JPH08114622A - Full-mode packaging-type acceleration sensor - Google Patents

Abstract

PURPOSE: To obtain an inexpensive, compact, light, high-performance, and surface-mount-type acceleration sensor by providing a thermal stress relaxation mechanism at a detection part structure body and a full-mold plastic part. CONSTITUTION: An acceleration detection part structure body 2 with a mass (weight) supported by a beam and a signal processing circuit 1 for outputting a signal corresponding to acceleration due to the displacement of the mass are fixed to a lead frame 3 with an adhesive. Then, the processing circuit 1 and the structure body 2 are connected by a conductor 7, the processing circuit 1 and an output adjustment terminal 5 are connected by a conductor 200, and the processing circuit 1 and an output terminal 4 are connected by wire bonding using a conductor 6. After that, a plastic material 8 is completely molded around the structure body 2 and the processing circuit 1. As a thermal stress relaxation mechanism, a thickness Tpa of the plastic material 8 on the upper part of the lead frame 3 is set to nearly equal to a thickness Tpb of the plastic material at the lower part, thus minimizing the bending deformation due to the temperature change of the plastic material 8 with the lead frame 3 as the center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for a vehicle safety system, and more particularly to an acceleration sensor used in an antilock / brake control system, an airbag system and the like.

[0002]

2. Description of the Related Art Conventionally, many types of acceleration sensors such as a semiconductor strain gauge type, an electrostatic capacitance type, and a piezoelectric type are known. For example, as described in JP-A-1-152369, the detection section structure of these acceleration sensors is housed in a metal package.

[0003]

Since the detector structure is mounted in the metal package, the mounting cost of the acceleration sensor is high and the output characteristics of the sensor must be adjusted before the package. Also, since the acceleration sensor is large in size and heavy in weight, problems such as resonance occur when it is surface-mounted on a control unit of an automobile application system. On the other hand, full-mold mounting of plastic materials is widely known as one of low-cost mounting methods for general-purpose ICs. When this mounting method is applied, the detection section structure of the conventional acceleration sensor is generally susceptible to thermal stress, unlike a general-purpose IC, so the temperature characteristics of the acceleration sensor are extremely poor. There was a problem that Further, there is a problem that the output characteristics of the acceleration sensor change due to the deformation of the plastic material due to moisture absorption. Also, because it is not a metal package,
There is also a problem that it is easily affected by electrical noise from the outside.

An object of the present invention is to provide a small-sized, lightweight and high-performance acceleration sensor that can adjust output characteristics after packaging at low cost and can be surface-mounted.

[0005]

An airtight detector structure of an acceleration sensor and a signal processing circuit with a digital adjusting function are fixed on a lead frame, and wire bonding between the detector structure, the signal processing circuit and the lead frame is performed. Once done, the plastic material is completely molded around it. At this time, various thermal stress relaxation mechanisms are provided in the detection part structure and the molded plastic part. After the molding is completed, the surface of the plastic part is coated with a semiconductive material or a hydrophobic material.

[0006]

The airtight detection part structure of the acceleration sensor and the signal processing circuit with digital adjustment function are fixed on the lead frame, and then the periphery thereof is fully molded with a plastic material to reduce the cost. The full-mold mounting makes it possible to reduce the size and weight of the acceleration sensor, enabling surface mounting of the acceleration sensor. By coating the outer surface of the molded plastic part with a semiconductive material, an acceleration sensor resistant to electrical noise can be obtained. By providing a thermal stress relaxation mechanism in the detector structure and the full-molded plastic part, deformation of the detector structure itself caused by thermal stress due to the difference in thermal expansion coefficient between the detector structure and the plastic material is minimized. To improve the temperature characteristics of the acceleration sensor. This thermal stress relaxation mechanism is also effective in preventing a change in output characteristics caused by the deformation of the plastic material due to moisture absorption. If the surface of the molded plastic is coated with a hydrophobic material, the deformation of the plastic due to moisture absorption can be minimized and the output change of the acceleration sensor can be prevented. By pulling out the lead terminal connected to the signal processing circuit to the outside of the full-molded plastic part, the output characteristics of the acceleration sensor can be adjusted using this terminal after the completion of full-molding.

[0007]

