Patent Publication Number: US-2011061907-A1

Title: Printed circuit board and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2009-0086584 filed on Sep. 14, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printed circuit board and a method of manufacturing the same, and more particularly, to a printed circuit board having a bump layer so that a circuit chip is electrically connected to an upper part of the bump layer, and a method of manufacturing the same. 
     2. Description of the Related Art 
     In general, methods of connecting chips to external substrates, such as printed circuit boards (PCBs) or wafer level packages (WLPs), may include a wire bonding method, a tape automated bonding method (TAB), and a flip chip method. 
     Among these methods, the flip chip method is widely being used in applications ranging from super computers requiring excellent electrical characteristics to portable electronic devices, because the flip chip method can increase speed and power through a short electron pathway, and also increase the number of pads per unit area. 
     Furthermore, according to the flip chip method, solder bumps are formed on a wafer in order to obtain appropriate bonding between a chip and an external substrate. The technique for manufacturing solder bumps has been developed into a method of manufacturing solder bumps having appropriate conductivity, uniform lengths and fine pitches. 
     According to the technique for forming solder bumps, the characteristics and the application range of solder bumps depend on what kind of material is being bumped. General solder bump forming techniques may include soldering in which a pad electrode comes into contact with molten solder, screen printing in which solder paste is formed on a pad electrode by screen printing and is subjected to a reflow process, a solder ball method of mounting a solder ball onto a pad electrode portion and reflowing the mounted solder ball, and plating in which solder plating is performed on a pad electrode. 
     Among them, screen printing has been widely used to form solder bumps in which the process of forming solder bumps in this manner is simple and manufacturing costs are low. However, as for the screen printing, solder is not completely transferred to a substrate when removing a mask. 
     In addition, due to the functional diversification and high integration of chips, the IO pin count increases. As a result, the line width and bump pitch of a printed circuit board to be mounted are being significantly reduced. Therefore, the uniform size of solder bumps, such as the height and the volume, become important factors in determining the reliability of the flip chip method. 
     Therefore, there is a need for a method of forming a solder bump that allows a fine pitch pattern to be applied to a printed circuit board and can form solder bumps having a uniform size. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a printed circuit board and a method of manufacturing the same that can be applied to a bump layer having a fine pitch and reduce a misalignment between a bump layer and an electrode portion. 
     According to an aspect of the present invention, there is provided a printed circuit board including: a board portion having an electrode portion provided on a surface thereof; a solder resist layer provided on the surface of the board portion and having an opening therein to expose the electrode portion to the outside; and a bump layer having the same diameter as the opening and providing an electrical connection with an external chip component. 
     The bump layer may be a plated layer growing into a shape of the opening. 
     The bump layer may protrude above the opening. 
     The bump layer may include a copper (Cu) layer. 
     The board portion may include a plurality of boards stacked upon one another. 
     According to another aspect of the present invention, there is provided a method of manufacturing a printed circuit board, the method including: forming a solder resist layer on a board portion having an electrode portion thereon; forming a dry film on the solder resist layer; forming an opening in the solder resist layer and the dry film to expose the electrode portion to the outside; and forming a bump layer in the opening by electroplating. 
     The forming of the bump layer by the electroplating may include: forming a copper post on a lower surface of the board portion; forming a bump layer in the opening formed in an upper surface of the board portion by the electroplating; and removing the copper post. 
     The forming of the copper post on the lower surface of the board portion may include: bonding a protective film to the dry film; forming copper posts on both surfaces of the board portion; and removing the protective film in order to remove a copper layer formed on the upper surface of the board portion. 
     The opening may be formed in the solder resist layer and the dry film by laser processing. 
     The solder resist layer and the dry film may be formed to have the same size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view illustrating a printed circuit board according to an exemplary embodiment of the present invention; and 
         FIGS. 2 through 8  are cross-sectional views illustrating a method of manufacturing a printed circuit board according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A printed circuit board and a method of manufacturing the same according to exemplary embodiments of the invention will be described in detail with reference to  FIGS. 1 through 8 . Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components. 
       FIG. 1  is a cross-sectional view illustrating a printed circuit board according to an exemplary embodiment of the invention. 
     Referring to  FIG. 1 , a printed circuit board may include a board portion  110 , solder resist layers  120 , and a bump layer  130 . 
     An electrode portion  112  is formed on a surface of the board portion  110  in order to provide an electrical connection with an external semiconductor chip. Here, as for the board portion  110 , an organic board portion or a ceramic substrate such as a low temperature co-fired ceramic (LTCC) substrate. 
     The solder resist layers  120  and the underfill layer  130  may be provided around the electrode portion  112  on the board portion  110 . The board portion  110  may have a plurality of layers, and circuit patterns may be formed so that the plurality opf layers are electrically connected to each other. 
     The electrode portion  112  may be formed on the board portion  110 . The electrode portion  112  may fill a via hole  114  in the board portion  110  and thus may be electrically connected to the surface of the board portion  110 . 
     The electrode portion  112  may be formed of aluminum (Al), copper (Cu), tin (Sn), nickel (Ni), gold (Au), platinum (Pt) or an alloy thereof, and may be a multi-layer having copper/gold/nickel stacked in a sequential manner. 
     The solder resist layers  120  are provided on the surfaces of the board portion  110 . The solder resistor layers  120  are formed around the electrode portion  112  to expose the electrode portion  112 . 
