Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-09-26
2001-12-18
Cuneo, Kamano (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S262000, C174S265000
Reexamination Certificate
active
06331679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer circuit board for a semiconductor device, particularly to a multilayer circuit using anisotropic electro-conductive adhesive layer.
2. Description of the Related Arts
When circuit patterns are formed in a multilayer manner while using substrates made of BT resin or the like, in general, the circuit patterns in the respective layers are electrically connected to each other via through-holes drilled through the laminated substrates and plated on the inner wall thereof with an conductive metal.
FIG. 7
illustrates a circuit board formed by laminating resinous substrates
60
. A through-hole
62
is bored through the resinous substrates
60
, and a plated layer (for example, copper)
64
is formed on the inner wall thereof to electrically connect circuit patterns
66
on the respective layers with each other.
As described above, when the multilayer circuit board is produced, processes for forming the through-hole
62
and plating the inner wall of the through-hole
62
are necessary after the resinous substrates
60
are laminated and bonded together, which results in the lowering of production efficiency of the circuit board. Also, according to the above method wherein the plated layer
64
is formed on the inner wall of the through-hole to electrically connect the same with the circuit patterns
66
in the respective layers, it is necessary to ensure the spread of a plating solution all over the inner wall of the through-hole
62
, and therefore, there is a limit in the reduction of a diameter of the through-hole. Generally, the lower limit of the diameter of the through-hole is about 0.3 mm, and the further integration of circuit patterns
66
is impossible.
To solve the above problems, Japanese Unexamined Patent Publication (Kokai) No. 7-94868 discloses a multilayer circuit board wherein circuit patterns in the respective layers are electrically connected with each other by using the electrical conductivity of an anisotropic electro-conductive adhesive. Such a multilayer circuit board is shown in
FIG. 8
, wherein a circuit pattern
72
is provided on one surface of a first substrate
70
, and a connection land
74
is provided on the other surface thereof. When the first substrate
70
is bonded to a second substrate
70
a
having the same structure as that of the first substrate
70
by an anisotropic electro-conductive adhesive
80
, the connection land
74
is electrically connected to a circuit pattern
72
provided on the second substrate
70
a
via electro-conductive particles
80
a
dispersed in the anisotropic electro-conductive adhesive
80
. In this regard, the electrical connection between surfaces of the respective substrate
70
,
70
a
, that is, that between the circuit pattern
72
and the connection land
74
is achieved by a through-hole
76
provided through the respective substrate
70
,
70
a
in the thickness direction and filled with an electro-conductive paste
78
.
The anisotropic electro-conductive adhesive
80
is used for bonding the substrates
70
and
70
a
with each other and is composed of a thermoplastic adhesive matrix having an electro-insulating property mixed with electro-conductive particles such as solder, and has a characteristic in that it becomes partially electro-conductive at a portion when it is pressed from both sides to evacuate the electro-insulating matrix therefrom, while maintaining the electro-insulating property in other portions.
However, since it is necessary to electrically connect the circuit patterns
72
provided on the upper and lower surfaces of the respective substrates
70
and
70
a
with the lands
74
as described above when the multilayer circuit board is formed while using the anisotropic electro-conductive adhesive
80
, there is a problem in that processes are required for forming through-holes
76
in the substrates and for filling the electro-conductive adhesive
78
therein, resulting in the lowering of production efficiency.
Also, there has been still another problem in that the high density arrangement of circuit patterns
72
is restricted because of the through-holes
76
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a multilayer circuit board which is inexpensive in production cost and capable of carrying micro-circuit patterns thereon at a high density, and a simple method for producing the same.
To achieve the above object, according to one aspect of the present invention, a multilayer circuit board using an anisotropic electro-conductive adhesive layer is provided, comprising a substrate on which a first circuit pattern is formed, an anisotropic electro-conductive adhesive layer formed on a surface of the substrate on which the first circuit pattern is provided, consisting of a thermosetting or thermoplastic resin adhesive containing electro-conductive particles dispersed therein, and a second circuit pattern formed on the anisotropic electro-conductive adhesive layer, wherein an end of the second circuit pattern is curved into the anisotropic electro-conductive adhesive layer to be closer to the substrate and electrically connected to the first circuit pattern via the electro-conductive particles.
Preferably, a through-hole is provided in the substrate at a position corresponding to an end of the first circuit pattern, to expose the end of the first circuit pattern for facilitating the connection of an external terminal therewith.
Preferably, the through-hole is filled with a solder and carries the external terminal which is a solder ball integral with the solder filling the through-hole.
According to another aspect of the present invention, a multilayer circuit board using an anisotropic electro-conductive adhesive layer is provided, comprising a substrate on which a first circuit pattern is formed, a first anisotropic electro-conductive adhesive layer formed on a surface of the substrate on which the first circuit pattern is provided, consisting of a thermosetting or thermoplastic resin adhesive containing electro-conductive particles dispersed therein, and a second circuit pattern formed on the first anisotropic electro-conductive adhesive layer, a second anisotropic electro-conductive adhesive layer formed on a surface of the first anisotropic electro-conductive adhesive layer on which the second circuit pattern is formed, and a third circuit pattern formed on the second anisotropic electro-conductive adhesive layer, wherein an end of the second circuit pattern is curved into the first anisotropic electro-conductive adhesive layer to be closer to the substrate and electrically connected to the first circuit pattern via the electro-conductive particles, and further an end of the third circuit pattern is curved into the second anisotropic electro-conductive adhesive layer to be closer to the substrate and electrically connected to the second circuit pattern via the electro-conductive particles.
In this case, preferably, the curved end of the second circuit pattern is overlaid with the curved end of the third circuit pattern to be brought into close contact with each other.
According to further aspect of the present invention, a method for producing a multilayer circuit board using an anisotropic electro-conductive adhesive layer is provided, comprising the steps of: a) preparing a substrate carrying a first circuit pattern thereon; b) forming an anisotropic electro-conductive adhesive layer consisting of a thermosetting or thermoplastic resin adhesive containing electro-conductive particles dispersed therein on a surface of the substrate carrying the first circuit pattern; c) forming an electro-conductive layer on the anisotropic electro-conductive adhesive layer, which is then processed to a second circuit pattern; and d) heating and softening the anisotropic electro-conductive adhesive layer to enhance the curvature of an end of the second circuit pattern into the anisotropic electro-conductive adhesive layer to be closer to the substrate whereby the
Cuneo Kamano
Pennie & Edmonds LLP
Shinko Electric Industries Co. Ltd.
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