United States Patent [191
`Koen
`
`(54) VERTICALLY MOUNTED
`ACCELEROMETER CHIP
`
`(75)
`
`Inventor: Edward F. Koen, Danville, Calif.
`
`[73] Assignee: IC Sensors, Inc., Milpitas, Calif.
`
`(21) Appl. No.: 189,948
`
`Feb. 1, 1994
`
`[22) Filed:
`Int. Cl.6
`.........................••............................. GOIP 1/02
`[51]
`[52) U.S. Cl ................................................................. 73/493
`[58] F ield of Search .............................. 73/493, 43 1, 777,
`731756, 866.5, 204.22, 856; 174/260
`
`[56]
`
`References Cited
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005503016A
`5,503,016
`[111 Patent Number:
`[45] Date of Patent:
`Apr. 2, 1996
`
`2720484A1 1111977 Germany .
`111985
`Japan .
`60-12750
`63-90774
`4/1988
`Japan .
`W091Jll722
`8/1991 W1PO.
`
`OTHER PUBLICATIONS
`
`"NEC's Automative Electronic Control Modules", NEC,
`sales brochure, date unknown.
`"Airbags Boom When IC Accelerometer Sees 50 G", by
`Frank Goodenough, Electronic Design, Aug. 8, 1991.
`
`Primary Examiner-Hezron E. Williams
`Assistant Examiner-Christine K. Oda
`Attorney, Agent, or Firm-Skjerven, Morrill, MacPherson,
`Franklin and Friel; Norman R. Klivans
`
`U.S. PA1ENT DOCUMENTS
`
`(57)
`
`ABSTRACT
`
`4,700,973
`5,012,316
`5,043,791
`5,044,201
`5,060,504
`5,109,341
`5,163,325
`5,221,400
`5,233,871
`5,233,873
`5,233,874
`5,241,861
`5,249,465
`5,261,694
`5,269,187
`5,394,326
`
`10/1987 Gademann ................................ 73/493
`3/1991 Silvermint ............................... 257/417
`8/1991 Stokes et al .............................. 357n0
`9/1991 Farace et al .•............................ 73/503
`10/1991 White et al . .............................. 73/1 D
`4/1992 Blackburn et al. ..................... 180/274
`ll/1992 White et al ........................... 73/517 R
`6/1993 Staller cl al. ........................... 156/292
`8/1993 Schwarz et al .
`.......................... 73/493
`8/1993 Mozgowiec ............................... 73/493
`8/1993 Putty et al .......................... 73/517 AV
`9/1993 Hulsing, n ................................ 73/505
`10/1993 Bennett et al. ........................... 73/510
`1111993 White et al . ............................ 280n35
`12/1993 Hanson ..................................... 73/495
`2/1995 Liu ..................................... 364/424.05
`
`FOREIGN PATENT DOCUMENTS
`
`0557917A1
`
`9/1993 European Pat. Off ..
`
`Micro-machined accelerometer chips have a sensitive axis
`perpendicular to the principle surface of the device. In an
`application where the desired sensing direction is in the
`plane of a supporting printed circuit board, the accelerom(cid:173)
`eter cannot be mounted directly on the printed circuit board
`and instead is mounted on a wall perpendicular to the printed
`circuit board. This requirement to wall-mount the sensor is
`eliminated by using an accelerometer chip packaged with a
`signal conditioning circuit in a multi layer ceramic chip
`carrier. Electrical connections are contained within the lay(cid:173)
`ers of the ceramic and terminate at a side surface of the chip
`carrier. Thus the accelerometer chip sits perpendicular to the
`printed circuit board and the ceramic chip carrier is attached
`directly thereto.
`
`18 Claims, 4 Drawing Sheets
`
`72
`
`14
`
`44
`
`8 _j
`
`Apple Inc.
