WO2022066407A1 - Glass article having a polyimide layer and method of increasing adhesion between metal and glass - Google Patents

Abstract

A coated substrate is provided. The coated substrate including a glass, glass ceramic, or silicon wafer substrate having a surface. A polyimide layer is disposed on the surface. Additionally, a metal layer is disposed on the polyimide layer, the polyimide layer promoting adhesion of the metal layer to the substrate.

Description

GLASS ARTICLE HAVING A POLYIMIDE LAYER AND METHOD OF INCREASING ADHESION BETWEEN METAL AND GLASS

[0001] This Application claims priority under 35 USC §119(e) from U.S. Provisional Patent Application Serial Number 63/082,546 filed on September 24, 2020 which is incorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

[0002] The present disclosure is generally directed to a glass or glass ceramic article having a polyimide layer formed on a surface thereof and methods for increasing the adhesion between a conductive metal and glass or glass ceramic.

BACKGROUND OF THE DISCLOSURE

[0003] Glass and glass ceramic substrates are frequently used in components of electrical devices because such substrates, generally, do not react with other elements in the electrical devices, have a low dielectric constant, and are thermally stable due to a low coefficient of thermal expansion (CTE). For example, glass and glass ceramic substrates are used as 3D interposers with through-glass-via (TGV) interconnects that connect a logic device on one side of the substrate with a memory on the other side of the substrate. The via interconnects are typically metallized with an electrically conductive material to provide a path through the interposer for electrical signals to pass.

[0004] As another example, glass and glass ceramic substrates are used as spacers in magnetic recording hard disk drives (HDD). HDDs store information on rotating disks (i.e., platters) that each consist of a substrate coated with a magnetic material. The disks all rotate in unison within the HDD at a precisely regulated speed. Spacers may be disposed between two disks to maintain a distance between the disks, to prevent radial displacement of the disks, and to reduce any vibrations of the disks. Typically, the spacers in an HDD are coated with an electrically conductive material to prevent build-up of any static electricity generated from the rotating disks. [0005] However, electrically conductive metals do not bond well with glass or glass ceramics. For example, due to CTE differences, some conductive materials, such as copper, do not adhere well to glass or glass ceramics. More specifically, copper and glass have a CTE mismatch, so that cracking and breakage may occur when these materials are adhered together.

[0006] Accordingly, a need exists for a method to increase the adhesion between glass or glass ceramics with a conductive metal.

SUMMARY OF THE DISCLOSURE

[0007] Embodiments of the present disclosure provide increased adhesion of metal to glass using a polyimide coating. The polyimide coating may be directly bonded to each of a glass substrate and a metal coating. The polyimide coatings of the present disclosure may be used in a variety of applications, including, for example, TGV interconnects and ring spacers in an HDD.

[0008] According to one embodiment, a coated substrate is provided. The coated substrate comprises a substrate comprised of glass, glass ceramic, or a silicon wafer and having a surface. A polyimide layer is disposed on the surface. Additionally, a metal layer is disposed directly on the polyimide layer, the polyimide layer promoting adhesion of the metal layer to the substrate.

[0009] According to another embodiment, a method of coating a substrate is provided. The method comprises depositing a polyimide layer on a substrate comprised of glass, glass ceramic, or a silicon wafer and depositing a metal layer on the polyimide layer. The method further comprising, after depositing the polyimide layer and the metal layer on the substrate, heating the substrate at a temperature in range from about 150°C to about 400°C.

[0010] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIGS. 1 A and IB are schematic diagrams illustrating a portion of an exemplary coated substrate, according to embodiments of the present disclosure;

[0012] FIG. 2A is a schematic diagram illustrating an exemplary coated substrate with a plurality of via holes, according to embodiments of the present disclosure;

[0013] FIG. 2B is a schematic diagram illustrating an exemplary coated spacer, according to embodiments of the present disclose;

[0014] FIG. 3 is a flow chart illustrating a process to form the coated substrate of the embodiments of the present disclosure;

[0015] FIG. 4 shows the peel strength of coated substrates with varying heating temperatures after an electroplating process;

[0016] FIG. 5A shows the results of coated substrates with varying heating temperatures and atmospheres after a polyimide coating process and with varying heating atmospheres after an electroplating process;

[0017] FIG. 5B shows the peel strength of the coated substrates of FIG. 5 A;

[0018] FIG. 6 shows the results of coated substrates with varying heating temperatures and durations after a polyimide coating process and with varying heating temperatures after an electroless process;

[0019] FIG. 7 shows the results of coated substrates according to embodiments of the present disclosure;

[0020] FIG. 8 is a plot of peel strength vs. metal layer thickness of coated substrates, according to embodiments of the present disclosure;

[0021] FIG. 9 shows an image of a metallized via substrate produced according to the embodiments of the present disclosure;

[0022] FIG. 10 shows the results of cross hatch tape tests performed on coated substrates;

[0023] FIG. 11 shows the results of cross hatch tape tests performed on coated substrates; and

[0024] FIG. 12 shows the results of cross hatch tape tests performed on coated substrates. DETAILED DESCRIPTION

[0025] Additional features and advantages of the disclosure will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description, or recognized by practicing the disclosure as described in the following description, together with the claims and appended drawings.

[0026] As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. [0027] In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.

[0028] It will be understood by one having ordinary skill in the art that construction of the described disclosure, and other components, is not limited to any specific material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.

[0029] It is also important to note that the construction and arrangement of the elements of the disclosure, as shown in the exemplary embodiments, is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel and nonobvious teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts, or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures, and/or members, or connectors, or other elements of the system, may be varied, and the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present disclosure. [0030] Reference will now be made in detail to the present preferred embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0031] Referring now to the figures, one embodiment of an article 10 produced from the methods disclosed herein is schematically depicted in FIG. 1A. As shown in FIG. 1A, article 10 comprises a substrate 20 comprised of glass, glass ceramic, or a silicon wafer and including at least a first surface 22 and a second surface 24. A polyimide layer 30 is disposed directly on at least one of first surface 22 and second surface 24. Thus, polyimide layer 30 is in direct contact with substrate 20. In some embodiments, poly imide layer 30 is disposed over an entire outer surface of substrate 20. Furthermore, article 10 comprises a metal layer 40 disposed directly on polyimide layer 30. Thus, metal layer 40 is in direct contact with polyimide layer 30. Metal layer 40 may also be disposed over an entire outer surface of substrate 20. As discussed further below, poly imide layer 30 promotes adhesion of metal layer 40 to substrate 20. For example, the bond energy between poly imide layer 30 and substrate 20 and the bond energy between polyimide layer 30 and metal layer 40 are each greater than the bond energy between substrate 20 and metal layer 40. It is also noted and discussed further below, that an electroless deposition process is important for the adherence of polyimide layer 30 to substrate 20.

