Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-05-11
2002-09-24
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S262000, C257S700000, C361S760000
Reexamination Certificate
active
06455783
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer printed circuit board and a method of manufacturing the same, and more particularly, to the manufacture of a thin insulating layer, the formation of conductive holes, and the protection of the circuit board from etching liquids.
BACKGROUND ART
In multilayer printed circuit boards, there has been a recent demand to thin insulating layers in order to shorten the distance between pattern layers, which transmit signals at high speeds.
FIG. 1
shows a conventional method for manufacturing a multilayer, printed circuit board. In the method, conductive holes
92
and conductive patterns
93
are formed on insulating substrates
91
, and a plural number of the substrates
91
are laminated together.
In the above method, however, the conductive holes
92
and the conductive patterns
93
must be formed beforehand on the insulating substrates
91
. This makes it difficult to thin the insulating substrates
91
.
FIG. 2
shows a conventional build-up process through which thin insulating layers are formed. In the build-up process, an insulating substrate
91
having a conductive hole
92
and a conductive pattern
93
is prepared. An insulating layer
911
, made of prepreg or the like, is laminated on the surface of the substrate
91
. A conductive pattern
931
is then formed on the surface of the insulating layer
911
. Afterward, the insulating layer
911
is irradiated with ultraviolet rays and developed to form a conductive hole
921
in the insulating layer
911
. A plating film
930
is then applied to the wall of the conductive hole
921
. Since thin insulating layers are laminated in this method, the distance between the conductive patterns
93
,
931
is decreased and high speed transmission of signals is enabled.
In the above build-up process, however, residual resin left on the insulating layer
911
after formation of the conductive hole can result in unsatisfactory conduction of the conductive hole
921
. Thus, the conductive hole
921
must be large. However, this makes it difficult to narrow the pitch between conductive holes.
Further, as shown in
FIG. 3
, in a multilayer printed circuit board having a mounting hole
94
, an exposed portion of the conductive pattern
93
in the mounting hole
94
may be corroded by copper foil etching liquid when forming the conductive hole
921
. This may result in unsatisfactory connection between the exposed portion of a bonding pad
942
in the mounting hole
94
and a bonding wire.
It is a first object of the present invention to provide a multilayer printed circuit board and a method for manufacturing the same that shortens the distance between patterns and facilitates the formation of minute conductive holes having superior conductive reliability.
It is a second object of the present invention to provide a multilayer electronic component mounting substrate and a method for manufacturing the same that has connection terminals having a superior corrosion resisting characteristic with respect to etching liquids and a superior connecting reliability with respect to bonding wires.
SUMMARY OF THE INVENTION
In a first aspect of the present invention, a method for manufacturing a multilayer printed circuit board is provided. First, a core substrate including a core pattern, which has a pad for covering a bottom opening of a conductive hole, is prepared. Then, a laminated plate is formed by laminating an insulating layer on the surface of the core substrate. Then, a surface pattern is formed on the surface of the laminated plate at portions other than where the conductive hole is formed. Then, the conductive hole, the bottom opening of which is covered by the pad, is formed by irradiating a laser beam at a conductive hole formation portion of the laminated plate. Then, the entire surface of the insulating layer, which includes the interior of the conductive hole, is coated with a thin plating film. Subsequently, a mask is applied to the thin plating film with the conductive hole in an opened state and the wall of the conductive hole is coated with a conductive coating. Afterward, the mask is removed. Further, the thin plating film excluding the portions coated by the conductive coating is removed.
The most significant features of the present invention are that a build-up process, which laminates insulating layers on the surface of the core substrate, is performed, and a conductive hole that reaches a pad is milled on a laminated plate by irradiating a laser beam.
In the present invention, a core pattern refers to one layer or two or more layers of conductive patters that are formed on the surface or interior of the core substrate. The surface pattern refers to a conductive pattern formed on the surface of the insulating layer. Further, pattern will refer to the core pattern and/or the surface pattern below.
In this method, the insulating layer is reinforced by the core substrate when forming the conductive hole and the surface pattern. This enables a thinner insulating layer to be formed.
It is preferred that a land surround a middle portion of the conductive hole formation portion. The land and the conductive coating that coats the wall of the conductive hole are both metal and thus have substantially the same coefficient of thermal expansion. This inhibits the conductive coating from falling off the wall of the conductive hole when a thermal impact is applied.
Further, even if the conductive hole is relatively deep, the thin plating film is applied to the wall of the conductive hole in a uniform manner and conduction reliability is improved by providing the land at the middle portion of the conductive hole.
When the land is used only to reinforce the conductive hole, the land and core pattern that are located on the same layer are insulated from each other. However, the land and core pattern located on the same layer may be electrically connected to each other.
It is preferred that the thin plating film have a thickness of 0.01 &mgr;m to 5 &mgr;m.
It is preferred that the insulative core substrate have a mechanical strength that enables the formation of a pattern and a hole. The core substrate includes a resin substrate filled with glass fiber or glass cloth. The core substrate includes a core pattern formed on at least one of the surface and interior of the core substrate.
It is preferred that the insulating layer have a thickness of 30 &mgr;m to 150 &mgr;m.
The insulating layer may be formed on either one side or both sides of the core substrate.
Further, the insulating layer may be formed by, for example, printing and applying prepreg, which is formed by semihardening resin impregnated in glass fiber or glass cloth, or applying a sheet of prepreg and then hardening the resin in the prepreg.
It is preferred that the conductive hole have a diameter of 30 &mgr;m to 300 &mgr;m.
It is preferred that the thin plating film be formed by, for example, a chemical plating film, which is made of conductive material such as copper, tin plating, the application of a solder palladium catalyst, or a lamination of these materials.
A second aspect of the present invention provides a multilayer printed circuit board comprising a core substrate including a core pattern, an insulating layer coating the surface of the core substrate, a surface pattern provided on the surface of the insulating layer, and a conductive hole for electrically connecting the surface pattern to the core pattern. The core pattern includes a pad covering a bottom opening of the conductive hole.
A third aspect of the present invention provides a method for manufacturing a multilayer electronic component mounting substrate. Initially, in a first step, a core substrate including an electronic component mounting hole, a connection terminal exposed together with the mounting hole, and a core pattern, which has a pad for covering a bottom opening of a conductive hole, are prepared. Then, in a second step, a laminated plate is formed by laminating an insulating layer on the surface of the core substrate with the mou
Asano Kouji
Ishida Naoto
Kondo Mitsuhiro
Minoura Hisashi
Tsukada Kiyotaka
Buyan Robert D.
Ibiden Co. Ltd.
Paladini Albert W.
LandOfFree
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