Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
2003-02-18
2004-08-03
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S669000
Reexamination Certificate
active
06770957
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to adhesives, more specifically adhesives for connecting a semiconductor chip to a substrate.
2. Background Art
Paste and film adhesives have been used to connect a semiconductor chip onto a substrate or a flexible wiring board.
Reference
101
in
FIG. 3
represents an electric device comprising a semiconductor chip
111
bonded to a flexible wiring board
105
with an adhesive
112
. Bump terminals
121
carried by the semiconductor chip
111
are in contact with metal lines
122
at the bottom of an opening
119
in the cover film
115
of the flexible wiring board
105
.
The terminals
121
on the semiconductor chip
111
are connected to its internal circuit not shown, so that the internal circuit of the semiconductor chip
111
and the metal lines
122
on the flexible wiring board
105
are electrically connected each other via the terminals
121
in the state shown in FIG.
3
.
The adhesive
112
has been cured, whereby the semiconductor chip
111
and the substrate
113
are also mechanically connected each other via this adhesive
112
.
If the adhesive
112
is used, the semiconductor chip
111
and the flexible wiring board
105
can be thus connected without using solder.
However, the flexible wiring board
105
may be curved in the parts between terminals
121
on the semiconductor chip
111
as shown in
FIG. 3
, when the conventional adhesive
112
is used. When the flexible wiring board
105
is curved, the internal stress may become uneven, which may result in a short circuit between the flexible wiring board
105
and the semiconductor chip
111
or connection failure after aging.
When the adhesive
112
used for connection is not a film but a paste, air tends to be included in the adhesive
112
during the process of applying the adhesive
112
or heating under pressure, whereby voids may be generated in the adhesive
112
between the semiconductor chip
111
and the flexible wiring board
105
. Reference
130
in
FIG. 3
represents voids generated in the adhesive
112
.
If many voids
130
are present in the adhesive
112
, when the electric device
101
has been left to stand for a long time (aging) under high temperature ambience, the semiconductor chip
111
may float from the adhesive
112
on the substrate
113
to invite connection failure in the electric device
101
.
What is needed, therefore, is an adhesive that less likely to cause voids in the adhesive and deformation of adherends when it is used for connection.
SUMMARY OF INVENTION
It has been discovered that curved “adherends” result from the uneven residual stress in adhesives resulting from uneven distribution of the adhesives on the adherends after curing.
After studies to prevent the phenomenon described above, it was discovered that when the specific gravity of adhesives is adjusted to 1.4 or more and 4.0 or less by adding a filler having a specific gravity of 3.0 or more and 9.0 or less, the adhesives are not excessively pushed aside during heating under pressure, whereby inclusion of voids or curved adherends can be prevented.
In one aspect, therefore, the present invention provides an adhesive comprising a binder based on a thermosetting resin, a hardener for the thermosetting resin and an insulating filler, wherein the filler has a specific gravity of 3.0 or more and 9.0 or less and the adhesive has an overall specific gravity of 1.4 or more and 4.0 or less.
In one embodiment, the present invention provides the adhesive described above wherein the filler is contained in an amount of 5 parts by volume or more on the basis of the total volume of the binder and the hardener representing 100 parts by volume.
In one embodiment, the present invention provides the adhesive described above wherein the filler is contained in an amount of 35 parts by volume or less on the basis of the total volume of the binder and the hardener representing 100 parts by volume.
In one embodiment, the present invention provides the adhesive described above wherein the thermosetting resin contained in the binder is an epoxy resin.
In one embodiment, the present invention provides the adhesive described above containing conductive particles and having a specific gravity of 1.0 or more and 4.0 or less when the conductive particles are included.
In one embodiment, the present invention provides the adhesive described above wherein the conductive particles comprise resin particles and a metal coating formed on the surfaces of the resin particles.
In one embodiment, the present invention also provides an adhesive film obtained by forming a film of an adhesive comprising a binder based on a thermosetting resin, a hardener for the thermosetting resin and an insulating filler, wherein the filler has a specific gravity of 3.0 or more and 9.0 or less and the adhesive has an overall specific gravity of 1.4 or more and 4.0 or less.
In one embodiment, the present invention also provides an electric device comprising a semiconductor chip and a substrate with an adhesive being inserted between the semiconductor chip and the substrate and cured by heat treatment, wherein the adhesive comprises a binder based on a thermosetting resin, a hardener for the thermosetting resin and an insulating filler, wherein the filler has a specific gravity of 3.0 or more and 9.0 or less and the adhesive has a specific gravity before hardening of the adhesive, 1.4 or more and 4.0 or less.
Advantageously, therefore, embodiments of the present invention provide adhesives having an overall specific gravity of 1.4 or more and 4.0 or less by including a filler having a specific gravity of 3.0 or more and 9.0 or less so that not only voids are less likely to occur in the adhesives during connecting an adherend or a substrate and a semiconductor chip but also the substrate is less likely to be curved after connection.
Thus, electric devices in which components are connected with adhesives formed in accordance with embodiments of the present invention have not only excellent appearance but also high connection reliability. As used herein, the “specific gravity” means the ratio of the density of a material to the density of water. Adhesives having an overall specific gravity of 4.0 or less are easy to handle during application because they have a low overall viscosity.
The adhesive of the present invention may contain a coupling agent. A coupling agent like a silane coupling agent has a high affinity for both organic materials and inorganic materials. Therefore, if a coupling agent is added to the adhesive of the present invention, the affinity between the adhesive comprising organic materials like binder and adherends comprising inorganic materials like metal wiring or glass substrate is improved.
When a filler having a specific gravity of 3.0 or more and 9.0 or less is added in an amount of 5 parts by volume or more and 35 parts by volume or less on the basis of the total volume of the binder and the hardener representing 100 parts by volume, the overall specific gravity of adhesives can be adjusted to 1.4 or more and 4.0 or less.
The adhesives of the present invention may contain a filler having a specific gravity of 3.0 or more and 9.0 or less and a filler having a specific gravity of less than 3.0 such as silica in combination. However, fillers having a specific gravity of less than 3.0 are not preferred to be used alone because the overall specific gravity of the adhesives becomes low. Fillers having a specific gravity exceeding 9.0 are not preferred because they are readily precipitated in the adhesives.
The binder used in the adhesives of the present invention may be preferably based on an organic compound such as a resin and contains at least a thermosetting resin. If a liquid epoxy resin is used as the thermosetting resin, a pasty adhesive can be obtained without using any organic solvent which has an adverse environmental effect during the process of preparing the adhesive and the process of connecting adherends.
The types of conductive particles added to the adhesi
Osha Novak & May L.L.P.
Potter Roy
Sony Chemicals Corp.
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