DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0068] Hereinafter, circuit board devices of preferred embodiments according to the present invention will be described in detail with reference to accompanying drawings.

[0069] Referring to FIGS. 1 to 9 , a first preferred embodiment of the present invention will be described, and in this preferred embodiment, examples in which the circuit board devices are applied to module substrates will be described.

[0070] Reference numeral 1 indicates a module substrate defining a substrate constituting a major portion of a circuit board device, and as shown in FIGS. 1 to 4 , the module substrate 1 is preferably a substantially rectangular flat plate composed, for example, of an insulating resin material and has a front surface 1 A, a rear surface 1 B, and four end surfaces 1 C. In addition, in each end surface 1 C of the substrate 1 , a plurality of grooves 1 D in the form, for example, of a substantially semicircle is arranged at predetermined intervals, and each groove 1 D extends in the thickness direction of the substrate 1 and has openings at the front surface 1 A and the rear surface 1 B.

[0071] Reference numeral 2 indicates a plurality of end-surface electrodes provided on each end surface 1 C of the module substrate 1 at predetermined intervals, and the end-surface electrodes 2 are formed, for example, by plating metal films in a substantially semicircular shape in the grooves 1 D of the substrate 1 and extend in the thickness direction thereof. In addition, one end in the longitudinal direction of each of the end-surface electrodes 2 is connected to a corresponding wire pattern 3 described below, and the other end is connected to a main land 8 described later

[0072] Reference numeral 3 indicates a plurality of wire patterns provided on the front surface 1 A of the module substrate 1 , and each wire pattern 3 is formed, for example, of a strip-shaped metal film and has at end portion thereof a substantially semicircular connection portion 3 A which is connected to the end-surface electrode 2 at a position surrounding the corresponding groove 1 D.

[0073] Reference numeral 4 indicates an electronic component mounted on the front surface 1 A of the module substrate 1 , and the electronic component 4 includes a plurality of elements including active elements such as semiconductor ICs, or transistors, or passive elements such as resistors, capacitors, or coils, and is connected to the end-surface electrodes 2 through the respective wire patterns 3 and other type of connections.

[0074] In addition, the electronic component 4 is subassembled on the substrate 1 and is then mounted on a motherboard 10 described later. In addition, the electronic component 4 is connected to wire patterns 11 on the motherboard 10 through the end-surface electrodes 2 and other elements of the module substrate 1 .

[0075] Reference numeral 5 indicates a plurality of metal films provided on the rear surface 1 B of the module substrate 1 for forming lands 8 and 9 described later, and as shown in FIG. 4 to 6 , the metal films 5 are in the form, for example, of a substantially rectangular thin-film and are provided at predetermined intervals, each of the metal films extending inside from the periphery of the substrate 1 at a position corresponding to the end-surface electrode 2 . In addition, the metal films 5 are each connected to the corresponding end-surface electrode 2 at a position surrounding the groove 1 D of the substrate 1 .

[0076] Reference numeral 6 indicates a resist film provided on the rear surface 1 B of the module substrate 1 , and the resist film 6 is formed, for example, of an insulating resist material and covers the rear surface 1 B of the substrate 1 including portions of the metal films 5 . In addition, substantially rectangular openings 6 A and 6 B are formed in the resist film 6 on each metal film 5 , and the openings 6 A and 6 B are formed at a distance from each other in the longitudinal direction of the metal film 5 .

[0077] Reference numeral 7 indicates partitions each including a portion of the resist film 6 which is located at a position between the openings 6 A and 6 B so as to separate the openings 6 A and 6 B from each other, and the partition 7 is a strip-shaped wall which crosses the metal film 5 in the midway along the longitudinal direction thereof and which protrudes downward from the metal film 5 toward the motherboard 10 .

[0078] As described above, the partitions 7 separate each of the metal films 5 into a mainland 8 and a sub-land 9 , which will be described later. Accordingly, in a solder-application step shown in FIG. 7 , solder 12 on the mainland 8 is prevented by the partition 7 from flowing into the sub-land 9 side, and in a soldering step shown in FIGS. 8 and 9 , the solder 12 pushed out from between the mainland 8 and the motherboard 10 is allowed to flow over the partition 7 so as to adhere to the sub-land 9 .

[0079] Reference numeral 8 indicates a plurality of mainlands provided on the rear surface 1 B of the module substrate 1 , and each mainland 8 is a portion of the metal film 5 in a substantially rectangular shape exposed in the opening 6 A of the resist film 6 and is connected to the corresponding end-surface electrode 2 at the periphery of the substrate 1 . In addition, in the solder-application step, the mainland 8 maintains the solder 12 , which flows from the end-surface electrode 2 side, in the state in which the solder 12 is largely protruded downward

[0080] Reference numeral 9 indicates a plurality of sub-lands each provided in the vicinity of the corresponding mainland 8 on the rear surface 1 B of the module substrate 1 , and each sub-land 9 is a portion of the metal film 5 having a substantially rectangular shape exposed in the opening 6 B of the resist film 6 and is separated from the mainland 8 by the partition 7 . In addition, the sub-land 9 is provided at a position further from the end-surface electrode 2 than that of the mainland 8 .

