Patent Application
20160163432
The present invention relates to the field of resistors, and more particularly, to a thin film resistor made at least in part having thermally sprayed layers and using thermal spraying techniques.
Thin film resistors are typically manufactured by depositing resistive films of various alloys onto a non-conductive substrate. Typically, an aluminum oxide or aluminum nitride ceramic substrate is used, but other substrate materials can be used including, but not limited to, glass, diamond, ruby and metallic substrates having a non-conductive coating. The deposited films range in thickness from a few hundred Angstroms to several thousand Angstroms, depending on the desired sheet resistance.
Formation of the resistive films can be accomplished through a range of processes including plasma enhanced chemical vapor deposition (PECVD), chemical vapor deposition (CVD) or physical vapor deposition (PVD), with PVD being the most typical method used for thin film resistor manufacturing. Film deposition with a PVD process is typically performed in a vacuum environment. Deposition rates for a PVD process vary between about 0.005 to about 0.2 micrometers per minute for typical materials used in resistor manufacturing.
In thin film resistor design, the resistor value may be determined through the combination of the sheet resistance of the deposited film, measured in Ohms/Square, and the number of squares defined by the resistor geometry. For example, a 100 ohm resistor can be manufactured using a 50 ohm/square film and a design that has a two (2) square resistor geometry.
While PVD thin film technologies are effective at manufacturing precision resistors at nominal values of 10 ohms or above, the feasibility of creating lower resistance values, such as those in the range of about 10 ohms or less, or about 1 ohm or less, diminishes rapidly due to limitations in achieving the necessary film thicknesses in a practical and commercially reasonable time period. Accordingly, there is a need for a process for manufacturing a resistor that is faster than known techniques, yet is still precise, efficient and cost effective.
Thermal spraying is a process whereby heat is used to soften a material such as a metal or a ceramic, and then particles of the softened material are propelled, such as by a gas, onto a substrate to be coated. Other forms of energy, such as kinetic energy, may be used to accelerate the particles to a velocity whereby plastic deformation occurs when the particles impact the substrate. The particles form a dense coating/layer on the substrate as the particles agglomerate. The material to be thermally sprayed is sometimes referred to as the “feedstock.” An example of equipment used for thermal spraying, and equipment that may be used for making a thin film resistor according to the present invention, is the Kinetic Metallization: Production Coating System, KM-PCS, offered by the Inovati Company of Santa Barbara, Calif.
Thermal spraying techniques can deposit metals at rates several times faster than PVD, PECVD or CVD processes generally used to form thin film resistors. For example, thermal spraying can deposit materials at a deposition rate of about at least 10 micrometers per minute. The high deposition rate of thermal spraying allows low value resistors to be made at a more competitive cost than known techniques. In contrast to thermal spraying, a PVD process cannot achieve the thicknesses required in a practical time period.
Thermal spraying, while typically performed in ambient conditions, can also be performed under a range of environments or conditions to control the oxide level and, to some extent, the structure of the thermally sprayed material. An advantage to spraying in ambient conditions is a reduction in processing time due to lack of required pump down time of a vacuum or other environmentally controlled system. Thermal spraying technologies available in the industry vary by the method of applying material, for example, the type of energy used and by the type of material used as the feedstock.
The present invention provides a means to address the time constraint and cost problems associated with deposition of resistive elements in thin film resistors using known techniques, by the application of thermal spraying technologies to the manufacture of thin film resistors.
In order to minimize the process time and cost in manufacturing thin film resistors, thermal spraying processes and technologies, typically used in a range of industries for rapid deposition of materials for mechanical wear purposes, corrosion resistance, restoration of surfaces and thermal barriers, may be used to deposit a resistive element on a substrate, and also to deposit other materials and layers, to form a thin film resistor, according to the teachings of the present invention.
It is therefore an object, feature, or advantage of the present invention to provide a thin film resistor that uses thermal spraying techniques in the manufacturing process.
According to an aspect of the present invention, a thin film resistor is provided comprising a thermally sprayed resistive element. The resistive element may be formed as a thermally sprayed layer comprising a material that has been thermally sprayed on at least a portion of the surface of a substrate or on a selected layer of the thin film resistor.
