Patent Publication Number: US-2006005382-A1

Title: Modular method for manufacturing circuit board

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a modular method for manufacturing printed circuit boards, which is a method of manufacturing multilayer printed circuit boards with blind and buried vias structure by using basic components as the assembly units. The method adopts a dry film lamination method to press a dry film dielectric (i.e. a dielectric material in the form of a dry film, which is a semi-sticky plastic state) at B-stage (i.e. the stage of a resin before its reaching a glass conversion state) onto a laminate after the photolithography and etching processes are performed. Vias are drilled at appropriate positions on the upper and lower layers that require an electric connection, and then a plastic conductive material is filled into the vias to produce basic components. To comprise the basic components, circuit boards having blind vias and single-sided or double-sided circuits, the dielectric materials and the copper clads according to the required multilayer printed circuit board mode, then heating and pressurization process is performed once to form the multilayer printed circuit boards with blind and buried vias structure. Such arrangement not only saves the time for aligning layers, pressing and blind via filled plating of the prior-art technology, but also enhances the yield rate and reduces the failure cost.  
      2. Description of the Related Art  
      In the traditional printed circuit board manufacturing, the design of a single-sided or a double-sided inserted component and via is common at early stage. However, more and more functions are required for the electronic products and cause a demand for a high circuit density. The design of printed circuit boards tends to be a multilayer board design. The layout area is increased by having more layers of a printed circuit board, and the plating through hole (PTH) method is still adopted for electrically connecting the layers.  
      Since the plate through hole method for electrically connecting the layers will waste the layout real estate for the printed circuit board that does not need an electric connection between layers, therefore a high density interconnect (HDI) method by using a laser drilling method to electrically connect a layer with the next layer is adopted to overcome the aforementioned shortcoming. The high density interconnect method become a common method for manufacturing a multilayer circuit board that has a structure with blind vias (vias electrically interconnecting the outmost layer of the circuit board to the next layer or the layer next to the next layer) and buried vias (vias electrically interconnecting layers within the circuit board only, but not electrically interconnected to the outmost layer directly).  
      In the build up process by using the laser drilling method to produce blind vias layer by layer, a special chemical solution of a higher cost is used to fill plate the blind vias for long hours in order to stack the blind vias at the built up layer on the blind vias at the next layer (Stack Via) to save the real estate and increase the electric conduction reliability.  
      Please refer to  FIGS. 1A  to  1 E for the illustrative views of the build up process and the flow of interconnecting the next layer according to a prior-art printed circuit board manufacturing technology. An electric circuit  110 ,  120  as shown in  FIG. 1A  is produced on a copper clad laminate  100  by photolithography and etching processes and a dielectric material  130  such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat and copper clad  140  is deposited on the electric circuit  110  as shown in  FIG. 1B . For laser drilling, carbon dioxide (CO 2 ) laser is generally used, and such laser can effectively burn the resin polymer layer of a circuit board, but cannot burn the metal layer of a circuit board. Therefore, it is necessary to use a photoresist agent to protect the metal layer  140  and expose the section that requires an electrical interconnect, and then etch the metal of the section  150  (this process is commonly known as “Conformal Window” process) as shown in  FIG. 1C . Then, drill a via  160  by laser drilling as shown in  FIG. 1D  and plate a metal layer  170  on the sidewall of the via  160  as shown in  FIG. 1E .  
      Please refer to  FIGS. 2A  to  2 J for the illustrative views of the flow of producing an 8-layer printed circuit board having blind and buried vias structure according to a prior-art printed circuit board manufacturing technology.  
      An electric circuit  210 ,  220  as shown in  FIGS. 2A and 2B  is produced on a copper clad laminate  200  by photolithography and etching processes and a dielectric  230  such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat and copper clad  240  is deposited on the electric circuit  210 , 220  as shown in  FIG. 2C , to perform a heating and pressurization process for a tight press as shown in  FIG. 2D , and then perform mechanical drilling and plating operations to give an electrical connection function between the layers that require electrical interconnection. A conductive material  250  fills the vias by a silk screen printing method to allow stack via (blind vias stack on the buried vias) and increase the electric conduction reliability between new built-up layers. An electric circuit is produced on the outer layer by the photolithography and etching method. Therefore, the core 4-layer circuit structure of the 8-layer circuit board having blind and buried via structure is completed (as shown in  FIG. 2E .)  
