JP2012060019A - Electronic circuit module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic circuit module in which leg pieces of a metal plate cover can be securely soldered to pattern lands provided in four corners of a circuit board and the solder bonding portions hardly cause appearance defects.SOLUTION: An electronic circuit module 1 comprises: a rectangular circuit board 2 having electronic elements 10 mounted thereon and having pattern lands 3 at four corners of the board; and a metal plate cover 5 in which leg pieces 7 are hung down from respective corner-cut portions of a corner-cut rectangular top panel part 6. The metal plate cover 5 covers the electronic elements 10, and the respective leg pieces 7 are soldered to the pattern lands 3. Exposed portions S2 of the pattern lands 3, which are not covered with the metal plate cover 5, are rounded projective areas each formed by cutting off the top part of a rectangular equilateral triangular shape along a predetermined circular arc, the circular arc being set to have a curvature radius equal to or greater than a radius of a virtual circle C inscribed in the pattern land 3.

Description

  The present invention relates to an electronic circuit module in which a sheet metal cover that covers an electronic element mounted on a circuit board has leg pieces at four corners, and each leg piece is soldered to a pattern land at the four corners of the circuit board. .

  Conventionally, as an electronic circuit module of this type, the upper surface of a rectangular circuit board on which electronic elements are mounted is covered with a sheet metal cover having a substantially identical top plate portion, and is suspended from the top plate portion at the four corners of this sheet metal cover. A structure in which leg pieces are soldered to pattern lands formed at four corners of a circuit board is widely known. Normally, this type of electronic circuit module is surface-mounted on a mother board. At this time, the top plate portion of the sheet metal cover serves as a suction surface for air chucking. Further, since the sheet metal cover is grounded via the pattern land, the electronic elements on the circuit board can be electromagnetically shielded by the sheet metal cover.

  FIG. 7 is a plan view of an essential part showing a conventional example of such an electronic circuit module (see, for example, Patent Document 1). Although only a part of the circuit board 20 is shown in the figure, the circuit board 20 has a rectangular shape as a whole, and has a large number of terminal electrodes 21 to be soldered to the lands of the mother board (not shown) at the periphery. It is lined up. A wiring pattern and electronic elements (not shown) are disposed on the upper surface of the circuit board 20, and pattern lands 22 having a right isosceles triangle shape are provided at four corners. The sheet metal cover 23 is formed by bending a metal plate, and covers almost the entire area of the upper surface of the circuit board 20 except for the four corners. That is, the top plate portion 24 of the sheet metal cover 23 has a rectangular shape with four corners cut off obliquely, and a tongue-shaped metal piece bent at a right angle at each corner cutting portion is formed as a leg piece 25. Are mounted on the pattern land 22 and joined by solder 26.

  In the electronic circuit module in which the leg pieces 25 hanging from the corner cut portions of the top plate portion 24 are soldered to the pattern lands 22 at the corner portions of the circuit board 20 as described above, a right angle along the corner shape of the circuit board 20 is obtained. The isosceles triangular pattern land 22 can be formed, and the leg pieces 25 can be mounted along the bottom side of the pattern land 22. Therefore, an amount of solder 26 necessary for soldering the leg pieces 25 can be provided on the pattern land 22 relatively easily, and the mounting strength of the sheet metal cover 23 can be easily secured. Further, since the sheet metal cover 23 can cover the vicinity of the periphery of the circuit board 20, a space for arranging the wiring pattern and the electronic elements can be easily secured on the upper surface of the circuit board 20, and the electronic circuit module can be downsized. It is easy to plan.

JP 2006-344812 A

  By the way, the surface of the pattern land 22 provided at the corner of the upper surface of the circuit board 20 in FIG. 7 is usually subjected to a surface treatment such as gold plating so as to improve connection reliability. However, since the molten solder is difficult to wet and spread on the right-angled part (vertex part) 22a of the right-angled isosceles triangular pattern land 22, as shown in FIG. 7, the solder 26 may not adhere to the right-angled part 22a. In this case, there is a problem that the right-angled portion 22a is easily visually recognized as a soldering defective portion. That is, even if the solder 26 is not attached to the right-angled portion 22a of the pattern land 22, there is almost no problem in the mounting strength of the sheet metal cover 23. However, if the gold plating is exposed, the solder is conspicuous. There was a high possibility of being misidentified as a bad attachment, and it was therefore a factor that caused unnecessary returns and doubts about reliability.