[0081] In addition, the sub-lands 9 are each connected to the corresponding wire pattern 11 of the motherboard 10 with the solder 12 together with the end-surface electrode 2 and the mainland 8 . As a result, the lands 8 and 9 , which have a large connection area, can be reliably connected to the wire pattern 11 . In this case, since the mainland 8 and the corresponding sub-land 9 are disposed in the openings 6 A and 6 B, respectively, which are recessed from the surface of the resist film 6 by the thickness thereof, the module substrate 1 can prevent the solder 12 , which flows into the lands 8 and 9 , from spreading outside, and hence the solder 12 can be stably disposed on the lands 8 and 9 .

[0082] Reference numeral 10 indicates a motherboard on which the module substrate 1 is mounted, and as shown in FIGS. 8 and 9 , a plurality of the wire patterns 11 (only one wire pattern is shown in the figure), another electronic circuit (not shown), and other elements are provided on the motherboard 10 . To these wire patterns 11 , the end-surface electrodes 2 and the lands 8 and 9 are connected with the solder 12 .

[0083] The circuit board device of this preferred embodiment has the structure as described above, and subsequently, referring to FIGS. 7 to 9 , a process for mounting the module 1 will be described.

[0084] First, in the solder-application step shown in FIG. 7 , for example, a granular solder material 12 ′ is disposed at a position corresponding to the connection portion 3 A of each wire pattern 3 and is then melted. As a result, as shown by the solid line shown in FIG. 7 , the solder 12 obtained by melting the solder material 12 ′ flows from the connection portion 3 A to the mainland 8 through the end-surface electrode 2 and extends along a portion having good wettability for the solder 12 .

[0085] In this step, since the flow of the solder 12 from the mainland 8 to the sub-land 9 is controlled by the partition 7 , a portion of the solder 12 , which reaches the mainland 8 , remains thereon. Subsequently, this portion of the solder 12 hangs from the mainland 8 by its surface tension and its own weight to form a protruding portion 12 A that largely protrudes downward, and the solder 12 in the state described above is then solidified. In this case, the protruding dimension of the protruding portion 12 A can be adjusted, for example, in accordance with the area ratio of the connection portion 3 A to the mainland 8 , the amount of the solder material 12 ′, and the viscosity.

[0086] Next, in a substrate mounting step shown in FIGS. 8 and 9 , the module substrate 1 is first placed on the motherboard 10 so that each protruding portion 12 A of the solder 12 faces the wire pattern 11 and then is brought into contact with the wire pattern 11 .

[0087] When the solder 12 in contact with the wire pattern 11 is heated, as shown in FIG. 8 , the protruding portion 12 A of the solder 12 is melted and is distorted between the mainland 8 and the wire pattern 11 , and as a result, the end-surface electrode 2 and the mainland 8 are connected to the wire pattern 11 with the solder 12 . In this case, for example, even when some protruding portions 12 A exist which are not in contact with the wire patterns 11 because of the warping of the substrate 1 and/or the motherboard 10 , since being sequentially melted and distorted, every protruding portion 12 A of the solder 12 is brought into contact with the mainland 8 and the wire pattern 11 Consequently, the warping and other defect of the substrate 1 can be ignored, and hence every end-surface electrode 2 of the substrate 1 can be reliably connected to the wire pattern 11 of the motherboard 10 .

[0088] In addition, when the solder 12 is melted and distorted between the mainland 8 and the wire pattern 11 , the solder 12 is then distorted by the weights of the module substrate 1 and the electronic component 4 , thereby generating a force facilitating the solder to extend along the wire patterns 11 in addition to a force of facilitating the flow of the solder out of the mainland 8 . Hence, being pushed out from therebetween, the solder 12 overflows the partition 7 into the sub-land 9 , and as a result, the sub-land 9 and the wire pattern 11 are connected to each other by the solder 12 .

[0089] As a result, in the state in which the module substrate 1 is mounted on the motherboard 10 , as shown in FIG. 9 , in addition to the connection between each end-surface electrode 2 and the corresponding wire pattern 11 , the mainland 8 and the sub-land 9 , which have a large connection area, can be connected to the wire pattern 11 where the end-surface electrode 2 and the corresponding wire pattern 11 are connected.

