Multilayer Electrical Devices

Abstract

In some embodiments, the multilayer electrical device may have a plurality of electrodes connected to respective terminals, with at least two specific terminals configured to allow relative movement with respect to one another to accommodate changes in the separation distance of each electrode due to temperature changes and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface. In some embodiments, the multilayer electrical device may further include a layer having a temperature dependent electrical property mounted between each of an adjacent pair of electrodes.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 134,316, filed January 6, 2021, entitled "MULTI-LAYER ELECTRICAL DEVICE," the disclosure of which is expressly incorporated herein by reference in its entirety.

[0002] SUMMARY The present disclosure relates to surface-mountable multilayer electrical devices. [Background technology]

[0003] Many electronic devices are configured to be mounted on the surface of a circuit board, and such devices are commonly referred to as surface-mount devices (SMD) or surface-mount technology (SMT) devices.

[0004] Some SMD or SMT devices are implemented as multi-layer electrical devices that include multiple layers, each layer formed of a material having electrical properties that can be implemented between each other such that the multiple electrical layers provide the desired electrical function. Summary of the Invention [Means for solving the problem]

[0005] In some embodiments, the present disclosure relates to a multilayer electrical device having a plurality of electrodes connected to respective terminals, with at least two particular terminals configured to allow relative movement with respect to one another to accommodate changes in the separation distance of each electrode due to temperature changes and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface.

[0006] In some embodiments, the multilayer electrical device may further include a temperature-dependent layer implemented between each pair of adjacent electrodes. The temperature-dependent layer may include a material having temperature-dependent electrical properties. The temperature-dependent layer may cause a change in the separation distance between each pair of adjacent electrodes with a change in temperature. The material having temperature-dependent electrical properties may be configured such that the separation distance between each pair of adjacent electrodes increases with increasing temperature.

[0007] In some embodiments, the plurality of electrodes may include first, second, and third electrodes connected to respective first, second, and third terminals such that a first temperature-dependent layer is present between the first electrode and the second electrode, a second temperature-dependent layer is present between the second electrode and the third electrode, and the first electrode is closest to the mounting surface when the multilayer electrical device is mounted on the mounting surface. The at least two specific terminals may include a first terminal and a third terminal. The first and third terminals may be mounted on a first surface of the multilayer electrical device, and the second terminal may be mounted on a second surface of the multilayer electrical device. The first and second surfaces of the multilayer electrical device may be on opposing surfaces of the multilayer electrical device.

[0008] In some embodiments, each of the first and second temperature-dependent layers may comprise a positive temperature coefficient (PTC) material such that the respective temperature-dependent electrical properties include a resistance that increases with increasing temperature. The positive temperature coefficient material may comprise a polymeric positive temperature coefficient (PPTC) material. The electrical device may be a resettable fuse.

[0009] In some embodiments, the first and second temperature dependent layers may be formed of the same material.

[0010] In some embodiments, a change in the dimension of each of the first and second temperature-dependent layers can cause a change in the separation distance between the first electrode and the third electrode. The temperature change can include an increase in temperature, and the change in the separation distance between the first electrode and the third electrode can include an increase in the separation distance between the first electrode and the third electrode.

[0011] In some embodiments, the first and third terminals may be configured to include respective gap portions such that the gap portion of the first terminal maintains a gap dimension relative to the gap portion of the third terminal. The gap dimension may be within a selected range during relative movement. The selected range of gap dimensions may be selected to allow solder material to flow from one gap portion to the other during a soldering process, thereby electrically connecting the first and third terminals.

[0012] In some embodiments, the change in dimension of each of the first and second temperature-dependent layers may include a change in thickness dimension in a first direction perpendicular to the plane of the first electrode. The gap portion of each of the first and third terminals may include an edge extending in a direction generally parallel to the first direction. The edge of each of the first and second terminals may define one side of a respective tab having a width. The width of the tab of the first terminal may be approximately the same as the width of the tab of the third terminal. The width of the tab of the first terminal may be greater than the width of the tab of the third terminal.

[0013] In some embodiments, the first terminal may include a flat portion defining a plane generally parallel to the plane of the first electrode, the flat portion having an inner edge, an outer edge, a thickness, and a mounting surface. The inner edge of the flat portion of the first terminal may be connected to an edge of the first electrode by a connector. The second terminal may include a flat portion defining a plane generally parallel to the plane of the second electrode, the flat portion having an inner edge, an outer edge, a thickness, and a mounting surface. The outer edge of the flat portion of the second terminal may be connected to an edge of the second electrode by a connector.

[0014] In some embodiments, the flat portion of the first terminal may define a cutout along the outer edge, and the third terminal may include a terminating edge having a tab extending from the third terminal. The tab may be dimensioned to reside at least partially within the cutout in the flat portion of the first terminal, such that the cutout forms a clearance portion of the first terminal, and the tab forms a clearance portion of the third terminal.

[0015] In some embodiments, the multilayer electrical device may further include a third temperature-dependent layer mounted on the third electrode and a fourth electrode on the third temperature-dependent layer. The fourth electrode may be electrically connected to a fourth terminal on a second surface of the multilayer electrical device. The second and fourth terminals may be sized to allow relative movement with respect to one another to accommodate changes in the dimensions of each of the second and third temperature-dependent layers due to temperature changes and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface.