[0032] Substrate 20 may be comprised of glass or glass ceramic such as, for example, silicate glass, an aluminosilicate glass, alkali aluminosilicate glass, alkaline aluminosilicate glass, borosilicate glass, boro-aluminosilicate glass, alkali aluminoborosilicate glass, alkaline aluminoborosilicate glass, soda-lime glass, fused quartz (fused silica), or other type of glass. Exemplary glass substrates include, but are not limited to, HPFS® ArF Grade Fused Silica sold by Corning Incorporated of Corning, New York under glass codes 7980, 7979, and 8655, and Corning® EAGLE XG® Glass, e.g., boro-aluminosilicate glass also sold by Corning Incorporated of Corning, New York. Other glass substrates include, but are not limited to, Corning Lotus™ NXT Glass, Corning Iris™ Glass, Corning® WILLOW® Glass, Corning® Gorilla® Glass, Corning VALOR® Glass, or PYREX® Glass sold by Corning Incorporated of Corning, New York. In some embodiments, the glass or glass ceramic has 50 wt.% or more, 60 wt.% or more, 70 wt.% or more, 80 wt.% or more, 90 wt.% or more, or 95 wt.% or more silica content by weight on an oxide basis. The glass or glass-ceramic material of substrate 20 should be compatible with bezel-beam laser cutting, in order to form the desired shape of substrate 20. In other embodiments, substrate 20 comprises a semi-conductor wafer, such as a silicon wafer. [0033] In some embodiments, substrate 20 is formed by a fusion forming process. Substrate 20 may have a Young’s modulus in a range between about 80 GPa and 86 GPa (for example, about 83 GPa), a Poisson’s ratio in a range between about 0.20 and 0.26 (for example, about 0.23), and a density in a range between about 2500 kg/m³ and 2700 kg/m³ (for example, about 2590 kg/m³). Furthermore, the glass or ceramic material of substrate 20 may have a CTE, at 20°C to 25°C, of less than about 10 ppm/K, or less than about 8 ppm/K, or less than about 5 ppm/K, or in a range of about 0.5 ppm/K to about 4.5 ppm/K, or about 2.5 ppm/k to about 4.0 ppm/K, or about 3.0 ppm/K to about 3.5 ppm/K. In some embodiments, the CTE is about 3.4 ppm/K, or about 3.5 ppm/K, or about 3.6 ppm/K, or about 3.8 ppm/K, or any range having any of these values as endpoints.

[0034] Substrate 20 is coated with an electrically conductive material (e.g., metal layer 40). It is noted that a conductive coating disposed directly on the material of substrate 20 may result in a CTE mismatch between the two materials, as discussed above. For example, copper has a CTE, at 20°C to 25°C, of about 16 ppm/K to about 17 ppm/K, which is significantly larger than the glass or glass ceramic CTE values disclosed above. Furthermore, copper does not intrinsically bond well to glass due to the fundamental difference in bonding nature between the materials. Therefore, direct bonding of these materials may cause mechanical, thermal, and/or electrical instabilities in article 10 during operation. Accordingly, the embodiments of the present disclosure include the application of a polyimide adhesion layer between the material of substrate 20 and the electrically conductive material of metal layer 40.

[0035] Poly imide layer 30 may function as an adhesion promoter between substrate 20 and metal layer 40. The polyimide composition may comprise a monomer, represented by the formula (1), as a repeating unit:

wherein Ri and R2 each independently represent a linear, branched, cyclic, or aromatic group made of C, O, N, and/or S elements.

[0036] In some embodiments, the polyimide composition comprises a monomer represented by the formula (2), as a repeating unit:

wherein R3 and R4 each independently represent an aromatic group made up of C, O, N, and/or S elements. In some embodiments, the aromatic groups contain about 6 carbon atoms to about 60 carbon atoms, or form about 6 carbon atoms to about 40 carbons atoms. The aromatic groups of R3 and R4 provide thermal stability to the polyimide. [0037] In some embodiments, the polyimide composition comprises a monomer represented by the formula (3), as a repeating unit:

[0038] Precursors to the polyimide of polyimide layer 30 may include a dianhydride and a diamine and/or dianhydride and a diisocyanate. The dianhydrides used as precursors may include pyromellitic dianhydride, benzoquinonetetracarboxy lie dianhydride and/or naphthalene tetracarboxylic dianhydride. Exemplary diamine building blocks include 4,4’ -diaminodiphenyl ether (DAPE), metaphenylenediamine (MDA), and 3,3 ’-diaminodiphenylmethane.

[0039] The polyimide used in the embodiments disclosed herein may be thermally cured from its soluble precursor poly(amic acid). There are many commercially available polyimide precursor solutions. One example is a polyamic acid solution from Sigma- Aldrich Corp., which contains 15.0% poly(pyromellitic dianhydride-co-4,4’-oxydianiline), amic acid, and 85% NMP (l-methyl-2-pyrrolidinone). After heating, the polyamic acid solution forms Kapton, a polyimide material developed by DuPont. The polyamic acid solution typically requires a separate adhesion promoter to improve metal-to-glass adhesion. The adhesion promoter could be, for example, (3 -aminopropyl)trimethoxy silane. Another example of a polyimide precursor solution is PI-2574 from HD MicroSystems, which contains 25.0% solids and 75.0% NMP. This polyimide precursor is self-priming and does not require an adhesion promoter. In general, the polyimide precursors disclosed herein should be diluted with a solvent, such as NMP, before coating in order to make a thin polyimide coating. Such diluted solutions may contain solids in the range of about 0.2 wt.% to about 6.0 wt.%.

[0040] Poly imide layer 30 may comprise a coupling agent 32 to couple poly imide layer 30 to substrate 20. For example, the coupling agent creates a surface functionalization of substrate 20. In some embodiments, the coupling agent is incorporated into the polyimide of layer 30. Exemplary coupling agents include silane coupling agents that are characterized by the functional groups alkyl, aryl, amino, epoxy, vinyl, methacryloxy, ureido, isocyanato, and mercapto. For example, the silane coupling agent may include silanes containing one or more nitrogen atoms with one or more functional groups, such as, for example, amine, amino, imino, amido, imido, ureido, or isocyanato. Specific, non-limiting examples of silane coupling agents include aminosilanes (e.g., 3-aminopropyltrimethoxysilane, 3 -aminopropyltri ethoxysilane, and 3-aminopropyl-trihydroxysilane), epoxy trialkoxysilanes (e.g., 3- glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3,4- epoxycyclohexylethyltrimethoxysilane), methyacryl trialkoxysilanes (e.g., 3- methacryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane), isocyanate silanes (e.g., isocyanate propyltriethoxy silane and isocyanate propyltrimethoxysilane), mercaptosilanes (e.g., mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane), hydrocarbon trialkoxysilanes, amino trihydroxysilanes, epoxy trihydroxysilanes, methacryl trihydroxy silanes, and/or hydrocarbon trihydroxysislanes. The coupling agent may further increase the adhesion between substrate 20 and metal layer 40 and may also improve heat resistance, weather durability, and moisture resistance of article 10.

