Abstract:
Provided is a printed circuit board structure that needs minimum manufacturing costs and in which there is little possibility that a solder bridge is formed. The printed circuit board structure is formed with via holes for electrically conductively connecting electrically conductive layers of a printed circuit board, and the via holes include a coated via hole with a land coated with solder resist and a non-coated via hole with a land not coated with solder resist, wherein the coated via hole is arranged in a place of the printed circuit board where a solder bridge or a solder ball is highly likely to be generated, and is electrically connected to at least one of the non-coated via hole in parallel.

Description:
[0001]    This application is a new U.S. patent application that claims benefit of JP 2016-149058, filed on Jul. 28, 2016. The entire content of JP 2016-149058 is hereby incorporated by reference. 
       FIELD 
       [0002]    The present invention relates to a printed circuit board structure. 
       BACKGROUND 
       [0003]    It is known to provide conduction among electrically conductive layers of a printed circuit board by forming a through-hole with an electrically conductive sidewall, which is called a via hole, on the printed circuit board. The space between via holes formed on a printed circuit board has been narrowed by reducing the size of electronic equipment, and, in some cases, a solder bridge is formed between the lands (portions of the electrically conductive material of the via holes exposed in a doughnut shape on the surface of the printed circuit board) of adjacent via holes during soldering. In addition, particularly in the vicinity of a portion of the printed circuit board where the heat capacity is large, in some cases, a solder ball is formed on the land of a via hole during soldering. When the solder bridge or the solder ball is separated and moved away from the printed circuit board due to some sort of shock or the like and short-circuits the wiring of the printed circuit board or the lead wires of components after the printed circuit board is incorporated into electronic equipment, the electronic equipment may malfunction. It is known to prevent the formation of the solder bridge or the solder ball by applying solder resist on the lands of all via holes that are not used for mounting of a component such that the solder does not adhere to the lands of the via holes during soldering (see, for example, Patent Document 1). 
       Related Documents 
       [0000]    
       
         [Patent Document 1] Japanese Laid Open Patent Document No. H11-154778 
       
     
       SUMMARY 
       [0005]    When, however, the solder resist is applied on the land of the via hole, in some cases, the solder resist blocks the opening of the via hole or, even if it does not block the opening, so-called dripping caused by the solder resist flowing into the through hole of the via hole occurs. When the via hole is blocked or the dripping occurs inside, there is a possibility that an etching solvent or the like used in a printed circuit board manufacturing process is not fully rinsed off, but remains within the via hole, and the via hole is disconnected when the residue of the remaining etching solvent or the like reacts with the electrically conductive material that covers the side surface of the via hole. The disconnection of the via hole interferes with the conduction between the layers of the printed circuit board and the electronic equipment may be eventually malfunction. 
         [0006]    The printed circuit board structure according to an embodiment solves the aforementioned problem, and it is an object to provide a printed circuit board structure in which there is little possibility that a solder bridge or a solder ball is formed and there is little possibility that malfunction of the electronic equipment due to disconnection of a via hole is generated. 
         [0007]    In order to realize the aforementioned object, a printed circuit board structure according to the embodiment is formed with via holes for electrically conductively connecting electrically conductive layers of a printed circuit board, wherein the via holes include a coated via hole with a land coated with solder resist and a non-coated via hole with a land not coated with solder resist, the coated via hole is arranged in a place of the printed circuit board where it is highly probable that the solder bridge or the solder ball is generated, and is electrically connected to at least one non-coated via hole in parallel. 
         [0008]    In addition, regarding the printed circuit board structure according to the embodiment, it is preferable that the coated via hole is arranged in a place where a distance between adjacent via holes is equal to or less than a predetermined distance, one of the adjacent via holes being the coated via hole and the other being the non-coated via hole. 
         [0009]    In addition, regarding the printed circuit board structure according to the embodiment, it is preferable that the coated via hole is arranged in a place where a distance from a metal member arranged on the printed circuit board is equal to or less than a predetermined distance. 
         [0010]    In addition, regarding the printed circuit board structure according to the embodiment, it is preferable to include a first region where an electronic component is soldered by a flow process or a dip process and a second region protected from solder by a masking jig when soldering is performed in the first region, wherein the coated via hole is preferably arranged in a place within the first region where a distance from a boundary with the second region is equal to or less than a predetermined distance. 
