JP2010219087A - Mounting structure and mounting method of surface mount device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mounting structure and a mounting method of a surface mount device, which can prevent a solder ball from occurring. <P>SOLUTION: A printed wiring board (PWB) 200 includes: a land L1, which corresponds to a mounting part M formed on a bottom surface of a body part C of the surface mount device, on a substrate surface; and a land L2, which is isolated from the land L1 on the surface of the PWB 200, and which is covered with the bottom surface of the body part C so as not to be exposed in the lateral direction of the body part C of the surface mount device. Fused solder RS, which flows beyond resist R between the land L1 and land L2 to reach the land L2, of fused solder RS pushed out from between the mounting part M and land L1 to spread on the surface of the PWB 200 is stuck on the land L2. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a mounting structure in which a surface mounting component is mounted on a printed wiring board, and a mounting method in the mounting structure.

  Conventionally, insertion mounting is known as a method of mounting electronic components on a printed wiring board. As is well known, in insertion mounting, a lead wire of an electronic component is passed through a through hole provided in a printed wiring board, and the lead wire is soldered to a copper foil for soldering provided around the through hole.

  However, in insertion mounting, in order to maintain the strength of the printed wiring board, it is necessary to secure the interval between the through holes. Therefore, high-density wiring and electronic components are integrated on the surface of the printed wiring board. It was difficult.

  As a mounting method for solving the above-described problem, surface mounting in which an electronic component is directly soldered on a printed wiring board surface is known. Hereinafter, an electronic component used for surface mounting is referred to as a “surface mounting component”. The copper foil for soldering is referred to as “land”.

  As is well known, in surface mounting, a land (hereinafter referred to as “land for mounting”) for soldering the mounting portion formed on the bottom surface of the body of the surface mounting component and protruding from the body of the surface mounting component is formed. Lands (hereinafter referred to as “terminal lands”) for soldering the formed terminal portions are provided on the surface of the printed wiring board, and paste solder (hereinafter referred to as “solder paste”) is preliminarily provided on each land. Apply. Then, the mounting portion and the terminal portion of the surface mounting component are brought into contact with each land to which the solder paste is applied, and the printed wiring board on which the surface mounting component is placed is passed through a high temperature furnace to melt the solder paste. Then, the mounting portion and the mounting land, and the terminal portion and the terminal land are respectively soldered.

  In the surface mounting method, since there is no need to provide a through hole for passing the lead wire of the electronic component in the printed wiring board, the strength of the printed wiring board can be maintained, and the printed wiring board surface has a high density. Wiring and electronic components can be integrated. Thereby, the size of the printed wiring board can be reduced.

  However, on the other hand, since the solder paste is applied not only to the terminal portion of the surface mounting component but also to the mounting portion, a part of the molten solder paste is pushed out between the mounting portion and the mounting land, It may protrude to the side of the surface mount component and harden into a ball shape. The solder solidified in a ball shape is generally called a “solder ball”. In the following Patent Documents 1 to 7, a mounting structure and a mounting method for preventing the generation of solder balls are disclosed.

JP-A-6-61635 JP-A-7-297526 Japanese Patent Laid-Open No. 7-302970 JP-A-11-97826 JP 2003-8184 A Japanese Patent Laid-Open No. 2004-6454 JP 2004-186250 A

  On the surface of the printed wiring board excluding each land portion, a resist is applied to prevent solder from adhering to achieve electrical insulation and to protect the printed wiring board from the external environment. For this reason, solder balls generated on the printed circuit board surface or on the side of surface-mounted components can easily be removed from the position where the printed circuit board is subjected to impact or vibration and move on the printed circuit board surface. To do.

  For example, when a solder ball moves between terminals of a surface-mounted component or between terminals of other electronic components adjacent to the surface-mounted component, a solder bridge due to the solder ball occurs between the terminals of the destination, An electrical failure such as a short circuit may occur.

  In view of the above-described problems, an object of the present invention is to provide a mounting structure for a surface-mounted component and a mounting method that can prevent the generation of solder balls.

