Method for making a pressure transducer

• US 5,544,399 A
• Filed: 02/17/1995
• Issued: 08/13/1996
• Est. Priority Date: 03/28/1994
• Status: Expired due to Fees

• Current Assignee: Sensata Technologies Incorporated (Sensata Technologies Holding Plc)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Bishop, Robert P., Hainey, Paul L.
• Primary Examiner(s): Vo, Peter
• Assistant Examiner(s): NGUYEN, KHAN
• Application Number:
  US08/394,526
• Time in Patent Office: 543 Days
• Field of Search: 29/25.41, 29/594, 29/595, 29/621.1, 361/283.4, 361/283.1, 73/724
• US Class Current: 29/25.41
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: Y10T 29/43 Electric condenser making
• CPC Class Codes: Y10T 29/49103 Strain gauge making

Abstract

A monolithic capacitive pressure transducer (12, 12'"'"') is made by separately forming under pressure a diaphragm (22, 22'"'"') and a base (24, 24'"'"') having a recess (26) in the top surface using ceramic powder coated with an organic binder. Metal layers are deposited on the two pieces and the pieces are then joined together to form a single unit. A spacer (36) may be inserted in the recess to ensure that a predetermined gap is maintained between the two parts during the joining operation. The parts are then heated to allow the binder organics, as well as the spacer organics if a spacer is employed, to be vaporized and/or decomposed and removed through the open pores of the diaphragm and base and then sintered to change the parts into a monolithic body and to convert the metallized layer into a conductive layer bonded to the ceramic. In one embodiment the metal layers include terminal pads (18b, 19c, 20c) formed on the diaphragm and joinder pads (19b, 20b) formed on the base around terminal receiving bores (34, 32) each in alignment with a terminal pad. In a second embodiment terminal pads (18b'"'"', 19d'"'"', 20d'"'"') are formed on the diaphragm with vias extending radially inwardly from terminal pads (19d'"'"', 20d'"'"') to respective connecting pads (19c'"'"', 20c'"'"') which are aligned with joinder pads (19b'"'"', 20b'"'"') formed on the base. The base has a recessed portion (24b'"'"') in its outer wall providing access to terminal pads (18b'"'"', 19d'"'"', 20d'"'"').

Claims

1. A method for making a capacitive transducer comprising the steps of

forming a flat diaphragm and a relatively thick base having a top and bottom surface and having a recess formed in the top surface of the base and a plurality of bores extending through the base from the top to the bottom surface spaced from the recess,

applying a metalized layer on a bottom surface of the diaphragm and on the top surface of the base, the metalized layer on the diaphragm including an interior portion on the diaphragm and having a via extending to a first terminal pad adjacent to and spaced from the outer periphery of the diaphragm, the metalized layer also including a second terminal pad being disposed adjacent to and spaced from the outer periphery and spaced from the first terminal pad,

the metalized layer on the top surface of the base including a portion on the top surface of the base within the recess with a via extending out of the recess to a first joinder pad on the base adjacent to and spaced from the outer periphery of the base, placing the diaphragm onto the top surface of the base with the interior portion of the metalized layer on the bottom surface of the diaphragm aligned with the metalized layer on the top surface of the base within the recess and the first terminal pad aligned with a first bore of said plurality of bores and the second terminal pad aligned with the first joinder pad and a second bore of said plurality of bores, placing conductive means into the bores in conductive engagement with the first and second terminal pads and inserting an electrically conductive pin in each of the first and second bores, each pin having a distal free end disposed within the conductive means in the respective bore adjacent the top surface thereof, to form a continuous electrical path from a terminal pin, through conductive means to the first terminal pad on the bottom surface of the diaphragm and from another conductive pin through conductive means to the second terminal pad and from there to the first joinder pad, via and metalized layer on the top surface of the base within the recess, and heating the diaphragm and base to form electrically conductive paths of the metalized layers and joining the diaphragm and base together.

2. The method of claim 1 wherein said first joinder pad has an outer periphery larger than the cross-sectional area of the second bore.

3. The method of claim 1 wherein said recess has a bottom wall in a first plane and a side wall.

4. The method of claim 3 in which the side wall is inclined relative to the first plane.

5. The method of claim 3 in which the side wall forms an angle of approximately 150°

with the first plane.

6. The method of claim 1 wherein said diaphragm and base have indexing means for properly aligning these parts one to another.

7. The method of claim 1 wherein said first joinder pad on the base is in the configuration of an annulus circumscribing the bore and second terminal pad on the lower surface of the diaphragm is generally circular having a diameter at least as large as the outer diameter of the annulus.

8. The method of claim 1 wherein said metalized layer on the top surface of the base includes a second separate and distinct portion on the top surface of the base and within the recess with a via extending out of the recess to a second joinder pad on the base adjacent to and spaced from the outer periphery of the base and the metalized layer on the bottom surface of the diaphragm includes a third terminal pad disposed adjacent to and spaced from the outer periphery of the diaphragm and spaced from the first and second terminal pads having at least a portion aligned with the second joinder pad, a third bore with conductive pin and conductive means being aligned with the second joinder pad and third terminal pad.

9. A method for forming a capacitive transducer comprising the steps of

taking ceramic powder particles coated with an organic binder and pressing the powder to form a flat diaphragm and a relatively thick base having a top and bottom surface and having a recess formed in the top surface of the base and a plurality of bores extending through the base from the top to the bottom surface spaced from the recess,

applying a metalized layer on a bottom surface of the diaphragm and on the top surface of the base, the metalized layer on the diaphragm including a portion centralized on the diaphragm and having a via extending to a first terminal pad adjacent to and spaced from the outer periphery of the diaphragm, the metalized layer also including a second terminal pad being disposed adjacent to and spaced from the outer periphery and spaced from the first terminal pad,

the metalized layer on the top surface of the base including a portion centralized on the top surface of the base and within the recess with a via extending out of the recess to a first joinder pad on the base adjacent to and spaced from the outer periphery of the base, a first bore extending through the base, a second bore extending through the base aligned with the first joinder pad, the first joinder pad having an outer periphery larger than the cross-sectional area of the second bore, placing the diaphragm onto the top surface of the base with the centralized metalized layer on the bottom surface of the diaphragm aligned with the centralized metalized layer on the top surface of the base and with the first terminal pad aligned with the first bore and the second terminal pad aligned with the first joinder pad and the second bore, placing conductive epoxy into the bores in conductive engagement with the first and second terminal pads and inserting an electrically conductive pin in each of the first and second bores, each pin having a distal free end disposed within the conductive epoxy in the respective bore adjacent the top surface thereof, to form a continuous electrical path from a terminal pin, through the conductive epoxy to the first terminal pad on the bottom surface of the diaphragm and from another conductive pin through conductive epoxy to the second terminal pad and from there to the first joinder pad, via and centralized metalized layer on the top surface of the base, and sintering the diaphragm and base to form a monolithic body.