`APL1022
`U.S. Patent No. 9,289,135
`
`001
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 1 of 4
`
`5,503,016
`
`FIG. 1 a
`(Prior Art)
`
`AXIS OF
`ACCEL
`
`FIG. 1 b
`(Prior Art)
`
`002
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 2 of 4
`
`5,503,016
`
`B L
`
`c
`c
`c
`
`c
`c
`c
`
`44
`
`B _j
`
`FIG. 2a
`
`FIG. 2b
`
`003
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 3 of 4
`
`5,503,016
`
`66a
`
`66b
`
`FIG. 2c
`
`44
`
`60
`
`AXIS OF
`ACCEL
`
`...
`
`c
`
`FIG. 2d
`
`004
`
`

`

`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 4 of 4
`
`5,503,016
`
`AXIS OF
`ACCEL
`
`78
`
`FIG. 3
`
`005
`
`

`

`5,503,016
`
`35
`
`40
`
`1
`VERTICALLY MOUNTED
`ACCELEROMETER CHIP
`
`BACKGROUND OF THE INVENTION
`
`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
`5 chip 16 are held on a ceramic substrate 20 fixed inside can
`1. Field of the Invention
`12. Also provided are screws 24a, 24b (and corresponding
`This disclosure relates to sensing variations in velocity
`holes not shown) for securing can 12 to a mounting bracket
`such as in a motor vehicle, and more particularly to a method
`(described below).
`and structure for mounting an accelerometer on a support.
`The electrical conductive leads which connect chips 14
`2. Description of the Prior Art
`10 and 16 to the remainder of the system (the actual connection
`Micro-machined chip accelerometers are well known in
`is not shown for simplicity here) terminate in this case at
`the art. Examples are disclosed in U.S. Pat. No. 5,060,504
`conventional edge clip terminations (pins) 28a, 28b, etc.
`issued Oct. 29, 1991 to White, eta!., U.S. Pat. No. 5,221,400
`These electrically connect to printed circuit board (PCB) 36
`issued Jun. 22, 1993 to Staller, and U.S. Pat. No. 5,233,874
`held by standoffs 38a, 38b on the floor of metal housing 40.
`issued Aug. 10, 1993 to Putty eta!. As is well known, an 15
`To better illustrate the structure of FIG. lA, a side view
`accelerometer is a device which measures acceleration, or
`along line A- A of FIG. 1a is shown in FIG. lb. The lid
`more accurately measures force exerted by a body as a result
`which seals (by a weld) can 12 (omitted from FIG. la) is
`of a change in the velocity of the body. A moving body
`designated by reference number Ui. FIG. 1b also illustrates
`possesses an inertia which tends to resist the change in
`the support structure for the can 12, which is mounted on a
`velocity. It is this resistance to any change in velocity that is
`20 metal base plate 28 with glass to metal seals. Base plate 28
`the source of the force exerted by the moving body. This
`in tum is attached by screws 24a, 24b to a mounting bracket
`force is directly proportional to the acceleration component
`34. Mounting bracket 34 is a robust structure formed for
`in the direction of movement when the moving body is
`instance of metal, plastic or ceramic. The purpose of mount(cid:173)
`accelerated.
`ing bracket 34 is to properly mount can 12 in a vertical
`In a typical micro-machined accelerometer formed of 25 orientation on the sidewall of housing 40. Bracket 34 is held
`silicon (a "chip"), a central, typically spherical or rectangu-
`onto the sidewall by screws, rivets, or other means (not
`lar shaped mass is suspended by one or more microbridges.
`shown). The direction of acceleration is as shown by the
`The bridges arc attached to a supporting substrate which
`arrow labelled "AXIS of ACCEL". Thus the sole purpose of
`circumscribes the mass, with a gap provided therebetween.
`base plate 28 and mounting bracket 34 is to vertically mount
`The mass is supported within and has free movement 30 can 12 so that it is perpendicular to PCB 36. Typically in a
`vehicle, PCB 36 is thereby installed in a plane parallel to that
`relative to the supporting substrate. The individual micro-
`bridges within e.g. each pair of micro-bridges are positioned
`of the surface of the earth.
`As shown, lead 28a (and the other leads 28b, ... , 28g)
`at opposing edges of the mass such that the pair's longitu-
`dina! axis constitutes a common axis across the surface of
`extend from behind metal can 12 (detail not shown for
`the mass.