  The mounting structure according to the present invention is a mounting structure in which a surface mounting component is mounted on a printed wiring board, and the printed wiring board is mounted on the mounting surface formed on the bottom surface of the main body portion of the surface mounting component. A corresponding first land and a second land that is isolated from the first land on the board surface and is covered by the bottom surface of the main body so as not to be exposed to the side of the main body of the surface mount component. The surface-mounted component is mounted on the printed wiring board surface by bonding the mounting portion and the first land with paste solder applied only to the first land.

  By doing in this way, among the molten solder pushed out from between the mounting portion and the first land, the molten solder that is not concentrated on the first land due to the surface tension of the molten solder is formed on the bottom surface of the main body portion of the surface mounting component. It adheres to the second land to be covered and does not protrude to the side of the main body of the surface mount component. For this reason, it is possible to prevent the solder balls from being generated by the molten solder.

  In the mounting structure of the present invention, it is preferable that the peripheral edge of the bottom surface of the main body portion of the surface mount component is located outside the second land.

  By doing in this way, even if the molten solder pushed out between the mounting portion and the first land spreads slightly beyond the second land, it does not protrude to the side of the main body portion of the surface mounting component. The generation of solder balls can be more effectively prevented.

  In the mounting structure of the present invention, the long side of the second land may be parallel to the peripheral edge of the first land facing the long side, and the first land may have the same shape as the mounting portion. .

  By doing so, the position of the center of gravity of the surface-mounted component placed on the printed wiring board becomes unstable due to the molten solder pushed out between the mounting portion and the first land, and the mounting position of the surface-mounted component or Even if the orientation is deviated, the mounting position and orientation of the surface mounting component are restored by the surface tension of the molten solder concentrated on the first land having the same shape as the mounting portion, and the center of gravity position of the surface mounting component is restored. Is stable. For this reason, it is possible to suppress a deviation in the mounting position and orientation that occurs when the surface-mounted component is mounted on the printed wiring board.

  In the mounting structure of the present invention, the second land may surround the first land.

  By doing in this way, it can prevent effectively that the molten solder extruded from between the mounting part and the 1st land protrudes in many directions.

  In the mounting structure of the present invention, the printed wiring board has, on the board surface, a third land corresponding to the terminal portion formed to protrude from the main body portion of the surface mount component, and the second land is the third land. And may be located between the first land and the third land.

  By doing in this way, it can prevent that the molten solder pushed out from between a mounting part and a 1st land adheres to the terminal part connected to a 3rd land, and an electrical failure generate | occur | produces. .

  A mounting method according to the present invention is a mounting method in which a surface-mounted component is mounted on a printed wiring board using the surface-mounted component and the printed wiring board described above, and paste-like solder is applied only to the first land. Then, the mounting part is brought into contact with the first land to which the paste-like solder is applied, and the printed wiring board on which the surface mounting components are mounted is heated to melt the paste-like solder, and then the printed wiring board is cooled. By doing so, the mounting portion and the first land are joined, and the surface mounting component is mounted on the printed wiring board.

  By doing in this way, among the molten solder pushed out from between the mounting portion and the first land, the molten solder that is not concentrated on the first land due to the surface tension of the molten solder is formed on the bottom surface of the main body portion of the surface mounting component. It adheres to the second land to be covered and does not protrude to the side of the main body of the surface mount component. For this reason, it is possible to prevent the solder balls from being generated by the molten solder.

  According to the present invention, among the molten solder extruded from between the mounting portion and the first land, the molten solder that is not concentrated on the first land due to the surface tension of the molten solder is covered by the bottom surface of the main body portion of the surface mounting component. Since it adheres to the second land and does not protrude to the side of the main body of the surface mount component, it is possible to prevent the solder balls from being generated by the molten solder.