      And then, the build up process is carried out as follows:  
      A dielectric  230  and a metal clad  240  used for pressing are deposited on such a core 4-layer circuit structure (as shown in  FIG. 2F ), and the heating and pressurization process is performed once again for a tight press, and then the conformal window, laser drilling, via filled plating, photolithography and etching processes are performed to electrically connect the core 4-layer circuit structure and the new build up circuit layer to produce the blind via  260  and the electric circuit as shown in  FIGS. 2G  to  2 H. Therefore, a core 6-layer circuit structure of the 8-layer circuit board having blind and buried via structure is completed.  
      Then, the build up process is performed once again.  
      A dielectric  230  and a metal clad  240  used for pressing are deposited on such a core 6-layer circuit structure, and the heating and pressurization process is performed for the third time for a tight press (as shown in  FIG. 2I ), and then the mechanical drilling, conformal window, laser drilling, via filled plating, photolithography and etching processes are performed to produce the blind via and the outermost electric circuit as shown in  FIG. 2J . Therefore, an 8-layer circuit board having blind and buried vias is completed.  
      Similarly, a circuit board with more layers having the blind and buried via structure can be made by repeating the procedure above.  
      However, it is noteworthy that the plated metal can just be deposited along the sidewall of the via (as indicated by  170  in  FIG. 1E ) in traditional plating, and the blind via cannot be filled. Therefore, a special chemical solution of a very high cost is needed for the foregoing via filled plating to achieve the purpose of filling the via by plating.  
      Further, the prior-art technology requires a pressing process each time for adding a layer. Since each pressing can only confirms the alignment between a new circuit layer and its next circuit layer, therefore a serious deviation on the alignment between different circuit layers caused by the increased times of pressings will be resulted.  
      From the foregoing process, it is obvious that the prior-art process takes long time, not only is difficult to enhance the yield rate, but also increase the cost of fault at a later stage of the manufacturing process.  
     SUMMARY OF THE INVENTION  
      In view of the description above, the inventor of the present invention based on years of experience on the related field to conduct experiments and tests to overcome the aforementioned shortcomings of the prior art and finally invented the method for manufacturing a multilayer printed circuit board having blind and buried vias structure by using a basic component as the assembling unit in accordance with the present invention.  
      The primary objective of the present invention is to provide a method for manufacturing multilayer printed circuit boards with blind and buried vias structure by using basic components as the assembly units. The method comprises the steps of producing an electric circuit on the surface of a copper clad laminate by photolithographic and etching methods, pressing a dry film dielectric onto the surface of the laminate by the dry film lamination method after the electric circuit layer is formed, drilling a via by a mechanical drilling method and plugging a plastic conductive material into the via, then removing the coversheet (i.e. a polyester film) on the surface of the dry film dielectric to obtain a basic component. When a multilayer printed circuit board having the blind and buried via structure is manufactured, to comprise the basic components, circuit boards having blind vias and single-sided or double-sided circuits, the dielectric materials and the copper clads according to the required multilayer printed circuit board mode, then heating and pressurization process is performed once to form the multilayer printed circuit boards with blind and buried vias structure. So compare with the prior-art technology that needs layers aligning, pressing and use of special chemical solution for blind via filled plating in each time build up process, the present invention has the following advantages:  
      1. Whatever layer counts of multilayer circuit board having blind and buried vias structure, just only once heating and pressurization process is needed to complete the manufacture. The present invention can reduce the times of the heating and pressurization processes. (The prior-art technology requires at least two times of heating and pressurization processes depending on the layer counts of the circuit board structure, and each time takes about 4˜5 hours).  
      2. The present invention provides an excellent alignment; since it only needs to go through the pressing process for one time, therefore the confirmation of the alignment between each circuit layer and its next layer can be done at one time to avoid a serious deviated alignment between the circuit layers caused by too many times of pressings.  
      3. The present invention does not need the special and high cost chemical solution to perform via-filled plating. The present invention directly fills plastic conductive material from the vias of basic components into the blind vias of circuit boards having blind vias and single-sided or double-sided circuits to achieve the same effect as the via-filled plating, and save much time and cost.  
