Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2009-0041646 filed on May 13, 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 bump printing apparatus, and more particularly, to a bump printing apparatus that can increase the printability of solder bumps being printed on a printed circuit board. 
     2. Description of the Related Art 
     In general, flip chip bonding, tape automated bonding and wire bonding are being used to interconnect external boards, such as printed circuit boards (PCBs) or wafer level packages (WLPs), to chips. 
     Among them, flip chip bonding has been widely used to manufacture portable electronic products since this method increases the number of pads per unit area. 
     According to flip chip bonding, solder bumps are formed on a wafer in order to appropriately bond chips and external circuitry. Particularly, a technique for manufacturing solder bumps has been developed to form solder bumps having appropriate conductivity, uniform lengths and fine pitches. 
     According to this solder bump forming technique for flip chip bonding, the characteristics of solder bumps and an application range thereof are determined according to the materials used to form solder bumps. Examples of the solder bump forming technique may include a soldering method of contacting pad electrodes to solder, a screen printing method of forming solder bumps on pad electrodes by screen printing and reflowing the solder bumps, a solder ball reflow method of mounting solder balls onto pad electrodes and reflowing the mounted solder balls, and a plating method of performing solder plating on pad electrodes. 
     Among them, a screen printing method has been widely used to form solder bumps in that the process of forming solder bumps in this manner is simple, manufacturing costs are low, and bumps of desired metallic material can be formed. 
     Solder bumps are printed according to this screen printing method by which, while a (metal) mask having holes arranged into a predetermined pattern makes close contact with a printed circuit board, a solder paste is compressed and moved across the upper surface of the mask to thereby fill the holes. 
     However, according to the current screen printing method, since the mask is merely placed onto and makes close contact with the upper surface of the printed circuit board, gaps may be generated between the board and the mask. 
     These gaps mostly occur around the edges of the board in surface contact with the mask, where printing defects, such as the spreading of the solder paste, short circuits and missing bumps, in which bumps are not formed, occur in large quantities. 
     As a result, the printability of the solder bumps is reduced to thereby cause a deterioration in product quality and a reduction in the reliability of a circuit board. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a bump printing apparatus that can improve the printability of solder bumps by preventing printing defects and increase the reliability of a board by preventing defects in solder bumps. 
     According to an aspect of the present invention, there is provided a bump printing apparatus including: a printing table onto which a board is mounted; a mask making close contact with the board and printing solder bumps on the board; and mask tables extending from the printing table to edges of the mask and sucking the edges of the mask to bring the edges of the mask into close contact with the board under vacuum. 
     The bump printing apparatus may further include air nozzles provided within the printing table and the mask tables, providing air suction so that the board and the mask make close contact with the printing table and the mask tables, respectively, and spraying air so that the mask is separated from the board. 
     The mask tables may extend towards outer surfaces of the printing table and be formed integrally with the printing table. 
     The mask tables may be detachably provided on the outer surfaces of the printing table. 
     An upper surface of the mask table may be located on the same horizontal plane as an upper surface of the board. 
     The mask tables may face each other on the basis of the printing table and protrude to a height corresponding to a thickness of the board so that a step is formed between the printing table and each of the mask tables. 
     The air nozzles may include: a plurality of board nozzles arranged along the upper surface of the printing table and providing air suction to bring the board into close contact with the printing table; and a plurality of mask nozzles arranged along upper surfaces of the mask tables, providing air suction to bring the mask into close contact with the board and the mask tables, and spraying air to separate the mask from the board. 
     The plurality of mask nozzles may be arranged along the upper surfaces of the mask tables and the printing table. 
     The board may have air holes formed therethrough so that air being sprayed through the air nozzles passes through the board and moves upward from the board. 
     The bump printing apparatus may further include a control unit controlling the air nozzles. 