         [0011]    In addition, regarding the printed circuit board structure according to the embodiment, it is preferable that the coated via hole is arranged on a power supply voltage pattern unit of the printed circuit board to which a power supply voltage is fed. 
         [0012]    In addition, regarding the structure of a printed circuit board according to the embodiment, it is preferable that the coated via hole is connected to a ground pattern unit of the printed circuit board to be grounded. 
         [0013]    With the structure of the printed circuit board according to the embodiment, it is possible to reduce the possibility that the solder bridge or the solder ball is formed, and it is possible to reduce the possibility that malfunction of the electronic equipment due to disconnection of a via hole is generated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1A  is a partial plan view of a printed circuit board according to a first embodiment. 
           [0015]      FIG. 1B  is a partial cross-sectional view of the printed circuit board illustrated in  FIG. 1A . 
           [0016]      FIG. 2A  is a first view for explaining a distance between a non-coated via hole and a coated via hole illustrated in  FIGS. 1A and 1B . 
           [0017]      FIG. 2B  is a second view for explaining a distance between a non-coated via hole and a coated via hole illustrated in  FIGS. 1A and 1B . 
           [0018]      FIG. 3  is a flow chart indicating a coated via hole determination processing for determining the coated via hole illustrated in  FIGS. 1A and 1B . 
           [0019]      FIG. 4  is a partial plan view of a printed circuit board according to a second embodiment. 
           [0020]      FIG. 5A  is an explanatory view in which a solder ball is formed on the land of a via hole. 
           [0021]      FIG. 5B  is a view for explaining a distance between a non-coated via hole and a coated via hole illustrated in  FIG. 4 . 
           [0022]      FIG. 6  is a flow chart indicating a coated via hole determination processing for determining the coated via hole illustrated in  FIG. 4 . 
           [0023]      FIG. 7  is a partial plan view of a printed circuit board according to a third embodiment. 
           [0024]      FIG. 8  is a view for explaining a distance between a non-coated via hole and a coated via hole illustrated in  FIG. 7 . 
           [0025]      FIG. 9  is a flow chart indicating coated via hole determination processing for determining the coated via hole illustrated in  FIG. 7 . 
           [0026]      FIG. 10A  is views illustrating an arrangement example of coated via holes in which arrangement example, the distance with respect to adjacent non-coated via holes is equal to or less than a solder bridge formation distance. 
           [0027]      FIG. 10B  is views illustrating an arrangement example of coated via holes in which arrangement example, the distance with respect to adjacent non-coated via holes is equal to or less than a solder bridge formation distance. 
           [0028]      FIG. 10C  is a view illustrating an arrangement example of coated via holes in which arrangement example the distance with respect to a boundary is equal to or less than a solder ball formation distance. 
           [0029]      FIG. 11A  is a view illustrating an example of a state of solder adhered to a via hole in a mounting structure according to a comparative example. 
           [0030]      FIG. 11B  is a view illustrating an example of a state of solder adhered to a via hole of the printed circuit board according to the present embodiments. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    A printed circuit board structure according to embodiments is described with reference to the drawings below. It should be noted, however, that the technical scope of the present invention is not limited to the embodiments, but covers equivalents of the invention stated in the claims. Regarding the printed circuit board structure according to the embodiments, the via holes include a non-coated via hole with the land not coated with solder resist and a coated via hole with the land coated with solder resist. A via hole the distance from which to an adjacent non-coated via hole is equal to or less than the distance of the formation of the solder bridge is selectively adopted as a coated via hole so as to minimize the number of coated via holes and minimize the possibility of the generation of disconnection of the via hole. 
         [0032]    (Printed Circuit Board Structure According to the First Embodiment) 
         [0033]      FIG. 1A  is a partial plan view of a printed circuit board according to the first embodiment, and  FIG. 1B  is a partial cross-sectional view of the printed circuit board illustrated in  FIG. 1A . 