1 shows an embodiment of a full-mold mounting type acceleration sensor according to the present invention. A signal that outputs the signal corresponding to the acceleration by detecting the displacement of the acceleration detection unit structure 2 having a mass (weight) supported by the beam and the displacement of the mass from the change of the capacitance or the resistance value of the strain gauge. After the processing circuit 1 is fixed to the lead frame 3 made of a metal material such as Fe-Ni with an adhesive (not shown), the signal processing circuit 1 and the detection unit structure 2 are connected to each other with a gold wire or the like. Conductor 7, between signal processing circuit 1 and output adjusting terminal 5
0, the conductor 6 between the signal processing circuit 1 and the power supply / output terminal 4
The wires are electrically connected through the wire bonding work. The detailed structure of the acceleration detector structure 2 will be described later. After the wire bonding work is completed,
As shown in the figure, the plastic material 8 is completely fully molded around the detector structure 2 and the signal processing circuit 1. The molding work of the plastic material 8 is 70 atm, 1
It was carried out under the conditions of 70 ° C. The thermal expansion coefficient of the plastic material 8 is preferably the same as that of silicon, which is the material of the beam and the mass, but the lower limit of the thermal expansion coefficient that can be applied is 8 pp due to the fluidity of the plastic material 8 during the molding operation.
It was m / ° C. The coefficient of thermal expansion of silicon is about 3 pp.
m / ° C. Thus, the difference in the coefficient of thermal expansion between the material forming the detector structure 2 and the plastic material 8 is about 5 pp.
It is as large as m / ° C., and due to this difference in thermal expansion coefficient, the detection unit structure 2 is deformed by being subjected to large thermal stresses such as compression and bending. Due to this deformation, the zero point and the sensitivity of the acceleration sensor greatly change depending on the temperature. Various thermal stress relaxation mechanisms for improving this temperature effect will be described with reference to this figure and the figures shown below. Since the effect of the plastic material 8 deformed by moisture absorption is apparently equivalent to a partial change in the thermal expansion coefficient of the plastic material 8, this thermal stress relaxation mechanism reduces the effect of the plastic material 8 due to moisture absorption deformation. It also has effective results in eliminating it. The output adjusting terminal 5, the power supply and the output terminal 4 are made of the same material as the lead frame 3, and these are mechanically connected by an external outer frame before the plastic material 8 is molded. After the plastic material 8 is fully molded, the outer frame is cut to eliminate these mechanical and electrical connections. The acceleration sensor is fixed to the control unit of the automobile system through the hole 9 with a screw or the like. Alternatively, the lower part 10 of the plastic material 8 is surface-mounted on the control unit. The thermal stress relaxation mechanism in this figure is based on the lead frame 3
That is, the thickness Tpa of the plastic material 8 at the upper part of the table is approximately equal to the thickness Tpb of the plastic material 8 at the lower part. By doing this, the lead frame 3
Bending deformation due to temperature change of the plastic material 8 centered on was minimized, and it was able to greatly contribute to the improvement of the temperature effect of the acceleration sensor. In the drawings shown below, the same numbers indicate the same elements.

FIG. 2 shows a thermal stress relaxation mechanism during full molding of the detector structure according to the present invention. The detector structure has a four-layer laminated structure of a silicon plate 11, a glass plate 12, a silicon plate 13 and a glass plate 14, and these four plates are laminated in a wafer state, and then a well-known anodic bonding method is used. And is diced to each detection unit structure by a method such as a dicer. A mass 16 supported by the beam 15 is formed on the silicon plate 13 by etching. (Note that the planar structure of the silicon plate 13 is shown in FIG. 8 for reference.) A fixed electrode 17 made of a metal film is formed on the surface of the glass plate 12 facing the mass 16 by a method such as sputtering or vapor deposition. There is. This fixed electrode 17
Is electrically connected to the silicon plate 11 by the inner surface of the through hole 19 formed in the glass plate 12 and the lead portion 20 provided on the upper surface of the glass plate 12. A part of the lead portion 20 is sandwiched between the silicon plate 11 and the glass plate 12 as shown in the figure. When acceleration acts on the detection unit structure, the mass 16 supported by the beam 15 has a function of a weight and is vertically displaced according to the magnitude of acceleration. The silicon plate 13 is a conductive material, and the mass 16 serves as a movable electrode. The dimensional change of the gap 18 between the mass 16 and the fixed electrode 17 can be measured from the change of the electrostatic capacitance to detect the displacement of the mass 16 according to the acceleration. That is, the acceleration detection unit structure shown in this figure is a capacitance type detection unit structure. Pads 21 are formed on the silicon plate 11 and pads 22 are formed on the silicon plate 13, and the detection unit structure is electrically connected to the signal processing circuit by the above-described wire bonding work via these pads. The chip size of the detection unit structure shown in this figure is about several millimeters square, and the thickness of each of the four plates is about several hundreds of microns (however, the thicker the glass plate 14 is, the better as will be described later). , Trout 16 and beam 1
The thickness of 5 is about several tens of microns, and the gap 18 is about several microns. Next, the thermal stress relaxation mechanism in this detector structure will be described. The temperature characteristics of the zero point and sensitivity in the capacitance type acceleration sensor are determined by the gap 18 between the mass 16 and the fixed electrode 18, so the purpose of the thermal stress relaxation mechanism is to prevent the size of the gap 18 from changing even if the temperature changes. Is to For this purpose, the deformation of the beam 15 supporting the glass plate 12 and the mass 16 due to thermal stress may be minimized. By forming the void 21 in the silicon plate 11, even if the detecting portion structure receives thermal stress such as compression, pulling, bending, etc. from the surrounding plastic material, it does not cause a problem in the temperature characteristics of the acceleration sensor. Board 1
The deformation of No. 2 could be reduced. The void 21 is a recess formed by etching the surface of the silicon plate 11. Further, the distance La from the dicing surface of the joint between the glass plate 12 and the silicon plate 11 is made smaller than the distance Lb from the dicing surface of the joint between the glass plate 12 and the silicon plate 13, whereby the glass plate 12 and the beam. Bending deformation of No. 15 could be reduced. As previously mentioned,
The thickness Tsa of the silicon plate 11, the thickness Tga of the glass plate 12,
The thickness Tsb of the silicon plate 13 is similar to about several hundreds of microns. On the other hand, the thickness Tgb of the glass plate 14 serving as the surface on which the detection unit structure itself is bonded to the lead frame having a different thermal expansion coefficient is about twice or more thicker than the three plates, It was effective as a thermal stress relaxation mechanism.

