Patent Application
20060055500
The present invention relates to the field of manufacturing electronic components. More specifically, this invention relates to encapsulated or insulated positive temperature coefficient (PTC) devices.
It is well known that the resistivity of many conductive materials changes with temperature. The resistivity of a positive temperature coefficient (“PTC”) material increases as the temperature of the material increases. Examples of such a material are crystalline polymers, made electrically conductive by dispersing conductive fillers therein. These polymers generally include polyolefins such as polyethylene, polypropylene and ethylene/propylene copolymers. Carbon black is an example of a conductive filler.
Typically, a conductive polymer PTC device comprises a layer of conductive polymer PTC material sandwiched between upper and lower metal foil electrodes. The prior art includes single layer devices and multilayer devices, the latter comprising two or more conductive polymer layers separated by one or more internal metal foil electrodes, with external metal foil electrodes on the upper and lower surfaces. Examples of such devices and their methods of manufacture are disclosed in the following U.S. patents, the disclosures of which are incorporated herein by reference: U.S. Pat. 6,429,533; U.S. Pat. No. 6,380,839; U.S. Pat. No. 6,242,997; U.S. Pat. No. 6,236,302; U.S. Pat. No. 6,223,423; U.S. Pat. No. 6,172,591; U.S. Pat. No. 6,124,781; U.S. Pat. No. 6,020,808; and U.S. Pat. No. 5,802,709.
At temperatures below a certain value, referred to generally as the critical or switching temperature, PTC materials of the type referred to above exhibit a relatively low, constant resistivity. However, as the temperature of the PTC material increases beyond this point, the resistivity of the material sharply increases with temperature. When the temperature of the material cools down below the critical or switching temperature, the resistivity reverts to its low, constant value.
This effect has been used in the production of electronic PTC devices providing overcurrent protection in electrical circuits, where they are generally placed in series with a load. Under normal operating conditions, the resistance of the load and the PTC device is such that a relatively small current flows in the PTC device. Under these conditions the temperature of the device due to ohmic heating remains below the critical or switching temperature of the PTC device. If, however, the load is short circuited or the circuit experiences a power surge, the current flowing through the PTC device increases and the temperature of the PTC device rises rapidly due to ohmic heating. As the PTC device reaches its critical temperature, a significant amount of power is dissipated in the PTC device. Typically, this power dissipation occurs only for a fraction of a second, but the increased power dissipation raises the temperature of the PTC device to a value where the resistance of the PTC device becomes so high that the current in the circuit is limited to a relatively low value. This limited current value is enough to maintain the PTC device at a high temperature/high resistance equilibrium point, but is suitably designed to prevent damage to other electrical circuit components. Thus, the PTC device performs the function of a fuse, reducing the current flow through the short circuit load to a safe, relatively low value when the temperature of the PTC device reaches or exceeds the critical temperature.
In order to allow the PTC device to cool down below its critical temperature and return to its normal operating, low resistance state, it is necessary to switch off the power or remove the fault condition responsible for the short circuit. Thus PTC devices of this type may be seen to operate as resettable electrical circuit protection devices.
Chu et al (U.S. Pat. No. 6,377,467) discloses a surface mount PTC device. The construction of the Chu device however suffers from a number of disadvantages including a limited effective area for the PTC material, and manufacturing difficulties arising from the provision of electrical connections to the laminar electrodes of the PTC material by interconnects passing adjacent to the electrodes.
McGuire et al (U.S. Pat. No. 5,907,272) and McGuire (U.S. Pat. No. 5,884,391) disclose a surface mount PTC device, which offers reliable connections to the laminar electrodes. It is suggested however that the manufacturing methods of these patents maybe inefficient and costly. Moreover, in certain environments and applications, it is necessary to protect the PTC device from external agents. The disclosed device leaves PTC material exposed to such agents. An example of such an environment is the use of PTC devices in battery straps. Battery straps are used to provide a protection circuit within a battery housing to prevent damage to the battery.
