm 2 . In that, it facilitates a tool to pass through the at least one hollow slot  43  to push against the exposed bottom of the second magnetic core  32  of the magnetic component  30 . Thereby, the second magnetic core  32  pre-mounted between the first circuit board  10  and the second circuit board  40  is exposed through the at least one hollow slot  43  after the reflow soldering process described above, and a tool is used to push the exposed bottom of the second magnetic core  32  of the magnetic component  30  through the at least one hollow slot  43 , so as to complete the assembly of the magnetic component  30  fixed on the first circuit board  10 . It is helpful of increasing the flexibility of the assembly process. 
     Moreover, in the embodiment, the first printed-circuit-board assembly  2  includes at least one driving chip  21  disposed on the first side  11  or the second side  12  of the first circuit board  10 . Preferably but not exclusively, the at least one driving chip  21  and the at least one power switch  20  are preset on the first circuit board  10  by one reflow soldering process. Certainly, the present disclosure is not limited thereto. Moreover, in the embodiment, the second printed-circuit-board assembly  3  includes at least one controlling chip  44  disposed on the third side  41  of the second circuit board  40 . Preferably but not exclusively, the at least one controlling chip  44  and the at least one conductive connection component  50  are pre-mounted on the third side  41  of the second circuit board  40 . The at least one controlling chip  44 , the first printed-circuit-board assembly  2 , at least one conductive connection component  50  and the second circuit board  40  undergo another reflow soldering process, so that the at least one controlling chip  44 , the printed-circuit-board assembly  2  and the at least one conductive connection component  50  disposed on the third side  41  of the second circuit  40  are achieved. The present disclosure is not limited thereto. In addition, the second circuit board  40  includes at least one pin  45  disposed on the fourth side  42  and used for external electrical connection with for example but not limited to a system end or a system motherboard. In other words, the at least one pin  45  is used as an input/output and control port of the power module  1 , which is connected to the system end or system motherboard externally. Preferably but not exclusively, the at least one pin  45  is a land grid array (LGA) pin or a ball grid array (BGA) pin. The present disclosure is not limited thereto. 
       FIG.  5    and  FIG.  6    are exploded views illustrating a power module structure according to a second embodiment of the present disclosure.  FIG.  7    and  FIG.  8    are perspective views illustrating the power module structure according to the second embodiment of the present disclosure. In the embodiment, the power module structure  1   a  is similar to the power module structure  1  shown in  FIGS.  1  to  4   , and the same labels of the components represent the same components, structures and functions, not redundantly described herein. In the embodiment, the first printed-circuit-board assembly  2 , the second printed-circuit-board assembly  3  and the at least one conductive connection component  50  of the power module structure  1   a  are assembled through one reflow soldering process. The number of reflow soldering processes undergone by a fine component such as the power switch  20  is reduced. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. After the reflow soldering process, the magnetic component  30  is combined on the first circuit board  10 . In the embodiment, the at least one hollow slot  43   a  includes a stepped structure and further has an accommodation region  431 . The accommodation region  431  is concavely formed from the third side  41  toward the fourth side  42 . Moreover, a projection area of the accommodation region  431  projected on the third side  41  is greater than a projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 . The second magnetic core  32  of the at least one magnetic component  30  is at least partially accommodated in the accommodation region  431 . In other words, the hollow slot  43   a  provides a tool for passing through to complete the assembly of the magnetic component  30  and the first circuit board  10 , and a portion of the second magnetic core  32  of the magnetic component  30  is received within the hollow slot  43   a , so as to reduce the height of the overall power module structure  1   a  and achieve the purpose of increasing power density. 
