Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2000-08-01
2002-08-20
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06435028
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration sensor used in automobile air bag, anti-lock brake and navigation systems, or other consumer appliances.
2. Description of the Background Art
Recently, many automobiles have been equipped with an air bag system. One of the important devices constituting the air back system is an acceleration sensor for detecting impact. The acceleration sensor is a sensor device that converts the acceleration subject to an object, into an electrical signal and then outputs it.
At present, acceleration sensors are mostly formed as an electron device which contains a semiconductor substrate prepared by photolithography, etching, micromachining, and other techniques. In general, such an acceleration sensor includes an acceleration detecting chip that detects acceleration and outputs it as an electrical signal, and a signal processing chip that processes the output signal from the acceleration detecting chip, converts acceleration to a numerical data or the like, and outputs it.
Meanwhile, to meet demanding requirements of miniaturization and low cost, one which is encapsulated with resin is used to replace a metal case, as an acceleration sensor package.
FIGS. 22 and 23
illustrate one acceleration detecting chip provided in an acceleration sensor.
FIG. 22
is a top plan view, and
FIG. 23
is a sectional view taken along the line C—C of FIG.
22
. An acceleration detecting chip ACg comprises a semiconductor substrate SB that has on its surface an acceleration detecting part AS. For example, a silicon substrate is used for the semiconductor substrate SB.
The acceleration detecting part AS includes a movable electrode ME, and two fixed electrodes FE
1
and FE
2
disposed so as to surround the movable electrode ME. Each side and bottom of the fixed electrodes FE
1
and FE
2
is fixed to the surface of the semiconductor substrate SB, in order that these electrodes will not easily swing when the acceleration detecting chip ACg receives impact. On the other hand, the movable electrode ME is mostly unfixed on its bottom but fixed on its side alone, to the semiconductor substrate SB, so that it will easily swing with the impact in the direction indicated by the arrow “P” in FIG.
22
.
On the surface of the semiconductor substrate SB, there are formed wiring layer ILc connected to the fixed electrode FE
1
, wiring layer ILd connected to the fixed electrode FE
2
, wiring layer ILe connected to the movable electrode ME, and pad electrodes PDa for wire bonding which are connected to the wiring layer ILc to ILe, respectively.
In the acceleration detecting chip ACg so constructed, when it receives the impact in the direction indicated by the arrow “P” in
FIG. 22
, the distance between the movable electrode ME and fixed electrode FE
1
or FE
2
, is increased or decreased. This causes variations in the electrostatic capacitance value between the movable electrode ME and fixed electrode FE
1
, and that between the movable electrode ME and fixed electrode FE
2
. Therefore, according to the amount of the variations in the capacitance values, acceleration can be detected.
FIG. 24
illustrates an acceleration sensor formed by encapsulating, in a resin package PK, a die pad DPc (i.e., a seat for mounting chips) that mounts an acceleration detecting chip ACg and a signal processing chip SCg, together with leads LD. The acceleration detecting chip ACg and signal processing chip SCg are fixed to the die pad DPc by an insulative adhesive, such as silicone resin, epoxy resin, or low-melting glass. The signal processing chip SCg is equipped with a semiconductor substrate that has on its surface signal processing wiring layer, circuit elements, and the like (not shown). That is,
FIG. 24
illustrates an acceleration sensor of a SOP (Small Outline Package) type.
On the surface of the signal processing chip SCg, there are formed pad electrodes PDb that receives the output from pad electrodes PDa of the acceleration detecting chip ACg, and pad electrodes PDc that outputs the processed signal via the leads LD to the exterior. There are formed bonding wires WR, composed of Au or the like, which connect the pad electrodes with the leads LD and the pad electrodes each other.
A protection cap CPd is disposed on the acceleration detecting chip ACg, to prevent the resin flowing into the position of the movable electrode ME, when encapsulating the resin package PK. The protection cap CPd has a conductivity, and also functions to shield the acceleration detecting part AS, with a ground potential fed from the exterior via pad electrodes PDf, which are disposed at a location other than that of the protection cap CPd on the acceleration detecting chip ACg.
In the conventional acceleration sensor shown in
FIG. 24
, the acceleration detecting chip ACg and signal processing chip SCg are provided in a parallel arrangement on the die pad DPc, it is thus forced to use a large die pad, making it difficult to reduce the size of the acceleration sensor.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, an acceleration sensor comprises an acceleration detecting chip including an acceleration detecting part having a movable part that shifts depending on acceleration, so that the chip outputs an electrical signal depending on the shift of the movable part; a signal processing chip having a through-hole and a circuit for processing the electrical signal from the acceleration detecting chip; and a die pad to which the acceleration detecting chip and the signal processing chip are adhered, wherein the acceleration detecting chip is disposed in the through-hole of the signal processing chip on the die pad.
Since the acceleration detecting chip is disposed in the through-hole of the signal processing chip, the area of the die pad can be lessened than if the acceleration detecting chip and signal processing chip were provided in a parallel arrangement on the die pad. This permits a reduction in the size of the acceleration sensor.
According to a second aspect, the acceleration sensor of the first aspect further comprises: a cap adhered to the signal processing chip so as to cover the through-hole; and a resin encapsulation package covering at least an adhesive portion between the signal processing chip and the cap.
With the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. In addition, by virtue of the cap, when forming the resin encapsulation package, there is no possibility of the resin flowing into the acceleration detecting part of the acceleration detecting chip.
Preferably, the acceleration detecting chip further comprises an electrode for outputting the electrical signal, and the signal processing chip further comprises an electrode connected via a bonding wire to the electrode of the acceleration detecting chip.
According to a third aspect, in the acceleration sensor of the second aspect, the cap is a plate-like and has a notch about its periphery; an electrical connection between the acceleration detecting chip and the signal processing chip is established at the notch; and the notch is filled with an insulating material.
It is able to realize an acceleration sensor of less thickness because the electrical connection between the acceleration detecting chip and signal processing chip is made at the notch disposed about the periphery of the plate-like cap.
According to a fourth aspect, the acceleration sensor of the first aspect further comprises: a cap adhered to the acceleration detecting chip so as to cover the acceleration detecting part of the acceleration detecting chip; and a resin encapsulation package covering at least an adhesive portion between the acceleration detecting chip and the cap.
With the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. In addition, by virtue of the cap, when forming the resin encapsulation package, there is no possibility of the
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