WO2009017693A1

WO2009017693A1 - Low cost slot card crash sensor

Info

Publication number: WO2009017693A1
Application number: PCT/US2008/009086
Authority: WO
Inventors: Chean Fay Cheng; Aik Huang Chan; Sze Lam Chua; Kai Chek Boh
Original assignee: Delphi Technologies, Inc.
Priority date: 2007-07-26
Filing date: 2008-07-25
Publication date: 2009-02-05

Abstract

Inexpensive yet robust sensor packaging for automotive applications employs a skeletal (with minimum layers of material) construct. As a result, non-traditional, less expensive materials are employed and assembly process steps are simplified or eliminated, effecting cost reduction and enhancing design flexibility. A 'slot card' sensor design can employ a conventional wiring harness connector body as a mounting point to enhance reliability and performance.

Description

LOW COST SLOT CARD CRASH SENSOR

RELATED APPLICATION

[0001] The present application claims the benefit of U.S. Provisional Application No.: U.S.S.N. 60/962,103, entitled "LOW COST MASS MARKET SLOT CARD (LCMM-SC) CRASH SENSOR" filed 26 July 2007, and is related to a PCT Application identified as Applicant Docket No.: DP-317019, entitled "AUTOMOTIVE CRASH SENSOR AND METHOD" filed on even date herewith and assigned to a common assignee of interest.

TECHNICAL FIELD

[0002] The present invention relates generally to the packaging and mounting of transducers within a host system such as a motor vehicle. More particularly, the present invention relates to a low cost crash sensor applicable for automotive passive restraint systems.

BACKGROUND OF THE INVENTION

[0003] The present invention relates, in its preferred application, to crash sensor systems adapted for installation on an automotive vehicle equipped with a passive occupant restraint device such as an inflatable air bag or seat belt tensioner. When such a vehicle is subject to deceleration of the kind accompanying a crash, and the crash sensor triggers, the air bag is inflated to provide a protective cushion for the occupant or the seat belt is pulled back against the occupant holding him in a safe position. [0004] Crash sensing switches traditionally employed in automotive applications traditionally include a ball or mass disposed within a sealed tube to bridge a pair of electrical contacts. During a crash event, the inertia of the ball causes it to move towards the contacts. For the ball to reach the contacts, air must flow between the ball and the tube. Viscosity of the air in combination with inertia of the air causes a pressure differential that opposes ball movement through the tube. It is believed that in most vehicle crashes the viscous contribution to the pressure differential predominates over the inertial contribution. Viscous flow is proportional to the pressure differential which is proportional to the product of the mass of the ball and the deceleration of the crash sensing switch. The proportionality of viscous flow to deceleration and the requirement that the ball move a predetermined distance to bridge the contacts causes the current production crash sensing switch to be an acceleration integrator that completes the firing circuit upon a predetermined vehicular velocity change. A permanent magnet in the commercial production crash sensing switch causes a bias force that urges the ball toward a normal resting position away from the electrical contacts. The bias force also causes the vehicular velocity change required for a switch closure to increase with the direction of the crash.

[0005] In another known crash sensing switch having a ball and a tube a spring provides the bias force. A permanent magnet has the advantage of simplicity but the cost is significant and its large size increases the size of the crash sensing switch. Another difference is that the magnetic force decreases as the ball moves toward the electrical contacts whereas the spring force increases. In most designs the bias force is small therefore sensors with spring bias and sensors with magnetic bias perform similarly.

[0006] It has recently become common to place an electronic crash sensing switch in or near the passenger compartment of a vehicle. These crash sensing switches are known as "single point crash sensors". This design is advantageous because it can eliminate the wiring and assembly time required when the crash sensing switch is located in the forward part of the vehicle. [0007] The present invention is an improved sensor packaging design which overcomes many of the shortcomings of prior art approaches. Specifically, the present invention provides what is needed in the industry, a robust, low cost packaging design which tolerates the use of non-traditional, low cost materials while maintaining precision of alignment and system integrity under a full range of harsh operating conditions. SUMMARY OF THE INVENTION

[0008] Generally, the present invention fulfills the forgoing needs by providing, in one aspect thereof, an extremely low cost sensor packaging arrangement. [0009] An object of the present invention is to provide a slot card sensor assembly which includes a substantially planar substrate which has its surface bifurcated into a circuit component mounting surface portion and a contact pad surface portion. A plurality of electrical circuit components, including a sensing element digitizing integrated circuit, are mounted on the circuit component mounting surface portion, and a plurality of contact pads are mounted on the contact pad mounting surface portion. Finally, a layer of electrically insulating over molding material is provided to conform with and cover the component mounting surface portion and simultaneously encase the circuit components, while exposing the contact pads.