         [0034]    A printed circuit board  1  includes a first surface  11  and a second surface  12  positioned opposite the first surface  11 , and is formed with via holes  20  and  21  in which the wall surfaces of through-holes  13  extending from the first surface  11  to the second surface  12  are covered with an electrically conductive material  14 , e.g., copper. In addition, in portions where the via hole is exposed on the first surface  11  and the second surface  12  of the printed circuit board  1 , a land  16  where the electrically conductive material  14  surrounds the circumference of the opening of the via hole in a doughnut shape is formed. An electronic component  30  is soldered on the first surface  11  or the second surface  12  of the printed circuit board  1  with solder. Solder resist  15  is applied on both the first surface  11  and the second surface  12  of the printed circuit board  1 . Regarding the printed circuit board  1 , a non-coated via hole and an electronic component, e.g., the electronic component  30 , are soldered by the flow process or the dip process. Herein, the flow process indicates a soldering process in which solder stored in a solder bath is jetted and the surface of the circuit board is washed by the jet, and the dip process indicates a soldering process in which a printed circuit board is dipped in solder stored in a solder bath. 
         [0035]    The via holes  20 - 21  include the non-coated via holes  20  with the lands  16  not coated with the solder resist  15  and the coated via holes  21  with the lands  16  coated with the solder resist  15 . A residue  90 , e.g., of an etching solvent, can remain in the coated via hole  21 . 
         [0036]      FIG. 2A  is a first view for explaining a distance between the non-coated via hole  20  and the coated via hole  21 , and  FIG. 2B  is a second view for explaining a distance between the non-coated via hole  20  and the coated via hole  21 . 
         [0037]    Regarding the printed circuit board  1 , a distance between the coated via hole  21  and the non-coated via hole  20  adjacent to the coated via hole  21  is equal to or less than a solder bridge formation distance D 1  where the solder for soldering the electronic component  30  forms a solder bridge  18 . In other words, when a distance with respect to an adjacent non-coated via hole  20  is equal to or less than the solder bridge formation distance D 1 , such a via hole is selected as the coated via hole  21 . Specifically, when a space between adjacent via holes is equal to or less than D 1 , one of the via holes is selected as the non-coated via hole  20  and the other is selected as the coated via hole  21 . In one example, a via hole the distance from which with respect to an adjacent non-coated via hole  20  is 0.75 mm or less is selected as the coated via hole  21 . When one of adjacent via holes is selected as the coated via hole  21 , the solder is not adhered to the land of the via hole  21 , so that the formation of the solder bridge with respect to the land of the non-coated via hole  20  can be prevented. 
         [0038]    Furthermore, the coated via hole  21  is electrically connected to any of the non-coated via holes  20  in parallel. Even if the via hole is disconnected by an etching solvent or the like remaining in the through-hole of the coated via hole  21 , the non-coated via hole  20  connected in parallel maintains the electrical connection, thereby reducing the possibility of malfunction of the electronic equipment. 
         [0039]    More preferably, the non-coated via hole  20  and the coated via hole  21  are provided on a pattern unit that constitutes a power supply feed line VDD of the printed circuit board or a pattern unit that constitutes a ground line VSS of the printed circuit board. The pattern units constituting the power supply feed line VDD or the ground line VSS is often grounded with a large number of via holes being electrically connected in parallel in order to reduce impedance or ensure more current capacity. In such a portion, even if one or a few coated via holes  21  are disconnected, the electrical connection is maintained by another large number of non-coated via holes  20  or the coated via holes  21 , which are not disconnected, thereby reducing the possibility of malfunction of the electronic equipment. 
         [0040]      FIG. 3  is a flow chart indicating coated via hole determination processing for determining the coated via hole  21 . The processing illustrated in  FIG. 3  is executed on each via hole formed on a printed circuit board by a circuit board design device (e.g., a printed circuit board design CAD system), which is not illustrated. 
         [0041]    First, the circuit board design device judges whether there is a possibility that soldering is performed by the flow process or the dip process on a via hole formed on a printed circuit board (S 101 ). When the circuit board design device judges that there is no possibility that soldering is performed by the flow process or the dip process on the via hole formed on the printed circuit board (S 101 —NO), the processing is completed. 
         [0042]    When the circuit board design device judges that there is a possibility that the soldering is performed on the via hole (S 101 —YES), the circuit board design device judges whether there is an adjacent via hole within the solder bridge formation distance D 1  where the solder bridge can be formed from the via hole on which the soldering is performed (S 102 ). When the circuit board design device judges that there is no adjacent via hole within the solder bridge formation distance D 1  from the via hole on which the soldering is performed (S 102 —NO), the processing is completed. 