  Further, as described above, it is relatively easy to provide the solder 26 in an amount necessary for soldering the leg pieces 25 mounted along the bottom side of the pattern land 22 having a right isosceles triangle shape. When downsizing of the electronic circuit module is promoted and the area of the pattern land 22 is reduced, it becomes increasingly difficult to attach a sufficient amount of solder 26 to the surface of the leg piece 25. Therefore, there is a demand for a structure that can reliably solder the leg pieces of the sheet metal cover even when the pattern land is reduced in area.

  The present invention has been made in view of such a state of the art, and the purpose thereof is to reliably solder the leg pieces of the sheet metal cover to the pattern lands provided at the four corners of the circuit board. An object of the present invention is to provide an electronic circuit module that is less likely to cause defects in appearance.

  In order to achieve the above object, the present invention provides a rectangular circuit board having electronic elements mounted on the upper surface and provided with pattern lands at the four corners, and a corner-cut rectangular top plate portion having the four corners cut off obliquely. In an electronic circuit module, comprising: a sheet metal cover that hangs a leg piece from each corner cut position; and the sheet metal cover covers the electronic element and the leg piece is soldered to the pattern land. The planar shape of the portion of the pattern land that is not covered by the sheet metal cover is a rounded convex shape obtained by cutting the top of an isosceles right triangle along a predetermined arc, and the radius of curvature of the arc is the pattern. The size is set to be equal to or larger than the radius of the virtual circle inscribed in the land.

  In an electronic circuit module in which such planar pattern lands are formed at the four corners of the upper surface of the circuit board, if the leg pieces are mounted on the pattern lands when the sheet metal cover is attached to the circuit board, a rounded convex shape The pattern land is exposed outside the leg piece. Therefore, when the solder applied to the exposed portion of the pattern land is melted, the molten solder easily spreads to the rounded portion of the top of the pattern land that is farthest from the leg piece, and the solder covering the entire exposed portion. Will adhere to the outer surface of the leg pieces to form a fillet. Therefore, each leg piece of the sheet metal cover can be reliably soldered to the pattern lands disposed at the four corners of the circuit board. In addition, there is no possibility that the surface of the pattern land soldered to the leg piece will be undesirably exposed, and it is unlikely that cracks due to insufficient solder amount will occur in a part of the pattern land. Is unlikely to occur.

  In the above configuration, not only the rounded portion at the top of the pattern land, but also the outer peripheral edge of the pattern land adjacent to both sides of the leg piece is curved in a rounded shape, so that the sheet metal cover of the pattern land is covered with the sheet metal cover. Solder melted in the outer region that does not exist tends to wet and spread to the inner region covered with the sheet metal cover by going around both sides of the leg piece. Therefore, the solder on the pattern land can be reliably attached not only to the outer surface of the leg piece but also to the inner surface, and the attachment strength of the sheet metal cover can be increased accordingly.

  Further, in the above configuration, a notch is formed in the lower end portion of the leg piece, and when the leg piece is mounted on the pattern land, a through hole having the pattern land as a bottom surface is defined by the notch. In this case, the solder melted in the outer region of the pattern land that is not covered with the sheet metal cover is likely to wet and spread to the inner region covered with the sheet metal cover through the notch. Therefore, even when the pattern land is reduced in size with the downsizing of the electronic circuit module, the solder on the pattern land can be reliably attached to the outer surface and the inner surface of the leg piece. It is easy to ensure the required mounting strength.

  Further, in the above configuration, a protrusion is vertically provided at the lower end portion of the leg piece, and an engagement hole that protrudes on the pattern land is provided in the circuit board, and the protrusion is inserted into the engagement hole. Thus, when the projection is positioned in the radial direction of the engagement hole, when a lateral external force acts on the sheet metal cover with the leg pieces soldered to the pattern land, Since excessive stress is less likely to act on the solder, the reliability of the electrical and mechanical connection of the leg pieces can be improved.

