WO2002035558A2

WO2002035558A2 - Circuit protection device

Info

Publication number: WO2002035558A2
Application number: PCT/US2001/031755
Authority: WO
Inventors: James Toth; Takashi Hasunuma; Takashi Sato; Naofumi Miyasaka; Masatoshi Sakamoto
Original assignee: Tyco Electronics Corporation
Priority date: 2000-10-25
Filing date: 2001-10-09
Publication date: 2002-05-02
Also published as: WO2002035558A3; TW573393B

Abstract

A circuit protection device (21) particularly suited for use with a laminar battery. The device has first and second laminar electrodes (27, 29) attached to first and second surfaces of a laminar PTC resistive element (23). A third laminar conductive member (31) is secured to the second face of the PTC resistive element in the area of an aperture (39) that runs between the first and second faces and is spaced apart from the second electrode. A first electrical lead (45) is secured to the third laminar conductive member (31) and a second electrical lead (47) is secured to the second electrode (29). The presence of the two electrical leads on the same surface of the device allows attachment onto a substrate, e.g. a battery (51), from one side, minimizing the total device thickness.

Description

ELECTRICAL DEVICE

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to electrical devices and their use in protecting batteries.

Introduction to the Invention

Circuit protection devices exhibiting a positive temperature coefficient of resistance (PTC behavior) are well-known. Such devices generally comprise a PTC element composed of a conductive polymer composition. First and second electrodes, e.g. in the form of metal sheets, are attached to the conductive polymer to allow electrical connection to the device. The use of circuit protection devices to protect batteries from overcurrent and overtemperature conditions is also well-known. See, for example, U.S. Patents Nos. 4,255,698 (Simon), 4,973,936 ((Dimpault-Darcy et al.), 5,801,612 (Chandler et al.), and 6,114,942 (Kitamoto et al), and Japanese Utility Model Application No. 4- 75287 (filed October 29, 1992), the disclosures of which are incorporated herein by reference. In these applications, a PTC device is connected in series with a battery terminal. During normal operation the PTC device is in a low resistance, low temperature condition (depending on circuit conditions, for example from room temperature to 40°C). On exposure to a very high current which may develop, for example, due to a short circuit, or exposure to a high temperature which may develop, for example, due to excessive charging and produce temperatures of 60 to 130°C, the device switches into a high resistance, high temperature condition, thus decreasing the current through the battery to a low level and protecting any components in contact with the battery.

Battery packs, containing one or more batteries (i.e. cells), are commonly used with electrical equipment such as cameras, video recorders, tools, portable phones and portable computers. It is desirable to make the battery packs as small and lightweight as possible, but still provide adequate protection in the event of a short circuit. Conventional battery packs may have a PTC device applied directly onto the button terminal of one or each battery. Other conventional packs attach a device by means of "straps", i.e. electrically conductive leads which are positioned on opposite surfaces of the PTC device, are electrically connected to the electrodes of the PTC device by means of solder, and extend, generally in opposite directions, from the PTC device. The leads are used to connect the device from a terminal on one battery to a terminal on a second battery in the pack. Neither approach for attaching a PTC device to a battery or battery pack is suitable when the battery or pack must be very thin, as is the case with such laminar batteries as lithium ion polymer batteries (also called "lithium polymer batteries") or nickel metal hydride batteries. Such batteries are rectangular in shape, with two major laminar surfaces and a peripheral edge. Lithium polymer batteries are generally very thin, having a thickness of less than 4 mm. It is very difficult to install a conventional strap PTC device at the edge of the battery without having the device extend beyond the thickness of the edge and interfere with the insulating packaging into which the battery must be inserted. Positioning the device on one of the major surfaces of the battery is desirable because it allows detection of changes in temperature in the center of the battery. However, such positioning creates an increase in thickness of the assembled battery and device, making the insulating packaging thicker, an undesirable consequence.