[0090] Accordingly, in this preferred embodiment, since the partition 7 is provided on the rear surface 1 B of the module substrate 1 for separating the metal film 5 into the mainland 8 and the sub-land 9 , for example, when the solder 12 is applied to the substrate 1 before assembly, the flow of the solder 12 from the mainland 8 to the sub-land 9 side can be controlled by the partition 7 , and hence a sufficient amount of the solder 12 can remain on the mainland 8 . As a result, the protruding portion 12 A of the solder 12 , which largely protrudes downward, can be solidified.

[0091] As a result, when the substrate 1 is mounted on the motherboard 10 , even when those are deformed by warping or other defect, the end-surface electrode 2 and the mainland 8 can be reliably connected to the wire pattern 11 at the motherboard 10 side, and hence connection defects thereof can be reliably prevented.

[0092] In addition, since the solder 12 overflows the partition 7 when the substrate 1 is mounted, both the mainland 8 and the sub-land 9 can be soldered to the wire pattern 11 , and a large connection area formed by soldering can be secured therebetween, so that the substrate 1 can be mounted on the motherboard 10 with a high strength. In addition, since an appropriate amount of the solder 12 is allowed to remain in an area from the end-surface electrode 2 to the mainland 8 , a fillet having an appropriate cross-sectional shape such as an approximate triangle can be securely formed so as to improve the connection strength between the substrate 1 and the motherboard 10 , and in addition, peeling therebetween caused by vibration, impact, and other causes can also be prevented Accordingly, for example, even when the structure is formed in which the area of the mainland 8 is decreased so that the protruding portion 12 A of the solder 12 largely protrudes from the mainland 8 , since the connection strength of the substrate 1 can be sufficiently secured by the two lands 8 and 9 , a preferable protruding dimension of the solder 12 and connection areas of the lands 8 and 9 can be easily obtained at the same time, thereby improving the reliability.

[0093] In addition, since the partitions 7 are each formed of a resist material, for example, by simply etching the resist film 6 provided on the metal film 5 , the partition 7 having accurate dimensions can be easily formed.

[0094] As a comparative example for the sake of comparison, the case in which the partitions 7 , the sub-lands 9 , and other elements are not formed will be described by way of example. In this case, for example, when a large amount of the solder material 12 ′ is adhered to the mainland 8 in order to absorb the warping or other defects of the motherboard 10 , solder 12 ″ may be pushed out from the mainland 8 , and as a result, for example, a spherical shape of the solder 12 ″ may be formed in some cases as indicated by the virtual line shown in FIG. 9 . In this state, even when a small impact or other force is applied to the solder 12 ″, cracking is likely to occur therein, and as a result, the bonding strength between the substrate 1 and the motherboard 10 is decreased. However, in this preferred embodiment, since an appropriate amount of the solder 12 can be applied to the end-surface electrode 2 and the mainland 8 , a fillet of the solder 12 having an appropriate shape can be formed.

[0095] Next, a second preferred embodiment of the present invention is shown in FIG. 10 , and in this preferred embodiment, the partitions are each formed of a silk member. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0096] Reference numeral 21 indicates a partition provided at the rear surface 1 B side of the module substrate 1 , and in a manner approximately equivalent to that in the first preferred embodiment, the partition 21 separates the metal film 5 into the mainland 8 and sub-land 9 . However, the partition 21 is not a part of a resist film 6 ′ and is formed, for example, by printing a silk member such as ink or paint on the metal film 5 by silk-screen printing or other suitable process.

[0097] By the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first preferred embodiment can also be obtained. In addition, particularly in this preferred embodiment, the partition 21 can be easily formed, for example, by silk-screen printing, and hence the shape, dimensions, and other characteristics of the partition 21 can be more easily changed.

[0098] Next, a third preferred embodiment of the present invention is shown in FIG. 11 , and in this preferred embodiment, the mainland is formed of a metal film that is different from that used for the sub-land, and the gap formed between the metal films described above is used as the partition. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0099] Reference numeral 31 indicates a mainland provided at the rear surface 1 B of the module substrate 1 , and in a manner approximately equivalent to that in the first preferred embodiment, the mainland 31 is formed, for example, of an approximately rectangular metal film and is connected to the end-surface electrode 2 at the periphery of the substrate 1 .

[0100] Reference numeral 32 indicates a sub-land which is formed, for example, of a metal film different from that for the mainland 31 and which is provided at the rear surface 1 B side of the substrate 1 . The sub-land 32 is provided inside the substrate 1 at a predetermined distance from the mainland 31 in a manner approximately equivalent to that in the first preferred embodiment.

[0101] Reference numeral 33 indicates a partition separating the mainland 31 from the sub-land 32 , and the partition 33 is formed of the gap (space) between the lands 31 and 32 .

