JPS6273937A - Multilayer printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] The polyimide multilayer printed board of the present invention uses a copper foil having a surface roughness of 2 to 8 μRz in contact with the adhesive sheet (prepreg), thereby making it possible to form through holes in the multilayer board after lamination. Such hole drilling sometimes prevents the occurrence of cracks that occur at the interfaces of each layer in the hole wall portion.

[Industrial application field]

The present invention relates to a polyimide multilayer printed board that prevents the occurrence of cracks that sometimes occur at layer interfaces in hole wall portions when holes such as through holes are formed in the multilayer board after a lamination process.

Currently, glass cloth-based epoxy resins are widely used as adhesive sheets for multilayer printed boards. However, with high multilayer boards (10 layers or more) for high-density mounting, there are problems with heat resistance during the mounting process, as well as continuity reliability due to resin smear and thermal expansion in the thickness direction. Fabric-based polyimide resins have been developed.

This glass cloth base polyimide resin can be used as an insulating layer of copper-clad laminates (hereinafter referred to as the base material), or as a sheet for adhesion between copper-clad inner layers or between copper-clad inner layers and copper-clad outer layers. (prepreg).

In this specification, a multilayer printed board using such a polyimide resin is referred to as a polyimide multilayer printed board I-+ffl.

[Conventional technology]

FIG. 2 is a cross-sectional view of a four-layer board before lamination, and FIG. 3 is a cross-sectional view after lamination and drilling.

As shown in Figure 2, surface copper foil 1, prepreg 2, base material 3
After the inner layer copper clad boards 3 and the like having circuit patterns 3b formed on both sides of the inner layer are laid up in order 7, they are pressed under pressure and heat. In addition, instead of the surface copper foil 1, an outer layer copper clad board having copper foil on one or both sides can also be used.

After lamination, as shown in FIG. 3, connections are made between the inner layer circuit patterns and with the surface layer pattern formed thereafter
Through holes 4 are made for connection between the surface layers.

[Problem that the invention seeks to solve]

By the way, when holes are made in a high multilayer board made of polyimide resin as described above, holes A and B in FIG. 3 are formed.

It was found that cracks were generated in the areas indicated by C, D, . . . . That is, cracks occurred in the wall portion of the through hole 4, at the interface between the copper foils 1 and 3b and the base material 3a and the prepreg 2, and at the interface between the prepreg 2 and the base material 3a shown by dotted lines. If such cracks were present in the printed board, ionic substances and the like would enter the cracks in subsequent processes and corrode the copper foil, resulting in a deterioration in quality.

In order to maintain adhesive strength, such conventional copper foil surfaces have a 10-point surface roughness of 10 to 15 μfez, a maximum grain size of 30 μm, and an average grain size of 15 to 18 μm.
Particles having an average particle diameter of 2.5 to 4.0 μm are added on top of the particles. The adhesion strength of such a copper foil with 35 layers and 1 m thickness is 1.5-2. Qkg/cm.

[Means for solving problems]

FIG. 1 is a sectional view showing a polyimide multilayer printed circuit board of the present invention.

In the figure, 1 is a surface copper foil, 2 is a prepreg, 3a is a base material, 3b is a circuit pattern copper foil, and 4 is a through hole.

A copper foil having a surface roughness of 2 to 8 μRz on at least one of the surfaces of the copper foils 1 and 3b is used.

[Effect]

By setting the surface roughness of the copper foils 1 and 3b to 2 to 8 μRz, for example, in the case of a 35 μm thick copper foil, the adhesive strength will be 0.7 to 1.5 kg/cm, and holes will sometimes occur in each layer. Cracks at the interface can be prevented.

〔Example〕

FIG. 1 is a cross-sectional view of essential parts of a multilayer printed board showing an embodiment of the present invention, and the same parts as in FIG. 3 are given the same reference numerals.

In this embodiment, one inner layer copper clad plate 3 with copper foil clad on both sides is used.
Three outer layer copper clad plates 5, each of which was covered with copper foil on both sides, were laminated on both sides, and two prepregs 2 were sandwiched between each copper clad plate. Therefore, it becomes a high multi-layer temporary fixing of 30 layers. In addition,
5b shows the circuit copper foil + 5c shows the surface i-whistle.

The copper foil thickness of each copper clad board 3 and 5 of the inner layer and outer layer is 35
μm, thickness of base material and prepreg is 0.1fl after lamination
It is.

As shown in the figure, base material 3a of copper clad board for inner layer and outer layer.
, the surface roughness of the copper foils 3b, 5b, and 5c in contact with the prepreg 2 is 4 μRz, and the surface roughness of the copper foils 3b, 5b, and 5c in contact with the prepreg 2 is 8 μRz.
When Rz was used, there were no cracks that had previously occurred.

The present inventor believes that if the surface roughness of the copper foil is kept within the range of 2 to 8 μRz, the average grain size is 3 μm or less, and the maximum grain size is 6 μm or less,
Anamei confirmed that no cracks occurred between the layers.

In case of surface roughness as above, 1tll of 35μm
The adhesive strength of the foil thickness was 0.7 to 1.5 kg/cm.

Note that the copper foils 3b, 5b, which are in contact with the base materials 3a, 5a,
When the roughness of the surface of 5a is set to 2 to 8 μRz and the roughness of the other surface is set to be less than 2 μRz or greater than 8 μRz, which is outside the above range, cracks will not occur in escape lands outside the above range. Furthermore, even if a crack occurs in the connection land, it remains on the surface of the land and there is no electrical problem, so the effect of the crack is small.

[Effect of the invention 1 The surface roughness of the copper foil of a multilayer printed board made of multiple layers of prepreg using copper foil and polyimide resin is 2 to 8 μRz.
By doing so, it is possible to prevent cracks between the layers, which sometimes occur when drilling holes after lamination, and this has a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view of printed board material before lamination, and FIG. 3 is a sectional view of the printed board showing cracks caused by drilling. In the drawing, 1 is the surface copper foil, 2 is the prepreg, 3 is the inner layer copper clad plate, 3
a, 5a are base materials, 3b, 5b are circuit copper foils, 4 are through holes, 5 is copper clad board for outer layer, 5c is surface copper foil ≦a) 4/l 5 plated 0 size Yohei r Mu it dent ts J
figure

Claims (1)

[Claims] A multilayer structure in which a copper foil (1) and an adhesive sheet (3) made of at least a polyimide resin are laminated, characterized in that at least one of the copper foil surfaces in contact with the adhesive sheet (3) has a surface roughness of 2 to 8 μRz. Multilayer printed board.