JP2002100880A - Multilayer circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deflection of a multilayer circuit board due to distortion by suppressing a thermal stress of the multilayer circuit board which occurs during heating/cooling in a solder reflow process and the like. SOLUTION: The multilayer circuit board comprises, at least one of, insulating built-up layers 3 and 4 formed on both surfaces of an insulating core layer 1, an internal wiring conductor 2 formed between the core layer 1 and the built-up layers 3 and 4, external wiring conductors 5 and 6 formed on the surface-side built-up layer 3, a circuit part 7 soldered and mounted on a part of the external wiring conductor 6, and a ground conductor 8 comprising a conductor film which is coated on the backside built-up layer 4. The ground conductor 8 comprises an intermittent part where the conductor film intermittently exists.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to at least one or more insulating built-up layers formed on both sides of an insulating core layer, and an internal wiring formed between the core layer and the built-up layer. A multi-layer circuit board having a conductor, wherein a circuit component is mounted on an external wiring conductor formed on a front-side build-up layer, and a ground conductor made of a conductive film is applied on the back-side build-up layer. To a multilayer circuit board.

[0002]

2. Description of the Related Art This type of multilayer circuit board has the following structure. Internal wiring conductors are formed on both surfaces of an insulating core layer made of glass-epoxy resin or the like in a predetermined pattern by a conductor film. An insulating built-up layer is formed by applying a resin or the like to both surfaces of the core layer on which the internal wiring conductor is formed and curing the resin. When the built-up layer has a plurality of layers, internal wiring conductors are further formed in a predetermined pattern by a conductor film on the underlying build-up layer, and thus an appropriate number of built-up layers are formed. . Finally, the outermost build-up layers on the front and back sides of the multilayer circuit board are formed. Further, an external wiring conductor is formed on the built-up layer on the front surface in a predetermined pattern by a conductor film. Further, a ground conductor is formed by uniformly forming a conductor film such as a copper foil on the built-up layer on the back surface side.

A part of the external wiring conductor on the front side of the multilayer circuit board serves as a land electrode for mounting a circuit component. Solder paste is applied on this land electrode,
Thereafter, circuit components are mounted on the multilayer circuit board, and terminals of the circuit components are mounted on land electrodes. Thereafter, the multilayer circuit board on which the circuit components are mounted is guided to a reflow furnace, and heated to reflow the solder paste. Furthermore, the multilayer circuit board is drawn out of the reflow furnace, and the board is cooled to room temperature, so that the terminals of the circuit components are soldered to the land electrodes, and the circuit components are mounted.

[0004]

In the above-described multilayer circuit board, a ground conductor made of a conductive film such as a copper foil is formed over the entire back surface or the most area thereof, and this ground conductor is built in the multilayer circuit board. It is so-called solid on the up layer. In such a multilayer circuit board, warpage may occur in the solder reflow step when mounting circuit components as described above. This is because during the heating and cooling processes in the solder reflow process, thermal stress is generated due to the difference in the coefficient of thermal expansion between the core layer or built-up layer made of glass epoxy resin and the ground conductor made of copper foil etc. This is due to distortion of the substrate.

The present invention has been made in view of the above-mentioned problems in the conventional multilayer circuit board, and suppresses the generation of thermal stress in the multilayer circuit board during the heating and cooling processes in a solder reflow process and the like, and warps the multilayer circuit board due to distortion. It is intended to prevent the occurrence of the above.

[0006]

According to the present invention, in order to achieve the above object, a discontinuous portion in which a conductor film does not partially exist is formed in a ground conductor 8 made of a conductor film. Alternatively, a discontinuous portion in which the conductive film is partially cut is formed. In any of these cases, thermal stress when heating and cooling the multilayer circuit board is reduced, and distortion such as warpage of the multilayer circuit board is eliminated.

More specifically, the structure of the multilayer circuit board according to the present invention will be described. This multilayer circuit board comprises at least one or more insulating built-up layers 3 formed on both sides of an insulating core layer 1. 4, the internal wiring conductor 2 formed between the core layer 1 and the built-up layers 3 and 4, the external wiring conductors 5 and 6 formed on the front-side built-up layer 3, and the external wiring conductor. 6 has a circuit component 7 mounted by soldering, and a ground conductor 8 made of a conductive film adhered on the built-up layer 4 on the back surface side. In this multilayer circuit board, the ground conductor 8 has a discontinuous portion in which a conductor film does not partially exist.