It is a perspective view of a surface mount component. It is a perspective view of a printed wiring board. It is a top view at the time of mounting a surface mounting component on a printed wiring board. It is the figure which showed the application method of paste-like solder. It is the figure which showed the application method of paste-like solder. It is the figure which showed the printed wiring board with which the paste-form solder was apply | coated, and surface mount components. It is the figure which showed the molten state of the paste-form solder. It is the figure which showed the molten state of the paste-form solder. It is the figure which showed the state by which the surface mounting components were joined to the printed wiring board. It is the figure which showed the other shape of the land. It is the figure which showed the other shape of the land. It is the figure which showed the other shape of the land. It is the figure which showed the other shape of the land.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 7 described later, the same reference numerals are given to the same or corresponding parts.

  FIG. 1A is a perspective view of the surface mount component 100 as viewed from above, and FIG. 1B is a perspective view of the surface mount component 100 as viewed from below. Hereinafter, the surface-mounted component is referred to as “SMD”.

  In the present embodiment, the SMD 100 is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Moreover, SMD100 is comprised from the main-body part C, the mounting part M, and the terminal parts T1-T3.

  The main body C is a resin mold made of, for example, an epoxy resin. An electronic circuit or the like (not shown) is accommodated in the main body C. The mounting part M is, for example, a plate-shaped heat sink formed by molding aluminum, copper, or the like. Moreover, the mounting part M is formed in most part of the bottom face Cf of the main-body part C, as shown to (b) of FIG. The mounting portion M is provided to dissipate heat generated in the SMD 100 during operation of the SMD 100 and suppress an excessive temperature rise in the SMD 100. The terminal portion T1 is a gate terminal of the MOSFET, the terminal portion T2 is a drain terminal of the MOSFET, and the terminal portion T1 is a source terminal of the MOSFET. Further, the terminal portions T1 to T3 are formed so as to protrude from the main body portion C as shown in FIG.

  Here, as shown in FIG. 1B, the mounting portion M is embedded in the bottom surface Cf of the main body portion C with the surface Mf exposed to the outside. The mounting portion M in the embedded portion is surrounded by the resin mold of the main body C on three sides. The bottom surface Cf of the main body C and the surface Mf of the mounting part M are on the same plane. Moreover, a part of the mounting part M protrudes in a direction opposite to the protruding direction of the terminal parts T1 to T3.

  FIG. 2 is a perspective view of a printed wiring board 200 on which the SMD 100 is mounted. Hereinafter, the printed wiring board is referred to as “PWB”.

  In PWB200, L1 to L5 are lands, and are formed of, for example, copper foil. R indicated by the hatched portion is a resist, and is made of, for example, a solder resist that prevents adhesion of solder to achieve electrical insulation and protects the PWB from the external environment. Details of the lands L1 to L5 will be described with reference to FIG. FIG. 3 is a top view when the SMD 100 is mounted on the PWB 200.

  As shown in FIG. 3, the land L1 is a land corresponding to the mounting portion M formed on the bottom surface Cf (the region within the one-dot chain line portion) of the main body C (one-dot chain line portion) of the SMD 100 (FIG. 1). The land L1 is an embodiment of the first land in the present invention. Further, the land L1 is formed in the same shape as the mounting portion M. However, since it becomes difficult to understand when the land L1 and the mounting portion M overlap with each other, in FIG. 3, the mounting portion M is illustrated inside the land L1.

  The land L2 is a land that is isolated from the land L1 on the PWB 200 surface and is covered with the bottom surface Cf of the main body C so as not to be exposed to the side of the main body C. The land L2 is an embodiment of the second land in the present invention. Moreover, the periphery (namely, the dashed-dotted line of FIG. 3) of the bottom face Cf of the main-body part C is located outside the land L2. Further, the long side of the land L2 is parallel to the peripheral edge of the land L1 facing the long side, and the land L2 surrounds the land L1. When the outer dimension of the mounting portion M is 55 [mm] × 50 [mm] and the outer dimensions of the terminal portions T1 to T3 are 10 [mm] × 7.5 [mm], the distance between the land L1 and the land L2 For example, the width d1 of the resist R is about 0.2 [mm] to 0.5 [mm].

