JP2001196718A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem, where when a leadless component is fitted to a printed wiring board, cracks are easy to occur at a solder joint part by both repeated expansion/contraction of under temperature changes, resulting in lower connection reliability. SOLUTION: A frame, which is formed of a material with almost the same thermal expansion factor as the main body of the leadless component and comprises an opening slightly larger than the circumference of the leadless component, is bonded around the leadless component while being above the part fitting surface.

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 capable of obtaining high connection reliability in mounting leadless components.

[0002]

2. Description of the Related Art There are two types of electronic components: leaded components in which electrodes are leads and leadless components in which electrodes are solder bumps. Generally, leadless components have higher connection reliability with printed wiring boards than leaded components. Is difficult to secure. This problem will be described below with reference to the drawings.

FIG. 7 shows, for example, NIKKEI MICRO
DEVICES Feb. 1998 (Document), page 49, is a cross-sectional view of a conventional printed wiring board, wherein 1 is a printed wiring board main body, 2 is a leadless component main body, and 3 is an electrode of a leadless component and is a component main body. The bumps 4 soldered to 2 and the surface conductors 4 of the printed wiring board to which the solder bumps 3 are soldered. FIG. 8 is a cross-sectional view of the solder bump 3 shown on page 50 of the document in a state in which a crack is formed, and 5 indicates a crack. FIG. 9 is a cross-sectional view of a printed wiring board to which components with leads are attached, and 6 is a lead. 7, 8, and 9, the same numbers indicate the same or equivalent products.

[0004] Usually, printed wiring boards and electronic components mounted thereon are exposed to temperature changes in various situations. First, at the time of soldering, the solder is heated to a high temperature in order to melt the solder, and then cooled to room temperature again. Next, during non-operation after soldering, there is a temperature change between day and night, and during operation, the heat generation and cooling of the components and the rise and cooling of the ambient temperature in the installed equipment are repeated as the power is turned on and off. When the temperature change is repeated in this manner, the leadless component body 2 and the printed wiring board body 1 repeat expansion and contraction, but a difference in thermal expansion always occurs because the materials are different. As a result, stress is applied to the solder bumps 3 in a direction parallel to the surface of the printed wiring board, and as shown in FIG. 8, the vicinity of the joint of the solder bumps 3 with the printed wiring board 1 and the vicinity of the joint with the leadless component body 2. Crack 5 occurs in the This crack grows by repeated expansion and contraction, and finally reaches a disconnection.

On the other hand, in the case of a component with a lead, as shown in FIG. 9, the lead 6 absorbs the difference in thermal expansion due to its elasticity, so that the stress at the solder joint between the lead 6 and the surface conductor 4 is relaxed and cracks are generated. Is less likely to occur.

[0006]

As described above, when a leadless component is mounted on a printed wiring board, cracks are likely to occur in the solder joint due to repetition of expansion and contraction of the two due to temperature changes, and high connection reliability is obtained. There is a problem that it cannot be obtained.

This problem is particularly important in military and industrial applications.
This is remarkable when the operating temperature range is wide, from a low temperature of not more than 100 ° C to a high temperature of around 100 ° C. First, ceramic is used as the material of the component body to withstand a wide operating temperature range,
The coefficient of thermal expansion of ceramic is significantly different from resin, which is the material of the printed wiring board, from 1/3 to 1/5. Further, since the range of the temperature change is wide, as a result, the difference in thermal expansion is large, the stress applied to the solder joint becomes large, and the disconnection occurs in a shorter period. There is a method of manufacturing the printed wiring board itself with ceramic instead of resin, but it is expensive and
It is not widely used because it is difficult to make large printed wiring boards made of ceramic.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a printed wiring board having high connection reliability in mounting leadless components.

[0009]

According to a first aspect of the present invention, a printed wiring board is formed using a material having a thermal expansion coefficient substantially equal to that of a body of a leadless component, and has an opening slightly larger than the outer periphery of the leadless component. The frame is bonded on the component mounting surface and around the leadless component.

In the printed wiring board according to the second invention, a groove is formed on the component mounting surface of the printed wiring board and around the leadless component so that the frame of the first invention is embedded in the groove. It was done.

Further, in the printed wiring board according to the third invention, a groove is formed around the leadless component on the back surface of the component mounting surface of the printed wiring board, and the frame of the first invention is embedded in the groove. It is like that.

