FIELD

The present disclosure relates to common mode filters.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

Chokes are commonly used in electronic circuits to block signal frequencies above a desired range, while at the same time allowing DC (direct current) or low frequency signals to pass. Thus, chokes have been employed to prevent electromagnetic interference (EMI) from disturbing various electronic devices. EMI is generated, for example, as a byproduct of switching regulators that have current and voltage waveforms with fast rise and fall times. Because switching regulators are typically contained in power supplies, EMI may be transmitted through an electronic device via the power supply conductors. Excessive EMI can lead to logic errors in a computer and can cause interference with other adjacent electronic components. Of course, there are many other applications where a choke may be needed to filter unwanted signals.

A choke is typically provided by a magnetic core through which, or around which, conductors or windings are positioned. Thus, a typical choke defines first and second mutually coupled magnetic paths. A choke may be schematically represented as a low pass filter. For any choke to function as intended, its inductance or inductive reactance should not fall below a specific minimum even though the current in a winding rises to a maximum value. Beyond the maximum current value, the reactance falls off significantly. The choke's ability to impede interference signals drops, thereby allowing the passage of unwanted signals. It is therefore typically desirable to prevent a choke from being driven into such a saturation condition.

SUMMARY This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

According to various aspects, exemplary embodiments are disclosed of common mode filters. In an exemplary embodiment, a common mode filter generally includes a magnetic substrate. The magnetic substrate includes an upper portion having one or more layers and a lower portion having one or more layers. A first interior conductor having a spiral pattern is on a top layer of the lower portion of the magnetic substrate. A second interior conductor having a spiral pattern is on a bottom layer of the upper portion of the magnetic substrate. A dielectric layer is between the first and second interior conductors to thereby electrically insulate the first interior conductor from the second interior conductor.

Also disclosed are methods for manufacturing common mode filters. In an exemplary embodiment, a method generally includes tape casting a magnetic substrate such that the magnetic substrate includes an upper portion having one or more layers and a lower portion having one or more layers. This exemplary method also includes forming a first interior conductor by a thick film process such that the first interior conductor has a spiral pattern on a top layer of the lower portion of the magnetic substrate. This exemplary method further includes forming a second interior conductor by a thick film process such that the second interior conductor has a spiral pattern on a bottom layer of the upper portion of the magnetic substrate. This exemplary method additionally includes forming a dielectric layer by a thick film process such that the dielectric layer is between the first and second interior conductors to thereby electrically insulate the first interior conductor from the second interior conductor.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure

FIG. 1 is a perspective view of a first exemplary embodiment of a common mode filter;

FIG. 2 is an exploded perspective view of the common mode filter shown in FIG. 1 , and illustrating its magnetic ferrite substrate that may be formed by tape casting, and its conductor patterns and dielectric layer that may be formed on the magnetic ferrite substrate by thick-film printing according to exemplary embodiments;

FIG. 3 is a top view of the common mode filter shown in FIG. 2, and illustrating the arrangement of the conductor patterns and dielectric layer;

FIGS. 4A through 4D are top views of the conductor patterns shown in FIG. 2;

FIG. 5 is an exemplary line graph including plots of impedance (in ohms (Ω) versus frequency (in megahertz (MHz)) measured for a physical prototype of a common mode filter according to the first exemplary embodiment in open, common, and normal modes;

FIG. 6 is an exemplary line graph including plots of impedance (Z), resistance (R), and inductive reactance (X) (all in ohms) versus frequency (in megahertz) measured for a physical prototype of a common mode filter according to the first exemplary embodiment in an open mode;

FIG. 7 is an exemplary line graph including plots of impedance (Z), resistance (R), and inductive reactance (X) (all in ohms) versus frequency (in megahertz) measured for a physical prototype of a common mode filter according to the first exemplary embodiment in a common mode; and

FIG. 8 is another exploded perspective view of the common mode filter shown in FIG. 1 , and illustrating coupling magnetic flux (as represented by arrows) between the conductors according to exemplary embodiments.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

The inventors hereof have recognized the following issues with some conventional common mode filters or chokes. For example, the inventors have discovered that the process for manufacturing the common mode filters is not simple because the process may require placement of multiple sheets to provide alternately connected conductor coils and a pair of magnetic cores. As a result, the manufacturing cost may not satisfy the customer expectations. The inventors have also discovered that some common mode filters are not compact or small enough for a given electrical performance to be used in small electronic devices, such as cellular phones, smart phones, tablet PCs, notebook PCs, etc.

