Abstract:
A method of manufacturing a printed circuit board with embedded electronic components fixed by a solder paste includes: providing a carrier board with a copper foil layer on the carrier board, an insulating layer on the copper foil layer, and an opening on the insulating layer by laser; putting a solder paste into the opening to form a solder paste layer; performing a high-temperature reflow process of the electronic components on the solder paste layer until the solder paste layer is molten; curing the solder paste layer after cooling to fix the components to the center position of the opening; placing the copper foil layer below the electronic components and removing the solder paste layer; and performing copper plating and electroplating processes in an electroplating space to form a plating copper. The cohesion of the molten solder paste pulls the electronic components towards the center to eliminate position offset produced when the electronic components are installed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of manufacturing a printed circuit board, and more particularly to a method of manufacturing a printed circuit board with embedded electronic components positioned by using a solder paste. 
       BACKGROUND OF THE INVENTION 
       [0002]    High speed and density are two major factors for driving the development of high technologies, not just lowering the production cost only, but most importantly also satisfying consumer requirements, so that electronic products and mobile communication products are tended to be developed with a light, thin, short and compact design, high reliability, and low cost, and these products are developed in a generation of every three to five years. To cope with the trend, electronic components occupying a relatively large area are also having an integrated revolution in the circuit design of the electronic products. 
         [0003]    In a printed circuit board, the area occupied by the electronic components is the main limitation to a compact product, and many soldering points are added to the printed circuit board, and thus reducing the system reliability as well as increasing the manufacturing cost. With the requirements of high performance, small volume, and light weight, a larger space is wanted to be created in the substrate area of the printed circuit board with a limited area to enhance the functionality of modules, so that the integration and embedment of electronic components are important development trends. 
         [0004]    To overcome the aforementioned issues, the electronic components are embedded traditionally, wherein a plastic carrier board is provided for fixing the electronic components, but this method is restricted to the precision of the SMT insertion machine, and if there is an offset occurred at the position of an electronic component with respect to the insertion machine, then a poor signal transmission will result. Alternatively, a solder paste is provided for fixing the electronic components and carrying out the electrical conduction, but the coefficient of expansion of the solder paste has a relatively large difference from the coefficient of expansion of other components in the printed circuit board, so that when there is a large temperature change, the thermal expansion and contraction of the solder paste gives rise to an unstable quality of the whole printed circuit board, and these are the drawbacks of the prior art. 
       SUMMARY OF THE INVENTION 
       [0005]    Therefore, it is a primary objective of the present invention to overcome the aforementioned drawbacks of the prior art by providing a method of manufacturing a printed circuit board with embedded electronic components positioned by using a solder paste. 
         [0006]    To achieve the aforementioned and other objectives, the present invention provides a method that uses the cohesion of a molten solder paste to pull electronic components towards the center in order to eliminate any position offset occurred during the process of installing the electronic components, and also uses a plating copper for the electrical conduction of a first copper foil layer with the electrodes of an electronic component. Compared with the traditional way of using a solder paste for the electrical conduction, the present invention uses a better method than the traditional methods. 
         [0007]    The method of the present invention comprises the following steps: 
         [0008]    Step 1: Provide a first carrier board, wherein the first carrier board has a first copper foil layer disposed thereon. 
         [0009]    Step 2: Attach or coat an insulating layer onto the first copper foil layer. 
         [0010]    Step 3: Form at least one opening on the insulating layer. 
         [0011]    Step 4: Inject a solder paste into the opening to form a solder paste layer, and then install an electronic component on the solder paste layer, wherein the electronic component has a plurality of electrodes. 
         [0012]    Step 5: Perform a high-temperature reflow process until the solder paste layer is molten, and use the cohesion of the molten solder paste to pull the electronic component towards the center of the opening of the solder paste layer on the first copper foil layer, so as to eliminate the position offset of the electronic component while installing the solder paste layer in Step 4. 
         [0013]    Step 6: Set a dielectric layer on the insulating layer, and set a second copper foil layer on the dielectric layer, and set a second carrier board on the second copper foil layer, and then carry out a lamination step. 
         [0014]    Step 7: Remove the first carrier board and the second carrier board after the lamination process, so as to complete the basic printed circuit board with an embedded electronic component. 
         [0015]    Step 8: Etch the first copper foil layer disposed under the electronic component by a process including the steps of attaching a photosensitive film, exposing the photosensitive film, removing the photosensitive film, and etching the desired layer, and also remove the solder paste layer to expose the electrodes of the electronic component, and form an electroplating space at the etching position of the first copper foil layer and at the position of removing the solder paste layer. 