A printed wiring board according to a fourth aspect of the present invention is a printed wiring board formed of a material having a coefficient of thermal expansion substantially equal to that of the body of the leadless component, and having a bottom area substantially equal to a bottom area of the leadless component. It is to be adhered on the back surface of the component mounting surface and directly below the leadless component.

A printed wiring board according to a fifth aspect of the present invention includes a through hole for connecting a surface conductor and a wiring conductor inside the printed wiring board at a position where the leadless component is mounted, and the thermal expansion of the main body of the leadless component. A sword-shaped panel formed of a material having substantially the same ratio and having a bottom area substantially equal to a bottom area of the leadless component is inserted into the through hole and fixed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a cross-sectional view showing a first embodiment of the present invention, and FIG. 2 is a view of the one shown in FIG. 1 as viewed from above. In FIG. 7 is the leadless component body 2
Is formed using a material having a thermal expansion coefficient substantially equal to that of the leadless component, and has an opening slightly larger than the outer periphery of the leadless component, and is bonded to the periphery of the leadless component on the component mounting surface of the printed wiring board main body 1. Have been. When a temperature change is applied, the thermal expansion coefficient of the frame 7 is substantially equal to that of the leadless component body 2, so that displacement of expansion and contraction of the printed wiring board body 1 in a direction parallel to the printed wiring board surface is changed. The expansion and contraction displacement of the main body 2 is suppressed to be equal. As a result, the difference in thermal expansion between the two becomes smaller, so that the stress applied to the solder bumps 3 is relaxed and cracks are less likely to occur.

Embodiment 2 FIG. 3 is a sectional view showing a second embodiment of the present invention. In the drawing, reference numerals 2, 3, 4, and 7 are the same as or equivalent to those of the first embodiment, and reference numeral 6 denotes a groove for embedding a frame 7. The printed wiring board main body is formed on the component mounting surface, and the frame 7 is embedded in the groove. When a temperature change is applied, the difference in thermal expansion between the printed wiring board main body 8 and the leadless component main body 2 is reduced by the frame 7 as in the first embodiment, so that the stress applied to the solder bumps 3 is alleviated and cracks are generated. Is less likely to occur.

Embodiment 3 FIG. 4 is a sectional view showing a third embodiment of the present invention. In the figure, reference numerals 2, 3, 4, and 7 are the same as or equivalent to those of the first embodiment, and 9 is a groove for embedding the frame 7. The printed circuit board main body is formed on the back surface of the component mounting surface, and the frame 7 is embedded in the groove. When a temperature change is applied, the difference in thermal expansion between the printed wiring board main body 8 and the leadless component main body 2 is reduced by the frame 7 as in the first embodiment, so that the stress applied to the solder bumps 3 is alleviated and cracks are generated. Is less likely to occur.

Embodiment 4 FIG. 5 is a cross-sectional view showing a fourth embodiment of the present invention. In FIG. 5, reference numerals 1 to 4 are the same as or equivalent to the conventional example, and reference numeral 10 denotes a material having a thermal expansion coefficient substantially equal to that of the leadless component body 2. Formed using
The panel has a bottom area substantially equal to the bottom area of the leadless component, and is bonded on the back surface of the component mounting surface of the printed wiring board main body 1 and directly below the leadless component. When a temperature change is applied, the difference in thermal expansion between the printed wiring board main body 1 and the leadless component main body 2 is reduced by the panel 10 as in the first embodiment. Is less likely to occur.

Embodiment 5 FIG. 6 is a sectional view showing a fifth embodiment of the present invention. In the drawing, reference numerals 1 to 4 are the same as or equivalent to the conventional example, and reference numeral 11 denotes a connection between the surface conductor 4 and the wiring conductor inside the printed wiring board. Through hole, 1
Reference numeral 2 denotes a sword-shaped panel formed of a material having a thermal expansion coefficient substantially equal to that of the leadless component body 2 and having a bottom area substantially equal to the bottom area of the leadless component. Is inserted into the through hole 11 and fixed directly below the leadless component. When a temperature change is applied, the difference in thermal expansion between the printed wiring board main body 1 and the leadless component main body 2 is reduced by the panel 12 as in the first embodiment, so that the stress applied to the solder bumps 3 is relaxed and cracks are generated. Is less likely to occur.