[0010] According to another aspect of the invention, various means are provided for fixedly mounting the slot card sensor assembly to an associated automobile. This has the advantage of providing a robust, flexible mounting system.

[0011] According to another aspect of the invention, the mounting means comprises a female connector assembly which is adapted to be configured at a terminus of an associated automobile wiring harness. The female connector assembly comprises a connector body which defines a cavity therein with an opening configured for aligned slip-fit engagement with the outer peripheral surface of the over molding material, and a plurality of electrical contacts which are insulatively carried within the connector body and arranged to electrically engage the contact pads upon insertion of the sensor subassembly within the sensor housing. Furthermore, the connector body includes a mounting retention feature, such as a fastener receiving passageway, a spring retainer or an adhesive, integrally formed therein or carried thereon. This arrangement has the advantage of employing the structural integrity of a host automobile wiring harness connector body to house and protect a skeletal structured slot card sensor subassembly and to enhance the performance and operation thereof. [0012] These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0014] FIG. 1, is a perspective view of the substrate portion of the preferred embodiment of the present invention, wherein the substrate is populated with surface mount technology circuit components including an accelerometer and an

ASIC, as bare dies;

[0015] FIG. 2, is a perspective view of the substrate of Figure 1, with a conforming layer of electrically insulating overmolding material covering the component mounting surface of the substrate to fully encase the circuit components and to support a resilient peripheral seal;

[0016] FIG. 3, is an exploded, peripheral view of the slot card sensor assembly of Figure 2, aligned for installation within a mating connector assembly;

[0017] FIG. 4, is a peripheral view of the slot card sensor assembly fully installed within the mating connector assembly of Figure 3; and

[0018] FIG. 5, is a cross-sectional plan view of the assembled slot card sensor assembly and mating connector assembly of Figure 4.

[0019] Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS

[0020] The manufacturing of crash sensors for automotive applications continues to becoming more and more competitive in terms of cost and technology. The current predominant packaging technology used widely in the market consists of a packaged sensing element and an application specific integrated circuit (ASIC) in a semiconductor packaging form (for example, small outline integrated circuit or SOIC) mounted on a printed circuit board which has the supporting discrete components surface mounted. The populated printed circuit board is then secured with adhesive in a housing to protect the circuit components with either a closure member or potting material. The housing includes means for mounting such as a bushing. Although finding previous commercial success, this form of packaging is not deemed to be sufficiently cost effective for future applications.

[0021] An essential idea behind the present invention is to provide a packaging method that is skeletal (with minimal layers of material) and yet proven to be robust to ensure that it can meet the performance and endurance specifications of the mass market. The associated assembly processes will also be reduced inasmuch as current housing and encapsulation methods are no longer required. Products embodying the present invention significantly reduce both production and shipping costs and result in improved products of reduced weight and size as well as optimized dimensional proportions.

[0022] The present invention describes a design and manufacturing process that overcomes the inherent cost limitations (such as excessive housing material costs and complex manufacturing process costs) for previous sensor designs by using minimal packaging material and simplified processes. The resulting end product will be small, light weight, cost competitive and significantly easy to assemble within a host vehicle.

[0023] For purposes of illustration, the present invention is implemented within a specific type of sensor, specifically a low cost slot card crash sensor (LCMM - CS) suitable for use with automobile air bag or seatbelt cinching safety systems. [0024] Referring to Figure 1, a generally rectangular, planer substrate 10 is bifurcated into a first or circuit component mounting surface portion 12 and a second or contact pad mounting surface portion 14. A plurality of circuit components, preferably surface mount technology (SMT) components, are first surface mounted on to the circuit component mounting surface portion 12 of the substrate 10. Included in the circuit components are a sensing element, such as an accelerometer 16, a sensing element digitizing integrated circuit embodied as an ASIC 18 and a number of additional discrete components 20. Preferably, the accelerometer 16 and ASIC 18 are employed as bare dies and are interconnected to conductive traces (not illustrated) on the substrate 10 by wire bonding. Alternatively, both the accelerometer 16 and ASIC 18 can be configured as packaged integrated circuits (ICs), thereby eliminating the need for wire bonding and wherein all circuit components are surface mounted. Such ICs would be reflow connected as with the other SMT components. [0025] Components that can be overmolded include ASICs of the digital and/or analog/digital mixed signal type devices. ASICs can be prepackaged (i.e. previously overmolded) of used bare die in the over molding operation. Inertial sensors for sensing linear acceleration or rotational velocity would also be included in the overmolding process. These sensors are typically fabricated using one of several processes for creating Micro Electrical Mechanical Systems (MEMS) devices in silicon. Examples of the manufacturing processes for MEMS include but are not limited to bulk micromachining techniques and surface micromachining techniques. The MEMS devices could be provided as bare silicon devices, or may be prepackaged like the ASICs in a previous overmolding process. In addition to the silicon devices mentioned, discrete resistor and capacitor elements can also be included in the assembly that is overmolded.