         [0016]    Step 9: Perform copper plating and electroplating processes to the bottom side of the first copper foil layer and the top side of the second copper foil layer in the electroplating space to form a plating copper, so that the first copper foil layer may be electrically conducted with the electrodes of the electronic component, wherein the plating copper at the bottom side of the first copper foil layer in the electroplating space is a first plating copper, and the plating copper at the top side of the second copper foil layer in the electroplating space is a second plating copper. 
         [0017]    Step 10: Form circuits on the first copper foil layer and the first plating copper to produce a first circuit layer, and form circuits on the second copper foil layer and the second plating copper to produce a second circuit layer. 
         [0018]    Wherein, the insulating layer as described in Step 2 is pure adhesive, liquid resin or epoxy resin, and coated onto the first copper foil layer by attaching a plastic plate or coating a liquid adhesive, and the insulating layer is formed after aging. 
         [0019]    Wherein, a step carried out between Steps 2 and 3 further comprises the following steps: In the first carrier board, the first copper foil layer and the insulating layer are drilled with a plurality of alignment holes and a plurality of fixing holes; the alignment holes are provided for alignment required in a follow-up process, and the fixing holes are provided for receiving a fastener for fixing required in a follow-up process. 
         [0020]    Wherein, the opening as described in Step 3 is a single opening, and the single opening has a size at least covering a portion of the electrodes of the embedded electronic component. 
         [0021]    Wherein, the opening as described in Step 3 includes a plurality of openings and each having a size at least covering a portion of an electrode of the embedded electronic component. 
         [0022]    Wherein, the electronic component as described in Step 4 is an active electronic component, a passive electronic component, a light emitting component, or a combination of the above. 
         [0023]    Wherein, the dielectric layer as described in Step 6 is a polyester film with high resin content, a dielectric film, or a combination of the polyester film and the dielectric film 
         [0024]    Wherein, the dielectric layer as described in Step 6 has a slot for receiving the electronic component in advance, and the slot is formed by mechanical drilling, laser drilling, or die punching 
         [0025]    Wherein, the dielectric layer as described in Step 6 includes a first dielectric layer, a second dielectric layer and a third dielectric layer, and in Step 6, a first dielectric layer is formed on the insulating layer; a second dielectric layer is formed on the first dielectric layer; a third dielectric layer is formed on the second dielectric layer and the electronic component; a first laminar circuit layer is added onto the third dielectric layer, and the first laminar circuit layer includes the second copper foil layer disposed on the third dielectric layer and the second carrier board disposed on the second copper foil layer. 
         [0026]    Wherein, the first dielectric layer, the second dielectric layer, the third dielectric layer and the first laminar circuit layer are drilled with a fixing hole at a position corresponsive to the first copper foil layer in advance, so that a penetrating fixing hole is formed and provided for receiving a fastener for the fixing purpose. 
         [0027]    Wherein, the solder paste layer as described in Step 8 is removed and washed away by a chemical solution such as a nitric acid solution. 
         [0028]    Wherein, the method further comprises the following step after removing the first carrier board and the two carrier boards as described in Step 7, and a penetrating hole is formed by mechanical drilling 
         [0029]    Wherein, the copper plating and electroplating processes as described in Step 9 further comprise the step of performing copper plating and electroplating processes to the penetrating hole together with its hole wall to form a plating copper, and the plating copper at the hole wall of the penetrating hole is a third plating copper. 
         [0030]    Wherein, the method further comprises the following steps after Step 10: A fourth dielectric layer is set under the first circuit layer, and a fifth dielectric layer is set on top of the second circuit layer, and a lamination process of the laminar circuit layer is performed to the outer layers of the fourth dielectric layer and the fifth dielectric layer. In other words, the process takes place at the outer layer of a third laminar circuit layer under the fourth dielectric layer and the outer layer of a fourth laminar circuit layer on top of the fifth dielectric layer, and the electronic component is electrically coupled to the third laminar circuit layer and the fourth laminar circuit layer, so as to form a multi-layer printed circuit board with embedded electronic components. 
         [0031]    Wherein, a penetrating hole is formed on the multi-layer printed circuit board by mechanical drilling, and copper metallization and through-hole plating are performed to the penetrating hole, so that the electronic component is electrically conducted to the first circuit layer, the second circuit layer, the third laminar circuit layer, and the fourth laminar circuit layer. 
