JP3503232B2 - Structure of printed wiring board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board structure.

[0002]

2. Description of the Related Art As a conventional printed wiring board structure,
For example, there is one as shown in FIG. First, the configuration will be described. The printed wiring board has a base portion 1 which is an insulator, and a wiring pattern 2 which is a conductor (copper foil) is formed thereon. Between the one wiring pattern 2 and the other wiring pattern 2 on the base portion 1, the surface of the printed wiring board is covered to prevent the solder 4 from adhering to unnecessary places during soldering. The solder resist 7 is formed. Furthermore, a paint layer 3 showing characters and figures for the purpose of recognition and visual confirmation when the component is mounted by a mounting machine or the like is formed on the solder resist 7 by silk printing. Further, in recent years, electronic parts are rapidly becoming smaller and higher in density. In addition to the above-mentioned recognition and visual confirmation, the paint layer 3 formed by silk printing has a narrow pitch surface mount component 5.
There is also an idea of having a role of preventing a solder bridge of a chip resistor, a chip capacitor, a QFP (quad flat package, etc.). In addition, 6 is a terminal of the surface mount component 5.

[0003]

However, in such a conventional printed wiring board structure, the purpose of the paint layer by silk printing is to improve the visibility and to improve the process yield such as prevention of bridges. However, the yield of required parts has been improved by the combination of components, but the long-term durability and reliability have been improved by combining components. From the standpoint of reliability, no progress has been made, and with the miniaturization and high density of electronic components being required for improved portability and environmental resistance, only long-term durability and reliability have been left behind. There was a problem.

The present invention has been made to solve the problems of the prior art as described above, and it is an object of the present invention to provide a structure of a printed wiring board capable of improving long-term durability and reliability with a simple structure. To aim.

[0005]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, in the invention according to claim 1, in the structure of a so-called printed wiring board in which a conductor wiring is formed on an insulator and a surface mounting component is solder-bonded on the conductor wiring, the surface mounting component is The solder resist is overlapped on a part of the land of the conductor wiring located immediately below the mounting planned portion, and the paint layer by silk printing is further provided on the overlapping portion of the land and the solder resist, on overlaid a part of the land of the conductor lines and the upper <br/> Symbol solder resist and the coating layer, the coating
The surface mount component is arranged in contact with the material layer . The above structure corresponds to, for example, the embodiment shown in FIG. 1 described later. In addition, the land of the conductor wiring means a portion of the conductor wiring to which solder is provided to connect the mounted components. In addition, the paint layer by silk printing is usually provided for the purpose of showing characters and figures for the purpose of recognition and visual confirmation when mounting a component by a mounting machine or the like. It is provided to get the standoff height.

[0006] Also, in the invention described in claim 2,
The land, the solder resist, and the portion of the paint layer formed by silk printing overlapping each other are arranged so as to surround the land along the outer periphery of the land of the surface-mounted component. In addition,
This configuration corresponds to, for example, the embodiment shown in FIG. 2 described later.

[0007]

As described above, in the present invention, the paint layer by silk printing and the solder resist are arranged in a structure different from the conventional one. In other words, by overlapping the solder resist and the paint layer by silk printing on the land of the wiring pattern and increasing the solder standoff height of the component, the structure is simple, and the long-term durability of the solder joint is achieved without increasing the process cost. It has improved reliability. As will be described later in detail, in a particularly harsh environment, the standoff height has a great influence on ensuring long-term durability and reliability, and according to an experiment by the present inventor, the standoff height is doubled. It became clear that the life would be more than four times longer.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 1 is a sectional view of an embodiment of the present invention. First, the structure will be described. A land 20 having a wiring pattern is formed on a base 11 which is an insulator. The land of the wiring pattern means a portion of the wiring pattern on which the solder 19 is provided and the mounting component (surface mounting component) 15 is connected. The land 20 is formed slightly larger in the longitudinal direction of the land of the mounted component than that of the conventional example. How large the film is to be formed depends on the printing resolution of the process, but about 0.3 mm is necessary.
However, the wiring pattern 12 in which no parts are to be placed may be exactly the same as a normal one. In addition, 16 is a mounted component 15
Is the terminal.

The solder resist 1 is formed so as to cover a part of the land 20 of the slightly larger wiring pattern.
8 is formed. The size of this cover also depends on the printing resolution of the process, but it is still necessary to have a size of about 0.3 mm. Further, the paint layer 17 is formed by silk printing on the solder resist 18 which covers a part. Since the paint layer 17 formed by silk printing is formed for the purpose of its thickness, it is not necessary to specify the thickness, but it is considered that about 0.1 to 0.2 mm is necessary. Then, the actual mounting component 15 (chip resistor, chip capacitor, QFP, etc.) is arranged on the base 11 on which the solder resist 18 and the paint layer 17 by silk printing are overlapped, and the land 19 is electrically connected to the land 20 by the solder 19. Mechanically connected.