BRIEF SUMMARY OF THE INVENTION

We have now found that it is possible to make a circuit protection device which is particularly suited for installation on a laminar battery because of its thinness and the position of its leads. Conventional devices generally have a structure which comprises (from top to bottom) a first electrical lead, a first layer of solder, a first electrode, a PTC element, a second electrode, a second layer of solder, and a second electrical lead. By placing the electrical leads on the same surface of the device, it is possible to eliminate at least one layer of solder and one layer of electrical lead. This removal allows the device to be thinner than a conventional device, saving space when the device is attached to the battery. Thus in a first aspect this invention provides a circuit protection device which comprises:

(1) a first laminar electrode;

(2) a second laminar electrode;

(3) a laminar PTC resistive element which (a) exhibits PTC behavior, (b) comprises a laminar element composed of a PTC conductive polymer, (c) has a first face to which the first electrode is secured and an opposite second face to which the second electrode is secured, and (d) defines an aperture which runs between the first and second faces;

(4) a third laminar conductive member which (a) is secured to the second face of the PTC resistive element in the area of the aperture, and (b) is spaced apart from the second electrode;

(5) a transverse conductive member which

(a) lies within the aperture defined by the PTC resistive element,

(b) runs between the first and second faces of the PTC element,

(c) is secured to the PTC element, and

(d) is physically and electrically connected to the first laminar electrode and to the third laminar conductive member but is not connected to the second laminar electrode;

(6) a first electrical lead which is secured to the third laminar conductive member; and

(7) a second electrical lead which is secured to the second electrode.

In a second aspect the invention provides a battery assembly which comprises

(A) a laminar battery which comprises first and second major surfaces, and

(B) a circuit protection device according to the first aspect of the invention which (i) is electrical connected to the battery by means of the first electrical lead, and (ii) is positioned on the first major surface of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by the drawings in which Figure 1 is a plan view of a prior art circuit protection device;

Figure 2 is a cross-sectional view along line II-II of Figure 1;

Figure 3 is a plan view of one side of a circuit protection device of the invention and Figure 4 is a plan view of the other side of the device;

Figure 5 is a cross-sectional view along line V-V of Figure 3;

Figure 6 is a cross-sectional view along line VI-VI of Figure 4;

Figure 7 is a schematic circuit diagram containing a battery assembly of the invention; and

Figure 8 is a perspective view of a battery assembly of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The circuit protection device of the invention comprises a laminar resistive element composed of a PTC conductive polymer composition. Such compositions comprise a polymeric component, and dispersed therein, a particulate conductive filler such as carbon black or metal. Conductive polymer compositions are described in U.S. Patent Nos. 4,237,441 (van Konynenburg et al), 4,304,987 (van Konynenburg), 4,514,620 (Cheng et al), 4,534,889 (van Konynenburg et al ), 4,545,926 (Fouts et al), 4,724,417 (Au et al)..4,774,024 (Deep et al), 4,935,156 (van Konynenburg et al), 5,049,850 (Evans et al), 5,378,407 (Chandler et al), 5,451,919 (Chu et al), 5,582,770 (Chu et al), 5,747,147 (Wartenberg et al), and 5,801,612 (Chandler et al), International Patent Publication No. WOO 1/09905 (Tyco Electronics Corporation, published February 8, 2001), and European Patent Publication No. 1091366 (Chen et al., published April 11, 2001). The disclosure of each of these patents and publications is incorporated herein by reference.

The composition used in the device exhibits positive temperature coefficient

(PTC) behavior, i.e. it shows a sharp increase in resistivity with temperature over a relatively small temperature range. The term "PTC" is used to mean a composition or device that has an R₁4 value of at least 2.5 and/or an R ₁00 value of at least 10, and it is preferred that the composition or device should have an R3₀ value of at least 6, where R1 is the ratio of the resistivities at the end and the beginning of a 14°C range, Rjoo is the ratio of the resistivities at the end and the beginning of a 100°C range, and R₃0 is the ratio of the resistivities at the end and the beginning of a 30°C range.

