JP2012078089A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor in which an insulating film with a gas sensing part is provided on one surface of a semiconductor chip, a cavity is provided to the semiconductor chip on the rear surface of the gas sensing part, the semiconductor chip penetrates from the one surface to the opposite surface, includes a conductive via electrically connected to the gas sensing part, and wiring which is provided on the opposite surface and connected to the via, and the gas sensing part is covered with a breathable cover fixed to the semiconductor chip.SOLUTION: A gas sensor is mounted on a printed circuit board with neither die bonding nor wire bonding to a package.

Description

  The present invention relates to a gas sensor having a gas sensitive part provided in a cavity of a semiconductor chip, and more particularly to a gas sensor mounting structure.

  Gas sensors in which a gas sensitive part is provided on a cavity of a semiconductor chip using MEMS (Micro Electro Mechanical Systems) technology have been studied. However, the mounting structure of such a gas sensor has not been studied much. When the MEMS type gas sensor is simply mounted, the semiconductor chip of the gas sensor is die-bonded to the package, the electrode pads are wire-bonded, and the chip is further protected by the cover. However, this makes the mounting structure complicated.

  Prior arts related here are disclosed in Patent Document 1: JP2001-337063A and Patent Document 2: JP2002-174608A in which a gas sensor substrate is flip-chip connected to a lead fixed to a package. The gas sensor is not a MEMS type, and a gas sensitive part is provided on a substrate by thick film printing.

JP2001-337063A JP2002-174608A

An object of the present invention is to enable a gas sensor to be mounted on a printed circuit board without die bonding or wire bonding to a package.
An additional object of the present invention is to provide a gas filter in the gas sensor.

  According to the present invention, in a gas sensor in which an insulating film having a gas sensitive part is provided on one surface of a semiconductor chip and a cavity is provided in the semiconductor chip on the back surface of the gas sensitive part, the semiconductor chip penetrates from one surface to the opposite surface. A conductive via electrically connected to the gas part and a wiring provided on the opposite surface and connected to the via, and the gas sensitive part covered with a breathable cover fixed to the semiconductor chip It is characterized by.

  In the present invention, a semiconductor chip can be directly connected to a printed circuit board or the like, no package is required, and neither die bonding nor wire bonding is required. Also, a cover covering the gas sensitive part is fixed to the semiconductor chip, and the cover is attached without a package.

Preferably, the cover is made of ceramic or glass, and a gas filter is provided in an air passage in the cover leading to the semiconductor chip. In this way, the gas filter can be provided in the MEMS type gas sensor.
More preferably, a recess for accommodating the gas filter is provided in the cover at a position opposite to the gas sensitive part. If it does in this way, a gas filter can be provided with the cover of a simple structure.

Particularly preferably, a metal lid covering the recess and having a hole is fixed to the cover. If it does in this way, drop-off of a gas filter can be prevented easily. Moreover, even if the cover is provided with a cover that covers the recess, the gas filter can be prevented from falling off.

Sectional drawing of gas sensor of example and printed circuit board Plan view of semiconductor chip in example Plan view of the cover in the embodiment Cross-sectional view of a modified gas sensor Sectional drawing of the gas sensor of 2nd Example Plan view of the cover in the second embodiment

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  1 to 5 show an embodiment and its modifications. 1 to 3 show a first embodiment, in which 2 is a gas sensor and 4 is a printed circuit board on which the gas sensor 2 is soldered. The gas sensor 2 includes a semiconductor chip 6 and a cover 8. The semiconductor chip 6 is made of silicon or GaAs. An insulating film 12 such as silica or tantalum oxide is provided on one surface of the gas sensor 2, and a cavity 10 is formed on the back surface side of the insulating film 12. Is provided. The cavity 10 may be provided by etching from the insulating film 12 side or from the opposite side of the chip 6.

  For example, a rectangular portion on the cavity 10 in the insulating film 12 is a base 14, and the base 14 is connected to the insulating film 12 outside the cavity 10 by a leg 15. A gas sensitive part 16 such as a metal oxide semiconductor gas sensor or a catalytic combustion type gas sensor is provided on the base 14. For example, four wirings 17 are connected to the gas sensitive part 16, and the other end is connected to a via 18 penetrating the chip 6 with conductivity shown in FIG. The via 18 is provided by reactive ion etching or the like on the chip 6 and is filled with a conductor such as Cu. A pad 20 is provided on the opposite side of the chip 6 as viewed from the gas sensitive part 16 and connected to the via 18. The pad is an example of wiring, and is soldered to the wiring 24 of the printed circuit board 4 via the solder bumps 22. In the MEMS type gas sensor, various configurations of the semiconductor chip 6 are known, and the configuration of the gas sensitive portion 16 and the configuration of the insulating film 12 can be changed as appropriate. The solder bump 22 is a part of the printed circuit board 4.

  A metal layer 26 is provided on the surface of the semiconductor chip 6 on the gas sensitive part 16 side so as to surround the four circumferences of the chip 6. The cover 8 is made of, for example, ceramic or glass, 30 and 34 are cavities, and a porous layer 32 is provided between the cavities 30 and 34. When the cover 8 is made of glass, a through hole is provided instead of the porous layer 32. A metal lid 35 is provided with a hole 36 and fixed to the metal layer 37 at the upper end of the cover 8 by welding or soldering. The lid 35 serves as a lid for the cavity 34, and the cavity 34 accommodates a gas filter 38 made of sheet-like activated carbon, sheet-like zeolite, or the like. A metal layer 39 is provided on the bottom surface of the cover 8 and is fixed to the metal layer 26 of the chip via bumps 40. FIG. 3 shows a state where the lid 35 and the gas filter 38 are removed from the cover 8.

