Abstract:
A stencil for printing solder paste on a printed circuit board improves an assembly process, cuts production costs, and saves storage space. The stencil is coupled to a fixing frame having a plurality of fixing portions and a motor unit. The motor unit generates a plurality of pulling forces. The stencil includes a solder paste printing region and a plurality of fixing regions. Vias are disposed in the solder paste printing region. The directions of the pulling forces are coplanar with the solder paste printing region. The edge of the solder paste printing region extends outward to define the fixing regions. The fixing regions are movably fixed to the fixing portions and bear the pulling forces to flatten the solder paste printing region of the stencil.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 100133342 filed in Taiwan, R.O.C. on Sep. 16, 2011, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The present invention is related to stencils, particularly to a stencil for printing solder paste on a printed circuit board. 
       BACKGROUND 
       [0003]      FIGS. 1 and 2  are a disassembled diagram and an assembled diagram, respectively, of a conventional assembled solder paste printing structure for printing solder paste on a printed circuit board. As illustrated in these figures, printing solder paste on the printed circuit board presently is, generally, necessary to use the conventional assembled solder paste printing structure  9  comprising a fixing frame  91 , a hollowed-out rectangular stretching net  92  and a steel plate  93 . The steel plate  93  is rectangular and has a rectangular solder paste printing region  931  and a fixing region  932 . The solder paste printing region  931  is surrounded, on its four sides, by the fixing region  932 , and provided with a plurality of vias  9311  for providing solder paste. The fixing region  932  is used to be stuck to inner edges of four sides of the stretching net  92 , in such a way that outer edges of four sides of the stretching net  92  may be applied with equal pulling forces to tension outwardly to flatten the steel plate  93 , and then clampingly fixed in clamping slots  911  on at four sides of the fixing frame  91 . When the conventional assembled solder paste printing structure  9  is used, a printed circuit board (not shown) is firstly fixed on a platform (not shown) of a machine (not shown) horizontally, followed by fixing the fixing frame  91  of the conventional assembled solder paste printing structure  9  on the machine, and lying the steel plate  93  of the conventional assembled solder paste printing structure  9  on the printed circuit board aligningly. Subsequently, solder paste is scraped across the solder paste printing region  931  of the steel plate  93 , in such a way that the solder paste is provided within the vias  9311  of the steel plate  93  and applied to the printed circuit board. Finally, the conventional assembled solder paste printing structure  9  is removed. The printed circuit board is then coated with a plurality of spot-like solder paste, to be further processed. 
         [0004]    For the conventional assembled solder paste printing structure, a whole structure, instead of a disassembled single steel plate, is required to correspond to each of a variety of printed circuit boards individually, resulting in the an increase in cost and occupation of storage space. In addition, the replacement or reproduction of the whole conventional assembled solder paste printing structure, instead of one single disassembled expired or damaged steel plate, is required needed when expiration or damage occurs, leading to wasting cost and consuming time. Moreover, the manufacturing process of fixing the steel plate of the conventional assembled solder paste printing structure in the fixing frame is complicated, because the steel plate should be stuck to the stretching net and then flattened. 
         [0005]    Therefore, it is imperative to provide a stencil for printing solder paste on a printed circuit board so as to improve an assembly process, cut production costs, and save storage space. 
       SUMMARY 
       [0006]    In view of above drawbacks of the prior art, the inventor of the present invention conducted extensive researches and experiments according to the inventor&#39;s years of experience in the related industry, and finally developed a stencil for printing solder paste on a printed circuit board, so as to improve an assembly process, cut production costs, and save storage space. 
         [0007]    For achieving above objectives, a stencil for printing solder paste on a printed circuit board of the present invention is used for combining with a fixing frame having a plurality of fixing portions and a motor unit. The motor unit is used for providing a plurality of pulling forces. The stencil comprises a solder paste printing region, provided with a plurality of first vias, the pulling forces being coplanar with the solder paste printing region; and a plurality of fixing regions, defined by outward extensions of edges of the solder paste printing region, the fixing regions being movably fixed to the fixing portions and allowed to bear the pulling forces so as to flatten the solder paste printing region of the stencil. 