[0041] In some embodiments, coupling agent 32 is added to the polyimide precursor mixture, which forms polyimide layer 30. Coupling agent 32 may be added in an amount ranging from about 0.01 wt.% to about 10.0 wt.% of the precursor mixture. For example, coupling agent 32 may be added in an amount from about 0.1 wt.% to about 5.0 wt.% of the precursor mixture. It is noted that in these embodiments, the coupling agent and the polyimide precursor material form a single layer together.

[0042] In other embodiments, coupling agent 32 is directly applied to a surface of substrate 20 such that coupling agent 32 forms a separate layer from polyimide layer 30. Coupling agent 32 may be applied to substrate 20 via vapor deposition, deposition via aqueous alcohol, deposition via aqueous solution, spray deposition, and other well-known methods. After the deposition of coupling agent 32 on substrate 20, polyimide layer 30 is then disposed on the coupling agent layer. [0043] Poly imide layer 30 may be a thin layer with a thickness ranging from about 5 nm to about 50 microns, or about 50 nm to about 30 microns, or about 100 nm to about 25 microns, or about 1 micron to about 20 microns, or about 8 microns to about 12 microns, or about 0.1 microns to about 10 microns, or about 0.3 microns to about 10 microns, or about 0.4 microns to about 8 microns, or about 0.5 microns to about 3 microns, or about 1 micron to about 2 microns. In some embodiments, the thickness is about 0.6 microns, or about 0.8 microns, or about 1.2 microns, or about 1.8 microns, or about 2 microns, or about 2.4 microns, or about 3 microns.

[0044] Metal layer 40 comprises, for example, a metal or metal alloy comprising at least one of copper (Cu), magnesium (Mg), titanium (Ti), tin (Sn), indium (In), chromium (Cr), molybdenum (Mo), aluminum (Al), niobium (Nb), tantalum (Ta), vanadium (Va), zinc (Zn), silver (Ag), nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), or combinations thereof. In some embodiments, pure copper is chosen as the metal due to its good conductivity properties.

[0045] Metal layer 40 has a resistivity in a range of about 1x1 O'⁶ Q-cm to about 10 Q-cm, or about IxlO'³ Q-cm to about 0.1 Q-cm, or about IxlO'² Q-cm to about 0.75 Q-cm, or about 0.5 Q- cm to about 1 Q-cm, or about 0.76 Q-cm, or about 0.78 Q-cm, or about 0.80 Q-cm, or about 0.85 Q-cm. When metal layer 40 is applied on a spacer in an HDD, for example, the above-disclosed resistivity amounts sufficiently discharge and prevent build-up of any static electricity generated from the rotating disks in the HDD. Additionally, metal layer 40 has a resistance of about 10⁶ ohms or less, or about 10⁴ ohms or less, or about 10³ ohms or less, or about 10² ohms or less.

[0046] Metal layer 40 has a thickness in a range from about 50 nm to about 100 microns or about 50 nm to about 50 microns, or about 50 nm to about 20 microns, or about 50 nm to about 10 microns, or about 50 nm to about 5 microns, or about 50 nm to about 1 micron, or about 50 nm to about 800 nm, or about 50 nm to about 500 nm, or about 50 nm to about 250 nm, or about 100 nm to about 200 nm, or about 50 nm, or about 75 nm, or about 100 nm, or about 120 nm, or about 150 nm, or about 175 nm, or about 200 nm, or about 225 nm, or about 250 nm, or any range having any of these values as endpoints. In other embodiments, metal layer 40 has a thickness in a range from about 1 micron to about 100 microns, or about 1 micron to about 20 microns, or about 3 microns to about 15 microns, or about 2 microns or greater, or about 4 microns or greater, or about 6 microns or greater. For example, metal layer 40 has a thickness of about 8 microns, or about 10 microns, or about 12 microns, or about 14 microns, or about 16 microns, or any range having any of these values as endpoints.

[0047] As discussed further below and as shown in FIG. IB, in some embodiments, metal layer 40 is formed of a first layer 42 formed by electroless deposition and a second layer formed by electroplating 44. First layer 42 has a thickness in a range from about 50 nm to about 20 microns, or about 500 nm to about 20 microns, or about 1 micron to about 10 microns, or about 50 nm to about 5 microns, or about 50 nm to about 1 micron, or about 50 nm to about 800 nm, or about 100 nm to about 800 nm, or about 200 nm to about 800 nm, or about 400 nm to about 800 nm, or about 600 nm to about 800 nm. Second layer 44 has a thickness, in some embodiments, in a range from about 1 micron to about 20 microns, or about 2 microns to about 16 microns, or about 3 microns to about 12 microns, or about 10 microns. It is also contemplated that metal layer 40 only includes first layer 42 and not second layer 44.

[0048] In some embodiments, an interface 50 (FIG. 1A) between polyimide layer 30 and metal layer 40 does not define a sharp boundary. Instead, interface 50 forms a transition region between poly imide layer 30 and metal layer 40. For example, the materials of polyimide layer 30 and metal layer 40 may form a gradient at interface 50. In some embodiments, the transition region that forms interface 50 may have a width between about 1 nm to about 10 nm, or about 2 nm to about 5 nm, or about 1.3 nm to about 1.7 nm, or about 1.4 nm to about 1.6 nm, or about 1.5 nm. Without being limited by theory, it is believed that the heating process (as discussed below) may, in some embodiments, change the nature of the interface and increase bond strength between polyimide layer 30 and metal layer 40 by creating an interface 50 that is not directly measurable. In such embodiments, the physical change in the nature of the interface between polyimide layer 30 and metal layer 40 may not have distinct borders and, therefore, may be difficult to directly observe. But the physical change is measurable, for example, by a tape test such as the 3 N/cm tape test (as discussed further below), based on the reasonable assumption that interface 50 is where failure occurs in an un-heated sample. [0049] Poly imide layer 30 increases the adhesion of metal layer 40 to substrate 20 by at least about 100%, or at least about 1,000%, or at least about 2,000%, or at least about 4,000%, or at least about 6,000%.

[0050] As discussed above, metal layer 40 may be directly bonded to polyimide layer 30. However, it is also contemplated in other embodiments, that metal layer 40 is indirectly bonded to polyimide layer 30. For example, an additional adhesion layer may be disposed between metal layer 40 and polyimide 30. Similarly, polyimide layer 30 may be indirectly bonded to substrate 20 such that, for example, an additional adhesion layer is disposed between polyimide layer 30 and substrate 20.

[0051] Metal layer 40 forms a coating on substrate 20 consisting of one or more layers of the metal material. Similarly, polyimide layer 30 forms a coating on substrate consisting of one or more layers of the polyimide material. Thus, in some embodiments, metal layer 40 and polyimide layer 30 may each consist of a single layer or a plurality of layers.