      4. Unlike the prior-art technology that needs to make the circuit board layer by layer, continuously repeat build up process from the inner layers to the outer layers (heating and pressurization, mechanical drilling, laser drilling, via-filled plating . . . etc.), the present invention separately manufacture the basic components and the circuit boards having blind vias and single-sided or double-sided circuits then select the good ones to perform once heating and pressurization. So the present invention not only save the overall manufacturing time, but also enhance the yield rate and lower the cost of fault at a later stage of the manufacturing process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use a preferred embodiment together with the attached drawings for the detailed description of the invention.  
      FIGS.  1 A˜ 1 E are illustrative views of the build up process and the flow of interconnecting the next layer according to a prior-art printed circuit board manufacturing technology.  
      FIGS.  2 A˜ 2 J are illustrative views of the flow of producing an 8-layer printed circuit board having blind and buried vias structure according to a prior-art printed circuit board manufacturing technology.  
      FIGS.  3 A˜ 3 E are illustrative views of producing a basic component of the present invention.  
      FIGS.  4 A˜ 4 D are illustrative views of producing a printed circuit board with the assembly and application of the basic components according to the present invention.  
      FIGS.  5 A˜ 5 C are illustrative views of a 6-layer printed circuit board manufacturing procedure according to a first preferred embodiment of the present invention.  
      FIGS.  6 A˜ 6 C are illustrative views of an 8-layer printed circuit board manufacturing procedure according to a second preferred embodiment of the present invention.  
      FIGS.  7 A˜ 7 B are illustrative views of a 10-layer printed circuit board manufacturing procedure according to a third preferred embodiment of the present invention.  
      FIGS.  8 A˜ 8 B are illustrative views of a 10-layer printed circuit board another manufacturing procedure according to a fourth preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention relates to a modular method for manufacturing circuit boards by using basic components as the assembling units to produce multilayer circuit boards having the blind and buried vias structure.  
      Please refer to  FIGS. 3A  to  3 E for the illustrative views of producing a basic component of the present invention. The method comprises the steps of using an electric circuit manufacturing process to produce an electric circuit layer  11 ,  12  on the surface of a copper clad laminate  10  by photolithographic and etching methods (as shown in  FIG. 3A ); pressing a dry film dielectric  20  which at B-stage (i.e. the stage of a resin before its reaching a glass conversion state) and having a coversheet (i.e. a polyester film) onto the electric circuit layer  11 ,  12  by the dry film lamination method (as shown in  FIG. 3B ); and drilling vias  13  at predetermined position by mechanical drilling method (as shown in  FIG. 3C ) and plugging plastic conductive material  30  into the vias  13 , and then removing the coversheet  21  on the surface of the dry film dielectric  20 , so that the plastic conductive material  30  will be protruded slightly from the vias  13 , such to obtain a basic component  40  (as shown in  FIG. 3E ).  
      Further, please refer to  FIGS. 4A  to  4 D for the illustrative views of producing a printed circuit board with the assembly and application of the basic components according to the present invention. The method comprises the steps of etching the surface of a copper clad laminate  55  to remove the metal at the position for producing laser vias (as shown in  FIG. 4A ), burning the resin to produce blind vias  53  by laser drilling method (as shown in  FIG. 4B ), plating a layer of metal  54  onto the surface of the blind via by plating method (as shown in  FIG. 4C ), and producing single-sided or double-sided circuits by the photolithography and etching processes (as shown in  FIG. 4D ) to obtain a circuit board component  50  having blind vias  53 . The double-sided circuit board is used in this embodiment.  
      Please refer to  FIGS. 5A  to  5 C for illustrative views of a 6-layer printed circuit board manufacturing procedure according to a first preferred embodiment of the present invention. To stack the circuit board component  50  having produced blind vias and single-sided electric circuit onto both the upper and lower sides of a basic component, and the produced electric circuit layer of the circuit board component  50  adjacent to the basic component  40 . In the meantime, align the blind vias  53  of the circuit board component  50  needs to interconnect with the buried vias of the basic component  40  (as shown in  FIGS. 5A and 5B ), since the plastic conductive material  30  is slightly protruded from the opening of the via after the coversheet on the surface of the dry film dielectric is removed, therefore the plastic conductive material  30  will fill up the blind vias  53  when carrying out the heating and pressurization process. After the pressing process is completed, the mechanical drilling and plating are performed to produce the via interconnection, and produce the outmost electric circuit by the photolithography and etching methods, such the required 6-layer circuit board having blind and buried vias structure is completed (as shown in  FIG. 5C ).  
