Thin film resistor having surface mounted trimming bridges for incrementally tuning resistance

A resistor assembly is disclosed and comprises a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. The resistor assembly also comprises a second layer disposed underneath the surface mounted layer. The second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer. The plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor. The resistor assembly also comprises a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

INTRODUCTION

The present disclosure relates to a thin film resistor. More particularly, the present disclosure relates to a thin film resistor having a plurality of surface mounted trimming bridges, where each trimming bridge is removable to incrementally tune a resistance of the thin film resistor.

BACKGROUND

Thin film resistors are typically created by depositing a thin film constructed of a metal alloy upon a substrate. Specifically, the thin film is deposited upon a substrate using a sputtering deposition process. Thin film resistors are found in laminate substrates used for electronic applications such as, for example, printed circuit boards.

A thin film resistor may be attached to a top surface of the electronic substrate or, alternatively, embedded within the laminate substrate. When embedded in a substrate, the thin film resistor is referred to as an embedded thin film resistor. Embedded thin film resistors are typically composed of nickel-chromium alloys such as, for example, nickel chromium aluminum silicon (NiCrAlSi). The nickel-chromium alloy is deposited upon a copper foil. The nickel-chromium alloy and the copper foil are then bonded to a dielectric layer using a lamination process, where the copper foil acts as a conductive layer and the nickel-chromium alloy acts as a resistive layer. The resistive layer is then etched to define discrete embedded thin film resistors. Any number of etching process may be used to define the embedded thin film resistors, however, the specific etching process is selected based on the specific metals included in the nickel-chromium alloy.

The resistance variation of a thin film resistor depends upon several factors. Specifically, physical properties such as, for example, film thickness, residual stress, uniformity, and surface roughness of the conductive layer may affect the resistance variation of the thin film resistor. Moreover, the sheet resistance of the nickel-chromium alloy before etching is inversely proportional to thickness. The thickness of the nickel-chromium layer is determined based on sputtering parameters such as linear speed and power, however, the sputtering parameters may be difficult to control. Additionally, the resolution and specific type of etching used to create the discrete resistor elements also affects the resistance variations. Finally, the temperature and cycle time of the lamination process also affects the resistance of the nickel-chromium alloy. Thus, it is challenging to control the resistance variation of a thin film resistor.

SUMMARY

According to several aspects, a resistor assembly is disclosed. The resistor assembly comprises a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. The resistor assembly also comprises a second layer disposed underneath the surface mounted layer. The second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer. The plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor. The resistor assembly also comprises a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

In another aspect, a multilayer substrate is disclosed. The multilayer substrate comprises an uppermost layer defining an uppermost surface of the multilayer substrate, a plurality of lower layers that are disposed underneath the uppermost layer, and a resistor assembly. The resistor assembly comprises a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. The surface mounted layer is disposed along the uppermost layer of the multilayer substrate. The resistor assembly further comprises a second layer disposed underneath the surface mounted layer within one of the plurality of lower layers, where the second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer. The plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor. The resistor assembly also includes a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

In still another aspect, a method for tuning a resistor assembly is disclosed. The method includes obtaining an initial resistance measurement of the resistor assembly by probing a surface mounted layer of the resistor assembly, where an embedded thin film resistor is electrically coupled to a tuning pattern of the surface mounted layer. The tuning pattern comprises one or more pairs of conductive traces. The method further comprises comparing the initial resistance measurement to a defined resistance criteria. In response to determining the initial resistance measurement does not satisfy the defined resistance criteria, the method includes removing one or more trimming bridges that are part of a plurality of trimming bridges of the surface mounted layer. Each pair of conductive traces are electrically coupled to one another by the plurality of trimming bridges.

DETAILED DESCRIPTION

A resistor assembly is disclosed. The resistor assembly comprises a thin film resistor electrically coupled to a surface mounted layer. The surface mounted layer of the resistor assembly is disposed along an uppermost layer of a multilayer substrate, and comprises of at least a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. In one approach, the thin film resistor is an embedded thin film resistor, however, in an alternative approach the thin film resistor is a surface mounted component disposed along the uppermost surface of the multilayer substrate. The resistance of the thin film resistor is fine-tuned by incrementally removing the trimming bridges to achieve a defined resistance criterion. Accordingly, the method of fine tuning the resistance of the thin film resistor is independent of the processes used to fabricate the thin film resistor and the multilayer substrate.

