Abstract:
Provided is a method and apparatus for mounting a plurality of electronic components. The method comprises mounting a first electronic component on a substrate; forming a mask on the substrate to expose the first electronic component and a region of the substrate on which a solder paste is to be applied; forming a guide on a portion of the mask disposed around the first electronic component; applying the solder paste onto the substrate by using a squeezer contacting a portion of the mask disposed around the region of the substrate on which the solder paste is to be applied; removing the guide and the mask; and mounting a second electronic component on the solder paste.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2007-0129010, filed on Dec. 12, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for mounting electronic components on a substrate. 
     2. Background 
     There are various kinds of electronic products, such as a digital camera, a cellular phone, a personal digital assistant (PDA), an MP3 player, and a personal multimedia player, on the market. Such electronic products are becoming more miniaturized for portability. Accordingly, more electronic components, such as semiconductor devices, should be mounted within a smaller area in the electronic products. 
     A conventional method of mounting electronic components includes printing a solder paste onto a substrate, mounting the electronic components on the solder paste, and reflow-soldering the electronic components. 
     Among the electronic components mounted on the substrate, there may be some exceptional electronic components having reliability under low temperature limits. Although conventional electronic components can withstand a temperature of about 260° C., some exceptional electronic components can withstand a temperature of just about 200° C. In order to mount the exceptional electronic components with the other electronic components on the same substrate, according to the conventional method, the exceptional electronic components have to be manually soldered on the substrate. 
     Another conventional method of mounting electronic components includes printing a first solder paste, mounting first electronic components, forming a mask covering the first mounted electronic components, printing a second solder paste by using the mask, and mounting second electronic components. However, if the first electronic components are thick, it is difficult to form the mask covering the thick first electronic components, and it is also very difficult to move a squeezer when applying the second solder paste. 
     Another conventional method includes mounting electronic components having reliability under different temperature limits on different substrates. However, this approach goes against the trend toward minimizing electronic products. 
     SUMMARY 
     The embodiments of the present invention provide a method and apparatus for mounting at least two types of electronic components, having reliability under different temperature limits, on the same substrate while minimizing damage, such as a crack in the electronic components. 
     According to an aspect of the present invention, there is provided a method of mounting at least two types of electronic components, the method comprising: preparing a substrate on which a first electronic component is mounted; forming a mask on the substrate to expose the first electronic component and a region of the substrate on which a solder paste is to be applied; forming a guide on a portion of the mask disposed around the first electronic component; applying the solder paste onto the substrate by using a squeezer contacting a portion of the mask disposed around the region of the substrate on which the solder paste is to be applied; removing the guide and the mask; and mounting a second electronic component on the solder paste. 
     The guide may be formed on the portion of the mask disposed around the first electronic component so as to prevent the solder paste from being introduced into the first electronic component. 
     Alternatively, the guide may be formed on a portion of the mask disposed between the first electronic component and the region of the substrate on which the solder paste is to be applied. 
     Furthermore, the guide may be formed on a portion of the mask between an opening through which the first electronic component is exposed and an opening through which the region of the substrate on which the solder paste is to be applied is exposed. 
     The guide may be further formed on an edge between the mask and the opening through which the first electronic component is exposed. 
     The solder paste may be applied by using the squeezer having at least one concave portion that accommodates the first electronic component and the guide. The solder paste may be applied by using the squeezer having a concave portion that accommodates both the first electronic component and the guide. 
     According to another aspect of the present invention, there is provided a method of mounting at least two kinds of electronic components, the method comprising: forming a first mask on a substrate to expose a region of the substrate on which a first solder paste is to be applied; applying the first solder paste onto the substrate by using a first squeezer; removing the first mask; mounting a first electronic component on the first solder paste; forming a second mask on the substrate on which the first electronic component is mounted to expose the first electronic component and a region of the substrate on which a second solder paste is to be applied; forming a guide on a portion of the second mask disposed around the first electronic component; applying the second solder paste onto the substrate by using a second squeezer having at least one concave portion that accommodates the first electronic component and the guide; removing the second mask and the guide; and mounting a second electronic component on the second solder paste. 
