Abstract:
A method of manufacturing a printed circuit board having a flow preventing dam, including: applying a dry film resist on a base substrate having a solder pad, and then primarily exposing the dry film resist to light; secondarily exposing the primarily exposed dry film resist formed on a peripheral area of the base substrate to light, thus forming a flow preventing dam; removing the unexposed dry film resist to expose the solder pad, thus forming an opening; printing the opening with a solder paste, and then forming a solder bump through a reflow process; and removing the primarily exposed dry film resist

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. divisional application filed under 37 CFR  1 . 53 ( b ) claiming priority benefit of U.S. Ser. No. 12/379,759 filed in the United States on Feb. 27, 2009, which claims earlier priority benefit to Korean Patent Application No. 10-2008-0112362 filed with the Korean Intellectual Property Office on Nov. 12, 2008, the disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a printed circuit board (PCB) having a flow preventing dam and a manufacturing method thereof, and more particularly to a PCB having a flow preventing dam, in which the flow preventing dam is provided on the peripheral area of the PCB so as to prevent the outflow of an underfill solution which is introduced between the PCB and a semiconductor chip which is flip chip bonded thereto. 
         [0004]    2. Description of the Related Art 
         [0005]    With the recent advancement of electronics industries, there is a demand for increasing performance and functionality of electronic components and reducing the size thereof. Accordingly, high integration, slimness and fine circuit patterning are also required on a substrate for surface mounting components, such as SIP (System in Package), 3D package, etc. 
         [0006]    In particular, in techniques for mounting electronic components on the surface of a substrate, a wire bonding process or a flip chip bonding process is utilized for electrical connection between an electronic component and a substrate. 
         [0007]    The wire bonding process includes bonding an electronic component having design circuits to a PCB using an adhesive, connecting a lead frame of the PCB to a metal terminal (i.e., pad) of the electronic component using a metal wire to transmit and receive information therebetween, and molding the electronic component and the wire with thermosetting resin or thermoplastic resin. 
         [0008]    The flip chip bonding process includes forming an external connection terminal (i.e., bump) having a size of tens of μm to hundreds of μm on an electronic component using a material such as gold, solder or another metal, and flipping the electronic component having the bump so that the surface thereof faces the substrate and is thus mounted on the substrate, unlike the mounting operation based on the wire bonding. 
         [0009]    Although the wire bonding process has higher productivity compared to other packaging processes, it needs wires for connection to the PCB, and thus the size of a module is increased and an additional procedure is required. Hence, the flip chip bonding process is mainly employed. 
         [0010]      FIGS. 1 and 2  are views showing a process of packaging a flip chip semiconductor package according to a conventional technique. 
         [0011]    As shown in  FIGS. 1 and 2 , the flip chip bonding according to the conventional technique is performed in a manner such that solder balls  16  are attached to the connection pads  14  of a PCB  12  and a semiconductor chip  18  is mounted on the PCB  12  by means of the solder balls  16 . 
         [0012]    In this way, however, when the semiconductor chip  18  is mounted on the PCB  12 , a gap G is formed between the semiconductor chip  18  and the PCB  12  due to the height of the solder balls  16  attached to the connection pads  14  of the PCB  12 , undesirably weakening the ability to support the semiconductor chip  18  and causing cracks around the soldering portion of the solder balls  16 . In particular, in the case where a temperature change occurs, the coefficient of thermal expansion between the semiconductor chip  18  and the PCB  12  is different, and thus thermal stress is applied to the solder balls  16 , thereby causing cracks on the solder balls  16 . 
         [0013]    Hence, with the goal of stably supporting the semiconductor chip  18 , an underfill solution  22  of a liquid material is introduced into the gap G between the semiconductor chip  18  and the PCB  12  using a dispenser  20 . 
         [0014]    The underfill solution  22  is introduced in a small amount between the semiconductor chip  18  and the PCB  12  and thus functions as an adhesive for holding the chip and plays a role in protecting the chip from the external environment, unlike a conventional semiconductor molding material (EMC) for packaging the entire semiconductor chip  18 . 
         [0015]    However, in the course of introducing the underfill solution  22  using the dispenser  20 , part of the underfill solution  22  which is introduced into the gap G between the semiconductor chip  18  and the PCB  12  may undesirably overflow the outer edge of the PCB  12  from the position where the dispenser  20  is located, causing defects. 