The polymeric component of the composition comprises one or more crystalline polymers. For some applications it may be desirable to blend the crystalline polymer(s) with one or more additional polymers, e.g. an elastomer or an amorphous thermoplastic polymer, in order to achieve specific physical or thermal properties, e.g. flexibility or maximum exposure temperature. For battery applications, it is preferred that the polymeric component comprise a polymer with a low melting point which is generally a polymer having a low density, i.e. a polymer having a density of less than about 0.935 g/cm³. Examples of such low density polymers are low density polyethylene and ethylene copolymers, e.g. ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, ethylene/butyl acrylate copolymer (also referred to as ethylene/n-butyl acrylate) and ethylene/isobutyl acrylate copolymer. The polymeric component has a melting temperature, as measured by the peak of the endotherm of a differential scanning calorimeter, of T_m. When there is more than one peak, T_m is defined as the temperature of the highest temperature peak. For compositions suitable for battery protection T_m is preferably at least 70°C, but is preferably less than 150°C, particularly less than 140°C. and is often less than 110°C. Particularly suitable conductive polymers for battery applications are disclosed in U.S. Patents Nos. 5,582,770 and 5,801,612, and European Patent Publication No. 1091366.

Dispersed in the polymeric component is a particulate conductive filler, generally comprising carbon black. For some applications, other particulate conductive materials such as graphite, metal, metal oxide, conductive coated glass or ceramic beads, particulate conductive polymer, or a combination of these, may also be present. Such particulate conductive fillers may be in the form of powder, beads, flakes, or fibers.

The conductive polymer composition may comprise additional components, such as antioxidants, inert fillers, nonconductive fillers, radiation crosslinking agents (often referred to as prorads or crosslinking enhancers), stabilizers, dispersing agents, coupling agents, acid scavengers (e.g. CaCO₃), or other components. The dispersion of the conductive filler and other components in the polymeric component may be achieved by any suitable means of mixing, including melt-processing and solvent-mixing. After mixing, the composition can be melt-shaped by any suitable method, e.g. melt-extrusion, injection-molding, compression-molding, or sintering, in order to produce a resistive element. The element may be of any shape, e.g. rectangular, square, circular, or annular. For many applications, it is desirable that the composition be extruded into sheet from which the resistive element may be cut, diced, or otherwise removed.

Devices of the invention comprise first and second laminar electrodes, preferably metal foil electrodes, with the laminar conductive polymer resistive element sandwiched between them so that the first electrode is secured to the first face of the laminar element and the second electrode is secured to the second face of the laminar element. Particularly suitable foil electrodes have at least one surface that is microrough, e.g. electrodeposited, preferably electrodeposited nickel or copper. Appropriate electrodes are disclosed in U.S. Patents Nos. 4,689,475 (Matthiesen), 4,800,253 (Kleiner et al.), and 5,874,885 (Chandler et al.) and International Patent Publication No. WO95/34081 (Raychem Corporation, published December 14, 1995), the disclosure of each of which is incorporated herein by reference. The electrodes may be attached to the resistive element by compression-molding, nip-lamination, or any other appropriate technique. The electrodes may be secured directly to the resistive element or attached by means of an adhesive or tie layer. For some devices it is preferred that the first and second laminar electrodes comprise metal layers formed by directly depositing metal onto the PTC resistive element, e.g. by plating, sputtering, or chemical deposition.

The device of the invention comprises a third laminar conductive member which is secured to the second face of the PTC resistive element and is spaced apart from the second electrode. Preferably the third laminar conductive member is in the area of the aperture, described below. The third laminar conductive member is preferably a residual member formed by removing part of a laminar conductive member, the remainder of one laminar conductive member which forms the third laminar conductive member then being the second electrode. The shape of the third member, and the shape of the gap between the third member and the second electrode, can be varied to suit the desired characteristics of the device and for ease of manufacture. Thus the third member is conveniently a small rectangle at one end of a rectangular device, separated from the second electrode by a rectangular gap. Alternate configurations are possible, e.g. the gap may be in the form of a chevron.