Referring toFIG. 1, an exemplary multilayer substrate10is shown. The multilayer substrate10comprises three or more dielectric layers12and a resistor assembly20. Specifically, the multilayer substrate10comprises of an uppermost layer14and a plurality of lower layers16that are disposed underneath the uppermost layer14. In the embodiment as shown, the lower layers16comprise of one middle layer18A and a carrier layer that is referred to as a bottommost layer18B. Although only one middle layer18A is shown, in an alternative approach the lower layers16comprise of more than one middle layer18A. The bottommost layer18B defines a lowermost surface22of the multilayer substrate10. A plurality of solder balls27are disposed along the lowermost surface22of the multilayer substrate10.

The resistor assembly20comprises a surface mounted layer24and a second layer26. The second layer26of the resistor assembly20is disposed underneath the surface mounted layer24and comprises an embedded thin film resistor28. The surface mounted layer24of the resistor assembly20is disposed along an uppermost surface30of the multilayer substrate10and is positioned within the uppermost layer14of the multilayer substrate10. In the embodiment as shown inFIG. 1, the second layer26of the resistor assembly20is disposed within the middle layer18A of the multilayer substrate10. In an embodiment, if the multilayer substrate10comprises more than one middle layer18A, then the thin film resistor28is disposed within any of the middle layers18A. In one non-limiting embodiment, the embedded thin film resistor28is constructed of a nickel-chromium alloy such as, but not limited to, nickel chromium aluminum silicon (NiCrAlSi). However, it is to be appreciated that the embedded thin film resistor28may be constructed of other resistive alloys as well.

FIG. 2is a top view of the uppermost surface30of the multilayer substrate10shown inFIG. 1, where the surface mounted layer24of the resistor assembly20is visible. The embedded thin film resistor28is not visible inFIG. 2, as the embedded thin film resistor28is disposed within the middle layer18A of the multilayer substrate10(seen inFIG. 1). AlthoughFIGS. 1, 2, and 3illustrate an embedded thin film resistor28, in an alternative approach seen inFIG. 10the resistor assembly20comprises a surface mounted thin film resistor428that is not embedded within the multilayer substrate10. Instead, the thin film resistor428is disposed along the uppermost surface30of the multilayer substrate10. The thin film resistor428is described below.

Referring back toFIG. 2, the surface mounted layer24comprises a first conductive section36. AlthoughFIG. 2illustrates the surface mounted layer24comprising of only the first conductive section36, in the embodiments shown inFIGS. 4A, 4B, and 5, the surface mounted layer24also comprises a second conductive section38as well, which is described below. Referring toFIG. 2, the first conductive section36of the surface mounted layer24comprises a first conductive trace40, a second conductive trace42, and a plurality of trimming bridges44that electrically couple the first conductive trace40to the second conductive trace42. As explained below, the plurality of trimming bridges44are each removeable to incrementally adjust a resistance of the embedded thin film resistor28.

AlthoughFIG. 2illustrates five trimming bridges44electrically coupling the first conductive trace40to the second conductive trace42, the surface mounted layer24may comprise any number of multiple trimming bridges44. It is to be appreciated that increasing the number of trimming bridges44results in the ability to adjust the resistance of the embedded thin film resistor28with greater precision. The surface mounted layer24of the resistor assembly20is constructed of a conductive alloy such as, but not limited to, copper or aluminum.FIG. 2also illustrates the plurality of trimming bridges44spaced at equal distances D from one another, where spacing the trimming bridges44at equal distances D from one another result in a linear increase in the resistance of the embedded thin film resistor28as each trimming bridge44is removed. In another embodiment, the trimming bridges44are spaced at unequal distances from one another. However, it is to be appreciated that spacing the trimming bridges44at unequal distances from one another results in a non-linear increase in resistance between each trimming bridge44.

In the embodiment as shown, the second conductive trace42is positioned radially outward relative to the first conductive trace40. The first conductive trace40and the second conductive trace42are arranged concentrically with respect to one another relative to a common central axis46. The first conductive trace40and the second conductive trace42are both comprised of a plurality of segments48that are arranged in an arcuate profile. Therefore, the first conductive trace40and the second conductive trace42both comprise an arcuate profile. Although an arcuate profile is illustrated in the figures, it is to be appreciated that the first conductive trace40and the second conductive trace42are not limited to the profile as shown in the figures and may comprise of other profiles shaped as open polygons. For example, in another embodiment, the first conductive trace40and the second conductive trace42are shaped as an open pentagon, where the fifth line segment of the pentagon is omitted. However, it is to be appreciated the arcuate profile as seen inFIG. 2is more compact and requires less space along the uppermost surface30of the multilayer substrate10when compared to some alternative profiles.

