119
`United States Patent
`5,503,016
`(11) Patent Number:
`Koen
`(45) Date of Patent:
`Apr. 2, 1996
`
`
`10
`
`[54] VERTICALLY MOUNTED
`ACCELEROMETER CHIP
`
`[75]
`
`Inventor: Edward F. Koen, Danville, Calif.
`
`2720484A1
`60-12750
`63-90774
`WOSL/11722
`
`11/1977 Germany .
`1/1985
`Japan .
`4/1988
`Japan .
`8/1991 WIPO .
`
`{73] Assignee:
`
`IC Sensors, Inc., Milpitas, Calif.
`
`OTHER PUBLICATIONS
`
`“NEC's Automative Electronic Control Modules”, NEC,
`sales brochure, date unknown.
`[21] Appl. No.: 189,948
`“Airbags Boom When IC Accelerometer Sees 50 G”, by
`[22] Filed:
`Feb. 1, 1994
`Frank Goodenough, Electronic Design, Aug. 8, 1991.
`GOIP 1/02
`[51]
`Int. CLS
`.
`.
`ays
`Bae: Ba: Ca ciccsanecssinusaiestbapsnstionsaaierstenccseceee tea 73/493
`
`[58] Field of Search .o...snsnnnesnn 731d, ai Try, eer Searniner—Hieaton B. Willa
`731756, 866.5, 204.22, 856; 174/260
` “18ststant Examiner—Christine K. Oda
`EEE
`Attorney, Agent, or Firm—Skjerven, Morrill, MacPherson,
`References Cited
`Franklin and Friel; Norman R. Klivans
`
`[56]
`
`ABSTRACT
`[57]
`U.S. PATENT DOCUMENTS
`Micro-machined accelerometer chips have a sensitive axis
`4,700,973
`10/1987 Gadermann ........cccceceseseseseseeneeese 731493
`pee Pe easstree
`se ee perpendicular to the principle surface of the device. In an
`
`
`9/1991 Feryse = ene 73/503
`5044201
`application where the desired sensing direction is in the
`
`5,060,504 10/1991 White et al.....
`_. T31D
`Plane of a supporting printed circuit board, the accelerom-
`
`4/1992 Blackburn etal
`. 180/274
`5,109,341
`eter cannot be mounteddirectly on the printed circuit board
`. 73/517 R
`11/1992 White et al.....
`5,163,325
`and instead is mounted on a wall perpendicular to the printed
`
`...
`.- 156/292
`5,221,400
`6/1993 Staller etal.
`circuit board. This requirement to wall-mount the sensoris
`
`
`5,233,871 8/1993 Schwarz et al.oe.csseeessseseeees 73/493 eliminated by using an accelerometer chip packaged with a
`
`8/1993 Mozgowiec.....
`-. 73/493
`5,233,873
`signal conditioning circuit in a multi layer ceramic chip
`
`.....
`73/517 AV
`9,233,874
`8/1993 Putty et al.
`carrier. Electrical connections are contained within the lay-
`ies pee oa a eae
`ers of the ceramic andterminate at a side surface ofthe chip
`5,261.69.4
`11/1993 White ct al.
`....
`980/735
`carrier. Thus the accelerometer chip sits perpendicular to the
`5.269.187 12/1993 Hanson ..........
`"73/495
`printed circuit board andthe ceramic chip carrier is attached
`5,394,326
`2/1995. Lin ......
`364/424.05
`directly thereto.
`FOREIGN PATENT DOCUMENTS
`
`
`
`0557917A1
`
`9/1993 European Pat. Off. .
`
`18 Claims, 4 Drawing Sheets
`
`14
`
`{|
`
`
`\ Vg
`
`
`oesa
`
` RNY
`
` KES
`
`0001
`
`Apple Inc.
`APL1039
`U.S. Patent No. 8,923,941
`
`Apple Inc.
`APL1039
`U.S. Patent No. 8,923,941
`
`0001
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 1 of 4
`
`5,503,016
`(Prior Art)
`
`FIG. 1a
`
`e
`
`FIG. 1b
`
`0002
`
`0002
`
`

`

`U.S. Patent
`
`Sheet 2 of 4
`
`Apr. 2, 1996
`
`5,503,016
`
`
`
`
`
`|oN
`
`
`
`0003
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 3 of 4
`
`5,503,016
`
`LLL£2(J
`LLLLLLLLL
`VLLLELLMM
`VLLLLLLLLLD
`
`44
`
`66a
`
`FIG. 2c
`
`68
`
`66b
`
`44
`
`60
`
`AXIS OF
`ACCEL
`
`66a
`
`62a
`
`FIG. 2d
`
`0004
`
`0004
`
`
`
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 4 of 4
`
`5,503,016
`
`
`
`FIG. 3
`
`0005
`
`

`

`5,503,016
`
`1
`VERTICALLY MOUNTED
`ACCELEROMETER CHIP
`
`BACKGROUND OF THE INVENTION
`
`1. Field ofthe Invention
`
`This disclosure relates to sensing variations in velocity
`such as in a motor vehicle, and more particularly to a method
`and structure for mounting an accelerometer on a support.