[0102] With the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first preferred embodiment can also be obtained. In addition, particularly in this preferred embodiment, since the partition 33 is defined by the gap between the lands 31 and 32 , the structure of the partition 33 can be further simplified and can be easily formed.

[0103] Next, a fourth preferred embodiment of the present invention is shown in FIG. 12 , and in this preferred embodiment, the shape of the mainland is in an approximately circular shape having an area larger than that of a semicircular shape. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0104] Reference numeral 41 indicates a substantially rectangular metal film provided at the rear surface 1 B side of the module substrate 1 , and in a manner approximately equivalent to that in the first preferred embodiment, the metal film 41 is connected to the end-surface electrode 2 at a position surrounding the groove 1 D of the substrate 1 .

[0105] Reference numeral 42 indicates a resist film provided at the rear surface 1 B of the module substrate 1 , and the resist film 42 covers the rear surface 1 B of the substrate 1 including the peripheral portions and other portions of the metal films 41 . In addition, an opening 42 A having a substantially circular or an oval shape (hereinafter referred to as “approximately circular shape”) and openings 42 B and 42 C, provided at positions surrounding the opening 42 A, are formed in the resist film 42 on each metal film 41 , and the entire shape defined by these openings 42 A to 42 C is an approximately rectangle slightly smaller than the metal film 41 .

[0106] Reference numeral 43 indicates a partition formed of parting portions between the openings 42 A and 42 B and between the openings 42 A and 42 C. The partition 43 , which is a thin and long wall in an approximately semicircular shape on the metal film 41 , surrounds the opening 42 A formed in the resist film 42 and protrudes downward from the metal film 41 to the motherboard side. In addition, in a manner approximately equivalent to that in the first preferred embodiment, the partition 43 separates the metal film 41 into a mainland 44 and sub-lands 45 and 46 , which are described below.

[0107] Reference numeral 44 indicates a mainland provided at the rear surface 1 B of the module substrate 1 , and the mainland 44 is a portion of the metal film 41 exposed in the opening 42 A formed in the resist film 42 . In addition, the mainland 44 is arranged so as to surround the corresponding end-surface electrode 2 of the substrate 1 and is connected thereto.

[0108] In this preferred embodiment, the mainland 44 has an approximately circular shape surrounded by the partition 43 . Hence, in a solder-application step, for example, when a predetermined amount of solder 12 is adhered to the mainland 44 so as to be protruded downward, the protruding dimension of the solder 12 can be made largest when being compared to any lands having various shapes. That is, for example, when solder is adhered to a substantially rectangular land, the solder spreads from the center to the four corners of each land to form a thin film, and the protruding dimension of the solder becomes small compared to that provided on the mainland 44 . On the other hand, for example, by adhering a necessary minimum amount of solder to the mainland 44 , the protruding dimension thereof can be made as large as possible.

[0109] In addition, the mainland 44 preferably has an approximately circular shape having an area, for example, larger than that of a substantially semicircular shape; a substantially circular arc portion 44 A defining the periphery of the mainland 44 has a central angel larger than 180°; and the center O of this substantially circular arc portion 44 A is disposed inside the substrate 1 and apart from the end surface 1 C. In addition, the width dimension (the dimension that is substantially parallel to the end surface 1 C of the substrate 1 ) of the mainland 44 becomes largest, equal to diameter D, at a position apart from the end surface 1 C. As a result, in a solder-application step, a required amount of the solder 12 can be reliably adhered to the mainland 44 having a sufficiently large area, and the protruding dimension of the solder 12 can be optionally set to a desired value in accordance with diameter D of the mainland 44

[0110] Reference numeral 45 indicates a sub-land provided in the vicinity of the mainland 44 , and the sub-land 45 is a portion of the metal film 41 exposed in the opening 42 B formed in the resist film 42 on the substrate 1 and is disposed apart from the end-surface electrode 2 . In addition, a portion of the periphery of the sub-land 45 , which is adjacent to the mainland 44 with a predetermined gap left therebetween, has a substantially circular arc portion 45 A in an approximately circular arc shape. Furthermore, on both sides of the mainland 44 , other sub-lands 46 , which are exposed in the openings 42 C formed in the resist film 42 , are provided along the end surface 1 C of the substrate 1 .

[0111] By the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first preferred embodiment can also be obtained. In addition, particularly in this preferred embodiment, since the mainland 44 has an approximately circular shape having an area larger than that of a semicircular shape, for example, by simply adhering a necessary minimum amount of the solder 12 to the mainland 44 in a solder-application step, the protruding dimension of the solder 12 protruding downward from the substrate 1 can be made sufficiently large and can also be desirably adjusted in accordance with diameter D of the mainland 44 . As a result, while the amount of the solder 12 , which is adhered to the mainland 44 , is appropriately controlled, soldering is accomplished regardless of warping or other defect of the module substrate 1 and the motherboard 10 .