`simplicity) to connect to electrical connectors on PCB 36.
`The movement of the mass is measured, for instance, by
`PCB 36 provides the connections to the actual air bag firing
`measuring a corresponding change in the output of a Wheat-
`device, typically housed in the steering wheel, whereas the
`stone bridge incorporating beam piezo-resistors formed in
`housing 40 is typically mounted under the dash board or on
`the micro-bridges.
`the floor board of the vehicle. The structure of FIGS. la and
`Typically such micro-machined silicon chip accelerom-
`lb functions satisfactorily. However it has the major disad-
`eters require external circuitry to process the signal output
`vantages of being relatively bulky and expensive due to the
`by the accelerometer, for instance for triggering an automo-
`rather elaborate mounting structure required to rigidly
`bile air bag deployment system. Such accelerometers hence
`mount the accelerometer chip in the desired orientation
`are commonly used in automobiles and other vehicles.
`45 relative to 1) its axis of sensitivity; and 2) the horizontally
`Accelerometers are constrained in that typically a micro-
`mounted PCB 36. Also, the relative complexity of the
`mechanical structure and leads 28 cause reliability prob-
`machined accelerometer as described above has a single axis
`sensitive to acceleration. That is, it can only measure accel-
`!ems.
`eration along a line perpendicular to a plane defined by the
`Analog Devices has disclosed (Electronic Design, Aug. 8,
`principal surface of the chip. The principal surface of the 50 1991, "Airbags Boom When IC Accelerometer Sees 500"
`chip is in the plane of the chips, from which side during
`see FIG. 5) a micro-machined accelerometer chip whose
`fabrication various fabrication steps (masking, etching, etc.)
`mass moves in the plane of the chip. This chip allows the
`are performed. For an automobile airbag system the direc-
`axis of sensitivity to be parallel to the expected acceleration
`lion of acceleration which must be sensed in the event of a
`phenomenon. However, this is a special accelerometer chip
`collision is typically along a line lying in a hori.zontal plane 55 apparently available only from this single supplier.
`(parallel to the ground).
`Thus it would be highly desirable to reduce the cost and
`A typical prior art structure for mounting such a micro-
`increase reliability of mounting accelewmeter chips in an
`machined accelerometer chip is shown in a front view in
`automobile, other vehicle, or other application without the
`FIG. la. Here a conventional metal "can" chip package 12
`need for an expensive and bulky mounting structure, and
`defines a central recess 10 in which are conventionally 60 using a standard accelerometer chip.
`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 65
`such accelerometers, this circuitry is integrated on the accel(cid:173)
`erometer chip itself.
`
`SUMMARY OF THE INVENTION
`In accordance with the invention, an accelerometer chip
`whose sensing direction is conventionalily perpendicular to
`the plane (principal surface) of the chip is housed in a chip
`carrier and mounted directly on the printed circuit board,
`
`006
`
`

`

`5,503,016
`
`5
`
`3
`edge-wise. That is, a side surface of the chip carrier (pack(cid:173)
`age) is mounted directly on the surface of the PCB.
`The conventional micro-machined silicon accelerometer
`chip, packaged with signal conditioning circuitry (e.g., an
`ASIC) in e.g. a multi-layer ceramic chip carrier, may be
`hermetically sealed with an e.g. Kovar lid. Electrical con(cid:173)
`nections are contained within the layers of the ceramic chip·
`carrier and terminated at the bottom (actually the side
`surface) of the chip carrier.
`The flexibility of types of terminations from the ceramic 10
`chip package offer a variety of mounting schemes to the
`supporting PCB, such as leadlcss surface mount, or formed
`metal leads such as J-formed leads, S-formed leads, gull
`wings, side brazed with standoff leads, and others.
`Alternatively, the accelerometer chip is packaged in a
`plastic SIP (single in-line package) chip package mounted
`on a lead frame, with the side of the package being mounted
`to the PCB and the leads connecting to the PCB.
`Thus in accordance with the invention a low cost, com- 20
`pact, and highly reliable mounting is provided for an accel(cid:173)
`erometer chip.