[0026] A plurality of contact pads 22 are first surface mounted to the contact pad mounting portion 14 of the substrate 10. Each contact pad 22 is electrically in-circuit with the circuit components via conductive traces (not illustrated) to form a crash sensor circuit. Although all of the circuit components and contact pads 22 are illustrated as arranged on the upper surface of the substrate 10, it is contemplated that they could be arranged on both the upper and lower surfaces of the substrate 10 as well as embedded within the substrate 10. The contact pads 22 can also be applied to an inner edge portion 24 of the substrate 10. Figure 1, thus illustrates a completed crash circuit subassembly 26. [0027] The substrate 10 can be formed of ceramic, as a printed circuit board (PCB) or other suitable configuration.

[0028] Referring to Figure 2, a slot card subassembly 28 is illustrated. Following mounting of the circuit components to the substrate 10, as depicted in Figure 1, the circuit component mounting portion 12 of the substrate 10 is over- molded by a relatively thin layer 30 of electrically insulating material. The contact pad mounting portion 14 of the substrate 10, as well as the contact pads 22 remain uncovered. The layer 30 serves to provide a thin "skeletal" structural support of circuit subassembly 26, to isolate and seal the circuit components from atmosphere borne contaminates and to mitigate thermal stresses and solder joint fatigue caused in part by large differences in the differential coefficients of thermal expansion (CTE) that exist between the substrate 10 and the surface mount device materials.

[0029] The thin rigid shell 30 formed by the overmolding material is laterally elongated along an axis parallel to the plane defined by the substrate 10 and defines an outer peripheral surface including flat, parallel upper and lower wall surfaces 32 and 34, respectively, and curved, opposed left and right side wall surfaces 36 and 38, respectively. The shell 30 is insert injection molded from relatively inexpensive thermoplastic resin material such as polyvinyl chloride (PVC). A resilient polymer O-ring seal 40 is affixed to the peripheral outer circumferential surface of shell 30.

[0030] The inner end portion (i.e., the left portion intermediate the O-ring seal 40 and the contact pads 22) of the shell 30 forms parallel guide slots 42 in upper wall surface 32. Similar guide slots (not illustrated) can be formed in the lower wall surface 42. The guide slots 42 open upwardly and are elongated along the axis of insertion of sensor subassembly 28 within the mating connector body (Refer Figure 3). The inner end portion of the shell 30 also forms opposed ramped engagement surfaces 44 extending upwardly from the upper wall surface 32 and the lower wall surface 34. The outer end portion of the shell 30 forms laterally opposed finger/tool engagement surfaces 46 to serve as an aide in installing and removing the sensor subassembly 28 from the mating connector body.

[0031] After initial fabrication of the slot card sensor subassembly 28, it can be applied within virtually any automobile configuration. Groups of such subassemblies 28 are thereafter sent to trim (i.e., programming of register/memory with product/application specific information) and test via the exposed gold contact pads 22. These process steps complete the LCMM SC sensor module 28 assembly.