       FIG.  9    and  FIG.  10    are exploded views illustrating a power module structure according to a third embodiment of the present disclosure.  FIG.  11    and  FIG.  12    are perspective views illustrating the power module structure according to the third embodiment of the present disclosure. In the embodiment, the power module structure  1   b  is similar to the power module structure  1  shown in  FIGS.  1  to  4   , and the same labels of the components represent the same components, structures and functions, not redundantly described herein. In the embodiment, the first printed-circuit-board assembly  2 , the second printed-circuit-board assembly  3  and the at least one conductive connection component  50  of the power module structure  1   b  are assembled through one reflow soldering process. The number of reflow soldering processes undergone by a fine component such as the power switch  20  is reduced. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. After the reflow soldering process, the magnetic component  30  is combined on the first circuit board  10 . In the embodiment, the at least one hollow slot  43   b  passes through the second printed-circuit-board assembly  3 , and a projection area of the at least one hollow slot  43   b  projected on the third side  41  is greater than a projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 , and the second magnetic core  32  of the at least one magnetic component  30  is at least partially accommodated in the at least one hollow slot  43   b . Thereby, the hollow slot  43   b  is used for allowing the second magnetic core  32  to pass through so as to complete the assembly of the magnetic component  30  and the first circuit board  10 , and a portion of the second magnetic core  32  of the magnetic component  30  is received within the hollow slot  43   b , so as to reduce the height of the overall power module structure  1   b  and achieve the purpose of increasing power density. 
     On the other hand, in response to the power module structure in the aforementioned embodiments, the present disclosure also provides an assembling method of a power module structure.  FIG.  13    is a flow chart showing an assembling method of a power module structure according to an embodiment of the present disclosure. Please refer to  FIGS.  1  to  4    and  FIG.  13   . Firstly, as shown in the step S 01 , the first printed-circuit-board assembly  2  of the foregoing embodiment is provided. The first printed-circuit-board assembly  2  includes a first circuit board  10 , at least one power switch  20  and at least one magnetic component  30 . The first circuit board  10  includes a first side  11 , a second side  12  and at least one through hole  13 . The first side  11  and the second side  12  are opposite to each other. The at least one through hole  13  passes through the first side  11  and the second side  12 . In the embodiment, the power switch  20  and the other devices such as the driving chip  21  of the first circuit board  10  undergo a reflow soldering process, so as to preset the power switch  20  and the driving chip  21  on the first side  11  of the first circuit board  10 . In the embodiment, the magnetic component  30  includes a first magnetic core  31  and a second magnetic core  32 . Preferably but not exclusively, the first magnetic core  31  and the second magnetic core  32  are an upper magnetic and a lower magnetic core cooperated with each other. In the embodiment, the first magnetic core  31  and the second magnetic core  32  are combined and connected after another subsequent reflow soldering process. 
     Then, as shown in the step S 02 , the second printed-circuit-board assembly  3  and at least one conductive connection component  50  are provided. In the embodiment, the second printed-circuit-board assembly  3  includes a second circuit board  40 . The second circuit board  40  includes a third side  41 , a fourth side  42  and at least one hollow slot  43 . The third side  41  and the fourth side  42  are opposite to each other. The at least one hollow slot  43  passes through the third side  41  and the fourth side  42 . Preferably but not exclusively, the at least one hollow slot  43  has a shape selected from the group consisting of a circle, a rectangle, a square and an ellipse. The present disclosure is not limited thereto. In an embodiment, the at least one hollow slot  43   a  includes a stepped structure and further has an accommodation region  431 , as shown in  FIG.  5   . In another embodiment, the hollow slot  43   b  has for example a large area passing through the third side  41  and the fourth side  42  of the second circuit board  40 , as shown in  FIG.  9   . In the embodiment, the controlling chip  44  and the other devices of the second circuit board  40  and the conductive connection component  50  undergo a reflow soldering process, so as to preset the controlling chip  44 , the conductive connection component  50  and the other devices on the third side  41  of the second circuit board  40 . The present disclosure is not limited thereto. In addition, the second circuit board  40  includes at least one pin  45  disposed on the fourth side  42  and used for external electrical connection with for example but not limited to a system end or a system motherboard. Preferably but not exclusively, the at least one pin  45  is a land grid array (LGA) pin or a ball grid array (BGA) pin. The present disclosure is not limited thereto. 
     Moreover, in the embodiment, the first printed-circuit-board assembly  2  is a power-board assembly and the second printed-circuit-board assembly  3  is a pin-board assembly. Preferably but not exclusively, the at least one conductive connection component  50  is a copper block or a pin header. The present disclosure is not limited thereto. 