         [0043]    When the circuit board design device judges that there is an adjacent via hole within the solder bridge formation distance D 1  (S 102 —YES), the circuit board design device judges whether the adjacent via hole within the solder bridge formation distance D 1  is electrically connected to the non-coated via hole  20  in parallel (S 103 ). When the circuit board design device judges that the adjacent via hole within the solder bridge formation distance D 1  is electrically connected in parallel to the non-coated via hole  20  (S 103 —YES), the circuit board design device determines the adjacent via hole as the coated via hole  21  (S 104 ). 
         [0044]    When the circuit board design device judges that the adjacent via hole within the solder bridge formation distance D 1  is not electrically connected to the non-coated via hole  20  in parallel (S 103 —NO), the circuit board design device reviews the arrangement of the via hole (S 105 ). In one example, the circuit board design device arranges the via hole, which has been judged to be not connected to the non-coated via hole  20  in parallel, apart from the non-coated via hole  20  by a distance larger than the solder bridge formation distance D 1 . 
         [0045]    (Printed Circuit Board Structure According to the Second Embodiment) 
         [0046]      FIG. 4  is a partial plan view of a printed circuit board according to the second embodiment. 
         [0047]    A printed circuit board  2  differs from the printed circuit board  1  in that a metal member  31  is arranged in addition to the electronic component  30 . In addition, the printed circuit board  2  differs from the printed circuit board  1  in that via holes  41  are formed in addition to the via holes  20 - 21 . Constituent elements of the printed circuit board  2  other than the metal member  31  and the via holes  41  are the same as the constituent elements of the printed circuit board  1 , which are designated with the same reference numerals, and their detailed descriptions are omitted. 
         [0048]    In one example, the metal member  31  is a heat dissipation fin or a shielding case for electrically shielding a component on the printed circuit board  2 , and is soldered on the first surface  11  of the printed circuit board  2  by the flow process or the dip process together with the electronic component  30 . In addition, the metal member  31  may be preliminarily arranged on the printed circuit board  2  independently of the electronic component  30  in a different process. 
         [0049]      FIG. 5A  is an explanatory view in which a solder ball is formed on the land of a via hole, and  FIG. 5B  is a view for explaining a distance between the metal member  31  and the coated via hole  41 . 
         [0050]    Regarding the printed circuit board  2 , a distance between the metal member  31  and the coated via hole  41  is equal to or less than a solder ball formation distance D 2  where the solder forms a solder ball  19  on the land of a via hole. In other words, when a distance between the metal member  31  and the coated via hole  41  is equal to or less than the solder ball formation distance D 2 , the via hole is selected as the coated via hole  41 . In one example, when a distance with the metal member  31  is 1.5 mm or less, the via hole is selected as the coated via hole  41 . Because the metal member  31  has a large heat capacity, there is a possibility that, when the electronic component  30  or the like is soldered by the flow process or the dip process, the temperature of the land of a via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  is not sufficiently increased, so that the solder is not well spread on the land and the solder ball is formed. When the solder resist is applied to a via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2 , the solder ball can be prevented from being formed on the land of the via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2 . 
         [0051]    Furthermore, as with the first embodiment, the coated via hole  41  is electrically connected to any of the non-coated via holes  20  in parallel, even if the via hole is disconnected by an etching solvent or the like remaining in the through-hole of the coated via hole  41 , the non-coated via hole  20  connected in parallel maintains the electrical connection, thereby reducing the possibility of malfunction of the electronic equipment, and more preferably, the non-coated via hole  20  and the coated via hole  41  are provided on a pattern unit constituting the power supply feed line VDD of the printed circuit board and on a pattern unit constituting the ground line VSS of the printed circuit board. 
         [0052]      FIG. 6  is a flow chart indicating coated via hole determination processing for determining the coated via hole  41 . The processing illustrated in  FIG. 6  is executed for each via hole formed on a printed circuit board by a circuit board design device, which is not illustrated. In addition, the processing of  FIG. 6  may be performed continuously to the processing indicated in  FIG. 3  by the circuit board design device of the first embodiment. 
         [0053]    First, the circuit board design device judges whether there is a via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  where the solder ball can be formed when the soldering is performed with the solder by the flow process or the dip process (S 201 ). When the circuit board design device judges that there is no via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  (S 201 —NO), the processing is completed. 
         [0054]    When the circuit board design device judges that there is a via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  (S 201 —YES), the circuit board design device judges whether the via hole is electrically connected to the non-coated via hole  20  in parallel (S 202 ). When the circuit board design device judges that the via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  is electrically connected to the non-coated via hole  20  in parallel (S 202 —YES), the circuit board design device determines the via hole as the coated via hole  41  (S 203 ). 