The first conductive trace40and the second conductive trace42both have the same width W. Furthermore, the first conductive trace40and the second conductive trace42have a constant width W along their respective lengths L. It is to be appreciated that the equal distances D between the trimming bridges44, the constant width W of the conductive traces40,42, and the arcuate profile of the conductive traces40,42all result in a linear difference in resistance as the trimming bridges44are incrementally removed. Thus, as explained below and as seen inFIGS. 6A-6E, when the trimming bridges44are removed, this results in a linear increase in resistance of the resistor assembly20.

FIG. 3is a perspective view of the resistor assembly20shown inFIGS. 1 and 2. Referring toFIGS. 1, 2, and 3, the resistor assembly20further comprises a plurality of vias50and a conductive path52, where the conductive path52is part of the second layer26of the resistor assembly20. Both the vias50and the conductive path52are constructed of a conductive alloy. The conductive path52is divided into a first portion52A and a second portion52B, where the resistor assembly20electrically couples the first portion52A of the conductive path52to the second portion52B of the conductive path52. Specifically, as seen inFIGS. 1 and 3, one of the plurality of vias50A electrically couples the first portion52A of the conductive path52to the second conductive trace42of the surface mounted layer24.

Referring specifically toFIG. 3, the embedded thin film resistor28comprises a first section60and a second section62. The first section60of the embedded thin film resistor28is shaped to correspond with a profile of the first conductive trace40. For example, in the embodiment as shown, the first conductive trace40comprises an arcuate profile. Accordingly, the first section60of the embedded thin film resistor28is shaped as an arcuate profile as well. The second section62of the embedded thin film resistor28comprises a linear profile. In the embodiment as shown inFIG. 3, the second section62of the embedded thin film resistor28defines a first end64and a second end66. The first end64of the second section62of the embedded thin film resistor28generally opposes but does not make electrical contact with an end68of the first portion52A of the conductive path52. However, the second end66of the second section62of the embedded thin film resistor28is electrically coupled to the second portion52B of the conductive path52. Specifically, in the embodiment as shown inFIG. 3, an electrical trace76electrically couples the second end66of the second section62of the embedded thin film resistor28with an end of the second portion52B of the conductive path52.

The plurality of vias50electrically couple the first conductive trace40of the surface mounted layer24to the embedded thin film resistor28. Specifically, the plurality of vias50electrically couple the first conductive trace40of the surface mounted layer24to the second section62of the embedded thin film resistor28. As mentioned above, the first conductive trace40is electrically coupled to the second conductive trace42by the trimming bridges44. Accordingly, as seen inFIG. 3, current C flows from the first portion52A of the conductive path52to the via50A, and from the via50A to the second conductive trace42. The current C then flows from the second conductive trace42to the first conductive trace40though the trimming bridges44, and from the first conductive trace40to the first section60of the embedded thin film resistor28by the vias50. The current C then flows through the thin film resistor28and to the second portion52B of the conductive path52through the electrical trace76.

FIG. 4Ais a top view of the uppermost surface30of the multilayer substrate10, where the surface mounted layer24of the resistor assembly20comprises both the first conductive section36and the second conductive section38.FIG. 4Bis an alternative embodiment of the surface mounted layer24shown inFIG. 4B.FIG. 5is an elevated perspective view of the resistor assembly20shown inFIG. 4A. Referring toFIGS. 4A and 5, in the embodiment as shown, the trimming bridges44of the first conductive section36are referred to as first trimming bridges144and the vias150of the first conductive section36are referred to as the first vias150. The resistor assembly20further comprises a third conductive trace70and a second conductive trace72that are electrically coupled to one another. Specifically, the third conductive trace70and the fourth conductive trace72are electrically coupled to one another by a plurality of second trimming bridges74. The third conductive trace70is electrically coupled to the embedded thin film resistor28by a plurality of second vias80.