      Please refer to  FIGS. 6A  to  6 C for illustrative views of an 8-layer printed circuit board manufacturing procedure according to another preferred embodiment of the present invention. To stack the circuit board component  60  having blind vias and double-sided circuits (produced by the same manufacturing method as the circuit board component  50 ) onto both the upper and lower sides of a basic component; stacking the dielectric material  61  such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat onto the circuit board  60  and then stacking the copper clad  62  on the surface of the dielectric material  61 . In the meantime, align the blind vias  63  of the circuit board component  60  needs to interconnect with the buried vias of the basic component  40  (as shown in  FIGS. 6A and 6B ), since the plastic conductive material  30  is slightly protruded from the opening of the via after the coversheet on the surface of the dry film dielectric is removed, therefore the plastic conductive material  30  will fill up the blind vias  63  when carrying out the heating and pressurization process. After the pressing process is completed, the mechanical drilling, laser drilling, via filled plating are performed to produce the via interconnection, then photolithography and etching processes are performed to produce the outermost electric circuit, such the required 8-layer circuit board having blind and buried vias structure is completed (as shown in  FIG. 6C ).  
      Please refer to  FIGS. 7A and 7B  for the illustrative views of a 10-layer printed circuit board manufacturing procedure by using a basic component  40  to produce a 10-layer circuit board having the blind and buried via structure according to the present invention. To stack two basic components  40 ; stacking the circuit board component  70  having blind vias and double-sided circuits (produced by the same manufacturing method as the circuit board component  50 ) onto both the upper and lower sides of the two mutually stacked basic component; stacking the dielectric material  71  such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat onto the circuit board  70  and then stacking the copper clad  72  on the surface of the dielectric material  61 . In the meantime, align the blind vias  73  of the circuit board component  70  needs to interconnect with the buried vias of the basic component  40  (as shown in  FIGS. 7A ), since the plastic conductive material  30  is slightly protruded from the opening of the via after the coversheet on the surface of the dry film dielectric is removed, therefore the plastic conductive material  30  will fill up the blind vias  73  when carrying out the heating and pressurization process. After the pressing process is completed, the mechanical drilling, laser drilling, via filled plating are performed to produce the via interconnection, then photolithography and etching processes are performed to produce the outermost electric circuit, such the required 10-layer circuit board having blind and buried vias structure is completed (as shown in  FIG. 7B ).  
      Please refer to  FIGS. 8A and 8B  for another method of manufacturing a 10-layer circuit board having blind and buried vias structure by using a basic component  40 . First, the circuit board component  80  having blind vias and double-sided circuits (produced by the same manufacturing method as the circuit board component  50 ) being held between the two basic components  40 ; then stacking the produced circuit board component  90  having blind vias and single-sided circuit (produced by the same manufacturing method as the circuit board component  50 ) onto the two basic components  40  at the side not adjacent to the circuit board component  80 . In the meantime, align the blind vias  83 , 93  of the circuit board component  80 , 90  needs to interconnect with the buried vias of the basic component  40  (as shown in  FIGS. 8A ), since the plastic conductive material  30  is slightly protruded from the opening of the via after the coversheet on the surface of the dry film dielectric is removed, therefore the plastic conductive material  30  will fill up the blind vias  83 , 93  when carrying out the heating and pressurization process. After the pressing process is completed, the mechanical drilling and plating are performed to produce the via interconnection, and produce the outmost electric circuit by the photolithography and etching methods, such the required 10-layer circuit board having blind and buried vias structure is completed (as shown in  FIG. 8B ).  
      In view of the foregoing embodiment described above, a printed circuit board with more layers can be produced just perform once heating and pressurization by using the basic components, the produced circuit board components with blind vias and single-sided circuit or double-sided circuit and the combination of dielectric material and copper clad. (To simplify the description, a dielectric material and a copper clad are adopted in the embodiment. However, in actual practice, the prior-art build up material of the resin coated copper (RCC) can be used to substitute the dielectric material and copper clad for the pressing). The quantity of the basic components and circuit board components used for assembling is the main difference of the application according to different structure of circuit board. In summary, whatever layer counts of multilayer circuit board having blind and buried vias structure could be made by two ways of the present invention, one is circuit boards having blind vias and single-side or double-sided circuits to be stacked with each basic component, the other is circuit boards having blind vias and single-sided or double-sided circuits to be stacked with components which having at least two basic components mutually stacked together, comprise the dielectric material and copper clad according to the multilayer circuit board mode, then perform once heating and pressurization process and the follow-up mechanical drilling, laser drilling, photolithography and etching operations.  