[0112] Next, a fifth preferred embodiment of the present invention is shown in FIG. 13 , and in this preferred embodiment, a mainland having an approximately circular shape is formed of a metal film that is different from that for a sub-land provided around the periphery of the mainland. The reference numerals of the constituent elements of the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0113] Reference numeral 51 indicates a mainland provided at the rear surface 1 B side of the module substrate 1 , and in a manner approximately equivalent to that in the fourth preferred embodiment, the mainland 51 is formed, for example, of a metal film having an approximately circular shape, has a substantially circular arc portion 51 A having a center angle larger than about 180°, and is connected to the end-surface electrode 2 of the substrate 1 .

[0114] Reference numerals 52 and 53 indicate sub-lands provided in the vicinity of the mainland 51 , and in a manner approximately equivalent to that in the fourth preferred embodiment, the sub-lands lands 52 and 53 are each disposed apart form the end-surface electrode 2 and at a predetermined distance from the mainland 51 In addition, the lands 51 , 52 , and 53 are formed of metal films that are different from each other. Reference numeral 54 indicates a partition having an approximately circular shape separating the mainland 51 from the sub-lands 52 and 53 , and the partition 54 1 s a gap formed between the mainland 51 and the sub-lands 52 and 53 .

[0115] By the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first, third, and fourth preferred embodiments can also be obtained.

[0116] Next, a sixth preferred embodiment of the present invention is shown in FIG. 14 , and in this preferred embodiment, a partition having a notch portion extending from the mainland side toward the sub-land side is formed. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0117] Reference numeral 61 indicates a notch portion formed in the partition 7 , and for example, the notch portion 61 is formed approximately at the central position in the length direction of the partition 7 extending so as to traverse the metal film 5 . This notch portion 61 is a cut 61 A having an approximately triangular shape which tapers (the distance between the two sides of the triangular shape is gradually decreased) from the mainland 8 side toward the sub-land 9 side. In addition, the notch portion 61 is formed at a position corresponding to an exposed triangular portion of the metal film 5 , which is exposed at the position of the cut 61 A, so as to directly face the mainland 8 .

[0118] With the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first preferred embodiment can also be obtained. Since the notch portion 61 is provided for the partition 7 in this preferred embodiment, when the substrate 1 is mounted, as indicated by the arrow shown in FIG. 14 , the solder 12 can be concentrated at the notch portion 61 so as to facilitate the flow of the solder 12 from the mainland 8 toward the sub-land 9 . Hence, even when a force pushing out the solder 12 is small since the module substrate 1 and the electronic component 4 are lightweight, the solder can reliably overflow the partition 7 .

[0119] In addition, since a position through which the solder 12 flows can be limited only to the notch portion 61 , even when the mainlands 8 are disposed at small intervals, the solder will not overflow into adjacent mainlands 8 . Hence, short-circuiting therebetween can be avoided so as to improve the isolation, resulting in the improvement in reliability.

[0120] Next, a seventh preferred embodiment of the present invention is shown in FIGS. 15 to 17 , and in this preferred embodiment, a partition having a notch portion is provided, and in addition, curved portions are provided at the corners of the sub-land apart from the corresponding partition. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0121] Reference numeral 71 indicates a notch portion provided for the partition 7 , and as is the notch portion 61 in the sixth preferred embodiment, the notch portion 71 is formed at the approximately central position (approximately middle position) in the length direction of the partition 7 and is a cut 71 A having an approximately triangular shape which tapers from the mainland 8 toward the sub-land 9 . In addition, the notch portion 71 is formed at a position corresponding to an exposed triangular portion of the metal film 5 , which is exposed at the position of the cut 71 A, so as to directly face the mainland 8 .

[0122] Reference numeral 72 indicates curved portions of the sub-land 9 which are spaced apart from the corresponding partition 7 , and the curved portions 72 are provided at two corners of the sub-land 9 having an approximately rectangular shape and are far from the notch portion 71 . For example, by forming the opening 6 B in the resist film 6 so as to have substantially circular arcs at positions corresponding to the corners of the sub-land 9 , the curved portions 71 are formed.

[0123] By the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first and sixth preferred embodiments can also be obtained. Since the curved portions 72 are provided at the corners of the sub-land 9 apart from the partition 7 in this preferred embodiment, when the substrate 1 is mounted, non-coated areas are not formed around the corners of the sub-land 9 , and hence the entire surface thereof can be reliably covered with the solder 12 .