The laminar PTC resistive element generally defines an aperture which runs between the first and second faces. The term "aperture" is used herein to denote an opening which, when viewed at right angles to the plane of the device, (a) has a closed cross section, e.g. a circle, an oval, or a generally rectangular shape, or (b) has a reentrant cross section, the term "reentrant cross section' being used to denote an open cross section which (i) has a depth at least 0.15 times, preferably at least 0.5 times, particularly at least 1.2 times, the maximum width of the cross section, e.g. a quarter circle or a half circle or an open-ended slot, and/or (ii) has at least one part where the opposite edges of the cross section are parallel to each other. Due to the positioning of the electrical leads, the aperture is generally of closed cross-section. However, for ease of electrical connection and inspectability, it is sometimes preferred that the aperture have an open cross section, and be located at the edge of the resistive element. For example, if the device is made by an assembly which can be divided into a plurality of electrical devices, the apertures will normally be of closed cross section, but if one or more of the lines of division passes through an aperture of closed cross section, then the apertures in the resulting devices will then have open cross sections.

The aperture can be a circular hole, and for many purposes this is satisfactory in both individual devices and assemblies of devices. However, if the assembly includes apertures which are traversed by at least one line of division, elongate apertures may be preferred because they require less accuracy in the lines of division.

The circuit protection device also comprises a transverse conductive member (also called a cross-conductor) which runs between the first and second faces of the PTC element, is secured to the PTC element, and is physically and electrically connected to the first laminar electrode and to the third laminar conductive member, but is not connected to the second laminar electrode. If, as is preferred, an aperture is present, the transverse conductive member lies within the aperture. The device may be symmetrical, i.e. in addition to the third laminar conductive member which is positioned on the second face of the PTC element and spaced apart from the second electrode, a fourth laminar conductive member may be present. The fourth laminar conductive member is secured to the first face of the PTC resistive element in the area of a second aperture which runs between the first and second faces and is spaced apart from the first electrode. Even if the device is prepared as symmetrical, the first and second leads will be positioned on the same side of the device.

When the aperture is not traversed by a line of division, it can be as small as is convenient for a transverse member having the necessary current-carrying capacity. For circuit protection devices, holes of diameter 0.1 to 5 mm, preferably 0.15 to 2.0 mm, e.g. 0.2 to 1.0 mm, are generally satisfactory. Normally each electrical connection, e.g. between the first laminar electrode and the third laminar conductive member, can be made by a single transverse member, but two or more transverse members can be used to make this single connection. The number and size of the transverse members, and, therefore, their thermal capacity, can have an appreciable influence on the rate at which the composite circuit protection device will trip into its high resistance state.

If apertures are present, they can be formed before the transverse members are put in place, or the formation of the apertures and the placing of the transverse members can be carried out simultaneously. A preferred procedure is to form the apertures, e.g. by drilling, slicing or any other appropriate technique, and then to plate or otherwise coat or fill the interior surface of the apertures. The plating can be effected by electroless plating, or electrolytic plating (i.e. electroplating), or by a combination of both. The plating can be a single layer or multiple layers, and can be composed of a single metal or a mixture of metals, in particular a solder. The plating will often also be formed on other exposed conductive surfaces of the assembly. If such plating is not desired, then the other exposed conductive surfaces must be masked or otherwise desensitized. Generally, however, the plating is carried out at a stage of the process at which such additional plating will not produce an adverse effect. In some embodiments, it is possible that the plating will produce not only the transverse members but also at least part of the laminar conductive members in the device.

The plating techniques which are used for making conductive vias through insulating circuit boards can be used in the present invention. However, in this invention the plating serves merely to convey current across the device, whereas a plated via must make good electrical contact with another component. Consequently, the plating quality required in this invention may be less than that required for a via.

Another technique for providing the transverse member is to place a moldable or liquid conductive composition in preformed apertures, and if desired or necessary to treat the composition, while it is in the apertures, so as to produce a transverse member of desired properties. The composition can be supplied selectively to the aperture, e.g. by means of a screen, or to the whole assembly, if desired after pretreating at least some of the assembly so that the composition does not stick to it. For example, a molten conductive composition, e.g. solder, could be used in this way, if desired, using wave soldering techniques.

