Patent Application
20230245803
This application claims the benefit of priority to, Chinese Patent Application No. 202210108518.1, filed Jan. 28, 2022, entitled “HIGH SOLDERING STRENGTH TERMINAL FOR SURGE PROTECTION DEVICE,” which application is incorporated herein by reference in its entirety.
Embodiments of the present disclosure relate to the field of circuit protection and, more particularly, to surge protection devices that employ thermal cutoff.
Overvoltage protection devices are used to protect electronic circuits and components from damage due to overvoltage fault conditions. Known variously as surge protection devices (SPDs), lightning surge protection (LSP) devices, and thermal cutoff (TCO) devices, some of these devices employ metal oxide varistors (MOVs). Varistors are voltage dependent, nonlinear devices composed primarily of ZnO with small additions of other metal oxides such as Bismuth, Cobalt, Manganese, and others, resulting in a crystalline microstructure that allows the MOV to dissipate very high levels of transient energy across the entire bulk of the device. MOVs are typically used for the suppression of lightning and other high energy transients found in industrial or AC line applications. Additionally, MOVs are used in DC circuits such as low voltage power supplies and automobile applications.
Some SPDs utilize spring elements soldered to the electrode of the MOV. When an abnormal condition occurs, the solder melts and the spring moves, resulting in an open circuit. In particular, when a voltage that is larger than the nominal or threshold voltage is applied to the device, current flows through the MOV, which generates heat. This causes the linking element, the solder, to melt. Once the link melts, the spring separates from the MOV electrode and an open circuit results, which prevents the MOV from catching fire.
The spring is thus considered an important element in the SPD. A reliable thermal link between the spring and the MOV electrode ensures the formation of an open circuit under the overvoltage condition. The traditional soldering interface between the spring and the MOV electrode may be deficient in terms of the volume of solder paste and the uniformity of application, resulting in unstable soldering strength, which compromises the operation of the SPD.
It is with respect to these and other considerations that the present improvements may be useful.
This Summary is provided to introduce a selection of concepts in a simplified form 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 as an aid in determining the scope of the claimed subject matter.
An exemplary embodiment of a surge protection device in accordance with the present disclosure may include a metal terminal and a spring. The metal terminal is located between two metal oxide varistors, where the metal terminal extends beyond the metal oxide varistors. The spring has a flat surface that is connected to the metal terminal using a soldering paste. The flat surface has an opening to allow air bubbles forming in the soldering paste to be released during the connection.
Another exemplary embodiment of a surge protection device in accordance with the present disclosure may include a metal terminal and a spring. The metal terminal is located between two metal oxide varistors, where the metal terminal extends beyond the metal oxide varistors. The spring has a flat surface that is connected to the metal terminal using a soldering paste. The flat surface has a bend on one end which forms a gap between the flat surface and the metal terminal.
An exemplary embodiment of surge protection device in accordance with the present disclosure may include a spring and a metal terminal. The spring has a flat surface. The metal terminal is located between two metal oxide varistors, where the metal terminal extends beyond the metal oxide varistors. The metal terminal is connected to the flat surface using a soldering paste and has a protrusion that forms a gap between the flat surface and the metal terminal.
A surge protection device with a thermal cutoff spring is disclosed. Within the soldering joints of the surge protection device are three features to facilitate successful placement of soldering paste between two flat surfaces: one or more openings, a bend, and a protrusion. The one or more openings and the bend are on the flat surface of a spring used for thermal cutoff. The protrusion is part of a metal terminal to which the flat surface is connected. The openings provide an exit for air bubbles within the soldering paste that may occur. The protrusions and the bend provide gaps between the two flat surfaces, which facilitate both control of the amount of soldering paste and targeted positioning of the paste.
For the sake of convenience and clarity, terms such as “top”, “bottom”, “upper”, “lower”, “vertical”, “horizontal”, “lateral”, “transverse”, “radial”, “inner”, “outer”, “left”, and “right” may be used herein to describe the relative placement and orientation of the features and components, each with respect to the geometry and orientation of other features and components appearing in the perspective, exploded perspective, and cross-sectional views provided herein. Said terminology is not intended to be limiting and includes the words specifically mentioned, derivatives therein, and words of similar import.
Above, below, and between the MOVs 104 are metal terminals, with the number of metal terminals being dependent on the number of MOVs. The exploded view of
With reference also to
In exemplary embodiments, the SPD 100 also includes a pair of springs 114a and 114b (collectively, “springs 114”). Each spring 114 features a flat surface for coupling (soldering) to metal terminals: flat surface 116a of spring 114a is soldered to metal terminal 108a and flat surface 116b of spring 114b is soldered to metal terminal 110a (collectively, “flat surfaces 116”). The springs 114 provide a mechanism by which the SPD 100 is uncoupled (released) from connection to a device, such as a power supply in response to an overvoltage condition.
