Abstract:
A PCB and a method of manufacturing a PCB with combined inlay-PCB process and embedded coin technology are disclosed. The method and device disclosed herein is able to manufacture an inlay part of a high frequency laminate into FR4 laminate. The present invention is advantageous in many aspects including having an inlay design on the PCB, which can save the cost of high frequency laminate. Further, the inlay PCB with embedded coin technologies can enhance the thermal reliability of the finished PCB.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 U.S.C. §119(e) of the U.S. Provisional Patent Application Ser. No. 61/649,126, filed May 18, 2012 and titled “INLAY PCB WITH EMBEDDED COIN SAMPLE BOARD EVALUATION STUDY,” which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of manufacturing printed circuit boards (PCBs). More specifically, the present invention relates to the field of manufacturing PCBs with enhanced thermal properties and increased reliability. 
     BACKGROUND OF THE INVENTION 
     In a typical PCB, a full panel of FR4 material is in hybrid with a full panel of high frequency material, such as Rogers RO4000® series high-frequency circuit materials and Taconic PTFE laminates. However, only a small portion of the PCB is designed for high frequency signal transfer, the unused portion of the high frequency material being wastes, unnecessarily increases manufacturing costs of the PCB. With increasing demand for high frequency products, there is a need to manufacture these products more efficiently and at reduced costs. 
     SUMMARY OF THE INVENTION 
     A PCB and a method of manufacturing a PCB with a combined inlay-PCB process and embedded coin technology are disclosed. The method allows the fabrication of an inlay part of high frequency laminate into an FR4 laminate. Advantageously, the inlay part is included on the PCB, a structure that reduces the cost of the high frequency laminate. Further, the inlay PCB with embedded coin technologies can enhance the thermal reliability of the finished PCB board. 
     In one aspect, an electronic circuit board comprises a printed circuit board having a first aperture and a second aperture, a high-frequency circuit material coupled to the first aperture, and a heat dissipating material coupled to the second aperture. 
     In some embodiments, the heat dissipating material comprises a coin. In one embodiment, the coin comprises copper. In some other embodiments, the high frequency material is fabricated/structured/configured to transfer a signal having a frequency of 500 MHz and above. In some embodiments, the high frequency circuit material is fabricated/structured/configured to transfer a microwave frequency signal. In other embodiments, the second aperture is deeper than the first aperture in the printed circuit board. In some other embodiments, the printed circuit board comprises an FR4 printed circuit board. 
     In another aspect, a method of making an electronic circuit board comprises forming a first aperture on an electronic circuit board, forming a second aperture on the electronic circuit board, placing a high-frequency circuit material in the first aperture, and placing a heat dissipating material in the second aperture. 
     In some embodiments, the method further comprises transferring a high-frequency signal on an area of the electronic circuit board. In other embodiments, the high-frequency signal has a microwave signal. In some other embodiments, the high-frequency signal has a frequency of 500 MHz and above. In some embodiments, the electronic circuit board comprises an FR4 PCB. In other embodiments, the heat dissipating material comprises a coin. In one embodiment, the coin comprises a copper coin. 
     In another aspect, a method of forming an inlay PCB board with an embedded coin comprises forming a high-frequency opening through first layers of a PCB, forming an opening for a coin through second layers of the PCB, performing oxide replacement, inserting a high-frequency laminate into the opening of the first layers of the PCB, and inserting a coin into the opening of the second layers of the PCB. 
     In some other embodiments, forming the high frequency opening and opening for the coin comprise routing. In other embodiments, the high-frequency opening has a size less than 2.5 mil per side larger than the high-frequency laminate. In some other embodiments, the opening for a coin has a size less than 5.5 mil per side larger than a size of the coin. In some embodiments, the first layers comprise fewer than 5 layers of laminates of the PCB. In other embodiments, the second layers comprise more than 7 layers of laminates of the PCB. 
     Other features and advantages of the present invention will become apparent after reviewing the detailed description of the embodiments set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments are described by way of examples, with reference to the accompanying drawings, which are meant to be exemplary and not limiting. For all figures described herein, like numbered elements refer to like elements throughout. 