`2. Description of the Prior Art
`Micro-machined chip accelerometers are well known in
`the art. Examples are disclosed in U.S. Pat. No. 5,060,504
`issued Oct. 29, 1991 to White,et al., U.S. Pat. No. 5,221,400
`issued Jun. 22, 1993 to Staller, and U.S. Pat. No. 5,233,874
`issued Aug. 10, 1993 to Putty et al. As is well known, an
`accelerometer is a device which measures acceleration, or
`more accurately measures force exerted by a body as a result
`of a change in the velocity of the body. A moving body
`possesses an inertia which tends to resist the change in
`velocity. It is this resistance to any change in velocity that is
`the source of the force exerted by the moving body. This
`force is directly proportional to the acceleration component
`in the direction of movement when the moving body is
`accelerated.
`
`In a typical micro-machined accelerometer formed of
`silicon (a “chip”), a central, typically spherical or rectangu-
`lar shaped mass is suspended by one or more microbridges.
`The bridges are attached to a supporting substrate which
`circumscribes the mass, with a gap provided therebetween.
`The mass is supported within and has free movement
`relative to the supporting substrate. The individual micro-
`bridges within e.g. each pair of micro-bridgesare positioned
`at opposing edges of the mass such thatthe pair’s longitu-
`dinal axis constitutes a common axis across the surface of
`the mass.
`
`The movementof the mass is measured, for instance, by
`measuring a corresponding changein the output of a Wheat-
`stone bridge incorporating beam piezo-resistors formed in
`the micro-bridges.
`Typically such micro-machined silicon chip accelerom-
`eters require external circuitry to process the signal output
`by the accelerometer, for instance for triggering an automo-
`bile air bag deployment system. Such accelerometers hence
`are commonly used in automobiles and other vehicles.
`Accelerometers are constrained in that typically a micro-
`machined accelerometeras described abovehas a single axis
`sensitive to acceleration. That is, it can only measure accel-
`eration along a line perpendicular to a plane defined by the
`principal surface of the chip. The principal surface of the
`chip is in the plane of the chips, from which side during
`fabrication various fabrication steps (masking, etching,etc.)
`are performed. For an automobile airbag system the direc-
`tion of acceleration which must be sensed in the event of a
`collision is typically along a line lying in a horizontal plane
`(parallel to the ground).
`A typical prior art structure for mounting such a micro-
`machined accelerometer chip is shown in a front view in
`FIG. la. Here a conventional metal “can” chip package 12
`defines a central recess 10 in which are conventionally
`mounted the actual accelerometer chip 14 and the associated
`electronic circuitry, here present in ASIC circuit 16. ASIC
`means Applications Specific Integrated Circuit which is
`typically used, but other types of integrated circuit will also
`perform this function. It is to be understood that in some
`such accelerometers,this circuitry is integrated on the accel-
`erometer chipitself.
`
`2
`The accelerometer chip 14 is electrically connected to the
`ASIC chip 16 by conductors 18 carrying electrical signals
`between the two chips 14, 16. The metal can 12 is sealed by
`a lid (not shown), while the accelerometer chip 14 and ASIC
`chip 16 are held on a ceramic substrate 20 fixed inside can
`12. Also provided are screws 24a, 24b (and corresponding
`holes not shown) for securing can 12 to a mounting bracket
`(described below).
`The electrical conductive leads which connect chips 14
`and 16 to the remainder ofthe system (the actual connection
`is not shown for simplicity here) terminate in this case at
`conventional edge clip terminations (pins) 28a, 28b, etc.
`Theseelectrically connectto printed circuit board (PCB) 36
`held by standoffs 38a, 38b onthe floor of metal housing 40.