FIG. 3 shows another embodiment of the thermal stress relaxation mechanism during full molding of the detector structure according to the present invention.
The detector structure has a five-layer structure including a silicon plate 23, a glass plate 24, a silicon plate 25, a glass plate 26, and a silicon plate 27, and they are joined by anodic bonding. A mass 29 supported by a beam 28 is formed on the central silicon plate 25 by etching. The fixed electrodes 32, 3 are provided on the upper and lower glass plates 24, 26 so as to face the mass 29.
4 are formed. These fixed electrodes 32 and 34 are provided on the inner surfaces of the through holes 30 and 31 and the glass plate 2, respectively.
It is electrically connected to the silicon plates 23 and 27 through the lead portions 33 and 35 formed on the surfaces of the plates 4 and 26. This detection unit structure is of the electrostatic capacitance type as in the previous figure, in which fixed electrodes are formed on both sides of the mass 29 which is a movable electrode, and the thickness of the mass 29 is thicker than the thickness of the beam 28. It is a feature. Next, the thermal stress relaxation mechanism in the present detector structure will be described. As a thermal stress relaxation mechanism, (1) cavities 36 and 37 are provided in the silicon plates 23 and 27, and (2) the silicon plate 25 and the glass plate 2 on the fixed end side of the beam 28.
The distance from the dicing surface at the joint between the glass plates 24 and 26 and the silicon plates 23 and 27 is set to be larger than the distance from the dicing surface at the joint between the glass plates 24 and 26 and the cavities 36 and 37. (3) Silicon It was effective to make the thickness of the plate 27 about twice or more than the thickness of the other four plates. In addition,
The cavities 36 and 37 are dents obtained by etching the surfaces of the silicon plates 23 and 27, and the depth thereof is about 10 μm as in the previous figure.

FIG. 4 shows another embodiment of the thermal stress relaxation mechanism during full molding of the detector structure according to the present invention.
The detection part structure is composed of a five-layer structure of silicon plates 38, 39, 40, 41 and 42, and has a thermal oxide film 43, 44, 45.
And 46 are hermetically bonded by a well-known direct bonding technique for silicon plates. This detection unit structure is also of a capacitance type, and the beam 4 is placed on the central silicon plate 40.
The mass 47 supported by 8 is formed by etching. Silicon plate 3 facing the mass 47 which is the movable electrode
Reference numerals 9 and 41 are conductive materials and are used as they are as fixed electrodes. Although not shown in the figure, the fixed electrode pads are provided on these silicon plates 39 and 41. Also in this case, as in the previous figure, as the thermal stress relaxation mechanism, (1) the voids 49, 50 are provided in the silicon plates 38, 42, and (2) the bonding dimension of the silicon plate 40 on the fixed end side of the beam 48 is diced. Empty space 49,50
Greater than the distance to (3) Silicon plate 42
It was effective to make the thickness of the above-mentioned about two times or more the thickness of the other four silicon plates.

FIG. 5 shows another embodiment of the thermal stress relaxation mechanism during full molding of the detector structure according to the present invention.
The detection unit structure has a three-layer structure of silicon plates 51, 52 and 53, and is hermetically bonded via thermal oxide films 54 and 55. This detector structure is of a capacitance type, and the silicon plate 52 at the center has a mass 5 supported by a beam 57.
6 is formed by etching. Since the surfaces of the silicon plates 51 and 53 are doped with boron at a high concentration in advance, and the etching rate of this high concentration part is extremely slower than that of the other parts, the both ends supporting structure is formed on the surfaces of the silicon plates 51 and 53. Thin plates 58 and 59 are formed. The thin plate portions 58 and 59 are high boron concentration portions. Holes 60 and 6 that were previously dry-etched
Via 1, the voids 62 and 63 are formed in the silicon plates 51 and 53 by anisotropic etching, respectively.
Thin plates 58 and 59 facing the mass 56 which is the movable electrode
Serves as a fixed electrode. The thermal stress relaxation mechanism in this case is as follows:
(2) The distance from the dicing surface of the joint between the silicon plate 52 and the silicon plates 51 and 53 not only to the fixed end side of the beam 57 but to the dicing surface from the dicing surface to the recesses 62 and 63. It is effective to be larger than the size, and (3) it is effective to make the thickness of the silicon plate 53 about twice or more the thickness of other silicon plates.

FIG. 6 shows another embodiment of the thermal stress relaxation mechanism of the detector structure according to the present invention. The detection portion structure has a three-layer structure of silicon plates 64, 65 and 66, and is hermetically bonded via thermal oxide films 67 and 68. The central silicon plate 65 has a mass 69 supported by a beam 70.
Are formed by etching. Silicon plate 64
Thin plates 71 and 72 having a one-sided support structure, which serve as fixed electrodes, and cavities 73 and 74 are formed by etching in and 66, respectively. As a thermal stress relaxation mechanism,
(1) The fixed electrode is a thin plate with one-sided support structure and a space is provided, (2) The bonding dimension of the central silicon plate on the beam fixed end side is larger than the distance from the dicing surface to the recess, (3) It is effective to make the thickness of the bottom silicon plate about twice or more the thickness of other silicon plates. Even if the detector structure is deformed by the thermal stress from the plastic material, the deformation of the beam 70 and the thin plates 71, 72 of the one-sided support structure is minimized. Even if the beam 70 and the thin plates 71 and 72 are deformed, the beam 69 and the thin plates 71 and 72 have the same beam shape.
The change in the gap between 1 and 72 is extremely small.