         [0016]    In order to solve this problem, there have been proposed methods of forming a dam on the peripheral area of the PCB using a dispensing process. 
         [0017]    However, the dispensing process which is used to form a linear dam through linear extrusion of epoxy resin from a dispensing nozzle is problematic in that the width of the dam may be non-uniform, and the shape of the dam may become winding due to frictional force at the end of the dispensing nozzle. 
         [0018]    Further, an additional dispensing apparatus is required to form the dam, and a process for forming the dam should be additionally carried out. 
       SUMMARY 
       [0019]    Accordingly, the present invention has been made keeping in mind the problems encountered in the related art and the present invention provides a PCB having a flow preventing dam, which is able to prevent the outflow of an underfill solution, and a manufacturing method thereof. 
         [0020]    In addition, the present invention provides a PCB having a flow preventing dam, in which the flow preventing dam is formed using a dry film resist for forming a solder bump without a need for an additional dispensing apparatus or dispensing process, and a manufacturing method thereof. 
         [0021]    According to a preferred embodiment of the present invention, a PCB having a flow preventing dam includes a base substrate having a solder pad, a solder bump formed on the solder pad of the base substrate, and a flow preventing dam formed on the peripheral area of the base substrate using a dry film resist. 
         [0022]    As such, a solder resist layer having an opening for exposing the solder pad may be formed on the base substrate. 
         [0023]    The flow preventing dam may include the dry film resist which is attached in a state of being overcured through excessive exposure to the solder resist layer. 
         [0024]    Also, a semiconductor chip which is flip chip bonded to the base substrate by means of the solder bump formed on the solder pad of the base substrate may be further included. 
         [0025]    The flow preventing dam may be provided to protrude from the base substrate along the outer edge of the semiconductor chip, in order to prevent the outflow of an underfill solution which is introduced into a gap between the semiconductor chip and the base substrate. 
         [0026]    The flow preventing dam may be formed to be lower than the upper surface of the semiconductor chip which is flip chip bonded to the base substrate and to be higher than the gap between the semiconductor chip and the base substrate. 
         [0027]    The flow preventing dam may be provided between the outer edge of the base substrate and the outer edge of the semiconductor chip. 
         [0028]    In addition, according to another preferred embodiment of the present invention, a method of manufacturing a PCB having a flow preventing dam includes (A) applying a dry film resist on a base substrate having a solder pad, and then primarily exposing the dry film resist to light, (B) secondarily exposing the primarily exposed dry film resist formed on a peripheral area of the base substrate to light, thus forming a flow preventing dam, (C) removing the unexposed dry film resist to expose the solder pad, thus forming an opening, (D) printing the opening with a solder paste and then forming a solder bump through a reflow process, and (E) removing the primarily exposed dry film resist. 
         [0029]    After (E) removing the primarily exposed dry film resist, (F) flip chip bonding a semiconductor chip to the base substrate by means of the solder bump formed on the solder pad of the base substrate may be further included. 
         [0030]    After (F) flip chip bonding the semiconductor chip, (G) introducing an underfill solution into a gap between the semiconductor chip and the base substrate may be further included. 
         [0031]    The flow preventing dam may be provided to protrude from the base substrate along the outer edge of the semiconductor chip, in order to prevent outflow of an underfill solution which is introduced into the gap between the semiconductor chip and the base substrate. 
         [0032]    The flow preventing dam may be formed to be lower than an upper surface of the semiconductor chip which is flip chip bonded to the base substrate and to be higher than the gap between the semiconductor chip and the base substrate. 
         [0033]    The flow preventing dam may be provided between the outer edge of the base substrate and the outer edge of the semiconductor chip. 
         [0034]    Also, a solder resist layer having an opening for exposing the solder pad may be formed on the base substrate. 
