JPH0878854A - Multilayered printed wiring board - Google Patents

Abstract

PURPOSE: To prevent generation of exfoliation on the interlayer between prepregs which is to be caused by the heating at the time of parts soldering, by using prepreg wherein glass cloth of high density excellent in drill workability is used as a reinforcing base. CONSTITUTION: An inner layer circuit board 4 is obtained by forming a specified copper foil circuit pattern 3 on a copper clad lamination board by an etching method. Prepregs 2 are put on both sides or a single side of the inner circuit board 4. Copper foils or outer layer boards 1 are put on the prepregs. These are integrally unified in a lamination body by heating and pressing. When a board for printed wiring is obtained in this manner, each prepreg wherein a plain glass cloth is impregnated with thermosetting resin and preliminarily dried is used between layers. The glass cloth is formed by using glass fibers of 500-1500 denier. The length density is 30-45 picks/25mm, and the weft density is 25-35 picks/25mm. The weight is 250-330g/m<2> , Thereby interlayer exfoliation at the time of soldering is not generated in the printed wiring board, and its other characteristics also are improved.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A multilayer printed wiring board is generally manufactured by the following procedure. First, a predetermined copper foil circuit pattern is formed on a copper-clad laminate by an etching method to obtain an inner layer circuit board. Next, a prepreg is placed on both sides or one side of this inner layer circuit board, and a copper foil or an outer layer substrate is further placed thereon, and heated and pressed to obtain a laminated and integrated multilayer printed wiring substrate.

As the prepreg used at this time, a prepreg obtained by impregnating a reinforcing base material such as glass cloth or glass non-woven cloth with a thermosetting resin such as epoxy resin or polyimide resin and predrying is used. 0.2 mm for the glass cloth of the reinforcing base material of the prepreg used for the substrate for the multilayer printed wiring board.
A prepreg with a thickness of less than or equal to that used is impregnated with a thermosetting resin and pre-dried in such a glass cloth to form a multilayer adhesive prepreg. In order to obtain an insulating layer of a predetermined thickness, two or more prepregs are generally used. Are stacked and molded. In this case, the thickness of the prepreg insulating layer is often determined in consideration of the characteristic impedance of the multilayer printed wiring board, and is 0.
It is often set with an insulation thickness of 30 mm. The thickness of commercially available prepreg for multilayer boards is only 0.2 mm or less, and the thickness is 0.2 mm or 0.15 m.
m, 0.10 mm, and 0.06 mm are the most common, and the following combinations are generally used to achieve the above-mentioned 0.3 mm. 0.2 mm and 0.10 mm each 1 sheet 2 sheets 0.15 mm 2 sheets 2 sheets 0.10 mm 3 sheets 3 sheets 3 sheets In any case, 2 or more prepregs are used to make a multilayer printed wiring board Had formed.

However, heating during soldering of components to the printed wiring board may cause peeling between the prepreg and the prepreg. The portion to be peeled between the layers includes the layer between the outer layer copper foil and the prepreg, the layer between the prepreg and the prepreg, the interface between the prepreg and the inner layer circuit board, or the inner layer circuit board itself. The blistering and peeling due to heating is because the thermosetting resin, which is an organic substance, absorbs moisture, and the moisture absorbed by heating undergoes gasification and expansion.Furthermore, from the viewpoint of thermal conductivity, peeling occurs on the part near the outside. The phenomenon is likely to occur. The outer layer copper foil is removed by etching except for the circuit when it is processed into a printed wiring board, its area is small, and it does not permeate moisture. Therefore, it is difficult to peel it off between the copper circuit and the prepreg. Therefore, most of the peeling occurs between the prepreg and the prepreg. This phenomenon became clear as the number of prepregs used increased.

[0005]

In order to solve the above-mentioned problems, the substrate for a multilayer printed wiring board of the present invention is made of a glass cloth having a thickness of 0.3 mm, which is excellent in drill workability and has a sufficient density. Only one prepreg used as a reinforcing base material was used between the layers.

The present invention will be described in detail below.
In order to eliminate peeling between the prepreg and the prepreg, it is necessary to eliminate the interlayer between the prepreg and the prepreg, that is, to form only one prepreg for forming each insulating layer. Moreover, the insulating layer thickness is 0.3.
mm, the thickness of one prepreg is 0.3 mm
Will be required. Therefore, it is conceivable that the resin content of the 0.2 mm thick glass cloth is further increased from the usual 40 to 55% to 60 to 65% to adjust the thickness to 0.3 mm. However, inclusion of such a high resin content in a 0.2 mm glass cloth is difficult to manufacture with a commonly used impregnation / dryer, and further increases the variation of the resin outflow amount at the time of laminate molding. This results in variations in the thickness of the insulating layer. Next, a method is conceivable in which the glass content is set to about 0.3 mm so that the resin content is in the range of 40 to 55% which facilitates lamination molding. However, such a thick glass cloth is 1
There was a coarse plain weave cloth with a density of 20 or less / 25 mm or a satin weave in the case of 20 or more, using a large yarn of 500 denier or more. The printed wiring board substrate having such a prepreg made of glass cloth has the following problems. Printed wiring boards are drilled and then through-hole plated to obtain conduction on the front and back sides.However, thick glass threads are difficult to cut by drilling, and the inner wall of the drill hole becomes rough, resulting in uneven plating thickness. Through hole reliability decreases. Furthermore, in order to obtain a thick thread, the filament diameter is also made thicker than 10 μm, and the drill machinability is further reduced. Since the density is coarse, the unevenness on the surface of the metal foil after laminating and forming becomes large, so that the accuracy of the circuit formation of the outer layer by the etching process is lowered. The satin weave is not suitable for printed wiring boards because of its remarkable anisotropy. For the above reasons, there is no example in which a thick plain weave glass cloth is used for a substrate for a multilayer printed wiring board, and a prepreg made of a glass cloth having a thickness of 0.2 mm or less has been used exclusively. So the inventor is 0.3
As a result of various studies on glass cloth for obtaining a mm prepreg, the following inventions have been reached.