[0052] FIG. 2 A shows a first embodiment of an article 100 that comprises a substrate 120 with a plurality of via holes 125 extending through a thickness of substrate 120. It is noted that via holes 125 may each extend through less than an entire thickness of substrate 120 (i.e., blind vias) or through the entire thickness of substrate 120. As shown in FIG. 2A, by way of example, via holes 125 extend from surface A to surface B. Furthermore, via holes 125 each comprise at least a first surface 122 and a second surface 124, which are interior surfaces of holes 125. Thus, first surface 122 and second surface 124 may together define an interior circumferential profile of holes (in embodiments where holes are circular in shape).

[0053] While FIG. 2A shows specific via hole configurations, various other via hole configurations may be used. By way of non-limiting example, vias having an hourglass shape, a barbell shape, beveled edges, or a variety of other geometries may be used instead of the cylindrical geometries shown in FIG. 2A. The via hole may be substantially cylindrical, for example having a waist (point along the via with the smallest diameter) with a diameter that is at least about 50%, or at least about 55%, or least about 60%, or at least about 65% or least about 70%, or at least about 75%, or at least about 80% of the diameter of an opening of the via on surface A and/or surface B. Thus, a diameter at a top portion and a diameter at a bottom portion of via holes 125 are each greater than a diameter at a middle portion (waist) of the via. In some embodiments, the diameter at the top portion and the diameter at the bottom portion of via holes are each in a range from about 80 microns to about 200 microns, or about 100 microns to about 150 microns.

[0054] Via holes 125 may have any suitable aspect ratio. For example, via holes 125 may have an aspect ratio of 1: 1, 2: 1, 3: 1, 4:1, 5: 1, 6:1, 7: 1, 8:1, 9: 1, 10: 1, 15: 1, 20:1, 30:1, 35:1 or any range having any two of these values as endpoints. It is also contemplated that other via geometries may be used in article 100.

[0055] In the embodiment of FIG. 2A, substrate 120 may have a thickness ranging from about 30 microns to about 1000 microns, or from about 40 microns to about 500 microns, or from about 50 microns to about 200 microns, or about 100 microns. The thickness of substrate 120 may vary depending on its end use. Thus, it should be understood that a glass, glass ceramic, or silicon wafer substrate of any suitable thickness may be utilized.

[0056] The interior surfaces of via holes 125 (e.g., first and second surfaces 122, 124) may be filled with an electrically conductive metal, such as metal layer 40. Poly imide layer 30 may be disposed on first surface 122 and/or second surface 124 of substrate 120 to promote adhesion of metal layer 40 to the glass, glass ceramic, or silicon wafer material of substrate 120, as discussed above.

[0057] FIG. 2B shows a second embodiment of an article 200 that comprises a substrate 220 and that may be used as a spacer in an HDD. As shown in this figure, article 200 is a ring shaped member (i.e., a disk or donut shaped member) comprising a first surface 222 (a top surface), a second surface 224 (a bottom surface), a third surface 226 (an inner side surface), and a fourth surface 228 (an outer side surface).

[0058] Article 200 is coated with an electrically conductive material (such as metal layer 40) to dissipate electrical static discharges in an HDD, which may cause harmful voltage buildup in the HDD. Polyimide layer 30 may be disposed on substrate 220 to promote adhesion of metal layer 40 to the glass, glass ceramic, or silicon wafer material of substrate 220, as discussed above. Both polyimide layer 30 and metal layer 40 may be disposed on first, second, third, and/or fourth surfaces 222, 224, 226, 228 of substrate 220.

[0059] In the embodiment of FIG. 2B, substrate 220 may have an outer diameter in a range from about 5 mm to about 100 mm, or about 10 mm to about 50 mm, or about 15 mm to about 40 mm, or about 25 mm to about 35 mm. Furthermore, substrate 220 may have an inner diameter in a range from about 1 mm to about 99 mm, or about 10 mm to about 45 mm, or about 15 mm to about 35 mm, or about 20 mm to about 25 mm, or about 24 mm to about 34 mm. A thickness of substrate 220 is in range from about 50 microns to about 10 mm, or about 100 microns to about 8 mm, or about 200 microns to about 5 mm, or about 500 microns to about 4 mm, or about 1.6 mm to about 2 mm.

[0060] FIG. 3 provides an exemplary method 300 of forming polyimide layer 30 and metal layer 40 on substrate 20. At step 310, one or more layers of the polyimide coating is deposited on substrate 20 to form polyimide layer 30. As discussed above, the poly imide coating may be disposed directly on a surface of substrate 20. The polyimide coating may be applied on substrate 20 using any well-known coating method, including, for example, chemical vapor deposition, spray coating, spin coating, dip coating, slot coating, and/or printing including inkjet printing. It is also contemplated in some embodiments, as discussed above, that a layer of coupling agent 32 is disposed on substrate 20 and then the polyimide coating is disposed on the coupling agent layer.

[0061] After the application of the polyimide coating on substrate 20, the poly imide coating may be heated in an air or nitrogen environment. The polyimide coating may be heated at a temperature in a range between about 100°C and about 400°C, or between about 150°C and about 350°C, or between about 200°C and about 400°C, or between about 200°C and about 300°C. The heating time may be about 5 seconds to 10 hours, depending on the temperature. Generally, a higher temperature requires a shorter heating time. In some exemplary embodiments, the polyimide coating is heated at a temperature of about 400°C for about 0.5 hours to about 2 hours. [0062] In some embodiments, a separate heating step may be not required after the deposition of the poly imide coating on substrate 20. For example, when a spray coating process is used to apply the polyimide coating on a heated substrate (for example, a substrate with a surface temperature of about 350°C), the polyimide coating may be heated in-situ for about 5 minutes to about 30 minutes.

[0063] The heated and cured poly imide coating on substrate 20 produces polyimide layer 30, which, in some embodiments, has a surface roughness Ra in a range from about 20 nm to about 3 microns, or about 60 nm to about 2 microns, or about 100 nm to about 1 micron.

[0064] At step 320, the polyimide-coated substrate 20 is catalyzed with a catalytic metal such as, for example, palladium (Pd), silver (Ag), ruthenium (Ru), and/or platinum (Pt). In one example, the catalyzation process is completed by depositing a core-shelled palladium-tin colloidal catalytic solution on the polyimide-coated substrate 20. In another embodiment, the polyimide-coated substrate 20 is catalyzed by depositing a palladium (II) complex on the polyimide-coated substrate 20, followed by reducing the palladium (II) complex to a palladium (0) complex. The catalyzation step is then followed by stripping of the tin layer. The catalyzation step 320 aids in the formation of metal layer 40 on polyimide layer 30.