         [0035]    The features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
         [0036]    Further, the terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept implied by the term to best describe the method he or she knows for carrying out the invention 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIGS. 1 and 2  are views showing a process of packaging a flip chip semiconductor package according to a conventional technique; 
           [0038]      FIG. 3  is a cross-sectional view showing a PCB having a flow preventing dam according to a preferred embodiment of the present invention; 
           [0039]      FIG. 4  is a cross-sectional view showing the PCB having a flow preventing dam according to the preferred embodiment of the present invention, to which a semiconductor chip is flip chip bonded; 
           [0040]      FIG. 5  is a top plan view of  FIG. 4 ; and 
           [0041]      FIGS. 6 to 13  are cross-sectional views showing the process of manufacturing the PCB having a flow preventing dam according to the preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0042]    The features and advantages of the present invention will be more clearly understood from the following detailed description and preferred embodiments taken in conjunction with the accompanying drawings. In the description, the terms “first”, “second” and so on do not indicate any particular amount, sequence or importance but are used only to distinguish one element from another element. Throughout the drawings, the same reference numerals refer to the same or similar elements, and redundant descriptions are omitted. In order to make the characteristics of the invention clear and for the convenience of description, a detailed description pertaining to the other known techniques may be omitted. 
         [0043]    Hereinafter, a detailed description will be given of the preferred embodiment of the present invention, with reference to the accompanying drawings. 
         [0044]    PCB having Flow Preventing Dam 
         [0045]      FIG. 3  is a cross-sectional view showing the PCB having a flow preventing dam according to the preferred embodiment of the present invention. With reference to this drawing, the PCB  100  having a flow preventing dam according to the preferred embodiment of the present invention is described below. 
         [0046]    As seen in  FIG. 3 , the PCB  100  having a flow preventing dam according to the present invention includes a base substrate  102  having solder pads  104 , solder bumps  116  formed on the solder pads  104 , and a flow preventing dam  110   c  formed on a peripheral area thereof. 
         [0047]    The base substrate  102  is configured such that the solder pads  104  are formed on either or both surfaces thereof and a solder resist layer  106  having openings for exposing the solder pads  104  is formed. 
         [0048]    The flow preventing dam  110   c  is composed of a dry film resist which is attached in a state of being overcured through excessive exposure to the solder resist layer  106 . 
         [0049]      FIGS. 4 to 5  are a cross-sectional view and a top plan view showing the PCB having a flow preventing dam according to the preferred embodiment of the present invention, to which a semiconductor chip is flip chip bonded; 
         [0050]    As shown in  FIGS. 4 and 5 , the semiconductor chip  118  is flip chip bonded to the base substrate  102  by means of the solder bumps  116  formed on the solder pads  104  of the base substrate  102 , and an underfill solution  120  is introduced between the semiconductor chip  118  and the base substrate  102 . 
         [0051]    The flow preventing dam  110   c  is provided to protrude from the base substrate  102  along the outer edge of the semiconductor chip  118 , thus preventing the outflow of the underfill solution  120 . 
         [0052]    The flow preventing dam  110   c  is provided between the outer edge of the base substrate  102  and the outer edge of the semiconductor chip  118 , and is formed to be higher than the gap G between the base substrate  102  and the semiconductor chip  118  and to be lower than the upper surface of the semiconductor chip  118 , in order to prevent the outflow of the underfill solution  120 . 
         [0053]    Method of Manufacturing PCB having Flow Preventing Dam 
         [0054]      FIGS. 6 to 13  are cross-sectional views showing the process of manufacturing the PCB having a flow preventing dam according to the preferred embodiment of the present invention. 
         [0055]    With reference to  FIGS. 6 to 13 , the method of manufacturing the PCB having a flow preventing dam according to the present invention is described below. 
         [0056]    As shown in  FIG. 6 , a dry film resist  110  is applied on the baser substrate  102  having solder pads  104 . 
         [0057]    The base substrate  102  is configured such that the solder pads  104  are formed on one surface thereof and the solder resist layer  106  having openings  108  for exposing the solder pads  104  is formed on the base substrate  102 . 
         [0058]    The dry film resist  110  includes a photoresist in a film form, a mylar film formed on one surface of the photoresist to impart flexibility thereto, and a cover film formed on the other surface thereof. 
         [0059]    The dry film resist  110  is applied in a state of peeling off the cover film using a typical dry film laminating apparatus. 
         [0060]    The dry film resist  110  may be formed to a predetermined thickness in consideration of the size of the solder bumps  116  and the height of the flow preventing dam  110   c.    
         [0061]    Next, as shown in  FIG. 7 , the portion of the dry film resist  110 , other than the portion of the dry film resist  110  applied on the solder pads  104 , is subjected to a primary exposure process. 
