JPH05347478A - Printed wiring board - Google Patents

Abstract

PURPOSE:To prevent warp by making contraction coefficient of an intermediate insulation layer of a printed wiring board wherein three insulation layers are laminated larger than that of its outer insulation layer. CONSTITUTION:An insulation layer 34 of large contraction coefficient such as an aramid resin layer is used for an intermidiate in thickness direction of three insulation layers of a printed wiring board 30 and an insulation substrate 17 laminated in its outer side is formed of ordinary glass epoxy of small contraction coefficient, for example. Therefore, in a manufacturing process of the printed wiring board 30, a central insulation layer 34 among insulation layers 17, 34, 17 contracts most and a stress is generated as shown by an arrow 31. The stress becomes larger as shown by an arrow 31' when warp is going to be generated. As a result, if the printed wiring board 30 is about to generate warp, a stress 31' to resist it is generated, thereby making warp hard to be generated and flatness of the printed wiring substrate 30 can be kept good.

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.

[0002]

2. Description of the Related Art Conventionally, a multilayer printed wiring board as a printed wiring board has a structure in which a plurality of double-sided wiring boards having conductive circuits on the front surface side and the back surface side are adhered and laminated by a prepreg (glass fiber reinforced resin). ing.

FIG. 9 shows an example of the structure of a conventional multilayer printed wiring board 20. In this wiring board, the copper foil
A blind via hole 15 is formed in the double-sided wiring board 11 to which 18 and 19 are adhered, and the copper plating 22 and the copper foil 19 applied to the entire surface including the blind via hole 15 have the same pattern on the back surface side (that is, the inner layer side). The conductive circuit is formed by etching.

The double-sided wiring board 11 and the other double-sided wiring board 12 processed in the same manner are thermocompression-bonded to each other on a surface having a circuit pattern by a prepreg 14 (for example, glass epoxy: glass fiber reinforced epoxy resin) to form a multilayer printed wiring. Formed on the plate 20.

A through hole 23 is formed at a predetermined position of the multilayer printed wiring board 20, and the through hole 23 is formed.
The copper plating 21 and the lower layers 22 and 18 provided on the entire surface including are etched into the same pattern and processed into conductive circuit patterns, respectively.

In this way, the double-sided wiring boards 11 and
A multilayer printed wiring board (20) is formed in which twelve outer layer circuits are connected to each other through through holes (23) and circuits on both sides of each double-sided wiring board (11, 12) are connected to each other through blind via holes (15).

However, it has been found that the above-mentioned conventional multilayer printed wiring board has the following problems.
Referring to FIG. 10, the prepreg 14 and the insulating substrate 17 are illustrated in a simplified manner for easy understanding in this figure.However, such a multilayer board has various processing steps during a manufacturing step as a printed wiring board. When passing through, a warp may occur as shown in the figure.

Such a tendency for the warp to occur tends to occur due to the thinning of the multi-layered plate due to the demand for lighter, thinner, shorter and smaller plates. That is, generally an insulating substrate with copper foils 18, 19 and 22.
The coefficient of thermal expansion of 17 is smaller than the coefficient of thermal expansion of the prepreg 14, and the prepreg 14 is more susceptible to thermal expansion in the heating process.

For this reason, as shown in FIG.
Will be deformed and warped. And in this case,
Since the conductive pattern (pattern of the conductor layer) such as copper foil in each layer is different for each layer, it is easy to lose the symmetry of the pattern in the thickness direction of the multilayer board, which is also a factor contributing to the above warpage. ing.

When the multilayer board 20 warps as described above,
In terms of the mounting process and connection reliability of mounted parts,
This is a serious problem because the connection using solder or the like cannot be performed well. For example, the warp may cause stress in the solder connection portion, resulting in peeling or the like.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to reduce or eliminate the warp in a printed wiring board in which at least three insulating layers are laminated like the above-mentioned multi-layer board, which causes troubles in the mounting process. It is to avoid the above, improve productivity, and improve connection reliability after mounting.

[0012]

The first invention of the present application is
In a printed wiring board in which at least three insulating layers are laminated, the shrinkage rate of the intermediate insulating layer is larger than the shrinkage rate of the outer insulating layer, which relates to the printed wiring board.

