Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-12-02
2003-07-01
Patel, Tulsidas (Department: 2839)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
Reexamination Certificate
active
06586686
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer printed wiring board and method for manufacturing the same, and more particularly to a multilayer printed wiring board having an interstitial via hole (IVH) structure and a method for manufacturing the same.
2. Description of the Related Art
A conventional multilayer printed circuit board is constituted by a laminate obtained by alternately laminating copper-clad laminates and prepregs. The laminate has a surface on which a surface wiring pattern has been formed. Moreover, an internal wiring pattern is formed between interlayer insulating layers. Through holes are, by punching formed in the direction of the thickness of the laminate to establish the electric connections among internal wiring patterns or among internal wiring patterns and the surface wiring patterns.
The multilayer printed circuit board having the above-mentioned through hole structure must have regions for forming the through holes. Therefore, the density at which elements are mounted cannot be easily raised. As a result, there arises a problem in that the multilayer printed circuit board having the through hole structure cannot easily address needs for considerable reductions in the sizes of the portable electronic apparatuses, realizing narrow pitch packages and practical use of MCM.
As an alternative to the foregoing multilayer printed circuit board having the through hole structure, a multilayer printed circuit board has recently received attention which is formed into a full-thickness interstitial via-hole (IVH) structure which is able to easily address raising of the density.
The multilayer printed circuit board having the full-thickness IVH structure is a printed circuit board having a structure in which via holes for electrically connecting conductive layers to one another are formed in each of the interlayer insulating layers which constitute the laminate. That is, the foregoing printed circuit board has the via holes (buried via holes or blind via holes) which do not penetrate the substrate on which the circuit is formed and which electrically connect the internal wiring patterns to one another or the internal wiring patterns and the surface wiring patterns to one another. Therefore, the multilayer printed circuit board having the IVH structure is free from a necessity of specially forming regions for forming the through holes. Therefore, arbitrary layers can freely be connected to one another through small via holes. As a result, size reduction, high density and high-speed propagation of signals can be easily realized.
The multilayer printed circuit board having the IVH structure is manufactured by a process arranged, for example, as shown in FIG.
6
.
Initially, a material having a structure in which an aramide nonwoven fabric cloth is impregnated with epoxy resin is employed as prepreg
112
. Then, an operation for forming holes in the prepreg
112
is performed by using carbon dioxide gas laser. Then, conductive paste
114
is enclosed in obtained hole portions
112
a
(see
FIG. 6
(A)).
Then, copper foil
116
is laminated on each of the two sides of the prepreg
112
, and then heat and pressure are applied to the prepreg
112
having the copper foil
116
by heat pressing. Hence it follows that the epoxy resin and the conductive paste of the prepreg
112
are hardened so that the electrical connection between the two copper foil members
116
on the two sides of the prepreg
112
is established (see
FIG. 6
(B)).
Then, the copper foil
116
on each side is patterned by an etching method so that a hard and double-sided substrate having via holes is obtained (see
FIG. 6
(C)).
Then, the obtained double-sided substrates are used as core layers to form a multilayer structure. Specifically, the prepreg and copper foil are sequentially laminated on the two sides of the foregoing core layer while the prepreg and the copper foil are being aligned. Then, heat pressing is again performed, and then the uppermost copper foil
116
is etched. Thus, a four-layer substrate is obtained (see
FIGS. 6
(D) and
6
(E)). When a structure having a large number of layers is formed, the foregoing process is repeated. Thus, a six-layer substrate or an eight-layer substrate can be obtained.
The foregoing conventional technique, however, must repeat the laminating process using heat pressing and the process for patterning the copper foil by performing the etching operation. Therefore, the manufacturing process becomes too complicated and considerable time is required to complete the manufacturing operation.
If the multilayer printed circuit board having the IVH structure which can be obtained by the above-mentioned manufacturing method encounters only one defective portion (only one defective process) in the patterning operation during the manufacturing process, the overall circuit board, which is the final product, becomes a defective product. Hence it follows that the manufacturing yield deteriorates excessively.
To overcome the above-mentioned problems, an object of the present invention is to provide a high-density multilayer printed circuit board having the IVH structure which can be manufactured by a very simple process and which permits a satisfactory high manufacturing yield to be realized and a manufacturing method therefor.
BRIEF SUMMARY OF THE INVENTION
To achieve the above-mentioned object, the present invention is structured as follows.
According to one aspect of the present invention, there is provided a method of manufacturing a multilayer printed circuit board comprising the steps (1) to (5):
(1) a step for forming a non-penetrating hole in an insulating base member, such as an organic insulating base member, having a metal layer formed on either surface thereof by a laser irradiation operation such that the non-penetrating hole reaches the metal layer;
(2) a step for forming via holes by enclosing a conductive material into the non-penetrating hole formed in step (1);
(3) a step for forming a conductive circuit by etching the metal layer;
(4) a step for forming projecting conductors on the surfaces of the via holes to form a single-sided circuit substrate;
(5) a step for laminating the single-sided circuit substrate and another single-sided circuit substrate or the single-sided circuit substrate and another substrate obtained in the steps (1) to (4) such that the projecting conductors of the single-sided circuit substrate and a conductive circuit of the other circuit are positioned opposite to each other through non-hardened resin which is an organic adhesive layer and applying heat and pressure to (heat-pressing) the laminate.
According to another aspect of the present invention, there is provided a method of manufacturing a multilayer printed circuit board comprising the steps (1) to (4):
(1) a step for forming a non-penetrating hole in an insulating base member, such as an organic insulating base member having a metal layer formed on either surface thereof by a laser irradiation operation such that the non-penetrating hole reaches the metal layer;
(2) a step for forming via holes by enclosing a conductive material into the non-penetrating hole formed in step (1) and forming projecting conductors on the surfaces of the via holes;
(3) a step for forming a conductive circuit by etching the metal layer;
(4) a step for laminating the single-sided circuit substrate and another single-sided circuit substrate or the single-sided circuit substrate and another substrate such that the projecting conductors of the single-sided circuit substrate and a conductive circuit of the other single-sided circuit substrate or the other conductive circuit are positioned opposite to each other through non-hardened resin which is an organic adhesive layer and applying heat and pressure to (heat pressing) the laminate.
In the foregoing aspects of the present invention, the projecting conductors are inserted into the non-hardened resin so that resin is squeezed out. That is, the projecting conductors penetrate the organic ad
Enomoto Ryo
Hiramatsu Yasuji
Ibiden Co. Ltd.
Patel Tulsidas
Tolpin Thomas W.
LandOfFree
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