Typically, battery straps comprise a PTC device having two leads (straps) soldered, or otherwise fixed to its terminals. These leads are used to provide device connections. In lithium battery applications, lithium salts or other electrolytes may leak on to the PTC device and damage the PTC material. Accordingly, it is necessary to protect the PTC device. One known way of providing protection is to wrap the PTC device in a protective tape. However, this is a costly and time consuming process. In addition, PTC devices are prone to damage from mechanical mishandling.
Another disadvantage of existing PTC devices is that the creepage distance between the two terminals is effectively the thickness of the PTC material. In certain environments, for example batteries, this distance may be bridged by contaminants such as swarf or battery salts rendering the PTC device ineffectual.
Accordingly, there is a need for an improved PTC device and method for manufacturing same.
Accordingly, in a first aspect the present invention provides an encapsulated electronic device comprising an element of electronically active material sandwiched between a first laminar electrode and a second laminar electrode. A region of insulating material encloses the first laminar electrode, the second laminar electrode and the element of active material. A first terminal is provided for facilitating an external electrical connection to the first laminar electrode and a second terminal is provided for facilitating an external electrical connection to the second laminar electrode. The first terminal and the first laminar electrode are connected by a first conductive interconnection that passes through the region of insulating material. A second conductive interconnection that passes through the region of insulating material electrically connects the second terminal and the second laminar electrode. At least one of the interconnections comprises a metal plating.
By encapsulating the active material and laminar electrodes within a region of insulating material, the active material is protected from external agents. The use of a metal plating to provide the interconnections between the electrode and terminal facilitates the manufacture of the devices using standard PCB processing techniques. Suitably, the first conductive interconnection and the second conductive interconnections are both provided by a metal plating.
The electronic device may be a leaded device having a first lead affixed to its first terminal and a second lead is affixed to its second terminal. A third terminal may be provided on the same side of the device as the first terminal and electrically connected to the second terminal by a first electrical connection formed between opposing sides of the device through said region of insulating material. The first electrical connection may be a plated through hole via. The resulting device may be a leaded device having a first lead affixed to said first terminal and a second lead affixed to said third terminal. Alternatively, the device may be a surface mountable device with the first and third terminals providing surface mount technology (SMT) connections. A fourth terminal may be provided on the same side of the device as the second terminal and electrically connected to the first terminal by a second electrical connection formed between opposing sides of the device through said region of insulating material. This second electrical connection may be a plated through hole via.
The region of insulating material may include a first layer of insulating material separating said first laminar electrode and said first terminal and/or a second layer of insulating material separating said second laminar electrode from said second terminal. The region of insulating material may comprise a printed circuit board material having an aperture defined therein in which said element of active material is received. Suitably, the active material is a positive temperature coefficient material, optionally a polymeric material.
In another aspect of the invention, an encapsulated PTC device is provided comprising a segment of insulating material having an aperture defined therein. An element of PTC material is received within the defined aperture. A first surface of the PTC element is covered by a first laminar electrode and a second surface of the PTC element is covered by a second laminar electrode. The first electrode is substantially covered by a first layer of insulating material and the second electrode is substantially covered by a second layer of insulating material. A first terminal for providing an external electrical connection to the first electrode is provided on top of the first layer of insulation and a second terminal is provided on the second layer of insulation for providing an external electrical connection to the second electrode. The first terminal is connected to the first electrode by a first conductive interconnection that passes through the first insulating layer and the second terminal is connected to the second electrode by a second conductive interconnection that passes through the second insulating layer.
The resulting encapsulated device has a structure which protects the PTC material from external agents and which may be manufactured using low cost printed circuit board manufacturing techniques. The first and second layers of insulating material may be provided as layers of resin. Suitably, the segment of insulating material comprises circuit board material. Optionally the circuit board material is a laminate structure of glass or aramid fibers bonded with a resin material. Alternatively, the first and second insulating layers may provide the segment of insulating material.