Referring toFIG. 4A, the fourth conductive trace72is positioned radially outward relative to the third conductive trace70. The first conductive trace and the second conductive trace are arranged concentrically with respect to one another. Similarly, the third conductive trace70and the fourth conductive trace72are arranged concentrically with respect to one another. The first conductive trace40, the second conductive trace42, the third conductive trace70, and the fourth conductive trace72are each positioned radially outward relative to the common central axis46. The first conductive trace40, the second conductive trace42, the third conductive trace70and the fourth conductive trace72each comprise an arcuate profile. As mentioned above, the first conductive trace40, the second conductive trace42, the third conductive trace70and the fourth conductive trace72are not limited to the profile as shown in the figures.

Referring toFIG. 5, the second portion52B of the conductive path52is electrically coupled to the fourth conductive trace72by one of the second vias80A. In the embodiment as shown inFIG. 5, the embedded thin film resistor28comprises the first section60, the second section62, and an additional third section164. The first section60of the embedded thin film resistor28is shaped to substantially correspond with a profile of the first conductive trace40, the second section62of the embedded thin film resistor28comprises a linear profile, and the third section164of the embedded thin film resistor28is shaped to substantially correspond with a profile of the third conductive trace70.

Referring back toFIG. 4A, in the embodiment as shown the surface mounted layer24defines an axis of symmetry A-A disposed along the uppermost surface30of the multilayer substrate10. The axis of symmetry A-A positioned perpendicular with respect to the common central axis C-C. As seen inFIG. 4A, the profiles of the first conductive trace40and the second conductive trace42are identical to the profiles of the third conductive trace70and the fourth conductive trace72. Furthermore, as seen inFIG. 4A, the surface mounted layer24comprises an equal number of first trimming bridges144and second trimming bridges74. Thus, the first conductive section36of the surface mounted layer24is symmetrical with respect to the second conductive section38of the surface mounted layer24.

AlthoughFIG. 4Aillustrates a symmetrical surface mounted layer24, it is to be appreciated that in another approach the surface mounted layer24is not symmetrical. For example, in the embodiment as shown inFIG. 4B, the surface mounted layer24comprises an unequal number of first trimming bridges144and second trimming bridges74. Specifically, in the example as shown, there are five first trimming bridges144but three second trimming bridges74. However, it is to be appreciated thatFIG. 4Bis merely exemplary in nature, and the surface mounted layer24may comprise other asymmetrical configurations as well. For example, in another embodiment, the first conductive trace40and the second conductive trace42comprises a profile that does not match the profile of the third conductive trace70and the fourth conductive trace72. In the example as shown inFIG. 4B, the ends190,192of the third conductive trace70and the ends194,196the fourth conductive trace72(shown in phantom line) are omitted.

FIGS. 6A-6Eillustrate an exemplary process of removing the trimming bridges74,144to tune a resistance of the embedded thin film resistor28(not shown inFIGS. 6A-6E). It is to be appreciated that as the trimming bridges74,144are removed, the resistance of the embedded thin film resistor28increases. For example,FIG. 6Aillustrates an initial condition, where all of the first trimming bridges144and the second trimming bridges74are intact. Before any trimming bridges74,144are removed, the resistor assembly20has an initial resistance of R+r0, where r0=0.

The individual first trimming bridges144are arranged as144A,144B,144C,144D,144E, where the first trimming bridge144A is disposed between the end180of the first conductive trace40and the end182of the second conductive trace. The first trimming bridge144E is disposed between the end184of the first conductive trace40and the end186of the second conductive trace42. The first trimming bridges144A,144B,144C,144D,144E are arranged in chronological order. Accordingly, the first trimming bridge144A is positioned directly adjacent to first trimming bridge144B, first trimming bridge144B is positioned directly adjacent to first trimming bridge144C, first trimming bridge144C is positioned directly adjacent to first trimming bridge144D, and first trimming bridge144D is positioned adjacent to first trimming bridge144E. Similarly, the individual second trimming bridges74are arranged as74A,74B,74C,74D,74E, where the second trimming bridge74A is disposed between the end190of the third conductive trace70and the end192of the fourth conductive trace72. The second trimming bridge74E is disposed between the end194of the third conductive trace70and the end196of the fourth conductive trace72. The second trimming bridges74A,74B,74C,74D,74E are arranged in chronological order.