[0065] At step 330, one or more layers of a metal coating is deposited on the polyimide-coated substrate 20 to form metal layer 40. In some embodiments, first layer 42 is applied via electroless deposition and second metal layer 44 is applied via electroplating. Electroless deposition is a slower process compared to electroplating. But, application via electroplating is limited to conductive surfaces, whereas electroless deposition can be performed on non- conductive surfaces. Once a thin, initial layer of a metal coating (i.e., first layer 42) is deposited via electroless deposition to form a conductive surface, electroplating may be used to more quickly deposit a thicker layer (i.e., second layer 44) of the metal coating. Furthermore, the electroless deposition increases the adhesion of metal layer 40 with substrate 20 as compared with processes that do not include such an electroless deposition step.

[0066] In some embodiments, metal layer 40 is formed only by electroless deposition, without the additional electroplating process. Therefore, metal layer 40 comprises only first layer 42 without the additional second layer 44. These embodiments may be utilized, for example, when a thin metal layer is desired.

[0067] The electroless deposition of first layer 42 may be performed by immersing the polyimide-coated substrate 10 in an aqueous bath comprising a metal source and a reduction agent. In some embodiments, the metal source is a metal salt, such as, for example, copper sulfate. Additionally, in some embodiments, the reduction agent is formaldehyde. First layer 42, as formed by the electroless deposition process, has a thickness in a range from about 50 nm to about 20 microns, as discussed above. It is noted that the thickness of this thin metal layer depends on the electroless deposition process time. However, it was found that, in certain applications, layers having a thickness of 400 nm or greater were preferred because such thicker layers helped to mitigate the formation of blisters after the electroplating and heating steps. It is noted that formation of blisters is an indication of non-uniform adhesion between metal layer 40 and substrate 20.

[0068] Next, after the electroless deposition step, article 10 is then heated. It has been found that this heating step is critical for adhesion between polyimide layer 30 and metal layer 40. The heating step can be conducted in a vacuum or a reduced atmosphere, such as a forming gas (for example, 3% H2 in N2). Furthermore, the heating step is conducted at a temperature in a range of about 200°C to about 500°C, or about 150°C to about 400°C, or about 250°C to about 400°C, or about 300°C to about 350°C.

[0069] In some embodiments, the electroless deposition may also include one or more intermediate heating steps. More specifically, a first electroless deposition layer may be applied to substrate 20, followed by an intermediate heating step. The first electroless deposition layer may have a thickness in a range from about 50 nm to about 1000 nm, or from about 50 nm to about 800 nm, or from about 50 nm to about 600 nm, or from about 50 nm to about 300 nm, or form about 100 nm to about 600 nm. During the intermediate heating step, substrate 20 may be heated to a temperature within a range from about 150°C to about 400°C, or from about 200°C to about 400°C, or from about 250°C to about 350°C, with a ramp rate of about l°C/min to about 5°C/min, or about 2°C/min to about 4°C/min. The intermediate heating step may be conducted for a duration from about 5 minutes to about 1 hour, or from about 10 minutes to 30 minutes. After the intermediate heating step, a second electroless deposition layer may be applied to substrate 20. In some embodiments, the second electroless deposition layer may be thicker than the first electroless deposition layer. For example, the second electroless deposition layer may have a thickness in a range from about 50 nm to about 20 microns, as disclosed above with reference to the thickness of first layer 42. In some embodiments, the second electroless deposition layer has a thickness in range from about 4 microns to about 10 microns.

[0070] It is further contemplated that in some embodiments, the intermediate heating step may include two or more intermediate heating steps, each followed by application of a separate electroless deposition layer. The intermediate heating steps disclosed herein may advantageously reduce the formation of stress during the metal plating process.

[0071] Furthermore, the embodiments disclosed herein that include the intermediate heating step(s) are still subjected to a final heating step, after the entire electroless process, as disclosed above.

[0072] The thin metal layer (i.e., first layer 42) formed on substrate 20 with the abovedisclosed electroless deposition processes may have a resistivity between about 2x10'⁸ Q/m to about 40x10'⁸ Q/m. It is noted that metal layer 42, as formed on substrate 20 with the abovedisclosed electroless deposition process, forms a different final product than by depositing the same metal via other deposition processes. For example, as disclosed above, metal layer 42 comprised of pure copper has a resistivity between about 2x10'⁸ Q/m to about 40x10'⁸ Q/m when deposited on substrate 20 with the above-disclosed electroless deposition processes. This is in contrast to pure copper deposited on the same substrate using an electroplating process, in which the copper will have a resistivity between about 5x10'⁸ Q/m to about 10x10'⁸ Q/m. Therefore, the resistivity of the electroless copper is greater than the resistivity of the electroplated copper, on the final product. Furthermore, pure copper in bulk form has a resistivity of about 1.7xl0'⁸ Q/m. Thus, the electroless plated copper has a different resistivity, and therefore different properties, from the copper in pure bulk form, showing that the electroless deposition process changed at least some of the properties of the copper. [0073] At step 330, an electroplating process is conducted in an acid-based bath that comprises a metal source and an acid, such as, for example, sulfuric acid. In some embodiments, the metal source is metal salt, such as, for example, copper sulfate. The electroplating process produces second layer 44 on article 10. However, as discussed above, it is noted that in some embodiments the electroplating process is not conducted.

[0074] A constant current density of about 2 mA/cm² to about 5 mA/cm² is applied during the electroplating process for about 1 to 4 hours, depending on the desired metal thickness. For example, deposition of a 10 micron thick copper film takes about 100 minutes under a current density of 5 mA/cm².

[0075] After the electroplating process, article 10 is heated to form metal layer 40. This heating step may be carried out in a vacuum oven or forming gas oven at various temperatures with a heating rate of about 1 °C/min or greater, or about 1.5 °C/min or greater, or about 2 °C/min or greater, or about 2.5 °C/min or greater, or about 3 °C/min or greater. In some embodiments, the heating step is carried out at a temperature in a range from about 200°C to about 450 °C, or about 250 °C to about 400 °C, or from about 150°C to about 400°C, or about 300 °C to about 350 °C. The heating time may range from about 10 minutes to 10 hours, or about 0.5 hours to about 2 hours, or about 0.5 hours to about 1 hour. For example, this heating step may be at 350°C for 30 minutes. A standard peel strength test or cross hatch tape test may then be performed to determine the metal-to-glass, metal-to-glass-ceramic, or metal-to-silicon adhesion strength.

[0076] In the exemplary examples disclosed below, the peel strength measurements were conducted using an MTS Sintech 2/G testing system with a 10-lbf load cell. The coated substrates were first prepared by scoring the metal layer of each substrate with a 10-mm wide strip. The width of 10-mm was used to ensure a constant peel width. The glass portions (or ceramic portions or silicon portions) of the substrates were then scored and broken along a line (“line A”), which was 10 mm from an edge of the substrate and perpendicular to the 10-mm wide strip. By scoring and breaking the glass along line A, a relatively smaller portion of the glass (10 mm from the edge of the substrate) was connected to a relatively larger portion of the glass (the remainder of the glass) only through the metal coating. Next, the metal layer was broken along line A but only along portions of line A that did not overlap with the 10-mm wide strip.