[0016] In some embodiments, the present disclosure relates to a method for manufacturing a multilayer electrical device, the method including mounting a plurality of electrodes connected to respective terminals, the method further including sizing at least two specific terminals to allow relative movement with respect to one another to accommodate changes in the separation distance of each electrode due to temperature changes and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface.

[0017] In some embodiments, the method may further include forming or providing a temperature-dependent layer between each of a pair of adjacent electrodes. The temperature-dependent layer may include a material having temperature-dependent electrical properties. The temperature-dependent layer may cause a change in the separation distance of each of the pair of adjacent electrodes with a change in temperature.

[0018] For purposes of summarizing the disclosure, certain aspects, advantages, and novel features of the present invention are described herein. It is to be understood that not all such advantages need be achieved in accordance with any particular embodiment of the invention. Thus, the present invention may be embodied or practiced to achieve or optimize one advantage or group of advantages as taught herein, without necessarily achieving other advantages as may be taught or suggested herein. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 illustrates a multilayer electrical device having two layers. [Figure 2] FIG. 10 is a diagram showing an example configuration in which three nodes associated with three respective electrodes are electrically connected to two nodes. [Figure 3] FIG. 1 illustrates a multilayer electrical device having three layers. [Figure 4] FIG. 10 is a diagram showing an example configuration in which four nodes associated with four respective electrodes are electrically connected to two nodes. [Figure 5A] 1A-1C illustrate various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. [Figure 5B] 1A-1C illustrate various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. [Figure 5C] 1A-1C illustrate various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. [Figure 5D] 1A-1C illustrate various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. [Figure 5E] 1A-1C illustrate various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. [Figure 6A] 5B is the same view as FIG. 5B of the multilayer electrical device when placed on a mounting surface. [Figure 6B] 6B is an end view of the multilayer electrical device of FIG. 6A from a first side. [Figure 6C] FIG. 6B is an enlarged view of a portion of FIG. 6A. [Figure 6D] FIG. 6C is an enlarged view of a portion of FIG. 6B. [Figure 7A] 6B illustrates the multilayer electrical device of FIG. 6A undergoing thermal expansion due to an increase in temperature. [Figure 7B] FIG. 6C is an end view similar to FIG. 6B of the multilayer electrical device during thermal expansion. [Figure 7C]FIG. 7B is an enlarged view of a portion of FIG. 7A when the multilayer electrical device is in a thermally expanded state. [Figure 7D] FIG. 7C is an enlarged view of a portion of FIG. 7B when the multilayer electrical device is in a thermally expanded state. [Figure 8A] 7B illustrates the multilayer electrical device of FIG. 7A attached to a mounting surface by a soldering process. [Figure 8B] 7B is an end view similar to FIG. 7B of the multilayer electrical device attached to a mounting surface. [Figure 8C] 8B is an enlarged view of a portion of FIG. 8A when the multilayer electrical device is attached to a mounting surface. [Figure 8D] 8C is an enlarged view of a portion of FIG. 8B when the multilayer electrical device is attached to a mounting surface. [Figure 9A] FIG. 1 illustrates that in some embodiments, a multilayer electrical device having one or more features as described herein may be configured to desirably achieve good engagement between each of a plurality of terminals and a mounting surface during the mounting process. [Figure 9B] FIG. 1 illustrates that in some embodiments, a multilayer electrical device having one or more features as described herein may be configured to desirably achieve good engagement between each of a plurality of terminals and a mounting surface during the mounting process. [Figure 9C] FIG. 1 illustrates that in some embodiments, a multilayer electrical device having one or more features as described herein may be configured to desirably achieve good engagement between each of a plurality of terminals and a mounting surface during the mounting process. [Figure 10] 5 illustrates a multilayer electrical device having three temperature-dependent layers and four electrodes configured such that the electrodes are electrically connected to two nodes, similar to the example of FIG. 4. [Figure 11] FIG. 10 is a bottom view of a multilayer electrical device having first, second and third terminals, the first and second terminals being configured to provide contact with a mounting surface similar to the example of FIGS. 5-9. [Figure 12A]FIG. 3 is a perspective view of a multilayer electrical device having two temperature-dependent layers and three corresponding electrodes similar to the example of FIGS. 1 and 2. [Figure 12B] FIG. 12B is an end view of the multilayer electrical device of FIG. 12A in an unexpanded state. [Figure 12C] FIG. 12B is the same end view of the multilayer electrical device of FIG. 12A in an expanded state. [Figure 13A] 12A-12C show unexpanded and expanded states of a multilayer electrical device similar to that of FIGS. 12A-12C, but configured to reduce the likelihood of tipping when its third terminal is separated from the mounting surface. [Figure 13B] 12A-12C show unexpanded and expanded states of a multilayer electrical device similar to that of FIGS. 12A-12C, but configured to reduce the likelihood of tipping when its third terminal is separated from the mounting surface. DETAILED DESCRIPTION OF THE INVENTION

[0020] Headings, if any, herein are for convenience only and do not necessarily affect the scope or intent of the claimed invention.

[0021] Examples are described herein that relate, inter alia, to multilayer electrical devices configured to provide improved packaging processes. For purposes of explanation, it will be understood that a multilayer electrical device may include multiple layers, each layer formed of a material having electrical properties. Each of such multiple layers may all be formed of the same material, each layer may be formed of a different material, or any combination thereof. Each layer may have first and second surfaces (e.g., opposing surfaces), and an electrode may be provided on each of such surfaces.