[0124] That is, as is a comparative example shown in FIG. 18 , when the curved portions are not formed, when the substrate 1 is mounted, since spreading from the notch portion 71 , the solder 12 might not reach the two corners of the sub-land 9 apart from the partition 7 , and as a result, the formation of the non-coated areas is prevented from occurring. If the non-coated areas would be formed to which the solder 12 is not applied, as described above, the corners of the sub-land 9 and a portion of the wire pattern 11 are exposed to the air, and hence a problem might arise in that corrosion, such as oxidation of the sub-land 9 and other problems, might occur.

[0125] In addition, when the flow of the solder 12 is stopped while spreading, since the solder 12 may have a cross-section in a substantially circular arc because of its surface tension, grooves each having an acute angle, such as an “a” portion shown in FIG. 19 , are likely to be formed between the solder 12 and the sub-land 9 and between the solder 12 and the wire pattern 11 . In this case, since stress is liable to concentrate at the “a” portion, a problem may arise in that peeling is liable to occur between the solder 12 and the sub-land 9 or the wire pattern 11 .

[0126] In contrast, in this preferred embodiment, since the curved portions 72 are formed at the corners of the sub-land 9 apart from the partition 7 , the solder 12 can spread over the entire surface of the sub-land 9 , and corrosion of the sub-land 9 , peeling of the solder 12 , or other problems can be prevented, resulting in improvement in reliability and durability.

[0127] In this preferred embodiment, the curved portions 72 having a substantially circular arc shape are provided at the corners of the sub-land 9 , and in addition, portions each having a linear shape may also be provided at the corners of the sub-land 9 .

[0128] Next, a eighth preferred embodiment of the present invention is shown in FIGS. 20 and 21 . In this preferred embodiment, a mainland having an approximately circular shape is connected to a plurality of strip-shaped sub-lands. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0129] Reference numeral 81 indicates a module substrate constituting a main body of a circuit board device. As shown in FIGS. 20 and 21 , in a manner approximately equivalent to that in the first preferred embodiment, the module substrate 81 has a front surface 81 A, a rear surface 81 B, four end surfaces 81 C, and a plurality of grooves 81 D, and in each groove 81 D, an end-surface electrode 82 is provided. In addition, the electronic component 4 is mounted on the module substrate 81 at the front surface 81 A side, and the rear surface 81 B side is mounted on a motherboard 88 described later.

[0130] Reference numeral 83 indicates a metal film provided at the rear surface 81 B side of the module substrate 81 , and the metal film 83 is processed, for example, by etching to form a mainland 84 and sub-lands 85 and 86 .

[0131] Reference numeral 84 indicates a mainland which is a portion of the metal film 83 and which is provided at the rear surface 81 B side of the module substrate 81 . In a manner approximately equivalent to that in the fourth preferred embodiment, the mainland 84 is arranged so as to surround the end-surface electrode 82 of the substrate 81 and is connected thereto.

[0132] In addition, the mainland 84 has, for example, an approximately circular shape having an area larger than that of a semicircle; a substantially circular arc portion 84 A of the mainland 84 , which forms the periphery thereof, has a central angle larger than about 180°; and the center O′ of this substantially circular arc portion 84 A is disposed inside the substrate 81 and apart from the end surface 81 C of the substrate 81 . Accordingly, as shown in FIG. 21 , when a protruding portion 87 A of a solder 8 described below is protruded downward from the mainland 84 , the protruding dimension of the solder 87 can be made largest when being compared to any lands having various shapes.

[0133] Reference numeral 85 indicates a plurality of sub-lands which are each defined by a portion of the metal film 83 other than that for the mainland 84 and which are each provided at the rear surface 81 B side of the module substrate 81 . As shown in FIG. 20 , each sub-land 85 has a strip shape and an area smaller than that of the mainland 84 , and width dimension W (dimension in the direction that is substantially parallel to the end surface 81 C of the substrate 81 ) is smaller than the width dimension (diameter D′) of the mainland 84 .

[0134] In this preferred embodiment, each sub-land 85 extends approximately linearly in the direction opposite to the end-surface electrode 82 (mainland 84 ) of the substrate 81 , and one end of the sub-land 85 in the longitudinal direction is separately connected to the mainland 84 through a narrow portion 85 A having a width smaller than width dimension W of the sub-land 85 . In addition, on the whole, the sub-lands 85 are disposed substantially parallel to each other to form a stripe pattern, and the intervals between the sub-lands 85 are each smaller than width dimension W of the sub-land 85 . In addition, other sub-lands 86 are connected to the periphery of the mainland 84 at positions which are different from those to which the sub-lands 85 are connected.

[0135] In addition, by forming an expansion portion 87 B of the solder 87 as described below, these sub-lands 85 and 86 secure a sufficiently large connection area between the module substrate 81 and the motherboard 88 .

