JP3140804U - 3-axis acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor free from a mold resin non-filling problem or a mold part peeling problem at the time of resin sealing.
SOLUTION: Each component to be resin-molded is stacked and arranged in a stepped substantially square frustum shape, and the surface of each component is machined by a diamond grindstone as much as possible, so that the mold resin at the time of resin sealing can be obtained. Obtain an acceleration sensor that is free from unfilling defects and peeling problems of molded parts.

[Selection] Figure 1

Description

The present invention is based on MEMS (Micro-Electro-Mechanical System).
ems) The present invention relates to an acceleration sensor having a chip sensor element and sealed with resin.

By combining semiconductor manufacturing process technology with machining technology and material technology,
The MEMS technology for realizing a system having a three-dimensional microstructure on a semiconductor substrate can be applied to a very wide range of fields. In particular, many acceleration sensors used for automobiles, airplanes, portable terminal devices, toys and the like have been manufactured. The acceleration sensor is characterized by having a movable part formed by MEMS technology. By detecting the amount of movement of the movable part by the resistance change or capacitance change of the piezoresistive element and performing data processing, values such as acceleration, angular velocity, and pressure can be obtained. Patent Documents 1 to 3 disclose acceleration sensors.

JP 2006-133123 A Japanese Patent Laid-Open No. 8-233851 Japanese Patent Laid-Open No. 11-160348

The structure of the acceleration sensor of Patent Document 1 will be briefly described with reference to FIGS. 3 and 4a).
FIG. 3a) shows an exploded perspective view of the triaxial acceleration sensor. FIG. 4a) shows a cross-sectional view. Case 5
3, the sensor chip 51 and the IC regulation plate 52 are fixed to each other with a predetermined interval by a spacer resin 67 such as an epoxy resin in which plastic balls serving as spacers are kneaded. The chip terminal 58 of the sensor chip 51 is connected to the IC restriction plate terminal 57 by the wire 55, the IC restriction plate terminal 57 is connected to the case terminal 59 by the wire 56, and the sensor signal is taken out from the external terminal 60. A case lid 54 is fixed to the case 53 with an adhesive 68 and sealed.
FIG. 3B) is a plan view of the sensor chip 51 as viewed from the upper surface of the sensor chip. A sensor element 71 and a chip terminal 58 are formed on the sensor chip 51. Sensor element 7
1 includes a beam portion 61 that forms a pair with a rectangular frame portion 63 and a weight portion 62, and the weight portion 62 is held at the center of the frame portion 63 by two pairs of beam portions 61. A piezoresistive element is formed on the beam portion 61. An X-axis piezo 64 and a Z-axis piezo 66 are formed on the pair of beams, and a Y-axis piezo 65 is formed on the other pair of beams.

In the triaxial acceleration sensor shown in FIGS. 3 and 4a), the case 53 and the case lid 54 are made of ceramic such as alumina. Due to the ceramic, there is a limit to reducing the thickness of the case 53 and the case lid 54, and it is difficult not only to reduce the size but also to reduce the weight. Since the metal case terminal 59 and the external terminal 60 are formed in the ceramic case and these are connected in the ceramic, the ceramic case becomes expensive, and it is difficult to realize an inexpensive acceleration sensor as long as the ceramic case is used. The case 53 and the case lid 54 are bonded and sealed with a resin 68. Since the resin is used, there is a problem that the air density decreases due to changes in the surrounding environment.

A method for increasing the airtightness is described in Patent Document 4. In this method, a plate serving as a cap is bonded to the upper and lower surfaces of at least the movable part of the sensor chip with a resin, a low melting point metal or the like. After joining the wafer with the sensor chip formed, the wafer with the upper cap formed, and the wafer with the lower cap formed, the wafer is cut and separated into sensor chip units to obtain sensor elements. . Since the movable part of the sensor chip is packaged in the wafer state, this process is called a wafer level package (WLP). The part to be sealed is limited to the movable part of the sensor chip, in other words, by shortening the total joint length, it is easy to ensure airtightness, and the reliability is improved. Figure 4b) shows the WLP
The cross section of the acceleration sensor using the sensor element 2 formed by is shown. After joining the upper cap 3 on the beam side which is the upper surface of the sensor chip 4 and the lower cap 5 on the opposite surface side with a low melting point metal,
The sensor element 2 obtained by dividing into pieces is fixed to the inner bottom of the case 53 with an adhesive or the like. A chip terminal 58 of the sensor chip and an external terminal 60 formed on the case are connected by a wire 69.
An acceleration sensor is obtained by bonding a case lid 54 to the case 53 with a resin or the like. However, if the sensor element 2 formed of WLP is put in the case as shown in FIG.