The encapsulated PTC device may be a leaded device with leads fixed to the first and second terminals. Moreover, the encapsulated device, when leaded, is particularly suitable as a battery strap.
A third terminal may be provided that is electrically connected to the second terminal by a first conductive interconnection that passes through the insulating segment. Leads may be fixed to the first and third terminals to produce a reduced height leaded encapsulated PTC device. This is particularly suitable for use as a battery strap. The first conductive interconnection that passes through the insulating segment may be a plated through hole via.
Additionally, a fourth terminal may be provided that is electrically connected to the first terminal by a second conductive interconnection that passes through the insulating segment. The second conductive interconnection that passes through the insulating segment may comprise a plated through hole via. The first, second, third and fourth terminals may be suitably disposed to provide a symmetrical device. The terminals of the device may be metal plated. Optionally, the metal plating is a combination of copper, nickel and/or gold. Moreover, the plating may comprise three separate metal plates of copper, nickel and gold.
In yet another aspect of the invention, a method of manufacturing an electronic device is provided. The method comprises the step of providing an element of electronically active material having a first metal layer as a first laminar electrode and a second metal layer as a second laminar electrode. The first laminar electrode, the second laminar electrode and the element of electronically active material are surrounded with a region of insulating material. A first terminal for facilitating an external electrical connection to the first laminar electrode and a second terminal for facilitating an external electrical connection to the second laminar electrode are provided. A first opening is created through the region of insulating material and a conductive path provided therein to electrically connect the first terminal and the first laminar electrode. Similarly, a second opening is created through the region of insulating material and a conductive path provided therein to electrically connect the second terminal and the second laminar electrode.
The step of surrounding the first laminar electrode, the second laminar electrode and the segment of electronically active material with a region of insulating material may comprise the steps of placing the element of active material into an aperture defined in a printed circuit board material. Leads may be fixed to the first terminal and to the second terminal.
The method may comprise the additional step of providing a third terminal on the same side of the device as the first terminal, and electrically connecting the third terminal to the second terminal using a first electrical connection formed between opposing sides of the device through said region of insulating material. The step of electrically connecting the third terminal to the second terminal may be performed by metal plating. Leads may be affixed to the first terminal and the third terminal.
The method may comprise the additional steps of providing a fourth terminal located on the same side of the device as the second terminal, and electrically connecting the fourth terminal to the first terminal using a second electrical connection formed between opposing sides of the device through said region of insulating material.
The step of electrically connecting the fourth terminal to the first terminal is implemented by metal plating. The step of surrounding the first laminar electrode, the second laminar electrode and the segment of electronically active material with a region of insulating material, may comprise the step of covering said first laminar electrode with a first layer of insulating material and/or the step of covering said second laminar electrode with a second layer of insulating material.
The active material may be a positive temperature coefficient material, optionally a polymeric material.
A further aspect of the invention, is a method of manufacturing an encapsulated PTC device comprising the steps of surrounding the perimeter of an element of PTC material with a segment of insulating material, providing said element of PTC material with a first laminar electrode substantially covering a first major surface of the PTC element, providing said element of PTC material with a second laminar electrode substantially covering a second major surface of the PTC element, forming a first layer of insulating material substantially covering the first electrode, forming a second layer of insulating material substantially covering the second electrode, providing a first terminal for facilitating an external electrical connection to the first laminar electrode, providing a second terminal for facilitating an external electrical connection to the second electrode, forming an electrical connection between the first terminal and the first electrode through said first insulating layer, and forming an electrical connection between the second terminal and the second electrode through said second insulating layer.
The segment of insulating material may comprise a circuit board material, optionally a laminate structure of glass or aramid fibers bonded with a resin material. The first and second layers of insulating material may be provided as layers of resin.
The step of surrounding the circumference of an element of PTC material with a segment of insulating material may be performed using the first and second insulating layers. The method may include the step of fixing leads to the first and second terminals. A third terminal may be provided electrically connected to the second terminal by the formation of a first conductive interconnection that passes through the insulating segment. Leads may be fixed to the first and third terminals. A metal plating process may be used to form the first conductive interconnection that passes through the insulating segment.
