Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
1998-11-17
2001-06-05
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S698000, C257S701000
Reexamination Certificate
active
06242799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present Invention relates to an anisotropic stress buffer and a semiconductor device using the same.
2. Description of the Related Art
It is usual to interpose a soft body having a low elastic modulus as a stress buffer between two members, which are made of a material having a different thermal expansion coefficient from that of the other, when the two members are bonded together or when one of the two members is heated after being bonded, for the purpose of releasing a stress generated due to the difference in thermal expansion coefficient between the two members.
For example, when a semiconductor device is mounted to a substrate, the above-mentioned soft body having a low elastic modulus (stress buffer) is interposed between the two to facilitate the electric connection between circuits on the semiconductor device and the substrate. As a typical example, there may be a case wherein the stress generated due to the thermal expansion is absorbed by the stress buffer provided on a chip scale semiconductor device, which formed in a size generally equal to that of a semiconductor chip, is connected (surface-mounted) to the substrate. To enable the high density mounting, such a chip size semiconductor device is closer in size to a bare chip as compared to the usual semiconductor device. However, the thermal expansion stress due to the heat generation from the semiconductor chip itself is liable to be directly applied thereto. It means that it is indispensable to provide a stress buffer for releasing the stress in the horizontal direction.
FIG. 6
is a sectional view illustrating the above-mentioned conventional chip size semiconductor device. An insulating member
20
is mounted on a surface
10
a
of a semiconductor chip
10
, on which an electrode terminal
12
of the semiconductor chip
10
is formed, without covering the electrode terminal
12
. The insulating member
20
composed of an elastomer
22
forming a stress buffer, as a main layer, is laminated to the semiconductor chip
10
via an adhesive
24
. A circuit pattern
30
has a land
32
to be connected to an external connection terminal at one end and a lead
34
which is a conductor layer at the other end. This circuit pattern
30
is supported by an insulating film
36
and forms together therewith a tape substrate
38
. An adhesive
35
adheres the circuit pattern
30
to the insulating film
36
. The tape substrate
38
is adhered onto the insulating member
20
at the land
32
and connected to the electrode terminal
12
by a bonding at the lead
34
. A resin shield
90
shields exposed portions of the lead
34
and the electrode terminal
12
after the lead
34
has been bonded. The external connection terminal is, for example, solder balls
40
connected to the land
32
.
The stress buffer is useful for improving the reliability in electric connection not only when the above-mentioned chip size semiconductor device is mounted onto the substrate but also when a usual semiconductor device, in which a semiconductor chip is mounted to a semiconductor package, is mounted to a substrate.
As described above, to solve problems of stress caused by the difference in thermal expansion coefficient when two members are bonded together, a stress buffer made of a soft material having a small elastic modulus (a low elastic modulus member) may be used for releasing the stress. However, there is a still further problem in that the elastic modulus of such a stress buffer is too small to result in a proper balance between the softness and rigidity in all the directions.
Also, there may be a case wherein a low elastic modulus (softness) is required in one direction, while a high elastic modulus (rigidity) is required in the other direction. For example, in the field of the above semiconductor device, the stress buffer having a low elastic modulus in a planar direction in parallel to a mounting surface of the substrate and a predetermined rigidity (Young's modulus higher than a predetermined value) in a direction vertical to the mounting surface. If the stress buffer has the predetermined rigidity in the thickness direction thereof, it is possible to electrically connect the semiconductor chip with the semiconductor device via a wire bonding. Since the prior art stress buffer has a small elastic modulus in all the directions, it is difficult to carry out the wire bonding on the circuits formed on the surface of the stress buffer. This is because, while the wire bonding must be carried out under a predetermined load while applying heat and ultrasonic wave, the stress buffer operates as a cushion to cancel the load.
In this regard, the electric connection according to the wire bonding has a high reliability backed up by actual results. Also, the wire bonding is capable of preventing the quality of the product from deteriorating and the production cost from rising in comparison with other methods. Further, since the connection structure can be simplified, it is possible to meet a demand for the high density (micro) mounting or the shortening of a production process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an anisotropic stress buffer capable of releasing a stress caused by the difference in thermal expansion coefficient or others when two members are bonded together, and having a proper rigidity in a predetermined direction.
Another object of the present invention is to provide a semiconductor device using such an anisotropic stress buffer.
According to the present invention, there is provided an anisotropic stress buffer comprising: a plate or sheet-like body having relatively low elastic modulus, the body having a thickness direction thereof and a planar direction perpendicular to the thickness direction; and a plurality of particles, each having relatively high elastic modulus, contained in the plate or sheet-like body, in such a manner that the buffer has a characteristic as a high elastic modulus member having a Young's modulus higher than a predetermined value with respect to a compression stress in the thickness direction and also has a characteristic as a low elastic modulus member having a Young's modulus lower than the predetermined value with respect to a tension stress in the planar direction.
The plate or sheet-like body has a first surface and a second surface opposite to the first surface and at least one of the first and second surfaces is adhesive so that the buffer maintains its characteristics after the buffer is adhered to another member.
Each of the particles is a pillar-like high elastic modulus particles arranged in the plate or sheet-like body penetrating through the thickness direction of the body and substantially uniformly distributed in the planar direction of the body.
Otherwise, the plurality of particles are high elastic modulus particles distributed in the plate or sheet-like body. In this case, the high elastic modulus particles are ball-like particles. Otherwise, the high elastic modulus particles are flat particles arranged in the planar direction of the plate or sheet-like body.
Each of the particles has, as a single particle, a Young's modulus of not less than 100 KPa and not more than 10 MPa at a temperature between 20° C. and 100° C.
In another aspect of the present invention, there is provided a semiconductor device comprising: an anisotropic stress buffer comprising: a plate or sheet-like body having a first surface and a second surface opposite to the first surface and having relatively low elastic modulus, the body having a thickness direction thereof and a planar direction perpendicular to the thickness direction; and a plurality of particles, each having relatively high elastic modulus, contained in the plate or sheet-like body in such a manner that the buffer has a characteristic as a high elastic modulus member having a Young's modulus higher than a predetermined value with respect to a compression stress in the thickness direction and also has a characteristic as a low el
Horiuchi Michio
Muramatsu Shigetsugu
Cruz Lourdes
Saadat Mahshid
Shinko Electric Industries Co. Ltd.
Staas & Halsey , LLP
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