JPH09181427A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent formation of a fillet on a lower part of a shield plate, by forming a groove or aperture of a shape corresponding to a junction surface of a surface mounting component with a board, on a land provided for mounting the surface mounting component on the board. SOLUTION: Rail-like lands 13 are provided on a printed wiring board 10, and a shield plate 3 is located so as to be sandwiched between the lands 13. A cream solder 14 is applied to each of the lands 13 and then caused to reflow. Thus, by providing the lands 13 at such positions as to sandwich the shield plate 3 without providing a copper foil portion on a lower part of the shield plate 3 and by preventing the cream solder 14 from being supplied to the lower part of the shield 3, the melted cream solder 14 does not flow under the shield plate 3 at the time of reflow. Therefore, formation of a fillet on the lower part of the shield plate 3 may be prevented.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. TECHNICAL FIELD OF THE INVENTION Conventional Technology (FIG. 10) Problems to be Solved by the Invention (FIGS. 11 to 13) Means for Solving the Problems Embodiments of the Invention (FIGS. 1 to 9)

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board, and is suitable for application to, for example, soldering surface mount components in a lump by reflow soldering.

[0003]

2. Description of the Related Art Conventionally, when a surface mount component is soldered to a printed wiring board, it is soldered by a reflow method in order to improve the efficiency of the soldering process. That is, in a desired wiring pattern formed on a printed wiring board, a solder layer is formed in advance by solder-printing creamy solder on each land portion on which the terminal portion of each mounting component is mounted. The terminals are placed on the lands, respectively, and the mounted components are temporarily fixed on the printed wiring board. By heating the printed wiring board on which the mounted components are arranged on the surface by, for example, a reflow furnace, the solder layer formed on the surface is heated and melted to form a flit for joining the land and the terminal of the mounted component. Thus, the components to be mounted on the printed wiring board can be soldered together.

By the way, in the printed wiring board, a metal plate called a shield plate is provided in order to prevent noise due to electromagnetic waves or the like from entering from the outside or generated inside from interfering with electronic parts and circuits on the printed wiring board. ing. The shield plate is connected to the ground line, and it prevents or reduces the influence of noise on electronic parts and circuits by catching the noise entering from the outside or the noise generated internally and letting it escape to the ground line. There is. When mounting such a shield plate on a printed wiring board, it is generally mounted by screws or the like.

However, in the case of such mounting, it is necessary to provide a mounting hole for a screw on the printed wiring board. Therefore, it is necessary to secure an extra area for mounting, which is unsuitable when high-density mounting is required. In order to avoid such a problem, a method of soldering the shield plate together with other components is used.

The shield plate thus mounted on the printed wiring board is visually inspected for the soldering condition by a detection method utilizing light reflection. As shown in FIG. 10, light is emitted from the light source 5 to the solder joint portion of the shield plate 3 mounted together with other electronic components 2 on the printed wiring board 1, that is, between the shield plate 3 and the land 4. The solder joint between the shield plate 3 and the land 4 is inspected by using the reflected light obtained by reflecting the light thus irradiated at the joint. For example, the reflected light is imaged by a CCD camera (not shown) and image processing is performed to visually inspect the solder joint. By such inspection, the shield plate 3 and the land 4 are reliably soldered, or the solder joining the shield plate 3 to the land 4 is bridged and short-circuited to the terminal of another electronic component 2. You can check whether it is not.

[0007]

By the way, in such a printed wiring board, in order to inspect the solder joint portion of the mounted shield plate 3, the reflected light of the light irradiated to the solder joint portion as described above is used. Is used. As shown in FIG. 11, the shield plate 3 (see FIG.
0) and the land 4 (FIG. 10) are joined to each other and the folds 5 formed by the solder spread on the side surface of the shield plate 3 in a skirt shape, the soldered state is obtained by performing the appearance inspection as described above. Can be easily inspected.

However, since the shield plate 3 and the land 4 are joined together, a solder layer is formed between the shield plate 3 and the land 4. Therefore, as shown in FIG. 12, the fillet 5 may be formed only on the lower portion of the shield plate 3. In this way, when the fillet 5 is formed only on the lower part of the shield plate 3 and a component having a high height is arranged around the shield plate 3, the irradiation angle of the light radiated to the solder joint is limited. Therefore, there is a problem that it is difficult to detect the soldering state by an appearance inspection using reflected light. However, in order to avoid this, if only the shield plate 3 is mounted in a separate process, the efficiency decreases due to the increase in the number of processes.

Further, when the fillet 5 is formed only on the lower part of the shield plate 3 as described above, the fillet 5 lifts the shield plate 3, and the height of the entire shield plate 3 is increased due to the bias of the solder. There is a problem of variation. When the printed wiring board 1 provided with such a shield plate 3 is to be housed in a predetermined housing, there are cases where the height-variable portions are supported by the surroundings and the housing cannot be housed in the housing.