  In order to manufacture the gas sensor 2 of FIGS. 1 to 3, for example, the via 18 and the pad 20 are first formed in the semiconductor chip. Next, the cavity 10, the base 14, the gas sensitive part 16 and the like are formed as in a normal MEMS gas sensor. Further, when the cover 8 is formed of ceramic, for example, three layers of ceramics are formed, a hole is provided in the lowermost ceramic sheet to form the cavity 30, and a hole is similarly provided in the uppermost ceramic sheet to form the cavity 34. Moreover, in the ceramic sheet of the intermediate layer, holes are provided in the porous layer 32 and filled with a material that maintains the porosity even after sintering. Next, the three layers are stacked and fired, the gas filter 38 is set in the cavity 34, and the lid 35 is bonded to the metal layer 37. Then, when the metal layers 26 and 39 are bonded using the bumps 40, the four circumferences around the gas sensitive part 16 can be sealed. In this way, the gas sensor 2 is completed and attached to the printed circuit board 4 by soldering. When the cover 8 is made of glass, cavities 30 and 34 are provided by etching or machining, and holes are similarly provided in the porous layer 32 portion. Further, instead of the bump 40 and the metal layers 26 and 39, the gap between the cover 8 and the chip 6 may be sealed with a resin adhesive or the like, or the sealing may be omitted. Similarly, the lid 35 may be fixed to the cover 8 with resin or the like. Further, if a tall bump, for example, a bump taller than the thickness of the gas sensitive portion 16 is used as the bump 40, the cavity 30 may not be provided.

  Preferably, a plate including a large number of covers 8 is flip-chip connected to a wafer including a large number of chips 6 or a sub-wafer including a large number of chips 6 by bumps 40. Here, a metal plate made of a large number of uncut lids 35 is preferably attached to the plate with a metal layer 37. Next, the wafer or sub-wafer to which the plate composed of a large number of covers 8 is attached is diced into individual gas sensors 2. In this way, the cover 8 can be attached to the chip 6 at the wafer or sub-wafer stage. Further, the lid 35 can be easily attached.

  FIG. 4 shows a modified example, and the same reference numerals as those in FIGS. 1 to 3 denote the same components. In the modification of FIG. 4, the semiconductor chip 6 is the same as the embodiment, and the cover 48 does not include the cavity 34, the gas filter 38, and the lid 35. The cover 48 is, for example, a ceramic cover, includes a cavity 30, and has air permeability at the porous layer 32 portion. In place of ceramic, a glass cover may be provided with through holes instead of the porous layer 32. Further, the porous layer 32 may be made of a gas filter material having low sinterability, such as γ-alumina, amorphous alumina, zeolite, or the like. In this case, the cover 48 is composed of two layers: a layer provided with the cavity 30 and a layer filled with a gas filter material in the hole.

  5 and 6 show a gas sensor 52 of the second embodiment, and the same reference numerals as those in FIGS. 1 to 3 denote the same components. 58 is a new cover made of ceramic or the like, and includes a lid 53 that covers the upper surface of the cavity 34 and a side wall 54 that covers three sides of the cavity 34, and an opening 55 is provided on the other side surface of the cavity 34. The insertion port for the gas filter 38 is used. An air passage between the cavities 30 and 34 is formed through the holes 50 or the porous layer. 5 and 6, a sheet-like gas filter 38 and the like can be set in the cavity 34 from the opening 55.

In the embodiment, the following effects can be obtained.
(1) The gas sensors 2 and 52 can be directly mounted on the printed circuit board 4. And no package, wire bond or die bond is required.
(2) The gas sensitive part 16 can be protected by the cover 8 or the like. The gap between the cover 8 and the chip 6 can be sealed with a bump 40 or the like, or can be sealed with a resin adhesive.
(3) By storing the gas filter 38 in the cavity 34, the toxic gas can be removed or unnecessary gas can be removed. The gas filter 38 is not limited to a sheet shape, and may be accommodated in the cavity 34 as a granule as it is or with an appropriate adhesive.

2,42 Gas sensor 4 Printed circuit board 6 Semiconductor chip 8 Cover 10 Cavity 12 Insulating film 14 Base 15 Leg 16 Leg 16 Sensitive part 17 Wiring 18 Via 20 Pad 22 Solder bump 24 Wiring 26 Metal layer 30, 34 Cavity 32 Porous layer 35 Lid 36 Hole 37 Metal layer 38 Gas filter 39 Metal layer 40 Bump 48, 58 Cover 50 Hole 52 Gas sensor 53 Lid 54 Side wall 55 Opening

Claims (5)

In a gas sensor in which an insulating film having a gas sensitive part is provided on one surface of a semiconductor chip, and a cavity is provided in the semiconductor chip on the back surface of the gas sensitive part,
The semiconductor chip includes a conductive via that penetrates from the one surface to the opposite surface and is electrically connected to the gas sensitive portion, and a wiring that is provided on the opposite surface and connected to the via,
The gas sensor is covered with a breathable cover fixed to a semiconductor chip.   The gas sensor according to claim 1, wherein the cover is made of ceramic or glass, and a gas filter is provided in a ventilation path in the cover leading to the semiconductor chip.   3. The gas sensor according to claim 2, wherein a concave portion for accommodating the gas filter is provided in the cover at a position opposite to the gas sensitive portion.   4. The gas sensor according to claim 3, wherein a metal lid that covers the recess and has a hole is fixed to the cover.   The gas sensor according to claim 3, wherein the cover includes a lid that covers the recess.

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