The transverse member can also be provided by a preformed member, e.g. a metal rod or tube, for example a rivet. When such a preformed member is used, it can create the aperture as it is put in place in the device.

The transverse member can partially or completely fill the apertures. When the aperture is partially filled, it can be further filled (including completely filled) during the process in which the device is connected to the leads, particularly by a soldering process. This can be encouraged by providing additional solder in and around the aperture, especially by including a plating of solder in and around the aperture. Normally at least a part of the transverse member will be put in place before the device is connected to the leads or other electrical components. However, for some embodiments, the transverse member is formed during a connection process, as for example by the capillary action of solder during a soldering process.

In another embodiment, no aperture is present and the transverse conductive member can be located at the edge of the device in order to connect the first and second faces on part or all of a flat transverse face of the device. The transverse member comprises a metal layer, e.g. a plating of metal applied by the techniques described above for coating the apertures.

In order to allow electrical connection to be made from the resistive element to a substrate, e.g. a battery, metal leads, e.g. in the form of wires or straps, are present. The first electrical lead is secured to the third conductive member and the second electrical lead is secured to the second electrode. The leads can be secured to the conductive member and the second electrode by any suitable means, e.g. solder, a conductive adhesive, welding. If the first electrical lead is in contact with the aperture and the transverse conductive member, a rivet or other connector can be used to attach the first lead directly into the transverse conductive member, or can, as indicated above, create the aperture and the transverse member as it is put in place. The leads preferably extend in the same direction from the resistive element to form a "radial" device, but for some applications, they may extend in opposite directions from the surface of the resistive element to form an "axial" device. The metal leads may be of any suitable material, e.g. nickel, copper, or steel. Full hard nickel may be appropriate for many battery applications. In order to minimize the thickness of the device when fully assembled, the leads should be as thin and light-weight as possible, while still maintaining appropriate current-carrying capability.

The devices of the invention containing cross-conductors can be prepared in any way. However, devices can be prepared very economically by carrying out all or most of the process steps on a large laminate (i.e. a laminar conductive polymer layer attached sandwiched between two metal layers), and then dividing the laminate into a plurality of individual devices to which the leads can be attached. The division of the laminate can be carried out along lines which pass through one or both or neither of the laminar conductive members or through none, some or all of the cross-conductors. The process steps prior to division can in general be carried out in any convenient sequence. Preferred processes for making the devices are disclosed in U.S. Patents Nos. 5,852,397 (Chan et al.), 5,831,510 (Zhang et al.), and 5,864,281 (Zhang et al.), the disclosures of which are incorporated herein by reference.

Devices of the invention preferably have a thickness of at most 0.50 mm, preferably at most 0.45 mm, particularly at most 0.40 mm, e.g. about 0.35 mm. This thickness measurement does not include any insulating layer, e.g. tape or encapsulant such as epoxy, which may be applied over the device. The resistance of the device at 25°C is generally less than 50 ohms, preferably less than 15 ohms, more preferably less than 10 ohms, particularly less than 5 ohms, especially less than 3 ohms, with yet lower resistance being possible, e.g. less than 1 ohm, even less than 0.5 ohm.

Devices of the invention are particularly useful in combination with a battery or battery pack to make a battery assembly. Batteries based on any type of battery chemistry may be used, including nickel metal hydride batteries, lithium ion batteries, and primary lithium batteries. Particularly preferred are lithium ion polymer batteries, which generally have a thickness of less than 5 mm, e.g. 3.4 to 3.8 mm. This thickness includes the metallized plastic insulation and/or outer casing, e.g. plastic shell, which may surround the battery. As a result, battery assemblies of the invention have a thickness of at most 6 mm, preferably at most 5.5 mm, particularly at most 5.0 mm, e.g. 4.5 mm. The device is preferably positioned on one major surface of the battery (the "top"), with the leads bent, if necessary, to make appropriate electrical connection to the battery and the external circuit. Positioning the device in this way allows better thermal contact between the device and the battery to regions of the battery, e.g. the center, that may experience overtemperature conditions.