         [0062]    The primary exposure process is performed by exposing the portion of the dry film resist  110 , other than the portion thereof applied on the solder pads  104 , to UV light, using a mask (not shown) having a predetermined pattern. 
         [0063]    The primarily exposed dry film resist  110   b , other than the unexposed dry film resist  110   a  applied on the solder pads  104 , is cured through polymerization in the primary exposure process. 
         [0064]    Next, as shown in  FIG. 8 , the primarily exposed dry film resist  110   a  formed on the peripheral area of the base substrate  102  is subjected to a secondary exposure process, thus forming the flow preventing dam  110   c.    
         [0065]    As such, the secondarily exposed dry film resist, which forms the flow preventing dam  110   c , is overcured through excessive exposure and is thus more firmly attached to the solder resist layer  106 . Accordingly, the dam is not removed in a subsequent dry film resist stripping process. 
         [0066]    Next, as shown in  FIG. 9 , the unexposed dry film resist  110   a  is removed through a development process to expose the solder pads  104 , thus forming openings  112 . 
         [0067]    The development process is performed by dissolving and removing the uncured portion other than the cured portion due to UV exposure, and thus the unexposed dry film resist  110   a  is removed using a developer such as sodium carbonate (Na2CO3) or potassium carbonate (K2CO3). 
         [0068]    Next, as shown in  FIG. 10 , the openings  112  are printed with a solder paste. 
         [0069]    The solder paste  114  is printed through a screen printing in a manner such that the base substrate  102  is disposed on a printing table, a mask having a plurality of openings is placed on the base substrate, and the solder paste is pressed into the openings of the mask using a squeegee. 
         [0070]    Next, as shown in  FIG. 11 , the printed solder paste  114  is subjected to a reflow process, thus forming solder bumps  116 . 
         [0071]    The solder paste  114  printed in the openings  112  of the dry film resist  110  is formed in a round shape through a reflow process to be lower than the flow preventing dam  110   c . In the case where the semiconductor chip  118  is mounted on the solder bumps  116 , the gap G between the base substrate  102  and the semiconductor chip  118  is lower than the flow preventing dam  110   c , and therefore the flow preventing dam  110   c  can prevent the outflow of the underfill solution which is introduced into the gap G. 
         [0072]    As shown in  FIG. 12 , the primarily exposed dry film resist  110   b  is removed. 
         [0073]    The primarily exposed dry film resist  110   b  may be stripped using a stripping solution such as NaOH or KOH. 
         [0074]    In the course of bonding the OH— of the stripping solution with the carboxyl group (COOH+) of the dry film resist, the primarily exposed dry film resist  110   b  gets loose and thus is stripped. Because the secondarily exposed dry film resist, namely, the flow preventing dam  110   c , is attached in a state of being overcured through excessive exposure to the solder resist layer  106 , it is not removed by the stripping solution. 
         [0075]    As shown in  FIG. 13 , the semiconductor chip  118  is flip chip mounted on the base substrate  102  by means of the solder bumps  116 , and the underfill solution  120  is introduced into the gap G between the base substrate  102  and the semiconductor chip  118 , thus completing a flip chip package. 
         [0076]    The flow preventing dam  110   c  is provided to protrude from the base substrate along the outer edge of the semiconductor chip  118 , and is formed to be higher than the gap between the base substrate  102  and the semiconductor chip  118  and to be lower than the upper surface of the semiconductor chip  118 , thereby preventing the outflow of the underfill solution. 
         [0077]    As described hereinbefore, the present invention provides a PCB having a flow preventing dam and a manufacturing method thereof. According to the present invention, the flow preventing dam is provided, thus preventing the expansion and outflow of an underfill solution. 
         [0078]    Also, according to the present invention, the flow preventing dam is formed through excessive exposure of a dry film resist used in the course of forming solder bumps, thus obviating a need for additional material, apparatus, and process. 
         [0079]    Also, according to the present invention, the flow preventing dam can be formed with the dry film resist, and thus the height and width thereof are uniform. 
         [0080]    Also, according to the present invention, the outflow of the underfill solution is prevented, thus improving the overall package reliability. 
         [0081]    Although the preferred embodiment of the present invention regarding the PCB having a flow preventing dam and the manufacturing method thereof has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible within the scope of the invention.