FIG. 7 shows another embodiment of the thermal stress relaxation mechanism during full molding of the detector structure according to the present invention.
The detector structure has a three-layer structure of a glass plate 75, a silicon plate 76, and a glass plate 77, and is airtightly bonded by anodic bonding. A mass 78 supported by a beam 79 is formed on the central silicon plate 76 by etching. A strain gauge 80 is formed near the fixed end of the beam 79 by diffusion and is protected by a thermal oxide film 82.
The detection unit structure is a strain gauge type that detects displacement of the mass 78 due to acceleration from a change in resistance value of the strain gauge. A polysilicon layer 83 is formed on the thermal oxide film 82, and a glass plate 75 having a void 81 is airtightly bonded to the silicon plate 76 by anodic bonding using the polysilicon layer 83. The void 81 is a recess having a depth of about 10 microns formed on the glass plate 75 by etching or another method. The strain gauge 80 is electrically connected to the signal processing circuit via the pad 84 formed on the silicon plate 76. As shown in the figure, the distance from the dicing surface to the void 81 is La, the distance to the upper fixed end of the beam 79 is Lb, and the distance to the lower fixed end is Lc. A space 81 is formed so that the dimension La becomes smaller than the dimensions Lb and Lc.
Determining the size of was effective as a thermal stress relaxation mechanism. Further, as in the case of the capacitance type, it was also effective that the thickness of the glass plate 77 adhered to the lead frame was about twice or more the thickness of the other two plates.

Silicon plate 1 of the detector structure shown in FIG.
A plan view of No. 3 is shown in FIG. As shown in FIG.
Are supported by two beams 15. A region 85 is a part joined to the glass plate 12 and a part flush with it, and a region 86 is a part where the pad 22 is formed, a region 87.
Is a region where the etching depth is about 100 microns, and the region 88
Is the same etching depth as the beam 15 and the mass 16 (gap size is determined by etching amount of several microns)
Part of.

FIG. 9 shows another embodiment of the thermal stress relaxation mechanism during full molding of the detector structure according to the present invention.
The beam mass system 93 is formed on the surface of the silicon substrate 90 by utilizing the sacrifice layer etching technique of the SOI substrate. The gap 94 below the beam / mass system 93 is a portion where the thermal oxide film 91 is removed by sacrificial layer etching. A glass plate 89 having a void 95 is formed on the silicon plate 9 through a polysilicon layer 92 formed on the thermal oxide film 91.
It is airtightly bonded to 0 by anodic bonding. The void 95 is a recess formed in the glass plate 89 by etching or the like. The silicon plate 90 is electrically connected to the signal processing circuit via the pad 97, and the beam mass system 93 is electrically connected to the signal processing circuit via the polysilicon layer 92 and the pad 96. This detector structure is Y
The acceleration in the Y-axis direction is detected. The thickness of the silicon plate 90 is at least about 100 times the thickness of the beam mass system 93 so that the beam mass system 93 and the silicon plate 90 are not deformed by thermal stress from the plastic material.
It was effective as a thermal stress relaxation mechanism to make the thickness more than double. The beam / mass system 93 has a thickness of several to several tens of microns. A plan view of the beam mass system 93 is shown in FIG. The beam-mass system consists of a mass 100 supported by four beams 99, each beam 99 having a fixed end 98.
The part is fixed on the thermal oxide film 91. This detection unit structure becomes a capacitance type detection unit if the mass 100 is used as a movable electrode and the silicon plate 90 is used as a fixed electrode, and a strain gauge is formed in the beam 99 and used. .

Another embodiment of the thermal stress relaxation mechanism of the detector structure according to the present invention is shown in FIG. This detector structure is shown in FIG.
It is manufactured by the same method as that of the structure shown in FIG. 9, and is different in the shape of the beam / mass system from FIG. 9, and is characterized in that the acceleration in the XX direction is detected. The acceleration is measured by detecting the dimensional change of the gap 103 between the mass 102 which is the movable electrode and the fixed electrode 101 from the change of the electrostatic capacitance. The contents of the thermal stress relaxation mechanism are the same as in the case of the detection unit structure shown in FIG. A plan view of the beam / mass system is shown in FIG. The mass 102 supported by the beam 105 and the fixed electrode 101 are comb-shaped. The comb-like shape is used to increase the facing area of the gap 103 and increase the sensitivity. Beam 105 and fixed electrode 101
Is fixed on the thermal oxide film 91 at the fixed end 104.

Another embodiment of the thermal stress relaxation mechanism of the detector structure according to the present invention is shown in FIG. The silicon plate 108, the silicon plate 109, and the silicon plate 110 are the thermal oxide film 11.
A mass 106, which has a three-layer structure that is airtightly bonded via 1 and 112 and is supported by a beam 107, is formed on a central silicon plate 109 by etching. This is a capacitance type detection unit structure in which the mass 106 is a movable electrode, and the upper and lower silicon plates 108 and 110 facing the mass 106 are fixed electrodes. Beam 107 and upper and lower silicon substrates 108 and 11 due to thermal stress from the plastic material
If the deformation of 0 can be minimized, the temperature characteristic of the acceleration sensor can be improved. For this purpose, the upper and lower silicon plates may be thickened so that the overall shape of the detection unit structure is close to a cube like a dice, and the joining size at the beam fixed end may be made sufficiently large. Assuming that the lateral width of the detection unit structure, that is, the lateral width dimension of the central silicon plate 109 is L, the thickness Tu of the silicon plate 108 and the thickness Td of the silicon plate 110 are at least half the lateral width dimension L or more as a thermal stress relaxation mechanism. Was effective. It was also extremely effective to set the joint dimension W between the central silicon plate 109 and the upper and lower silicon plates 108 and 110 on the fixed end side of the beam 107 to at least 10% or more of the lateral width dimension L.