         [0055]    When the circuit board design device judges that the via hole the distance from which to the metal member  31  is equal to or less than the solder ball formation distance D 2  is not electrically connected to the non-coated via hole  20  in parallel (S 202 —NO), the circuit board design device reviews the arrangement of the via hole (S 204 ). In one example, the circuit board design device arranges the via hole, which has been judged to be not connected to the non-coated via hole  20  in parallel, apart from the metal member  31  by a distance larger than the solder ball formation distance D 2 . 
         [0056]    (Printed Circuit Board Structure According to the Third Embodiment) 
         [0057]      FIG. 7  is a partial plan view of a printed circuit board according to the third embodiment. 
         [0058]    A printed circuit board  3  differs from the printed circuit board  1  in that the printed circuit board  3  includes a first region  51  in which an electronic component is soldered by the flow process or the dip process and a second region  52  in which an electronic component is soldered by a reflow process. The reflow process indicates a soldering process in which solder paste is printed on a printed circuit board and is heated with an electronic component being arranged on the printed solder paste. A boundary  50  to be descried below is present between the first region  51  and the second region  52 . Preferably, a line indicating the boundary  50  is printed by silkscreen printing or the like. The printed circuit board  3  differs from the printed circuit board  1  in that an electronic component  32  is arranged in addition to the electronic component  30 . In addition, the printed circuit board  3  differs from the printed circuit board  1  in that via holes  61  are formed in addition to the via holes  20 - 21 . Constituent elements of the printed circuit board  3  other than the electronic component  32  and the via holes  61  are the same as the constituent elements of the printed circuit board  1 , which are designated with the same reference numerals, and their detailed descriptions are omitted. 
         [0059]    The electronic component  32  is soldered by the reflow process and is arranged in the second region  52 . Then, the electronic component  30  is soldered by the flow process or the dip process and is arranged in the first region  51 . The reflow process is suitable for soldering a small-sized component, and the flow process or the dip process is suitable for soldering a large-sized component. Using such techniques enables adoption of a suitable soldering method when a small-sized component and a large-sized component are arranged together on one printed circuit board. Furthermore, when the electronic component  30  is soldered by the flow process or the dip process and is arranged in the first region  51 , the second region  52  is protected by being covered with a metallic masking jig so that the electronic component  32 , which is preliminarily soldered by the reflow process and is arranged in the second region  52 , is not removed by being washed by the solder in the flow process or the dip process. In this case, the boundary  50  is a line indicating a range where the metallic masking jig contacts the printed circuit board  3 . 
         [0060]      FIG. 8  is a view for explaining a distance between the boundary  50  and the coated via hole  61 . 
         [0061]    Regarding the printed circuit board  3 , a distance between the boundary  50  and the coated via hole  61  is equal to or less than the solder ball formation distance D 2  where the solder for soldering the electronic component  30  forms the solder ball  19 . In other words, when a distance between the boundary  50  and the coated via hole  61  is equal to or less than the solder ball formation distance D 2 , the via hole is selected as the coated via hole  61 . In one example, when a distance with the boundary  50  is 1.5 mm or less, the via hole is selected as the coated via hole  61 . As described above, the boundary  50  indicates a range where the metallic masking jig contacts the printed circuit board  3  when the electronic component, e.g., the electronic component  30 , arranged in the first region  51  is soldered by the flow process or the dip process. Because the metallic masking jig has a large heat capacity, there is a possibility that, when the electronic component  30  or the like is soldered by the flow process or the dip process, the temperature of the land of the via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  is not sufficiently increased, so that the solder is not well spread on the land and the solder ball is formed on the land. When the solder resist is applied over a via hole the distance from which to the boundary  50  is equal or less than the solder ball formation distance D 2 , the solder ball can be prevented from being formed on the land of the via hole lying within the solder ball formation distance D 2 . 
         [0062]    Furthermore, as with the first embodiment, the coated via hole  61  is electrically connected to any of the non-coated via holes  20  in parallel, even if the via hole is disconnected by an etching solvent or the like remaining in the through-hole of the coated via hole  61 , the non-coated via hole  20  connected in parallel maintains the electrical connection, thereby reducing the possibility of malfunction of the electronic equipment, and more preferably, the non-coated via hole  20  and the coated via hole  61  are provided on a pattern unit constituting the power supply feed line VDD of the printed circuit board and on a pattern unit constituting the ground line VSS of the printed circuit board. 