The discontinuous portions of the ground conductor 8 where the conductor film does not partially exist are, for example, a plurality of holes 9, 10, 11 provided in the ground conductor 8. In such a multilayer circuit board, when the core layer 1, the built-up layers 3, 4 and the ground conductor 8 constituting the multilayer circuit board are thermally expanded or contracted by heating and cooling, the distortion of the ground conductor 8 is reduced. It is absorbed in the holes 9, 10, 11 side. Also,
The area of the ground conductor 8 in close contact with the build-up layer 4 is reduced by the area of the holes 9, 10, and 11. For this reason, the thermal stress between the core layer 1 and the built-up layers 3 and 4 as the insulating material and the ground conductor 8 as the metal material is reduced, and the multilayer circuit board is less likely to warp due to the thermal stress.

In this case, the plurality of holes 11 provided in the ground conductor 8 are polygonal, and the adjacent polygonal holes 11
If the width of the conductor film between them is constant, distortion due to thermal expansion of the ground conductor 8 is uniformly absorbed as a whole.
Moreover, since the electric resistance of the ground conductor 8 becomes uniform as a whole, the impedance is also improved.

In another embodiment of the multilayer circuit board according to the present invention, the ground conductor 8 has a discontinuous portion in which a conductor film is partially cut. The discontinuous portion where the conductor film of the ground conductor 8 is partially cut is, for example, the ground conductor 8
Are provided in the slit 12. Also in such a multilayer circuit board, as in the above-described case, the slit 12 allows distortion due to the thermal stress of the ground conductor 8 during heating and cooling, and does not generate a large thermal stress in the multilayer circuit board.

In such a multilayer circuit board, if the adjacent slits 12 are arranged at an angle of 90 °, the distortion due to the thermal expansion of the ground conductor 8 is absorbed and dispersed vertically and horizontally. When the slits 12 are arranged without crossing each other, the ground conductor 8 is entirely electrically connected, so that the electrical resistance of the ground conductor 8 does not partially increase and the impedance is also reduced. It will be good. Further, by making the intervals between the adjacent slits 12 equal, the electric resistance between all the slits 12 becomes uniform, and the impedance is further improved.

[0012]

Embodiments of the present invention will now be described specifically and in detail with reference to the drawings.
FIG. 1 shows a state in which a chip-shaped circuit component 7 is mounted on the front side of a completed multilayer circuit board, and among the external wirings 5 and 6 on the surface of the multilayer circuit board, the external wirings 6 and 6 serving as land electrodes are connected to the circuit. An example in which terminals at both ends of a component 7 are soldered is shown. In the multilayer circuit board according to the present invention, besides the chip-shaped circuit component 7, a package component having a large number of terminals is mounted.

The structure of such a multilayer circuit board will be described according to its manufacturing method. First, an insulating core layer 1 made of glass-epoxy resin or the like is prepared, and a conductive foil such as copper is crimped or plated on both surfaces of the core layer 1 to form a conductive foil. Next, a resist film is printed in a predetermined pattern on the conductor foils on both surfaces of the core layer 1, and portions not covered with the resist film are selectively etched to pattern the conductor foil. Thereafter, the resist film is washed and removed, thereby forming the internal wiring conductors 2 and 2 made of a conductor film patterned in a predetermined pattern on both surfaces of the core layer 1.

Next, a resin sheet is pressure-bonded to both surfaces of the core layer 1 on which the internal wiring conductors 2 and 2 are formed, or a resin paste is applied and cured to form an insulating built-up layer 3 or 4. To form In the example of FIG. 1, one built-up layer 3 and 4 are formed on both surfaces of the core layer 1 respectively. However, when a plurality of built-up layers 3 and 4 are further formed, a built-in Up layer 2, 2
A circuit wiring pattern serving as an internal wiring conductor is formed thereon in the same manner as that formed on the core layer 1. In order to connect the internal wiring conductors on the built-up layers 3 and 4 to the internal wiring conductors 2 and 2 on another layer, via holes are drilled, and the via holes are plated to form via hole conductors. Form.

After the appropriate number of built-up layers 3 and 4 are formed in this way, a conductive foil such as a copper foil is crimped or plated on the last built-up layer 3 on the front side. After forming a conductor foil, the conductor foil is patterned by the same means as that for forming the internal wiring conductors 2 and 2 on both surfaces of the core layer 1 to form external wiring conductors 5 and 6. On the other hand, the last built-up layer 4 on the back side
Similarly, a conductor foil is formed thereon, and is patterned by the same means to form a ground conductor 8. The outer wiring conductors 5 and 6 and the ground conductor 8 on the outermost built-up layers 3 and 4 are also connected to the inner wiring conductors 2 and 2.
In order to connect to the via hole, a via hole is formed, and the via hole is plated to form a via hole conductor (not shown). Thus, a multilayer circuit board as shown in FIG. 1 is completed.