[0032] Referring to Figures 3 and 4, a connector assembly 48 configured to mate with slot card sensor subassembly 28 is illustrated prior to insertion (Figure 3) and after insertion (Figure 4). The connector assembly 48 serves to electrically interconnect the sensor subassembly 28 with a host vehicle electrical system, including power source, control logic and safety devices. Preferably, the connector assembly 48 is a terminus of a vehicle wiring harness 50, wherein at least a pair of insulated wires 52 and associated strain relief devices 54 extend within a female connector body 56. The connector body 56 also defines a mounting retention feature for affixing the fully assembled sensor subassembly 28 and connector assembly 48 depicted in Figure 4. The mounting can be accomplished by threaded fasteners, clips or adhesive. Dressing of the harness 50 is first affected on the host vehicle. The connector body 56 is then secured to the desired location of the vehicle via screw mounting, adhesive mounting or clip mounting. The LCMM SC is then slotted into the connector assembly 48. Within the connector body 56, electrical contacts, such as tulip connections, arranged in-circuit with harness wires 52 are used to engage the gold contact pads 22 on the LCMM SC to complete the circuit. When fully assembled, as illustrated in Figure 4, ramped engagement surfaces interlock the LCMM SC substantially entirely within the connector body 56 and the O-ring will provide a seal between the LCMM SC and the connector body 56. [0033] Referring to Figures 3 - 5, a typical installation of a slot card crash sensor assembly 58 upon a designated mounting surface 60 location of a host automobile 62 is depicted. Initially, the connector assembly 48, along with the remainder of the wiring harness 50 is dresses and mounted to the automobile 58. The female connector body 56 includes a passage 64 extending entirely there through. A bushing 66 constructed of electrically conductive material is insert molded or press fit within through passage and preferably extends entirely there through whereby its end surfaces are substantially flush with adjacent surface portions of the outer surfaces of the female connector body. The bushing has a connector lead 68 extending within the connector body 56 from the bushing 66 to an associated connector (not illustrated) to establish a ground path from one of the contact pads 22 to the automobile 62 body.

[0034] The connector assembly 48 is affixed to the automobile 62 by a bolt 70 extending through the bushing 66 and a registering hole 72 in the automobile 62 secured by a nut 74. Upon assembly, the bolt 70 compressively loads the bushing 66 against the surface location 60. The bushing is formed of material having substantially a higher modulus of elasticity than the material forming the connector body 56, thus preventing creep or distortion over time, to ensure precise positioning of sensor subassembly 28. Furthermore, the connector body 56 has a locating tab 76 integrally formed and extending from the lower wall thereof into a registering hole 78 in the vehicle 62 to ensure precisely fixed positioning of the sensor assembly 58 with respect to the vehicle 62. [0035] Strain relief devices 54 are provided at the lead-in of each wire 52 to also prevent wire chaffing and enhance sealing. Strain relief devices 54 can be formed of resilient material such as plastic, rubber, or the like and can be pressed in place or insert molded within the connector body 56. [0036] The connector body 56 defines a substantially closed cavity 80 therein emerging through a shaped opening 82 in the leading edge 84. An opposed pair of blind recesses 86 opening within the cavity 80 are configured to snap-engage the cooperating ramped engagement surfaces 44 of slot card sensor subassembly 28 to hold the sensor assembly together. The opening 82 is horizontally elongated and has a vertical centerline which intersects the vertical axis of the through passage 64. When the sensor subassembly 28 is installed within the cavity 80 of the connector body 56, the applied forces are directed substantially through the fastening axis to ensure that the final assembly 58 remains properly aligned with respect to the host automobile 62. As the opening 82 transitions into the cavity 80, the inner walls are tapered to ensure compression of the CD- ring seal 40 to affect hermetic sealing of the cavity 80. [0037] Each wire 52 terminates within the connector body 56 in a resilient connector 88. The connectors 88 are laterally arranged to individually register with an associated contact pad 22 on the substrate 10 to ensure reliable electrical interconnection there between.

[0038] Guide slots 42 register with cooperating guide surfaces (not illustrated) integrally formed on interior walls of connector body 56 forming cavity 80. The guide slots 42 and cooperating guide surfaces ensure that the sensor subassembly 28 remains in register with the connector body 56 during the entire insertion process.

[0039] The over molding material 30 includes outwardly directed integral walls 90 forming an inwardly directed abutment surface 92 which provides a sealing surface acting in cooperation with the O-ring seal 40 and also abuts the leading edge 84 of the connector body 56 to define an insertion stop for the sensor subassembly 28.

[0040] The over molding material 30 is formed having a nominal thickness (designated "T-om") and the walls of the connector body 56 have a nominal thickness (designated "T-cb"). Because the sensor subassembly 28 is precisely nestingly received within the connector body 56, the thickness T-om is minimalized and most of the structural support of the crash circuit subassembly 26 is provided by the connector body, T-cb » T-om. Furthermore, the over molding material 30 can be formed from material having a higher modulus of elasticity, which better accommodates the thermal expansion properties of the substrate 10 and the components 16, 18 and 20 mounted thereon. [0041] It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art. [0042] Furthermore, it is contemplated that many alternative, common inexpensive materials can be employed to construct the basis constituent components. Accordingly, the forgoing is not to be construed in a limiting sense.