     The mounting of the first electronic component may comprise positioning the first electronic component on the first solder paste and applying heat at a first temperature, and the mounting of the second electronic component may comprise positioning the second electronic component on the second solder paste and applying heat at a second temperature that is different from the first temperature. The first temperature may be higher than the second temperature. 
     The applying of the first solder paste may comprise applying the first solder paste by using the first squeezer contacting a portion of the first mask disposed around the region of the substrate on which the first solder paste is to be applied, and the applying of the second solder paste may comprise applying the second solder paste by using the second squeezer contacting a portion of the second mask disposed around the region of the substrate on which the second solder paste is to be applied. 
     The first solder paste may be applied by using the first squeezer having no concave portion, and the second solder paste may be applied by using the second squeezer having a concave portion that accommodates the first electronic component and the guide. 
     According to another aspect of the present invention, there is provided an apparatus for mounting at least two types of electronic components, the apparatus comprising: a substrate on which a first electronic component is mounted; a mask formed on the substrate to expose the first electronic component and a region of the substrate on which a solder paste is to be applied; a guide formed on a portion of the mask disposed around the first electronic component; and a squeezer contacting a portion of the mask disposed around the region of the substrate on which the solder paste is to be applied. 
     The guide may be formed on a portion of the mask between an opening through which the first electronic component is exposed and an opening through which the region of the substrate on which the solder paste is to be applied is exposed. 
     The squeezer may have at least one concave portion that accommodates the first electronic component and the guide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a cross-sectional view showing a first mask forming on a substrate according to an exemplary embodiment. 
         FIG. 2-3  are cross-sectional views showing a first solder paste being applied to a substrate according to an exemplary embodiment. 
         FIGS. 4-5  are cross-sectional views showing a first electronic component being mounted according to an exemplary embodiment. 
         FIG. 6  is a cross-sectional view showing a second mask forming on a substrate according to an exemplary embodiment. 
         FIG. 7  is a top view showing a guide on a substrate according to an exemplary embodiment. 
         FIGS. 8-9  are cross-sectional views showing a second solder paste being applied to a substrate according to an exemplary embodiment. 
         FIGS. 10-11  are cross-sectional views showing a second electronic component being mounted according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. 
       FIGS. 1 through 11  are cross-sectional views and a plan view for explaining a method of mounting at least two types of electronic components, according to an embodiment of the present invention. The method of mounting of  FIGS. 1 through 11  involves a surface mount packaging technology in which electronic components, are mounted on the same substrate by using at least two types of solder pastes. 
     In  FIGS. 1 through 11 , a first electronic component has a first temperature limit and a second electronic component has a second temperature limit that is lower than the first temperature limit. For example, the first electronic component includes a tall first electronic component and a short first electronic component that can be mounted irrespective of their heights. 
     Referring to  FIG. 1 , a first mask  20  is formed on a substrate  10  to expose a region of the substrate  10  to which a first solder paste is to be applied. 
     The substrate  10  may be a printed circuit board (PCB) that is formed by printing a circuit line pattern, formed of a conductive material, such as copper, onto an insulating substrate. A PCB refers to a circuit board that positions electronic components and fixedly prints circuit lines connecting the electronic components onto a surface in order to densely mount the electronic components on the surface. 
     The substrate  10  may be a single-layer PCB, or a multi-layer PCB, i.e., a build-up PCB, in which a plurality of PCB layers are stacked. The multi-layer PCB can increase yield and achieve high density and minimization by precisely connecting wires between the PCB layers. Accordingly, the multi-layer PCB can be used in a cellular phone, a camera, a notebook computer, and the like, which require high integration and thin design. 
     The substrate  10  may be a through-hole PCB. Any PCB applicable to a surface mount packaging technology can be used. 