[0022] For example, FIG. 1 illustrates a multilayer electrical device 70 having two layers 91, 92. A first layer 91 is shown having first and second surfaces (e.g., a bottom surface and a top surface when oriented as shown), and an electrode is shown provided on each of such first and second surfaces. More specifically, an electrode 81 is shown mounted on the first surface of the first layer 91, and an electrode 82 is shown mounted on the second surface of the first layer 91. Similarly, an electrode 82 is shown mounted on the first surface of the second layer 92, and an electrode 83 is shown mounted on the second surface of the second layer 92.

[0023] In the above example, the electrode 82 between the first and second layers 91, 92 is configured as a common electrode. However, it will be appreciated that the region between the first and second layers 91, 92 may be provided with separate electrodes that may or may not be electrically connected.

[0024] 1, three electrodes 81, 82, and 83 are shown as being electrically connected to respective nodes (node ​​1, node 2, and node 3). In some embodiments, such three nodes may be electrically separate nodes or may be electrically connected to two nodes when multilayer electrical device 70 is mounted on a circuit board.

[0025] 2 illustrates an example configuration 71 in which three nodes associated with respective electrodes 81, 82, 83 are electrically connected to two nodes. More specifically, the first and third nodes (node ​​1 and node 3) associated with the first and third electrodes 81, 83 are shown as being electrically connected, and the second node (node ​​2) associated with the second electrode 82 is shown as being alone.

[0026] In another example, FIG. 3 illustrates a multilayer electrical device 72 having three layers 91, 92, and 93. A first layer 91 is shown having first and second surfaces (e.g., bottom and top surfaces when oriented as shown), and an electrode is shown provided on each of such first and second surfaces. More specifically, an electrode 81 is shown mounted on the first surface of the first layer 91, and an electrode 82 is shown mounted on the second surface of the first layer 91. An electrode 82 is shown mounted on the first surface of the second layer 92, and an electrode 83 is shown mounted on the second surface of the second layer 92. An electrode 83 is shown mounted on the first surface of a third layer 93, and an electrode 84 is shown mounted on the second surface of the third layer 93.

[0027] In the above example, the electrode 82 between the first and second layers 91, 92 is configured as a common electrode, and the electrode 83 between the second and third layers 92, 93 is configured as a common electrode. However, it will be appreciated that the region between the first and second layers 91, 92 may be provided with separate electrodes that may or may not be electrically connected, and / or the region between the second and third layers 92, 93 may be provided with separate electrodes that may or may not be electrically connected.

[0028] 3, four electrodes 81, 82, 83, and 84 are shown as being electrically connected to respective nodes (node ​​1, node 2, node 3, and node 4). In some embodiments, such four nodes may be electrically separate nodes or may be electrically connected to two or more nodes when the multilayer electrical device 72 is mounted on a circuit board.

[0029] 4 illustrates an example configuration 73 in which four nodes associated with each electrode 81, 82, 83, 84 are electrically connected to two nodes. More specifically, the first and third nodes (node ​​1 and node 3) associated with the first and third electrodes 81, 83 are shown electrically connected, and the second and fourth nodes (node ​​2 and node 4) associated with the second and fourth electrodes 82, 84 are shown electrically connected.

[0030] It should be noted that when a multilayer electrical device, such as any one of the examples in Figures 1-4, is subjected to a change in temperature, some or all of the various components may thermally expand or contract. For example, an increase in temperature may cause a portion of the multilayer electrical device to thermally expand. While various examples are described in the context of positive thermal expansion (increasing temperature results in an increase in a dimension), it will be understood that one or more features of the present disclosure may also be utilized in situations involving negative thermal expansion (increasing temperature results in a decrease in a dimension).

[0031] It should also be noted that in many applications, each layer between each electrode of a multilayer electrical device (such as any one of the examples in Figures 1-4) is formed of a material (e.g., a non-metallic material) exhibiting desired electrical properties. For example, such layers can be formed of a polymer or polymer-based material, such as a polymeric positive temperature coefficient (PPTC) material. Such PPTC materials include temperature-dependent electrical properties, such as low resistivity (and therefore high conductivity) at normal operating temperatures and increasing resistivity (and therefore decreasing conductivity) with increasing temperature. For example, a multilayer electrical device having a layer of PPTC material may be configured to provide a resettable fuse function between a first node (e.g., nodes 1 and 3 electrically connected together in Figure 2) and a second node (node ​​2 in Figure 2).

[0032] It will be understood that multilayer electrical devices having one or more features described herein may be constructed to include materials other than the PPTC or other polymer-based materials described above. For example, a multilayer electrical device having a metal oxide layer may be implemented as a metal oxide varistor. In another example, a multilayer electrical device having a dielectric layer may be implemented as a capacitor.

[0033] It will also be understood that the temperature increase described above that causes thermal expansion of a multilayer electrical device may or may not be the same as the temperature increase that causes an indicative change in the electrical properties of an associated layer of material, such as a PPTC material. For example, thermal expansion of a multilayer electrical device may be caused by heat applied during the process of soldering the multilayer electrical device onto a circuit board, while an increase in resistivity of a PPTC material in a multilayer electrical device may be caused by an increase in temperature that accompanies an increase in current flow through the multilayer electrical device.

