PPTC Flat-Type Small SMD Temperature Sensor and Overcurrent Device

Abstract

To provide polymeric positive temperature coefficient (PPTC) devices with reliable trip temperatures.SOLUTION: A device assembly for surface mount devices includes a matrix 200 of SMD skeletons, and a polymeric positive temperature coefficient (PPTC) material disposed over the matrix. The matrix consists of multiple rows. Each SMD skeleton 100a, 100b has a pair of terminals 102a, 102b, and multiple whiskers perpendicular to and between the terminals. The PPTC material connects the terminals to the whiskers.SELECTED DRAWING: Figure 2A

Description

Technical Field

[0001] Embodiments of the present disclosure relate to PPTC planar small surface mount devices and challenges in their manufacture.

Background Art

[0002] Polymer positive temperature coefficient (PPTC) devices can be used as overcurrent or overheat protection devices and current or temperature sensors, among other applications. In overcurrent or overheat protection applications, a PPTC device can be considered a resettable fuse designed to exhibit low resistance when operating under designed conditions such as low current. The resistance of a PPTC device can change by direct heating due to a temperature rise in the environment of the circuit protection element or by resistive heating caused by current passing through the circuit protection element.

[0003] For example, a PPTC device may include a polymer material and a conductive filler, which provide a mixture that transitions from a low resistance state to a high resistance state due to a change in the polymer material such as a melting transition or a glass transition. Such a transition temperature, sometimes called the trip temperature, where the trip temperature can often be in the range of room temperature or higher, the polymer matrix expands and inhibits the electrically conductive network, significantly reducing the electrical conductivity of the composite material. This change in resistance gives the PPTC material properties like those of a fuse, and this resistance can be reversible when the PPTC material is cooled back to room temperature.

[0004] The behavior of a PPTC device may be adjusted to meet various criteria including robust performance and operating temperature. For example, known fluoropolymer-based PPTC devices can provide a reliable trip temperature in the range of 160 °C or higher. This performance may not be suitable for all applications.

[0005] PPTC materials may be combined with electrical conductors and terminals to form discrete surface mount devices (SMDs), where the SMDs may operate as temperature sensors or overcurrent devices. In particular, when small form factor manufacturing is involved, problems arise due to the different materials that make up PPTC SMD temperature sensors and overcurrent devices.

[0006] This improvement may be useful with respect to these and other considerations.

Summary of the Invention

[0007] This summary is provided to introduce a selected simplification of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be helpful in determining the scope of the claimed subject matter.

[0008] An exemplary embodiment of a device assembly for a surface mount device according to the present disclosure may comprise a matrix and a polymer positive temperature coefficient (PPTC) material disposed on the matrix. The matrix consists of a plurality of columns, each column including a plurality of surface mount device (SMD) skeletons, each skeleton including a terminal pair and a plurality of whiskers perpendicular to the terminals and between the terminals. The PPTC material connects the terminals to the whiskers.

[0009] An exemplary embodiment of a method according to the present disclosure may comprise the operations of punching, adhering, and spin coating. Punch a matrix of SMD skeletons from an electrically conductive material. Adhere a substrate to the matrix on a first side and a second matrix of landing pads to the second side, the second side being opposite the first side. Spin coat a thin film PPTC material onto the matrix to form a PPTC SMD device assembly.

Brief Description of the Drawings

[0010]

Figure 1A

Figure 1B

[0011]

Figure 2A

Figure 2B

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Figure 3A

Figure 3B

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Figure 4A

Figure 4B

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Figure 5A

Figure 5B

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Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0016] Disclosed is a PPTC SMD assembly in which an SMD skeleton matrix is installed on a base material such as a PCB or a flexible tape. The SMD skeleton matrix consists of several SMD skeletons each comprising a plurality of whiskers (comb-shaped fingers) arranged orthogonally between two terminals. The back side of the base material has a pair of landing pads arranged opposite to each terminal, and each pair of landing pads is associated with one of the SMD skeletons. None of the elements of the SMD skeletons touch each other. The PPTC material is applied to the SMD skeleton matrix by spin coating, spraying, painting, or some other means. The PPTC material forms connections between the whiskers, terminals, and landing pads of each individual PPTC SMD. To remove the individual PPTC SMDs, the SMD skeleton matrix with the PPTC is etched or diced.