Therefore, the metal layer was not broken in the area encompassing the 10-mm wide strip, and the relatively smaller portion of the glass remained connected to the relatively larger portion of the glass only through the metal layer in the 10-mm wide strip. The relatively smaller portion of the glass was then attached to a load cell, and the relatively larger portion of the glass was secured to a base of the testing system. The strip of metal layer in the 10-mm wide strip was then peeled off the glass at a constant rate of 50 mm/min, with a constant peel angle of 90°. The peel strength was then recorded for the samples.

[0077] Provided below are examples that are intended for exemplary purposes only and are not intended to limit the scope of the disclosure.

[0078] Example 1

[0079] In this first example, a polyimide coating was deposited on a front surface of each of five glass substrates (substrates 1A, IB, 1C, ID, and IE) by a spray coating method followed by heating. The glass substrate were each comprised of EAGLE XG® Glass. Before deposition of the polyimide coating, a Visqueen film was removed from the glass substrates and the glass substrates were cleaned. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 :7. During the deposition of the polyimide coating on the glass substrates, the substrates were maintained at a temperature of 350°C. The substrates were coated with the poly imide coating using an airbrush operating at about 30 psi for a coating time of 15 seconds. Once coated, the substrates were maintained at the temperature of 350°C for 5 minutes . The five polyimide-coated substrates each had an average polyimide coating thickness of about 3 microns and a surface roughness Ra of about 89 nm (±6 nm).

[0080] The polyimide-coated substrates were then catalyzed with palladium (Pd) by immersing the substrates in an Sn/Pd solution for 8 minutes. Next, the substrates were immersed in an accelerator solution for 3 minutes to strip the Sn and expose the active Pd catalyst. The five substrates were now ready for deposition of the metal layer. [0081] In this first example, the five substrates were exposed to an electroless deposition process to deposit a first, thin copper layer on the polyimide-coated substrates. The electroless deposition process was carried out using a commercial bath from Uyemura comprising copper sulfate, formaldehyde, and sodium hydroxide such that the bath had a pH of 13. The electroless bath was heated to 35°C and the substrates were immersed in the bath for about 12 minutes. The plating rate of the copper metal on the substrates was about 30 nm/min. Therefore, a 400 nm thick layer of copper was deposited on each of the five substrates after the electroless bath.

[0082] After the electroless deposition process, the substrates were rinsed with deionized water and dried using nitrogen gas. Then the substrates were heated at 250°C for 30 minutes in forming gas.

[0083] Next, the substrates were exposed to an electroplating process by immersing the substrates in bath comprising copper sulfate and sulfuric acid. Electroplating was carried out using a constant current density of 5 mA/cm² for 100 minutes. The resulting electroplated copper coating was measured to be about 10 microns thick on each substrate. Four of the substrates (1 A, IB, 1C, and ID) were then heated in a vacuum oven at 350°C for 30 minutes with a ramp rate of 2°C/min. Substrate IE was not heated following the electroplating process. [0084] The adhesion strength of substrates 1A, IB, 1C, ID, and IE was measured by a peel strength test, as discussed above. As shown in FIG. 4, substrates 1A, IB, 1C, and ID (which were each exposed to heating after the electroplating process) had an average adhesion strength of about 2.8 N/cm. However, substrate IE (which was not subjected to heating after the electroplating process) had an adhesion strength of about 0.5 N/cm. Thus, Example 1 shows that heating after the electroplating process advantageously increases the adhesion between the metal layer and the polyimide-coated substrate.

[0085] Example 2

[0086] This example provides a comparison of the heating temperature and atmosphere post deposition of the polyimide coating along with the heating atmosphere post electroplating deposition of the metal coating. First, a polyimide coating was deposited on a front surface of each of eight glass substrates (substrates 2A, 2B, 2C, 2D, 2E, 2F, 2G, and 2H) by a spray coating method (similar to Example 1). The glass substrates were each comprised of EAGLE XG® Glass. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 :7.

[0087] Following the deposition of the polyimide coating, the eight substrates were then heated in either an air or nitrogen environment, as shown in Table 1. Additionally, as also shown in Table 1, the heating step was conducted at a temperature of either 350°C or 400°C for 30 minutes. This resulted in polyimide-coated substrates with a 3.6 micron thick polyimide coating. [0088] The polyimide-coated substrates were then catalyzed with palladium, and a copper coating was deposited on the substrates using the electroless and electroplating processes disclosed above in Example 1. Following the electroplating process, a 10 micron thick copper coating was deposited on each of the eight samples. Next, the substrates were heated in either a vacuum or forming gas, as shown in Table 1.

Table 1

[0089] FIG. 5 A shows the results of the electroplated copper substrates of Example 2, and FIG. 5B shows the peel strength for each of the substrates. In FIG. 5A, each image to the right represents a front, coated surface of the substrate, and each image to the left represents a back, uncoated surface of the substrate. However, the coating on the front side of the substrate is viewable through the back surface of the substrate. As shown in FIG. 5A, substrates 2D and 2H (which were both heated at 400°C post-polyimide deposition and used forming gas post-metal electroplating deposition) resulted in the smallest and fewest blisters, indicating that both post- polyimide deposition heating temperature and post-metal electroplating deposition heating atmosphere play a role in mitigating blister formation. Furthermore, FIG. 5B shows that higher post-polyimide deposition heating temperatures in a nitrogen gas atmosphere along with postmetal electroplating deposition heating in forming gas (substrate 2H) resulted in a higher adhesion strength.

[0090] Example 3

[0091] This example provides a comparison of the heating temperature and time post deposition of the polyimide coating along with the heating temperature post electroless deposition of the metal coating. A polyimide coating was deposited on a front surface of each of six glass substrates (substrates 3A, 3B, 3C, 3D, 3E, and 3F) by a spray coating method followed by heating (similar to Example 1). The glass substrate were each comprised of EAGLE XG® Glass. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 :7.

[0092] After the deposition of the polyimide coating, the substrates were heated in a nitrogen gas atmosphere. As shown in Table 2, substrates 3 A and 3B were heated at 350°C for 6 hours and substrates 3C, 3D, 3E, and 3H were heated at 400°C for either 0.5 hours or 2 hours. This resulted in polyimide-coated substrates with a 1.8 micron thick polyimide coating.

[0093] The substrates were then catalyzed with palladium, and a copper coating was deposited on the substrates using the process disclosed above in Example 1 (specifically following the process of 1A, 1C, ID, and IE). However, following the electroless deposition process, the substrates were heated at a temperature of 250°C, 350°C, or 400°C, as shown in Table 2, for 30 minutes. As disclosed above in Example 1, the substrates were the subjected to an electroplating process following the electroless deposition of the metal layer. A 10 micron thick copper coating was deposited on each of the six samples.