    
    
     
       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. 1A  is a perspective view schematically illustrating a bump printing apparatus according to an exemplary embodiment of the present invention; 
         FIG. 1B  is a cross-sectional view schematically illustrating the bump printing apparatus shown in  FIG. 1A ; 
         FIG. 2A  is a cross-sectional view schematically illustrating an example of mask tables and a printing table of the bump printing apparatus, shown in  FIGS. 1A and 1B ; 
         FIG. 2B  is a cross-sectional view schematically illustrating another example of mask tables and a printing table of the bump printing apparatus, shown in  FIGS. 1A and 1B ; 
         FIG. 3A  is a plan view schematically illustrating an example of mask tables from the mask tables and the printing table, shown in  FIGS. 1A and 1B ; 
         FIG. 3B  is a plan view schematically illustrating another example of mask tables from the mask tables and the printing table, shown in  FIGS. 1A and 1B ; 
         FIG. 4A  is a cross-sectional view schematically illustrating an example of board nozzles and mask nozzles of the mask tables and the printing table, shown in  FIGS. 1A and 1B ; 
         FIG. 4B  is a cross-sectional view schematically illustrating another example of board nozzles and mask nozzles of the mask tables and the printing table, shown in  FIGS. 1A and 1B ; 
         FIG. 5A  is a plan view illustrating a state in which a board is placed onto the mask tables and the printing table, shown in  FIG. 3A ; 
         FIG. 5B  is an enlarged cross-sectional view taken along the line y-y of  FIG. 5A ; 
         FIG. 6  is a plan view illustrating a state in which a board is placed onto the mask tables and the printing table, shown in  FIG. 3B ; and 
         FIGS. 7A through 7D  are schematic views illustrating a solder bump printing process using a bump printing apparatus according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 1A  is a perspective view schematically illustrating a bump printing apparatus according to an exemplary embodiment of the present invention.  FIG. 1B  is a cross-sectional view schematically illustrating the bump printing apparatus shown in  FIG. 1A .  FIG. 2A  is a cross-sectional view schematically illustrating an example of mask tables and a printing table of the bump printing apparatus, shown in  FIGS. 1A and 1B .  FIG. 2B  is a cross-sectional view schematically illustrating another example of mask tables and a printing table of the bump printing apparatus, shown in  FIGS. 1A and 1B .  FIG. 3A  is a plan view schematically illustrating an example of mask tables from the mask tables and the printing table, shown in  FIGS. 1A and 1B .  FIG. 3B  is a plan view schematically illustrating another example of mask tables from the mask tables and the printing table, shown in  FIGS. 1A and 1B .  FIG. 4A  is a cross-sectional view schematically illustrating an example of board nozzles and mask nozzles of the mask tables and the printing table, shown in  FIGS. 1A and 1B .  FIG. 4B  is a cross-sectional view schematically illustrating another example of board nozzles and mask nozzles of the mask tables and the printing table, shown in  FIGS. 1A and 1B . 
       FIG. 5A  is a plan view illustrating a state in which a board is placed onto the mask tables and the printing table, shown in  FIG. 3A .  FIG. 5B  is an enlarged cross-sectional view taken along the line y-y of  FIG. 5A .  FIG. 6  is a plan view illustrating a state in which a board is placed onto the mask tables and the printing table, shown in  FIG. 3B . 
     Referring to  FIGS. 1 through 6 , a bump printing apparatus  1  according to this embodiment includes a printing table  10 , a mask  20 , mask tables  30  and air nozzles  40 . 
     The printing table  10  is a jig member that is used to secure a board b to be mounted onto an upper surface thereof so as to perform screen printing to print solder bumps  70 . 
     As shown in  FIGS. 1A and 1B  through  6 A and  6 B, the printing table  10  generally has a rectangular shape corresponding to a shape of the board b. However, the present invention is not limited thereto. 
     As for the board b, general boards, such as a ceramic board and a printed circuit board (PCB), formed of resin materials, including rigid and flexible PCBs, may be used. 
     Here, a plurality of air holes h are formed through the board b so that air being sprayed through the air nozzles  40  passes through the board b and moves upward from the board b. 
     The air holes h are formed so that air being sprayed from the printing table  10  separates the mask  20  in close contact with the board b without being interrupted by the board b. A detailed description of the air holes h will be described in detail below. 
     The mask  20  is provided on an upper surface of the board b that is mounted on the printing table  10 . The mask  20  has pattern holes  21 , arranged in a predetermined pattern, and is supported by a jig  22 . 
     The mask  20  makes close contact with and is secured to the upper surface of the board b. After a solder paste p is compressed and moved using a squeegee s in order to print the solder bumps  70 , the mask  20  is separated from the board b again to thereby form the solder bumps  70  on the board b. 
     At this time, as a vacuum is substantially created between the mask  20  and the board b, the mask  20  and board b are not misaligned during a screen printing process to thereby accurately print the solder bumps  70  at design positions. 
     The mask  20  may be a general metal mask. However, the present invention is not limited thereto. A mask of another material may be provided as the mask  20 . 
     The mask tables  30  extend from the printing table  10  to the edges of the mask  20  and suck the edges of the mask  20  to bring the edges of the mask  20  into close contact with the board b under vacuum. 
