Fluid pressure transducer apparatus and method for assembling

• US 6,209,398 B1
• Filed: 09/17/1998
• Issued: 04/03/2001
• Est. Priority Date: 09/18/1998
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Tomlinson, James L., Fowler, John R. Jr., Davis, Gerald F.
• Primary Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US09/156,103
• Time in Patent Office: 929 Days
• Field of Search: 73/756, 73/724, 73/718, 73/727, 73/726, 73/721, 73/720
• US Class Current: 73/724
• CPC Class Codes: G01L 19/0038 being part of the housing other details about the housing G01L19/14
• CPC Class Codes: G01L 19/069 Protection against electromagnetic or electrostatic interferences
• CPC Class Codes: G01L 19/141 Monolithic housings, e.g. molded or one-piece housings

Abstract

A fluid pressure transducer assembly (10) includes an exemplary silicon or ceramic capacitive transducer (22) having a relatively flexible diaphragm portion (22e) mounted on a ceramic substrate or circuit board (18) over a bore (18a) so that the diaphragm is exposed to fluid pressure from a port (12m) received through the bore. The circuit board is received in a plastic housing (12) laterally positioned by guides (12e, 12f) on three height control pins (12d) to vertically position the circuit board a defined, precise distance above a platform (12b) on which a bead of adhesive sealing material has previously been placed, the sealing material having a height greater than the distance between a plane in which the free end of the height control pins lie and a plane in which the top surface of the platform lies. As a result, the circuit board is sealed to the plastic housing through a bead having a uniform, precise height all around its circumference to isolate temperature expansion stresses. According to another feature of the invention an electrically conductive layer (30a) is formed on the top surface of the circuit board beneath the transducer (22) and another electrically conductive layer (30b) is formed on the top surface of the transducer (22) electrically joined together to form an EMI shield.

Claims

1. A fluid pressure transducer assembly comprising

a housing having a bottom wall circumscribed by a platform having a top surface positioned above the bottom wall and lying in a first plane and forming a lower cavity, the platform circumscribed by a sidewall extending upwardly to form an upper cavity,

a plurality of height control pins extending upwardly from the bottom wall to their respective free distal ends lying in a second plane extending parallel to and further removed from the bottom wall than the first plane,

a circuit board received on the height control pins and extending over the platform on all sides thereof,

adhesive sealing material received on the top surface of the platform between the circuit board and the top surface of the platform,

a fluid pressure transducer having a flexible diaphragm portion the transducer sealingly mounted on a selected portion of the circuit board in alignment with a bore formed through the circuit board so that the diaphragm is exposed to fluid pressure received through the bore,

a fluid pressure port extending into the lower cavity, and

an aperture formed in the sidewall for passage of electrical signal leads.

2. A fluid pressure transducer assembly according to claim 1 in which the fluid pressure port extends through the bottom wall.

3. A fluid pressure transducer assembly according to claim 1 in which the fluid pressure transducer is capacitive.

4. A fluid pressure transducer assembly according to claim 1 in which there are three height control pins.

5. A fluid pressure transducer assembly according to claim 1 in which the housing is formed of plastic material and the circuit board is formed of ceramic.

6. A fluid pressure transducer assembly according to claim 5 in which the adhesive sealing material is RTV.

7. A fluid pressure transducer assembly according to claim 1 in which the fluid pressure transducer has a top surface and further comprising an electrically conductive layer formed on the top surface of the circuit board beneath the fluid pressure transducer and an electrically conductive layer formed on the top surface of the fluid pressure transducer, the electrically conductive layers electrically connected together to form an EMI shield.

8. A transducer assembly comprising a housing formed of electrically insulative material, circuit board having electrical traces on a top surface thereof mounted within the housing, a transducer mounted on the circuit board and electrically connected to electrical traces on the circuit board, the transducer having top and bottom surfaces, an electrically conductive layer formed on each of the top surface of the circuit board beneath the transducer and on the top surface of the transducer essentially covering the entire top surface of the transducer, the electrically conductive layers being electrically connected together and being adapted for connection to a predetermined voltage for providing protection against electromagnetic interference.

9. A transducer assembly comprising a transducer having a flexible diaphragm member for providing an electrical signal responsive to a selected condition upon deflection of the diaphragm member and having top, bottom and side surface areas, and electrically conductive metal layer formed on at least the top surface area, and a circuit board with an electrically conductive metal laver disposed on a selected area of the circuit board with the transducer member mounted on the selected area, the electrically conductive metal layers being electrically connected together and having an electrical connection for attachment to a predetermined voltage for providing protection of the electrical signal from electromagnetic interference.

10. A transducer assembly according to claim 9 in which the transducer of the transducer assembly includes silicon.

11. A method for packaging a fluid pressure transducer in a housing comprising the steps of

forming a plastic housing having a bottom wall circumscribed by a platform having a top surface lying in a first plane,

forming height control pins which extend upwardly from the bottom wall to respective distal free ends lying in a second plane parallel to and spaced above the first plane by a selected, defined distance,

dispensing a curable adhesive sealing material on the top surface of the platform to a height greater than the distance between the first and second planes,

mounting a fluid pressure transducer on a circuit board in fluid tight sealed relation over a bore formed through the circuit board and,

placing the circuit board on the sealing material prior to curing of the sealing material and forcing the circuit board downwardly into engagement with the height control pins so that sealing material is disposed completely around the platform between the top surface of the platform and the circuit board having a precise, uniform height, the sealing material forming a fluid tight seal.

12. A method according to claim 11 in which the circuit board is formed of ceramic and the adhesive sealing material is RTV.