     As described above, the region of the substrate  10  on which the first solder paste is to be applied is determined, and the first mask  20 , exposing the region of the substrate  10  on which the first solder paste is to be applied, is aligned on the substrate  10  on which a conductive circuit line pattern is formed. The first mask  20  has a first opening  12  through which the region of the substrate  10  on which the first solder paste is to be applied is exposed. The first mask  20  may be a thin metal plate such as a stainless steel printing plate. 
     Referring to  FIG. 2 , a first solder paste  30  is applied to the substrate  10  on which the first mask  20  is aligned by moving a first squeezer  40  in a y-direction, such that the first solder paste  30  is introduced into the first opening  12  of the first mask  20 . To this end, the first squeezer  40  must contact a portion of the first mask  20 , which is around the region of the substrate  10  in which the first solder paste  30  is to be applied. Accordingly, the first solder paste  30  can be forced into the first opening  12  due to a predetermined pressure occurring when the first squeezer  40  is moved as the first squeezer  40  is applied. 
     Referring to  FIG. 3 , the first solder paste  30  is forced into the first opening  12  by moving the first squeezer  40  in the y-direction. In detail, the first solder paste  30  is formed by continuously mixing solid alloy particles with a liquid flux. Accordingly, as the first squeezer  40  is moved on the first mask  20  in the y-direction, the first solder paste  30  is pushed into the first opening  12  to fill the first opening  12 . 
     After the first solder paste  30  is filled into the first opening  12 , the first mask  20  is removed. Referring to  FIG. 4 , a short first electronic component  50   a  and a tall first electronic component  50   b  are positioned on the first solder paste  30  to form a first electronic component  50 . 
     Referring to  FIG. 5 , the substrate  10 , on which the first electronic component  50  is mounted, is subjected to a reflow process in an oven, such that the first solder paste  30  melts down and the first electronic component  50  is adhered to the substrate  10 . A heat treatment temperature during the reflow process should be higher than a melting temperature, that is, a soldering temperature, of the first solder paste  30 , and should be lower than a temperature that the first electronic component  50  can withstand. Accordingly, an upper limit of the heat treatment temperature should be determined by considering temperature limits under which the first electronic component  50  has reliability. 
     Referring to  FIG. 6 , a second mask  22  and guides  60  are sequentially formed on the substrate  10  on which the first electronic component  50  is mounted. 
     The second mask  22  formed on the substrate  10  includes a second opening  14  through which the first electronic component  50  is exposed and a third opening  16  through which a region of the substrate  10 , on which a second solder paste  32  of  FIG. 8  is to be applied, is exposed. The second mask  22  may be a thin metal layer like the first mask  20 . 
     The guide  60 , formed on the second mask  22  barriers an introduction of the second solder paste into the first electronic component  50 . The guide  60  is positioned on a portion of the second mask  22 , which is between the first electronic component  50  and the region of the substrate  10  on which the second solder paste  32  is to be applied. Alternatively, the guide  60  may be formed on a portion of the second mask  22 , which is between the second opening  14  through which the first electronic component  50  is exposed and the third opening  16  through which the region of the substrate  10  on which the second solder paste  32  is to be applied is exposed. 
     Preferably, as in the present embodiment, the guide  60  may be further formed on an edge between the second mask  22  and the second opening  14  through which the first electronic component  50  is exposed. In detail,  FIG. 7  is a top view of the substrate  10  on which the guide  60  is positioned. Referring to  FIG. 7 , the second mask  22  including the second openings  14  and the third openings  16  positioned on the substrate  10 , and the guide  60  is positioned between the second opening  14  and the third opening  16 . For example, the guide  60  may be positioned on a portion of the second mask  22  between the second mask  22  and the second opening  14 . The guide  60  may be further formed on an edge between the second mask  22  and the second opening  14 . In order to reinforce the barrier function of the guide  60  to barrier an introduction of the second solder paste  32  into the first electronic component  50 , the guide  60  may correspondingly surround at least one surface of the first electronic component  50 . 