     The solder resist layers  120  provide electrical insulation and relieve thermal stress. The solder resistor layers  120  may be formed of an insulating material containing a polymer. Here, the solder resist layers  120  may be formed of an insulating material containing a photosensitive polymer in order to open the electrode portion  112 . The electrode portion  112  may be partially opened by performing exposure and development of the insulating material. 
     Here, in this embodiment, the solder resist layers  120  are formed. However, the invention is not limited thereto, and the solder resist layers  120  may be removed. 
     The bump layer  130  is formed in the opening  122  in the solder resist layers  120  by electroplating. Further, the bump layer  130  may be formed to have the same diameter as the opening  122  of the solder resist layers  120 . 
     Since the bump layer  130  and the opening  122  have the same diameter, the centers of the bump layer  130  and the opening  122  are naturally aligned with each other. Therefore, a misalignment between the centers of the bump layer  130  and the electrode portion  112  can be prevented. Therefore, a problem that an external chip component and a board portion are not electrically connected to each other in a case of the center misalignment can be solved. 
     Here, the bump layer  130  protrudes above the opening  122  to allow an external chip component to make contact with the bump layer  130 , whereby the bump layer  130  is electrically connected to the external chip component. 
     Furthermore, the bump layer  130  may be a copper (Cu) layer. Therefore, in order to form the bump layer  130  by electroplating, a copper post may be provided around the opening  122 . However, the material of the bump layer  130  is not limited thereto. 
       FIGS. 2 through 8  are cross-sectional views illustrating a method of manufacturing a printed circuit board according to an exemplary embodiment of the invention. 
     Referring to  FIG. 2 , according to a method of manufacturing a printed circuit board, the solder resist layers  120  are formed on the board portion  110  on which the electrode portion  112  is formed. 
     Here, the solder resist layers  120  are formed by applying photosensitive materials to both sides of the board portion  110 . Here, the board portion  110  may include a plurality of boards stacked upon each other. The electrode portion  112  may fill the via hole  114  formed through the plurality of boards. 
     Referring to  FIG. 3 , after the solder resist layers  120  are formed on both sides of the board portion  110 , a dry film  140  is formed on one of the solder resist layers  120  formed on the board portion  110 . 
     Adhesive power of the dry film  140  may be maintained to prevent a separation between the dry film  140  and the solder resist layer  120 . 
     Here, a protective film  142  is formed on the dry film  140 . The dry film  140  is used after removing the protective film  142 . In this embodiment, the protective film  142  is not removed. 
     Referring to  FIG. 4 , as the board portion  110 , formed on the dry film  140 , undergoes chemical-copper plating, copper (Cu) posts  150  are automatically formed on both sides of the board portion  110 . 
     Here, since the dry film  140  is not formed on a bottom surface of the board portion  110 , the copper post  150  may make in close contact with the surface of the electrode portion  112   110  and the board portion  110 . 
     Then, referring to  FIG. 5 , by removing the protective film  142  formed on the dry film  140 , the copper post  150  formed on the protective film  142  may further be removed. The copper post  150  induces the formation of the bump layer  130  formed of copper. 
     Here, the dry film  140  is formed on the copper post  150  to thereby protect the copper post  150 . 
     Referring to  FIG. 6 , the opening  122  is formed in the dry film  140  by laser processing (L) to expose the electrode portion  112 . The opening  122  is formed by laser processing (L) so that the dry film  140  and the solder resist layers  120  have the same diameter. However, a method of manufacturing the dry film  140  and the solder resist layers  120  to have the same diameter is not limited to the above-described laser processing. 
     Referring to  FIG. 7 , when electroplating is performed on the board portion  110  having the opening  122  therein, currents flow through the other side where the copper post  150  is formed, due to the electrode portion  112  filling the via hole  114  and the copper post  150 , so that the materials of the bump layer  130  may naturally fill the opening  122 . 
     Through these processes, the bump layer  130  has the same size as the opening  122  formed in the solder resist layer  120  and the dry film  140 . 
     Referring to  FIG. 8 , after the bump layer  130  is formed in the opening  122 , the dry film  140  is removed. 
     Therefore, when the dry film  140  is removed, the bump layer  130  protrudes above the opening  122  in the solder resist layers  120 . Therefore, the external semiconductor chip is easily bonded to the protruding portion of the bump layer  130  and thus is electrically connected to the board portion  110 . 
     When the copper post  150 , formed on the lower surface of the board portion  110 , shown in  FIG. 8 , is removed, the printed circuit board, shown in  FIG. 1 , can be manufactured. 
     Therefore, the printed circuit board and the method of manufacturing the same according to the embodiments of the invention include the bump layer  130  having the same diameter as the opening  122 , thereby realizing the bump layer  130  having a fine pitch. 
     Furthermore, the printed circuit board according to this embodiment is formed so that the center of the bump layer  130  and the center of the opening  122  coincide with each other, thereby preventing a misalignment between the bump layer  130  and the electrode portion and forming the bump layer  130  having a uniform size, so that a board having high reliability can be provided. 
     As set forth above, according to exemplary embodiments of the invention, the printed circuit board and the method of manufacturing the same include a bump layer having the same diameter as the opening to thereby realize a bump layer having a fine pitch, prevent a misalignment between the bump layer and an electrode portion, and form a bump layer having a uniform size, thereby providing a board having high reliability. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.