The method may include providing a fourth terminal and electrically connecting it to the first terminal by forming a second conductive interconnection that passes through the insulating segment. A metal plating process may be used to provide the first conductive interconnection that passes through the insulating segment.
The method may position the first, second, third and fourth terminals to provide a symmetrical device. The terminals may be plated using a metal plating process. Another aspect of the invention is a method of manufacturing a paralleled device comprising the steps of supplying a first matrix comprising a plurality of devices, each device in the first matrix comprising at least one element of electronically active material sandwiched between two laminar electrodes, wherein a terminal is provided for each of the two electrodes on both sides of the first matrix; depositing a conductive fixing material on the terminals on the top surface of the matrix; and, placing a second matrix comprising a plurality of devices, each device in the second matrix comprising at least one element of electronically active material sandwiched between two laminar electrodes, wherein a terminal is provided for each of the two electrodes on at least the underside of the matrix, such that the arrangement of terminals on the top surface of the first matrix aligns with the arrangement of terminals on the bottom surface of the second matrix, resulting in a combined matrix of paralleled devices.
The use of this method facilitates the concurrent production of a significant number of paralleled devices, which otherwise would have to be produced individually. The method may comprise the further step of singulating paralleled devices from the combined matrix. The electronically active material may be a PTC material, optionally a polymeric PTC-material.
In yet another aspect of the invention, a matrix of devices is provided wherein each device comprises a first laminar electrode, a second laminar electrode, a segment of electronically active material sandwiched between said first laminar electrode and said second laminar electrode, a first terminal for facilitating a connection to the first laminar electrode, a second terminal for facilitating a connection to the second laminar electrode, a first layer of insulating material separating the first terminal from the first laminar electrode, and a second layer of insulating material separating the second terminal from the second laminar electrode, wherein adjacent elements of electronically active material are separated from each other by a region of insulating material.
The region of insulating material may be a section of PCB material having apertures or pockets defined therein for receiving the elements of electronically active material. Alternatively, the region of insulating material comprises the first layer of insulating material and said second layer of insulating material. The electrical interconnections may be provided between the first terminal and the first electrode by at least one plated blind via passing through the first layer of insulating material. The electrical interconnections between the second terminal and the second electrode suitably may be provided by at least one plated blind via passing through the second layer of insulating material. Each device in the matrix may have a third terminal located on the same surface of the matrix as the first terminal and electrically connected to the second terminal by a first electrical connection formed between opposing surfaces of the matrix through said region of insulating material by a plated through hole via. The individual devices of the matrix may be configured as surface mountable devices said first and third terminals providing SMT connections. A fourth terminal for each device may be located on the same surface of the matrix as the second terminal and electrically connected to the first terminal by a second electrical connection formed between opposing surfaces of the device through said region of insulating material by a plated through hole via. The active material in the matrix may be a positive temperature coefficient material, optionally a polymeric material, or it may be a dielectric material, a resistive material, a magnetic material, or a semiconductor material. A shared region of metal may provide the terminals of adjacent devices in the matrix.
The invention also provides for a component singulated from the matrix. The component may be configured as a SIP component, in which the first and second terminals of each device are aligned along one edge of the device. The first terminal in the component device may be connected to an underlying third terminal by means of a first plated through-hole connection through the region of insulating material. The second terminal in the component device may be connected to an underlying fourth terminal by means of a second plated through hole connection passing through the region of insulating material. Alternatively, the component may be configured as a DIP component. The component may be a leaded device with a suitable lead frame attached to the first and second terminals. The component may include two or more devices. One or more of the devices in the component may be a PTC device, optionally of the conductive polymer type. The component may be adapted to have one or more circuit protection devices or components of another type mounted thereon, such as, for example, a thyristor, a metal oxide varistor, and/or a gas discharge tube.
