Sensor assembly having embedded wires within a powder metal core and a method therefor

• US 5,315,245 A
• Filed: 11/25/1992
• Issued: 05/24/1994
• Est. Priority Date: 02/27/1992
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Schroeder, Thaddeus, Lequesne, Bruno P. B., Ward, Robert W., Leung, Chi H.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/983,064
• Time in Patent Office: 545 Days
• Field of Search: 324/207.20, 324/207.21, 324/173, 324/174, 324/251, 324/252, 335/296, 335/302, 338/32 R, 338/32 H, 29/595, 29/607, 29/608, 148/101
• US Class Current: 324/207.21
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: H10N 50/80 Constructional details
• CPC Class Codes: Y10T 29/49007 Indicating transducer
• CPC Class Codes: Y10T 29/49076 From comminuted material

Abstract

A semiconductor magnetoresistive sensor and a method for its assembly is specifically provided. The preferred assembly method of this invention is compatible with automated semiconductor chip placement and packaging technology, so as to alleviate the previous requirement that the semiconductor sensing element be separately packaged. The sensor leads are substantially embedded within a powdered metal permanent magnet body. An exposed terminal end of each lead is available for electrical and adhesive contact to a subsequently attached magnetoresistive semiconductor sensing element, using conventional semiconductor placement and packaging techniques. The powdered metal magnetic body is preferably formed by utilizing powder metal compaction techniques, wherein the powder metal is compacted around the interior electrical leads. The teachings of this invention may also be employed to form a variety of electrical sensors and devices, wherein the leads are substantially embedded within a metal core so as to produce a solid assembly. The embedded leads may have a variety of shapes, such as straight or coiled, may range in number from one to a plurality, and may have a variety of physical properties, such as magnetic or non-magnetic, depending on the desired application.

Claims

1. A sensor comprising:

a magnetic body having a first portion and a second portion, said second portion defining a first surface of said magnetic body, said first portion of said magnetic body comprising compacted particles of a high coercivity magnetic material which are substantially individually coated with an electrically insulative coating, said second portion of said magnetic body comprising compacted particles of a ferromagnetic material which are substantially individually coated with an electrically insulative coating, said compacted particles of said ferromagnetic material being disposed adjacent said first surface of said magnetic body; and

at least one electrically conductive wire substantially embedded within said magnetic body, said at least one electrically conductive wire being coated with an electrically insulative material, said at least one electrically conductive wire having a terminal end which terminates substantially at said first surface of said magnetic body;

whereby the presence of said terminal and of said at least one electrically conductive wire at said first surface of said magnetic body facilitates the subsequent electrical connection of said at least one electrically conductive wire to a sensing element subsequently disposed on said first surface of said magnetic body.

2. A sensor as recited in claim 1 wherein said high coercivity magnetic material is primarily neodymium-iron-boron.

3. A sensor as recited in claim 1 wherein said sensing element is a semiconductor type.

4. A sensor as recited in claim 1 wherein said at least one electrically conductive wire extends outwardly from said magnetic body at a second surface of said magnetic body which is oppositely disposed from said first surface of said magnetic body.

5. A magnetoresistive position sensor comprising:

a magnetic body having a first portion and a second portion, said second portion defining a first surface of said magnetic body, said first portion of said magnetic body comprising compacted particles of a neodymium-iron-boron alloy having high magnetic coercivity which are substantially individually coated with an electrically insulative coating, said second portion of said magnetic body comprising compacted particles of a ferromagnetic material which are substantially individually coated with an electrically insulative coating, said compacted particles of said ferromagnetic material being disposed adjacent said first surface of said magnetic body; and

a plurality of electrically conductive wires embedded within said magnetic body, said plurality of electrically conductive wires being coated with an electrically insulative material, each of said electrically conductive wires having a terminal end which terminates substantially at said first surface of said magnetic body so as to be substantially coplanar with said first surface of said magnetic body; and

a semiconductor sensing element electrically connected to at least one of said plurality of electrically conductive wires at said first surface of said magnetic body;

whereby said magnetic body, said plurality of electrically conductive wires and said semiconductor sensing element form a stationary portion of the magnetoresistive position sensor, said semiconductor sensing element being adapted to sense flux density variations along a width of said magnetic body in a direction of relative movement by an exciter portion which is adapted to move past said stationary portion.