FIG. 2 shows an example of a pattern of the ground conductor 8. In the ground conductor 8 shown in FIG. 2, the conductor foil is patterned, circular holes 9 are provided at equal intervals in the vertical and horizontal directions, and the ground conductor 8 is partially provided with a discontinuous portion where no conductive film exists. By doing so, the area of the ground conductor 8 can be smaller than that of a normal multilayer circuit board. For example, in a typical multilayer circuit board, the ratio of the area occupied by the external wiring conductors 5 and 6 on the front surface to the area occupied by the ground conductor 8 on the rear surface is about 2, whereas the ratio is 1.
It can be around 4.

In the multilayer circuit board thus manufactured, the internal wiring conductor 2 between the core layer 1 and the built-up layers 2 and 2, the external wiring conductors 5 and 6 on the front surface, and the ground conductor 8 on the back surface are formed. They are connected as circuit wiring and are connected by via-hole conductors (not shown). The ground conductor 8 functions as a ground.

The external wiring conductor 5 on the front side of the multilayer circuit board,
Some of the external electrodes 6 are land electrodes for mounting the circuit components 7, and a solder paste is applied on the external electrodes 6 which are the land electrodes. Thereafter, the circuit component 7 is mounted on the multilayer circuit board, and terminals at both ends of the circuit component 7 are mounted on the external wiring conductors 6, which are land electrodes.
Thereafter, the multilayer circuit board on which the circuit components 7 are mounted is guided to a reflow furnace and heated to reflow the solder paste. Further, the terminals of the circuit component 7 are soldered to the external wiring conductors 6 by drawing the multilayer circuit board out of the reflow furnace and cooling the board to room temperature.

In this soldering step, when the ground conductor 8 on the back surface of the multilayer circuit board is about to thermally expand due to heating and cooling of the multilayer circuit board, the distortion of the ground conductor 8 is caused by the hole 9.
Is absorbed by In addition, the area of the ground conductor 8 in close contact with the build-up layer 4 is reduced by the area of the hole 9, and the area ratio between the ground conductor 8 on the back surface and the external wiring conductors 5 and 6 on the front surface can be reduced. For this reason, the thermal stress of the multilayer circuit board in the soldering step is reduced, and the multilayer circuit board is less likely to warp.

FIG. 3 shows another example of the pattern of the ground conductor 8. In this ground conductor 8, small holes 10 having a smaller diameter are arranged between the holes 9 in addition to the holes 9 of the ground conductor 8 described above with reference to FIG. With such a combination of the large-diameter holes 9 and the small-diameter holes 10, distortion due to thermal stress of the ground conductor 8 when the multilayer circuit board is heated and cooled can be more uniformly dispersed.

FIG. 4 shows another example of the pattern of the ground conductor 8. In this ground conductor 8, instead of the circular hole 9 of the ground conductor 8 described above with reference to FIG.
1 is provided. One diagonal line connecting the opposing vertices of the hexagonal hole 11 faces in the same direction. That is, in FIG. 4, the pair of opposing vertices are oriented in the up-down direction. Further, the adjacent holes 11 are arranged at regular intervals in the direction of ± 45 ° with respect to the diagonal line, whereby the width of the conductor film between the holes 11 is reduced between all the holes 11. It is uniform. Therefore, the distortion due to the thermal stress of the ground conductor 8 when the multilayer circuit board is heated and cooled is uniformly dispersed. Moreover, since the width of the conductor film between all the holes 11 is the same, their electric resistance becomes uniform and the impedance becomes good.

FIG. 5 shows another example of the pattern of the ground conductor 8. The ground conductor 8 has a slit 12 in which the conductor film of the ground conductor 8 is partially cut, instead of the hole as in the ground conductor 8 described above with reference to FIGS. As shown in FIG.
2 are arranged at an angle of 90 ° without intersecting with each other, and the slits 12 adjacent to each other are arranged.
Are equal. For this reason, the distortion due to the thermal stress of the ground conductor 8 when the multilayer circuit board is heated and cooled is uniformly dispersed in the vertical and horizontal directions. Moreover, since the intervals between the adjacent slits 12 are all equal, these slits 12
, The electrical resistance between them becomes uniform, and the impedance becomes good.