In
In exemplary embodiments, the soldering paste is selected to have a particular melting point that is consistent with the rating of the SPD 100. For example, the soldering paste may be low melting point solder paste consisting of 42% tin (Sn) and 58% bismuth (Bi), which has a melting point of 138° C. Until an overvoltage condition for which the SPD 100 is designed occurs, current flows through the SPD (normal operation).
To provide surge protection, the SPD 100 does the following: An overvoltage condition occurs, causing the MOV stack 102 to overheat. Heat is transferred to the metal terminals 106, 108, 110, and 112, with more substantial heat being transferred to the metal terminals that are in between MOVs 204, namely, the metal terminals 108 and 110. Respective soldering joints 118a and 118b melt, causing the flat surface 116a of spring 114a to move away from the metal terminal 108a and the flat surface 116b of spring 114b to move away from the metal terminal 110a.
The springs 114 of the SPD 100 are designed to become uncoupled from respective metal terminals upon occurrence of an overvoltage event for which the SPD is rated. Once the overvoltage event occurs, the flat surface 116a of the spring 114a becomes uncoupled from the metal terminal 108a and the flat surface 116b of the spring 114b becomes uncoupled from the metal terminal 110a. In this way, an open circuit is formed.
SPD devices are thus successful by having a reliable thermal link between the flat portion of the spring and the metal electrode to which they are affixed to form open circuit under the overvoltage condition. This depends on having the correct soldering paste for the overvoltage characteristics of the SPD device, as well as the proper placement and quantity of soldering paste. In exemplary embodiments, the SPD 100 includes features in the soldering joints 118 that improve the quality of soldering between the flat surfaces and the metal terminals. To understand and appreciate the improved features, a discussion of an SPDs according to the prior art is appropriate.
Above, below, and between the MOVs 204 are metal terminals, with the number of metal terminals being dependent on the number of MOVs. Although there is no exploded view of the SPD 200, the configuration of metal terminals and MOVs is similar to that of the exemplary SPD 100, with the visible portions of the metal terminals being called out herein. A first metal terminal consists of a long terminal 206a and a body 206b (collectively, “metal terminal 206”); a second metal terminal consists of a short terminal 208a and a long terminal 208b (collectively, “metal terminal 208”); a third metal terminal consists of a short terminal 210a and a long terminal 210b (collectively, “metal terminal 210”).
Metal terminal 206 is disposed atop the MOV stack 202, specifically, adjacent the MOV 204a; metal terminal 208 is disposed between MOV 204a and MOV 204b; metal terminal 210 is disposed between MOV 204b and MOV 204c; a fourth terminal (not shown) is disposed at the bottom of the MOV stack 202, specifically, adjacent the MOV 204c. The long terminals 206a, 208b, and 210b are to be bent for connection to a PCB (not shown).
As with the exemplary SPD 100, the prior art SPD 200 includes a pair of springs 214a and 214b (collectively, “springs 214”). Each spring 214 features a flat surface for soldering to metal terminals: flat surface 216a of spring 214a is soldered to metal terminal 208a and flat surface 216b of spring 214b is soldered to metal terminal 210a (collectively, “flat surfaces 216”).
In
As with the SPD 100 (
SPD devices are thus successful by having a reliable thermal link between the flat portion of the spring and the metal electrode to which they are affixed to form an open circuit during the overvoltage event. The reliable thermal link depends on having the correct soldering paste for the overvoltage characteristics of the SPD device. Further, the traditional soldering interface for the SPD 200 is for a first flat surface to directly touch a second flat surface.
First, the volume of solder paste cannot be precisely controlled and easily be pushed away during application on the prior art SPD 200. The solder paste is to be applied to the metal terminal 210a, then the flat surface 216b of the spring 214b is positioned over the soldering paste. The soldering paste is thus sandwiched between the metal terminal 210a and the flat surface 216b. Depending on the precise application of the flat surface 216b on the soldering paste, the pressure applied to the metal terminal 210a, and other factors, the soldering paste may ooze out between the two surfaces, resulting in an inconsistent amount of soldering paste in between the two flat surfaces. By not having a consistent amount of soldering paste at the soldering interface, an unstable soldering strength may result.
Second, the application of the soldering paste may result the formation of air bubbles between the two flat surfaces, the metal terminal 210a and the flat surface 216b. It is difficult to determine whether there are air bubbles during application because the flat surface 216b of the spring 214b is not transparent. Further, even when the presence of the air bubbles is known, it is difficult to eliminate the air bubbles from forming between the two flat surfaces. The presence of air bubbles may depend to some extent on the chemical makeup of the soldering paste. Since the soldering paste is formulated based on a desired melting point of the soldering paste and thus voltage rating of the SPD, the air bubbles present an additional condition that negatively affects the soldering strength and reliability.