Further, the amount of solder supplied to form the solder layer between the shield plate 3 and the land 4 is limited so that only a predetermined amount is supplied. For this reason, as shown in FIG. 13, when the solder is biased to a part to form the fillet 5, a part where the fillet 5 is not formed occurs due to insufficient solder. Therefore, there is a problem that the electrical connection between the shield plate 3 and the printed wiring board 1 cannot be perfected and the shield effect is reduced to half.

The present invention has been made in consideration of the above points, and an object thereof is to propose a printed wiring board which can improve the reliability of soldering and can easily inspect the soldered portion. .

[0012]

In order to solve such a problem, according to the present invention, a land provided for mounting a surface mount component on a substrate has a shape corresponding to a surface to be joined with the substrate. A groove or an opening is formed.

When the solder applied to the surface of the land is heated and melted, it does not flow into the groove or opening, and a fillet is formed on a portion other than the contact surface of the surface-mounted component with the substrate to mount the surface-mounted component on the land. It is possible to suppress the unevenness of the height of the contact surface of the surface mount component, and it is possible to eliminate an unbonded portion with the substrate.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

In FIG. 1, reference numeral 10 denotes a printed wiring board as a whole, and a land 11 and a land 12 for mounting an electronic component 2 (FIG. 10) and a shield plate 3 (FIG. 1).
0) are mounted on the surface of the substrate. The shield plate 3 is provided at an intermediate position that separates the lands 11 or 12 from each other in order to prevent noise due to electromagnetic waves generated by the lands 11 or 12 from affecting the lands 12 or 11. That is, the land 13 for mounting the shield plate 3 on the printed wiring board 10 is connected to the ground line (not shown), and catches noise generated by the electronic components 2 mounted on the land 11 and the land 12. As a result, the noise is prevented from interfering with each electronic component 2 and the circuit.

As shown in FIG. 2, the land 13 is formed in a rail shape for mounting the flat shield plate 3, and the interval between the rails is made slightly larger than the thickness of the shield plate 3. . A solder resist is applied on the printed wiring board 10 other than the lands 11, 12 and 13 so that the solder does not spread. However, the solder resist is not applied between the rail-shaped lands 12. In addition, as shown in FIG. 3, the printed wiring board 10 includes the shield plate 3 between the rail-shaped lands 13.
And the cream solder 14 is supplied onto each land 13 by, for example, a printing method. After the solder is supplied to the land 13 in this manner, the printed wiring board 10 is reflowed. As shown in FIG. 4, in the printed wiring board 10 thus reflowed, the cream solder 14 is melted to form the fret 15, and the flute 15 joins the shield plate 3 to the land 13. ing.

In the above structure, the printed wiring board 1
0 is provided with rail-shaped land 13 and land 13
The shield plate 3 (FIG. 10) is arranged so as to be sandwiched between them, and the cream solder 14 is applied to each of the lands 13 and then reflowed. As described above, the copper foil portion is not provided under the shield plate 3, the land 13 is provided at a position where the shield plate 3 is sandwiched, and the cream solder 14 is not supplied to the lower portion of the shield plate 3, so that the reflow process is not performed. The melted cream solder 14 sometimes does not flow into the lower part of the shield plate 3. Therefore, the fillet 15 is not formed in the lower part of the shield plate 3, but is formed only in the side surface part, and it is possible to prevent the fillet plate 3 from being lifted by the fillet 15. Can be suppressed.

Since the melted cream solder 14 is prevented from flowing into the lower portion of the shield plate 3 in this way, the fillet 15 is formed only on the side surface portion of the shield plate 3. As a result, the cream solder 14 that has melted and flowed into the lower portion of the shield plate 3 can be prevented from being partially biased. Thus, the fillet 15 is uniformly formed on the side surface of the shield plate 3, and the portion where the shield plate 3 and the substrate are not joined can be eliminated.

According to the above configuration, when reflow soldering is performed together with other electronic components 2, the land 13 having a rail shape is provided, and the shield plate 3 is arranged between the lands 13 for soldering. As a result, when the cream solder 14 applied to the land 13 is heated and melted, the cream solder 14 does not flow into the land 13 and does not flow into the side surface of the shield plate 3 only.
Since the shield plate 3 can be joined to the land 13 by forming 5, the variation in the height of the shield plate 3 can be suppressed and the unjoined portion of the shield plate 3 with the substrate can be eliminated. Thus, it is possible to realize the printed wiring board 10 which can improve the reliability of soldering and can easily inspect the soldered portion.

In the above-described embodiment, the case where the rail-shaped lands 13 are provided and soldered to the shield plate 3 arranged so as to be sandwiched between the lands 13 has been described, but the present invention is not limited to this. However, the lands having height differences may be provided, and the shield plate 3 may be arranged between the lands.