[0019]

According to the first aspect of the present invention, when a temperature change is applied, the expansion and contraction displacement of the printed wiring board main body 1 in the direction parallel to the printed wiring board surface is reduced by the frame 7. Is suppressed to be equal to the displacement of expansion and contraction. As a result, the difference in thermal expansion is reduced, so that the stress applied to the solder bumps 3 is relaxed and cracks are less likely to occur.

According to the second aspect, when a temperature change is applied, the thermal expansion difference is reduced by the frame 7 as in the first aspect, so that the stress applied to the solder bumps 3 is relaxed and cracks occur. It becomes difficult. Since the frame 7 is embedded in the printed wiring board main body 8, there is an advantage that the stress for suppressing the difference in thermal expansion works strongly.

According to the third aspect, when a temperature change is applied, the thermal expansion difference is reduced by the frame 7 as in the first aspect, so that the stress applied to the solder bumps 3 is relaxed and cracks occur. It becomes difficult. Also, since this frame 7 is mounted on the back of the component mounting surface,
There is an advantage that dead space does not occur on the component mounting surface side.

According to the fourth aspect, when a temperature change is applied, the thermal expansion difference is reduced by the panel 10 as in the first aspect, so that the stress applied to the solder bumps 3 is relaxed and cracks occur. It becomes difficult. This panel 1
Since 0 is a flat plate, processing is easy, and since it is mounted on the back surface of the component mounting surface, there is an advantage that dead space does not occur on the component mounting surface side.

According to the fifth invention, when a temperature change is applied, the thermal expansion difference is reduced by the panel 12 as in the first invention, so that the stress applied to the solder bumps 3 is relaxed and cracks occur. It becomes difficult. This panel 1
2 is inserted into the through-hole of the printed wiring board main body 1 and thus has an advantage that the stress for suppressing the difference in thermal expansion works strongly. In addition, since it is mounted on the back surface of the component mounting surface, a dead space is provided on the component mounting surface side. There is an advantage that no occurrence occurs.

[Brief description of the drawings]

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

FIG. 2 is a top view of the first embodiment of the printed wiring board according to the present invention;

FIG. 3 is a sectional view showing a second embodiment of the printed wiring board according to the present invention;

FIG. 4 is a sectional view showing a third embodiment of the printed wiring board according to the present invention;

FIG. 5 is a sectional view showing a fourth embodiment of a printed wiring board according to the present invention;

FIG. 6 is a sectional view showing a fifth embodiment of a printed wiring board according to the present invention;

FIG. 7 is a cross-sectional view showing a state in which a leadless component is mounted on a conventional printed wiring board.

FIG. 8 is a sectional view showing a state in which a solder bump of a leadless component has a crack.

FIG. 9 is a cross-sectional view showing a state in which a component with leads is attached to a conventional printed wiring board.

[Explanation of symbols]

1 printed wiring board body, 2 leadless parts body,
7 frame, 8 printed wiring board main body, 9 printed wiring board main body, 10 panel, 11 through hole, 12
Sword mountain-shaped panel.

Claims (5)

[Claims] 1. A printed wiring board on which a leadless component is surface-mounted, wherein the printed wiring board is formed using a material having a thermal expansion coefficient substantially equal to that of the main body of the leadless component, and has an opening slightly larger than the outer periphery of the leadless component. A printed wiring board characterized in that a frame having the same is bonded on a component mounting surface and around a leadless component. 2. The printed wiring board according to claim 1, wherein a groove is formed on the component mounting surface of the printed wiring board and around the leadless component, and the frame is embedded in the groove. 3. The printed wiring board according to claim 1, wherein a groove is formed on the back surface of the component mounting surface of the printed wiring board and around the leadless component, and the frame is embedded in the groove. . 4. A printed wiring board for surface-mounting a leadless component, wherein the printed wiring board is formed using a material having a coefficient of thermal expansion substantially equal to that of the body of the leadless component, and has a bottom substantially equal to a bottom area of the leadless component. A printed wiring board having a panel having an area adhered on the back surface of a component mounting surface and directly below a leadless component. 5. A printed wiring board on which a leadless component is surface-mounted, comprising a through hole at a mounting position of the leadless component for connecting a surface conductor to a wiring conductor inside the printed wiring board. A sword-shaped panel formed by using a material having a thermal expansion coefficient substantially equal to that of the main body of the leadless component and having a bottom area substantially equal to a bottom area of the leadless component, wherein the panel is inserted into the through hole and fixed. Wiring board.