  The lands L <b> 3 to L <b> 5 are lands corresponding to terminal portions T <b> 1 to T <b> 3 (two-dot chain line portions) formed so as to protrude from the main body portion C of the SMD 100. These lands L3 to L5 are an embodiment of the third land in the present invention. The lands L3 to L5 are formed smaller than the land L1. Further, the lands L3 to L5 are located outside the bottom surface Cf of the main body C. When the outer dimensions of the mounting portion M are 55 [mm] × 50 [mm] and the outer dimensions of the terminal portions T1 to T3 are 10 [mm] × 7.5 [mm], the lands L3 to L5 and the lands L2 The width d2 of the resist R in between is about 1.3 [mm] to 1.5 [mm], for example. That is, the land L2 is isolated from the lands L3 to L5 and is located between the lands L1 and L3 to L5.

  When the SMD 100 having the above configuration is mounted on the PWB 200, in this embodiment, no solder paste is applied to the lands L2, and only the lands L1, L3, L4, and L5 have paste-like solder (hereinafter, “ Apply “solder paste”. Then, the mounting portion M is brought into contact with the land L1 to which the solder paste is applied. Similarly, the terminal portions T1, T2, and T3 are brought into contact with the lands L3, L4, and L5 to which the solder paste is applied, respectively. Next, the PWB 200 on which the SMD 100 is placed is heated to melt the solder paste. Thereafter, by cooling the PWB 200, the mounting portion M and the land L1 are joined, and the terminal portions T1, T2, and T3 are joined to the lands L3, L4, and L5. The SMD 100 is mounted on the PWB 200 through the above steps.

  Hereinafter, the procedure of the mounting method will be described in more detail. First, a method of applying a solder paste to the land L1 and the lands L3 to L5 on the PWB 200 surface will be described with reference to FIGS.

  In FIG. 4, reference numeral 300 denotes a covering member (hereinafter referred to as “mask”) used when applying solder paste to each land on the PWB 200 surface. The mask 300 is, for example, a plate obtained by molding a nickel alloy or the like. It is comprised from the shaped member. The mask 300 has holes H1 to H4 for applying solder paste to the lands on the surface of the PWB 200, and the holes have the same shape as the corresponding lands.

  Specifically, the mask 300 is formed with a hole H1 corresponding to the land L1, a hole H2 corresponding to the land L3, a hole H3 corresponding to the land L4, and a hole H4 corresponding to the land L5. Yes. In the present embodiment, since no solder paste is applied to the lands L2, holes corresponding to the lands L2 are not formed in the mask 300.

  When applying the solder paste to the lands L1, L3 to L5, as shown in FIG. 5, the lands 300 and the holes corresponding to the lands are aligned with each other, and the mask 300 is overlaid on the PWB 200. Then, after applying the solder paste PS (colored portion) on the mask 300, the solder paste PS is embedded only in the holes H1 to H4 using a spatula member such as a squeegee (not shown).

  When applying the solder paste PS, the solder paste PS is embedded in each hole so that the surface of the mask 300 and the surface of the solder paste PS in each hole are on the same plane. Thereby, it is possible to prevent the SMD 100 mounted on the PWB 200 from being inclined when the mounting portion M and the terminal portions T1 to T3 are brought into contact with each land to which the solder paste PS is applied.

  Next, the SMD 100 is placed on the PWB 200 to which the solder paste PS is applied. Details will be described with reference to FIG.

  As shown in FIG. 6, when the SMD 100 is placed on the PWB 200, the mask 300 used for applying the solder paste PS is slowly lifted from the surface of the PWB 200 and removed. As a result, lands L1 and lands L3 to L5 coated with the same thickness of solder paste PS appear on the PWB 200 surface.

  Subsequently, using a surface mounter (not shown), the mounting portion M is brought into contact with the land L1 to which the solder paste PS has been applied and the land to which the solder paste PS has been applied in a state along the broken line in the drawing. The terminal portions T1 to T3 are brought into contact with L3 to L5, respectively. Thereby, SMD100 will be in the state mounted on PWB200.