6. A magnetoresistive position sensor as recited in claim 5 wherein said plurality of electrically conductive wires extend outwardly from said magnetic body at a second surface of said magnetic body which is oppositely disposed from said first surface of said magnetic body.

7. A method for manufacturing a magnetoresistive position sensor, comprising the following steps:

providing at least one electrically conductive wire coated with an electrically insulative material;

locating said at least one electrically conductive wire within a molding die so that said at least one electrically conductive wire extends from a first surface of said molding die into a cavity;

filling said cavity with a first powder metal composition, a floor of said cavity being defined by said first surface of said molding die, and walls of said cavity being defined by an interior surface of a mold, said first powder metal composition comprising particles of a high coercivity magnetic material which have been substantially individually coated with an electrically insulative coating;

adding to said cavity a second powder metal composition comprising particles of a ferromagnetic material which have been substantially individually coated with an electrically insulative coating, said at least one electrically conductive wire being enveloped by said first and second powder metal compositions within said cavity; and

compacting said first and second powder metal compositions at a sufficient pressure and temperature and for a sufficient duration, so as to form a fully dense magnetic body from said powder metal compositions wherein said at least one electrically conductive wire is substantially embedded within said magnetic body, and wherein said ferromagnetic material is disposed adjacent a first end of said magnetic body, the remainder of said magnetic body comprising said high coercivity magnetic material;

such that a terminal end of said at least one electrically conductive wire is substantially coplanar with said first end of said magnetic body, so as to facilitate the subsequent electrical connection of said at least one electrically conductive wire to a semiconductor magnetoresistive sensor disposed on said first end of said magnetic body.

8. A method for manufacturing a magnetoresistive position sensor as recited in claim 7 wherein said high coercivity magnetic material is primarily neodymium-iron-boron.

9. A method for manufacturing a magnetoresistive position sensor as recited in claim 7 wherein said temperature during said compacting step ranges from about 150°

F. to about 600°

F.

10. A method for manufacturing a magnetoresistive position sensor as recited in claim 7 wherein said at least one electrically conductive wire extends outwardly from said magnetic body at a second end which is oppositely disposed from said first end.

11. A method for manufacturing a magnetoresistive position sensor comprising the following steps:

providing at least one electrically conductive wire coated with an electrically insulative material;

locating said at least one electrically conductive wire within a molding die so that said at least one electrically conductive wire extends from a surface of said molding die into a cavity;

filling said cavity with a first powder metal composition, a floor of said cavity being defined by said surface of said molding die, and walls of said cavity being defined by an interior surface of a mold, said first powder metal composition comprising particles of high coercivity neodymium-iron-boron permanent magnet material which have been substantially individually coated with an electrically insulative coating;

adding to said cavity a second powder metal composition comprising particles of a ferromagnetic material which have been substantially individually coated with an electrically insulative coating, said at least one electrically conductive wire being enveloped by said first and second powder metal compositions within said cavity; and

compacting said first and second powder metal compositions at a sufficient pressure and temperature and for a sufficient duration, so as to form a fully dense magnetic body from said powder metal compositions wherein said at least one electrically conductive wire is substantially embedded within said magnetic body, and wherein said ferromagnetic material is disposed adjacent a first surface of said magnetic body, the remainder of said magnetic body comprising said high coercivity magnetic material, such that said at least one electrically conductive wire terminates substantially at said first surface of said magnetic body; and

electrically connecting a semiconductor magnetoresistive sensing element to said at least one electrically conductive wire at said first surface of said magnetic body, such that said sensing element is adapted to sense flux density variations along the width of said magnetic body in a direction of relative movement by an exciter portion which is adapted to move past said stationary portion.

12. A method for manufacturing a magnetoresistive position sensor as recited in claim 11 wherein said temperature during said compacting step ranges from about 150°

F. to about 600°

F.

13. A method for manufacturing a magnetoresistive position sensor as recited in claim 11 wherein said at least one electrically conductive wire extends outwardly from said magnetic body at a second surface which is oppositely disposed from said first surface.

14. A method for manufacturing a magnetoresistive position sensor as recited in claim 11 further comprising the step of precompacting said first powder metal within said cavity prior to the step of adding said second powder metal composition to said cavity.