`
`15
`
`4
`'JYpically additional sets of such traces and wire bonds are
`present, but these are not shown here for simplicity. Alter(cid:173)
`native bonding methods include TAB, flip chip, and others
`known in the art. Also shown are conductive traces 48 to the
`left of ASIC 16, which penetrate through the multi-layers of
`chip carrier 44, and emerge at the side surface (here shown
`as a lower portion) of chip carrier 44 at solder pads 64a, ..
`. ' 64f.
`Both ASIC 16 and accelerometer chip 14 are housed in
`stepped recess 54 in chip carrier 44.
`A cross section through line B- B of FIG. 2a is shown in
`FIG. 2b, showing the chip carrier 44, recess 54, chips 14 and
`16 and the Kovar cap 60 which seals the chip carrier package
`44. Kovar cap 60 has formed on its inner surface a conven-
`tiona! solder sealing ring of tin and gold which mates to
`corresponding ring 72 of layered, tungsten, nickel, and gold
`on chip package 44. Also shown are wire bonds 50, 52. The
`ASIC 16 is considerably thinner than the accelerometer chip
`14 and hence is housed in a shallower portion of stepped
`recess 54, so as to achieve coplanarity for easier wire
`bonding. (This detail is not critical.)
`FIG. 2c shows a "bottom" view of a chip carrier 44 i.e.
`shows the 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 for illustrative purposes. Mechani(cid:173)
`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-
`30 trical and mechanical contact solder pads 64a, 64/ (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 shows a side view of chip carrier 44 with the cap
`35 60 in place and again showing the actual solder fillet 62a to
`solder pad 66a as in FIG. 2a. Dimensions a, band c in FIGS.
`2a, 2d are in one embodiment respectively 0.5 inch, 0.125
`inch, and 0.29 inch. These dimensions are illustrative only,
`as are the materials described herein, and are not intended to
`40 be limiting.
`The accelerometer chip 14 used in accordance with the
`invention may be conventional (piezo-electric, piezoresis(cid:173)
`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 having its 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. Thus reliability is increased w.hile 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
`mount type shown in FIGS. 2a and 2d. For instance, formed
`metal leads of various types could be attached to pads 64a,
`... , 64/ for contact to PCB 42.
`In an alternate embodiment, accelewmeter chip and sig(cid:173)
`nal conditioning chip 16 are stacked up and connected in a
`flip-chip configuration, then held in chip carrier 44.
`Another embodiment shown in 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 oontacts lead 80 other
`leads and conductors (not shown) which connects to PCB
`
`25
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1a and FIG. 1b show respectively front and side
`views of a prior art accelerometer mounting structure.
`FIGS. 2a, 2b, 2c and 2d show respectively a front view,
`a cross 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
`FIG. 2a shows a 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 45
`carrier 44 is shown removed. Chip carrier 44 is mounted on
`a conventional PCB 42 by solder pads 64a, .. . , 64/(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 attaclunent to corresponding 50
`metallized areas on the printed circuit board 42. The actual
`fillets of the two resulting solder bonds are designated by
`reference number 62a, 62b. PCB 42 is the PCB convention(cid:173)
`ally present in vehicles, as described above, for mechani(cid:173)
`cally supporting and electrically connecting to an acceler- 55
`ometer chip.
`PCB 42 is conventionally GlO/FR.-4 material, but may be
`other materials as are well known in the art. In this view of
`FIG. 2a, the axis of acceleration is into or out of the page,
`and hence is not illustrated. The principal surface of chip 14 60
`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 SO
`(and others, not shown) to the ASIC chip 16. (Accelerometer 65
`chip 14 also may have one or more electrical connections
`direct to the outside of chip package 44 via traces 18).
`
`007
`
`

`

`5,503,016
`
`5
`82. Here lead 80 is part of the lead frame on which chip 14
`(and a signal conditioning chip, not shown, if needed) is
`mounted. Alternatively, the lead frame terminations (leads)
`are staggered for additional support (not shown).
`In accordance with the invention not only an accelerom- 5
`eter may be so mounted, but so may other force or other
`sensors (transducers) which have a single axis of sensitivity.