The above-mentioned advantages of the present invention, as well as others, will be more readily appreciated from the detailed description that follows.
Referring now to the drawings,
The conductive PTC material may be made of any suitable PTC material, including for example suitable conductive polymer compositions. An example of a suitable conductive polymer composition would be high density polyethylene (HDPE) into which is mixed an amount of carbon black that results in the desired electrical operating characteristics. An example of such a mixture is disclosed in WO97/06660, the disclosure of which is incorporated herein by reference The metal layers may comprise any suitable metal foils, with copper being preferred, although other metals, such as nickel and aluminum and a number of alloys are also acceptable. In a specific preferred embodiment, a copper foil is used that has an inner surface that is formed with a micro-textured surface (a “nodularized” surface). The nodularized surface is plated with a very thin passivation layer of nickel, preserving the micro-textured surface profile for improved adhesion to a conductive polymer layer sandwiched between the foil layers.
A laminated sheet, from which a plurality of individual PTC segments 10 may be singulated, may be fabricated by any of several suitable processes that are well known in the art, as exemplified by the above referenced publication WO97/0660. Suitable techniques for singulation are well known in the art and include routing, guillotining, dicing, punching, laser cutting and scoring.
A segment 18 of a board 17, as illustrated in
In practice, the board 17 may be suitably dimensioned and arranged, as shown in
The process begins, as shown in
To ensure that individual segments 10 may be placed with ease within the apertures 19 defined in the board section 18, the apertures are dimensioned to be slightly larger than the corresponding laminated segments 10. For example, if the segment is about 14 mm long and 4 mm wide in size, the aperture might be dimensioned to provide a spacing of approximately 20 microns around the segment when positioned in the aperture.
It is intended that the thickness of the segments 10 is substantially the same as the thickness of the board. However, an exact match is not essential and appropriate thicknesses may be selected for convenience. For example, a typical thickness for a Printed Circuit Board (PCB) would be 300 microns, whereas a typical thickness for the laminated segment might be in the range of 260 microns to 280 microns.
Although the segments may be placed within the apertures using a manual technique, i.e. hand placing, there are a number of techniques which are more suitable to mass production, for example, pick and place machines or shaking tables.
To retain the PTC element 10 within the aperture 19 of the board section 18, a first layer of insulating material 20 is provided to cover the first layer 12 of metal and the bottom surface of the board section 18, as shown in
Exemplary insulating materials would include plastic (e.g. epoxy resin). Fibers (e.g. glass) may be included within the insulating material to provide mechanical strength.
Although the above method steps have been described with reference to the use of a board having a plurality of pre-defined apertures for receiving elements of active material, alternative methods may be used to effectively encapsulate the PTC segment. Moreover, configurations are possible in which the PTC segment itself defines and is used to form the aperture in which it is effectively encapsulated. In one exemplary alternative method, a first layer of insulating, e.g. pre-preg, material is placed on a surface. Advantageously, the first layer of insulating material may be combined with a metal layer [e.g. using a resin coated copper (RCC) material] the advantage of which will be appreciated from the description below. Individual PTC segments, comprising a layer of PTC material sandwiched between two metal electrodes, may then be placed on top of the layer of insulating material, for example using a pick and place machine or other suitable technique. A second layer of insulating material (advantageously RCC material) may then be laid on top of the first layer of insulating material and PTC segments. The resulting structure may be placed in a laminating press or similar device. The heat and pressures of the lamination press will cause the first and second insulating layers to join and effectively encapsulate the PTC segments, resulting in a structure equivalent to that shown in
Reverting to the main method and referring to
Advantageously, the steps of applying a layer of insulating material and providing a metal layer may be combined into a single step using a resin clad metal material, for example RCC. The use of RCC allows the metal and insulating layers to be applied concurrently. A suitable RCC material would be a 1080 glass fabric impregnated with approximately 62% resin content and clad with a thickness of copper of about 18 microns. The adherence of the insulating layers to the first and second metal layers 12, 14 and to the third and fourth metal layers 24, 26 may be achieved by conventional PCB techniques including the use of a lamination press in a multi layer PCB technique familiar to those skilled in the art. It is believed that an advantage of using a laminating press is that during the lamination process, heat developed will cause the PTC material to expand, as it would during a short circuit fault. When the device cools after lamination, the contracting PTC material will cause a flexing of the insulating material in a controlled matter. It is believed that this self-tripping of the PTC material during the lamination process improves the ultimate performance of the device. It will be appreciated that the order of assembly described above is not essential and that the alternative orders may be used, for example the process may start with a sheet of RCC material onto which the board having apertures defined therein may be placed. The PTC elements may then be placed into the apertures and then the board covered with a further sheet of RCC material.