         [0032]    The technical characteristics, contents, advantages and effects of the present invention will be apparent with the detailed description of a preferred embodiment accompanied with the illustration of related drawings as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  shows Step 1 of a manufacturing method of an embodiment of the present invention; 
           [0034]      FIG. 2  shows Step 2 of a manufacturing method of an embodiment of the present invention; 
           [0035]      FIG. 3  shows a follow-up procedure of Step 2 of a manufacturing method of an embodiment of the present invention; 
           [0036]      FIG. 4A  shows Step 3 of a manufacturing method of an embodiment of the present invention; 
           [0037]      FIG. 4B  shows Step 3 of a manufacturing method of an embodiment of the present invention; 
           [0038]      FIG. 5  shows Steps 4 and 5 of a manufacturing method of an embodiment of the present invention; 
           [0039]      FIG. 6  shows Step 6 of a manufacturing method of an embodiment of the present invention; 
           [0040]      FIG. 7  shows Step 7 of a manufacturing method of an embodiment of the present invention; 
           [0041]      FIG. 8  shows Step 8 of a manufacturing method of an embodiment of the present invention; 
           [0042]      FIG. 9  shows Step 9 of a manufacturing method of an embodiment of the present invention; 
           [0043]      FIG. 10  shows Step 10 of a manufacturing method of an embodiment of the present invention; and 
           [0044]      FIG. 11  shows a step of lamination of a manufacturing method of an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]    With reference to  FIGS. 1-11  for a method of manufacturing a printed circuit board with embedded electronic components positioned by using a solder paste in accordance with an embodiment of the present invention, the method comprises the following steps: 
         [0046]    Step 1: Provide a first carrier board  20  as shown in  FIG. 1 , wherein the first carrier board  20  has a first copper foil layer  22  disposed thereon; the first carrier board  20  is provided for a carrying purpose in the manufacturing process, and the first carrier board  20  is removed after use, and the first carrier board  20  may be a metal board or a FR4 board (which is a board made of a FR4 graded material specified according to the standard of National Electrical Manufacturers Association (NEMA) and used as a substrate of a PCB). 
         [0047]    Step 2: Attach or coat an insulating layer  24  onto the first copper foil layer  22  as shown in  FIG. 2 , wherein the insulating layer  24  is made of pure adhesive, liquid resin (adhesive gel) or epoxy resin and manufacturing by attaching a plastic plate or coating a liquid adhesive onto the first copper foil layer  22 , and the adhesive or resin is aged to form the insulating layer  24  which is provided for the insulation purpose. 
         [0048]    A step is carried out between Steps 2 and 3 as shown in  FIG. 3 , and this step further comprises the following steps. The first carrier board  20 , the first copper foil layer  22  and the insulating layer  24  are drilled to form a plurality of alignment holes  26  and fixing holes  50 ; wherein the alignment holes  26  are formed by a drilling method including but not limited to laser drilling or mechanical drilling, and the alignment holes  26  are provided for alignment required by a follow-up process (for example, an opening is formed by laser for installing an electronic component). 
         [0049]    The fixing holes  50  are provided for receiving a fastener for the fixing purpose required in a follow-up process. 
         [0050]    Step 3: At least one opening  28  is formed on the insulating layer  24  as shown in  FIGS. 4A and 4B , and the tool for manufacturing the opening  28  is not limited, and the opening  28  may be formed by laser or drilling In  FIG. 4A , the opening  28  is a single opening, but the size of the single opening must be large enough to cover the portion of the electrodes of the embedded electronic component. In  FIG. 4B , the opening  28  includes a plurality of openings  28 , and the size of each opening  28  must be large enough to cover the portion of an electrode of the embedded electronic component. 
         [0051]    Step 4: In  FIG. 5 , a solder paste is injected into the opening  28  to form a solder paste layer  30 , and an electronic component  32  is set on the solder paste layer  30 , and the electronic component  32  has a plurality of electrodes  34 ; wherein, the electronic component  32  is an active electronic component (such as a chip), a passive electronic component (such as a resistor, a capacitor, and an inductor), a light emitting device (such as a light emitting diode, LED), or a combination of the above, and the type and quantity of the electronic component  32  are not limited. In this embodiment, a passive electronic component (a capacitor) is used for illustrating the invention. 