Another embodiment of the thermal stress relaxation mechanism of the detector structure according to the present invention is shown in FIG. Silicon plate 108,1
09 and 110 are glass layers 11 having a thickness of about several tens of microns
Anodically bonded via 3 and 114 3
The beam 10 has a layered structure and is formed on the central silicon plate 109.
7 is a capacitance type detection unit structure formed by etching the mass 106 supported by 7. Fixed electrodes 115 and 116 made of metal thin films are formed on the surfaces of the glass layers 113 and 114 facing the mass 106, and are electrically connected to the silicon plates 108 and 110, respectively. This detector structure is different from the one shown in the previous figure only in the joining method, and the same thermal stress relaxation mechanism as in the previous figure was applicable.

FIG. 15 shows an embodiment of the thermal stress relaxation mechanism of the molded plastic part according to the present invention. In order to reduce the thermal stress exerted by the plastic material portion 8 on the detection portion structure 2, it is sufficient to provide the plastic material portion 8 with grooves or recesses 117 and 118 as shown in the figure. These grooves were effective as a thermal stress relaxation mechanism for improving temperature characteristics.

FIG. 16 shows another embodiment of the thermal stress relaxation mechanism of the molded plastic part according to the present invention. The thickness (height) of the signal processing circuit 1 is about several hundreds of microns, whereas the detection unit structure 2 is often as thick as 1 mm or more. As a thermal stress relaxation mechanism in this case, it is effective to use the plastic material 8 on the upper part of the detection part structure 2 as the convex part 119. The thickness of the plastic material above the signal processing circuit 1 and the upper portion of the detection unit structure 2 becomes the same, and the fluidity of the plastic material during full molding can be secured. As a result, the difference in the local thermal expansion coefficient of the plastic material 8 disappears, and the thermal stress exerted on the detection portion structure 2 by the plastic material portion 8 can be made uniform overall. Another embodiment of the thermal stress relaxation mechanism of the molded plastic part according to the present invention is shown in FIG. Depending on the mounting method of the system using the acceleration sensor, it may be more convenient to provide the metal plate 120 under the plastic material portion 8 and perform full molding at the same time. At this time, it is necessary to prevent the plastic material portion 8 from being entirely warped by the bimetal effect. As a thermal stress relaxation mechanism in this case, it is effective to make the thickness Tpb of the plastic material portion 8 below the lead frame thicker than the thickness Tpa of the lead frame upper portion.

Another embodiment of the thermal stress relaxation mechanism of the molded plastic part according to the present invention is shown in FIG. This figure shows the relative positional relationship between the signal processing circuit 1 and the detection unit structure 2. The signal processing circuit 1 is an IC made of a silicon substrate.
And has a higher rigidity than the plastic material 8. The fixed end side of the beam 122 supporting the mass 121 is placed on the opposite side of the signal processing circuit 1 so that the internal structure of the detection unit structure 2 is not deformed by bending due to the material having high rigidity. Arranging the structure 2 was effective as a thermal stress relaxation mechanism.

Another embodiment of the thermal stress relaxation mechanism of the molded plastic part according to the present invention is shown in FIG. The periphery of the plastic material portion 8 is coated with a hydrophobic material 123. As a result, the plastic material part 8
Since it is possible to prevent deformation due to moisture absorption, it is effective as a thermal stress relaxation mechanism. Further, if the coating film 123 is a conductive or semi-conductive material, the acceleration sensor is less susceptible to external electrical noise.

FIG. 20 shows another embodiment of the mounting method of the full mold type acceleration sensor according to the present invention. This figure shows an integrated signal processing circuit and detector structure.
Reference numeral 4 denotes an integrated detector structure. Even in such a case, the method of the thermal stress relaxation mechanism of the detection part structure and the plastic material part described so far can be applied as it is.

FIG. 21 shows another embodiment of the mounting method of the full mold type acceleration sensor according to the present invention. If the lead frame 4 which is a power source or an output terminal is made thicker, for example, 0.5 mm or more to increase the rigidity of the lead frame, the acceleration sensor can be directly connected to the control unit of various automobile application systems through the lead frame 4. Can be implemented.

FIG. 22 shows another embodiment of the mounting method of the full mold type acceleration sensor according to the present invention. It is the same mounting method as a well-known general-purpose IC, and after the signal processing circuit unit 1 and the detection unit structure 2 are enclosed in a plastic material 8, a lead frame 4 which is a power supply and output terminal and a lead which is an output adjustment terminal. The frame 5 is bent at a right angle as shown in the figure.

FIG. 23 is a manufacturing process diagram of the full-mold mounting type acceleration sensor according to the present invention. The detector structure and the signal processing circuit are bonded onto the lead frame with an epoxy adhesive having a thickness of about several tens of microns. After electrically connecting the detection unit structure, the signal processing circuit and the lead frame by wire bonding, these are mounted in a molding jig,
Plastic is molded in an atmosphere of 170 ° C. and 70 atm. Next, the outer frame of the lead frame of this molded product is removed by cutting, and the power supply, the output terminal and the adjustment terminal are electrically separated from each other. The output characteristic of the acceleration sensor is digitally adjusted using the adjustment terminal. Finally, the product is inspected.

FIG. 24 shows a schematic configuration of the signal processing circuit.
The signal processing circuit 1 is a portion 1 that detects a change in capacitance (or a change in resistance value of a strain gauge) in the detection unit structure 2.
25, a portion 126 that amplifies the signal of the detection unit and a portion 127 that adjusts characteristics such as zero point and sensitivity and outputs the output signal Vo.

