JPH0384994A - Multilayer printed-circuit board - Google Patents

Abstract

PURPOSE:To increase the degrees of design freedom and the wiring density of circuit patterns by forming through holes concentrically in inner via hole regions so as to electrically connect between circuit patterns outside the inner circuit patterns. CONSTITUTION:Via holes 2 are formed in inner layers to electrically connect between inner capacitor patterns 3a and 3b. Through holes 4 are formed to electrically connect between circuit patterns, such as outer circuit patterns 5a and 5b arranged outside the inner patterns 3a and 3b. The via holes and through holes are concentrically aligned. Therefore, more regions are available for formation of circuit patterns, thus increasing the degrees of freedom of circuit pattern layout and the wiring density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a multilayer printed wiring board, and particularly to an improvement of a multilayer printed wiring board having inner layer via holes or blind through holes.

(Prior Art) In response to the miniaturization and higher functionality of electronic devices, multilayer printed wiring boards have been put into practical use for the purpose of increasing the density of circuit configurations and miniaturizing circuit parts. In other words, multilayer printed wiring boards are widely used in a variety of electronic devices, in which inner layer circuit patterns are arranged and integrated in multiple stages via insulating layers, and outer surface circuit patterns are integrated to form complex circuits. used in equipment. Incidentally, in this type of multilayer printed wiring board, inner layer circuit patterns are often electrically connected to each other, or inner layer circuit patterns and outer layer circuit patterns are electrically connected to each other. Electrical connections between the inner layer circuit patterns or between the inner layer circuit patterns and the outer layer circuit patterns are performed as follows. That is, first, the required inner layer via hole (blind through hole) is drilled in a predetermined area of the inner layer circuit board by drilling or laser processing, and the inner wall surface of the inner layer via hole is coated with chemical plating or electroplating to form the circuit. Make conductor connections between patterns.

Thereafter, the necessary inner layer circuit boards and outer layer circuit boards, including the inner layer circuit board provided with the inner layer via holes, are stacked on top of each other with prepreg layers interposed therebetween and pressure-molded to obtain a multilayer printed wiring board. A required through hole is drilled in a predetermined area by drilling or laser processing, and chemical plating or electroplating is applied to the inner wall surface of the through hole to connect outer layer circuit patterns to each other or to connect an outer layer circuit pattern to another inner layer circuit pattern. is being carried out.

FIG. 4 is a sectional view of a main part of a conventional multilayer printed wiring board 1 having inner layer via holes for electrically connecting between inner layer circuit patterns, and 2 is an inner layer via hole for electrically connecting between inner layer circuit patterns 3a and 3b. A hole 4 is a through hole 3c that electrically connects between the outer layer circuit patterns 5a and 5b.
6 indicates another inner layer circuit pattern, and 6 indicates an insulating layer that electrically insulates between the circuit patterns.

(Problem to be solved by 9! Ming) However, the multilayer printed wiring board having the above-mentioned inner layer via hole has the following disadvantages.

That is, in order to electrically connect circuit patterns (inner layer and outer layer circuit patterns) arranged in multiple layers, it is necessary to form the required inner layer via holes and through holes at different positions. In other words, separate areas are required for drilling inner layer via holes and through holes, which limits the layout of the circuit pattern.
Additionally, there is a problem in that it is impossible to improve the wiring density (circuit pattern density).

The present invention addresses the above-mentioned circumstances and provides a multilayer printed wiring board that allows a high degree of freedom in designing circuit patterns and increases circuit pattern density.

[Structure of the invention]

(Means for Solving the Problems) The present invention is a multilayer printed wiring board having inner layer via holes that electrically connect inner layer circuit patterns,
A through hole for electrically connecting the circuit patterns on the outer layer side of the inner layer circuit pattern is formed coaxially within the inner layer via hole region.

(Function) According to the present invention, an inner layer via hole region that connects predetermined inner layer circuit patterns is utilized, and a through hole that electrically connects the inner layer circuit patterns is formed coaxially within this region. be done. In other words, since the inner layer via holes and through holes are provided coaxially in a predetermined area, the area in which circuit patterns can be formed is widened, and it is easy to improve the flexibility of circuit pattern layout and wiring density. You will get it.