Accordingly, the inventors have developed and disclose herein exemplary embodiments of common mode filters or chokes. For example, disclosed herein are chip type common mode filters that have a laminated structure and that comprise a ferrite magnetic substrate, a dielectric layer, and interior conductors. The dielectric layer and/or interior conductors may be laminated on the magnetic substrate in a direction of thickness. At least one pair of adjacent or overlapped conductors are configured or provided with spiral conductor patterns. The dielectric layer may be printed on a conductor pattern by a thick-film process to electrically insulate it. This exemplary embodiments includes a novel footprint with better or improved electrical properties as compared to a conventional common mode filter. Also, this exemplary embodiment of a common mode filter may be manufactured by a more simple or less complex manufacturing process as it allows for elimination of step for placing multiple sheets in order to provide alternately connected conductor coils, dielectric layers, and magnetic cores.

With reference now to the figures, FIG. 1 illustrates an exemplary embodiment of a common mode filter embodying one or more aspects of the present disclosure. As shown in FIG. 1 , the common mode filter 100 has a monolithic structure in that its components may be mounted directly onto surfaces of laminated layers of the magnetic ferrite substrate 1 10 by surface mount technology (SMT). The common mode filter 100 can be used in power circuits such as automotive electronics, etc. Or, for example, the common mode filter 100 may be used in small electronic devices such as mobile phones, smart phones, tablet PCs, notebook PCs, etc.

In FIG. 1 , the common mode filter 100 is illustrated with a generally rectangular body. The body is box-shaped or a cuboid having six generally rectangular flat sides. Alternative embodiments may be shaped differently, e.g., shaped as a cube or prism, etc.

A first pair of end conductors 120 are located on or at a first end portion 1 12 of the magnetic ferrite substrate 1 10. A second pair of end conductors 130 are on or at a second end portion 1 14 of the magnetic ferrite substrate 1 10. The first and second end portions 1 12, 1 14 of the magnetic ferrite substrate 1 10 face in opposite directions to each other.

The table below provides representative physical dimensions for the common mode filter 100 according to the exemplary embodiment shown in FIG. 1. These dimensions (as are all dimensions herein) are examples only as other embodiments may be sized differently.

FIG. 2 is an exploded perspective view of the common mode filter 100 according to the exemplary embodiment. The magnetic ferrite substrate 1 10 includes first, second, third, and fourth layers or portions 140, 140', 142, 142', which are joined together, e.g., layers of ferrite tape laminated together to form the substrate 1 10. The layers 140, 140', 142, 142' may be formed by tape casting, etc. In this example, the magnetic ferrite substrate 1 10 includes a lower portion 170 comprised of layers 140, 142, and an upper portion 172 comprised layers 140', 142'. In this example, the magnetic ferrite substrate 1 10 thus includes four layers 140, 140', 142, 142' although other embodiments may include more or less than four layers. The common mode filter 100 also includes electrically-conductive material forming first, second, third, and fourth interior conductors 150, 150', 152, 152'. The conductors 150, 150', 152, 152' and their patterns may be formed on the magnetic ferrite substrate 1 10 by thick-film printing, etc. Various electrically-conductive materials may be used for the interior conductors 150, 150', 152, and 152'. By way of example only, the materials forming the conductor patterns may generally include silver, gold, silver palladium alloy, etc. By way of further example, the electrically-conductive material (e.g., silver, gold, silver palladium alloy, etc.) may first be formed into an electrically-conductive conductive ink or paste, which is then printed on the substrate to form the conductor patterns of the interior conductors 150, 150', 152, 152'.

The common mode filter 100 further includes a dielectric layer or portion 160. The dielectric layer 160 may be formed on the magnetic ferrite substrate 1 10 by thick- film printing, etc.

With continued reference to FIG. 2, the conductors 150, 152 comprise a first pair of conductors having patterns formed on the respective layers 140, 142 of the lower portion 170 of the magnetic ferrite substrate 1 10. The conductor 150', 152' comprise a second pair of conductors having patterns formed on the respective layers 140', 142' of the upper portion 172 of the magnetic ferrite substrate 1 10.

Each layer 140, 140', 142, 142' of the upper and lower portions 172, 170 of the magnetic ferrite substrate 1 10 has only one conductor pattern thereon. Specifically, the layer 140 includes the conductor 150. The layer 140' includes the conductor 150'. The layer 142 includes the conductor 152. And, the layer 142' includes the conductor 152'.

In addition, at least one pair of the conductors are provided or configured with or in spiral conductor patterns. In this exemplary embodiment, the conductors 150, 150' have generally rectangular spiral conductor patterns. Also in this exemplary embodiment, the conductors 152, 152' are generally operable or configured to function mainly as the leads for the two coils or spiral conductor patterns. The conductors 152, 152' may also be used to help equalize open mode impedance of the two coils.