     Thereafter, as shown in the step S 03 , the second printed-circuit-board assembly  3  and other components that have undergone one reflow soldering process are stacked on the second side  12  of the first circuit board  10 . The second side  12  of the first circuit board  10  faces the third side  41  of the second circuit board  40 . The magnetic component  30  is disposed at a position of the first circuit board  10 , which spatially corresponds to the hollow slot  43  of the second circuit board  40 . In the embodiment, the second magnetic core  32  of the magnetic component  30  spatially corresponds to the hollow slot  43 . The second magnetic core  32  is pre-mounted between the first circuit board  10  and the second circuit board  40 . Moreover, the second magnetic core  32  of the magnetic component  30  is exposed through the at least one hollow slot  43 . Since the conductive connection component  50  and the magnetic component  30  are misaligned to each other, the second magnetic core  32  can be pre-mounted between the second side  12  of the first circuit board  10  and the third side  41  of the second circuit board  40 . Thereby, the bottom of the second magnetic core  32  is exposed through the at least one hollow slot  43 , and the conductive connection component  50  is correspondingly disposed between the second side  12  of the first circuit board  10  and the third side  41  of the second circuit board  40  through solder. 
     Then, as shown in the step S 04 , the at least one conductive connection component  50 , the first printed-circuit-board assembly  2  and the second printed-circuit-board assembly  3  are connected with each other through a reflow soldering process. At this time, the second magnetic core  32  is kept placed between the second side  12  of the first circuit board  10  and the third side  41  of the second circuit board  40 , and the bottom of the second magnetic core  32  is exposed through the hollow slot  43 . 
     Finally, as shown in the step S 05 , a tool passes through the hollow slot  43  and pushes against the bottom of the second magnetic core  32 , and the first magnetic core  31  disposed on the first side  11  and the second magnetic core  32  disposed on the second side  12  are collaboratively combined on the first circuit board  10 , to form the planar transformer required. In this way, the number of reflow soldering processes undergone by the fine component such as the power switch  20  and the driving chip  21  of the first printed-circuit-board assembly  2  is controlled within two. Moreover, the controlling chip  44  of the second printed-circuit-board assembly  2  undergoes one reflow soldering process merely. Therefore, the assembling method of the power module structure  1  of the present disclosure has the advantage of reducing the number of reflow soldering processes undergone by the fine component. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. On the other hands, after undergoing the reflow soldering process described above, the magnetic component  30  pre-placed is combined on the first circuit board  10  by using a tool passing through the hollow slot  43  to push against the exposed bottom of the second magnetic core  32  of the magnetic component  30 , so as to complete the assembly of the magnetic component  30  fixed on the first circuit board  10 . It is helpful of increasing the flexibility of the assembly process. 
     Please refer to  FIGS.  5  to  8    and  FIG.  13   . In the embodiment, the at least one hollow slot  43   a  includes a stepped structure and further has an accommodation region  431 . The accommodation region  431  is concavely formed from the third side  41  toward the fourth side  42 . Moreover, a projection area of the accommodation region  431  projected on the third side  41  is greater than a projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 . Thereby, the second magnetic core  32  of the at least one magnetic component  30  can be at least partially accommodated in the accommodation region  431 . In the foregoing step S 05 , the tool passes through the hollow slot  43   a  to push against the bottom of the second magnetic core  32 , to make the second magnetic core  32  to attach to the second side  12  of the first circuit board  10 . In this way, the first magnetic core  31  disposed on the first side  11  and the second magnetic core  32  disposed on the second side  12  are connected through the through holes  13  of the first circuit board  10  and collaboratively combined on the first circuit board  10 . Thus, the planar transformer with the required specifications is formed, and the power module structure  1   a  is completed. The tool can be removed after the assembly is completed. The present disclosure is not limited thereto. Similarly, the assembling method of the power module structure  1   a  of the present disclosure has the advantage of reducing the number of reflow soldering processes undergone by the fine component. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. On the other hands, after undergoing the reflow soldering process described above, the magnetic component  30  pre-placed is combined on the first circuit board  10  by using a tool passing through the hollow slot  43   a  to push against the exposed bottom of the second magnetic core  32  of the magnetic component  30 , so as to complete the assembly of the magnetic component  30  fixed on the first circuit board  10 . It is helpful of increasing the flexibility of the assembly process. Moreover, the projection area of the accommodation region  431  projected on the third side  41  is greater than the projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 . Thereby, the second magnetic core  32  of the at least one magnetic component  30  can be at least partially accommodated in the accommodation region  431  of the hollow slot  43   a , so as to reduce the height of the overall power module structure  1   a  and achieve the purpose of increasing power density. 