         FIG. 1A  is a top view of a circuit board with an inlay PCB with an embedded coin in accordance with some embodiments of the present invention. 
         FIG. 1B  is a side cross-sectional view of the circuit board of  FIG. 1A . 
         FIG. 2  illustrates a method of manufacturing a circuit board having an inlay PCB with an embedded coin in accordance with some embodiments of the present invention. 
         FIG. 3  illustrates a process of manufacturing a PCB board in accordance with some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is made in detail to the embodiments of an inlay PCB with embedded coin manufacturing method and apparatus of the invention, examples of which are illustrated in the accompanying drawings. While the invention is described in conjunction with the embodiments below, it is understood that they are not intended to limit the invention to these embodiments and examples. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which can be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to more fully illustrate the present invention. However, it is apparent to one of ordinary skill in the prior art having the benefit of this disclosure that the present invention can be practiced without these specific details. 
       FIG. 1A  is a top view illustrating a circuit board  100  with an inlay PCB with an embedded coin in accordance with some embodiments of the present invention.  FIG. 1B  is a side cross-sectional view of the circuit board  100 . 
     Referring to both  FIGS. 1A and 1B , in some embodiments, the circuit board  100  contains a PCB board  106  having an inlay part  102  and an FR4 part  108 . FR4 is a composite material of woven fiberglass cloth with an epoxy resin binder. FR4 is described herein as an exemplary material. Other materials, such as G-10, G-11, and FR5, can be used to manufacture the laminate of the PCB board are within the scope of the present invention. The inlay part  102  can contain a high frequency portion  110  for high frequency signal transfer. In some embodiments, the inlay part  102  contains an embedded coin part  104 . In some embodiments, the embedded coin part  104  contains a coin. In some embodiments, the FR4 part  104  has between 2-4 layers. Examples of the FR4 part include EMC, EM 370, high glass transition temperature (High-Tg) FR4 materials, and HF FR4. In some embodiments, the inlay part  102  has an inlay capture size  132  having a predetermined drilling size of +20 mil and an inner layer capture size  130  having a predetermined drilling size of +10 mil. The inlay protrusion  128  can be +/−1 mil. The coin depression  126  can be +/−0.02 microns. The coin protrusion  124  can be 0-0.04 microns. 
       FIG. 2  illustrates a method of manufacturing a board  200  having an inlay PCB with an embedded coin. At Step  201 , the dimensions of a high frequency laminate  202  and a coin  202 D are measured. In some embodiments, the high frequency laminate  202  comprises RO4350B. A person of ordinary skill in the art will appreciate that any high frequency laminate, such as a laminate for transferring signals in microwave frequency, is able to be used within the scope of the present invention. In some embodiments, the coin  202 D is a metal coin, such as a copper coin. A person of ordinary skill in the art will appreciate that other coins of any material can be used so long as they are able to facilitate heat dissipation of the board  200 . The high frequency laminate  202  comprises an electric circuit  202 A. In some embodiments, the layers L1-L14 (layer 1 to layer 14) are first fixed together by bonding and riveting. 
     At Step  203 , an embedded space  202 B to fit the high frequency laminate  202  is determined and is routed out. In some embodiments, the size  202 C of the embedded space  202 B is 1-2 mil per side larger than the size of the high frequency laminate  202 . In some embodiments, the size of the embedded space  202 B is controlled to be in a range that is sufficient to fit the high frequency laminate  202  and not so large that it requires a lot of resin to fill in a gap between the high frequency laminate  202  and a hosting FR4 PCB board  204 . After the location of the embedded space  202 B is determined, the location is outlined by routing. In some embodiments, the location of the embedded space  202 B is outlined first. The size of the outlined embedded space  202 B is compared with a measured size of the high frequency laminate  202 . If after the comparison it is determined that the location of the embedded space  202 B is not within the pre-determined limits, adjusted routing is performed. This procedure is able to keep the size difference between the embedded space  202 B and the high frequency laminate  202  within 2-3 mils. The size matching, between the embedded space  202 B and the high frequency laminate  202 , enhances an alignment accuracy of the high frequency laminate  202  on the board  200 . 