FIG. 25 shows an example of the evaluation result of the temperature characteristics of the full-mold mounting type acceleration sensor according to the present invention. This figure shows the sensitivity error of the acceleration sensor for the measurement range of 0 to ± 50G. Here, 1G = 9.8 m / s ² . The temperature characteristics when the detector structure shown in FIG. 2 is molded by the method described in FIG.
Within a wide temperature range of -40 ℃ to + 85 ℃, the sensitivity error is ± 1.
The accuracy was less than%. What was described as "before countermeasures" was when the thermal stress relaxation mechanism according to the present invention was not applied at all, and the sensitivity error was as large as about ± 25%. The effect of the thermal stress relaxation mechanism according to the present invention was confirmed even for an acceleration sensor having a small measurement range of 0 to ± 1 G. By matching the optimum spring constant of the beam system that supports the mass to the measurement range, the temperature characteristics can be measured regardless of the measurement range.
It was possible to improve as in No. 5.

[0029]

As described above, according to the present invention, it is possible to obtain a small-sized, low-cost, high-performance acceleration sensor suitable for surface mounting.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a full-mold mounting type acceleration sensor according to the present invention.

FIG. 2 is a diagram showing an example of a thermal stress relaxation mechanism of a detection unit structure according to the present invention.

FIG. 3 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 4 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 5 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 6 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 7 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

8 is a plan view of a central silicon plate of the detection unit structure shown in FIG.

FIG. 9 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

10 is a plan view of a beam-mass system of the detection unit structure shown in FIG.

FIG. 11 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

12 is a plan view of a beam / mass system of the detection unit structure shown in FIG.

FIG. 13 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 14 is a diagram showing another embodiment of the thermal stress relaxation mechanism of the detection unit structure according to the present invention.

FIG. 15 is a view showing an example of a thermal stress relaxation mechanism of a plastic part according to the present invention.

FIG. 16 is a view showing another embodiment of the thermal stress relaxation mechanism of the plastic part according to the present invention.

FIG. 17 is a view showing another embodiment of the thermal stress relaxation mechanism of the plastic part according to the present invention.

FIG. 18 is a view showing another embodiment of the thermal stress relaxation mechanism of the plastic part according to the present invention.

FIG. 19 is a view showing another embodiment of the thermal stress relaxation mechanism of the plastic part according to the present invention.

FIG. 20 is a diagram showing another embodiment of a mounting method for a full-mold type acceleration sensor according to the present invention.

FIG. 21 is a view showing another embodiment of the mounting method of the full-mold type acceleration sensor according to the present invention.

FIG. 22 is a view showing another embodiment of the mounting method of the full-mold type acceleration sensor according to the present invention.

FIG. 23 is a manufacturing process diagram of a full-mold mounting type acceleration sensor according to the present invention.

FIG. 24 is a schematic configuration diagram of a signal processing circuit.

FIG. 25 is a diagram showing temperature characteristics of a full-mold mounting type acceleration sensor according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Signal processing circuit, 2 ... Detection part structure, 3 ... Lead frame, 4 ... Power supply, output terminal, 5 ... Output adjustment terminal, 6,
7,200 ... Lead wire, 8 ... Plastic material part, 9, 6
0, 61 ... Hole, 10 ... Lower part, 11, 13, 23, 25,
27, 38, 39, 40, 41, 42, 51, 52, 5
3, 64, 65, 66, 76, 90, 108, 109,
110 ... Silicon plate, 12, 14, 24, 26, 75,
77, 89 ... Glass plate, 15, 28, 48, 57, 7
0, 79, 99, 105, 107, 122 ... Beam, 1
6, 29, 47, 56, 69, 78, 100, 102,
106, 121 ... Trout 17, 32, 34, 101, 1
15, 116 ... Fixed electrode, 18, 94, 103 ... Gap, 19, 30, 31 ... Through hole, 20, 33, 3
5 ... Lead portion, 21, 36, 37, 49, 50, 62,
63, 73, 74, 81, 95 ... voids, 22, 84, 9
6,97 ... Pads, 43, 44, 45, 46, 54, 5
5, 67, 68, 82, 91, 111, 112 ... Thermal oxide film, 58, 59, 71, 72 ... Thin plate, 80 ... Strain gauge,
83, 92 ... Polysilicon layer, 85, 86, 87, 88
... Area, 93 ... Beam-mass system, 98, 104 ... Fixed end, 113, 114 ... Glass layer, 117, 118 ... Groove,
Recesses 119 ... Convex part, 120 ... Metal plate, 123 ... Coating material, 124 ... Integrated detection unit structure, 125 ... Capacitance change detection unit, 126 ... Amplification unit, 127 ... Adjustment unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Norio Ichikawa 2477 Kashima Yatsu, Katsuta-shi, Ibaraki Pref. 3 Hitachi Hitachi Engineering Co., Ltd. (72) Inventor Akio Hokawa 502 Kintachi-cho, Tsuchiura, Ibaraki Mechanical Research Laboratory, Hiritsu Factory (72) Masayuki Sato, 2520 Takaba, Takata, Ibaraki Prefecture Hitachi, Ltd., Automotive Equipment Division, Hitachi, Ltd. (72) Shigemasa Umemura 2520, Takaba, Katsuta, Ibaraki Hitachi, Ltd. Automotive Equipment Division (72) Inventor Keiji Hanzawa 2477 Kashima Yatsu, Katsuta City, Ibaraki Pref. 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Masayoshi Suzuki, Katsuta City, Ibaraki 2520 Takata Co., Ltd. Hitachi, Ltd. From the Automotive Equipment Division (72) Satoshi Shimada 7-1-1 Omika-cho, Hitachi City, Hitachi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Masayuki Miki 7-1-1 Omika-cho, Hitachi City, Ibaraki Hitachi Company Hitachi Research Laboratory (72) Inventor Masahiro Matsumoto 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Akira Koide 502 Kintate-cho, Tsuchiura-shi, Ibaraki Hiritsu Seisakusho Co., Ltd. In the laboratory