[0034] In some embodiments, the multilayer electrical device can be configured to accommodate thermal expansion that occurs during processing when the multilayer electrical device is mounted on a circuit board. Various examples of multilayer electrical devices that provide such configurations are described in more detail herein.

[0035] In some embodiments, the multilayer electrical device may be implemented as a surface mount technology (SMT) device configured to be mounted on the surface of a circuit board, such as a printed circuit board (PCB). In many applications, such SMT devices are also referred to as surface mount devices (SMD). It will be understood that one or more features of the present disclosure may also be implemented in non-SMT electrical devices.

[0036] In some embodiments, the multilayer electrical device may include a plurality of electrodes connected to respective terminals. A temperature-dependent layer may be mounted between each pair of adjacent electrodes. At least two specific terminals may be configured to allow relative movement relative to one another to accommodate changes in the separation distance of the respective electrodes due to changes in temperature, and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface. Examples related to such multilayer electrical devices are described in more detail herein.

[0037] 5A-5E are various views of an example multilayer electrical device implemented as a surface mount technology (SMT) device. FIG. 5A is a top plan view of the multilayer electrical device 100 as it rests on a mounting surface. FIG. 5B is a side view of the multilayer electrical device 100 of FIG. 5A, FIG. 5C is an end view of the multilayer electrical device 100 of FIG. 5A, FIG. 5D is another end view of the multilayer electrical device 100 of FIG. 5A, and FIG. 5E is a bottom view of the multilayer electrical device 100 of FIG. 5A.

[0038] 5A-5E, a multilayer electrical device 100 is shown including first, second, and third electrodes 101, 103, and 105 connected to respective first, second, and third terminals 111, 112, and 113. More specifically, the first electrode 101 is connected to the first terminal 111 via a connecting member 116, the second electrode 103 is connected to the second terminal 112 via a connecting member 117, and the third electrode 105 is connected to the third terminal 113 via a connecting member 118.

[0039] 5A-5E, the first and third electrodes 101, 105 are electrically connected when soldered to a mounting surface to form a first node, and the second electrode 103 is itself electrically connected to a second node. Such electrical connection between the first and third electrodes 101, 105 may be made via the first and third terminals 111, 113, as described herein.

[0040] A temperature dependent layer is implemented between adjacent pairs of electrodes. More specifically, a first temperature dependent layer 102 is shown implemented between the first and second electrodes 101, 103, and a second temperature dependent layer 104 is shown implemented between the second and third electrodes 103, 105. In this manner, the alternating arrangement of electrodes 101, 103, 105 and temperature dependent layers 102, 104 forms a multi-layer configuration.

[0041] In some embodiments, each of the first and second temperature-dependent layers 102, 104 may be formed of a polymer or polymer-based material, such as a polymeric positive temperature coefficient (PPTC) material. Such PPTC materials may include temperature-dependent electrical properties such that the material has low resistivity (and therefore high conductivity) at normal use temperatures, and the resistivity increases (and therefore the conductivity decreases) with increasing temperature.

[0042] Figure 6A is the same view as Figure 5B of multilayer electrical device 100 when positioned on mounting surface 124. Figure 6C is an enlarged view of the portion generally designated 120 in Figure 6A. Figure 6B is an end view from a first side of multilayer electrical device 100 with an arrangement (generally designated 122) of first and third terminals 111, 113. Figure 6D is an enlarged view of arrangement 122 of Figure 6B.

[0043] 5 and 6, the third terminal 113 is shown to include a tab 108 extending downwardly from a lower edge of the connecting member 118 that connects the third electrode 105 to the third terminal 113. Such tab of the third terminal 113 is shown to be disposed within a cutout 107 formed in the outer edge of the first terminal 111.

[0044] Constructed as described above, and shown in the enlarged views of FIGS. 6C and 6D, various dimensions can be provided as shown in Table 1.

[0045] [Table 1]

[0046] 6A to 6D, it can be seen that the third terminal 113 is movable relative to the first terminal 111 while maintaining at least some of the gaps listed in Table 1 within a certain tolerance range.

[0047] For example, Figure 7A shows the multilayer electrical device 100 of Figure 6A undergoing thermal expansion due to an increase in temperature (126) (e.g., due to heating for a soldering process). Figure 7B is an end view similar to Figure 6B of the multilayer electrical device 100 undergoing thermal expansion. Figure 7C is an enlarged view of the portion generally designated 120 in Figure 7A when the multilayer electrical device 100 is in a thermally expanded state. Figure 7D is an enlarged view of the arrangement generally designated 122 in Figure 7B when the multilayer electrical device 100 is in a thermally expanded state.

[0048] 7C and 7D, thermal expansion, including expansion of the temperature-dependent layers 102 and 104, leads to an increase in their respective thicknesses. Accordingly, the separation distance d4 between the first and second electrodes 101 and 103 increases by Δd4, and the separation distance d2 between the second and third electrodes 103 and 105 increases by Δd2. Because the second terminal (112 in FIG. 6A) connected to the second electrode 103 is itself for the second node, relative movement of the second terminal 112 is not a concern. However, the expansion of the first and second temperature-dependent layers 102 and 104 generally leads to the first and third electrodes 101 and 105 becoming separated, and therefore, the respective first and third terminals 111 and 113 may be configured as described herein to accommodate such increased separation of same-node (first node) electrodes.