For example, as shown in FIG. 5, lands 16 having a height difference are provided, and the shield plate 3 is arranged between the lands 16. The land 16 has an L-shape having a low height near the side surface of the shield plate 3, and cream solder is supplied to this low portion. By reflowing the printed wiring board provided with such lands 16, the heated and melted cream solder forms the fillet 17 on the side surface of the shield plate 3. At this time, since the land 16 is provided with a height difference, the melted cream solder can be flowed only to the side surface portion of the shield plate 3 by playing a so-called role. Thus, the fillet 17 on the side of the shield plate 3
Can be formed more reliably.

In the above embodiment, the case where the land 13 having a rail shape is provided and the shield plate 3 is mounted is described, but the present invention is not limited to this.
You may apply to the land which mounts another electronic component on a board | substrate. For example, as shown in FIG. 6, QFP (Quarter Flat P
It may be applied to the land 18 for mounting an ackage type electronic component on the substrate.

In the QFP type electronic component, the terminals to be joined to the lands are provided on all sides, so the lands 18 are arranged on all sides. The land 18 is
A groove corresponding to the size of the terminal is provided at a position where the terminal of the QFP type electronic component comes into contact with the surface of the substrate. The parts are arranged so that the terminals are fitted in the grooves. Here, the groove of the land 18 is provided with a slightly larger area than the surface of the terminal of the QFP type electronic component that contacts the substrate. As shown in FIG. 7, the land 1
The terminal 20 of the QFP type electronic component 19 is provided in the groove provided in FIG.
Are placed and then cream solder 21 is applied to the land 18 for reflow. As shown in FIG. 8, the cream solder 21 heated and melted by the reflow process is
The terminals 20 are joined to the lands 18 by forming the fi les 22 on the upper surface and the back surface of the.

As described above, by joining the terminals 20 using the lands 18 having the grooves corresponding to the size of the terminals 20, the melted cream solder 21 does not flow into the groove portions, and the fillet 22 is not formed. For this reason, the cream solder 21 that has flowed into the lower portion of the terminal 20 is
It is possible to prevent the solder-unbonded state (templar) of the terminal 20 from occurring due to the height variation due to the lifting. As shown in FIG. 9, if the variation in the height of the terminal 20 is within the thickness of the land 18, the unsoldered state can be avoided as in the case described above.

[0025]

As described above, according to the present invention, a groove or opening having a shape corresponding to the joint surface of the surface mount component with the substrate is formed in the land provided for mounting the surface mount component on the substrate. As a result, when the solder applied to the land surface is heated and melted, it does not flow into the groove or opening, and the surface mount component is formed by forming a fillet on the part other than the contact surface with the substrate. Can be joined to the land,
It is possible to suppress variations in the height of the abutting surface of the surface-mounted component, and to eliminate unbonded parts with the board. In doing so, the reliability of soldering can be improved and the soldered parts It is possible to realize a printed wiring board that can be easily inspected.

[Brief description of the drawings]

FIG. 1 is a plan view showing a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a side view provided for explaining an arrangement state of rail-shaped lands.

FIG. 3 is a side view showing a state of a shield plate and solder before reflow.

FIG. 4 is a side view showing a state of a shield plate and a fillet after reflow.

FIG. 5 is a side view showing a shape of a land according to another embodiment.

FIG. 6 is a plan view showing a shape of a land according to another embodiment.

FIG. 7 is a side view showing a state of terminals and solder before reflow.

FIG. 8 is a side view showing a state of the terminal portion and the fillet after the reflow.

FIG. 9 is a side view provided for explaining the limit of the height of the terminal that varies during soldering.

FIG. 10 is a side view showing a visual inspection method of a solder joint portion using reflected light.

FIG. 11 is a side view showing a case where the inspection can be performed easily.

FIG. 12 is a side view showing a case where the inspection cannot be performed easily.

FIG. 13 is a perspective view showing a non-formed state due to bias of solder.

[Explanation of symbols]

1, 10 ... Printed wiring board, 2, 19 ... Electronic component, 3 ... Shield plate, 4, 11, 12, 13, 16,
18 ... Land, 5 ... Light source, 14, 21 ... Cream solder, 15, 17, 22 ... Fillet, 20 ... Terminal.

Claims (3)

[Claims] 1. A printed wiring board for mounting a surface mount component on a substrate by reflow soldering, wherein a groove or opening having a shape and size corresponding to a solder joint surface of the surface mount component with the substrate is formed. A printed wiring board comprising a land provided. 2. The printed wiring board according to claim 1, wherein the groove or opening is formed slightly larger than the solder joint surface of the surface mount component. 3. The printed wiring board according to claim 1, wherein the land has an outer peripheral portion higher than an inner peripheral portion of the groove or opening.