According to another aspect of the present invention, a thin film resistor is provided with an alloy bond layer deposited on at least a portion of the surface of a substrate. A thermally sprayed resistive layer is thermally sprayed on at least a portion of the alloy bond layer to form a thermally sprayed resistive element.
A method of making a thin film resistor is also provided. In an embodiment, a thin film resistor is formed by thermally spraying a selected material on a surface of a substrate, or on a selected layer of the thin film resistor, using a thermal spraying process to form a thermally sprayed resistive element.
In another aspect of the present invention, a method of manufacturing a thin film resistor is provided, wherein an alloy bond layer is applied to at least a portion of a surface of a substrate, and a thermally sprayed resistive layer is applied, by a thermal spraying process, to at least a portion of the alloy bond layer, to form a thermally sprayed resistive element.
In another aspect of the present invention, a thin film resistor is provided comprising a substrate having a first surface and an opposite second surface, an alloy bond layer deposited on at least a portion of the first surface of the substrate, and a thermally sprayed resistive layer thermally sprayed on at least a portion of the alloy bond layer. Conductor pads are provided adjacent sides of the thermally sprayed resistive layer and extending along a portion of the alloy bond layer. The conductor pads may comprise first conductor layers and second conductor layers. Adhesion layers may be applied beneath the first conductor layers. An electrical connection is provided from a first surface of the resistor to a second opposite surface of the resistor. Alloy adhesion layers are applied extending from adjacent the conductor pads, along the sides of the substrate, and along portions of the second surface of the substrate. Third conductor layers may be applied over the adhesion layers. Additional fourth conductor layers may be applied over the third conductor layers. Barrier layers may be applied over the fourth conductor layers. A solder finish may be provided over the barrier layers.
In yet another aspect of the present invention, a method of forming a thin film resistor is provided, comprising the steps of: providing a substrate having a first surface, side surfaces, and a second surface opposite the first surface; depositing an alloy bond layer over at least a portion of the first surface; thermally spraying a thermally sprayed resistive layer over at least a portion of the alloy bond layer; forming conductor pads adjacent sides of the thermally sprayed resistive layer; providing an overcoat over exposed parts of the thermally sprayed resistive layer; and, electrically connecting the first surface and the second surface of the resistor.
Forming conductor pads may comprise the steps of: depositing adhesion layers adjacent sides of the thermally sprayed resistive layer and over portions of the alloy bond layer; depositing first conductor layers over the adhesion layers; and plating second conductor layers over the first conductor layers.
Providing an overcoat may comprise the steps of: providing a moisture passivation layer over at least a portion of the thermally sprayed resistive layer; and providing a mechanical protection layer over at least a portion of the moisture passivation layer.
Electrically connecting the first surface and the second surface may comprise the steps of: depositing adhesion layers adjacent the conductor pads, along portions of the first surface and sides of the substrate, and at least partially along portions of the second surface of the substrate; depositing third conductor layers over the adhesion layers; and, plating fourth conductor layers over the third conductor layers. Barrier layers may be applied over the fourth conductor layers, and solder may be applied over the barrier layers.
The alloy bond layer and the thermally sprayed resistive layer may have a similar chemical composition. The thermally sprayed resistive layer may be chemically bonded to an alloy bond layer selected to have a similar chemical composition. In another embodiment of the present invention, the alloy bond layer and the thermally sprayed resistive layer may have dissimilar chemical compositions.
In another aspect of the present invention, the thermally sprayed resistive layer is deposited by a thermal spraying process at a rate of about between about 10 to 60 micrometers per minute. In another aspect of the present invention, the thermally sprayed resistive layer is deposited by a thermal spraying process at a rate of about at least 10 micrometers per minute.
In another aspect of the present invention, the thermally sprayed resistive element comprises an alloy of copper, nickel, tantalum or titanium.
In another aspect of the present invention, the alloy bond layer comprises an alloy of copper, nickel, tantalum or titanium.