[0043] The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation. [0044] Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, the bolt 70 and nut 74 can be replaced by a spring clip element or an adhesive material layer to retain the crash sensor assembly in its design intent position. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for illustrative purposes and convenience and are not in any way limiting, the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents, may be practiced otherwise than is specifically described.

Claims

1. A slot card sensor assembly comprising: a subassembly, including: a substantially planar substrate having a circuit component mounting surface portion and a contact pad mounting surface portion; a plurality of circuit components, including a sensing element digitizing integrated circuit, mounted on said component mounting surface portion; a plurality of contact pads mounted on said contact pad mounting surface portion and in-circuit with said circuit components; and a layer of electrically insulating overmolding material configured to conform with and cover said component mounting surface portion and encase said circuit components, while exposing said contact pads.

2. The slot card sensor assembly of claim 1, further comprising a resilient seal carried with and extending peripherally about the outer circumferential surface of said overmolding material.

3. The slot card sensor assembly of claim 1, wherein said sensing element digitizing integrated circuit comprises an accelerometer.

4. The slot card sensor assembly of claim 1, wherein said contact pads are formed of gold material.

5. The slot card sensor assembly of claim 1, further comprising means for fixedly mounting said slot card sensor assembly to an associated automobile in a predetermined orientation.

6. The slot card sensor assembly of claim 5, wherein said means for fixedly mounting said slot card sensor assembly comprises an adhesive material.

7. The slot card sensor assembly of claim 5, wherein said means for fixedly mounting said slot card sensor assembly comprises a retaining clip.

8. The slot card sensor assembly of claim 5, wherein said means for fixedly mounting said slot card sensor assembly comprises a female connector assembly adapted to be configured at a terminus of an associated wiring harness.

9. The slot card sensor assembly of claim 8, wherein said female connector assembly comprises: a connector body defining a cavity therein with an opening configured for registered slip-fit engagement with outer peripheral surfaces of said over molding material; and a plurality of electrical contacts insulatively carried within said connector body and arranged to electrically engage said contact pads upon insertion of said subassembly within said connector body, wherein said connector body includes a mounting retention feature integrally formed therein.

10. The slot card sensor assembly of claim 9, wherein said mounting retention feature comprises a bushing disposed within a through passage formed in said connector body along an axis substantially normal to a plane defined by said substrate, said bushing configured to receive a fastener therein for fixedly mounting said slot card sensor assembly to a host automobile.

11. The slot card sensor assembly of claim 10, wherein said bushing extends entirely through said through passage.

12. The slot card sensor assembly of claim 10, wherein said bushing is formed of material having a substantially higher modulus of elasticity than the characteristic modulus of elasticity of material forming said connector body.

13. The slot card sensor assembly of claim 10, wherein said bushing is formed of electrically conductive material in-circuit with at least one of said electrical contacts and operative to establish an electrical ground path to an associated host vehicle body.

14. The slot card sensor assembly of claim 10, wherein said connector body opening is elongated and has an axis of symmetry which approximately intersects said through passage axis.

15. The slot card sensor assembly of claim 9, wherein said sensor subassembly is adapted for assembly with said connector body by insertion through said cavity opening to effect engagement of associated pairs of contacts and contact pads, wherein said substrate and circuit components are substantially fully disposed within said connector body cavity.

16. The slot card sensor assembly of claim 9, wherein said overmolding material defines an integral finger hold surface for enabling installation and removal of said sensor subassembly from said connector body.

17. The slot card sensor assembly of claim 8, wherein said overmolding material has a characteristic modulus of elasticity which is substantially greater than the characteristic modulus of elasticity of material forming said connector body.

18. The slot card sensor assembly of claim 8, wherein overmolding material has a thickness which is substantially less than the nominal thickness of material forming said connector body.

19. The slot card sensor assembly of claim 8, further comprising cooperating snap-acting engagement features integrally formed on an exterior surface portion of said overmolding material and an interior portion of said connector body defining said cavity operative, upon insertion, to positively engage said subassembly within said connector body.

20. The slot card sensor assembly of claim 8, further comprising cooperating guide features substantially aligned with an insertion axis of said overmolding material and said connector body to maintain alignment of said subassembly and female connector assembly throughout the insertion process..

21. The slot card sensor assembly of claim 8, further comprising means operative to positionally index said female connector assembly with respect to a mounting location of an associated automobile.

22. The slot card sensor assembly of claim 21, wherein said indexing means comprises an external protuberance integrally formed on an element of said female connector assembly.

23. The slot card sensor assembly of claim 1, wherein said sensing element digitizing integrated circuit functions as a vehicle crash sensor.