Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-11-20
2001-11-27
Paladini, Albert W. (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S524000, C174S257000, C257S673000, C257S778000
Reexamination Certificate
active
06323434
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit substrate for mounting a semiconductor device, particularly a circuit substrate which can be adapted to fine-pitch wiring of a semiconductor device or high-density packaging, as well as a process for manufacturing it.
PRIOR ART
Previously known circuit substrates of this kind have a structure as described in, for example, JPA No. 77293/94.
As shown in
FIG. 4
, this semiconductor device
101
comprises a conductive circuit
105
buried not to be bared from both faces of insulating layers
103
,
104
, and pairs of conducting paths
106
,
107
opening to both faces of the conductive circuit
105
and displaced from each other along the plane of the conductive circuit
105
. The conducting paths
106
,
107
are connected to bumps
108
,
109
, respectively, whereby the conductive circuit
105
is connected to the bumps
108
,
109
via the conducting paths
106
,
107
, respectively.
The bumps
108
formed in the conducting paths
106
on one side of a film carrier
102
are electrically connected to electrodes
112
formed on a substrate
111
of a semiconductor element
110
by contact therewith, whereby the semiconductor element
110
is mounted on the film carrier
102
.
An insulating resin layer
113
is formed in contact with the upper face of the insulating layer
103
to cover the semiconductor element
110
.
However, said prior art involving inserting the conductive circuit
105
between the film-like insulating layers
103
,
104
required the step of bonding them with an adhesive or the like, resulting in complication of the manufacturing process.
This semiconductor device
101
is mounted on a mother board
114
generally by soldering the bumps
109
projecting beneath the insulating layer
104
to a lead pattern
116
on the mother board
114
by reflow-soldering, but the bumps
109
to be connected to the semiconductor element
110
may also be fused during then to cause disadvantages in mounting operations such as misalignment of the semiconductor element
110
.
In view of the above problems, an object of the present invention is to provide a circuit substrate comprising a conductive circuit on an insulating base, an electrode for connection to an IC (Integrated Circuit) and an electrode for connection to a mother board substrate, which eliminates the step of bonding the film-like insulating base and the conductive circuit to simplify the manufacturing process, as well as a process for manufacturing it.
Another object of the present invention is to provide a circuit substrate comprising a conductive circuit on an insulating base, an electrode for connection to an IC and an electrode for connection to a mother board substrate, wherein only the surface portion of the metal projection for connection to a mother board substrate can be fused during soldering the circuit substrate to a mother board substrate to ensure reliable packaging, as well as a process for manufacturing it.
DISCLOSURE OF THE INVENTION
The present invention provides a circuit substrate for mounting an IC device on a mother board substrate, comprising:
a first insulating base made of a polyimide obtained by terminating imidation reaction of a polyamide acid as a precursor for the polyimide,
a conductive circuit formed on said first insulating base,
a second insulating base formed on said first insulating base carrying said conductive circuit and made of a polyimide obtained by terminating imidation reaction of a polyamide acid as a precursor for the polyimide,
an electrode for connection to the mother board substrate, which is connected to said conductive circuit and projects from said first insulating base, and
an electrode for connection to the IC, which is connected to said conductive circuit and projects from said second insulating base.
The present invention also provides a circuit substrate for mounting an IC device on a mother board substrate, comprising:
a first insulating base,
a conductive circuit formed on said first insulating base,
a second insulating base formed on said first insulating base carrying said conductive circuit,
an electrode for connection to the mother board substrate, which is connected to said conductive circuit and projects from said first insulating base to form a metal projection on its surface, and
an electrode for connection to the IC, which is connected to said conductive circuit and projects from said second insulating base to form a metal projection on its surface with the surface portion having a melting point higher than the melting point of the metal projection of said electrode for connection to the mother board substrate.
In the circuit substrate according to the present invention, the melting point of the surface portion of the metal projection of the electrode for connection to the IC may be at least 50° C. higher than the melting point of the metal projection of the electrode for connection to the mother board substrate.
In the circuit substrate according to the present invention, the first and second insulating bases may be made of a polyimide obtained by terminating imidation reaction of a polyamide acid as a precursor for the polyimide.
The present invention also provides a process for manufacturing a circuit substrate for mounting an IC device on a mother board substrate, comprising the steps of:
applying a polyamide acid solution as a precursor for a polyimide on a metal foil and terminating imidation reaction thereof to form a first insulating base layer made of the polyimide,
processing said metal foil to form a conductive circuit on said first insulating base layer,
applying a polyamide acid solution as a precursor for a polyimide on said first insulating base layer carrying said conductive circuit and terminating imidation reaction thereof to form a second insulating base layer made of the polyimide,
forming an electrode for connection to the mother board substrate, which is connected to said conductive circuit and projects from said first insulating base, and forming an electrode for connection to the IC, which is connected to said conductive circuit and projects from said second insulating base.
The process for manufacturing a circuit substrate according to the present invention may further comprises the step of forming through holes for forming electrodes in the first and second insulating base layers by photolithography after applying a polyamide acid solution.
The process for manufacturing a circuit substrate according to the present invention may further comprises the steps of forming a metal projection on the surface of the electrode for connection to the mother board substrate, and forming a metal projection on the surface of the electrode for connection to the IC with the surface portion having a melting point higher than the melting point of the metal projection of said electrode for connection to the mother board substrate.
According to the present invention as characterized above, the first and second insulating bases are made of a polyimide obtained by imidation of a polyamide acid to eliminate the previously required step of bonding the film-like insulating bases and the conductive circuit, whereby the manufacturing process can be simplified to attain improved productivity and reduced costs.
According to the present invention, through holes for forming electrodes can be provided more readily than according to the prior art, by forming through holes for forming electrodes in the first and second insulating base layers by photolithography after applying a polyamide acid solution.
Also according to the present invention, the melting point of the surface portion of the metal projection for connection to an IC can be higher than the melting point of the metal projection for connection to a mother board substrate, particularly at the surface portion thereof, by forming a metal layer such as a solder layer on the surface of the metal projection for connection to an IC by plating or other means.
According to the present invention, the melting point of the surface portion
Fujimoto Masahiro
Kurita Hideyuki
Takahashi Satoshi
Tsutsumi Akira
Paladini Albert W.
Rosenthal & Osha L.L.P.
Sony Chemicals Corp.
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