Third, there are two flat surfaces, the metal terminal 210a, which is stationary, and the flat surface 216b of the spring 214b, which, until the soldering paste is applied, is not stationary. Further, the shape of the flat surfaces is not identical: the rectangular shape of the metal terminal 210a has a larger area than the rectangular shape of the flat surface 216b. Thus, during application of the soldering paste, the flat surface 216b may move closer to the MOVs 204b and 204c or farther away from the MOVs, as shown by arrow, x. Or the flat surface 216b may move in parallel to the MOVs 204b and 204c but move in the directions shown by arrow, y (orthogonal to x). Even still, the flat surface 216b may move so that it is not orthogonal to the metal terminal 210a. Because the flat surfaces of the metal terminal 210a and the flat surface 216b are able to easily slide relative to one other and are not fixed, the resulting soldering strength is unpredictable. Any one of the above problems may produce defective soldering, and thus deficient operation of the prior art SPD 200.
In exemplary embodiments, the openings 324 are located in the flat surfaces 116 of the springs 114. Although three openings 324a, 324b, and 324c are shown, the flat surfaces 116 may have more or fewer openings. Further, the openings 324 do not have to be circular, they may any shape or size depending on what is needed. A soldering paste made of a thicker composition of materials may warrant having larger openings, for example. In exemplary embodiments, as the soldering paste is applied between the flat surfaces 116 and the metal terminals 108a and 110a, the openings 324 provide a pathway in which air bubbles formed in the soldering paste are able to escape.
Using the spring 114a and the metal terminal 108a as an example, the soldering paste is applied to the metal terminal 108a, then the flat surface 116a of the spring 114a is disposed over and pressed toward the metal terminal. If air bubbles form within the soldering paste, the openings 324 provide an escape route for the air bubbles to move upward during the downward press of the flat surface 116a onto the metal terminal 108a. The openings 324 thus help to void air bubbles that form inside the soldering joints 118.
In exemplary embodiments, the bend 326 is a modification of the flat surface 116 of the spring 114. Both springs 114 include bends 326, though one is featured in the detailed drawings of
While the openings 324 and the bend are part of the springs 114, the protrusions 328 are part of the metal terminals 108a and 110a. As illustrated in
The prior art spring 214 is illustrated in
The first portion 302 touches and rests on the surface to which the SPD 200 is mounted, such as a printed circuit board. The second portion 304 is somewhat orthogonal to the first portion 302 and is connected between the first portion and the third portion 306. The third portion 306 is bent relative to the second portion 304 at an obtuse angle (e.g., greater than 90 degrees). The flat surface 216, as already shown and described, is designed to be soldered to a metal electrode of the SPD 200, and is disposed at an obtuse angle relative to the third portion 306. The four portions are arranged so that the flat surface 216 will move upward in response to an overvoltage event, thus disengaging the flat surface from the metal electrode of the SPD 200.
The novel spring 114 in
In exemplary embodiments, the openings 324 help to mitigate the occurrence of air bubbles in the soldering paste that may be disposed between the metal terminal of the SPD 100 and the flat surface 116 while the bend 326 helps to prevent soldering paste oozing from between the flat surface 116 and the metal terminal. Further, as illustrated in
The bend 326 extends along one side of the flat surface 116 and has a width, w2 while the flat surface has a width, w3. In exemplary embodiments, the two widths are the same, that is, w2=w3. The bend 326 may alternatively be on another side of the flat surface 116, whether the side orthogonal or opposite to its current location. Or the spring 114 may have multiple bends disposed on more than one side of the flat surface 116.
The prior art metal terminal, which may be either metal terminal 208 or metal terminal 210 (
The novel metal terminal is similarly made up of an electrically conductive material, with a short terminal 108a/110a, a long terminal 108b/110b and a body 108c/110c. The short terminal 108a/110a and the long terminal 108b/110b stick out from the MOV stack, with the long terminal being bent while the body 108c/110c is disposed between two MOVs (see, e.g.,
In exemplary embodiments, the protrusion 328 provides a gap, w4, between the metal terminal 108a/110a and the flat surface of the spring. Like the bend 326 of the novel spring 114, the protrusion 328 provides space for a controlled amount of soldering paste to be applied between the flat surface 116 of the spring 114 and the metal terminal 108a/110a. In exemplary embodiments, the gap of the bend 326, w1, is equal to the gap of the protrusion 328, w4, w1=w4.
As illustrated in
In exemplary embodiments, the novel SPD 100 which provides a high soldering strength thermal cutoff terminal can be extended to all flat surfaces of the SPD. The use of the openings 324 and the bend 326 in the spring as well as the protrusion 328 in the metal terminal can be extended to other flat surfaces being connected using soldering paste, not just the springs and the metal terminals. With ease of assembly and low cost, the principles described herein can be applied to a wide variety of metal soldering operations. The result is high soldering performance to enhance soldering strength and product reliability.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
While the present disclosure makes reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claim(s). Accordingly, it is intended that the present disclosure not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210108518.1 | Jan 2022 | CN | national |