         [0063]      FIG. 9  is a flow chart indicating coated via hole determination processing for determining the coated via hole  61 . The processing illustrated in  FIG. 9  is executed on each via hole formed on a printed circuit board by a circuit board design device, which is not illustrated. In addition, the processing of  FIG. 9  may be performed continuously to the processing illustrated in  FIG. 3  or  FIG. 6  by the circuit board design device of the first embodiment or the second embodiment. 
         [0064]    First, the circuit board design device judges whether there is a via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  where the solder ball can be formed when the soldering is performed with the solder by the flow process or the dip process (S 301 ). When the circuit board design device judges that there is no via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  (S 301 —NO), the processing is completed. 
         [0065]    When the circuit board design device judges that there is a via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  (S 301 —YES), the circuit board design device judges whether the via hole is electrically connected to the non-coated via hole  20  in parallel (S 302 ). When the circuit board design device judges that the via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  is electrically connected to the non-coated via hole  20  in parallel (S 302 —YES), the circuit board design device determines the via hole as the coated via hole  61  (S 303 ). 
         [0066]    When the circuit board design device judges that the via hole the distance from which to the boundary  50  is equal to or less than the solder ball formation distance D 2  is not electrically connected to the non-coated via hole  20  in parallel (S 302 —NO), the circuit board design device reviews the arrangement of the via hole (S 303 ). In one example, the circuit board design device arranges the via hole, which has been judged to be not connected to the non-coated via hole  20  in parallel, apart from the boundary  50  by a distance larger than the ball formation distance D 2 . 
         [0067]    In the description above, the electronic component  32  arranged in the second region  52  is soldered by the reflow process. However, the method of arranging the electronic component  32  to be arranged in the second region  52  is not limited thereto, but other soldering methods (the flow method and the dip method) or other joining methods (bonding with electrically conductive paste or the like) may be used. In short, the printed circuit board structure of the present embodiments may be adopted insofar as a technique of protecting the second region  52  with a masking jig is adopted so that the solder does not enter the second region  52  where the electronic component  32  is already arranged when the soldering is performed in the first region  51  by the flow process or the dip process. 
         [0068]      FIG. 10  is a view illustrating an example of the printed circuit board described in the first embodiment to the third embodiment.  FIG. 10A  is a first view illustrating an arrangement example of the coated via holes  21 ,  FIG. 10B  is a second view illustrating an arrangement example of the coated via holes  21 , and  FIG. 10C  is a view illustrating an arrangement example of the coated via holes  61 . In  FIG. 10A , the coated via holes  21  are indicated by square marks, in  FIG. 10B , the coated via holes  21  are indicated by circular marks, and in  FIG. 10C , the coated via holes  61  are indicated by triangular marks. 
         [0069]    In the example illustrated in  FIG. 10 , the printed circuit board is a glass epoxy substrate, which is also called an FR-4 (Flame Retardant Type 4). The printed circuit board has a thickness of 1.6 mm, and the via holes formed on the printed circuit board have a diameter of 0.3 mm. The solder for soldering the electronic component by the flow process or the dip process is Sn—3.0% Ag—0.5% Cu (tin 96.5%, silver 3%, copper 0.5% (lead free). 
         [0070]    The temperature of the solder in the solder bath used when the soldering is performed in the first region  51  by the flow process or the dip process is 320° C.±5° C. Soldering time for soldering by the flow process or the dip process is about six seconds or less although temperature increase time, fillet formation time and the like vary with conditions such as the size and the shape of an electronic component, and the size, the material and the shape of a terminal. 
         [0071]    The coated via holes  21  illustrated by square marks in  FIG. 10A  are via holes the distance from which to adjacent non-coated via holes  20  is 0.75 mm or less and which are connected to the power supply feed line VDD. The coated via holes  21  illustrated by circular marks in  FIG. 10B  are via holes the distance from which to adjacent non-coated via holes  20  is 0.75 mm or less and which are connected to the ground line VSS. The coated via holes  61  indicated by triangular marks in  FIG. 10C  are via holes the distance from which to the boundary  50  is 1.5 mm or less and which are connected to the ground line VSS. 