Applying the resin sealing technology of semiconductor as disclosed in Patent Document 5, the sensor element 2
Accelerometers covered with mold resin are beginning to be put into practical use. FIG. 4c) shows an example of a resin-sealed acceleration sensor. By reducing the thickness of the mold resin 16 to such an extent that the sensor element 2, the wire 69, etc. do not directly touch the outside air, it is possible to reduce the size and weight. Further, since the bonding operation of the case as shown in FIG. 4B is not necessary, the manufacturing cost can be reduced.

Japanese Patent Laid-Open No. 3-2535 JP-A-10-170380

FIG. 4c) shows a structure without an electric circuit, but what is strongly required in the market is a type incorporating an IC circuit for processing the signal of the sensor chip 51 as shown in FIG. 4a).
FIG. 5 shows an example of a resin-molded acceleration sensor having a circuit board for processing signals.
The sensor element 2 is fixed to the circuit board 11, which is an IC circuit, with an adhesive 15, and the circuit board 11 is fixed to the terminal board 13 with the adhesive 15. If the sensor element 2, the adhesive 15, the circuit board 11, and the terminal board 13 have different end face positions and the end faces are uneven, a resin unfilled part 31 and a peeled part 32 are produced when resin molding is performed. was there.

If the end surface of the circuit board 11 is recessed from the end surface of the sensor element 2 or if the adhesive coating is insufficient and a recess is formed at the end, the mold resin 16 is not filled as shown by the diagonal lines. Generation of the part 31 and the peeling part 32 as shown with a broken line were easy to generate | occur | produce. When the unfilled part 31 and the peeling part 32 generate | occur | produce, unnecessary stress will be added to the sensor element 2, and the offset voltage generate | occur | produced will be large although acceleration is not added. Further, when the ambient temperature of the acceleration sensor changes, the stress generated in the unfilled part 31 and the peeling part 32 also changes, so that the temperature stability of the acceleration sensor also decreases. The sensor element 2, the circuit board 11, and the terminal board 13 have dimensions and shapes that can be most efficiently taken from wafers and materials. From the viewpoint of manufacturing cost, the actual condition is to accept the unevenness of the end face.

SUMMARY OF THE INVENTION An object of the present invention is to provide an acceleration sensor that does not have a mold resin unfilling problem or a mold part peeling problem during resin sealing.

The triaxial acceleration sensor of the present invention includes a sensor chip having a movable part and an electrode on the upper surface,
At least the upper surface side of the movable part of the sensor chip is sealed with an upper cap and the lower surface side is sealed with a lower cap. The lower surface side of the lower cap is fixed to the upper surface side of the circuit board with a die attach film a, and the lower surface side of the circuit board is It is fixed to the upper surface side of the wiring board with a die attach film b, and the sensor element electrode and the circuit board electrode, and the circuit board electrode and the wiring board electrode are wired with wires, and a resin is used except for a part of the wiring board. It is sealed. The side surface of the sensor element and the side surface of the lower cap and the side surface of the die attach film a are the same surface, at least the side surface of the sensor element and the side surface of the lower cap are cut surfaces, and the side surface of the circuit board and the side surface of the die attach film b are It is preferable that at least the side surface of the circuit board is a cut surface on the same surface.

The die attach film a is fixed to the lower surface side of the lower cap, and the die attach film a is also cut with a diamond grindstone at the same time when the sensor element is singulated, so that the end face of the lower cap and the end face of the die attach film a are matched. Can do. The die attach film b is fixed to the lower surface side of the circuit board, and the die attach film b is also cut at the same time when the circuit board is separated, so that the end face of the circuit board and the end face of the die attach film b can be matched. . By matching the end face of the die attach film b and the end face of the lower cap, and the end face of the die attach film and the end face of the circuit board, it is possible to prevent occurrence of unfilled portions and peeled portions of the mold resin. No. 1000 to 3000 diamond whetstones can be used.

By dividing the sensor element and the circuit board into pieces by cutting, a processing speed faster than that of wet etching can be obtained, and processing costs can be reduced. Further, by making the end surface a cut surface, the adhesiveness with the mold resin is also improved, which leads to a reduction in defects such as mold resin peeling.