The second invention of the present application is that in a printed wiring board in which at least three insulating layers are laminated, the coefficient of thermal expansion of the intermediate insulating layer is smaller than the coefficient of thermal expansion of the outer insulating layer. The present invention relates to a characteristic printed wiring board.

In the above, at least three insulating layers are laminated, conductor layers are provided on both sides of each of these insulating layers, and an intermediate insulating layer exists at the center position in the thickness direction of the printed wiring board. Is desirable.

Further, according to the present invention, the first and second double-sided wiring boards having conductive circuits on the front surface side and the back surface side are laminated on each other with an insulating layer interposed therebetween, and the blind via holes formed in the double-sided wiring board are passed through. Conductive circuits on both sides are connected to each other, a through hole is formed through the first and second double-sided wiring boards and the insulating layer, and at least the first and second double-sided wiring boards are formed through the through holes. It can be applied to a printed wiring board in which conductive circuits on the outer surface side are connected.

[0016]

EXAMPLES Examples of the present invention will be described below.

First, an example of a printed wiring board (multilayer printed wiring board) according to the present invention will be described with reference to FIG. This example is characterized in that a pair of double-sided wiring boards 11 and 12 are used as in the case shown in FIG. 9, and these are laminated via an insulating layer 34 having a large shrinkage ratio. However, copper foil or copper layer 1
8, 19, and 22 are shown as single layers for simplicity.

That is, in this printed wiring board 30, an insulating layer 34 having a large shrinkage ratio, for example, an aramid resin layer, is used at the central position (middle) in the thickness direction among the three insulating layers and is laminated on the outer side thereof. Since the insulating substrate 17 to be formed is formed of, for example, ordinary glass epoxy, as shown in FIG.
In the manufacturing process of the printed wiring board, the central insulating layer 34 contracts most among the insulating layers, and stress is generated as shown by an arrow 31. This stress becomes larger like 31 'when warping is attempted.

As a result, when the printed wiring board (multilayer board) is going to warp, stress 31 'is applied so as to resist it.
As a result, warpage is less likely to occur. Therefore, the flatness of the printed wiring board can be maintained satisfactorily, troubles in the mounting process, peeling of the connection parts of the mounted components, etc. can be eliminated, and productivity and connection reliability can be greatly improved.

In the above case, as the printed wiring board 30,
Three insulating layers (17-34-17) or four or more conductor layers (18-19-19-18, and even 22) were used, but as shown in Fig. 3, five insulating layers were used. Alternatively, the number of conductor layers may be six or more.

That is, according to the example of FIG. 3, in addition to the structure of FIG.
And a conductor layer (copper foil or copper plating layer) 28 on the uppermost and lowermost surfaces.

In this case, as the center layer in the thickness direction of the printed wiring board 30, that is, the insulating layer 34, the upper and lower insulating layers 17 and
By using a material having a smaller coefficient of thermal expansion than 37, the center insulating layer 34 is less likely to expand (and therefore less likely to expand) even when warping occurs at high temperatures as shown in FIG. The plate 30 is less likely to warp.

Therefore, the flatness of the printed wiring board can be maintained as in the example of FIG. 1, and the same effect can be obtained.
For this purpose, an aramid resin having a low coefficient of thermal expansion, glass epoxy containing a large amount of glass fiber, or the like is used as the material of the insulating layer 34.

Next, an example of a structure embodying the example of FIG. 1 is shown in FIG.
8 will be described. That is, when manufacturing a printed wiring board, copper foil is formed on both surfaces of the insulating substrate 17 as shown in FIG.
A blind via hole 15 is formed on the double-sided wiring board material 11A to which 18 and 19 are adhered, and the copper plating 22 and the copper foil 19 applied to the entire surface including the blind via hole 15 have the same pattern on the back surface side (that is, the inner layer side). To form a conductive circuit.

Then, as shown in FIG. 5, double-sided wiring board material 11A
Is heat-pressed with the aramid resin 34 on the other side double-sided wiring board material 12A processed in the same manner and on the surface having the circuit pattern to form a multilayer printed wiring board material 30A.