The invention is illustrated by the drawing in which Figure 1 is a plan view of a prior art circuit protection device 1 and Figure 2 is a cross-sectional view of device 1 of Figure 1 along line II-II. Attached to PTC element 3, which is composed of conductive polymer 5, are first electrode 7 and second electrode 9. First and second solder layers 11,13 allow the attachment of first and second leads 15,17 to first and second electrodes 7,9, respectively. In use, first lead 15 may be bent, if necessary, to make appropriate connection to a battery terminal.

Figures 3 to 6 show a device 21 of the invention. The plan views of one side of device 21 in Figure 3 and the other side of the device in Figure 4 show resistive element 23, aperture 39, first and second electrical leads 45,47, and gap 49 which lies between second electrode 29 and third laminar conductive member 31. Figure 5 is a cross- sectional view along line V-V of Figure 3 and Figure 6 is a cross-sectional view along line VI- VI of Figure 4. Conductive polymer element 25 is sandwiched between first electrode 27 and second electrode 29. Third laminar conductive member 31 is separated from second electrode 29 by gap 49, and is prepared by etching. First copper layer 33 is positioned on first electrode 27, second copper layer 35 is positioned on second electrode 29, and third copper layer 37 is positioned on third laminar conductive member 31 and extends into aperture 39 to form a transverse conductive member. First solder layer 41 attaches first lead 45 to third conductive laminar member 31 via third copper layer 37 and second solder layer 43 attaches second lead 47 to second electrode 29 via second copper layer 35.

Figure 7 shows a circuit diagram in which device 21 is electrically in series with battery 51 to form a battery assembly 53 which can be used to connect to a load, e.g. an electronic device.

Figure 8 shows a perspective view of battery 51 physically in contact with device 21 to form battery assembly 53. Electrical connections are not shown. The invention is illustrated by the following Examples, in which Example 3 is a comparative example.

Example 1

A conductive polymer formulation was made by preblending 55.8% by volume (41.1% by weight) ethylene/n-butyl acrylate copolymer (Enathene™ EA 705-009, containing 5% n-butyl acrylate, having a melt index of 3.0 g/10 min and a melting temperature of 105°C, available from Equistar), 6.2% by volume (4.6% by weight) high density polyethylene (Petrothene™ LB832, available from Equistar), and 38% by volume (54.3%o by weight) carbon black (Raven™ 430 Ultra, having a particle size of about 82 nm, a structure (DBP number) of 80 cm³/ 100 g, and a surface area of 34 m²/g, available from Columbian Chemicals). The blend was mixed in a Buss™ kneader, pelletized, and extruded into a sheet having a thickness of 0.127 mm (0.005 inch). The sheet was laminated with two layers of electrodeposited nickel-copper foil (Type 31 , having a thickness of 0.033 mm (0.0013 inch), available from Fukuda) to produce a laminate. Holes with a diameter of 2 mm (0.08 inch) were drilled through the thickness of the laminate in a regular pattern to provide one hole for each device. The exposed surfaces of both the nickel/copper foil layers and the conductive polymer surrounding the drilled hole were sensitized using a palladium chloride solution, and a first copper layer approximately 0.002 mm (0.00008 inch) thick was electroless plated onto the sensitized surfaces. A second copper layer having a thickness of 0.025 mm (0.001 inch) was then electroplated onto the first copper layer. Using a standard photoresist process, a pattern was etched onto the laminate. First a dry film (Mylar™ polyester) resist was laminated onto one surface of the laminate and was then exposed to ultraviolet light to generate a pattern. Second, a ferric chloride solution was used to chemically etch the pattern. Third, the etched laminate was rinsed and the resist was stripped away.