     Please refer to  FIGS.  9  to  12    and  FIG.  13   . In the embodiment, the projection area of the at least one hollow slot  43   b  projected on the third side  41  is greater than the projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 . In the foregoing step S 05 , the second magnetic core  32  is capable of passing through the hollow slot  43   b  directly to attach to the second side  12  of the first circuit board  10 . Thereby, the first magnetic core  31  disposed on the first side  11  and the second magnetic core  32  disposed on the second side  12  are connected through the through holes  13  of the first circuit board  10  and collaboratively combined on the first circuit board  10 . Thus, the planar transformer with the required specifications is formed, and the power module structure  1   b  is completed. In the embodiment, the number of reflow soldering processes undergone by the fine component such as the power switch  20  and the driving chip  21  of the first printed-circuit-board assembly  2  is controlled within two. Moreover, the number of reflow soldering processes undergone by the controlling chip  44  of the second printed-circuit-board assembly  3  is controlled within two. Therefore, the assembling method of the power module structure  1   b  of the present disclosure has the advantage of reducing the number of reflow soldering processes undergone by the fine component. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. On the other hands, after undergoing the reflow soldering process described above, the second magnetic core  32  of the magnetic component  30  is capable of passing through the hollow slot  43   b  to combine with the first magnetic core  31  disposed on the first side  11  through the through hole  13 , so as to complete the assembly of the magnetic component  30  fixed on the first circuit board  10 . It is helpful of increasing the flexibility of the assembly process. Moreover, since the projection area of the at least one hollow slot  43   b  projected on the third side  41  is greater than the projection area of the second magnetic core  32  of the at least one magnetic component  30  projected on the third side  41 , the second magnetic core  32  of the at least one magnetic component  30  can be partially accommodated in the at least one hollow slot  43   b , so as to reduce the height of the overall power module structure  1   b  and achieve the purpose of increasing power density. 
     In an embodiment, the power module includes a plurality of magnetic components  30 , which are disposed as the foregoing embodiments. Correspondingly, the second circuit board  40  includes a plurality of hollow slots  43 . The principle shown in the embodiments of the present disclosure can be used to control the number of reflow soldering processes undergone by the fine components in the power module within two. 
     In summary, the present disclosure provides a power module structure and an assembling method thereof. A first printed-circuit-board assembly such as a power-board assembly and a second printed-circuit-board assembly such as a pin-board assembly are assembled through at least one conductive connection component and completed by one reflow soldering process, to reduce the number of reflow soldering processes undergone by a fine component such as a power device on the power-board assembly. Moreover, the purposes of simplifying the manufacturing process and reducing production costs are achieved at the same time. On the other hand, a pin board of the pin-board assembly includes at least one hollow slot disposed thereon. The at least one hollow slot spatially corresponds to a magnetic component including an upper magnetic core and a lower magnetic core, and the conductive connection component and the magnetic component are misaligned. Moreover, the projections of the magnetic component and the hollow slot are at least partially overlapped on a plane of the pin board, so as to expose a bottom surface of the lower magnet core through the hollow slot. Thus, the magnetic component arranged on the power-board assembly is passed through the hollow slot of the pin board after one reflow soldering process, and a tool is used to push the lower magnetic core of the magnetic component through the hollow slot to complete the assembly of the magnetic component fixed to the power-board assembly. It is helpful of increasing the flexibility of the assembly process. In addition, a portion of the lower magnetic core of the magnetic component is received within the hollow slot, so as to reduce the height of the overall structure and achieve the purpose of increasing power density. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.