     At Step  205 , the embedded space  202 B for fitting the high frequency laminate  202  is routed out by forming an embedded window  202 C. The embedded window  202 C has a surface area and geometry shown as the embedded space  202 B. The height of the embedded window  202 C extends from layer L14 to layer L10 or L 11 of the laminates of the board  200 . 
     At Step  207 , a coin window  202 E is routed out. Similar to the process of opening windows for the high frequency laminate  202 , a coin space (coin window  202 E) has a pre-determined equal to the size of the coin  202 D, plus 4.5 mil per side. The depth of the coin window  202 E extends from the layer L1 to the layer L 10. In some embodiments, a space for pre-preg (e.g., pre-impregnating an epoxy material) is opened, with a size equal to the coin size plus 6 mil per side or a size of the high frequency laminate  202  plus 6 mil per side. 
     At Step  209 , both the coin  202 D and the high frequency laminate  202 , such as RO4350B, are inserted into the opening of the FR4 PCB board  204  in a lay-up table. Because there are no guiding holes for the coin  202 D and the high frequency laminate  202  to align on the board  204 , this method of controlling the opening size and location, such as by pre-measuring the actual size of the coin  202 D and the high frequency laminate  202  to dynamically adjust the hole/window opening size and location, provides better alignments of the above components. In some embodiments, the accuracy of the alignment is controlled within 3 mil shift of a pre-determined location. 
       FIG. 3  illustrates a process  300  in accordance with some embodiments of the present invention. The process  300  comprises a part  301  and a part  303 . In some embodiments, the part  301  comprises procedure groups A, B, C and D. Group A comprises steps  302 ,  304 , and  306 . Group B comprises steps  308 ,  310 , and  312 . Group C comprises steps  314  and  316 . Group D comprises step  318 . In some embodiments, after the steps of a group are performed, the steps included in the part  303  are performed. For example, the procedure in Group A is performed first. Next, the steps of part  303  are performed. Next, the steps of Group B are performed, followed by the steps of part  303 . The steps of Group A include preparing FR4 core L1-L14 laminate in the step  302 , opening HF PCB (high frequency printed-circuit board) window and coin window by routing in the step  304 , and performing oxide replacement (OR) in the step  306 . The steps of Group B comprise inserting a high frequency laminate, such as RO 4350B, in the step  308 , performing routing in the step  310 , and performing oxide replacement in the step  312 . Group C comprises inserting a coin in the step  314  and performing oxide replacement in the step  316 . Group D comprises panel plating the open coin window and panel plating the HF PCB window. 
     The part  303  comprises the steps of pressing in a step  320 , routing panel edge in a step  322 , performing oxide replacement in a step  324 , drilling in a step  326 , performing plasma etching in a step  328 , performing desmear and plating through-holes in a step  330 , plating a 1 st  panel in a step  332 , performing hole plugging in a step  334 , plating a 2 nd  panel in a step  336 , etching in a step  338 , performing solder mask in a step  340 , performing an electroless nickel immersion gold (ENIG) process in a step  342 , routing in a step  344 , and testing in a step  346 . A person of ordinary skill in the art appreciates that any other surface finishing process are able to be used at the step  342 . In the present specification, 14 layers of the laminates are used as an example. Any other numbers of layers of the laminates are within the scope of the present invention, such as from 4 layers to 30 layers. The size (depth/area) of the openings for the high frequency laminate and the coin can be proportional to the numbers of the layers of the FR4 laminates. RO 4350B and EM 370 are used as exemplary embodiments. Other high frequency laminates and FR4 laminates are able to be used as a material for inlay and are all with the scope of the present invention. 
     The methods and devices disclosed herein can be utilized to manufacture inlay PCB with embedded coin. 
     In operation, the high frequency part, such as RO4350B, is first routed out and its actual size is measured. Next, an opening on the PCB board (FR4 PCB) is routed out per the size of the high frequency part by changing routing compensation such that the size differences between the opening and the actual size of the high frequency part are within 2-3 mil. Through these methods, windows for both the high frequency part and the coin are opened. Next, the high frequency part and the coin are inserted into the windows. 
     The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It is readily apparent to one skilled in the art that other various modifications can be made in the embodiments chosen for illustration without departing from the spirit and scope of the invention as defined by the appended claims.