[0049] Table 2 shows the various dimensions of Table 1 in the thermally expanded state of FIG. 7D.

[0050] [Table 2]

[0051] In the expansion example of Figures 7C and 7D and Table 2, the expansion associated with the electrodes 101, 103, 105 and their respective terminals 111, 112, 113 is considered negligible or sufficiently small compared to the expansion associated with the temperature dependent layers 102, 104. For example, metals or alloys used as electrodes typically have a linear thermal expansion coefficient value (α, in units of 10) below 20. -6 m / (m°C)), whereas polymeric materials such as PPTC materials have much higher linear thermal expansion coefficient values ​​(e.g., greater than 50 or 100). It should be noted that one or more features of the present disclosure may still be practiced even when the expansion associated with the electrodes and terminals is not negligible.

[0052] 7C and 7D and the corresponding dimensions in Table 2, a soldering process can be applied to mount the multilayer electrical device 100 to the mounting surface 124. When the solder flows during such a process, at least a portion of the gaps in the thermally expanded state can remain small enough to be filled with solder material, thereby securing the first and third terminals 111, 113 to one another and thereby electrically connecting the first and third electrodes 101, 105.

[0053] For example, Figure 8A shows the multilayer electrical device 100 of Figure 7A attached to a mounting surface by a soldering process. Figure 8B is an end view similar to Figure 7B of the multilayer electrical device 100 attached to a mounting surface. Figure 8C is an enlarged view of the portion generally designated 120 in Figure 8A when the multilayer electrical device 100 is mounted to a mounting surface. Figure 8D is an enlarged view of the arrangement generally designated 122 in Figure 8B when the multilayer electrical device 100 is mounted to a mounting surface.

[0054] 8C and 8D , the enlarged views show that solder material 130 has reflowed into cutout 107 of first terminal 111 to a sufficient height (e.g., at least d13+Δd13) to secure tab 108 of third terminal 113 to first terminal 111 and mounting surface 124. Solder material 130 may also flow higher to fill some or all of the gap between tab 108 of third terminal 113 and respective portions of cutout 107 of first terminal 111. For example, the gaps shown as d12 and d14 in FIGS. 7C and 7D may be filled with solder material 130.

[0055] 7 and 8, it should be noted that the first and second terminals 111, 112 are secured to the mounting surface 124 by their respective reflow solder structures. The third terminal 113 is secured to the first terminal 111 by its respective reflow solder structure. Thus, the third terminal 113 is also secured to the mounting surface 124, thereby securing the multilayer electrical device 100 to the mounting surface 124.

[0056] 8A-8D , when the multilayer electrical device 100 is mounted on the mounting surface 124, the temperature-dependent layers 102 and 104 (e.g., PPTC layers) are in an expanded state, and the electrodes 101, 103, and 105 and their respective terminals 111, 112, and 113 are in relative positions that accommodate the expanded state of the temperature-dependent layers 102 and 104. When the multilayer electrical device 100 cools after the mounting process, the PPTC layers 102 and 104 tend to contract as their temperature decreases. When each PPTC layer is bonded to electrodes on either side (e.g., by solder joints formed with solder paste at the interface surfaces on each side of the PPTC layers, followed by a reflow process, preferably at a temperature higher than the temperature that results in the expanded state of the PPTC layers), the contracting PPTC layers 102 and 104 can result in mechanical stress being introduced into some or all of the electrode / terminal assemblies associated with the electrodes 101, 103, and 105.

[0057] However, in some embodiments, securing a multilayer electrical device to a mounting surface while a temperature-dependent layer (such as a PPTC layer) is in an expanded state is preferable to a situation in which the temperature-dependent layer is not allowed to expand freely during the mounting process (even with the aforementioned mechanical stresses resulting from cooling). For example, when the temperature-dependent layer is a PPTC layer, it is noted that the positive temperature coefficient (PTC) effect arises, at least in part, due to the volume expansion of the polymer matrix, which disrupts the conductive path through a given PPTC layer. Therefore, when the PPTC volume is constrained, the level of the PTC effect is reduced. Furthermore, such a constrained PPTC volume with a reduced PTC effect can result in higher leakage currents, which can lead to premature damage or destruction of the corresponding multilayer electrical device.

[0058] 6-8, the configuration of the electrodes 101, 103, 105 and their respective terminals 111, 112, 113 allows the temperature dependent layers 102, 104 (such as PPTC layers) to expand during the mounting process. Furthermore, the terminals 111, 112, 113 may be configured as described herein to allow the multilayer electrical device 100 to be mounted and secured to a mounting surface while the temperature dependent layers 102, 104 are in an expanded state.

[0059] 9A-9C illustrate that, in some embodiments, a multilayer electrical device having one or more features as described herein can be configured to desirably provide good engagement between each of a plurality of terminals and a mounting surface during the mounting process. For example, FIG. 9A is a side view, similar to the example of FIG. 6A, of a multilayer electrical device 100 disposed on a mounting surface 124 in a non-thermally expanded state. In such an example configuration, electrodes 101, 103, and 105, respective terminals 111, 112, and 113, and respective connecting members (116, 117, and 118 in FIG. 6A) can be sized such that the surfaces of first and second terminals 111 and 112 are flush (or nearly flush) with mounting surface 124.