In the illustrated example, the outermost slit 12 of the ground conductor 8 is connected to each side of the ground conductor 8 by 90 degrees.
Each of the slits 12 forming an angle of ゜ is the other slit 1
2 and reaches each side of the ground conductor 8. On the other hand, in the outermost slit 12 of the ground conductor 8,
Slit 1 at an angle of 90 ° with each side of ground conductor 8
Of course, it is also possible that 2 has the same length as the other slits 12.

FIG. 6 shows another example of the pattern of the ground conductor 8. In this ground conductor 8, holes 9 are provided between the slits 12 in the pattern of the ground conductor 8 described above with reference to FIG. In the pattern of the ground conductor 8, the effect of reducing the thermal stress of both the slit 12 and the hole 9 is used together, so that the distortion due to the thermal stress of the ground conductor 8 when the multilayer circuit board is heated and cooled is dispersed. It is easy to be.

[0025]

As described above, in the multilayer circuit board according to the present invention, when the multilayer circuit board is about to expand or contract due to heating or cooling, the core layer 1 or the built-up layer 3, which is an insulating material, The thermal stress between the metal substrate 4 and the ground conductor 8, which is a metal material, is reduced, and the multilayer circuit board is less likely to be warped due to the thermal stress.

[Brief description of the drawings]

FIG. 1 is a partial vertical sectional side view showing an example of a multilayer circuit board according to an embodiment of the present invention.

FIG. 2 is a rear view showing an example of a ground conductor pattern of the multilayer circuit board according to one embodiment of the present invention.

FIG. 3 is a back view showing another example of the pattern of the ground conductor.

FIG. 4 is a back view showing another example of the pattern of the ground conductor.

FIG. 5 is a back view showing another example of the pattern of the ground conductor.

FIG. 6 is a rear view showing another example of the pattern of the ground conductor.

[Explanation of symbols]

 Reference Signs List 1 core layer 3 build-up layer 4 build-up layer 2 internal wiring conductor 5 external wiring conductor 6 external wiring conductor 7 circuit component 8 ground conductor 9 ground conductor hole 10 ground conductor hole 11 ground conductor hole 12 ground conductor slit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Masaya Shimamura, Inventor Taiyo Electric Power Co., Inc. 6-16-20 Ueno, Taito-ku, Tokyo (72) Inventor Hideji Mugitani 6-16-20, Ueno, Taito-ku, Tokyo Taiyo F Term (in reference) 5E346 AA45 CC04 CC09 EE31 FF45 GG15 GG25 GG28 HH31

Claims (7)

[Claims] 1. At least one or more insulating built-up layers (3) and (4) formed on both sides of an insulating core layer (1), and these core layers (1) and built-up layers (3). Internal wiring conductors (2) formed between the layers 3) and (4), external wiring conductors (5) and (6) formed on the built-up layer (3) on the front side, and the external wiring conductors A multilayer circuit having a circuit component (7) mounted on a part of (6) by soldering, and a ground conductor (8) made of a conductive film applied on a built-up layer (4) on the back side. A multilayer circuit board, characterized in that the board has a discontinuous portion where the conductor film does not partially exist in the ground conductor (8). 2. The plurality of holes (9), (10), and (11) provided in the ground conductor (8) are discontinuous portions where the conductor film of the ground conductor (8) is partially absent. The multilayer circuit board according to claim 1, wherein: 3. The discontinuous portion of the ground conductor (8) where the conductor film does not partially exist is a plurality of polygonal holes (11) provided in the ground conductor (8). 3. The multilayer circuit board according to claim 1, wherein the width of the conductor film between the holes is constant. 4. 4. At least one or more insulating built-up layers (3) and (4) formed on both surfaces of the insulating core layer (1), and the core layer (1) and the built-up layer (4). Internal wiring conductors (2) formed between the layers 3) and (4), external wiring conductors (5) and (6) formed on the built-up layer (3) on the front side, and the external wiring conductors A multilayer circuit having a circuit component (7) mounted on a part of (6) by soldering, and a ground conductor (8) made of a conductive film applied on a built-up layer (4) on the back side. A multilayer circuit board, wherein the ground conductor (8) has a discontinuous portion in which a conductor film is partially cut off. 5. The ground conductor (8) according to claim 4, wherein the discontinuous portion in which the conductor film of the ground conductor (8) is partially cut is a slit (12) provided in the ground conductor (8). Multilayer circuit board. 6. The multilayer circuit board according to claim 5, wherein the adjacent slits (12) are arranged vertically and horizontally so as to form an angle of 90 ° without intersecting with each other. 7. The multilayer circuit board according to claim 5, wherein the adjacent slits 12 are arranged so that their intervals are equal to each other.