PTC elements with dimensions of 8x1 1x0.21 mm (0.31x0.43x0.008 inch) were cut from the laminate and were heat-treated in an oven with settings such that the temperature of the elements reached 165 to 185°C for about 30 seconds. The elements were then irradiated to a total of about 10 Mrads using a Co⁶⁰ γ irradiation source. Nickel leads having dimensions of 3.0x15.5x0.075 mm (0.12x0.61x0.003 inch) were attached by solder onto the second electrode and the third laminar conductive member, as shown in Figures 3 and 4. A length of 8 mm (0.31 inch) of each of the leads extended from the same side of the PTC element. The device was then thermally cycled six times, each cycle being from -40 to 80 to -40°C at a rate of 1 °C/minute with a 60 minute dwell at - 40°C and 80°C. The total thickness of the device, including the PTC element, the solder, and the lead, was 0.35 mm (0.013 inch). The device had a resistance at 25°C of 0.013 to 0.026 ohm.

The hold current of the device at 25°C, i.e. the maximum current at which the device will not trip into the high resistance state, was measured to be 2.2A and the trip current of the device at 25°C, i.e. the minimum current at which a device will trip into the high resistance state, was measured to be 5.5A.

Example 2

A device was prepared following the procedure of Example 1, but with dimensions of 10.6x1 1x0.127 mm (0.42x0.43x0.005 inch). The total thickness of the device, including the PTC element, the solder, and the lead, was 0.35 mm (0.013 inch). The device had a resistance of 0.010 to 0.020 ohm. The hold current at 25°C was 2.5A and the trip current at 25°C was 6.2A.

Example 3 (Comparative Example)

A conductive polymer composition was prepared, pelletized, extruded, and laminated, according to Example 1. The laminate was coated with Sn/Pb solder, and PTC elements with dimensions of 5x12x0.127 mm (0.20x0.47x0.005 inch) were cut from the laminate. The elements were heat-treated and irradiated as in Example 1. Nickel metal leads with dimensions of 4x16x0.125 mm (0.16x0.63x0.005 inch) were attached to opposite sides of the PTC elements by reflowing the solder. The metal leads were each positioned so that a tab 5 mm (0.20 inch) extended from the edge of the PTC element in opposite, axial, directions, as shown in Figure 1. Each device was temperature cycled six cycles from -40°C to 85°C with a dwell time at -40°C and 85°C of 30 minutes. The total thickness of the device, including the PTC element, the two layers of solder, and the two leads was about 0.55 to 0.60 mm (0.021 to 0.024 inch), substantially higher than that of Examples 1 or 2. The device had a resistance of 0.018 to 0.030 ohm. The hold current at 25°C was 2.1 A and the trip current at 25°C was 4.7A.

It will be understood that the above-described arrangements of apparatus are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims.

Claims

What is claimed is:

1. A circuit protection device which comprises:

(1) a first laminar electrode;

(2) a second laminar electrode;

(5) a transverse conductive member which

(a) lies within the aperture defined by the PTC resistive element,

(b) runs between the first and second faces of the PTC element,

(c) is secured to the PTC element, and

(7) a second electrical lead which is secured to the second electrode.

2. A device according to claim 1 wherein the first lead is secured to the third laminar conductive member and the second lead is secured to the second electrode by means of solder.

3. A device according to claim 1 wherein the first lead is secured to the third laminar conductive member and the second lead is secured to the second electrode by means of a weld.

4. A device according to claim 1 which has a thickness of at most 0.50 mm, preferably at most 0.45 mm.

5. A device according to claim 1 wherein the first and second leads extend from the PTC resistive element in the same direction.

6. A device according to claim 1 wherein the first and second electrodes and the third laminar conductive member comprise metal foil, preferably wherein the metal foil comprises nickel or copper.

7. A device according to claim 1 wherein the first and second electrodes and the third laminar conductive member comprise metal layers formed by directly depositing metal onto the PTC resistive element.

8. A battery assembly which comprises

(A) a laminar battery which comprises first and second major surfaces, and

(B) a circuit protection device according to claim 1 which (i) is electrically connected to the battery by means of the first electrical lead and (ii) is positioned on the first major surface of the battery.

9. An assembly according to claim 8 wherein the first and second leads extend from the PTC resistive element in the same direction.

10. An assembly according to claim 8 wherein the battery is a lithium polymer battery or a nickel-metal hydride battery.

11. An assembly according to claim 10 which has a thickness of at most 6.0 mm, preferably at most 5.0 mm.