         [0052]    Step 5: A high-temperature reflow process is performed as shown in  FIG. 5 , so that the solder paste layer  30  is molten, and the cohesion of the molten solder paste is used to pull the electronic component  32  towards the center of the opening  28  formed on the first copper foil layer  22  and wherein the solder paste layer  30  is located, and the solder paste layer  30  is cured after cooling, so as to fix the electronic component  32  to the center position of the opening  28  formed on the first copper foil layer  22  and wherein the solder paste layer  30  is located, so as to eliminate any position offset occurred while installing the electronic component  32  on the solder paste layer  30  in Step 4, and one of the traditional methods uses a plastic carrier board to fix the electronic component, but such method is limited by the precision of the SMT insertion machine, and if there is an offset of the position of the electronic component, a poor signal transmission will be resulted, and such traditional method is unable to achieve the effect of the present invention which can pull the electronic component  32  towards the center of the opening  28  formed on the first copper foil layer  22  and wherein the solder paste layer  30  is located. Further, the compositions of the molten solder paste layer  30  include a flux and a metal alloy powder, and the metal alloy powder is an alloy composed of different metals such as tin (Sn) silver (Ag), copper (Cu), and bismuth (Bi) of different proportions. Since the high-temperature molten metal and the metal are attracted to each other, therefore the molten solder paste layer  30  will be attracted to the electrode  34  of the electronic component  32 , and the molten solder paste layer  30  is moved inwardly by cohesion, so that if there is a position offset of the electronic component  32  and the molten solder paste layer  30  is moved inwardly, the electronic component  32  will be pulled towards the center of the opening  28  formed on the first copper foil layer  22  and where the solder paste layer  30  is located, so as to achieve the effect of pulling the electronic component  32  to the correct position. 
         [0053]    Step 6: A dielectric layer is set on the insulating layer  24 , and a second copper foil layer  46  is set on the dielectric layer, and a second carrier board  47  is set on the second copper foil layer  46 , and a lamination step is performed as shown in  FIG. 6 . 
         [0054]    Further, the dielectric layer comprises a first dielectric layer  40 , a second dielectric layer  42  and a third dielectric layer  44 . In this step, a first dielectric layer  40  is set on the insulating layer  24 , wherein the first dielectric layer  40  has a slot (not shown in the figure) formed thereon in advance for receiving the electronic component  32 ; and a second dielectric layer  42  is set on the first dielectric layer  40  wherein the second dielectric layer  42  has a slot (not shown in the figure) formed thereon in advance for receiving the electronic component  32 ; a third dielectric layer  44  is set on the second dielectric layer  42  and the electronic component  32 , wherein the third dielectric layer  44  has a slot (not shown in the figure) formed thereon in advance for receiving the electronic component  32 , or not slot is formed on the dielectric layers (no slot is shown in the figure); a first laminar circuit layer  45  is added to the third dielectric layer  44 , wherein the first laminar circuit layer  45  includes the second copper foil layer  46  on the third dielectric layer  44  and a second carrier board  47  on the second copper foil layer  46 . In an embodiment, the first dielectric layer  40 , the second dielectric layer  42 , the third dielectric layer  44  and the first laminar circuit layer  45  are drilled with a hole at the fixing hole  50  of the first copper foil layer  22 , and a penetrating fixing hole  50  is formed, and the fixing holes  50  are provided for receiving a fastener  53  (which is a rivet in this embodiment) to achieve a fixing effect. Wherein, the first dielectric layer  40 , the second dielectric layer  42  and the third dielectric layer  44  are made of a mouldable material such as a polyester film (Prepreg) with high resin content, a dielectric film, and a combination of the polyester film and the dielectric film. With the mouldable property of the first dielectric layer  40 , the second dielectric layer  42  and the third dielectric layer  44 , the gap between the electronic component  32  and the opening  28  can be filled tightly to enhance the fixing strength of the electronic component  32 . Similarly, when the first laminar circuit layer  45  is processed, the buffering effect and pressure resistance can be improved to prevent the embedded electronic component  32  from being pressed and damaged by gravitational force during the manufacturing process. Wherein, the first dielectric layer  40  and the second dielectric layer  42  have slots formed thereon in advance for receiving the electronic component  32 , and the slots may be formed by a drilling method including but not limited to mechanical drilling, laser drilling or die punching 
         [0055]    Step 7: The first carrier board  20 , the second carrier board  47  and the fasteners  53  are removed after lamination as shown in  FIG. 7 . In an embodiment, a penetrating hole  56  is formed by mechanical drilling, so as to produce a basic printed circuit board with an embedded electronic component  32 . Wherein, after the first dielectric layer  40 , the second dielectric layer  42  and the third dielectric layer  44  are laminated as described in Step 6, the three dielectric layers are combined with one another, which is indicated by the middle dielectric layer  48  in  FIG. 7 . 