[0017] For convenience and clarity, terms such as "upper", "lower", "above", "below", "vertical", "horizontal", "lateral", "sideways", "radial", "inner", "outer", "left", and "right" may be used in this specification to describe the relative placement and orientation of features and components with respect to the geometry and orientation of other features and components appearing in the perspective, exploded perspective, and cross-sectional views provided in this specification. The terms are not intended to be limiting and include the specifically recited words, derivatives thereof, and words having similar meanings.

[0018] Figures 1A - 1B are representative drawings of an SMD skeleton 100 used in the manufacture of a PPTC SMD assembly 400 (Figures 4A - 4B) according to an exemplary embodiment. Figure 1A is a top view of the SMD skeleton 100 and Figure 1B is a photograph of the SMD skeleton 100. In the exemplary embodiment, the SMD skeleton 100 consists of the electrically conductive components of a PPTC SMD such as a PPTC SMD 500 (Figure 5A).

[0019] The SMD skeleton 100 features a terminal pair consisting of a terminal 102a disposed at one end and a terminal 102b (collectively referred to as "terminals 102") disposed at the other opposite end. The SMD skeleton 100 also features a plurality of whiskers, also known as comb-shaped fingers, with whiskers 104a, 104b, and 104c closer to terminal 102a and whiskers 104d, 104e, 104f, and 104g closer to terminal 102b (collectively referred to as "whiskers 104").

[0020] The whiskers 104 are aligned perpendicular to the two terminals 102 and parallel to each other. Whisker 104a is adjacent to and sandwiched between whiskers 104d and 104e. Whisker 104e is adjacent to and sandwiched between whiskers 104a and 104b. Whisker 104b is adjacent to and sandwiched between whiskers 104e and 104f. Whisker 104f is adjacent to and sandwiched between whiskers 104b and 104c. Whisker 104c is adjacent to and sandwiched between whiskers 104f and 104g. Whisker 104d is at one end, and whisker 104g is at the other opposite end. The SMD skeleton 100 may have more or fewer whiskers 104, so the number of whiskers 104 is not intended to be limiting, and the size of the terminals 102 is adjusted in their length to approximate the distance by which each whisker is spaced apart.

[0021] The terminals 102 of the SMD skeleton 100 each have a via for connecting the terminal to a pad on the surface of a printed circuit board (PCB), flexible tape, or other material used to provide a ground for the SMD skeleton. Terminal 102a has a via 106a, and terminal 102b has a via 106b (collectively referred to as "vias 106"). In an exemplary embodiment, both the terminals 102 and the whiskers 104 are made of an electrically conductive material such as copper. None of the whiskers 104 contact each other, and none of the whiskers contact either of the terminals 102.

[0022] Figures 2A - 2B are representative drawings of an SMD skeleton matrix used in the manufacture of a PPTC SMD assembly 400 according to an exemplary embodiment. Figure 2A is a top view of the SMD skeleton matrix 200, and Figure 2B is a photograph of the SMD skeleton matrix 200. The SMD skeleton matrix 200 features a plurality of columns of SMD skeletons 100 spaced approximately equidistant from each other along each column, and each column is approximately equidistant from each other column. The SMD skeletons 100 are placed on a substrate material 202 such as a PCB made of FR4 or other materials, flexible tape, ceramic, plastic, etc.

[0023] The representative drawing (Figure 2A) shows 8 SMD skeletons 100 in 3 columns, but the number of SMD skeletons 100 constituting the SMD skeleton matrix 200 is not intended to be limiting, so there may be more or fewer SMD skeletons 100. The partial photograph shows a very large number of SMD skeletons 100 occupying the SMD skeleton matrix 200.

[0024] Figures 3A - 3B are representative drawings of a substrate material 202 used to support the SMD skeleton matrix 200 of Figures 2A and 2B according to an exemplary embodiment. Figure 3A is a top view of the back side of the substrate material 202, and Figure 3B is a photograph of the back side of the substrate material 202. The back side of the substrate material 202 features a plurality of columns of landing pad pairs spaced approximately equidistant from each other along each column, and each column is approximately equidistant from each other column. Similar to the front side of the substrate material featuring a matrix of SMD skeletons 100, the back side of the substrate material features a matrix of landing pad pairs, with one landing pad pair dedicated to each SMD skeleton.