`This disclosure is illustrative and not limiting; further
`modifications will be apparent to one of ordinary skill in the
`art in light of this disclosure and are intended to fall within 10
`the scope of the appended claims.
`I claim:
`1. A transducer assembly comprising:
`a transducer chip having an axis of sensitivity, the axis of 15
`sensitivity being perpendicular to a principal surface of
`the transducer chip;
`a chip package housing the transducer chip; and
`a circuit board, wherein a side surface of the chip package
`is mounted directly to a surface of the circuit board, the 20
`side surface of the package being perpendicular to the
`principal surface of the transducer chip, so that the axis
`of sensitivity lies parallel to a plane defined by the
`surface of the circuit board.
`2. The assembly of claim 1, wherein the transducer chip 25
`is a micro-machined accelerometer.
`3. The assembly of claim 1 wherein the chip package is a
`multi-layer ceramic chip carrier defining an interior recess in
`which the transducer chip is fixed.
`4. The assembly of claim 1, further comprising a plurality 30
`of conductive elements connected to the transducer chip and
`extending through the chip package to a side surface thereof
`perpendicular to the principal surface of the transducer chip,
`the conductive elements connecting to contact pads on the
`circuit board.
`5. The assembly of claim 4, wherein the conductive
`elements each include a conductive pad formed on the side
`surface of the package.
`6. The assembly of claim 1, further comprising a plurality
`of attachment pads formed on the side surface of the 40
`package, the attachment pads being bonded to the surface of
`the circuit board.
`7. The assembly of claim 3, further comprising a lid
`located over the recess and attached to the package.
`8. The assembly of claim 3, further comprising an inte- 45
`grated circuit mounted in the recess in the package, the
`integrated circuit being electrically connected to the trans(cid:173)
`ducer chip.
`9. The assembly of claim 1, wherein the chip package is
`a plastic lead frame package in which the transducer chip is 50
`affixed.
`
`6
`10. A method of mounting a transducer on a circuit board,
`comprising the steps of:
`providing a transducer having an axis of sensitivity per(cid:173)
`pendicular to a principal surface of the transducer;
`providing a package having conductive traces extending
`on a side surface of the package;
`fixing the transducer in the package, so that the axis of
`sensitivity lies parallel to a plane defined by the side
`surface of the package and the principal surface of the
`transducer is perpendicular to the side surface of the
`package; and
`mounting the package on a surface of the circuit board,
`the side surface of the package being in direct contact
`with the surface of the circuit board, and the conductive
`traces being in electrical contact with associated traces
`on the surface of the circuit board.
`11. A transducer assembly for mounting on a circuit board
`comprising:
`a transducer chip having an axis of sensitivity perpen(cid:173)
`dicular to a principal surface thereof;
`a chip package in which the transducer chip is affixed, the
`chip package having a side surface lying in a plane
`parallel to the axis of sensitivity and being perpendicu(cid:173)
`lar to the principal surface of the transducer chip; and
`a plurality of attachment points on the side surface of the
`chip package adapted to mounting the side surface
`directly to the circuit board.
`12. The assembly of claim 11, wherein the transducer chip
`is a micro-machined accelerometer.
`13. The assembly of claim 11, wherein the chip package
`is a multi-layer ceramic chip carrier defining an interior
`recess in which the transducer chip is fixed.
`14. The assembly of claim 11, further comprising a
`35 plurality of conductive elements contacting the transducer
`chip and extending through the chip package to the side
`surface thereof, the conductive elements adapted to contact(cid:173)
`ing contact pads on the circuit board.
`15. The assembly of claim 14, wherein the conductive
`elements each include a conductive pad formed on the side
`surface of the chip package.
`16. The assembly of claim 13, further comprising a lid
`located over the recess and attached to the chip package.
`17. The assembly of claim 13, further comprising an
`integrated circuit mounted in the recess in the chip package,
`the integrated circuit being electrically connected to the
`transducer chip.
`18. The assembly of claim 11, wherein the chip package
`is a plastic lead frame package.
`
`* * * * *
`
`008
`
`