         [0008]    Thereby, the objectives of easy to assemble, cutting cost and reducing storage space may be achieved by a fixing frame and an assembled fixing device for printing solder paste on a printed circuit board of the present invention 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a disassembled diagram of a conventional assembled solder paste printing structure for manufacturing a printed circuit board; 
           [0010]      FIG. 2  is an assembled diagram of a conventional assembled solder paste printing structure for manufacturing a printed circuit board; 
           [0011]      FIG. 3  is a diagram of a fixing frame and pulling forces born by a stencil according to one embodiment of the present invention; 
           [0012]      FIG. 4  is a diagram of a fixing region of the stencil according to the embodiment of the present invention; 
           [0013]      FIG. 5  is a diagram of pulling forces born by a stencil according to another embodiment of the present invention; and 
           [0014]      FIG. 6  is a diagram of pulling forces born by a stencil according to a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A detailed description will be made to the present invention by means of following embodiments in cooperation with accompanied drawings for fully understanding the objectives, features and effects of the present invention. 
         [0016]      FIG. 3  is a diagram of a fixing frame and pulling forces born by a stencil according to one embodiment of the present invention. As illustrated in this figure, a stencil  2  for printing solder pasted on a printed circuit board (not shown) of the present invention is used for combining with a fixing frame  8  having a plurality of fixing portions  81  and at least one motor unit (not shown). The motor unit is used for providing a plurality of pulling forces  223 . The fixing frame  8 , shown in this figure, is a hollowed-out rectangular frame and provided with four fixing portions  81 , in which top and bottom fixing portions  81  are provided with a plurality of circular snapping posts  811 , while a left fixing portion  81  is provided with a plurality of T-shaped snapping posts  812 . The stencil  2  comprises a solder paste printing region  21  and a plurality of fixing regions  22 . The fixing regions  22  are defined by outward extensions of edges of the solder paste printing region  21 . The solder paste printing region  21  is rectangular in appearance. The fixing regions  22  are defined by outward extensions of four edges of the solder paste printing region  21 . The solder paste printing region  21  is provided with a plurality of first vias  211  passing through the stencil  2 , and the pulling forces  223  are coplanar with the solder paste printing region  21 . Due to the first vias  211 , solder paste can be readily applied to the printed circuit board. As shown in this figure, the solder paste printing region  21  is provided with a plurality of vias  211  for holding a portion of the solder paste therein and further, applying the portion of the solder paste to the printed circuit board, after the solder paste is scraped across the solder paste printing region  21 . The fixing regions  22  are movably fixed to the fixing portions  81  of the fixing frame  8  together and allowed to bear the pulling forces  223  equal in magnitude and coplanar with the solder paste printing region  21 . The stencil  2 , shown in this figure, is provided on the fixing frame  8 , in which each of the fixing portions  22  is provided on each of the fixing portions  81 , respectively, while the solder paste printing region  21  is then provided within the hollowed-out fixing frame  8 . The right and bottom fixing regions  22  each may be defined to be movably clamped by the fixing portion  81  (for instance, the fixing portion  22  is clamped by top and bottom clamping plates (not shown)), while the left and top fixing regions  22  each may be defined to be movably snapped by the fixing portion  81  (for instance, second vias  221  are provided to circular snapping posts  811 , or T-shaped snapping slots  222  are provided to T-shaped snapping posts  812 ). In addition, except for being movably clamped by the fixing portion  81 , the bottom fixing portion  22  may be also movably snapped cooperatively, so as to avoid the relative slip between the fixing region  22  and the fixing portion  81 . After all of the fixing regions  22  are combined with the fixing portions  81 , the fixing portions  81  may be then moved outwardly, so as to apply the pulling forces  223  to each of the fixing regions  22 , with the pulling forces  223  being combined to become a total pulling force  225  with respect to each fixing region  22 . The stencil  2  may be assembled to the fixing frame  8  or dismounted therefrom easily and quickly by means of the fixing regions  22 , as well as stored independently so as to save storage space, and replaced alone when