  According to the electronic circuit module of the present invention, when the leg piece is mounted on the pattern land when the sheet metal cover is attached to the circuit board, the rounded convex pattern land is exposed to the outside of the leg piece. It is easy to wet and spread the molten solder over the entire exposed portion of the land. Therefore, each leg piece of the sheet metal cover can be reliably soldered to the pattern lands disposed at the four corners of the circuit board. In addition, there is no risk that the pattern land soldered to the leg piece will be undesirably exposed, and it is unlikely that cracks due to insufficient solder amount will occur in a part of the pattern land, resulting in appearance defects at the solder joints. And therefore eliminates the risk of unnecessary returns and doubts about reliability.

1 is an external perspective view of an electronic circuit module according to an embodiment of the present invention. FIG. 2 is a plan view corresponding to FIG. 1. It is sectional drawing of this electronic circuit module. It is a bottom view of the electronic circuit module. It is a principal part perspective view of the sheet metal cover used with this electronic circuit module. It is a schematic plan view of a circuit board used in the electronic circuit module. It is a principal part top view which shows a prior art example.

  Embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 to 4, an electronic circuit module 1 according to this embodiment includes a rectangular circuit board 2, a plurality of electronic elements 10 mounted on the circuit board 2, and these electronic elements 10. It mainly comprises a sheet metal cover 5 having a top plate portion 6 to be covered and attached to the circuit board 1. A wiring pattern (not shown) connected to the electronic element 10 is provided on the upper surface of the circuit board 2, and pattern lands 3 are provided at the four corners. The sheet metal cover 5 hangs the leg pieces 7 from the four corners of the top plate portion 6 and hangs the side plates 8 from each side except the four corners of the top plate portion 6. Each leg piece 7 is mounted on the corresponding pattern land 3 of the circuit board 2, and as shown in FIG. 3, these leg pieces 7 are joined to the pattern land 3 by solder 9. However, the solder 9 is not shown in FIGS.

  As shown in FIGS. 1 and 4, a large number of terminal electrodes 4 having through-holes halved are arranged in the periphery of the circuit board 2, and these terminal electrodes 4 are arranged on a connection land of a mother board (not shown). The electronic circuit module 1 is surface-mounted on the mother board by being mounted on and soldered. At that time, the top plate portion 6 of the sheet metal cover 5 serves as an air chucking suction surface. Further, since the sheet metal cover 5 is grounded via the pattern land 3, the electronic element 10 on the circuit board 2 can be electromagnetically shielded by the sheet metal cover 5. In consideration of the concentration of stress due to thermal expansion at the center and end of each side of the circuit board 2, as shown in FIG. 4, the three terminal electrodes 4 positioned at the center and both ends of each side are shown. Is set wider than the others. Further, the interval between the adjacent terminal electrodes 4 is also designed in consideration of the difference in stress due to thermal expansion. In the case of this embodiment, the interval between the central terminal electrode 4 and the adjacent terminal electrode 4 is set to be the same. However, in some cases, the distance between the terminal electrode 4 at both ends and the adjacent terminal electrode 4 is wider than the distance between the other terminal electrodes 4.

  The pattern lands 3 provided at the four corners of the circuit board 2 are formed in a planar shape as shown in FIGS. That is, the pattern land 3 is formed in a substantially pentagonal shape that can be divided into a horizontally long trapezoidal non-exposed portion S1 covered by the sheet metal cover 5 and a rounded substantially triangular exposed portion S2 that is not covered by the sheet metal cover 5. The leg piece 7 is mounted on the boundary between the non-exposed part S1 and the exposed part S2. The non-exposed portion S <b> 1 is formed narrow along the inner surface of the leg piece 7 so as not to narrow the wiring pattern formation region and the electronic element 10 mounting region on the circuit board 2. The exposed portion S2 is a rounded convex region that can be regarded as having formed the first rounded portion 3a by cutting out the apex of a right-angled isosceles triangle along a predetermined arc, and the arc of the first rounded portion 3a. Is set to be slightly larger than the radius of the virtual circle C (see FIG. 6) inscribed in the pattern land 3. As shown in FIG. 1, two locations adjacent to both side portions of the leg piece 7 in the outer peripheral edge of the pattern land 3 are curved as second round portions 3 b, and the arcs of the second round portions 3 b are curved. The curvature radius is set to be considerably smaller than that of the first rounded portion 3a. Further, at the four corners of the circuit board 2, there are formed engaging holes 2a into which the protrusions 7b (see FIG. 5) of the leg pieces 7 are inserted, and these engaging holes 2a are formed at the boundary portion of the pattern land 3. I'm coming out. Since the diameter of the engagement hole 2a is set substantially equal to the maximum width dimension of the protrusion 7b, the position of the protrusion 7b is regulated in the radial direction of the engagement hole 2a. In FIG. 6, the electronic element 10 and the wiring pattern are not shown.