  Finally, the SMD 100 is mounted on the PWB 200. That is, the PWB 200 is heated to melt the solder paste PS between the mounting portion M and the land L1, and the solder paste PS between the terminal portions T1, T2, and T3 and the lands L3, L4, and L5 is melted. . Thereafter, the molten solder paste is cooled to join the mounting portion M and the land L1, and the terminal portions T1, T2, and T3 and the lands L3, L4, and L5 are joined. Details will be described with reference to FIGS. In addition, about joining of each terminal part (T1-T3) and each land (L3-L5) corresponding to the said terminal part, since there is no direct relationship with this invention, description is abbreviate | omitted below.

  FIG. 7 is a top view when the SMD 100 is mounted on the PWB 200, and shows a state where the solder paste between the mounting portion M and the land L1 is melted. As shown in the colored portion of FIG. 7, when the solder paste is melted, the melted solder paste (hereinafter referred to as “molten solder”) RS is pushed out from between the mounting portion M and the land L1, and on the surface of the PWB 200. To spread. In FIG. 7, the molten solder RS extends beyond the resist R between the land L1 and the land L2.

  Since the center of gravity of the SMD 100 including the mounting portion M becomes unstable due to the spread of the molten solder RS in this manner, a mounting position or orientation shift occurs between the mounting portion M and the land L1. There is. For example, the position of the mounting portion M (indicated by the dotted line in FIG. 7) that has fallen within the land L1 may be shifted to the lower left as indicated by the dotted line in FIG. In addition, when the position of the mounting part M shift | deviates, the position of the main-body part C and the terminal parts T1-T3 will also shift. That is, the mounting position and the orientation are shifted throughout the SMD 100.

  However, as shown in FIG. 9, the molten solder RS that has reached the land L2 out of the molten solder RS that has spread beyond the resist R between the land L1 and the land L2 adheres to the land L2. Then, the molten solder RS that has not adhered to the land L2 is pulled back to the land L1 by the surface tension of the molten solder RS and is collected there. Thereafter, the molten solder RS concentrated on the land L1 is cooled, and the land L1 and the mounting portion M are joined. As a result, the SMD 100 is mounted on the PWB 200.

  As described above, in the above-described embodiment, the molten solder RS pushed out from between the mounting portion M and the land L1 and spread on the surface of the PWB 200 exceeds the resist R between the land L1 and the land L2. Then, the molten solder RS that has reached the land L2 adheres to the land L2. Further, the molten solder RS that has not adhered to the land L2 is concentrated in the land L1 having the same shape as the mounting portion M due to the surface tension of the molten solder RS.

  Thereby, it is possible to prevent the molten solder RS, which has been pushed out from between the mounting portion M and the land L <b> 1 and spread, from protruding to the side of the main body portion C of the SMD 100. That is, by preventing the spread of the molten solder RS from the land L2 and preventing the molten solder RS from protruding to the side of the main body C of the SMD 100, it is possible to prevent the generation of solder balls.

  Further, since the periphery of the bottom surface Cf of the main body C of the SMD 100 is located outside the land L2, the molten solder RS pushed out between the mounting portion M and the land L1 spread slightly beyond the land L2. However, it does not reach the side of the main body C of the SMD 100. Thereby, generation | occurrence | production of a solder ball can be prevented more effectively.

  Further, the mounting position and orientation of the SMD 100 are restored by the surface tension of the molten solder RS concentrated on the land L1 having the same shape as the mounting portion M, and the center of gravity position of the SMD 100 is stabilized. For this reason, it is possible to suppress a deviation in mounting position and orientation that occurs when the SMD 100 is mounted on the PWB 200.

  Further, since the land L2 surrounds the land L1, it is possible to effectively prevent the molten solder RS pushed out between the mounting portion M and the land L1 from protruding in multiple directions.