         [0072]    The distance between the coated via hole  21  and the non-coated via hole  20 , and the distance between the boundary  50  and the coated via hole  61  were determined based on an experiment in which the soldering time was changed with respect to various types of components. The minimum value of the soldering time is minimum time that can ensure the connection strength of the solder, and the upper limit value of the soldering time is six seconds. 
         [0073]    (Technical Effect of the Printed Circuit Board Structure According to the Embodiments) 
         [0074]    Regarding the printed circuit board structure according to the embodiments, the solder resist is applied over a via hole the distance from which to an adjacent via hole is equal to or less than the solder bridge formation distance where the solder bridge is formed and on which the soldering is not performed. Regarding the printed circuit board structure according to the embodiments, because the solder resist is applied over a via hole the distance from which to an adjacent via hole is equal to or less than the solder bridge formation distance and on which the soldering is not performed, the formation of the solder bridge can be prevented during the soldering by the flow process or the dip process. 
         [0075]      FIG. 11A  is a view illustrating an example of a state where the solder is adhered to a via hole in a mounting structure according to a comparative example, and  FIG. 11B  is a view illustrating an example of a state where the solder is adhered to a via hole in a printed circuit board according to the present embodiment. In the example illustrated in  FIG. 11A , the solder resist is not applied over the via hole on which the soldering is not performed, and in the example illustrated in  FIG. 11B , as in the case of the printed circuit boards  1  to  3 , the non-coated via hole and the coated via hole are arranged. 
         [0076]    In the example illustrated in  FIG. 11A , because the solder is adhered to a land exposed portion during the soldering by the flow process or the dip process, the solder bridge or the solder ball can be formed. In contrast, in the example illustrated in  FIG. 11B , because unnecessary solder is not adhered during the soldering by the flow process or the dip process, there is no possibility that the solder bridge or the solder ball is formed. 
         [0077]    In addition, regarding the printed circuit board structure according to the embodiments, the solder resist is applied over a via hole the distance from which to a metal member is equal to or less than the solder ball formation distance where the solder ball is formed and on which the soldering is not performed. Regarding the printed circuit board structure according to the embodiments, because the solder resist is applied over a via hole the distance from which to a metal member is equal to or less than the solder ball formation distance and on which the soldering is not performed, the formation of the solder ball on the land of the via hole can be prevented during the soldering by the flow process or the dip process. 
         [0078]    In addition, regarding the printed circuit board structure according to the embodiments, the solder resist is applied over a via hole the distance of which with respect to the boundary with respect to the region where the soldering is performed by the reflow process and on which the soldering is not performed. In addition, in the printed circuit board structure according to the embodiments, the solder resist is applied to a via hole the distance from which to the boundary with the region where the soldering is performed by the reflow process is equal to or less than the solder ball formation distance where the solder ball is formed and on which the soldering is not performed. Regarding the printed circuit board structure according to the embodiments, because the solder resist is applied over a via hole the distance from which to the boundary is equal to or less than the solder ball formation distance and on which the soldering is not performed, the formation of the solder ball due to influences of a masking jig can be prevented during the soldering by the flow process or the dip process. 
         [0079]    In addition, regarding the printed circuit board structure according to the embodiments, the coated via hole, which is coated with the solder resist, is electrically connected to any of the non-coated via holes, which are not coated with the solder resist, in parallel. Regarding the printed circuit board structure according to the embodiments, because the coated via hole is connected to the non-coated via hole, even when the disconnection occurs in the coated via hole, because an electric signal is transmitted and received via the non-coated via hole, there is no possibility that the function of the printed circuit board is lost. 
         [0080]    In addition, regarding the printed circuit board structure according to the embodiments, because any of the coated via holes is connected to the power supply voltage line connected to the non-coated via hole, even when the disconnection occurs in the coated via hole, a power supply voltage can be fed via the non-coated via hole. 
         [0081]    In addition, regarding the printed circuit board structure according to the embodiments, because any of the coated via holes is connected to the ground line connected to the non-coated via hole, even when the disconnection occurs in the coated via hole, grounding can be made via the non-coated via hole. 
         [0082]    The via holes  20  and  41  are arranged on the printed circuit board  2 , and the via holes  20  and  61  are arranged on the printed circuit board  3 . However, the via holes  41  and  61  may be arranged on the printed circuit board according to the embodiments.