The resulting device structure after lamination, as shown in
To obtain a device that functions as a PTC device requires the provision of electrical connections to the laminar electrodes (first and second metal layers) 12, 14 of the PTC element through the insulating barrier 18, 20, 22. Moreover, it is necessary to provide electrical interconnections between the first and third metal layers 12, 24 through the first insulating layer 20 and between the second and fourth metal layers 14, 26 through the second insulating layer 22.
Before an electrical connection between the first and third metal layers 12, 24 may be established, an opening is required from the lower surface of the sheet (third metal layer 24) through to the surface of the first metal layer 12. Suitable methods for forming such an opening include laser drilling and etching.
One etching technique which is particularly suitable is a two step etching process in which the first step is a conventional photo resist and etching process, familiar to those skilled in the art, which selectively removes metal from the third metal layer 24, in areas 30 where an electrical interconnection is required, the result of which is illustrated in
Similarly, as shown in
Once the micro-vias 30, 32 have been formed, conductive electrical interconnections may be provided through them by disposing conductive material within the micro-vias. One method of providing the conductive interconnection is plating. The electrical connections may also be provided by inserting a conductive material, for example conductive epoxy or solder paste, into the micro-vias 30, 32. Using a suitable plating process, as shown in
The electroless plating process may be a copper based electroless plating system. If copper plating is used, however, further plating steps may be advantageously employed to passivate the copper and thus prevent or minimize migration. In particular, an electroless nickel plating process may be used to passivate the copper. In a nickel electroless plating process, nickel will only form a plating on exposed areas of copper. To provide a final terminal surface suitable for soldering and other processes, a final electroless plating process may be used to provide a gold plating on exposed areas of plated nickel.
The resulting structure provides a PTC device in which the PTC material 16 is insulated by the surrounding board section 18 in combination with the first and second layers of insulating material 20, 22 that cover the laminar electrodes 12, 14 of the segment 10. Electrical connections to the resulting device are available from the top and bottom terminals 42, 44 (plated third and fourth metal layers respectively) which are electrically connected to the underlying laminar electrodes 12, 14, respectively, by the first and second interconnections 46, 48, respectively, that are formed within the micro-vias 30, 32, as described above.
As the device is effectively protected by the insulating material, less care is required in the packaging of the individual devices, resulting in lower packaging and handling costs.
To facilitate the use of the device in particular electronic applications, first and second leads 50, 52 may be attached to the device, as shown in
In certain applications where there is limited headroom, the height of components is a critical issue. In the case of battery strap applications, where the PTC device is intended to be housed within the housing of the battery, any reduction in height is desirable as the battery tends to occupy a significant space within modern electronic devices, e.g. mobile phones, and any reduction in this space is important to reduce the overall size of electronic devices.
In a further embodiment of the invention, a device is provided, as illustrated in
In order to place the leads 70, 72 on the same side of the device, it is necessary to provide an electrical connection 60 between the opposing sides of the PTC device. The provision of this electrical connection will now be described with reference to
Once the aperture 56 has been formed, an electrical connection 60 may be established through this aperture 56 between the third metal layer 24 and fourth metal layer 26, as shown in
The electrical connection 60 may be provided at the same time as providing the first electrical interconnection 46 between the first and third metal layers and the second electrical interconnection 48 between the second and forth metal layers, or in a separate process.
