Film-type power resistor combination with anchored exposed substrate/heatsink

• US 5,304,977 A
• Filed: 04/06/1992
• Issued: 04/19/1994
• Est. Priority Date: 09/12/1991
• Status: Expired due to Term

• Current Assignee: Caddock Electronics, Inc.
• Original Assignee: Caddock Electronics, Inc.
• Inventors: Caddock, Richard E. Jr.
• Primary Examiner(s): Lateef, Marvin M.
• Application Number:
  US07/863,851
• Time in Patent Office: 743 Days
• Field of Search: 338/278, 338/312, 338/253, 338/258, 338/273-274, 338/51, 338/329, 338/315, 338/226, 338/322, 338/324, 338/159
• US Class Current: 338/275
• CPC Class Codes: H01C 1/034 the housing or enclosure being formed as coating or mould without outer sheath H01C1/032 takes precedence
• CPC Class Codes: H01C 1/084 using self-cooling, e.g. fins, heat sinks

Abstract

The film-type electrical power resistor includes a flat ceramic chip on the upper surface of which is screen-printed a resistive film. Terminals (leads) are mechanically and electrically connected to the upper chip surface, the terminals being such that the chip may be positioned by the terminals in a predetermined position in a mold cavity during manufacture of the resistor--prior to introduction of synthetic resin. The synthetic resin forms a molded electrically insulating body that embeds the portions of the terminals that are relatively near the chip, and also embeds the upper portion of the chip, but does not embed the bottom surface of the chip. The relationships are such that the lower chip surface may be engaged flatwise with a flat region of a chassis or heatsink. Accordingly, the chip is a substrate for the film, a heatsink for the film, an insulator maintaining the film electrically insulated from the chassis, and a spacer maintaining the terminals spaced from the chassis. The resistor does not contain any metal layer that is either in an electric circuit or projects outwardly relative to the edges of the chip. To permit assembly of the resistor with a chassis or heatsink, a bolthole extends through the body at a region outside the chip.

Claims

1. A film-type electrical power resistor, which comprises:

(a) a flat nonmetal chip having an upper surface and a lower surface, having a high dielectric strength, and having relatively high thermal conductivity for a nonmetal,

(b) a resistive film applied to said upper surface of said chip,

(c) terminals connected mechanically to said upper surface of said chip and connected electrically to said resistive film, said terminals being such that said chip with said film thereon may be positioned by said terminals in a predetermined position in a mold cavity, during manufacture of the power resistor, prior to introduction of synthetic resin into said mold cavity,

(d) a molded electrically insulating body embedding those portions of said terminals that are relatively adjacent said chip, and also embedding only the upper portion and edge portions of said chip,

said molded body not having any mold cup therearound.

said lower chip surface and said body being so related to each other that said lower surface may be engaged in flatwise relationship to a flat region of a chassis or heatsink.

said chip serving as a substrate for said film, as a heatsink for heat generated by said film, as an insulator maintaining said film electrically insulated from said chassis, and as a spacer maintaining said terminals spaced from said chassis.

said resistor not containing any metal layer that is either in an electric circuit or projects outwardly relative to the edges of said chip, and

(e) a bolthole extended through said body for clamping of said resistor in effective heat-transfer relationship to said flat region of said chassis or heatsink.

2. The invention as claimed in claim 1, in which said chip is a ceramic.

3. The invention as claimed in claim 2, in which said ceramic is selected from a group consisting of aluminum oxide, beryllium oxide and aluminum nitride.

4. The invention as claimed in claim 3, in which said ceramic is aluminum oxide.

5. The invention as claimed in claim 1, in which said body is molded of an epoxy.

6. The invention as claimed in claim 1, in which said resistive film is a thick film which has been screen-printed onto the upper surface of said chip.

