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Publication numberUS3793604 A
Publication typeGrant
Publication dateFeb 19, 1974
Filing dateApr 9, 1973
Priority dateApr 9, 1973
Publication numberUS 3793604 A, US 3793604A, US-A-3793604, US3793604 A, US3793604A
InventorsDow J, Duggan G
Original AssigneeGte Sylvania Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High strength electrical lead for disk type thermistors
US 3793604 A
Abstract
A disk type thermistor has a conductive metallic coating bonded to each face thereof. A lead-in wire is soldered to each metallic coating, each lead-in wire extending beyond the edge of the thermistor in a plane generally parallel to the face thereof. Each lead-in wire is shaped so that the solder bond between the lead-in wire and the metallic coating does not extend to the periphery of the thermistor.
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United States Patent [1 1 Duggan et al.

[451 Feb. 19, 1974 HIGH STRENGTH ELECTRICAL LEAD FOR DISK TYPE THERMISTORS [75] Inventors: George L. Duggan, Bedford; Judith A. Dow, Danvers, both of Mass.

[73] Assignee: GTE Sylvania Incorporated,

' Danver s, Mass.

[22] Filed: 'Apr. 9, 1973 [21] Appl. N0.: 348,946

[52] US. Cl 338/22 R, 338/324, 338/329 [51] Int. Cl H0lc 7/04 [58] Field of Search 338/22 R, 22 SD, 23, 25, 28,

[56] References Cited UNITED STATES PATENTS 3,547,835 12/1970 Short 338/22 SD 2,720,573 10/1955 Lundquist 338/22 R 3,452,314 6/1969 Sapoff et a1 338/22 3,182,118 5/1965 DeProost et a1. 338/322 X 3,381,081 4/1968 Schalliol 338/329 X 2,418,460 4/1947 Buehler 338/322 Primary Examiner-C. L. Albritton Attorney, Agent, or Firm.lames Theodosopoulos [57] ABSTRACT A disk type thermistor has a conductive metallic coating bonded to each face thereof. A lead-in wire is soldered to each metallic coating, each lead-in wire extending beyond the edge of the thermistor in a plane generally parallel to the face thereof. Each lead-in wire is shaped so that the solder bond between the lead-in wire and the metallic coating does not extend to the periphery of the thermistor.

1 Claim, 1 Drawing Figure HIGH STRENGTH ELECTRICAL LEAD FOR DISK TYPE THERMISTORS SUMMARY OF THE INVENTION Thermistors are relatively simple, two-terminal semiconductor devices the electrical resistance of which varies in a known retraceable manner with temperature. They are'commonly manufactured invarious shapes, such as rods, disks, washers, beads and molded.

This invention relates to disk type thermistors and particularly to such thermistors having generally radial lead-in wires. In such thermistors a lead-in wire is laid across the face of the thermistor and soldered thereto. The solder bond therebetween extends from the inner end of the lead-in wire to the periphery of the thermistor, the lead-in wire extending therebeyond.

We have found that such a construction does not produce an adequately strong lead-in wire bond in those situations where the peel strength requirement of the lead-in wire is quite high. The peel strength is determined by measuring the amountof force required to rupture the bond between the wire and the disk face. The force is applied to the wire outside the periphery of the disk and in a direction substantially parallel to the axis of the disc, the effect being to peel the wire up from the face of the disk.

We have found that the peel strength of such lead-in wires can be substantially increased by the use of a lead-in wire bent in such a manner that the solder bond between the-wire and disk face does not extend to the periphery of the disk. That is to say, at about the point where the lead-in wire extends beyond the periphery of the disk, the wire should be sufficiently above the surface of the disk so that a solder fillet therebetween does not extend to the periphery of the disk.

The single FIGURE in the drawing is a perspective view of a thermistor in accordance with this invention.

In one embodiment of this invention, thermistor l was a disk type barium titanate thermistor, made by the usual process of blending thermistor material in powder form, pressing the powder into a disk shape and then firing the disk at an elevated temperature, above about l,000 C. In this example, the fire disk had a diameter of 9% inch and a thickness of 125 mils.

A conductive metallic coating 2 was then applied in known manner to each face of the disk to provide an ohmic contact, Such a coating is made of a powdered metal, such as silver, aluminum or copper, dispersed in a liquid vehicle. The coating also contains a small amount of inorganic binder, such as glass frit. After coating 2 has dried, the thermistor is fired at a temperature above the melting point of the glass frit to provide a good bond between the condcutive coating and the thermistor surface. It is necessary that coating 2 provide good ohmic contact and be readily wettable by solder.

In some cases it may be desirable that coating 2 consist of two coatings, the first coating selected to provide ohmic contact and a good bond to the thermistor surface and the second coating selected to bond well to the first coating and also provide better solderability than the first coating. In such a case, the first coating could contain silver or aluminum in an amount that provides good ohmic contact to the barium titanate. The second coating could contain a higher percentage of metal, e.g. silver, to provide better solderability.