  The sheet metal cover 5 is formed by bending a metal plate. As shown in FIG. 2, the sheet metal cover 5 covers almost the entire area of the upper surface of the circuit board 2 except for the four corners. The top plate portion 6 of the sheet metal cover 5 is formed in a rectangular shape with four corners cut off obliquely, and a tongue-shaped metal piece bent at a right angle at each corner cutting portion is formed as a leg piece 7. The leg piece 7 is formed in a shape as shown in FIG. 5, and has two semicircular cutouts 7a at the lower end thereof, and the above-mentioned protrusion 7b hangs from between the cutouts 7a. . As shown in FIG. 1, when the sheet metal cover 5 is attached to the circuit board 2, each leg piece 7 is mounted on the corresponding pattern land 3, and at this time, the pattern land 3 is set to the bottom surface by the notch 7a. A through hole is defined. Further, as shown in FIG. 3, each protrusion 7b is inserted into the engagement hole 2a protruding from the corresponding pattern land 3, but as described above, the inner wall of the engagement hole 2a positions the protrusion 7b in the radial direction. In order to regulate, the sheet metal cover 5 is mounted on the circuit board 2 with the projections 7 b at the four corners being regulated by the circuit board 2. As shown in FIG. 5, the protrusion 7 b has a shape swelled asymmetrically in the left-right direction, and adjacent protrusions among the protrusions 7 b formed at the four positions of the top plate portion 6 of the sheet metal cover 5. Since the 7b has a line-symmetric shape, the position can be accurately regulated, and each protrusion 7b can be easily inserted into the corresponding engagement hole 2a.

  As described above, in the electronic circuit module 1 according to this embodiment, when the leg piece 7 is mounted on the pattern land 3 when the sheet metal cover 5 is attached to the circuit board 2, as shown in FIGS. 3 exposed portions S2 are exposed outside the leg pieces 7 as rounded convex regions. Therefore, when the solder applied to the exposed portion S2 is melted, the molten solder easily wets and spreads to the first rounded portion 3a farthest from the leg piece 7 in the pattern land 3, as shown in FIG. The solder 9 covering the entire surface of the exposed portion S2 adheres to the outer surface of the leg piece 7 to form a fillet. Therefore, the leg pieces 7 of the sheet metal cover 5 can be reliably soldered to the pattern lands 3 arranged at the four corners of the circuit board 2. In addition, there is no possibility that the surface of the pattern land 3 is undesirably exposed by the solder 9 covering the entire surface of the exposed portion S2 in this way, and there is a low possibility that cracks due to insufficient solder amount occur in a part of the pattern land 3. The appearance of defects in solder joints is less likely to occur, and therefore there is no risk of unnecessary returns or doubts about reliability.

  Further, in the electronic circuit module 1 according to the present embodiment example, two of the outer peripheral edge portions of the pattern land 3 adjacent to the both side portions of the leg piece 7 are curved as the second rounded portion 3b. Solder melted on the exposed portion S2 of the land 3 goes around both sides of the leg piece 7 and easily spreads on the non-exposed portion S1. Therefore, the solder 9 on the pattern land 3 can be reliably attached not only to the outer surface of the leg piece 7 but also to the inner surface, and the mounting strength of the sheet metal cover 5 is increased (see FIG. 3).