7. The invention as claimed in claim 1, in which said bolthole does not pass through said chip.

8. A film-type power resistor, which comprises:

(a) a flat substrate having substantially parallel upper and lower surfaces,

said substrate being formed of a substance that is electrically insulating and has substantial thermal conductivity,

(b) a resistive film applied to said upper surface,

(c) elongate terminal means disposed above said resistive film,

said terminal means being mechanically connected to said upper surface of said substrate and being electrically connected to said resistive film, said terminal means extending across said substrate,

said terminal means having one portion disposed outboard of one edge of said substrate and having another portion disposed outboard of an opposite edge of said substrate,

said terminal means being such that said substrate with said film thereon may be positioned by said terminal means in a predetermined position in a mold cavity, during manufacture of the power resistor, prior to introduction of synthetic resin into said mold cavity,

(d) a molded synthetic resin body embedding said resistive film and only the upper and edge portions of said substrate,

said molded body not having any mold cup therearound,

said synthetic resin body also embedding at least said one outboard portion of said terminal means, and also embedding that part of said other outboard portion of said terminal means that is adjacent said opposite edge of said substrate, but not embedding the part of said other outboard portion of said terminal means that is remote from said opposite edge,

said terminal means holding said substrate in position in said body,

said resistor not containing any metal layer that is either in an electric circuit or projects outwardly relative to the edges of said substrate, and

(e) a bolthole extended through said body for clamping of said resistor in effective heat-transfer relationship to said flat region of said chassis or heatsink.

9. The invention as claimed in claim 8, in which said terminal means has tabs forming part of said one portion, to increase the strength of embedment in said body.

10. The invention as claimed in claim 8, in which said terminal means comprises two elongate parallel terminals each having one part thereof seated on said substrate, being the part mechanically connected to said substrate.

11. The invention as claimed in claim 10, in which said one part and said other part of each terminal are connected to each other by a riser, said riser being readily bendable prior to molding of said body, and in which the bottom surface of said substrate is not embedded in said body but is instead exposed for flatwise engagement with a flat region of a chassis.

12. A low-cost high-power film-type resistor, which comprises:

(a) a flat chip formed of ceramic,

said chip having substantially parallel upper and lower surfaces,

(b) first and second trace and pad films screen-printed onto said upper surface,

(c) a thick-film resistive film screen-printed onto said upper surface and electrically in contact with said trace and pad films,

(d) first and second terminals having portions conductively bonded to said trace and pad films,

said terminals also having outer end portions extending away from at least one edge of said chip to regions relatively remote from said chip,

said terminals being such that said chip with said film thereon may be positioned by said terminals in a predetermined position in a mold cavity, during manufacture of the power resistor, prior to introduction of synthetic resin into said mold cavity,

(e) a molded body of synthetic resin embedding said films and said upper surface of said chip as well as said edge portions of said chip,

said resin body not having any mold cup therearound,

said resin body also embedding said terminals except at said regions of said terminals relatively remote from said chip,

said resin body having bottom portions that at least substantially encompass said edges of said chip,

said bottom portions of said resin body having bottom surfaces that are substantially flush with said lower surface of said chip, said lower surface of said chip not being coated by said resin body, and

(f) a bolthole provided through the other end portion of said body for use in bolting said body to a flat portion of a chassis or heatsink.

said lower surface of said chip then being in flatwise heat-transfer engagement with said flat portion of a chassis or heatsink,

said resistor not containing any metal layer that is either in an electric circuit or projects outwardly relative to the edges of said chip.

13. The invention as claimed in claim 12, in which said body is rectangular and elongate and has an upper surface generally parallel to said lower surface of said chip, and in which said chip is generally square and is relatively near one end of said body,

14. The invention as claimed in claim 12, in which a trimming slot is provided through said resistive film, in which said termination traces are substantially parallel to each other, and in which said trimming slot is substantially perpendicular to said termination traces, whereby said trimming slot is parallel to the direction of current flow through said resistive film between said termination traces, and in which there is no substantial trimming slot or slot portion that is not substantially perpendicular to said termination traces.

15. The invention as claimed in claim 14, in which a barrier coating is provided over said resistive film, between it and said synthetic resin body, to prevent said synthetic resin body from adversely affecting said resistive film.

16. The invention as claimed in claim 15, in which said synthetic resin body is high thermal-conductivity synthetic resin.

17. The invention as claimed in claim 16, in which said barrier coating is glass having a firing temperature much lower than that of said resistive film.