it is replaced so as to reduce costs. Each fixing region  22 , in addition, may be designed for movably snapping or movably clamping as required, and for bearing the pulling forces  223  or not for bearing a plurality of pulling forces. For two fixing regions  22  corresponding to each other, either of them may be designed for movably snapping or movably clamping, respectively, as well as either both of them may be designed for bearing the plurality of pulling forces  223 , or one fixing region  22  is allowed for bearing the pulling forces  223 , while the other fixing region  22  is not allowed for bearing a plurality of pulling forces. In fact, when one fixing region  22  is allowed for bearing the pulling forces  223 , while the other fixing region  22  is not allowed for bearing a plurality of pulling forces, reaction forces  224  of the pulling forces  223  may be also generated actually in the other fixing region  22 . That is to say, since the pulling forces  224  in the opposite direction with respect to the pulling forces  223  may be combined as a total pulling force  226  of the other fixing region  22 , even if a plurality of pulling forces is not born, the reaction forces of the pulling forces  223  are still born by the other fixing region  22  necessarily. Furthermore, when the plurality of pulling forces  223  which is equal in magnitude and coplanar with the solder paste printing region  21  is born by the fixing regions  22 , an uniform distribution of tension within the solder paste printing region  21  is ensured, and the concentration of stress at specific locations of the fixing regions  22  is also avoided because of an increased number of the pulling forces  223 . Finally, the total pulling forces  225 ,  226  pass through a centroid  212  of the solder paste printing region  21 , and the sum of the total pulling forces  225 ,  226  is zero, so as to flatten the solder paste printing region  21  of the stencil  2 , in the case of non-deformation of the first vias  211 . The deformation of the first vias  211  indicates that the stencil  2  is damaged and thus unusable. Therefore, it is also necessary to control the magnitude of the pulling forces  223  when the solder paste printing region  21  of the stencil  2  is flattened, so as to avoid the damage caused to the stencil  2  by the pulling forces  223 . Moreover, the generation of torque within the solder paste printing region  21  and the displacement of the stencil  2  are avoided, when the total pulling forces  225 ,  226  pass through the centroid  212  of the solder paste printing region  21  and the sum of the total pulling forces  225 ,  226  is zero. To sum up, the stencil for printing solder paste on a printed circuit board of the present invention is precisely lain on the printed circuit board, so as for solder paste to be applied to the printed circuit board accurately. 
         [0017]    Each of the above-mentioned fixing regions  22  is strip-like and is provided along the edge of the solder paste printing region  21 . The fixing region  22  is strip-like, such that it is easy to manufacture and design as a movably clamping structure, and it is easy to design for use with the solder paste printing region  21  with a movably snapping structure. 
         [0018]      FIG. 4  is a diagram of the fixing region of the stencil according to the embodiment of the present invention. Referring to  FIG. 3  together, as illustrated in these figures, the above-mentioned fixing region  22  may be provided with the plurality of second vias  221 , the plurality of snapping slots  222 , or the plurality of second vias  221  and the plurality of snapping slots  222 , thereby movably fixed to the fixing portion  81  of the fixing frame  8  and allowed to bear the pulling forces  223 . The second vias  221 , the snapping slots  222 , or the second vias  221  and the snapping slots  222  are easy for snapping to the exterior, such as snapping with a cylinder or snapping with a pillar having a shape corresponding to that of the snapping slot, for example, and they also hardly come off when the pulling forces  223  are born by the fixing region  22 . In addition, the generation of slip between the fixing region  22  and the fixing portion  81  is truly avoided, when the movably clamped fixing region  22  is designed together with the second vias  221 , the snapping slots  222 , or the second vias  221  and the snapping slots  222 . 
         [0019]    The above-mentioned snapping slots  222  are L-shaped or T-shaped, or take any other shapes as appropriate, so as to be designed as a snapping structure. 
         [0020]    The above-mentioned stencil  2  is made of metallic material, such as steel, for example, thus having the advantage of being capable of coming off solder paste more easily, in such a way that the solder paste can be accurately applied to the printed circuit board when the stencil  2  is separated from the printed circuit board. 