Table 2

[0094] FIG. 6 shows the results of the substrates of Example 3. As shown in FIG. 6, the substrates subjected to the 400°C post-polyimide deposition heating temperature produced consistent 4-5 N/cm adhesion peel strength results. However, substrates 3A and 3B, which were subjected to the 350°C post-polyimide deposition heating temperature, produced relatively lower adhesion peel strength results. Furthermore, FIG. 6 shows that the 400°C post-polyimide deposition heating temperature produced superior results, regardless of the heating time and regardless of the post-copper electroless deposition heating temperature, for the ranges tested herein.

[0095] Example 4

[0096] A polyimide coating was deposited on front and back surfaces of each of two glass substrates (substrates 4A and 4B) by a dip coating method. The glass substrate were each comprised of EAGLE XG® Glass. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 : 15.

[0097] After dip coating, the two substrates were dried in air at 150°C for 1 hour, followed by heating at 350°C in air for 30 minutes. Substrate 4A had about a 1 micron thick polyimide coating, and substrate 4B had about a 0.7 micron thick poly imide coating. After electroless deposition, a 400 nm copper coating was deposited on each substrate (similar to Example 1). Following electroless deposition, the substrates were heated at 350°C in forming gas for 30 minutes. Then, the substrates were deposited with a 10 micron thick copper coating via electroplating, followed by heating at 350°C in forming gas for 30 minutes. As shown in FIG. 7, a copper coating of good quality was formed on both sides of each of substrates 4A and 4B. No blisters were observed on either substrate. Substrate 4A resulted in a peel strength of about 4.5 N/cm. Substrate 4B resulted in breakage of the copper coating during the peel strength adhesion test, which is an indication of an even higher peel strength than that of substrate 4A.

[0098] Example 5

[0099] Polyimide and copper coatings were deposited on a surface of each of five glass substrates (substrates 5A, 5B, 5C, 5D, and 5E) according to the process disclosed in Example 1. However, in this example, the electroless deposition process produced different copper thicknesses on the substrates, as shown in Table 3. The glass substrates of Example 5 were each comprised of EAGLE XG® Glass, and the polyimide coating on each substrate ranged from about 0.7 microns to about 1.1 microns in thickness. After the electroless deposition, the substrates were electroplated, as discussed above in Example 1 (specifically following the process of 1A, IB, 1C, and ID), resulting in 10 micron thick layer of copper coating.

Table 3

[00100] FIG. 8 shows the peel strength results of the substrates of Example 5. As shown in FIG. 8, peel strength increases as a function of the thickness of the electroless copper coating.

[00101] Example 6

[00102] In this example, two glass substrates (substrates 8A and 8B) were coated with polyimide and copper coatings according to the process disclosed in Example 1 (specifically following the process of 1A, IB, 1C, and ID). However, in this example, the polyimide coating did not contain the silane coupling agent. The polyimide coating was prepared by mixing 15% PMDA-ODA PAA solution from Aldrich with an NMP solvent in a volume ratio of 1 : 7. The glass substrates of Example 6 were each comprised of EAGLE XG® Glass. The same spraycoating process as in Example 1 was applied on a surface of the substrates, which produced a polyimide coating thickness of about 1.3 microns. After being heating in nitrogen at 350°C for 6 hours, the substrates were then deposited with a 400 nm thick electroless copper layer and heated at 350°C for 30 minutes in forming gas. Next, the substrates were subjected to an electroplating process, as disclosed in Example 1. However it was found that the copper coating did not adhere well to the glass substrates and fell off after the electroplating process. Thus, the silane coupling agent helps to promote adhesion between the glass substrate and the polyimide coating, which results in good overall adhesion of the metal coating with the glass substrate.

[00103] Example 7

[00104] In this example, three glass substrates (7A, 7B, and 7C) were coated with polyimide and copper coatings. However, in this example the copper coatings were coated using a plasma vapor deposition process instead of the electroless deposition process of Example 1. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 :7, similar to Example 1. The glass substrates of Example 7 were each comprised of EAGLE XG® Glass. The same spray-coating process as in Example 1 was applied on a surface of the substrate, which produced a poly imide coating thickness of about 1.5 microns. After being heated in nitrogen at 400°C for 2 hours, the substrates were deposited with a 300 nm thick copper layer via a standard plasma vapor deposition process. Then the substrates were heated at 350°C for 30 minutes in forming gas. Next, the substrates were electroplated with a 10 micron copper coating and heated at 350°C for 30 minutes in forming gas, simlar to that disclosed above in Example 1. However, during this last heating step, the copper coating delaminated from each of substrates 7A, 7B, and 7C, which is an indication of poor copper-to- glass adhesion. Accordingly, the thin layer of metal applied via electroless deposition provides stronger adhesion strength than when the electroless deposition layer is replaced with a plasma vapor deposition layer.

[00105] Example 8

[00106] This example describes an exemplary process for deposition of the polyimide and copper coatings along inside surfaces of a via, according to embodiments of the present disclosure. The glass substrates in this example were each 2-inch by 2-inch samples comprised of HPFS® ArF Grade Fused Silica. The vias extended through an entire thickness of the substrates and had via dimensions of about 80-100 micron diameter at the top and bottom of the via and about 50 micron diameter at the via center (waist). The glass substrates had a thickness of about 300 microns.

[00107] The glass substrates were cleaned with SCI within 24hr before the deposition of the polyimide coating. The inner surfaces of the vias were coated with the polyimide coating using a dip coating process (i.e., each substrate was dipped into the polyimide coating solution for about 10 seconds before withdrawal). After dip coating, the substrates were dried in air at 150°C for 1 hour, followed by heating at 400°C in nitrogen gas for 2 hours.

[00108] The via substrates were then catalyzed with palladium (Pd) by immersing the substrates in an Sn/Pd solution for 8 minutes. Next, the via substrates were immersed in an accelerator solution for 3 minutes to strip the Sn and expose the active Pd catalyst. The via substrates were now ready for deposition of the copper layer.

[00109] Similar to the process of Example 1, the inner surfaces of the vias were then coated with a thin layer of copper via an electroless deposition process. This process was carried out using a commercial bath from Uyemura that comprised copper sulfate, formaldehyde, and sodium hydroxide. The bath had a pH of about 13. The electroless bath was heated to 35°C and the substrates were immersed in the bath for 18 minutes. The plating rate of the copper was about 30 nm/min. Therefore, a 600 nm thick layer of copper was deposited on the inner surfaces of each via after the electroless bath.

[00110] After the electroless deposition process, the via substrates were rinsed with deionized water and dried using nitrogen gas. Then the substrates were heated at 250°C for 30 minutes in forming gas.

[00111] Next, the via substrates were exposed to an electroplating process by immersing the substrates in a bath comprising copper sulfate and sulfuric acid. Electroplating was carried out using a constant current density of 2.5 mA/cm² for 2 hours. The resulting electroplated copper coating was measured to be about 7 to 8 microns thick on the inner surfaces of each substrate. The via substrates were then heated in a vacuum oven at 350°C for 30 minutes with a ramp rate of 2 °C/min. [00112] Fig. 9 shows an image of the metallized inner surfaces of a via substrate produced according to the process of Example 8. As shown in FIG. 9, the plating thickness of the copper layer on the inner via surfaces is about 7.9 microns.