The filament diameter of the glass cloth as the reinforcing substrate is generally 3, 5, 6, 7, 9, 10, 11, 13 μm.
However, in the case of glass cloth woven with threads that bundle filaments with a diameter of 10 μm or more, the inner wall of the hole becomes rough because the wear of the drill bit during drilling is severe and the hole quality is high. The printed wiring board will be inferior. In order to maintain good hole quality, filaments having a diameter of 9 μm or less may be used, but filaments having a diameter of 9 μm are used in the present invention because filaments that are too thin are expensive. If the thread is thin, you cannot weave a thick cloth,
If the thread is thick, the weave density will be rough. As a result of intensive studies, we have come to the conclusion that in order to achieve the purpose, a yarn of 500 to 1500 denier is sufficient. Regarding the weaving density, when the density is rough, the unevenness of the surface state of the copper foil after laminating and forming becomes large, which hinders the formation of fine circuits in the etching step for forming copper circuits. On the other hand, it is difficult to manufacture the densities so that there is no gap. Therefore, as a result of various studies, as a range in which the production of the glass cloth is easy and the surface property is not affected, the above-mentioned 500 to
For 00 denier yarn, the warp direction is 30 to 45 yarns /
It was 25 mm and the horizontal direction was 25 to 35 lines / 25 mm. Regarding the resin content, if it is 40% or less, voids are likely to occur during lamination molding, and if it is 60% or more, resin outflow is large at the time of lamination molding and it is difficult to control the outflow amount, resulting in large variation in plate thickness. 40 to 60%, more preferably 42 to 58% is desirable. Weaving density above,
The weight of the glass cloth must be in the range of 250 to 330 g / m ² in order to make the thickness of the prepreg around 0.3 mm in consideration of the three points of thread thickness and resin content. .

The glass is not particularly limited, but generally known E glass, T glass, D glass, quartz glass and the like can be used, but E glass which is excellent in workability and cost is preferable. The thermosetting resin with which the glass cloth is impregnated includes, but is not limited to, phenol resin, epoxy resin, polyimide resin, unsaturated polyester resin, etc. Epoxy resin with well-balanced price and performance is often used. It A glass cloth is dipped and impregnated in a varnish obtained by diluting such a thermosetting resin with an organic solvent, and then the solvent is allowed to pass through a drying furnace to cause some reaction to obtain a prepreg. The prepreg, the inner layer circuit board, and the outer layer substrate or the metal foil are used and laminated and integrated by a conventional method. An example of the configuration cross section is shown in FIG. 1 in the case of a substrate for a 4-layer multilayer printed wiring board, and in FIG. 2 in the case of a substrate for a 6-layer multilayer printed wiring board. In the case of a multilayer printed wiring board substrate having more layers, an inner layer circuit board and a prepreg are added in the same manner. 1 in the figure
Is an outer layer substrate or metal foil, 2 is a prepreg, 3 is a conductor circuit pattern, and 4 is an inner layer circuit board.

[0009]

Examples and Comparative Examples Table 1 shows the contents of the glass cloth, and Table 2 shows the prepreg obtained by impregnating the glass cloth with an epoxy resin and predrying.

[0010]

[Table 1]

[0011]

[Table 2]

The inner layer circuit board and each prepreg are made into a circuit board by etching the copper foil of the 0.8 mm thick glass epoxy double-sided copper clad laminate (70 μm copper foil) and the insulating layer thickness is 0.3 mm. So that they overlap, and then 1 on each side
An 8-μm copper foil was placed, heated and pressed to prepare a 4-layer multilayer printed wiring board substrate having the configuration of FIG. 1 and evaluated. The results are shown in Table 3.

[0013]

[Table 3] Test method: Solder heat resistance: The outermost copper foil was removed by etching, the sample cut into 50 mm square was boiled for 2 hours, and then
It was immersed in a solder bath at 260 ° C. for 1 minute, and the presence or absence of peeling was observed. Roughness in the drill hole: 60,000 rp with a 0.9 mm diameter drill
m, 50 μm / revolution, holes were made, and the roughness of the cross section was measured with a microscope. Surface roughness: 1 according to JIS B 601
The average roughness was indicated by 0 point.

[0014]

As is clear from Table 3, the multilayer printed wiring board substrate of the present invention did not cause delamination during soldering heat resistance and had other excellent properties.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a four-layer multilayer printed wiring board substrate.

FIG. 2 is a cross-sectional view showing a configuration example of a substrate for a 6-layer multilayer printed wiring board.

[Explanation of symbols]

 1 ... Outer layer substrate or metal foil 2 ... Prepreg 3 ... Conductor circuit 4 ... Inner layer circuit board

Claims (1)

[Claims] 1. A multilayer printed wiring board substrate in which one or more inner layer circuit boards are laminated and integrated by arranging an outer layer substrate or a metal foil on at least one surface through a prepreg and laying them together. Using 1500 denier glass yarn, the density is vertical 30-45 threads / 25 mm, horizontal 25-
A substrate for a multilayer printed wiring board, characterized in that a plain woven glass cloth having a weight of 35 to 25 mm and a weight of 250 to 330 g / m ² is impregnated with a thermosetting resin and predried, and one prepreg is used for each layer.