One or more trimming bridges74,144are then removed to incrementally increase the resistance of the resistor assembly20. For example, referring toFIG. 6B, one of the first trimming bridges144and one of the second trimming bridges74are removed. Specifically, the trimming bridges144A and74A are removed using laser ablation. Accordingly, the resistance of the resistor assembly20is now R+r1, where r represents a resistance value that is created by the removal of trimming bridges74A and144A. Similarly, as seen inFIG. 6C, the trimming bridges74B and144B are removed using laser ablation. Since the surface mounted layer24is symmetrical, r2 is twice the value of r1. Accordingly, the resistance of the resistor assembly20is now R+r2, where r2 is twice the value of r1. Referring now toFIG. 6D, in an embodiment, the trimming bridges74C,144C are removed using laser ablation, and the resistance of the resistor assembly20is now R+r3, where r3 is three times the value of r1. Finally, as seen inFIG. 6E, the trimming bridges74D,144D are removed using laser ablation, and the resistance of the resistor assembly20is now R+r3, where r4 is four times the value of r1.

The surface mounted layer24shown inFIGS. 6A-6Eis symmetrical, and therefore there is a linear increase in resistance are the trimming bridges74,144are removed. However, if the surface mounted layer24is asymmetrical, then the resistance simply increases in value (i.e., r1<r2<r3<r4). Furthermore, it is to be appreciated that while laser ablation is described, other methodologies may also be used to remove the trimming bridges73,144as well. Some examples of other approaches to remove the trimming bridges74,144include, but are not limited to, chemical etching or mechanical removal.

Referring generally toFIGS. 6A-6E, adjacent trimming bridges74,144are removed, which results in an incremental linear increase in resistance. Specifically, the first trimming bridge144A and the second trimming bridge74A are removed. Next, the first trimming bridge144B is removed, where the first trimming bridge144B is positioned directly adjacent to the first trimming bridge144A. Moreover, the second trimming bridge74B is removed, where the second trimming bridge74B is positioned directly adjacent to the second trimming bridge74A. Accordingly, there is a linear increase in resistance of r1.

FIG. 7is a schematic diagram of an exemplary four-point probe200configured to probe the surface mounted layer24of the resistor assembly20(seen inFIGS. 6A-6E) and obtain resistance measurements. Specifically, the four-point probe200performs four-point sensing, which is also referred to as Kelvin sensing. The four-point probe200comprises two insulated clips201A,201B. The insulated clip201A comprises two probes202A,204A, and the insulated clip201B comprises probes202B,204B. The probes202A,202B are configured to measure a current and the probes204A,204B configured to measure voltage.

FIG. 8is an illustration of the surface mounted layer24of the resistor assembly20. A first probing location206A is located on the end182of the second conductive trace42of the surface mounted layer24and corresponds to the clip201A. The four-point probe200measures a first current measurement I1and a first voltage measurement V1at the first probing location206A. A second probing location206B is located on the end196of the third conductive trace72and corresponds to the clip201B. the four-point probe200measures a second current measurement I2and a second voltage measurement V2. The current measurements I1, I2and the voltage measurements V1, V2are used to determine the resistance of the resistor assembly20.

FIG. 9is an exemplary process flow diagram illustrating a method300for tuning the resistance of the resistor assembly20. Referring generally toFIGS. 5, 6A-6E, and 7-9, the method300begins at block302. In block302, an initial resistance measurement of the resistor assembly20is obtained by probing the surface mounted layer24of the resistor assembly20by the four-point probe200. Referring specifically toFIG. 5, the surface mounted layer24of the resistor assembly20is electrically coupled to the embedded thin film resistor28by a tuning pattern disposed along the surface mounted layer24of the resistor assembly20. The tuning pattern comprises one or more pairs of conductive traces (i.e., the conductive traces40,42and the conductive traces70,72), where each pair of conductive traces are electrically coupled to one another by the plurality of trimming bridges74,144. The method300can then proceed to block304.

In block304, the initial resistance measurement is compared to a defined resistance criteria. The defined resistance criteria indicates a resistance range or, alternatively, a resistance threshold of the resistor assembly20. For example, in one non-limiting embodiment, the predefined resistance criteria is a resistance range that comprises of a tolerance of two percent. The method300can then proceed to decision block306.

In decision block306, the method300can either proceed to block308or terminate. Specifically, if the initial resistance measurement satisfies the defined resistance criteria, then the method300can then terminate. However, in response to determining the initial resistance measurement does not satisfy the defined resistance criteria the method300can then proceed to block308.