A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:
The present invention is directed to the use and application of thermal spraying processes, techniques and technologies to the manufacture of thin film resistors. Table 1 provides a summary of typical thermal spraying processes, energy sources, environmental conditions, and the types of feedstock that may be used. Any of these methods could be used to achieve the rapid material deposition rates required for low resistance value thin film resistor manufacturing, as well as any others understood in the art to fall within the scope of thermal spraying.
A thin film resistor according to an embodiment of the present invention is shown in
A thin film resistor according to an embodiment of the present invention generally comprises a ceramic or non-metallic substrate 12, an alloy bond layer 14 deposited on the substrate 12, and a thermally sprayed resistive layer 18 thermally sprayed to the alloy bond layer 14. The material to be used in forming the thermally sprayed resistive layer 18 may be referred to herein as the “thermally sprayed material 16.” The thermally sprayed material 16 will be used as the feedstock for a thermal spraying process, to apply, by thermal spraying, the thermally sprayed resistive element 20 of a finished resistor.
A potential difficulty with applying a thermally sprayed material to a ceramic or other non-metallic substrate lies in achieving a substantial bond strength, e.g., a bond that will not readily separate, between the thermally sprayed material and the underlying substrate or surface. For example, during the thermal spraying process on ceramic or non-metallic materials, a bond is achieved which is primarily mechanical. In typical thermal spraying applications, the surface of the substrate is grit blasted to remove oxides and to texture the surface thereby promoting mechanical adhesion between the feedstock and the substrate.
However, in the manufacture of thin film resistors, the thickness of the ceramic substrate ranges generally between about 0.010 inches to 0.025 inches thick. Grit blasting of ceramic or non-metallic substrates of such a thickness can result in distortion of the substrate well before a sufficient surface roughness is achieved. Thus, known grit blasting techniques are inappropriate, and generally inapplicable, to the process of making a thin film resistor.
In order to create a strong bond between the ceramic or non-metallic surface of the substrate 12 and the thermally sprayed material 16 that will form the thermally sprayed resistive element 20 of the resistor according to the present invention, an alloy bond layer 14 is deposited on the substrate 12. The alloy bond layer 14 may comprise, for example, a nickel chromium alloy. Other alloys may be used depending on the alloy used for the thermally spray material that will be applied. The alloy bond layer 14, may comprise, but is not limited to, alloys comprising nickel, tantalum, titanium, copper and aluminum, other known alloys suitable for use as the alloy bond layer, or combinations thereof. The alloy bond layer 14 is preferably applied by a PVD process, but it is appreciated that other thin film deposition technologies and/or processes may be used. By use of the alloy bond layer 14, grit blasting the substrate can therefore be avoided.
As shown for example in
The alloy bond layer 14 is preferably formed using a PVD process, though other vapor deposition processes including, but not limited to, PECVD or CVD may be used. The alloy bond layer 14 forms a strong mechanical bond with the ceramic or nonmetallic surface of the substrate 12.
As shown in
In order to define the area where the alloy bond layer 14 and/or thermally sprayed material 16 are to be applied, mechanical masking may be used. This mechanical masking, shown in
Further geometry modifications can be made to the thermally sprayed resistive element 20, during deposition, using varying hard mask geometries and after deposition using chemical etching, laser machining and/or grinding or abrasive machining. Modification of these geometries affects the resistor area A and hence the electrical properties of the finished device. The geometry of the thermally sprayed resistive element 20 can be selected to achieve a particular selected geometry having particular selected electrical properties. Examples of geometries that may be used for the thermally sprayed resistive element 20 include a block pattern, a serpentine pattern, a top hat pattern, and a ladder pattern. Accordingly, a method for selecting a resistive material geometry to achieve specific electrical properties is provided as part of the thermal spraying process and method of forming a thin film resistor as described herein.