A through hole 23 is formed at a predetermined position of the multilayer printed wiring board material 30A as shown in FIG.
Further, as shown in FIG. 7, the copper plating 21 and the lower layers 22 and 18 provided on the entire surface including the through hole 23 are etched into the same pattern as shown in FIG. 8 and processed into conductive circuit patterns, respectively.

The laminated double-sided wiring boards 11 and
A multilayer printed wiring board (30) is formed in which twelve outer layer circuits are connected to each other through through holes (23) and circuits on both sides of each double-sided wiring board (11, 12) are connected to each other through blind via holes (15).

Although the embodiments of the present invention have been described above, the above embodiments can be further modified based on the technical idea of the present invention.

For example, the insulating layer 34 as the above-mentioned central layer
The materials of the materials 17, 17 and 37 can be variously and relatively selected, and can be determined in consideration of the above-mentioned shrinkage rate or thermal expansion coefficient. A material having a small thermal expansion coefficient may be used as the insulating layer 34 in the example of FIG. 1, or a material having a large shrinkage rate may be used as the insulating layer 34 in the example of FIG.

Further, the number of insulating layers can be set to 4 or 6 as the layer structure of the multilayer board. The conductor layer is also a single layer,
A plurality of materials may be used, and the material thereof may be changed. Further, the position of the insulating layer 34 is preferably at the center in the thickness direction, but it does not necessarily have to be so and may be in the middle.

[0031]

As described above, according to the present invention, the shrinkage rate of the intermediate insulating layer is made larger than that of the outer insulating layer, or the coefficient of thermal expansion of the former is made smaller than that of the latter, so that warpage occurs. Therefore, the flatness of the printed wiring board can be maintained well, troubles in the mounting process, peeling of the connecting portion of the mounted components, etc. can be eliminated, and productivity and connection reliability can be greatly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a multilayer printed wiring board according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a situation in which stress that prevents warpage of the wiring board occurs.

FIG. 3 is a cross-sectional view of an essential part of a multilayer printed wiring board according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a step in the method of manufacturing the wiring board shown in FIG.

FIG. 5 is a cross-sectional view showing one step in a method for manufacturing the same wiring board.

FIG. 6 is a cross-sectional view showing one step in a method for manufacturing the same wiring board.

FIG. 7 is a cross-sectional view showing one step in a method for manufacturing the same wiring board.

FIG. 8 is a cross-sectional view showing one step in a method for manufacturing the same wiring board.

FIG. 9 is a cross-sectional view of a conventional multilayer printed wiring board.

FIG. 10 is a schematic diagram for explaining a situation in which the wiring board is warped.

[Explanation of symbols]

 11, 12 ・ ・ ・ Double-sided wiring board 14 ・ ・ ・ Prepreg 15 ・ ・ ・ Blind via hole 17,37 ・ ・ ・ Insulating substrate 18, 19 ・ ・ ・ Copper foil 20, 30 ・ ・ ・ Printed wiring board (multilayer printed wiring) Plate) 21,22 ・ ・ ・ Copper plating layer 23 ・ ・ ・ Through through hole 31, 31 '・ ・ ・ Stress 34 ・ ・ ・ Insulation layer with high shrinkage or low thermal expansion

Claims (4)

[Claims] 1. A printed wiring board in which at least three insulating layers are laminated, wherein the shrinkage rate of the intermediate insulating layer is larger than that of the outer insulating layer. 2. A printed wiring board in which at least three insulating layers are laminated, wherein a coefficient of thermal expansion of an intermediate insulating layer is smaller than a coefficient of thermal expansion of an insulating layer outside thereof. 3. At least three insulating layers are laminated, conductor layers are provided on both sides of each of these insulating layers, and an intermediate insulating layer is present at a central position in the thickness direction of the printed wiring board. The printed wiring board according to claim 1 or 2. 4. The first and second double-sided wiring boards having conductive circuits on the front surface side and the back surface side are laminated on each other with an insulating layer interposed therebetween, and conductive circuits on both surfaces are passed through blind via holes formed in the double-sided wiring board. Between the first and second double-sided wiring boards and at least the outer surface side of the first and second double-sided wiring boards through which the through holes are formed. The printed wiring board according to claim 1, wherein the conductive circuits are connected to each other.