`[11] Patent Number:
`[193
`United States Patent
`
`Keen
`[45] Date of Patent:
`Apr. 2, 1996
`
`||||1| llllllll ||| Illll Illll Illll lllll ||||| ||||l Illll ||||| Illlll Ill |l||| ||||
`US005503016A
`
`[54] vnnrrcnrm Moumnn
`ACCELERQMETER C]-[I]?
`
`[75]
`
`Inventor: Edward F. Koen,Danvil1e, Calif.
`
`1I!19?? Germany.
`2120434.“
`I.-‘I935
`Japan.
`60-12750
`53-90774 mass
`Japan.
`W09”11731
`‘"1991
`‘W0-
`
`[73] Assignee:
`
`IC Sensors, Inc., Milpitas. Calif.
`
`OTHER PUBLICATIONS
`
`“NEC‘s Automative Electronic Control Modules", NBC,
`sales brochure, date unknown.
`“Airbags Boom When IC Accelerometer Sees 50 G", by
`Frank Goodenough, Electronic Design, Aug. 8, 1991.
`.
`.
`.
`.
`P””"“’3' E’‘“’’‘‘"‘’’‘H°‘’°“ 5' W‘"““““
`Assisrarzr Examiner—Ch1'istine K. Oda
`Attorney Agent, or Ft'rm—SkjenI'en, Morrill, MacPherson,
`Franklin and Fricl; Norman R. Klivans
`
`[57]
`
`ABSTRACT
`
`Micro-machined accelerometer chips have a sensitive axis
`perpendicular to the principle surface of the device. In an
`application where. Ll1e desired sensing direction is in the
`plane of a supporting printed Cl1'C1.ltl. board, the ‘accelerom-
`eter cannot mounted directly on the printed circuit board
`and instead 18 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. Eiectrical connections are contained within the ]ay-
`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.
`
`[21] APP1' No‘: 189348
`[22]
`Filfidi
`FEE 1; 1994
`Gun, “"2
`__
`[51] km C15
`...................... .. 73.3493
`[52] U.S. Cl.
`[53] Field or Search .............................. 739993. 431, 777,
`73n56’ 8655' 20422’ B56; 1?
`References Cit“!
`
`[56]
`
`'?3t‘493
`
`U.S. PATENT DOCUMENTS
`l0;‘1937 Gademarm .............................. ..
`4-,700,9?3
`3.-‘I991 Silverrnint .......
`5,012,316
`811991 Stokes et al.
`5,043,791
`5,044,201 W199] Farace et al.
`5,060,504 10.5199] White el: al.
`5.109.341 M1992 Blackburn eta}
`5,163,325
`11!I992 White etal.
`5,221,400
`6.-‘I993 Staller ct a1.
`5,233.8".-'1
`8fI993 Schwarz eta].
`5,233,8?3
`811993 Mozgowiec
`5,233,874
`$1993 Putty et a1.
`5,241,861
`9!I993 Hu}sing,]} .... ..
`5,249,465 1011993 Bennett etal.
`.
`5,261,694
`ll.-‘I993 White etal.
`5,269,181 1211993 Hanson ..
`5,394,326
`211995 Liu .... ..
`
`
`
`73553
`73,1 D
`13(};214
`, 731517 R
`1564292
`733493
`733493
`731517 AV
`wsos
`
`73,495
`3:54;-424.05
`
`FOREIGN PATENT DOCUMENTS
`
`DS5'I911A1
`
`911993 European Pat. otr. .
`
`18 Claims, 4 Drawing Sheets
`
`14
`
`44
`
`53
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`U.S. Patent No. 89239
`
`Apple Inc.
`APL1039
`U.S. Patent No. 8,923,941
`
`0001
`
`
`
`U.S. Patent
`
`Apr. 2, 1996
`
`Sheet 1 of 4
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`5,503,016
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`Apr. 2, 1995
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`Sheet 2 of 4
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`Apr. 2, 1996
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`Sheet 3 of 4
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`
`AXIS OF
`ACCEL
`
`FIG. 2c
`
`44
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`60
`
`6a
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`623
`
`66a
`
`FIG. 2d
`
`42
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`0004
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`
`U.S. Patent
`
`Apr. 2, 1995
`
`Sheet 4 of 4
`
`5,503,016
`
`FIG. 3
`
`0005
`
`
`
`5,503,016
`
`1
`VERTICALLY MOUNTED
`ACCELEROIVIETER CHIP
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the 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 ai. 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
`die 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'’). :1 ccrltral, 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—bridges are positioned
`at opposing edges of the mass such that the pair’s longitu-
`dinal axis constitutes a common axis across the surface of
`the mass.