`To better illustrate the structure of FIG. 1A, a side view
`along line A—Aof FIG. 1a is shown in FIG. 1b. Thelid
`which seals (by a weld) can 12 (omitted from FIG. 1a) is
`designated by reference number 26. FIG. 1b also illustrates
`the support structure for the can 12, which is mounted on a
`metal base plate 28 with glass to metal seals. Base plate 28
`in turn is attached by screws 24a, 24b to a mounting bracket
`34. Mounting bracket 34 is a robust structure formed for
`instance of metal, plastic or ceramic. The purpose of mount-
`ing bracket 34 is to properly mount can 12 in a vertical
`orientation on the sidewall of housing 40. Bracket34 is held
`onto the sidewall by screws, rivets, or other means (not
`shown). The direction of acceleration is as shown by the
`arrow labelled “AXIS ofACCEL”. Thusthe sole purpose of
`base plate 28 and mounting bracket34 is to vertically mount
`can 12 so that it is perpendicular to PCB 36. Typically in a
`vehicle, PCB 36 is thereby installed in a planeparallelto that
`of the surface of the earth.
`
`. , 28g)
`.
`As shown, lead 28a (and the other leads 28, .
`extend from behind metal can 12 (detail not shown for
`simplicity) to connect to electrical connectors on PCB 36.
`PCB 36 provides the connectionsto the actual air bag firing
`device, typically housed in the steering wheel, whereas the
`housing 40 is typically mounted under the dash board or on
`the floor board of the vehicle. The structure of FIGS. 1a and
`1b functionssatisfactorily. Howeverit has the major disad-
`vantages of being relatively bulky and expensive due to the
`rather elaborate mounting structure required to rigidly
`mount the accelerometer chip in the desired orientation
`relative to 1) its axis of sensitivity; and 2) the horizontally
`mounted PCB 36. Also,
`the relative complexity of the
`mechanical structure and leads 28 cause reliability prob-
`lems.
`
`Analog Devices has disclosed (Electronic Design, Aug. 8,
`1991, “Airbags Boom When IC Accelerometer Sees 50G”
`see FIG. 5) a micro-machined accelerometer chip whose
`mass moves in the plane of the chip. This chip allows the
`axis of sensitivity to be parallel to the expected acceleration
`phenomenon. However,this is a special accelerometer chip
`apparently available only from this single supplier.
`Thus it would be highly desirable to reduce the cost and
`increase reliability of mounting accelerometer chips in an
`automobile, other vehicle, or other application without the
`need for an expensive and bulky mounting structure, and
`using a standard accelerometer chip.
`
`10
`
`20
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`30
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`35
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`40
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`45
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`55
`
`SUMMARY OF THE INVENTION
`
`65
`
`In accordance with the invention, an accelerometer chip
`whose sensing direction is conventionally perpendicular to
`the plane (principal surface) of the chip is housed in a chip
`carrier and mounted directly on the printed circuit board,
`
`0006
`
`0006
`
`

`

`5,503,016
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. la and FIG. 1b show respectively front and side
`viewsof a prior art accelerometer mounting structure.
`FIGS. 2a, 2b, 2c and 2d show respectively a front view,
`across sectional view, a side surface view (when mounted),
`and a second side view of a mounting structure for an
`accelerometer chip in accordance with the invention.
`FIG. 3 shows a cross sectional view of a plastic chip
`carrier for an accelerometer chip in accordance with the
`invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`3
`4
`edge-wise. Thatis, a side surface of the chip carrier (pack-
`Typically additional sets of such traces and wire bonds are
`present, but these are not shown here for simplicity. Alter-
`age) is mounted directly on the surface of the PCB.
`The conventional micro-machinedsilicon accelerometer
`native bonding methods include TAB, flip chip, and others
`knownin the art. Also shown are conductive traces 48 to the
`chip, packaged with signal conditioning circuitry (e.g., an
`left of ASIC 16, which penetrate through the multi-layers of
`ASIC) in e.g. a multi-layer ceramic chip carrier, may be
`chip carrier 44, and emergeat the side surface (here shown
`hermetically sealed with an e.g. Kovar lid. Electrical con-
`as a lowerportion) of chip carrier 44 at solder pads 64a,..
`nections are contained within the layers of the ceramic chip.
`., 64
`carrier and terminated at the bottom (actually the side
`Both ASIC 16 and accelerometer chip 14 are housed in
`surface) of the chip carrier.
`stepped recess 54 in chip carrier 44.
`Thefiexibility of types of terminations from the ceramic
`Across section through line B—BofFIG. 2a is shown in
`chip package offer a variety of mounting schemes to the
`FIG.2b, showing the chip carrier 44, recess 54, chips 14 and
`supporting PCB, such as leadless surface mount, or formed
`16 and the Kovar cap 60 which seals the chip carrier package
`metal leads such as J-formed leads, S-formed leads, gull
`44. Kovar cap 60 has formed onits inner surface a conven-
`wings, side brazed with standoff leads, and others.