Claims (33)

[Claims] 1. A silicon plate is etched to form a mass supported by a beam, and the displacement of the mass is caused by a change in electrostatic capacitance between a fixed electrode and a mass arranged facing the mass or by a beam. An acceleration sensor having an acceleration detection unit structure capable of detecting acceleration from a change in resistance value of a strain gauge arranged, and a detection unit composed of the mass and the beam in an acceleration sensor of a type in which the detection unit structure is completely molded and mounted with a plastic material. The structure itself is a completely airtight structure, so that the deformation of the detection part structure itself caused by thermal stress due to the difference in thermal expansion coefficient between the detection part structure and the plastic material is minimized. Alternatively, a full-mold mounting type acceleration sensor, characterized in that a thermal stress relaxation mechanism is provided in a plastic structure surrounding the detection unit structure. 2. The acceleration sensor according to claim 1, wherein the detection section structure is fixed on a lead frame, and detects a change in capacitance or a change in resistance value and outputs a signal corresponding to acceleration to the outside. A processing circuit, the signal processing circuit is integrally integrated with the detection unit structure or is fixed to a lead frame in the vicinity of the detection unit structure separately from the detection unit structure. An acceleration sensor characterized by the above. 3. The acceleration sensor according to claim 2, wherein the thermal stress relaxation mechanism is such that the fixed end of the beam in the detection unit structure is relatively located on the opposite side of the signal processing circuit. An acceleration sensor having a signal processing circuit fixed on a lead frame. 4. The acceleration sensor according to claim 2, wherein a power source composed of a lead frame, an input / output terminal and an adjustment terminal are pulled out to the outside, and the contents of a digital memory provided in a signal processing circuit section are used for the adjustment. An acceleration sensor characterized in that output characteristics such as zero point and sensitivity can be adjusted after molding a plastic material by digitally changing it using terminals. 5. The acceleration sensor according to claim 2, wherein the thermal stress relaxation mechanism is characterized in that the plastics above and below the lead frame have substantially the same thickness. 6. The acceleration sensor according to claim 2, wherein when a metal plate is mounted on the plastic surface of the lower part of the lead frame, the thickness of the plastic of the lower part of the lead frame is changed to the thickness of the plastic of the upper part of the lead frame as a thermal stress relaxation mechanism. An acceleration sensor characterized by being made thicker than the thickness. 7. The acceleration sensor according to claim 1, wherein at least one groove or recess is provided in the plastic portion as a thermal stress relaxation mechanism. 8. The acceleration sensor according to claim 1, wherein a part of the plastic surface is coated with a semiconductive material or a hydrophobic material. 9. The acceleration sensor according to claim 2, wherein the acceleration sensor itself can be directly surface-mounted on a control unit of a system using the acceleration sensor via lead frames such as a power supply and an input / output terminal. Acceleration sensor. 10. The acceleration sensor according to claim 9, wherein
Accelerometer characterized in that the lead frame is bent horizontally or almost at a right angle midway. 11. The acceleration sensor according to claim 1, wherein
The detection unit structure is of a type that detects displacement of a mass supported by a beam from a change in capacitance, and a first silicon plate and a second silicon plate on which the beam and the mass are formed, respectively. Which has a four-layer structure in which a second silicon plate is bonded to the first glass plate on the upper side,
A structure in which a fixed electrode is arranged on the surface portion of the first glass plate facing the mass which is the movable electrode, and a space is provided between the second silicon plate and the first glass plate as a thermal stress relaxation mechanism. Acceleration sensor characterized by. 12. The acceleration sensor according to claim 11, wherein the void is a recess formed on at least one of the surfaces of the first glass plate and the second silicon plate. 13. The acceleration sensor according to claim 12, wherein the bonding dimension of the second silicon plate and the first glass plate from the dicing surface is the bonding dimension of the first silicon plate and the first glass plate from the dicing surface. An acceleration sensor characterized in that the size of the void is determined so as to be smaller than the size. 14. The acceleration sensor according to claim 11, wherein the thickness of the second glass plate directly fixed to the lead frame is the thickest among the four plates forming the detection part structure. Characteristic acceleration sensor. 15. The acceleration sensor according to claim 1,
The detection unit structure is of a type that detects displacement of a mass supported by a beam from a change in electrostatic capacity, and includes a second and a third surface on the upper surface and the lower surface of the first silicon plate on which the beam and the mass are formed, respectively. And a fifth layer structure in which fourth and fifth plates are bonded to the opposite surfaces of the second and third plates, respectively.