In block308, one or more trimming bridges74,144that are part of the surface mounted layer24are removed. For example, in the embodiment as shown inFIGS. 6A-6E, the surface mounted layer24comprises two pairs of conductive traces (40,42, and70,72). Therefore, two trimming bridges74,144are removed at a time. However, in the embodiment as shown inFIGS. 2 and 3, the surface mounted layer24comprises only one pair of conductive traces40,42. Accordingly, one trimming bridge44is removed at a time. As mentioned above, the trimming bridges74,144are removed using laser ablation. The method300can then proceed to block310.

In block310, a subsequent resistance measurement of the resistor assembly20is obtained by probing the surface mounted layer24of the resistor assembly20by the four-point probe200. The method300can then proceed to block312.

In block312, the subsequent resistance measurement of the resistor assembly20is compared to the defined resistance criteria. The method300can then proceed to decision block314.

In decision block314, the method300can either proceed to block308or terminate. Specifically, if the subsequent resistance measurement satisfies the defined resistance criteria, then the method300can then terminate. However, in response to determining the subsequent resistance measurement does not satisfy the defined resistance criteria the method300can then proceed to block316.

In block316, one or more subsequent trimming bridges74,144that are part of the surface mounted layer24are removed. For example, the one or more subsequent trimming bridges74,144are shown inFIG. 6Cas trimming bridges74B,144B. In the embodiment as shown inFIG. 6D, the one or more subsequent trimming bridges74,144are shown as74C,144C. In the embodiment as shown inFIG. 6E, the one or more subsequent trimming bridges74,144are shown as74D,144D. The method300can then return to block310to obtain another subsequent resistance measurement.

FIG. 10illustrates an alternative embodiment of a resistor assembly20comprising a thin film resistor428. As seen inFIG. 10, the thin film resistor428is not embedded within the multilayer substrate10. Instead, the thin film resistor428is part of the surface mounted layer24. In other words, the thin film resistor428is disposed along the uppermost surface30of the multilayer substrate10(FIG. 1). However, it is to be appreciated that surface mounting the thin film resistor428requires more area along the uppermost surface30of the multilayer substrate10when compared to the embedded thin film resistor28. Similar to the embodiment as shown inFIG. 5, the first conductive trace40is electrically coupled to the second conductive trace42by the plurality of first trimming bridges144, and the third conductive trace70is electrically coupled to the fourth conductive trace72by the plurality of second trimming bridges74.

The thin film resistor428is electrically coupled to the first conductive trace40by an electrical trace450. Specifically, the thin film resistor428defines a first end460and a second end462, where the first end460of the thin film resistor428is electrically coupled to the first conductive trace40by the electrical trace450. The thin film resistor428is electrically coupled to the third conductive trace70by an electrical trace452. Specifically, the second end462of the thin film resistor428is electrically coupled to the third conductive trace70by the electrical trace452. Both electrical traces450,452are conductive lines or, alternatively, solder drops.

The second conductive trace42is electrically coupled to the first portion52A of the conductive path52by an electrical trace456. Similarly, the fourth conductive trace72is electrically coupled to the second portion52B of the conductive path52by an electrical trace458. The electrical traces450,452,456, and458are all part of the surface mounted layer24of the resistor assembly20.

Referring generally to the figures, the present disclosure offers various technical effects and benefits. Specifically, the resistance of the thin film resistor is fine-tuned by incrementally removing the trimming bridges to achieve a defined resistance criterion. Accordingly, the disclosure provides a system and method for fine-tuning the resistance of the thin film resistor that is independent of the processes used to fabricate the thin film resistor and the multilayer substrate. The disclosed approach for fine-tuning a thin film resistor is especially advantageous, since it may be relatively difficult to control the fabrication processes used to create the thin film resistor and the corresponding multilayer substrate.

Further, the disclosure comprises embodiments according to the following clauses:

Clause 1: resistor assembly, comprising: a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace; a second layer disposed underneath the surface mounted layer, wherein the second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer, wherein the plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor; and a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

Clause 2: the resistor assembly of clause 1, wherein the plurality of trimming bridges are spaced at equal distances from one another, and wherein spacing the trimming bridges at equal distances from one another results in a linear increase in the resistance of the embedded thin film resistor as each trimming bridge is removed.

Clause 3: the resistor assembly of any of clauses 1 or 2, wherein the first conductive trace and the second conductive trace are arranged concentrically with respect to one another.