[0060] 9B shows the multilayer electrical device 100 in a thermally expanded state, where the temperature dependent layers 102, 104 have expanded due to the heat applied for the mounting process. Thus, the separation distance between the first and second electrodes 101, 103 has increased due to the expansion of the first temperature dependent layer 102, and the separation distance between the second and third electrodes 103, 105 has increased due to the expansion of the second temperature dependent layer 104.

[0061] As described herein, the net effect of the aforementioned separation distances of electrodes 101, 103, 105 results in relative movement between first and third terminals 111, 113, which may be configured to accommodate such movement and enable both terminals to be secured to mounting 124. In FIG. 9B, the effect of increasing the separation distance between first and second electrodes 101, 103 is depicted as a gap 140 provided between second terminal 112 and mounting surface 124.

[0062] 9C shows the multilayer electrical device 100 tilted toward the second terminal (112) due to the gap 140 of FIG. 9B. Thus, the multilayer electrical device 100 still maintains two contact locations 141, 142 in the tilted position. More specifically, the first contact location 141 is shown along one edge of the first terminal 111, and the second contact location 142 is shown along one edge of the second terminal 112.

[0063] It should be noted that even if the surfaces of the first and second terminals 111, 112 are no longer flush with the mounting surface 124 (as in FIG. 9A ), the first and second contact locations 141, 142 remain flush with the mounting surface 124. Thus, during the reflow process, an effective solder structure can be formed to the first and second terminals 111, 112 via the respective contact locations 141, 142.

[0064] 9A-9C, the multilayer electrical device 100 is configured to provide coplanarity between the surfaces of the mating terminals (e.g., 111, 112) and the plane of the mounting surface when in an unexpanded state. It will be understood that a multilayer electrical device having one or more features as described herein may be configured in other manners. For example, the multilayer electrical device may be pre-tilted when in an unexpanded state and configured to provide a coplanar arrangement between the surfaces of the terminals and the mounting surface when in an expanded state.

[0065] In the examples described with reference to Figures 5-9, the multilayer electrical device is shown to include two temperature dependent layers and three electrodes. It will be understood that in some embodiments other numbers of temperature dependent layers and electrodes can be implemented.

[0066] For example, Figure 10 shows a multilayer electrical device 100 having three temperature dependent layers 102, 104, and 106 and four electrodes 101, 103, 105, and 107. In some embodiments, such a multilayer electrical device can be configured such that the electrodes 101, 103, 105, and 107 are electrically connected to two nodes, similar to the example of Figure 4.

[0067] 10, the first and third terminals 111, 113 associated with the respective first and third electrodes 101, 105 may be configured as described herein with reference to Figures 5-9. In some embodiments, the second and fourth terminals 112, 114 associated with the respective second and fourth electrodes 103, 107 may also be configured in a similar manner to allow relative movement between the second and fourth terminals 112, 114 due to expansion of the temperature dependent layers 102, 104, 106.

[0068] In the examples described with reference to Figures 5-9, a multilayer electrical device is shown including a pair of terminals configured to accommodate thermal expansion of multiple temperature-dependent layers while allowing such terminals to be secured to a mounting surface. In such examples, terminal 111, which contacts the mounting surface, includes a cutout 107 that is sized to receive tab 108 of the other terminal 113 and allow tab 108 to move relative to cutout 107 as the temperature-dependent layers thermally expand. Such exemplary cutouts are depicted along the outer edge of terminal 111 such that cutout 107 has an open face. It will be understood that cutouts and tabs providing similar functionality to the exemplary cutouts 107 and tabs 108 described above may be configured in different manners.

[0069] For example, Figure 11 shows a bottom view of a multilayer electrical device 100 having first, second, and third terminals 111, 112, and 113, where the first and second terminals 111, 112 are configured to provide contact with a mounting surface, similar to the examples of Figures 5-9. However, in the example of Figure 11, the cutout 107' in the first terminal 111 is shown mounted such that all sides of the cutout 107' lie laterally within the area of ​​the first terminal. Thus, the cutout 107' does not have an open side like the cutout 107 in the examples of Figures 5-9.

[0070] 11, the enclosed cutout 107′ can be dimensioned to allow relative movement of the tab of the third terminal 113, similar to the examples of FIGS. 5-9. As a result, when the multilayer electrical device 100 undergoes a soldering process, reflow solder can secure the third terminal 113 to the first terminal 111, as described herein.

[0071] 5-11, each multilayer electrical device 100 includes two terminals having flat mounting surfaces. More specifically, each multilayer electrical device 100 includes a first terminal 111 having a generally flat mounting surface and a second terminal 112 having a generally flat mounting surface, with at least the first terminal 111 configured to allow movement of another terminal (e.g., third terminal 113) relative to the first terminal.

[0072] In some embodiments, a multilayer electrical device may be configured without the flat mounting surfaces of the terminals described above, yet still allow for relative movement of one terminal with respect to the other, thereby allowing the two terminals to be secured together by reflow solder during the soldering process. Figures 12 and 13 show examples of such a multilayer electrical device.

[0073] Figure 12A is a perspective view of a multilayer electrical device 100 having two temperature dependent layers 102, 104 and three corresponding electrodes 101, 103, 105, similar to the example of Figures 1 and 2. Figure 12B is an end view of the multilayer electrical device 100 in an unexpanded state, and Figure 12C is the same end view of the multilayer electrical device 100 in an expanded state.

