Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1999-06-18
2001-11-27
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S417000, C257S415000, C257S254000
Reexamination Certificate
active
06323529
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor acceleration sensor having such functional elements including an acceleration sensor chip and signal-processing chip sealed in a resin molding package, and to a method of manufacturing such a semiconductor acceleration sensor.
Airbag systems, antilock brake systems (ABS), and navigation systems are exemplary of the increasingly common automotive systems that rely on a semiconductor acceleration sensor to detect vehicle acceleration and impact. A semiconductor acceleration sensor typically comprises an acceleration sensor chip and a signal-processing chip in a package that both protects the internal chips from the external environment and determines the outside shape of the sensor unit. In many conventional systems, these packages are protected by a metal cover. As these systems have been adapted for smaller, lower priced vehicles, demand for compact, low cost systems has led to the adoption of systems in which the components are sealed in a molded resin package.
FIG. 6
is a section view of a resin sealed semiconductor acceleration sensor according to the related art. In this conventional semiconductor acceleration sensor
50
, the acceleration sensor chip
53
is fixed to the die pad
61
by a die bond resin
63
. The signal-processing chip
55
is mounted on the acceleration sensor chip
53
, and is electrically connected via metal wires
59
a
to acceleration sensor chip
53
. A plurality of outer leads
57
is disposed around the chips
53
and
55
with each outer lead
57
electrically connected to the signal-processing chip
55
via a metal wire
59
b
. The components are then secured in their specified positions and protected from the outside environment by resin molding
52
, leaving only the outside parts of the outer leads
57
exposed.
The acceleration sensor chip typically detects acceleration or impact by detecting the minute displacement of a mass. As a result, it is preferably not exposed to external stresses other than that being detected. An acceleration sensor chip sealed in a resin molding as described above, however, is subject to stress produced by the expansion or contraction of the resin package resulting from changes in the temperature of the external environment. The offset and output sensitivity of the acceleration sensor depend on the temperature characteristics of the sensor and can vary greatly when this external stress exceeds a particular level, thereby making it difficult to assure good acceleration and impact detection precision.
To avoid this problem and absorb and alleviate stress from the resin molding
52
acting on the acceleration sensor chip
53
, a damping member
54
made of rubber or other resilient material is typically provided around the outside surfaces of the acceleration sensor chip
53
in this conventional semiconductor acceleration sensor
50
. In this example according to the related art, the damping member
54
is fixed to the outside circumference surface of the acceleration sensor chip
53
by way of die bond resin
63
.
As described above, a damping member
54
surrounding the outside of the acceleration sensor chip
53
is used in this conventional semiconductor acceleration sensor
50
to absorb and buffer stress on the acceleration sensor chip
53
from the resin molding
52
, and is sealed together with the acceleration sensor chip
53
and signal-processing chip
55
in the resin package. As will be understood from
FIG. 7
, however, the package resin
52
may displace the die bond resin between the damping member
54
and acceleration sensor chip
53
during the packaging process. When this happens, thermal expansion and contraction of resin
52
a
between the damping member
54
and acceleration sensor chip
53
will directly stress the acceleration sensor chip
53
.
SUMMARY OF THE INVENTION
With consideration for the above-described problems, an object of the present invention is therefore to provide a semiconductor acceleration sensor, in which the acceleration sensor chip is protected from resin sealing the package, thereby assuring good detection precision.
In one aspect of the present invention, there is provided a semiconductor acceleration sensor in which functional elements including an acceleration sensor chip and signal processing chip are sealed in a resin package comprises a damping member disposed along the outside surfaces of the acceleration sensor chip to buffer stress from the resin package on the acceleration sensor chip, and a cover for covering a top edge part of the damping member and a top edge of the acceleration sensor chip.
The cover in this semiconductor acceleration sensor is preferably formed integrally with the damping member.
Alternatively, the damping member has a hollow layer formed heightwise to the damping member. In this case, the hollow layer is preferably filled with a gel type reinforcing filler. Yet further preferably, the reinforcing filler is a silicon gel. As a further alternative, the damping member can be formed integrally with the covering member and still be made with a hollow portion, or, as a further alternative, the hollow portion can be filled with a silicon gel.
In a further aspect of the present invention, there is a method of manufacturing a semiconductor acceleration sensor in which functional elements including an acceleration sensor chip and signal-processing chip are sealed in a resin package, comprising the steps of: disposing a damping member along an outside surface of the acceleration sensor chip to alleviate stress from the resin package on the acceleration sensor chip; and disposing a covering member which cover a top edge part of the damping member and a top edge of the acceleration sensor chip.
It is an advantageous effect according to the present invention that, since a semiconductor acceleration sensor has a damping member disposed along the outside surfaces of the acceleration sensor chip to buffer stress from the resin package on the acceleration sensor chip, and a covering member which cover a top edge part of the damping member and a top edge of the acceleration sensor chip, the chance of resin penetrating the gap between the sensor chip and damping member during the process in which the components of the semiconductor acceleration sensor are sealed with resin is eliminated. The sensor chip is thus protected from stresses from the resin package, and the semiconductor acceleration sensor can therefore assure good detection precision.
It is also an effect according to the present invention that, since the damping member is formed with the covering member, the number of parts is reduced, and thus the required manufacturing process is simplified.
It is further an effect according to the present invention that, since the damping member has a hollow layer heightwise to it, the lateral flexibility of the damping member is increased, thereby further enhancing the ability of the sensor chip to reliably absorb and alleviate stress on the sensor chip from the resin molding.
Furthermore when this hollow layer of the damping member is filled with a gel type reinforcing filler, the strength of the damping member is increased while retaining substantial lateral flexibility in the damping member. The reinforcing filler is preferably a silicon gel because of its outstanding resistance to aging and heat, and minimal change in viscosity as the temperature changes, thus achieving a damping member with stable lateral flexibility and strength.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5847445 (1998-12-01), Wark et al.
patent: 6049120 (2000-04-01), Otani et al.
patent: 7-225240 (1995-08-01), None
Lee Eddie
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Richards N. Drew
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