  Furthermore, among the molten solder RS that is pushed out from the mounting portion M and the land L1 and spreads, the molten solder RS that spreads toward the lands L3 to L5 also adheres to the land L2, so that the molten solder RS is connected to the lands L3 to L5. It is possible to prevent an electrical failure such as a short circuit from occurring due to adhesion to the terminal portions T1 to T3 connected to the.

  In the present invention, various embodiments other than those described above can be adopted. For example, in the above embodiment, the SMD 100 is a MOSFET, but the present invention is not limited to this, and may be a CPU (Central Processing Unit), a three-terminal regulator, or the like.

  Moreover, in the said embodiment, although the mounting part M was made into the plate-shaped heat sink which shape | molded aluminum, copper, etc., it is not restricted to this, What is necessary is just a member which can join a solder. Further, the heat sink function may not be provided. For this reason, the terminal for transmitting an electric signal like terminal part T1-T3 may be sufficient, for example.

  Moreover, in the said embodiment, although the shape of the land L1 was made into the square, it is not restricted to this, What is necessary is just the shape corresponding to the shape of the mounting part M. In this case, the land L2 is also formed according to the shape of the land L1. For example, the shapes of the land L1 and the land L2 may be the shapes shown in FIGS.

  Moreover, in the said embodiment, although the land L2 was a continuous shape, as shown in FIG. 12, the shape which has a discontinuous part in part may be sufficient, for example.

  In the above embodiment, the land L2 surrounds the land L1. However, the present invention is not limited to this. For example, as shown in FIG. 13, the land L2 may have a linear shape that does not surround the land L1.

  Further, in the above-described embodiment, the width d1 of the resist R between the lands L1 and L2 is about 0.2 [mm] to 0.5 [mm], and is between the lands L3 to L5 and the lands L2. The width d2 of the resist R is set to about 1.3 [mm] to 1.5 [mm]. However, these widths are not limited to the above, and depending on the specifications (shape and size) of the surface mount component to be mounted. Adjust it.

100 Surface mount components (SMD)
200 Printed wiring board (PWB)
C body portion Cf bottom surface M mounting portion R resist T1 to T3 terminal portion L1 to L5 land PS paste-like solder RS molten solder

Claims (6)

In a mounting structure in which surface-mounted components are mounted on a printed wiring board,
The printed wiring board is separated from the first land on the board surface, the first land corresponding to the mounting part formed on the bottom surface of the main body part of the surface-mounted component, and the first land on the board surface. A second land that is covered by the bottom surface of the main body so as not to be exposed to the side of the main body of the mounting component;
The surface mounting component is mounted on the printed wiring board surface by bonding the mounting portion and the first land with paste solder applied only to the first land. Mounting structure for surface mounting components. The mounting structure according to claim 1,
A mounting structure for a surface-mounted component, wherein a peripheral edge of a bottom surface of the main body is located outside the second land. In the mounting structure according to claim 1 or 2,
A long side of the second land is parallel to a peripheral edge of the first land facing the long side, and the first land has the same shape as the mounting portion. Implementation method. In the mounting structure according to any one of claims 1 to 3,
The method for mounting a surface-mounted component, wherein the second land surrounds the first land. In the mounting structure according to any one of claims 1 to 4,
The printed wiring board has a third land corresponding to a terminal part formed on the board surface so as to protrude from the main body part of the surface-mounted component,
The surface mount component mounting structure, wherein the second land is isolated from the third land and positioned between the first land and the third land. Surface mount components,
A first land corresponding to the mounting portion formed on the bottom surface of the main body portion of the surface mount component on the substrate surface, and the first land on the substrate surface is isolated from the first land, and is on the main body portion side of the surface mount component. A printed wiring board having a second land that is covered with the bottom surface of the main body so as not to be exposed, and mounting the surface-mounted component on the printed wiring board,
Applying paste solder only to the first land, bringing the mounting portion into contact with the first land to which the paste solder has been applied, and heating the printed wiring board on which the surface mount component is mounted Melting the paste-like solder, and then cooling the printed wiring board to join the mounting portion and the first land, and to mount the surface-mounted component on the printed wiring board. A mounting method of a surface mount component which is a feature.

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