     That is, the mask  20  for screen printing has a larger size than the printing table  10 . When the mask  20  makes close contact with the printing table  10  onto which the board b is mounted, the edges of the mask  20  are placed outside the printing table  10 . 
     In this case, since the mask  20  cannot maintain a horizontal state, gaps occur between the mask  20  and the board b. 
     Therefore, the edges of the mask  20  are supported using the mask tables  30  so that the mask  20  makes close contact with the board b while maintaining the horizontal state to prevent the generation of gaps between the board b and the mask  20 . 
     In particular, the mask tables  30  include a plurality of mask nozzles  42  and  44  and suck the edges of the mask  20  to bring the edges of the mask  20  into close contact with the board b under vacuum. This Will be described in detail below. 
     As shown in  FIG. 2A , the mask tables  30  may extend toward the outside of the printing table  10  by die-casting or cutting and be formed integrally with the printing table  10 . 
     Alternatively, as shown in  FIG. 2B , the mask tables  30  may be detachably mounted on the outside of the printing table  10 . 
     Here, as the mask tables  30 , provided separate from the printing table  10 , are attached to and detached from the outside of the printing table  10 , the mask tables  30  can be replaced according to the size and thickness of the mask  20  or the board b. 
     Furthermore, repairs and maintenance thereof are facilitated. 
     The mask tables  30  face each other on the basis of the printing table  10 . The mask tables  30  each protrude to a height h corresponding to a thickness t of the board b so that a step is formed between each of the mask tables  30  and the printing table  10 . 
     That is, as shown in  FIG. 3A , one pair of mask tables  30  are arranged on both left and right surfaces of the printing table  10  and face each other. 
     As shown in  FIG. 3B , two pairs of mask tables  30  are arranged along four edges of the printing table  10  to thereby surround the printing table  10 . Here, the height h of the step corresponding to a difference in height between the mask table  30  and the printing table  10  is substantially the same as the thickness t of the board b. 
     Therefore, an upper surface of the mask table  30  is located on the same horizontal plane as the upper surface of the board b that is mounted onto the printing table  10 . 
     Therefore, the mask  20 , placed on the board b and the mask table  30 , may maintain the horizontal state without sag and make close contact with the board b. 
     Meanwhile, the air nozzles  40  are provided within the printing table  10  and the mask table  30 , provide air suction such that the board b and the mask  20  make close contact with the printing table  10  and the mask table  30 , respectively, and spray air to separate the mask  20  from the board b. 
     As shown in  FIG. 4A , the air nozzles  40  include board nozzles  41  and the mask nozzles  42  and  44 . The board nozzles  41  provide air suction so that the board b makes close contact with the printing table  10 . The mask nozzles  42  and  44  provide air suction so that the mask  20  makes close contact with the board b and the mask tables  30 , and spray air so that mask  20  is separated from the board b. 
     The plurality of board nozzles  41  are arranged along the upper surface of the printing table  10  and provide air suction at constant pressure to thereby secure the board b to be mounted on the upper surface of the printing table  10  by vacuum suction. 
     The plurality of mask nozzles  42  and  44  are arranged along the upper surfaces of the printing table  10  and the mask tables  30 , respectively, and provide air suction at constant pressure to secure the mask  20  to the upper surfaces of the board b and the mask tables  30 . 
     Therefore, the mask  20 , which maintains the horizontal state with the use of the mask tables  30 , makes close contact with the board b by air suction of the mask nozzles  42  and  44 , thereby preventing the generation of gaps between the mask  20  and the board b. 
     Further, the mask nozzles  42  and  44  spray air between the mask  20  and the board b and generate air pressure between the mask  20  and the board b in close contact under vacuum to thereby separate the mask  20  and the board b from each other. 
     In particular, the mask nozzles  42  and  44  spray air while adjusting the pressure of air being sprayed so that the mask  20  can be separated from the board b while maintaining the horizontal state. 
     That is, while printing the solder bumps  70 , like the board nozzles  41 , the mask nozzles  42  and  44  provide air suction so that the mask  20  makes close contact with the upper surface of the board b. To separate the board b and the mask  20  from each other when finishing the printing process, the mask  20  is not forcibly separated like the related art, although the mask  20  sags, but the mask  20  is separated from the board b while maintaining the horizontal state by air pressure caused by air blowing, so that the solder paste p can be easily withdrawn from the pattern holes to thereby form the solder bumps  70 . 