         [0056]    Step 8: The first copper foil layer  22  disposed under the electronic component  32  is etched to remove the solder paste layer  30  by a process including the steps of attaching a photosensitive film, exposing the photosensitive film, removing the photosensitive film, and etching the desired layer, and also remove the solder paste layer to expose the electrodes of the electronic component, and form an electroplating space at the etching position of the first copper foil layer and at the position of removing the solder paste layer as shown in  FIG. 8 , so that the electrode  34  of the electronic component  32  is exposed, and an electroplating space  52  is formed at the position of etching the first copper foil layer  22  and at the position of removing the solder paste layer  30 , wherein one of the methods of removing the solder paste layer  30  is wash away the solder paste layer  30  by a chemical solution, wherein the chemical solution includes a nitric acid solution, with a concentration of 15°%˜40% by weight, and the nitric acid solution is capable of washing the solder paste layer  30  away from the printed circuit board by a chemical reaction. 
         [0057]    Step 9: Copper plating and electroplating processes are performed to the bottom side of the first copper foil layer  22 , the top side of the second copper foil layer  46 , the hole wall of the penetrating hole  56  and the electroplating space  52  to form a plating copper as shown in  FIG. 9 , so that the first copper foil layer  22  is electrically conducted with the electrode  34  of the electronic component  32 , and the first copper foil layer  22  and the first plating copper  54  are electrically conducted with the second copper foil layer  46  and the second plating copper  55 , wherein the plating copper on the bottom side of the first copper foil layer  22  in the electroplating space  52  is a first plating copper  54 , and the plating copper on the top side of the second copper foil layer  46  is a second plating copper  55 , and the plating copper on the hole wall of the penetrating hole  56  is a third plating copper  58 . The aforementioned plating coppers are used for electrically conducting the first copper foil layer  22  with the electrode  34  of the electronic component  32 , and the method of the present invention is better than the traditional way of using a solder paste to achieve the effect of the electrical conduction, since the printed circuit board of the present invention contains no solder paste, and the solder paste is different from materials of the printed circuit board, so that the difference between the coefficients of expansion the materials are large. If there is a large temperature change, the thermal expansion and contraction of the solder paste will cause unstable quality of the whole printed circuit board. Therefore, the present invention using a plating copper for electrically conducting the first copper foil layer  22  with the electrode  34  of the electronic component  32  is better than the traditional method. 
         [0058]    Step 10: Circuits are formed on the first copper foil layer  22  and the first plating copper  54  to produce a first circuit layer  62  and circuits are formed on the second copper foil layer  46  and the second plating copper  55  to produce a second circuit layer  64  as shown in  FIG. 10 . 
         [0059]    The method further comprises the following steps after Step 10 as shown in  FIG. 11 . A fourth dielectric layer  74  is set under the first circuit layer  62 , and a fifth dielectric layer  70  is set on top of the second circuit layer  64 , and a lamination process of the laminar circuit layer is performed on the outer layers of the fourth dielectric layer  74  and the fifth dielectric layer  70 . In other words, a lamination process of a third laminar circuit layer  76  is performed under the fourth dielectric layer  74 , and a lamination layer of a fourth laminar circuit layer  72  is performed at the top of the fifth dielectric layer  70 , and the electronic component  32 , the third laminar circuit layer  76  and the fourth laminar circuit layer  72  are electrically conducted with each other, so as to complete manufacturing a multi-layer printed circuit board with embedded electronic components. 
         [0060]    Wherein, the penetrating hole  66  is formed by mechanical drilling, and copper plating and electroplating processes are performed, so that an electroplating layer  78  is formed at the inner periphery of the penetrating hole  66 , and the electronic component  32  is electrically conducted with the first circuit layer  62 , the second circuit layer  64 , the third laminar circuit layer  76 , and the fourth laminar circuit layer  72 . 
         [0061]    In the method of manufacturing a printed circuit board with embedded electronic components positioned by using a solder paste in accordance with the present invention, the cohesion of a molten solder paste is used to pull the electronic component towards the center in order to eliminate any position offset occurred while installing the electronic component, and the present invention further uses a plating copper for electrically conducing the first copper foil layer with the electronic component, and this method is better the traditional method of using a solder paste for the electrical conduction. 
         [0062]    In summation of the description above, the present invention is a major breakthrough of the prior art and complies with patent application requirements, and is thus duly filed for patent application. While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.