       FIG. 8  is a cross-sectional view taken along an X-axis and  FIG. 9  is a cross-sectional view taken along a Y-axis, illustrating that the second solder paste  32  is applied to the substrate  10 . 
     Referring to  FIGS. 8 and 9 , the second solder paste  32  is applied to the substrate  10  on which the second mask  22  and the guide  60  are sequentially formed. The second solder paste  32  applied to the substrate  10  is forced into the third opening  16  by a second squeezer  42 . 
     The second squeezer  42  may not contact the guide  60  and a portion of the second mask  22 , which is around the second opening  14  through which the first electronic component  50  is exposed, but may contact a portion of the second mask  22 , which is around the third opening  16 . To this end, the second squeezer  42  may have at least one concave portion  44  that accommodates the first electronic component  50  and the guide  60 . Alternatively, the second squeezer  42  may have concave portions  44 , respectively accommodating the first electronic component  50  and the guide  60 , or one concave portion  44  that accommodates both the first electronic component  50  and the guide  60 . 
     The second solder paste  32  may have a melting temperature, that is, a soldering temperature, which is different from that of the first solder paste  30 . For example, the first solder paste  30  may allow soldering at a relatively high temperature whereas the second solder paste  32  may allow soldering at a relatively low temperature. For example, if temperature limits under which the first electronic component  50  and a second electronic component  52  have reliabilities that are different from each other, the first electronic component  50  having a higher temperature limit may be soldered with the first solder paste  30 , and the second electronic component  52  having a lower temperature limit may be soldered with the second solder paste  32 . Accordingly, the first electronic component  50  and the second electronic component  52  having reliabilities under different temperature limits can be mounted on the same substrate while minimizing damage to the first electronic component  50  and the second electronic component  52 . 
     Since a soldering temperature of a solder paste varies depending on elements, composition ratios, additives, and so on, a solder paste suitable for each electronic component is determined by considering a reliable temperature range, cost, environmental impact, etc. 
     Referring to  FIG. 10 , after the second solder paste  32  is applied, the guide  60  and the second mask  22  are removed. Hence, the second electronic component  52  is positioned on the second solder paste  32 . 
     Referring to  FIG. 11 , the substrate  10  on which the second electronic component  52  is positioned is subjected to a reflow process in an oven, such that the second electronic component  52  is adhered onto the substrate  10 . Thus, a heat treatment temperature during the reflow process for the second electronic component  52  may be lower than that during the reflow process for the first electronic component  50 . 
     For example, if the first electronic component  50  can withstand a temperature of about 260° C. whereas the second electronic component  52  can withstand a temperature of about 200° C., the first solder paste  30  which is less expensive and has higher adhesive strength than the second solder paste  32  may be used for the first electronic component  50 . If the second electronic component  52  is soldered with the first solder paste  30 , the second electronic component  52  may not withstand a heat treatment during a reflow process and thus may be damaged. Accordingly, the second solder paste  32  having a lower melting temperature may be used for the second electronic component  52 . For example, the first electronic component  50 , which can withstand a higher temperature, is soldered and then the second electronic component  52 , which can withstand a lower temperature, is soldered with the suitable solder pastes, and thus, both the first electronic component  50  and the second electronic component  52  can prevent damage such as a crack due to the heat treatment temperatures during the reflow processes. 
     As described above, the method and apparatus for mounting at least two types of electronic components according to the present invention can improve packaging reliability by applying two types of solder pastes having different melting temperatures on desired regions of the same substrate and mounting electronic components, having reliabilities under different temperature limits, while minimizing damage to the electronic components, irrespective of the heights of the electronic components. 
     Moreover, the method and apparatus for mounting at least two types of electronic components on the same substrate according to the present invention is suitable for electronic components, such as a digital camera, a cellular phone, a personal digital assistant (PDA), an MP3 player, and a portable multimedia player (PMP), which are being increasingly minimized. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.