With reference now to FIGS. 1 and 2, the first and second pairs of end conductors 120, 130 (FIG. 1 ) are each electrically connected to the conductors 150, 150', 152, 152' (FIG. 2). Each of the first and second end portions 1 12 and 114 of the magnetic ferrite substrate 1 10 (shown in FIG. 1 ) is electrically connected with and electrically contacts both the lower portion 170 and the upper portion 172 of the magnetic ferrite substrate 1 10.

As shown in FIG. 2, the common mode filter 100 includes first and second connectors 181 , 181 '. By way of example, the connectors 181 , 181 ' may comprise thru- holes or vias that are punched or otherwise formed in the layers layers 140, 140' of the magnetic ferrite substrate 1 10. The thru-holes or vias are plated or filled with electrically-conductive material (e.g., silver, gold, silver palladium alloy, etc.). For example, the thru-holes or vias may be filled with electrically-conductive ink or paste by thick-film printing such that the electrically-conductive material extends through the layers 140, 140' of the magnetic ferrite substrate 1 10 for connecting the conductors on opposite sides of the layers 140, 140'.

The conductors 150, 152 include terminals or end portions 180, 182 electrically connected by the connector 181. By extending through the ferrite layer 140, the connector 181 is able to electrically connect the terminals 180, 182 even though they are along or on opposite sides of the ferrite layer 140. Similarly, the conductors 150', 152' includes terminals or end portions 180', 182' that are along or on opposite sides of the ferrite layer 140'. The connector 181 ' extends through the ferrite layer 140' to electrically connect the terminals 180,' 182'.

The conductors 150, 152 and their patterns may be formed by a thick film process on the upper surfaces 190, 192 of the layers 140, 142. Likewise, the conductors 150', 152' and their patterns may also be formed by a thick film process on the lower surfaces 190', 192' of the layers 140', 142'. This exemplary embodiment thus includes the interior conductors 150, 150', 152, 152' that are internal to or inside the magnetic ferrite substrate 1 10 and also the end conductors 120, 130 that are exposed on the outside of the magnetic ferrite substrate 1 10.

The dielectric material layer 160 is formed or provided between the lower and upper portions 170, 172 of the magnetic ferrite substrate 1 10. The dielectric material layer 160 is sandwiched between the upper conductor 150 of the lower pair of conductors 150, 152 and the lower conductor 150' of the upper pair of conductors 150', 152'. The dielectric material layer 160 may have a configuration, shape, or pattern that substantially matches or corresponds and is inclusive of the spiral patterns of the conductors 150, 150'. Accordingly, the dielectric material layer 160 is thus operable to electrically insulate the upper conductor 150 from the lower conductor 150' by preventing direct physical galvanic contact between the adjacent or overlapped conductors 150, 150'.

The dielectric material layer 160 may be formed or printed by a thick film process either on the conductor 150 of layer 140 or on the conductor 150' of the layer 140'. The dielectric material layer 160 may comprise a non-magnetic dielectric material, such as titania or titanium dioxide, for example, although other materials may also be used.

FIG. 3 is a top view showing the patterns of the conductors 150, 150', 152, 152' of the common mode filter 100. The arrangement of the conductors' patterns and the dielectric material layer 160 allows the dielectric material layer 160 to electrically insulate the conductor 150 of the lower pair of conductors 150, 152 from the conductor 150' of the upper pair of conductors 150', 152'.

As shown in FIG. 3, the connectors 181 , 181 ' in the laminated ferrite layers 140, 140' (shown in FIG. 2) are aligned with each other. Also, the connector 181 is aligned with the terminals 180, 182 of the respective conductors 150, 152. Similarly, the connector 181 ' is aligned with the terminals 180', 182' of the respective conductors 150', 152'.

FIGS. 4A through 4D are individual top views of the patterns of the respective conductors 150, 150', 152, 152'. As shown by FIG. 4A, the conductor 150 has a generally rectangular spiral pattern. FIG. 4D illustrates the generally rectangular spiral pattern of conductor 150'. Accordingly, the pair of conductors 150, 150' have spiral conductor patterns, and the other pair of conductors 152, 152' have non-spiral conductor patterns.

FIGS. 5 through 7 provide analysis results measured for a sample prototype of the common mode filter 100. These analysis results shown in FIGS. 5 through 7 are provided only for purposes of illustration and not for purposes of limitation.

More specifically, FIG. 5 is an exemplary line graph including plots of impedance (in ohms) versus frequency (in megahertz) for a sample common mode filter according to an exemplary embodiment in open, common, and normal modes. It can be observed in FIG. 5 that the common mode impedance has little difference with open mode impedance, which signifies that there is a very strong coupling between the conductors 150, 150' having the spiral patterns. The coupling between the two conductors 150, 150' having the spiral patterns is realized by common magnetic flux. According to inductor principle, a higher common magnetic flux means a stronger coupling, which, in turn, means higher common mode impedance. FIG. 8 generally illustrates coupling magnetic flux (as represented by arrows) between coil 1 and coil 2.