Next, the operation will be described. In this embodiment, the wiring pattern 20 (usually 35 μm in thickness), the solder resist 18 (usually 20 to 40 μm in thickness) and the paint layer 17 (usually around 25 μm in thickness) by silk printing are superposed on each other. With a very simple structure, a large standoff height (usually 80 to 100 μm) can be formed. It cannot be said to be definitive because it depends on the size of the mounted components and the linear expansion coefficient of the printed wiring board, but in experiments by the present inventor, this standoff height is several μm to several tens of μm in a particularly severe environment. It has been found that it is difficult to secure reliability to some extent. Moreover, according to the experiment of the present inventor,
It was found that when the standoff height is doubled, the life is more than four times longer.

Conventionally, an improvement plan for the purpose of process yield / inspection (for example, disclosed in Japanese Patent Laid-Open No. 62-118478) or a process is largely changed to use additional members to increase the standoff height. Method (for example, JP-A-64-47)
However, the structure of the present embodiment has a much simpler structure than the above-mentioned conventional example, and the drawing considerations (the land 20 may be slightly different) when designing a mask for a printed wiring board. All that has to be done is to increase the size and set the position of the paint layer 17 by silk printing, and no change in the manufacturing process is required. Therefore, there is almost no cost increase. Further, the above-mentioned conventional method (Japanese Patent Laid-Open No. 64-47)
No. 092), because of its structure, it is necessary to limit the wiring pattern that passes directly under the component, or to raise the central portion to increase the standoff height, so the so-called Manhattan phenomenon (also called tombstone phenomenon. Due to the large surface tension, one side of the mounted component floats up, and the mounted component may rise frequently). In this respect, in the present embodiment, since the size of the land of the wiring pattern which originally exists is only slightly increased, the influence on the limitation of the wiring pattern immediately below the component is extremely small, and a structure for lifting the vicinity of both ends of the component is adopted. Since it has, there is no fear that the Manhattan phenomenon frequently occurs.

Next, FIG. 2 is a sectional view showing a second embodiment of the present invention. First, the configuration will be described. A wiring pattern 12 on which no components are mounted is formed on a base 11 which is an insulator. In addition, QFP31 which is a surface mount component
The land 20 of the wiring pattern located in the lower part of is formed slightly larger than that normally formed. The size to be specifically expanded greatly depends on the size and shape of the QFP 31, and therefore cannot be uniformly determined, but the effect of the present embodiment cannot be expected unless it is larger than the outer circumference of the epoxy resin of the QFP 31. In this embodiment, an overlapping portion of the land, the solder resist, and the paint layer formed by silk printing is arranged so as to surround the land along the periphery of the land of the surface mount component. Note that, similarly to the embodiment of FIG. 1, it is also provided directly below the surface mount component.

A solder resist 18 is formed on the land 20 having a larger size. The solder resist 18 needs to overlap the land 20 at least about 0.3 mm. A paint layer 17 formed by silk printing is formed on the solder resist 18 and the land 20 which are overlapped with each other. The thickness of the paint layer 17 formed by silk printing cannot be unequivocally related to the pin pitch of the QFP 31, but about 0.1 mm is required. And land 20
A terminal (lead frame) 32 of the QFP 31 is electrically and mechanically joined to the top by the solder 19.

Next, the operation will be described. The operation is basically the same as the operation shown in FIG. 1, and the standoff height of the solder 19 is increased to improve the life of the solder joint. When the component to be mounted is QFP, the lead frame 3 may be used to prevent solder bridging in some cases.
A method of flowing excess solder in the tip direction of 2 may also be effective. In such a case, the solder resist formed on the tip end direction of the lead frame 32 shown in FIG. 2 and the paint layer by silk printing are not essential.

[0015]

As described above, according to the present invention, the solder standoff height of a component is simple with a structure in which a solder resist and a paint layer by silk printing are superposed on the land of the wiring pattern. And the long-term durability reliability of the solder joint can be improved without increasing the process cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base part 13 ... Paint layer 2 by silk printing ... Wiring pattern 15 ... Surface mount component 3 ... Paint layer by silk printing 16 ... Terminal 4 of surface mount component 15 ... Solder 17 ... Paint layer 5 by silk print ... Surface mount component 18 ... Solder resist 6 ... Surface mount component 5 terminals 19 ... Solder 7 ... Solder resist 20 ... Wiring pattern land 11 ... Base material 31 ... QFP 12 ... Wiring pattern 32 ... QFP31
Terminal

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H05K 3/28 H05K 1/18 H05K 3/34

Claims (2)

(57) [Claims] 1. In a structure of a so-called printed wiring board in which a conductor wiring is formed on an insulator and a surface mounting component is solder-bonded on the conductor wiring, directly below a portion where the surface mounting component is to be mounted. A solder resist is overlaid on a part of the land of the conductor wiring, and a paint layer by silk printing is further provided on a portion where the land and the solder resist are overlapped with each other. A structure of a printed wiring board, characterized in that a part, the solder resist, and the paint layer are superposed on each other, and the surface mount component is placed in contact with the paint layer . 2. The land, the overlapping portion of the solder resist, and the paint layer by silk printing are arranged so as to surround the land along the periphery of the land of the surface mount component. Printed wiring board structure.