Patent Publication Number: US-2013240254-A1

Title: Printed circuit board and method for manufacturing printed circuit board

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to printed circuit board and method for manufacturing printed circuit board. 
     2. Description of Related Art 
     Referring to  FIGS. 4-5  a printed circuit board (PCB)  300  is formed by a layer of conducting material deposited on the surface of an insulating substrate  310 . A plurality of pads  320  and printed wirings (such as copper tracks)  330  are designed on the substrate  310  for connecting electric component (not shown). Each pad  300  includes a copper foil  321  covering on the substrate and a solder resist  322  arranged around the copper foil  321 . A permanent mold coating  324 , such as solder paste, is coated on the copper foil  321  to hold the electronic components in place until the permanent mold coating  324  is melted. 
     However, during the typical manufacturing of the PCB  300 , when the permanent mold coating  324  is coated on the copper foil  321 , the permanent mold coating  324  is substantially convex shaped with the middle portion higher than the surrounding portion (see  FIG. 5 ). As a result, when the electronic component is connected to the pad  320  by manually melting the leads of the electronic component to the permanent mold coating  324 , it is difficult for the user to position the leads in the middle of the permanent mold coating  324  because of the convex shape. 
     Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the five views. 
         FIG. 1  is a partial perspective view of a printed circuit board in accordance with an embodiment. 
         FIG. 2  is a partially cross-sectional view of the printed circuit board of  FIG. 1 . 
         FIG. 3  is a flow chart of a method for manufacturing the printed circuit board of  FIG. 1 . 
         FIG. 4  is a partial perspective view of a related art printed circuit board. 
         FIG. 5  is partially cross-sectional view of the related art printed circuit board of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
       FIGS. 1-2 , illustrate a printed circuit board (PCB)  100  of one embodiment. The PCB  100  includes a substrate  110 , a plurality of pads  120  designed on the substrate  110 , permanent mold coatings  130  coated on the pads  120 , a plurality of copper tracks  140  for linking electronic components (not shown) soldered to the pads  120 . In the embodiment, the substrate  110  used in printed circuit board  100  is a glass fiber reinforced (fiberglass) epoxy resin with copper foil bonded on to one or both sides. 
     Each pad  120  includes a copper foil  121  bonded to the substrate  110  and a solder resist  122  surrounding the copper foil  121 . The copper foil  121  is substantially rectangular and defines an opening  124 . The opening  124  is substantially rectangular and is arranged in the middle of the copper foil  121 . The opening  124  is further coated with solder resist  122 . The solder resist  122  is used to prevent the permanent mold coatings  130  from coating on the substrate  110 . The solder resist  122  is green lacquer in the embodiment. 
     The permanent mold coatings  130  in the embodiment are solder paste. The permanent mold coatings  130  are coated on the copper foil  121  with surface mount technology (SMT), to protect the copper foil  121  and further to enhance welding performance of the pad  120 . Because the opening  124  is defined in the middle of the copper foil  121  and is coated with the solder resist  122 , the permanent mold coatings  130  only cover on the copper foil  121  and surround the opening  124  to form a recess  125 . As a result, the permanent mold coatings  130  are dimple-shaped with the middle portion being recessed. By aligning the leads in the recess  125 , the operator can easily position the leads of the electronic components and further accurately melt the leads with the pads  120 . Furthermore, during the hot-melting process, the recess  125  receives the melted solder to avoid burrs being generated, and the soldered pads  120  are not needed to be washed. 
       FIG. 3 , is a flow chart of a method for manufacturing the PCB  100 . The method includes the follow steps: 
     In step S 310 , a substrate  110  is provided. In the embodiment, the substrate  110  used in printed circuit board  100  is a glass fiber reinforced (fiberglass) epoxy resin with copper foil bonded on to one or both sides. 
     In step S 320 , a circuit pattern corresponding to the PCB  100  is designed. Each PCB has a unique function for a particular product and must be designed to perform that function in the space allotted. Board designers use computer-aided design systems with special software to layout the circuit pattern. The circuit pattern includes a plurality of pins corresponding to the pads  120  of the PCB  100  respectively. Each pin defines a vacancy corresponding to the opening  124  of the pads  120 . 
     In step S 330 , the designed circuit pattern is converted to PCB layout, and the PCB layout is printed on a transparency and becomes known as a PCB mask. The PCB mask further covers on the surface of the substrate with copper foil (referred as the foil surface). The foil surface with the PCB mask pass through a vacuum chamber where a layer of positive photoresist material is pressed firmly onto the entire surface of the foil. A positive photoresist material is a polymer that has the property of becoming more soluble when exposed to ultraviolet light. After passing through the vacuum chamber, the foil surface covered with the PCB mask and photoresist material is exposed to an intense ultraviolet light. Because the mask is clear in the areas of the printed circuit pattern, the photoresist in those areas is irradiated and becomes very soluble. 
     In step S 340 , after being exposed to an intense ultraviolet light, the substrate  110  with copper foil is etched to leave the desired pattern including copper tracks  140  and pads  120  having copper foil  121  with an opening  124  defined therein. 
     In step S 350 , when removed from the etching solution, the substrate  110  is washed and a PCB eraser is used to remove any film from the tracks. 
     In step S 360 , the substrate  110  is further coated with the solder resist  122  to prevent the permanent mold coatings  130  from coating on the substrate  110  and the copper foil  121 . In the embodiment, the solder resist  122  is coated surrounding each pad  120  and further coat on opening  124 . 
     In step S 370 , the permanent mold coatings  130  coat on the copper foil  121  to protect the copper foil  121  from being oxidized and further to enhance welding performance of the pad  120 . Because the opening  124  is defined in the middle of the copper foil  121  and is coated with solder resist  122 , the permanent mold coatings  130  only cover on the copper foil  121  and surround the opening  124  to form a recess  125 . As a result, the permanent mold coatings  130  are dimple-shaped with the middle portion being recessed. 
     In step S 380 , the leads of the electronic component is aligned with the recess  125 , and further accurately being melt with the pads  120  to solder the electronic component to the PCB  100 . 
     It is to be understood, even though information as to, and advantages of, the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.