FIG. 6 is an exemplary line graph including plots of impedance (Z), resistance (R), and inductive reactance (X) (all in ohms) versus frequency (in megahertz) for a sample prototype of the common mode filter 100 in open mode. FIG. 7 is an exemplary line graph including plots of impedance (Z), resistance (R), and inductive reactance (X) (all in ohms) versus frequency (in megahertz) for a sample prototype of the common mode filter 100 in a common mode. Generally, FIGS. 5, 6 and 7 show that the exemplary embodiment of the common mode filter 100 has excellent electrical performance compared with a conventional common mode filter having the same footprint.

Also disclosed are exemplary embodiments of methods of making or manufacturing common mode filters or chokes (e.g., common mode filter 100, etc.) having a laminated structure which is comprised of a magnetic substrate, dielectric material layer, and interior conductors. The dielectric material layer and interior conductors may be laminated on the magnetic substrate in a direction of thickness.

In an exemplary embodiment, a method generally includes forming a magnetic substrate by tape casting, such that the magnetic substrate includes an upper portion with one or more layers and a lower portion with one or more layers. In this example, the upper and lower portions of the magnetic substrate may each include two ferrite tape layers.

This exemplary method also includes forming conductors on surfaces of the layers of the magnetic substrate by a thick film process, including at least one pair of conductors that have spiral patterns. One of the conductors with a spiral pattern may be printed by the thick film process on the uppermost or top layer of the lower portion of the magnetic substrate. The other one of the conductors with a spiral pattern may be printed by the thick film process on the lowermost or bottom layer of the upper portion of the magnetic substrate. Additional conductors may be formed on surfaces of the other layers of the upper and lower portions of the magnetic substrate, such that each magnetic substrate layer may include only one conductor pattern thereon.

The method further includes forming a dielectric layer between the upper and lower portions of the magnetic substrate by a thick film process, such that the dielectric layer is between the conductors having the spiral patterns to thereby electrically insulate the conductors having the spiral patterns from each other. The dielectric layer may be printed by the thick film process either on the conductor of the uppermost layer of the lower portion of the magnetic substrate or on the conductor pattern of the lowermost layer of the upper portion of the magnetic substrate.

With further regard for the conductors, the conductors on the layers of the upper portion of the magnetic substrate may be formed by the thick film process on lower surfaces of the layers of the upper portion. Conversely, the conductors on the layers of the lower portion of the magnetic substrate may be formed by the thick film process on upper surfaces of the layers of the lower portion. Accordingly, the conductors are thus formed such that they are within or internal to the magnetic substrate, and accordingly also referred to herein as interior conductors.

In addition, the method includes forming or providing first and second pairs of end conductors on the respective first and second end portions of the magnetic substrate. The end conductors are electrically connected to the interior conductors. The first and second end portions face in opposite directions to each other.

The method further includes providing, forming, or establishing an electrical connection between the terminals of the pair of interior conductors of the lower portion, and between the terminals of the pair of conductors of the upper portion. These electrical connections may be established by using connectors, such as vias or thru- holes extending through the layers separating the terminals to be connected and filled with electrically-conductive material (e.g., filled with electrically-conductive ink by thick- film printing, etc.). The uppermost or top layer of the upper portion does not include any such vias or thru-holes in this example. Likewise, the lowermost or bottom layer of the lower portion also does not include any such vias or thru-holes in this example.4

Exemplary embodiments disclosed herein may provide one or more (but not necessarily any or all) of the following advantages. For example, exemplary embodiments may provide common mode filters that have better or improved electrical performance (e.g., impedance, resistance, inductive reactance, etc.), are relatively simple to manufacture, and have a similar or same footprint size as some conventional common mode filters or chokes. Exemplary embodiments may provide relatively flat high-current common mode filters that have good high common mode and/or low differential mode impedance. Exemplary embodiments may provide multi-layer structures with high impedance and/or with relatively flexible designs.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. In addition, advantages and improvements that may be achieved with one or more exemplary embodiments of the present disclosure are provided for purpose of illustration only and do not limit the scope of the present disclosure, as exemplary embodiments disclosed herein may provide all or none of the above mentioned advantages and improvements and still fall within the scope of the present disclosure.

Specific dimensions, specific materials, and/or specific shapes disclosed herein are example in nature and do not limit the scope of the present disclosure. The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter (i.e., the disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter). Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being "on", "engaged to", "connected to" or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The term "about" when applied to values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning, then "about" as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters. For example, the terms "generally", "about", and "substantially" may be used herein to mean within manufacturing tolerances.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as "inner," "outer," "beneath", "below", "lower", "above", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements, intended or stated uses, or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.