Thus, for example the electrical connection 60 may be provided by the same process described above or a separate plating process, or by the insertion of solder paste or other conductive material within the aperture 56.
In order to facilitate connections to the bottom surface of the resultant device, metal may be selectively removed from the third metal layer (for example, by etching), to provide two separate terminals 64, 66 separated by a region 62 where metal has been removed, as shown in
Once the openings 30,32 for the micro-vias have been formed, a region of metal may be selectively removed from the third metal layer (for example, by etching), to provide two separate regions 58, 59 for terminals separated by a region 62 where metal has been removed, as shown in
An alternative method of forming the electrical connections to that of the method described above with reference to
As described above, plating or other processes may be used to provide electrical connections through the micro-vias (effectively to form plated micro-vias), connections through the aperture 56 from the top surface to the bottom surface and to provide a protective conductive coating on the terminals.
The resulting structure, as shown in
The device illustrated in
To provide a symmetrical device, the bottom layer is divided into two terminals 64, 66 as previously described, and similarly the top layer of the device (plated fourth metal layer) is divided into two terminals 74, 76, for example by means of a conventional photo resist and etching technique using the methods described previously in respect of the division of the bottom layer to define two terminals.
This results in a structure, as shown in
As explained above, a plurality of devices are intended to be constructed in a single matrix 90 as shown in
The embodiment of
The resulting IC type device may be readily modified for use as a dual in-line package (DIP) by appropriate fixing of a lead frame.
Although DIP packages are popular, in circumstances where board space is at a premium, single in-line packages (SIP) are preferred. The present invention may be readily adopted for use as a SIP package by providing paired terminals for connecting to each PTC device along one side of the array rather than on opposing sides of the device. An exemplary arrangement for a SIP package is shown in
Although, this exemplary SIP package is suitable for use with a lead frame that attaches to both the top and bottom surfaces of a device, it is not suitable for use in situations where the leads of the lead frame are attached to a single surface of the device. In these situations, it is necessary to provide a connection between the terminals on opposing surfaces of the device as was described with reference to the use of the plated through hole 60 of
A drawback of the embodiment of
Depending on the application, the individual characteristics of the PTC devices of the multi-PTC device (e.g. SIPs, and DIPs) may be equivalent or different. Different characteristics may be achieved by having differently sized PTC segment areas and correspondingly sized apertures in the board for receiving each of the individual PTC segments.
As the PTC devices described herein are manufactured using conventional PCB techniques, the resulting devices may be used as miniature printed circuit boards onto which further circuit protection devices, for example a battery charge controller or over voltage protection devices including gas discharge tubes, thyristors or metal oxide varistors (MOV) may be fixed, for example by direct soldering to the terminals, to provide a circuit protection module. For example, the exemplary differential line protection circuit shown in
A drawback of existing PTC devices is that the effective area of the PTC material limits the trip currents of the devices. However, as circuit board space is generally at a premium, designers are reluctant to use devices having large device footprints. One solution to this problem is the previously described SIP packages. Another, known solution is to provide PTC devices in a parallel configuration using a multilayer device construction. However, these known constructions are overly complex in their manufacture.
The matrix construction of the present invention facilitates a simple and efficient method of providing two or more devices in parallel in a quasi-multilayer construction. A side view of a section of a matrix of devices (of the symmetrical type shown in
Although, the present invention has been described with reference to an active material of the PTC type, it will be appreciated that the manufacturing process of the present invention may be advantageously applied to other active polymer materials and PTC materials and also to other materials including dielectrics, resistive, magnetic and semiconductor materials.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US03/02339 | 1/24/2003 | WO | 6/9/2005 |
| Number | Date | Country | |
|---|---|---|---|
| 60432552 | Dec 2002 | US |