[0074] 12A-12C, the first electrode 101 is shown connected to a first terminal 111 via a connecting member 116, the second electrode 103 is shown connected to a second terminal 112 via a connecting member 117, and the third electrode 105 is shown connected to a third terminal 113 via a connecting member 118. Each of the three terminals 111, 112, 113 is shown to include feet having edges that engage or are proximate to the mounting surface 124 when the multilayer electrical device 100 is placed on the mounting surface 124.

[0075] 12A-12C, the connecting members 116, 118 of the first and third terminals 111, 113, respectively, can be configured to form a gap 150 that allows relative movement between the two terminals during thermal expansion of the multilayer electrical device 100. Configured in this manner, when the multilayer electrical device 100 is in the unexpanded state of FIG. 12B, at least some of the feet of each of the three terminals 111, 112, 113 are shown engaging the mounting surface 124. In the expanded state of FIG. 12C, the feet of each of the first and second terminals 111, 112 are shown engaging the mounting surface 124, while the foot of the third terminal 113 is shown lifted from the mounting surface 124 (forming a gap 152) due to the expansion of the temperature-dependent layers 102, 104.

[0076] In some embodiments, the gap 150 between the connecting members 116, 118 of the first and third terminals 111, 113 can be dimensioned to be within a range that allows solder material to flow from one terminal (e.g., the first terminal 111) to the other terminal (e.g., the third terminal 113) during the soldering process, thereby allowing the two terminals to be electrically connected and secured to the mounting surface 124 even when one terminal (e.g., the third terminal 113) is not in direct contact with the mounting surface 124.

[0077] In the example orientation in the expanded state of FIG. 12C , the third terminal 113 of the multilayer electrical device 100 is shown separated from the mounting surface, creating a gap 152. Thus, prior to reflow of the solder material, the multilayer electrical device 100 may be tilted toward the third electrode 113 (e.g., tilted right-side down when viewed as in FIG. 12C ), or may not be tilted. When the multilayer electrical device 100 is not tilted, two contact locations can be provided by the first and second terminals 111 and 112, and the third terminal 113 can be secured as described herein. When the multilayer electrical device 100 is tilted, three contact locations can be provided by the first, second, and third terminals 111, 112, and 113, and the third terminal 113 can be further secured to the first terminal 111 as described herein.

[0078] In some embodiments, it may be preferable not to tilt the multilayer electrical device when it is in an expanded state and prior to the reflow process. For example, Figures 13A and 13B show unexpanded and expanded states of a multilayer electrical device 100 similar to that of Figures 12A-12C, but configured to reduce the likelihood of tilting when its third terminals 113 are separated from the mounting surface 124 (as in Figure 13B). In some embodiments, the feet of the first terminals 111 may be sized to be wider than the feet of the third terminals 113, such that the wider first terminals 111 remain in a relatively stable position even when the narrower third terminals 113 are separated from the mounting surface 124.

[0079] Unless the context clearly requires otherwise, throughout the specification and claims, words like "comprises," "comprising," and the like should be interpreted in an inclusive sense, i.e., a sense of "including" rather than being limited thereto, as opposed to an exclusive or exhaustive sense. Generally, as used herein, the term "coupled" means that two or more elements are directly connected or connected via one or more intermediate elements. Also, the words "herein," "above," "below," and similar phrases, when used in this application, refer to this application as a whole and not to any particular portions thereof. Where the context permits, words in the singular or plural form in the specification can include the plural or singular, respectively. The word "or" referring to a list of two or more items includes all of the following interpretations: any of the items in the list, all of the items in the list, and any combination within the list.

[0080] The above detailed description of embodiments of the present invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the present invention have been described above for illustrative purposes, various equivalent modifications are possible within the scope of the present invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are shown in a certain order, alternative embodiments may perform routines having steps or use systems having blocks in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks may be shown as being performed in serial, these processes or blocks may instead be performed in parallel or at different times.

[0081] The teachings of the invention provided herein may be applied to other systems, not necessarily limited to the systems described above. Elements and acts of the various embodiments described above may be combined to provide further embodiments.

[0082] While several embodiments of the present invention have been described, these embodiments are presented for illustrative purposes only and are not intended to limit the scope of the present disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms, and various omissions, substitutions, and modifications of the forms of the methods and systems described herein may be made without departing from the spirit of the present disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the present disclosure.

Claims

1. A multilayer electrical device having a plurality of electrodes connected to respective terminals, wherein at least two particular terminals are configured to allow relative movement with respect to one another to accommodate changes in separation distance of each of the electrodes due to temperature changes, and to allow solder to provide a connection between the multilayer electrical device and a mounting surface when the multilayer electrical device is soldered onto the mounting surface.

2. 10. The multilayer electrical device of claim 1 further comprising a temperature dependent layer mounted between each pair of adjacent electrodes.

3. 3. The multilayer electrical device of claim 2, wherein the temperature dependent layer comprises a material having temperature dependent electrical properties, the temperature dependent layer causing the separation distance of each of the pair of adjacent electrodes to change with the temperature change.

4. 4. The multilayer electrical device of claim 3, wherein the material having temperature dependent electrical properties is configured such that the separation distance between each of the adjacent pairs of electrodes increases with increasing temperature.