[0136] The module substrate 81 according to this preferred embodiment has the structure as described above, and next, a solder-application step, a substrate mounting step, and other steps performed for the module substrate 81 will be described which are performed in a manner approximately equivalent to that described in the first preferred embodiment.

[0137] First, when being applied to the module substrate 81 , the solder 87 melted at the end-surface electrode 82 side is adhered to the mainland 84 in an approximately circular shape as shown in FIG. 21 , and as approximately equivalent to the fourth preferred embodiment, the protruding portion 87 A of the solder 87 largely protrudes from the mainland 84 even when the amount thereof is relatively small.

[0138] In addition, a portion of the solder 87 adhered to the mainland 84 flows into the sub-land 85 side through the corresponding narrow portion 85 A. In this case, a small amount of the solder 87 corresponding to a small area (width dimension W) of the sub-land 85 flows thereinto, and subsequently, the part of the solder 87 slowly flows along the strip-shaped sub-land 85 . In addition, a portion of the solder 87 also flows into the other sub-land 86 side as described above.

[0139] Accordingly, the solder 87 flowing into each of the sub-lands 85 and 86 protrudes downward from the module substrate 81 , and the protruding dimension thereof is smaller than that of the protruding portion 87 A, thereby forming the thin expansion portions 87 B in a stripe pattern extending along the sub-lands 85 and 86 . Subsequently, the protruding portion 87 A and the expansion portion 87 B, which are in the state described above, can be solidified.

[0140] Accordingly, in the substrate mounting step, when the solder 87 is heated while the module substrate 81 is placed on the motherboard 88 , the protruding portion 87 A of the solder 87 is melted and distorted between the substrate 81 and the motherboard 88 in a manner approximately equivalent to that of the first preferred embodiment. Accordingly, even when the warping or other defect occurs between the substrate 81 and the motherboard 88 , the mainland 84 of the substrate 81 and a corresponding wire pattern 89 at the motherboard 88 side can be reliably connected to each other with the solder 87 .

[0141] In addition, in the step described above, the expansion portions 87 B of the solder 87 are melted on the sub-lands 85 and 86 and then spread across the lands 85 and across the lands 86 , and as a result, the sub-lands 85 and 86 are placed in the state of solder wetting (close to the state in which treatment using a solder leveler is performed). Hence, a portion of the solder 87 which is distorted at the mainland 84 side and pushed out therefrom can be smoothly spread along these sub-lands 85 and 86 in the state of solder wetting.

[0142] By the structure of this preferred embodiment as described above, advantages approximately equivalent to those described in the first and the fourth preferred embodiments can be obtained. That is, since the mainland 84 has an approximately circular shape, for example, by simply adhering a necessary minimum amount of the solder 87 to the mainland 84 , the protruding dimension of the protruding portion 87 A, which protrudes downward from the substrate 81 , can be made sufficiently large, and in addition, the protruding dimension can be optionally adjusted in accordance with diameter D′ of the mainland 84 .

[0143] In particular in this preferred embodiment, since the structure in which the plurality of strip-shaped sub-lands 85 is disposed in a stripe pattern and is connected to the mainland 84 , when the solder 87 is applied to the substrate 81 , a portion of the solder 87 is allowed to flow to the sub-land 85 side, and hence the expansion portions 87 in a stripe pattern extending in a predetermined area can be formed. In this case, by adjusting width dimension W of the sub-land 85 and the shape of the narrow portion 85 A beforehand, the amount of the solder 87 flowing from the mainland 84 to the sub-land 85 side and the thickness or the characteristics of the expansion portion 87 A can be appropriately determined, and hence, while the amount of the solder 87 (protruding dimension of the protruding portion 87 A) remains at the mainland 84 side can be sufficiently secured, the sub-lands 85 and 86 can be placed beforehand in the state of solder wetting.

[0144] Accordingly, when the module substrate 81 is mounted on the motherboard 88 , a portion of the solder 87 adhered to the mainland 84 side can be spread reliably along the sub-lands 85 and 86 , and hence the module substrate 81 can be securely soldered to the motherboard 88 by the mainland 84 and the sub-lands 85 and 86 , which have a large area. As a result, non-uniform soldering or other defect between the substrate 81 and the motherboard 88 can be reliably prevented, and thereby the bonding strength therebetween can be further increased.

[0145] Next, a ninth preferred embodiment of the present invention is shown in FIG. 22 , and in this preferred embodiment, the eighth embodiment is applied to a substantially rectangular mainland. The same reference numerals of the constituent elements in the eighth preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0146] Reference numeral 91 indicates a metal film provided at the rear surface 81 B side of the module substrate 81 , and the metal film 91 defines a mainland 92 and a sub-land 93 , which will he described below.