Lead-in wire 3 was made of 25 mil tinned copper wire and had an overall length of about 1% inches. The end, segment 4, of lead-in wire 3 that was soldered to coating 2 was straight and had a length of A inch. Segment 4 was positioned on the face of the thermistor so that acute angle bend 5 in lead-in wire 3 raised lead-in wire 3 sufficiently above the surface of the thermistor that solder fillet 6 did not extend to the periphery of the thermistor. We have found that in order to prevent solder fillet 6 from extending to the periphery of the thermistor, lead-in wire 3 should be elevated above the face of the thermistor, at its periphery, at least about double the wire diameter of lead-in wire 3. Both lead-in wires 3, one on each face of the thermistor, were bent so that the space between them, at their outer ends, was about equal to the thickness of the thermistor.

Lead-in wires 3 were soldered to thermistor I by the process shown in US. Pat. No. 3,721,003, where both lead-in wires 3 constituted a prebent single wire which was cut after soldering. Prior to soldering, the thermistor, held between the lead-in wires, was dipped into a liquid flux and was then dipped in molten solder. In this example the solder was 96.5% tin 3.5% silver having a melting point of about 221 C. The solder formed a fillet all around segment 4 and securely bonded lead-in wire 3 to coating 2'.

Disk thermistors in accordance with this invention had a lead-in wire peel strength at least 50% greater than that of similar prior art thermistors, where the solder bond between the lead-in wire and the thermistor extend to the periphery of the disk.

We claim:

1. A barium titanate disk type thermistor having a solderable coating securely bonded to each face thereof and a separate bent lead-in wire fastened with solder to each of said coatings, the solder bond between said coating and said lead-in wire extending across the face of the thermistor but not as far as the periphery thereof, each of said lead-in wires having a bend so as to be elevated above the face of the thermistor at the periphery thereof by a distance at least about double the thickness of the lead-in wire, a peelstrength-improving solder fillet between said thermistor face and said lead-in wire at said bend of the lead-in wire and each of said lead-in wires having additional bends so that their outer ends are substantially parallel and spaced apart about the thickness of the thermistor.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2418460 *Dec 31, 1943Apr 8, 1947Bell Telephone Labor IncResistor
US2720573 *Jun 27, 1951Oct 11, 1955Lundqvist Dick O RThermistor disks
US3182118 *Apr 17, 1963May 4, 1965Philips CorpMethod of providing contacts on semiconductive ceramic bodies of n-type oxidic material and contacts produced thereby
US3381081 *Apr 16, 1965Apr 30, 1968Cts CorpElectrical connection and method of making the same
US3452314 *May 22, 1967Jun 24, 1969Victory Eng CorpLow noise thermistor assembly and method
US3547835 *Jun 9, 1969Dec 15, 1970Du PontProcesses of producing and applying silver compositions,and products therefrom
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4058701 *Dec 21, 1976Nov 15, 1977Schoeller & Co. Elektrotechnische Fabrik Gmbh & Co.Glow element arrangement for electric cigarette lighters
US4685025 *Mar 14, 1985Aug 4, 1987Raychem CorporationConductive polymer circuit protection devices having improved electrodes
US4695818 *Feb 14, 1986Sep 22, 1987Siemens AktiengesellschaftElectrical resistor with a negative temperature coefficient for incremental resistance values and method for manufacturing same
US4714910 *Mar 5, 1987Dec 22, 1987Siemens AktiengesellschaftElectrical component having high strength given stressing due to temperature change and due to surge currents, particularly a varistor
US4730102 *Sep 15, 1986Mar 8, 1988Gte Products CorporationElectroceramic heating devices
US4746784 *Jun 5, 1986May 24, 1988Littelfuse-Tracor, B.V.Method of attaching a lead to a metal end cap of a safety fuse
US4827634 *Aug 27, 1985May 9, 1989Murata Manufacturing Co., Ltd.Three-terminal capacitor
US5117089 *Dec 27, 1990May 26, 1992Emerson Electric Co.Structural support for hermetic terminal assembly heater apparatus
US5557251 *Mar 28, 1994Sep 17, 1996Murata Manufacturing Co., Ltd.Thermistor with electrodes for preventing inter-electrode migration
US6150918 *Apr 26, 1996Nov 21, 2000Bc Components Holdings B.V.Degaussing unit comprising one or two thermistors
US6177857 *Jan 24, 1996Jan 23, 2001Murata Manufacturing Co., Ltd.Thermistor device
US7075407 *Apr 5, 2000Jul 11, 2006Murata Manufacturing Co., Ltd.Temperature sensor
US7148785 *Apr 30, 2004Dec 12, 2006Tyco Electronics CorporationCircuit protection device
US7164341 *Sep 27, 2001Jan 16, 2007Murata Manufacturing Co., Ltd.Surface-mountable PTC thermistor and mounting method thereof
US7193498May 22, 2006Mar 20, 2007Murata Manufacturing Co., Ltd.Method of producing temperature sensor and mounting same to a circuit board
EP0001750A1 *Sep 26, 1978May 16, 1979Siemens AktiengesellschaftMethod for affixing a terminal conductor onto an electrical PTC resistor
EP0193854A1 *Feb 26, 1986Sep 10, 1986Siemens AktiengesellschaftElectrical resistance having a negative temperature coefficient, and production process therefor
EP0243602A1 *Feb 24, 1987Nov 4, 1987Siemens AktiengesellschaftElectric component having a higher solidity versus temperature variations and current pulses, especially a varistor
Classifications
U.S. Classification338/22.00R, 338/329, 338/324
International ClassificationH01C1/14, H01C1/144
Cooperative ClassificationH01C1/144
European ClassificationH01C1/144