`tional solder sealing ring of tin and gold which mates to
`Alternatively,
`the accelerometer chip is packaged in a
`corresponding ring 72 of layered, tungsten,nickel, and gold
`plastic SIP (single in-line package) chip package mounted
`on chip package 44. Also shown are wire bonds 50, 52. The
`on a lead frame, with the side of the package being mounted
`ASIC 16 is considerably thinner than the accelerometer chip
`to the PCB and the leads connecting to the PCB.
`14 and hence is housed in a shallower portion of stepped
`Thus in accordance with the invention a low cost, com-
`recess 54, so as to achieve coplanarity for easier wire
`pact, and highly reliable mounting is provided for an accel-
`bonding. (This detail is notcritical.)
`erometer chip.
`FIG. 2c shows a “bottom” view of a chip carrier 44 i.e.
`showsthe side surface 68 of chip carrier 44 in FIG. 2a which
`is in intimate contact with PCB 42 as shown in FIG.2a. Here
`the PCB 42 is not shown forillustrative purposes. Mechani-
`cal mounting solder pads 66a, 66b on the side surface 68 of
`chip carrier 44 extend the length of each end of the side
`surface 68 to achieve firm mechanical mounting to the
`underlying PCB 42. Pads 66a, 66b are optional. The elec-
`trical and mechanical contact solder pads 64a, 64f (and
`others not marked by reference numbers) are, as described
`above,in electrical contact with the accelerometer chip 14
`and the circuitry of ASIC 16.
`FIG. 2d showsa side view of chip carrier 44 with the cap
`60 in place and again showingthe actual solderfillet 62a to
`solder pad 66a as in FIG. 2a. Dimensionsa, b and c in FIGS.
`2a, 2d are in one embodimentrespectively 0.5 inch, 0.125
`inch, and 0.29 inch. These dimensionsareillustrative only,
`as are the materials described herein,and are not intended to
`be limiting.
`The accelerometer chip 14 used in accordance with the
`invention may be conventional (piezo-electric, piezoresis-
`tive, capacitive) or of other types. The ASIC chip 16 of
`course is dispensed with if its functions are integrated on
`accelerometer chip 14. Advantageously the structure in
`accordance with the invention havingits axis of sensitivity
`being parallel to the plane of the PCB reduces the overall
`size of the package, reduces the number of components,
`makes fabrication easier, and eliminates interconnections
`(electrical and mechanical) which are typically a source of
`failures. Thusreliability is increased while cost of materials
`and assembly is decreased over the prior art. As described
`above, the actual connections to the printed circuit board
`may be of various types in addition to the leadless surface
`mounttype shown in FIGS. 2a and 2d. For instance, formed
`metal leads of various types could be attached to pads 64a,
`..., 64f for contact to PCB 42.
`In an alternate embodiment, accelerometer chip and sig-
`nal conditioning chip 16 are stacked up and connected in a
`flip-chip configuration, then held in chip carrier 44.
`Another embodiment shownin FIG. 3 in cross section in
`a side view has accelerometer chip 14 on support (die attach
`lead frame portion) 74 mounted in an SIP plastic chip carrier
`76. The side surface of chip carrier 76 is then mounted to
`PCB 82. Conductor 78 from chip 14 contacts lead 80 other
`leads and conductors (not shown) which connects to PCB
`
`FIG, 2a showsa front view of a accelerometer chip 14 and
`a signal conditioning (e.g. an ASIC) chip 16 housed in a
`multi-layer ceramic chip carrier 44 of the type well known
`in the art. Conventional accelerometer chip 14 and ASIC
`chip 16 are housed in a recess 54 which is stepped to
`accommodate the different thicknesses of these two devices.
`In FIG. 2a, the lid which would normally seal the chip
`carrier 44 is shown removed. Chip carrier 44 is mounted on
`a conventional PCB 42 by solder pads 64a, ... , 64f (only
`a portion of which is shown in FIG. 2a) each of which is
`formed on the underside of chip carrier 44 and thus provide
`a mechanical and electrical attachment to corresponding
`metallized areas on the printed circuit board 42. The actual
`fillets of the two resulting solder bonds are designated by
`reference number62a, 62b. PCB 42 is the PCB convention-
`ally present in vehicles, as described above, for mechani-
`cally supporting and electrically connecting to an acceler-
`ometer chip.
`PCB 42 is conventionally G10/FR-4 material, but may be
`other materials as are well knownin the art. In this view of
`FIG.2a, the axis of acceleration is into or out of the page,
`and hence is notillustrated. The principal surface of chip 14
`is illustrated with the conventional protective cap installed.