`
`The movement of the mass is measured, for instance, by
`measuring a corresponding change in 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 extcrnal circuitry to process the signal output
`by the accelerometer. for instance for uiggerirtg 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 n1icro-
`rnachined accelerometer as described above has 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 strucnrre for mounting such a n1icro-
`machined accelerometer chip is shown in a front view in
`FIG. In. 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
`moans 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 chip itself.
`
`20
`
`30
`
`35
`
`40
`
`45
`
`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 cart
`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 of the system (the actual connection
`is not shown for simplicity here) terminate in this case at
`conventional edge clip terminations (pins) 28a, 28?), etc.
`These electrically connect to printed circuit board (PCB) 36
`held by standofis 38a, 38b on the floor of metal housing 40.
`To better illustrate the structure of FIG. 1A, a side view
`along line A—A of FIG. 1a is shown in FIG. 1b. The lid
`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 23 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 4|]. Bracket 34 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 ofACCBL”. Thus the sole purpose of
`base plate 23 and mounting bracket 34 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 plane parallel to that
`of the surface of the earth.
`
`. , 28g)
`.
`As shown, lead 28a (and the other leads 28b, .
`extend front behind metal can 12 {detail not shown for
`simplicity] to connect to electrical connectors on PCB 36.
`PCB 3-6 provides the connections to 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. Ia and
`lb functions satisfactorily. However it 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 rnicro-rnachincd 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.
`
`SUMMARY OF 'I'I-IE. INVENTION
`
`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
`
`3
`edgc—wise. That is, a side surface of the chip carrier (pack-
`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 c.g. Kovar lid. Electrical con-
`nections are contained within the layers of the cerarltic chip-
`carrier and terminated at the bottom (actually the side
`surface) of the chip carrier.
`The flexibility of types of terminations from the ceramic
`chip package offer a variety of mounting schemes to the
`supporting PCB, such as leadless surface mount, or formed
`metal leads such as J-formed leads, S-formed leads, gull
`wings, side brazed with standofli 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, oom-
`pact, and highly reliable mounting is provided for an accel-
`erometer chip.
`
`BRIEF DESCRIPTION OF THE. DRAWINGS
`
`FIGS. la 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 (eg. an ASIC} chip 115 housed in a
`multi-layer ceramic chip carrier 44 of the type well known
`in the an. Conventional accelerometer chip 14 and ASIC
`chip 115 are housed in a recess 54 which is stepped to
`accommodate the diflcrent 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
`rnetallized areas on the printed circuit board 42. The actual
`fillets of the two resulting solder bonds are designated by
`reference number 62a, 62!). 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 GIOKFR-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
`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 theASIC chip 16. (Accelerometer
`chip 14 also may have one or more electrical connections
`direct to the outside of chip package 44 via traces 18).
`
`3-5
`
`40
`
`45
`
`SD
`
`55
`
`60
`
`4
`
`Typically additional sets of such traces and wire bonds are
`present, but these are not shown here for simplicity. Alter-
`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, .
`.
`. , 64}:
`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. 25, 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 slnface a conven-
`tional 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 SI], 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. 242. Here
`the PCB 42 is not shown for illustrative purposes. Mechani-
`cal mounting solder pads 66a, 66!; on the side surface 63 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, 66!) 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. 22' shows a side view of chip carrier 44 with the cap
`60 in place and again showing the actual solder fillet 62a to
`solder pad 66a as in FIG. 20. Dimensions 21. b andc 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
`be limiting.
`The accelerometer chip 14 used in accordance with the
`invention may be conventional {piezo-electric, pieeoresis-
`Live, 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 strucuire 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. Tl'1us reliability 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
`mount type shown in FIGS. 2a and 2a‘. For instance, formed
`metal leads of various types could be attached to pads 64a,
`.
`.
`. ,64fforcontact 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 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 contacts lead 80 other
`leads and conductors (not shown) which connects to PCB
`
`0007
`
`0007
`
`
`
`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. Altematively, the lead frame terminations (leads)
`are staggered for additional support (not shown).
`In accordance with the invention not only an accelerom-
`eter may he 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
`the scope of the appended claims.
`1 claim:
`1. A transducer assembly comprising:
`a transducer chip having an axis of sensitivity, the axis of
`sensitivity being perpendicularto 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
`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
`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
`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, fiirther comprising a plurality
`of attachment pads formed on the side surface of the
`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-
`grated circuit mounted in the recess in the package, the
`integrated circuit being electrically connected to the trans-
`ducer chip.
`9. The assembly of claim 1. wherein the chip package is
`a plastic lead frame package in which the transducer chip is
`afiixed.
`
`2|]
`
`30
`
`35
`
`45
`
`SD
`
`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-
`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
`uansducer 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-
`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-
`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 mic1'o~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
`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-
`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 hi 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.
`
`‘F
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`
`0008
`
`0008