         [0021]    The above-mentioned motion may be either movable snapping or movable clamping. In movably snapping, the second vias  221  or snapping slots  222 , for example, are provide on the fixing region  22 , followed by providing the second vias  221  to the circular snapping posts  811  on the fixing portion  81 , or providing the T-shaped snapping slots  222  to the T-shaped snapping posts  812  on the fixing portion  81 . In movably clamping, the fixing portion  81 , for example, is provided with top and bottom clamping plates (not shown), so as to clamp the fixing region  22 . Moreover, the puling forces are applied to the fixing regions  22  only if the snapping posts  811 ,  812  or top and bottom clamping plates are moved outwardly. 
         [0022]      FIG. 5  is a diagram of pulling forces born by a stencil according to another embodiment of the present invention. As illustrated in  FIG. 5 , a solder paste printing region  21 ′ of the present invention is triangular in appearance or takes any other shapes as appropriate, except for the above-mentioned rectangular solder paste printing region  21 , as required, only if the condition of pulling forces  223 ′ meets that stated above. As illustrated in  FIG. 5 , the fixing regions  22 ′ at two legs are designed for being movably clamped (by means of second vias  221 ′ and snapping slots  222 ′), and allowed to bear the plurality of pulling forces  223 ′, which are equal in direction, equal in magnitude and coplanar with the solder paste printing region  21 ′. The fixing region  22 ′ at the bottom is then designed for being movably clamped and generating reaction forces of the pulling forces  223 ′ (pulling forces  224 ′, in one direction opposite to that of the pulling forces  223 ′ and combined as a total pulling force  226 ′). All of two total pulling forces  225 ′ on the fixing portions  22 ′ at two legs and the total pulling force  226 ′ (the reaction force) on the bottom fixing region  22 ′ pass through a centroid  212 ′ of the solder paste printing region  21 ′, and the sum of the total pulling forces  225 ′,  226 ′ is zero, in the case of non-deformation of the first vias  211 ′. Thereby, the solder paste printing region  21 ′ in triangular shape is flattened. In addition, a plurality of pulling forces is born by the bottom fixing region  22 ′ instead, and the solder paste printing region  21 ′ in triangular shape is flattened, only if the condition of pulling forces meets that stated above. 
         [0023]      FIG. 6  is a diagram of pulling forces born by a stencil according to a further embodiment of the present invention. As illustrated in this figure, a solder paste printing region  21 ″ of the present invention is round in appearance or takes any other shapes as appropriate, except for the above-mentioned rectangular solder paste printing region  21 , as required, only if the condition of pulling forces  223 ″ meets that stated above. As illustrated in  FIG. 6 , a fixing region  22 ″ on the left side is designed for being movably clamped (by means of second vias  221 ″), and allowed to bear the plurality of pulling forces  223 ″, which are directed radially, equal in magnitude and coplanar with the solder paste printing region  21 ″. The fixing region  22 ″ at right side is then designed for being movably clamped, and allowed to generate reaction forces of the pulling forces  223 ″ (pulling forces  224 ″, in one direction opposite to that of the pulling forces  223 ″ and combined as a total pulling force  226 ″). Both of the total pulling forces  225 ″ on the left fixing portions  22 ″ and the total pulling force  226 ″ (the reaction force) on the right fixing region  22 ″ pass through a centroid  212 ″ of the solder paste printing region  21 ″, and the sum of the total pulling forces  225 ″,  226 ″ is zero, in the case of non-deformation of the first vias  211 ″. Thereby, the solder paste printing region  21 ″ presented as a circle may be thus flattened. In addition, a plurality of pulling forces may be also born by the right fixing region  22 ″ instead, and the solder paste printing region  21 ″ formed as a circle may be also thus flattened, only if the condition of pulling forces meets that stated above. Furthermore, the amount of  2  is designed for the fixing regions  22 ″ in this embodiment, however, the amount of  3 ,  4  and etc., may be also possible as practically required. 
         [0024]    The present invention is disclosed by embodiments in foregoing description. However, it should be understood by those skilled in the art that the embodiments are merely used for describing the present invention and not considered as restrictive. It should be noted, that all equivalent variations and substitutions may be included within the scope of the present invention. Therefore, the present invention to be protected should be defined by appended claims