In the triaxial acceleration sensor of the present invention, it is preferable that the upper surface side of the upper cap and the lower surface side of the lower cap are ground surfaces.

The sensor element is composed of a wafer with a sensor chip, a wafer with an upper cap, and a wafer with a lower cap, and then cut the wafer into individual sensor chips. Yes. Since the upper cap wafer and the lower cap wafer are subjected to WLP with a thickness larger than that of the upper cap and the lower cap constituting the sensor element in consideration of prevention of breakage during handling or joining, before the individualization. It is preferable that the upper and lower cap wafers are ground with a diamond grinding wheel. Further, it is preferable to expose the chip terminal of the sensor chip as a structure in which the upper cap is thinned while being thinned. In order to expose the chip terminal, the end face of the upper cap is recessed from the end face of the sensor chip. Although the upper and lower cap wafers can be thinned by wet etching, it is difficult to adopt them in terms of manufacturing man-hours and costs because operations such as production of protective masks for chip terminals are required. No. 1000 to 3000 diamond whetstones can be used.

By making the upper cap side of the upper cap and the lower cap lower surface side a ground surface, an effect of increasing the adhesive strength between the die attach film and the mold resin can be obtained.

In the triaxial acceleration sensor of the present invention, the lower surface side of the circuit board is preferably a ground surface with a diamond grinding wheel.

The acceleration sensor can be miniaturized by grinding the bottom surface of the circuit board where no circuit is formed with a diamond grindstone and making it as thin as possible. By grinding using a diamond grindstone, a high processing speed can be obtained, and the manufacturing cost can be reduced. Although it is possible to reduce the thickness of the circuit board using wet etching, it is necessary to cut off the circuit pattern from the etching solution, and it is difficult to adopt it in terms of manufacturing man-hours and costs because work such as protective mask preparation is required. . By using a ground surface, the effect of increasing the adhesive strength with the die attach film can be obtained.

In the triaxial acceleration sensor of the present invention, the lengths of adjacent sides of the wiring board and the circuit board, the lower cap, and the upper cap are preferably upper cap <lower cap <circuit board <wiring board.

If the wiring board is the bottom part and the top cap is the top part, the parts have small sides as they go from the bottom to the top. Can be reliably molded.

The three-axis acceleration sensor of the present invention has a stepped substantially square pyramid in the order of the die attach film 2, the circuit board, the die attach film 1, the lower cap, the sensor element, and the uppermost upper cap with the wiring board as the lowermost step. It is preferable to be laminated in a shape.

The staircase shape of a substantially quadrangular pyramid can be easily understood by imagining a stepped pyramid.
Since the upper side is shorter than the lower side and the upper side is positioned within the lower side length, the unfilled portion of the mold resin can be eliminated. Further, by adopting a stepped substantially quadrangular pyramid shape, even if the number of mold resin injection ports is reduced, the resin can reach every corner and a simple mold can be obtained.

The 3-axis accelerometer of the present invention is constructed by laminating and arranging each part in a stepped, substantially quadrangular pyramid shape, and by machining the surface of each part as much as possible with a diamond grindstone. Thus, it was possible to obtain a three-axis acceleration sensor that is free from mold resin unfilled defects and peeling-off of molded parts.

Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals may be used for the same parts and parts.

FIG. 1 shows an exploded perspective view of the three-axis acceleration sensor of the present invention. 2 is a cross-sectional view of the triaxial acceleration sensor, FIG. 2a) is a mm ′ cross-sectional view of FIG. 1, and FIG. 2b) is a nn ′ cross-sectional view of FIG. The structure will be described with reference to FIGS. The circuit board 11 is fixed on the lowermost wiring board 23 with a die attach film b (Die Attach Film) 7, and the sensor element 2 is fixed on the circuit board 11 with a die attach film a 6. The chip terminal 8 of the sensor element 2 and the circuit board terminal 12 of the circuit board 11 are electrically connected by a gold bare wire a21. The circuit board terminal 12 of the circuit board 11 is electrically connected to the wiring board terminal portion 25 of the wiring board 23 by a bare gold wire b22. Except for the lower surface side and one side surface of the wiring board terminal portion 21,
The triaxial acceleration sensor 1 is formed by resin molding with the mold resin 16. In FIG. 1, the two-dot chain line indicates the mold resin, and the broken line indicates the approximate joining position of each component.