(Example) The present invention will be described in detail below with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view showing the main structure of a multilayer printed wiring board 1 according to the present invention, in which 2 is an inner layer via hole that electrically connects inner layer circuit patterns 3a and 3b, and 4 is an outer layer circuit pattern. A through hole electrically connects between 5a and 5b, 3C indicates another inner layer circuit pattern, and 6 indicates an insulating layer electrically insulating between the circuit patterns. That is, in the multilayer printed wiring board 1 according to the present invention, the inner layer via hole 2 electrically connects the required inner layer circuit patterns 8a, 3b, and the circuit arranged outside the inner layer circuit patterns 3a, 3b. It has a structure in which patterns such as through holes 4 for electrically connecting the outer layer circuit patterns 5a and 5b are coaxially formed.

The multilayer printed wiring board having the above structure can be manufactured, for example, as follows. First, as shown cross-sectionally in FIG.
A material for an inner layer circuit board made by pasting 8μ copper foil is prepared, and holes 4a for inner layer via holes are bored in required areas. Next, the hole 4 for the inner layer via hole that has been drilled is
After cleaning the inside of the copper foil, the copper foil is photoetched to form the required inner layer circuit patterns 8a and 3b as shown in cross section in FIG. A conductive layer is formed on the inner wall surface by, for example, chemical plating to provide necessary inner layer via holes. Thereafter, as shown in cross section in FIG. 3, an inner layer circuit board 1 is formed by electrically connecting the inner layer circuit patterns 3a and 3b with the inner layer via holes 2.
a. Another inner layer circuit board 1b and a copper foil 7 for forming an outer layer circuit pattern are laminated with a prepreg layer 8 interposed therebetween, and pressure molded to obtain a multilayer printed wiring board. Note that the inner layer circuit board 1a and the other inner layer circuit board ib
When laminating the copper foil 7 for forming the outer layer circuit pattern with the prepreg layer 8 interposed therebetween, the circuit pattern 5a located outside the inner layer circuit board 1a is prepared in advance.
, 56 is set so as to maintain a coaxial positional relationship with the inner layer via hole 2 of the inner layer circuit board 1a. The double-sided copper foil 7 of the multilayer printed wiring board thus obtained is drilled with holes for necessary through-hole connections, and selectively photoetched to form an outer layer circuit pattern 5a. Next, a desired multilayer printed wiring board is obtained by depositing a conductive layer on the inner wall surface of the through-hole connection hole that has been drilled and formed, if necessary, by, for example, chemical plating, and making the required through-hole connection 4. be able to. That is, instead of forming the conductive layer on the inner wall surface by chemical plating or the like, the through-hole connection 4 may be made using a lead wire, and in that case, the diameter of the hole for through-hole connection may be A value of about 0.51 or less is sufficient, and even more preferable results can be obtained.

[Effects of the Invention] According to the present invention, within the area of an inner layer via hole that electrically connects between predetermined inner layer circuit patterns, a through hole that electrically connects between circuit patterns located outside thereof is coaxial. It is drilled and formed in. In other words, the conductor layer that connects the required circuit patterns is formed in the form of double through holes.

In this way, connections between required circuit patterns are made in the form of double through holes, and the area required for this can be reduced, which can contribute to improved circuit pattern formation density and freedom in layout.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the main part configuration of a multilayer printed wiring board according to the present invention, and FIG. 2 is a sectional view of an inner layer circuit board having inner layer via holes constituting the multilayer printed wiring board according to the present invention. FIG. 3 is a cross-sectional view schematically showing a mode of manufacturing a multilayer printed wiring board according to the present invention, and FIG. 4 is a cross-sectional view showing the main structure of a conventional multilayer printed wiring board. 1...Multilayer printed wiring board la, lb.
...Inner layer circuit board 2...Inner layer via holes 8a, 3b.
...Inner layer circuit pattern 3c connected by inner layer via hole...Other inner layer circuit pattern 4...
...Through holes 5a, 5b...Outer layer circuit pattern 6...Insulating layer 7...Copper foil 8... prepreg layer

Claims (1)

[Claims] A multilayer printed wiring board having an inner layer via hole that electrically connects between inner layer circuit patterns, wherein a through hole that electrically connects between the circuit patterns on the outer layer side of the inner layer circuit pattern is coaxial within the inner layer via hole region. A multilayer printed wiring board characterized in that it is formed by