`Accelerometer chip 14 is connected by wire bonds 52 to
`conductive traces 18 formed on the exposed surface of the
`ceramic chip carrier 44 and hence connects via wire bond 50
`(and others, not shown) to the ASIC chip 16. (Accelerometer
`chip 14 also may have one or moreelectrical connections
`direct to the outside of chip package 44 via traces 18).
`
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`5,503,016
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`3
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`5
`10. A method of mounting a transducer on a circuit board,
`82. Here lead 80 is part of the lead frame on which chip 14
`(and a signal conditioning chip, not shown, if needed) is
`comprising the steps of:
`mounted. Alternatively, the lead frame terminations (leads)
`providing a transducer having an axis of sensitivity per-
`are staggered for additional support (not shown).
`pendicular to a principal surface of the transducer;
`In accordance with the invention not only an accelerom-
`providing a package having conductive traces extending
`on a side surface of the package;
`eter may be so mounted, but so may other force or other
`sensors (transducers) which haveasingle axis of sensitivity.
`fixing the transducer in the package, so that the axis of
`sensitivity lies parallel to a plane defined by the side
`This disclosure is illustrative and not limiting; further
`surface of the package and the principal surface of the
`modifications will be apparent to oneof ordinary skill in the
`transducer is perpendicular to the side surface of the
`art in light of this disclosure and are intended to fall within
`package; and
`the scope of the appended claims.
`I claim:
`mounting the package on a surface of the circuit board,
`1. A transducer assembly comprising:
`the side surface of the package being in direct contact
`with the surface of the circuit board, and the conductive
`a transducer chip having an axisofsensitivity, the axis of
`traces beingin electrical contact with associated traces
`sensitivity being perpendicular to a principal surface of
`on the surface ofthe circuit board.
`the transducer chip;
`11. A transducer assembly for mounting onacircuit board
`a chip package housing the transducer chip; and
`comprising:
`acircuit board, wherein a side surface ofthe chip package
`a transducer chip having an axis of sensitivity perpen-
`is mounted directly to a surface ofthe circuit board, the
`dicular to a principal surface thereof;
`side surface of the package being perpendicular to the
`a chip package in which the transducerchipis affixed, the
`principal surface ofthe transducer chip,so that the axis
`chip package having a side surface lying in a plane
`of sensitivity lies parallel to a plane defined by the
`surface of the circuit board.
`parallel to the axis of sensitivity and being perpendicu-
`lar to the principal surface of the transducer chip; and
`2. The assembly of claim 1, wherein the transducer chip
`is a micro-machined accelerometer.
`a plurality of attachmentpoints on theside surface of the
`3. The assembly of claim 1 wherein the chip package is a
`chip package adapted to mounting the side surface
`multi-layer ceramic chip carrier defining an interior recess in
`directly to the circuit board.
`12. The assembly of claim 11, wherein the transducer chip
`which the transducerchip is fixed.
`is a micro-machined accelerometer.
`4. The assembly of claim 1, further comprising a plurality
`of conductive elements connected to the transducer chip and
`13. The assembly of claim 11, wherein the chip package
`extending throughthe chip packageto a side surface thereof
`is a multi-layer ceramic chip carrier defining an interior
`perpendicular to the principal surface of the transducer chip,
`recess in which the transducerchipis fixed.
`the conductive elements connecting to contact pads on the
`14. The assembly of claim 11, further comprising a
`circuit board.
`plurality of conductive elements contacting the transducer
`chip and extending through the chip package to the side
`5. The assembly of claim 4, wherein the conductive
`elements each include a conductive pad formed on the side
`surface thereof, the conductive elements adapted to contact-
`surface of the package.
`ing contact pads on the circuit board.
`6. The assembly of claim 1, further comprisinga plurality
`15, The assembly of claim 14, wherein the conductive
`elements each include a conductive pad formed onthe side
`of attachment pads formed on the side surface of the
`package,the attachmentpads being bonded to the surface of
`surface of the chip package.
`the circuit board.
`16. The assembly of claim 13, further comprising a lid
`located over the recess and attached to the chip package.
`7. The assembly of claim 3, further comprising a lid
`located over the recess and attached to the package.
`17. The assembly of claim 13, further comprising an
`8. The assembly of claim 3, further comprising an inte-
`integrated circuit mountedin the recess in the chip package,
`the integrated circuit being electrically connected to the
`grated circuit mounted in the recess in the package, the
`integrated circuit being electrically connected to the trans-
`transducer chip.
`18. The assembly of claim 11, wherein the chip package
`ducerchip.
`is a plastic lead frame package.
`9. The assembly of claim 1, wherein the chip package is
`a plastic lead frame package in which the transducer chip is
`affixed.
`
`*
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