Clause 4: the resistor assembly of any of clauses 1, 2, or 3, wherein the first conductive trace and the second conductive trace both comprise an arcuate profile.

Clause 5: the resistor assembly of any of clauses 1, 2, 3, or 4, further comprising a conductive path that is part of the second layer of the resistor assembly, wherein one of the plurality of vias electrically couples a first portion of the conductive path to the second conductive trace of the surface mounted layer.

Clause 6: the resistor assembly of any of clauses 1, 2, 3, 4, or 5, wherein a second portion of the conductive path is electrically coupled to the embedded thin film resistor.

Clause 7: the resistor assembly of any of clauses 1, 2, 3, 4, 5, or 6, wherein the plurality of vias are a plurality of first vias and the plurality of trimming bridges are first trimming bridges, and wherein the surface mounted layer further comprises: a third conductive trace and a fourth conductive trace electrically coupled to one another, wherein the third conductive trace and the fourth conductive trace are electrically coupled to the embedded thin film resistor by a plurality of second vias.

Clause 8: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, or 7, wherein the third conductive trace and the fourth conductive trace are electrically coupled to one another by a plurality of second trimming bridges.

Clause 9: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7, or 8, wherein the first conductive trace and the second conductive trace are arranged concentrically with respect to one another, and the third conductive trace and the fourth conductive trace are arranged concentrically with respect to one another.

Clause 10: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein first conductive trace, the second conductive trace, the third conductive trace, and the fourth conductive trace each comprise an arcuate profile.

Clause 11: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the surface mounted layer comprises an equal number of first trimming bridges and second trimming bridges.

Clause 12: a multilayer substrate, comprising: an uppermost layer defining an uppermost surface of the multilayer substrate; a plurality of lower layers that are disposed underneath the uppermost layer; and a resistor assembly, comprising: a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace, wherein the surface mounted layer is disposed along the uppermost layer of the multilayer substrate; a second layer disposed underneath the surface mounted layer within one of the plurality of lower layers, wherein the second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer, wherein the plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor; and a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

Clause 13: the multilayer substrate of clause 12, wherein the lower layers further comprise a one middle layer and a lower layer, wherein the embedded thin film resistor is disposed within the middle layer.

Clause 14: the multilayer substrate of any of clauses 12 or 13, wherein the plurality of trimming bridges are spaced at equal distances from one another, wherein spacing the trimming bridges at equal distances from one another results in a linear increase in the resistance of the embedded thin film resistor as each trimming bridge is removed.

Clause 15: the multilayer substrate of any of clauses 12, 13 or 14, wherein the plurality of vias are a plurality of first vias and the plurality of trimming bridges are first trimming bridges, and wherein the surface mounted layer further comprises: a third conductive trace and a fourth conductive trace electrically coupled to one another, wherein the third conductive trace and the fourth conductive trace are electrically coupled to the embedded thin film resistor by a plurality of second vias.

Clause 16: the multilayer substrate of any of clauses 12, 13, 14, or 15, wherein the third conductive trace and the fourth conductive trace are electrically coupled to one another by a plurality of second trimming bridges.

Clause 17: a method for tuning a resistor assembly, the method comprising: obtaining an initial resistance measurement of the resistor assembly by probing a surface mounted layer of the resistor assembly, wherein an embedded thin film resistor is electrically coupled to a tuning pattern of the surface mounted layer, wherein the tuning pattern comprises one or more pairs of conductive traces; comparing the initial resistance measurement to a defined resistance criteria; and in response to determining the initial resistance measurement does not satisfy the defined resistance criteria, removing one or more trimming bridges that are part of a plurality of trimming bridges of the surface mounted layer, wherein each pair of conductive traces are electrically coupled to one another by the plurality of trimming bridges.

Clause 18: the method of clause 17, further comprising: obtaining a subsequent resistance measurement of the resistor assembly is obtained by probing the surface mounted layer of the resistor assembly by the four-point probe; and comparing the subsequent resistance measurement of the resistor assembly to the defined resistance criteria.

Clause 19: the method of any of clauses 17 or 18, further comprising: in response to determining the subsequent resistance measurement does not satisfy the defined resistance criteria, removing one or more subsequent trimming bridges that are part of the surface mounted layer.

Clause 20: the method of any of clauses 17, 18, or 19, wherein the one or more trimming bridges are removed using laser ablation.