The sensor element 2 has an upper cap 3 and a lower cap 5 fixed to a movable part of the sensor chip 4 with a low melting point metal (not shown). The upper cap 3 is made smaller than the sensor chip 4 in order to expose the chip terminal 8 region of the sensor chip 4. The lower cap 5 has the same area as the sensor chip 4. The sensor chip 4 is joined to the upper cap 3 and the lower cap 5 with a low melting point metal, and the movable part of the sensor chip 4 is sealed. The structure of the sensor chip 4 is the same as that of the sensor chip 51 of FIG. Wiring board 23
The circuit board 11 is fixed not only to the wiring board bonding part 24 but also to a part of the wiring board terminal part 25 with a die attach film b7. A mold resin 16 is filled between the wiring board bonding part 24 and the wiring board terminal part 25.

The outline dimensions and materials of the three-axis acceleration sensor of this embodiment are as follows. The outer dimension of the triaxial acceleration sensor 1 is 2.5 mm × 2.5 mm × 1.0 mm thick. Wiring board 23 is 2.5mm
The wiring board adhesion part 24 and the wiring board terminal part 25 are formed by pressing with copper of x2.5 mm x 0.2 mm thickness. The circuit board 11 is 2.0 mm × 2.0 mm × 0.1 mm thick silicon. The diattachi film b7 is an epoxy resin having the same area as the circuit board 11 and a thickness of 0.02 mm. The lower cap 5 constituting the sensor element 2 is 1.2 mm × 1.3 mm × 0.1
mm thickness, sensor chip 4 is 1.2 mm x 1.3 mm x 0.4 mm thick, upper cap 3 is 1
. It is 0 mm x 1.0 mm x 0.1 mm thick, and all are silicon. The thickness of the mold resin 16 on the upper cap 3 is 0.06 mm. The mold resin 16 is an epoxy resin. The wires a21 and b22 are bare gold wires having a diameter of 20 μm. Needless to say, there is no need to be concerned with the dimensions shown in the present embodiment as long as they have a dimensional relationship that provides a stepped substantially quadrangular pyramid shape.

As described above, the area of the constituent members of the triaxial acceleration sensor 1 is such that the lowermost wiring board 23 is the largest and the uppermost upper cap 3 is the smallest.
As shown in FIG. By adopting a stepped substantially quadrangular pyramid shape, it was possible to suppress the occurrence of unfilled portions 31 and peeling portions 32 of the resin during resin molding.

A method for manufacturing the three-axis acceleration sensor of this embodiment will be briefly described.上 Upper cap and lower cap patterns are formed on a 6-inch silicon wafer using photolithography technology, film formation, and etching technology. Similarly, a sensor chip is formed on an SOI (silicon-on-insulator) wafer, and the upper cap, sensor chip, and lower cap are formed. These three wafers were positioned and pressed and heated to join with a low melting point metal. The upper cap side and the lower cap side of the wafer on which the sensor element was formed were ground with a No. 2000 diamond grindstone to obtain a predetermined thickness. The upper cap is separated into pieces when it reaches a predetermined thickness. A die attach film was attached to the lower cap side at 100 ° C. The sensor element wafer to which the die attach film was affixed was cut with a No. 2000 diamond whetstone to obtain the sensor element 2 to which the die attach film a6 was affixed. Since it cut | disconnected with the diamond grindstone, the sensor chip 4, the lower cap 5, and the die attach film a6 are the same dimensions, and the cut surface is the same surface. The surface roughness of the grinding surface of the upper cap and the cut surfaces of the sensor chip 4 and the lower cap 5 was Ra ≦ 200 nm. Measurement of surface roughness Ra is based on JIS
B0601 was followed.

The back surface of the 8-inch silicon circuit board wafer on which the electric circuit was formed was ground with a No. 2000 diamond grindstone to a predetermined thickness, and a die attach film was attached to the ground surface at 100 ° C. The circuit board wafer to which the die attach film was attached was cut with a No. 2000 diamond grindstone to obtain the circuit board 11 to which the die attach film b7 was attached. Since it cut | disconnected with the diamond grindstone, the circuit board 11 and the die attach film b7 are the same dimensions, and the cut surface is the same surface. The circuit board 11 with the die attach film b7 attached and the sensor element 2 with the die attach film a6 attached are stacked on the wiring board 23 connected in plural, and fixed at 150 ° C. to 170 ° C. while applying a load of 2N. . The wire 21 was welded to the chip terminal 8 and the circuit board terminal 12 with ultrasonic waves. Similarly, the wire 22 was welded to the circuit board terminal 12 and the wiring board terminal part 25 with ultrasonic waves.