      It is noteworthy that when the B-stage dry film dielectric of the basic component disclosed in the foregoing preferred embodiments is pressed onto a laminate by a dry film lamination method, the dielectric resin still remains at the B-stage since the dry film pressure is controlled below the glass conversion temperature (Tg) of the resin. Therefore, the resin could be softened again and can be attached onto the metal or dielectric material of the circuit board components having blind vias and single-sided or double-sided circuit during the heating and pressurization process.  
      Unlike another prior-art technology, this feature is generally used for manufacturing circuit boards with the specification of a very fine circuit (50 μm) and space (50 μm) between circuits. Such method for manufacturing fine circuits also uses a dry film dielectric as the dielectric material for building up the layers of the circuit board, and controls the temperature of for the dry film lamination above the temperature of glass conversion temperature (Tg) of the resin, so that the dielectric resin is converted into the C-stage. (The stage for the resin to reach the glass conversion temperature. The resin is hardened completely once it reaches C-stage, and cannot be softened or have the adhesive action with any metal or dielectric material of the circuit board by applying whatever temperature.) The follow-up drilling, electroless plating, photoresist masking and lithography, plating and photoresist removal operations are performed to produce via interconnection and electric circuits as the core circuit boards for building up layers.  
      The general pressing method used a copper clad as the substrate for etching electric circuits is limited by the etching factor and cannot produce a very fine circuit (50 μm) and a short space (50 μm) between circuits, but the method of manufacturing an electric circuit by converting dry film dielectric into the C-stage after dry film lamination could overcome this problem. Using the dry film dielectric technology to produce electric circuit is by plating method and isn&#39;t by etching as the prior-art technology, due to no etching factor issue and thus can produce a very fine circuit.  
      On present invention, since dry film dielectric of the basic component must be softened again and have the adhesive action with metal or dielectric material of the circuit board component, therefore the dry film pressure is controlled below the glass conversion temperature (Tg) of the resin when the dry film is pressed on the laminate by the dry film lamination method enable the dielectric resin still remains at the B-stage and has the adhesive actions of attaching a metal or dielectric material of the circuit board component. Thus the application and purpose of using the dry film dielectric are different between the present invention and the prior-art technology which is aimed at fine circuit PCB (Printed circuit board).  
      From the aforementioned pressing method, it is obvious that the present invention has the following advantages:  
      1. Whatever layer counts of multilayer circuit board having blind and buried vias structure, just only once heating and pressurization process is needed to complete the manufacture. The present invention can reduce the times of the heating and pressurization processes. (The prior-art technology requires at least two times of heating and pressurization processes depending on the layer counts of the circuit board structure, and each time takes about 4˜5 hours).  
      2. The present invention provides an excellent alignment; since it only needs to go through the pressing process for one time, therefore the confirmation of the alignment between each circuit layer and its next layer can be done at one time to avoid a serious deviated alignment between the circuit layers caused by too many times of pressings.  
      3. The present invention does not need the special and high cost chemical solution to perform via-filled plating. The present invention directly fills plastic conductive material from the vias of basic components into the blind vias of circuit boards having blind vias and single-sided or double-sided circuits to achieve the same effect as the via-filled plating, and save much time and cost.  
      4. Unlike the prior-art technology that needs to make the circuit board layer by layer, continuously repeat build up process from the inner layers to the outer layers (heating and pressurization, mechanical drilling, laser drilling, via-filled plating . . . etc.), the present invention separately manufacture the basic components and the circuit boards having blind vias and single-sided or double-sided circuits then select the good ones to perform once heating and pressurization. So the present invention not only save the overall manufacturing time, but also enhance the yield rate and lower the cost of fault at a later stage of the manufacturing process. In summation of the description above, the modular method for manufacturing circuit boards, which is a method of manufacturing multilayer printed circuit boards with blind and buried vias structure by using basic components as the assembly units according to the present invention overcomes the shortcomings of the prior-art technology and enhances the performance, further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.  
      While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.