5. 3. The multilayer electrical device of claim 2, wherein the plurality of electrodes includes first, second, and third electrodes connected to first, second, and third terminals, respectively, a first temperature-dependent layer present between the first electrode and the second electrode, a second temperature-dependent layer present between the second electrode and the third electrode, and the first electrode being closest to the mounting surface when the multilayer electrical device is mounted on the mounting surface.

6. 6. The multilayer electrical device of claim 5, wherein said at least two particular terminals include said first terminal and said third terminal.

7. 7. The multilayer electrical device of claim 6, wherein the first and third terminals are mounted on a first side of the multilayer electrical device and the second terminal is mounted on a second side of the multilayer electrical device.

8. The multilayer electrical device of claim 7 , wherein the first and second sides of the multilayer electrical device are on opposite sides of the multilayer electrical device.

9. 7. The multilayer electrical device of claim 6, wherein each of the first and second temperature dependent layers comprises a positive temperature coefficient (PTC) material such that the respective temperature dependent electrical properties include a resistance that increases with increasing temperature.

10. 10. The multilayer electrical device of claim 9, wherein the positive temperature coefficient material comprises a polymeric positive temperature coefficient (PPTC) material.

11. 11. The multilayer electrical device of claim 10, wherein the electrical device is a resettable fuse.

12. 7. The multilayer electrical device of claim 6, wherein said first and second temperature dependent layers are formed of the same material.

13. 7. The multilayer electrical device of claim 6, wherein a change in a dimension of each of said first and second temperature dependent layers causes a change in a separation distance between said first electrode and said third electrode.

14. 14. The multilayer electrical device of claim 13, wherein the temperature change comprises an increase in temperature and the change in separation distance between the first electrode and the third electrode comprises an increase in separation distance between the first electrode and the third electrode.

15. 7. The multilayer electrical device of claim 6, wherein the first and third terminals are configured to include respective gap portions, the gap portion of the first terminal maintaining a gap dimension relative to the gap portion of the third terminal, the gap dimension being within a selected range during the relative movement.

16. 16. The multilayer electrical device of claim 15, wherein the selected range of gap dimensions is selected to allow solder material to flow from one gap portion to the other gap portion during a soldering process, thereby electrically connecting the first terminal and the third terminal.

17. 16. The multilayer electrical device of claim 15, wherein the dimensional change of each of the first and second temperature dependent layers comprises a change in thickness dimension in a first direction perpendicular to the plane of the first electrode.

18. 18. The multilayer electrical device of claim 17, wherein the interstitial portions of each of the first and third terminals include edges extending in a direction generally parallel to the first direction.

19. 20. The multi-layer electrical device of claim 18, wherein the edge of each of the first and second terminals defines one side of a respective tab having a width.

20. 20. The multilayer electrical device of claim 19, wherein the width of the tab of the first terminal is approximately the same as the width of the tab of the third terminal.

21. 20. The multilayer electrical device of claim 19, wherein the width of the tab of the first terminal is greater than the width of the tab of the third terminal.

22. 20. The multilayer electrical device of claim 17, wherein the first terminal includes a flat portion defining a plane generally parallel to a plane of the first electrode, the flat portion having an inner edge, an outer edge, a thickness, and a mounting surface.

23. 23. The multilayer electrical device of claim 22, wherein the inner edge of the flat portion of the first terminal is connected to an edge of the first electrode by a connection.

24. 24. The multilayer electrical device of claim 23, wherein the second terminal includes a flat portion defining a plane generally parallel to a plane of the second electrode, the flat portion having an inner edge, an outer edge, a thickness, and a mounting surface.

25. 25. The multilayer electrical device of claim 24, wherein the outer edge of the flat portion of the second terminal is connected to an edge of the second electrode by a connection.

26. 24. The multilayer electrical device of claim 23, wherein the flat portion of the first terminal defines a cutout along the outer edge, and the third terminal includes a terminating edge having a tab extending therefrom, the tab being dimensioned to reside at least partially within the cutout in the flat portion of the first terminal, such that the cutout forms the gap portion of the first terminal and the tab forms the gap portion of the third terminal.

27. a third temperature dependent layer mounted on the third electrode; a fourth electrode on the third temperature dependent layer, the fourth electrode electrically connected to a fourth terminal on a second surface of the multilayer electrical device, the second terminal and the fourth terminal being sized to allow relative movement with respect to one another to accommodate changes in dimensions of each of the second and third temperature dependent layers due to temperature changes and to allow solder to provide a connection between the multilayer electrical device and the mounting surface when the multilayer electrical device is soldered onto the mounting surface; 10. The multilayer electrical device of claim 1 further comprising:

28. 1. A method for fabricating a multilayer electrical device, comprising: Implementing a plurality of electrodes connected to respective terminals; sizing at least two particular terminals to allow relative movement with respect to one another to accommodate changes in separation distance of each of said electrodes due to temperature changes and to allow solder to provide a connection between said multilayer electrical device and said mounting surface when said multilayer electrical device is soldered onto said mounting surface; A method comprising:

29. 30. The method of claim 28, further comprising forming or providing a temperature dependent layer between each adjacent pair of electrodes.

30. 30. The method of claim 29, wherein the temperature dependent layer comprises a material having temperature dependent electrical properties, the temperature dependent layer causing a change in separation distance between each adjacent pair of electrodes with a change in temperature.

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