Once the alloy bond layer 14 and thermally sprayed resistive layer 18 are applied to the substrate 12, conductor pads 38, which may be single or multiple layers, as shown in
As shown in
While formation of the conductor pads 38 may be accomplished using a vapor deposited adhesion layer and seed layers (e.g., the PVD deposited layers that are used to initiate the electrolytic plating process, such a PVD deposited gold layer thick enough to initiate the electrolytic gold plating process), followed by, for example, a plating process, other processes and materials may be used to form the conductor pads 38. For example, an additional mechanical mask and an additional thermal spraying process may be used to form the conductor pads 38.
Alternately, as shown in
Termination patterns or designs can be varied to modify the resistor geometry in order to increase or decrease the square count of the resistor and to impact or otherwise control the electrical properties of the finished resistor. The geometry of the thermally sprayed resistive element 20 may be modified using laser trimming and/or machining processes to achieve the desired resistance value. While laser trimming may be used, other processes may be used including, but not limited to, chemical etching, grinding or abrasive machining, to establish the final resistance value. After the final resistance value is obtained, an overcoat 50 may be applied to the thermally sprayed resistive layer 18 comprising a moisture passivation layer 40 and a mechanical protection layer 42. The moisture passivation layer 40 may be, for example, a polymer, while the mechanical protection layer 42 may be, for example, an epoxy. Those of skill in the art will recognize various polymers and similar compositions that may be used in forming an overcoat.
As shown for example in
As shown in
In another embodiment, shown in
An exemplary method of manufacturing a thin film resistor according to the teachings of the present invention is shown diagrammatically in
To form conductor pads 38, as shown in step 106, an alloy adhesion layer 28 is deposited on a top or first surface of the thermally sprayed resistive layer 18 adjacent the opposite side ends of the thermally sprayed resistive layer 18. The alloy adhesion layer 28 is also applied to at least a portion of a top or first surface of the alloy bond layer 14 on opposite sides of the thermally sprayed resistive layer 18, as shown in
As shown in
Turning to
Turning to
It is appreciated that the steps shown in
It is further appreciated that, while various adhesion, bond and conductor layers have been described, not all are necessary in order to create a resistor according to the present invention. Examples of variations in the layers include, but are not limited to, the following.
As shown in
The conductor pads 38 may be formed by applying a thermally sprayed alloy directly to the thermally sprayed resistive layer 18 to form the conductor pads 38, without applying an adhesion layer 28.
As shown in
A PVD applied copper alloy conductor layer may be applied directly to the surface of the conductor pad 38, extending onto the surface of the substrate 12, around the side ends 204, 206 of the resistor and onto the bottom of the substrate 12, thereby replacing the nickel alloy adhesion layer 28 and the nickel alloy conductor layer 32.
A PVD copper alloy may also be applied in combination with an alloy adhesion layer, such as a nickel alloy, directly to the surface of the conductor pads 38, extending onto the surface of the substrate 12, around the side ends 204, 206 of the resistor and onto the bottom of the substrate 12, thereby replacing or as an alternative to the nickel alloy adhesion layer 54 and the nickel alloy conductor layer 56 shown in
A sample thin film resistor was created using a thermal spray technique according to the present invention, shown in
To form the conductor pads 38, a PVD applied thin film titanium alloy adhesion layer 28 was applied at sides of the upper surface of the thermally sprayed resistive layer 18. A PVD applied thin film gold first conductor layer 32 was applied over the alloy adhesion layer 28. A gold second conductor layer 36 was plated over the first conductor layer 32.
To electrically connect the upper side and the lower side of the resistor, a nickel barrier layer 48 was applied by plating running from the conductor pads 38 along the sides of the substrate 12, and along a portion of the bottom of the substrate. A thin film nickel alloy conductor layer 56 was applied by PVD over the adhesion layer. A copper conductor layer 52 was applied by plating over the nickel alloy conductor layer 56. A nickel barrier layer 48 was applied by plating over the copper conductor layer 52. A hot dipped lead free solder layer 46 was applied over the nickel barrier layer 48.
In the examples shown in
It will be appreciated that the foregoing is presented by way of illustration only and not by way of any limitation. It is contemplated that various alternatives and modifications may be made to the described embodiments without departing from the spirit and scope of the invention. Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do not alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and/or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.