A laminated structure in which the circuit board 11 and the sensor element 2 are fixed to a plurality of wiring boards 23 with a die attach film was molded into a mold resin 16 using a transfer molding method. The structure was completely sealed in an epoxy resin by molding at 175 ° C. The three-axis acceleration sensor 1 was obtained by taking out from the molding machine and cutting the continuous portion of the wiring board.

When 200 triaxial acceleration sensors manufactured in the present example were disassembled and the occurrence frequency of the resin unfilled portion 31 and the peeling portion 32 was examined, the resin unfilled portion 31 and the peeling portion 32 were not generated. . In the conventional acceleration sensor shown in FIG. 5, the occurrence frequency of the unfilled portion 31 and the peeled portion 32 of the resin was 2-3%. The difference in the occurrence frequency is due to the effect that the lowermost wiring board 23 is the largest and the uppermost upper cap 3 is the smallest, and the stacked shape is a stepped substantially square pyramid shape as shown in FIG. It is believed that there is. Further, since the upper surface of the upper cap 3 is a ground surface and the side surface of the sensor chip and the lower cap is a cut surface, no peeling occurred at the interface with the mold resin 16. This is thought to be because the surface was wet-etched with silicon and was ground or cut with a diamond grindstone, resulting in a moderately rough surface and improved adhesion to the mold resin.

It is a disassembled perspective view of the Example of the 3-axis acceleration sensor of this invention. It is sectional drawing of the Example of the triaxial acceleration sensor of this invention. It is a disassembled perspective view which shows the structure of the conventional triaxial acceleration sensor. It is sectional drawing of the conventional triaxial acceleration sensor. It is a figure which shows the unfilled part and peeling part of the mold resin of the conventional triaxial acceleration sensor.

Explanation of symbols

1 Accelerometer,
2 sensor elements,
3 Upper cap,
4 Sensor chip,
5 Lower cap,
6 Die attach film a,
7 Die attach film b,
8 Chip terminal,
11 Circuit board,
12 Circuit board terminals,
13 Terminal board,
14 External terminal
15 Adhesive,
16 Mold resin,
21 Wire a,
22 wire b,
23 Wiring board,
24 Wiring board adhesion part,
25 Wiring board terminal part,
31 Unfilled part,
32 Peeling part,
51 sensor chip,
52 IC regulation plate,
53 cases,
54 Case lid,
55 wires,
56 wires,
57 IC regulation plate terminal,
58 chip terminals,
59 Case terminal,
60 external terminals,
61 Beam,
62 weight part,
63 Frame,
64 X-axis piezo,
65 Y-axis piezo,
66 Z-axis piezo,
67 Spacer resin,
68 resin,
69 wires,
70 terminal board,
71 External terminal.

Claims (5)

A sensor chip having a movable part and an electrode on the upper surface, and at least the upper surface side of the sensor chip is sealed with an upper cap and the lower surface side is sealed with a lower cap, and the lower surface side of the lower cap is die-attached to the upper surface side of the circuit board. Fixed with film a, the lower surface side of the circuit board is fixed to the upper surface side of the wiring board with a die attach film b, and the electrode of the sensor chip and the electrode of the circuit board, and the electrode of the circuit board and the electrode of the wiring board are wired with wires An acceleration sensor sealed with resin except for a part of the wiring board, wherein the side surface of the sensor chip and the side surface of the lower cap and the side surface of the die attach film 1 are the same surface, and at least the side surface of the sensor chip and the lower cap The side surface of the circuit board is a cut surface, and the side surface of the circuit board and the side surface of the die attach film 2 are the same surface, at least the circuit board side. 3-axis acceleration sensor, wherein it is cut processed surface. The triaxial acceleration sensor according to claim 1, wherein the upper cap and the lower cap lower surface are ground surfaces. The triaxial acceleration sensor according to claim 1 or 2, wherein the lower surface side of the circuit board is a ground surface. 4. The length of adjacent sides of the wiring board and the circuit board, the lower cap, and the upper cap is an upper cap <lower cap <circuit board <wiring board, 3. Axial acceleration sensor. Die attach film b, circuit board, die attach film a with the wiring board at the bottom
5. The triaxial acceleration sensor according to claim 1, wherein the three-axis acceleration sensor is stacked in a stepped substantially quadrangular pyramid shape in order of a lower cap, a sensor chip, and an upper cap on the uppermost stage.

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