     As shown in  FIG. 4B , the plurality of mask nozzles  44  may be arranged along the upper surfaces of the mask tables  30  alone. In this case, the mask nozzles have a simplified configuration, thereby facilitating the manufacture of the mask tables  30  and the printing table  10   
     The board nozzles  41  and the mask nozzles  42  and  44  are connected to pipes  47  and  48 , respectively, which do not communicate with each other and separately guide the flow of air. The pipes  47  and  48  are connected to air pumps  51  and  52 , respectively, which are provided outside the printing table  10 . 
     The air pumps  51  and  52  are controlled independently of each other so that air suction through the board nozzles  41  and air suction and spraying through the mask nozzles  42  and  44  are performed independently of each other. 
     The air nozzles  40 , which are controlled according to the driving operation of the air pumps  51  and  52 , can be more accurately controlled by a control unit  60  that is separately provided. 
     A solder bump printing process using a bump printing apparatus according to an exemplary embodiment of the present invention will now be described in detail with reference to  FIG. 7 . 
       FIGS. 7A through 7D  are schematic views illustrating a sold bump printing process using a bump printing apparatus according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 7A , the board b for printing the solder bumps  70  is placed on the upper surface of the printing table  10  having the printing board nozzles  41  and the mask nozzles  42  and  44  therein. 
     The plurality of air holes h are formed through the board b. Therefore, when the board b is placed on the printing table  10 , the board b is arranged so that the air holes h and the mask nozzles  42  overlap and communicate with each other. 
     The air pump  51 , connected to the board nozzles  41 , is then operated to provide air suction through the board nozzles  41  so that the board b is secured to the printing table  10  by vacuum suction. 
     Then, as shown in  FIG. 7B , the mask  20 , which has the pattern holes  21  arranged in the predetermined pattern and is supported by the jig  22 , is brought into close contact with the board b. 
     Here, the air pump  52 , connected to the mask nozzles  42  and  44 , is operated to provide air suction so that the mask  20  in close contact with the board b is subject to vacuum suction while maintaining the horizontal state. 
     As such, by compressing and moving the solder paste p across the upper surface of the mask  20  using the squeegee s while the board b and the mask  20  are in surface contact with each other, the solder paste p fills in the pattern holes  21  of the mask  20  to perform a printing process. 
     After the printing process is completed, as shown in  FIG. 7C , the air pump  52 , connected to the mask nozzles  42  and  44 , is reversely operated to spray air through the mask nozzles  42  and  44  so that the mask  20  and the board b are separated from each other. 
     Here, since the mask nozzles  42  communicate with the air holes h of the board b, air, sprayed through the mask nozzles  42 , may pass through the air holes h and move towards the upper surface of the board b. 
     Therefore, air pressure causing separation of the mask  20  and the board b from each other is generated by air being introduced between the board b and the mask  20 . 
     Here, the board nozzles  41  continuously provide air suction to keep the board b secured to the printing table  10 . 
     Then, as shown in  FIG. 7D , after the mask  20  is separated from the board b, the spraying of air through the mask nozzles  42  and  44  is terminated, and air suction through the board nozzles  41  is terminated, so that the board b is removed from the printing table  10 . 
     A new board b is arranged on the printing table  10 , and a printing process continues to be performed on the board b. 
     The air pumps  51  and  52 , connected to the board nozzles  41  and the mask nozzles  42  and  44 , respectively, may be controlled independently of each other by the control unit  60 . In particular, the control unit  60  controls the pressure of air sprayed through the mask nozzles  42  and  44  so as to maintain the horizontal state of the mask  20 . 
     Therefore, elaborate management to separate the sagging mask  20  from the board in the related art is unnecessary. 
     As such, while the mask  20  can maintain the horizontal state with the use of the mask tables  30 , the mask  20  makes close contact with the board b by air pressure caused by air suction of the mask nozzles  42  and  44 , thereby effectively preventing the generation of gaps between the mask  20  and the board b. 
     Furthermore, the mask  20  is separated from the board b by air pressure caused by air blowing of the mask nozzles  42  and  44  while the mask  20  maintains the horizontal state, so that the solder paste can be easily withdrawn from the pattern holes to easily print the solder bumps  70 . 
     Therefore, defects of the solder bumps  70  can be effectively prevented to increase printability and yield, which may increase the reliability of the board b. 
     As set forth above, according to exemplary embodiments of the present invention, the bump printing apparatus effectively prevents defects of solder bumps to increase printability and yield, thereby increasing the reliability of a board. 
     Furthermore, apparatus productivity is improved, and application and process management are facilitated because of a simplified configuration thereof. 
     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 present invention as defined by the appended claims.

Technology Category: b