An acceleration sensor, wherein a space is provided between the second and fourth plates and between the third and fifth plates as a thermal stress relaxation mechanism. 16. The acceleration sensor according to claim 15, wherein the void is a recess formed on at least one of the surfaces of the second and fourth plates and the third and fifth plates. . 17. The acceleration sensor according to claim 16, wherein the size of the void is set so that the joint dimension of the fourth and fifth plates from the dicing surface is smaller than the joint dimension of the first plate from the dicing surface. Acceleration sensor characterized in that 18. The acceleration sensor according to claim 15, wherein the thickness of the fifth plate directly fixed to the lead frame is the thickest among the five plates forming the detection part structure. And an acceleration sensor. 19. An acceleration sensor according to claim 15, wherein the second and third plates are glass plates, and the fourth and fifth plates are silicon plates, and the detection part structure is formed by stacking five plates. Is assembled by anodic bonding the five plates at the same time, and fixed electrodes are arranged on the surface portions of the second and third plates facing both sides of the mass which is the movable electrode. Sensor. 20. The acceleration sensor according to claim 15, wherein the first, second, third, fourth and fifth plates are all made of silicon plates, and the detection part structure in which these silicon plates are laminated is The second and third plates, which are assembled by joining at a high temperature with a thermal oxide film obtained by oxidizing silicon, and which face the mass that is the movable electrode, are conductive materials and therefore can be used as they are as fixed electrodes. An acceleration sensor characterized by being capable. 21. The acceleration sensor according to claim 1, wherein
The detection unit structure is of a type that detects displacement of a mass supported by a beam from a change in electrostatic capacity, and includes a second and a third surface on the upper surface and the lower surface of the first silicon plate on which the beam and the mass are formed, respectively. Both sides are supported by at least one of the second and third silicon plates facing each other on both sides of the mass, which is a movable electrode, as a thermal stress relaxation mechanism. Alternatively, the acceleration sensor is characterized in that a fixed electrode made of a silicon thin plate supported on one side is formed by etching. 22. The acceleration sensor according to claim 21, wherein the surface of at least one of the second and third silicon plates is heavily doped with boron before etching, and the fixed electrode is made of a silicon thin plate by the doped portion. Is formed, and by the thin plate-shaped fixed electrode,
An acceleration sensor characterized in that a void is formed in at least one of the third silicon plates. 23. The acceleration sensor according to claim 22, wherein the size of the void is determined such that the distance from the dicing surface to the void is smaller than the bonding dimension of the first silicon plate from the dicing surface. Characteristic acceleration sensor. 24. The acceleration sensor according to claim 21, wherein a third structure fixed to the lead frame is used as a thermal stress relaxation mechanism in the detection part structure in which three silicon plates are laminated.
The acceleration sensor characterized in that the silicon plate of is the thickest. 25. The acceleration sensor according to claim 1, wherein
The detector structure is of a type that detects displacement of a mass supported by a beam from a change in capacitance, and the beam and the mass are manufactured by etching a surface of a silicon plate using a sacrificial layer, and The silicon plate is electrically insulated from the silicon plate by a thermal oxide film. As a thermal stress relaxation mechanism, the thickness of the silicon plate is made 100 times or more thicker than the thickness of the beam and the mass, and the beam and the mass are separated from each other. An acceleration sensor characterized in that a cap made of a glass plate is hermetically bonded to a polysilicon layer formed on the thermal oxide film so as to surround the void. 26. The acceleration sensor according to claim 25, wherein the silicon plate itself is a fixed electrode material. 27. The acceleration sensor according to claim 25, wherein a fixed electrode facing a mass that is a movable electrode is formed on the surface of the silicon plate by etching using a sacrificial layer, similarly to the mass. Acceleration sensor. 28. The acceleration sensor according to claim 27, wherein both the mass and the fixed electrode, which are movable electrodes, have a comb tooth shape. 29. The acceleration sensor according to claim 1, wherein
The detector structure is of a type that detects displacement of a mass supported by the beam from a change in resistance value of a strain gauge formed on the beam, and the upper and lower surfaces of the first silicon plate on which the beam and the mass are formed. The first and second glass plates are anodically bonded to each other to form a three-layer structure, and as a thermal stress relaxation mechanism, the first plate is anodically bonded via a polysilicon layer formed on a thermal oxide film on the surface of the silicon plate. An acceleration sensor, characterized in that a recess is provided on the surface of the glass plate of 1. 30. The acceleration sensor according to claim 29, wherein the bonding distance from the dicing surface between the first silicon plate and the second glass plate at the beam fixed end where the strain gauge is formed is the first silicon plate and the second silicon plate. An acceleration sensor having a bonding distance from the dicing surface between the first glass plate and the second glass plate. 31. The acceleration sensor according to claim 29, wherein in the detection part structure having a three-layer laminated structure, the second glass plate has the largest thickness. 32. The acceleration sensor according to claim 1, wherein
The detector structure is of a type that detects displacement of a mass supported by a beam from a change in resistance value of a strain gauge formed in the beam, and the beam and the mass are formed by etching a surface of a silicon plate using a sacrificial layer. The thickness of the silicon plate itself is made 100 times thicker than the thickness of the beam and the mass as a thermal stress relaxation mechanism, and is formed on the surface of the silicon plate so as to surround the beam and the mass in the cavity. An acceleration sensor characterized in that a cap made of a glass plate is hermetically bonded to the polysilicon layer. 33. The acceleration sensor according to claim 1, wherein
The detector structure is formed by airtightly stacking a second silicon plate and a third silicon plate above and below a first silicon plate having a mass supported by a beam. And the thickness of the third silicon plate is at least half or more of the width dimension of the first silicon plate,
An acceleration sensor, characterized in that the joint margin between the first silicon plate and the second and third silicon plates is at least 10% or more of the lateral width dimension of the first silicon plate.