[0147] Reference numeral 92 indicates an approximately rectangular mainland defined by a portion of the metal film 91 , and the mainland 92 is disposed so as to surround the end-surface electrode 82 of the module substrate 81 and is connected thereto.

[0148] Reference numeral 93 indicates a plurality of sub-lands each formed of the other portion of the metal film 91 , and as is the sub-land 85 of the eighth preferred embodiment, the sub-lands 93 each have a strip shape and a smaller area than that of the mainland 92 . In addition, the sub-lands 93 extend in the direction opposite to the mainland 92 and the end-surface electrode 82 so as to form a stripe pattern and are each separately connected to the mainland 92 through a narrow portion 93 A provided at one end of the sub-land 93 in the longitudinal direction.

[0149] By the structure of this preferred embodiment described above, advantages approximately equivalent to those in the eighth preferred embodiment can also be obtained.

[0150] Next, a tenth preferred embodiment of the present invention is shown in FIG. 23 , and in this preferred embodiment, a land having an approximately circular shape is provided on a module substrate. The same reference numerals of the constituent elements in the first preferred embodiment designate the same constituent elements in this preferred embodiment, and descriptions thereof are omitted.

[0151] Reference numeral 101 indicates a land which is composed of a metal film or other suitable element and is provided at the rear surface 1 B of the module substrate 1 , and as is the fourth preferred embodiment, the land 101 has an approximately circular shape having an area larger than that of a semicircular shape. In addition, the land 101 has a substantially circular arc portion 101 A, which forms the periphery thereof, having a central angle larger than about 180°, and a center O″ of the circular arc portion 101 A is disposed inside the substrate 1 and apart from the end surface 1 C. The width dimension of the land 101 has the maximum value equivalent to diameter D″ at a position apart from the end surface 1 C. In addition, the land 101 has an area approximately equivalent to the total area of the mainland 44 and the sub-land 45 in the fourth preferred embodiment.

[0152] When a necessary minimum amount of the solder 12 is adhered to the land 101 , the protruding dimension thereof can be made as large as possible in accordance with diameter D″, and while the amount of the solder 12 adhered to the land 101 is appropriately controlled, the warping and other defects of the module substrate 1 and the motherboard 10 can be reliably ignored.

[0153] By the structure of this preferred embodiment described above, advantages approximately equivalent to those in the first and the fourth preferred embodiments can also be obtained.

[0154] In the first and the second preferred embodiments, the partitions 7 and 21 are each formed as a strip-shaped wall across the metal film 5 . However, the present invention is not limited thereto, and for example, according to a first modified preferred embodiment as shown in FIG. 24, a cut portion 112 may be provided in the approximately central portion of a partition 111 along the longitudinal direction. In addition, for example, as is a second modified preferred embodiment shown in FIG. 25, a partition 113 may be formed of a plurality of island-shaped members 113 A which are disposed at predetermined intervals therebetween.

[0155] In addition, in the first and the second preferred embodiments, the resist film 6 is arranged so as to cover the periphery of the metal film 5 . However, the present invention is not limited thereto, and for example, as in the third modified preferred embodiment shown in FIGS. 26 and 27 , a resist film 6 ″ may be disposed at a distance from the metal film 5 .

[0156] In the third preferred embodiment, the partition 33 is a gap formed between the lands 31 and 32 . However, the present invention is not limited thereto, and for example, various materials having poor solder wettability, such as a resist material or a silk-screen material, may be filled between the lands 31 and 32 .

[0157] In the eighth to tenth preferred embodiments, for example, by etching the metal films 83 and 91 , lands 84 , 85 , 86 , 92 , 93 , 101 , and so on are formed. However, the present invention is not limited thereto, and lands having the same shapes as those of the eighth to tenth preferred embodiments may be formed in a manner approximately equivalent, for example, to that of the first preferred embodiment. In addition, in this case, for example, by forming a resist film or other element on the metal film formed on the rear surface of the module substrate followed by etching of the resist film, openings are formed in the resist film, and as a result, lands 84 , 85 , 86 , 92 , 93 , 101 , and so on are each formed of the metal film exposed in each opening. Accordingly, since the lands each recessed from the surface of the resist film can be formed, solder flowing into the lands is prevented from overflowing outside, and hence the solder can be securely disposed on the lands.

[0158] In the fourth, fifth, eighth, and tenth preferred embodiments, the lands 44 , 51 , 84 , 101 , and so on each have an approximately circular shape. However, the present invention is not limited thereto, and lands having an approximately oval shape may also be used.

[0159] In the fourth, fifth, and eighth preferred embodiments, in addition to primary sub-lands 45 , 52 , and 85 , the other sub-lands 46 , 53 , and 86 are provided at the end surfaces 1 C, 81