  In addition, in the present embodiment, when the sheet metal cover 5 is mounted on the circuit board 2, a through-hole having the pattern land 3 as the bottom surface is defined by the notch 7 a formed at the lower end portion of the leg piece 7. The solder melted on the exposed portion S2 of the land 3 can be wetted and spread on the non-exposed portion S1 through the notch 7a. Therefore, the mounting strength of the sheet metal cover 5 of the electronic circuit module 1 is also increased from this point. If the area of the pattern land 3 is reduced as the electronic circuit module 1 is reduced in size, it becomes difficult to secure on the pattern land 3 a route for molten solder that goes around both sides of the leg piece 7. However, in this case as well, it is relatively easy to form a notch for allowing molten solder to pass through at the lower end portion of the leg piece 7, so that the notch is effective in securing the required mounting strength for the sheet metal cover 5. It is.

  Further, in the electronic circuit module 1 according to the present embodiment example, the protrusion 7b is suspended from the lower end portion of the leg piece 7, and the engagement hole 2a that protrudes to the pattern land 3 and is inserted into the circuit is provided in the circuit. Protrusions 7b provided on the substrate 2 and inserted into the engagement holes 2a are regulated in the radial direction of the engagement holes 2a. That is, the sheet metal cover 5 is mounted on the circuit board 2 in a state in which the projections 7b at the four corners are positioned on the inner walls of the corresponding engagement holes 2a. Even if it acts, it is difficult for excessive stress to act on the solder 9 on the pattern land 3, and therefore the reliability of the electrical and mechanical connection of the leg piece 7 is increased.

  In the above-described embodiment, the radius of curvature of the arc of the first rounded portion 3 a farthest from the leg piece 7 in the pattern land 3 is slightly larger than the radius of the virtual circle C inscribed in the pattern land 3. However, if the radius of curvature of the arc of the first rounded portion 3a is set to be equal to or larger than the radius of the virtual circle C, the molten solder on the exposed portion S2 is first It is possible to reliably spread and spread up to the rounded portion 3a.

  In the above embodiment, the non-exposed portion S1 covered with the sheet metal cover 5 in the pattern land 3 is formed in a horizontally long trapezoidal shape. However, the wiring pattern formation region on the circuit board 2 and the electronic element 10 If the mounting area is not restricted, the non-exposed portion S1 can be formed not only in the shape of a horizontally long trapezoid but also in an arbitrary shape.

DESCRIPTION OF SYMBOLS 1 Electronic circuit module 2 Circuit board 2a Engagement hole 3 Pattern land 3a 1st round part (R round part)
3b Second round portion 5 Sheet metal cover 6 Top plate portion 7 Leg piece 7a Notch 7b Protrusion 9 Solder 10 Electronic element S1 Non-exposed portion S2 Exposed portion C Virtual circle

Claims (4)

Leg pieces are suspended from each corner of a rectangular circuit board with electronic elements mounted on the top surface and pattern lands provided at the four corners, and a corner-cut rectangular top plate with the four corners cut diagonally. A sheet metal cover, wherein the sheet metal cover covers the electronic element and the leg piece is soldered to the pattern land,
The planar shape of the portion of the pattern land that is not covered by the sheet metal cover is a rounded convex shape obtained by cutting the top of an isosceles right triangle along a predetermined arc, and the radius of curvature of the arc is An electronic circuit module having a size equal to or greater than a radius of a virtual circle inscribed in a pattern land.   2. The electronic circuit module according to claim 1, wherein an outer peripheral edge portion of the pattern land adjacent to both side portions of the leg piece is curved in a round shape.   The notch is formed in the lower end part of the said leg piece in Claim 1 or 2, When this leg piece is mounted on the said pattern land, the through-hole which uses the said pattern land as a bottom face by the said notch An electronic circuit module, wherein:   The projection according to any one of claims 1 to 3, wherein a protrusion is vertically provided at a lower end portion of the leg piece, and an engagement hole that protrudes on the pattern land is provided in the circuit board. The electronic circuit module is characterized in that, by inserting the protrusion into the engagement hole, the position of the protrusion is regulated in the radial direction of the engagement hole.

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