[0025] Landing pad 204a is disposed on the opposite side of the base material 202 from terminal 102a (FIG. 2A), while landing pad 204b is disposed on the opposite side of the base material from terminal 102b (collectively referred to as "landing pad 204"). In other words, base material 202 is sandwiched between landing pad 204a and terminal 102a, and base material 202 is sandwiched between landing pad 204b and terminal 102b. Further, in an exemplary embodiment, the size of each landing pad 204 is substantially the same as the size of its respective terminal 102. Thus, the illustrated landing pads 204 are intended to be connected to the SMD skeleton 100a illustrated in FIG. 2A, while landing pads 204c and 204d are intended to be connected to the SMD skeleton 100b. Similar to terminals 102, each landing pad 204 also has a via 206. The landing pads 204 are soldered to dedicated pads on the circuit assembly to which the PPTC SMD (e.g., PPTC SMD 500 of FIG. 5A) is oriented.

[0026] Figures 4A - 4B are representative drawings of a PPTC SMD assembly 400 according to an exemplary embodiment. FIG. 4A is a top view of the PPTC SMD assembly 400, and FIG. 4B is a photograph of the PPTC SMD assembly 400. The PPTC SMD assembly 400 features an SMD matrix 200 (FIG. 2A) that provides the electrically conductive portions of the respective PPTC SMDs. Additionally, the PPTC SMD assembly 400 features a thin film of PPTC material 402 deposited over the entire SMD matrix 200.

[0027] In an exemplary embodiment, the PPTC material 402 is a thin film coating of a PPTC ink material sprayed onto the terminals 102 and the whiskers 104. In an exemplary embodiment, the PPTC material 402 has a thickness of approximately 100 μm. Whether the substrate material is a PCB, a flexible tape, a substrate, a wafer, or the like, the PPTC material 402 is applied using, for example, spin coating, ink spraying, or an injection process as a means of applying the ink onto the substrate material 202. If the substrate material 202 has an etching structure, it should be easy to construct a conductive film with a thickness of 100 μm as the PPTC material 402. In an exemplary embodiment, the PPTC material 402 may be applied to a flexible surface. Although the PPTC material 402 is shown as being transparent, the photograph in FIG. 4B shows that in some embodiments the PPTC material 402 covers the SMD skeleton matrix 200.

[0028] In an exemplary embodiment, the PPTC material 402 connects between the whiskers 104 and the terminals 102 of each SMD skeleton 100 that makes up the SMD skeleton matrix 200. In an exemplary embodiment, the connection is based on the proximity of the whisker 104 and the terminal 102. Thus, looking at the SMD skeleton 100 (FIG. 1A), when the PPTC material is applied to the matrix, the whiskers 104a, 104b, and 104c will be connected to the terminal 102a, while the whiskers 104d, 104e, 104f, and 104g will be connected to the terminal 102b. These connections show how current is transmitted between the terminals.

[0029] Furthermore, in an exemplary embodiment, the PPTC material 402 leaks from each via 106 of each terminal through each landing pad via 206 of each landing pad 204 on the opposite side of the substrate 202. Since the PPTC material 402 allows current to flow there, this means that each SMD skeleton 100 is electrically coupled to each landing pad 204 on the opposite side of the substrate 202 via its terminal 102.

[0030] Figures 5A - 5B are representative drawings of a PPTC SMD assembly 400 according to an exemplary embodiment, and an individual PPTC SMD 500 removed from the assembly. FIG. 5A is a top view of the PPTC SMD assembly 400 and the PPTC SMD 500, and FIG. 5B is a photograph of the PPTC SMD assembly 400 and the PPTC SMD 500. Both the top view 500a and the bottom view 500b of the PPTC SMD are shown (collectively referred to as "PPTC SMD 500"). Marks for etching or dicing are made on the PPTC SMD assembly 400 so that the individual components can be removed. The SMD skeleton 100 can be seen in the PPTC SMD 500a, while the landing pads 204 can be seen in the PPTC SMD 500b. In the photographic image (FIG. 5B), several individual PPTC SMDs 500 are separated from the other devices of the PPTC SMD assembly 400.

[0031] FIG. 6 is a flowchart of a method 600 for manufacturing a PPTC SMD assembly, such as the PPTC SMD assembly 400, according to an exemplary embodiment. A matrix of SMD skeletons (e.g., FIG. 1A) is punched out from an electrically conductive material such as copper (block 602). The matrix is then adhered to a substrate material having a matrix of landing pads on its back side, and each pair of landing pads will be associated with and aligned with each pair of terminals constituting the SMD skeleton (block 604). Next, a thin film of PPTC material is spin-coated onto the SMD skeleton matrix to cover both the terminals and the whiskers of each SMD skeleton (block 606), which includes the PPTC material leaching into the vias of each pair of terminals and emerging from the vias of each landing pad.

[0032] Optionally, when the PPTC material is dry, an additional coating material may be coated onto the PPTC SMD assembly (block 608). The coating may be a polymer material, ceramic, plastic, etc. Next, individual PPTC SMDs are etched or diced from the PPTC SMD assembly as individual components (block 610). Thus, by method 600, a stand-alone PPTC device can be constructed, or a batch process type approach for integrating PPTC into an existing wafer or piece-parted substrate-based product becomes available.

[0033] As used herein, elements or steps recited in the singular and preceded by the word "a" or "an" should be understood as not excluding a plurality of elements or steps, unless such exclusion is explicitly recited. Further, reference to "one embodiment" of the present disclosure is not intended to be construed as excluding the existence of additional embodiments that also incorporate the recited features.

[0034] Although the present disclosure refers to specific embodiments, many modifications, alterations, and changes can be made to the described embodiments without departing from the scope and range of the present disclosure as defined in the appended claims. Accordingly, the present disclosure is not limited to the described embodiments, but is intended to cover the full scope defined by the language of the following claims and their equivalents.

Claims

1. A matrix having a number of columns, each column including a number of SMD skeletons, each SMD skeleton being Terminal pair, a plurality of whiskers, the plurality of whiskers being disposed orthogonally between the pair of terminals; a polymeric positive temperature coefficient (PPTC) material disposed on the matrix, the PPTC material coupling the terminal pairs to the plurality of whiskers; and a substrate on which said matrix is ​​disposed, Equipped with the substrate further includes a landing pad pair disposed on an opposite side of the terminal pair, the substrate being sandwiched between the landing pad pair and the terminal pair; the terminal pair includes a first terminal having a first via and a second terminal having a second via; the landing pad pair includes a first landing pad with a third via and a second landing pad with a fourth via; A device assembly for a surface mounted device (SMD), wherein the PPTC material leaks from the first via to the third via and from the second via to the fourth via.

2. 2. The device assembly for an SMD according to claim 1, wherein the substrate is a printed circuit board.

3. The device assembly for an SMD according to claim 1 , wherein the substrate is a flexible tape.

4. The PPTC material is coupling the first terminal to the first landing pad; coupling the second terminal to the second landing pad; A device assembly for the SMD according to claim 1.

5. The PPTC material is establishing an electrical connection between the first terminal and the first landing pad; establishing an electrical connection between the second terminal and the second landing pad; A device assembly for the SMD according to claim 1.

6. 6. A device assembly for an SMD according to claim 1, wherein each SMD skeleton comprises an electrically conductive material.

7. 7. The device assembly for an SMD according to claim 6, wherein the electrically conductive material comprises copper.

8. stamping a matrix of surface mounted device (SMD) skeletons from an electrically conductive material; affixing a substrate to the matrix, the substrate including a first side and an opposing second side, where the matrix is ​​affixed to the first side and a second matrix of landing pads is affixed to the second side; and spin-coating a thin film polymeric positive temperature coefficient (PPTC) material onto the matrix to form a PPTC SMD assembly; and Equipped with the SMD skeleton includes a terminal pair; the second row of landing pads includes pairs of landing pads; the substrate is sandwiched between the landing pad pair and the terminal pair, the terminal pair includes a first terminal having a first via and a second terminal having a second via; the landing pad pair includes a first landing pad with a third via and a second landing pad with a fourth via; the PPTC material leaks from the first via to the third via and from the second via to the fourth via; A method for manufacturing a PPTC SMD assembly.

9. 9. The method of manufacturing a PPTC SMD assembly according to claim 8, further comprising the step of etching a PPTC SMD from said PPTC SMD assembly.

10. Each SMD skeleton includes a plurality of whiskers disposed between the first terminal and the second terminal.

9. A method for manufacturing the PPTC SMD assembly of claim 8, comprising:

11. 11. The method of manufacturing a PPTC SMD assembly as claimed in claim 10, wherein the PPTC material bonds a first whisker of the plurality of whiskers to the first terminal and a second whisker of the plurality of whiskers to the second terminal.

12. 9. The method of manufacturing a PPTC SMD assembly according to claim 8, further comprising the step of coating the PPTC SMD assembly with a protective material.

13. 13. The method of manufacturing a PPTC SMD assembly according to claim 12, wherein said protective material is ceramic.

14. 13. The method for manufacturing a PPTC SMD assembly as claimed in claim 12, wherein said protective material is plastic.

15. 15. A method for manufacturing a PPTC SMD assembly according to any one of claims 8 to 14, wherein the thin film PPTC material is 100 μm thick.

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