[00113] Example 9

[00114] This example is similar to the process disclosed in Example 1 , except it is directed to the embodiments that do not include the electroplating process. Therefore, the metal layer is applied only via an electroless deposition process.

[00115] Similar to Example 1, in this example, a polyimide coating was deposited on a surface of each of six glass substrates (substrates 9A, 9B, 9C, 9D, 9E, and 9F) by a spray coating method. The glass substrate were each comprised of Corning Lotus™ NXT Glass. Before deposition of the polyimide coating, a Visqueen film was removed from the glass substrates and the glass substrates were cleaned. The polyimide coating was prepared by mixing 25% PI-2574 solution with an NMP solvent in a volume ratio of 1 :7.

[00116] During the deposition of the polyimide coating on the glass substrates, the substrates were maintained at a temperature of 350°C. The substrates were coated using an airbrush operating at about 30 psi for a coating time of 15 seconds. Once coated, the substrates were heated at 350°C for 30 minutes. The six polyimide-coated substrates each had an average polyimide coating thickness of about 3 microns to about 4 microns and a surface roughness Ra of about 20 nm to about 180 nm.

[00117] The polyimide-coated substrates were then catalyzed with palladium (Pd) by immersing the substrates in an Sn/Pd solution for 8 minutes. Next, the substrates were immersed in an accelerator solution for 3 minutes to strip the Sn and expose the active Pd catalyst. The six substrates were now ready for deposition of the metal layer.

[00118] In this example, the six substrates were exposed to an electroless deposition process to deposit a thin copper layer on the polyimide-coated substrates. The electroless deposition process was carried out using a commercial bath from Uyemura comprising copper sulfate, formaldehyde, and sodium hydroxide such that the bath had a pH of 13. The electroless bath was heated to 35°C and the substrates were immersed in the bath for about 3 minutes. The plating rate of the copper metal on the substrates was about 30 nm/min. Therefore, a 100 nm thick layer of copper was deposited on each of the six substrates after the electroless bath.

[00119] After the electroless deposition process, the substrates were rinsed with deionized water and dried using nitrogen gas. Substrates 9A and 9B were heated at 250°C for 30 minutes in forming gas, and substrates 9C and 9D were heated at 350°C for 30 minutes in forming gas. Substrates 9E and 9F were not heated after the electroless deposition process.

[00120] As shown in FIG. 10, substrates 9A, 9B, 9C and 9D all passed the 3N/cm cross hatch tape test, while substrates 9E and 9F failed the test. Thus, heating after the electroless deposition helps to promote metal-to-glass adhesion.

[00121] Example 10

[00122] In this example, four glass substrates (10A, 10B, 10C, and 10D) were coated with polyimide and copper coatings similar to the process disclosed in Example 9. Thus, the process of this example did not include the electroplating steps.

[00123] In this example, a polyimide coating was deposited on front and back surfaces of the substrates by a dip coating method. The glass substrate were each comprised of Corning Lotus™ NXT Glass. Two polyimide coatings were prepared by mixing 25% PI-2574 solution with an NMP solvent. The first polyimide coating contained the components in a volume ratio of 1 : 7, and the second polyimide coating contained the components in a volume ratio of 1 : 15. [00124] Substrates 10A and 10B were coated with the first polyimide coating via the dip coating process. Substrates 10C and 10D were coated with the second polyimide coating via the dip coating process. The substrates were then dried in an oven at 150°C for 30 minutes, followed by heating at 350°C for 30 minutes. Substrates 10A and 10B had a polyimide coating thickness of about 1.8 microns. Substrates 10C and 10D had a polyimide coating thickness of about 0.8 microns and about 1.0 microns, respectively.

[00125] Next, the substrates were subjected to an electroless deposition process as disclosed in Example 9. A 100 nm thick layer of copper was deposited on each of the four substrates after the electroless deposition process. The substrates were then heated at 350°C for 30 minutes in forming gas. As shown in FIG. 11, substrates 10A, 10B, 10C, and 10D all passed the 3N/cm tape test, showing that sufficient results were achieved with both the first and second polyimide coatings disclosed above.

[00126] Example 11

[00127] In this example, two glass substrates (11 A and 1 IB) were coated with poly imide and copper coatings according to the process disclosed in Example 9. Thus, the process of this example did not include the electroplating steps. Furthermore, in this example, the polyimide coating did not contain the silane coupling agent.

[00128] The polyimide coating was prepared by mixing 15% PMDA-ODA PAA solution from Aldrich with an NMP solvent in a volume ratio of 1 : 7. The glass substrates of Example 11 were each comprised of Corning Lotus™ NXT Glass. The same spray-coating process as in Example 9 was applied on a surface of the substrates, which produced a polyimide coating thickness of about 1.3 microns on substrate HA and about 1.7 microns on substrate 11B.

[00129] The substrates were then dried in an oven at 150°C for 30 minutes, followed by heating at 350°C for 30 minutes. Next, the substrates were subjected to an electrodeposition process as disclosed in Example 9. A 100 nm thick layer of copper was deposited on the substrates after the electroless deposition process. The substrates were then heated at 350°C for 30 minutes in forming gas. As shown in FIG. 12, substrates 11 A and 1 IB both failed the 3N/cm tape test. Thus, the silane coupling agent helps to couple the polyimide coating with the glass substrate, which promotes adhesion between the metal coating and the glass substrate.

[00130] Example 12

[00131] In this example, three glass substrates were coated with polyimide and copper coatings according to the process disclosed in Example 9. Thus, the process of this example did not include the electroplating steps. Furthermore, in this example, the polyimide coating did not contain the silane coupling agent. However, in this example, the silane coupling agent was added as a separate layer (i.e., a separate layer from the polyimide coating).

[00132] The glass substrates of Example 12 were each comprised of EAGLE XG® Glass. Before application of the silane coupling agent layer, the glass substrates were pretreated with aminosilanes. Then, the glass substrates were each coated with a different silane coupling agent using a dip-coating process. The silane coupling agents included 3-aminopropyl triethoxysilane (APTES), 3-aminopropyl methyl diethoxysilane (APMDES), and 3-aminopropyl dimethyl ethoxysilane (APDMES). After dip-coating, the samples were dried in an oven at 120°C for 5 minutes. Then, the polyimide coating was applied to the glass substrates.

[00133] The polyimide coating was prepared by mixing 15% PMDA-ODA PAA solution from Aldrich with an NMP solvent in a volume ratio of 1 :7. The same spray-coating process as in Example 9 was applied on two surfaces of the substrates.

[00134] The substrates were then dried in an oven at 150°C for 30 minutes, followed by heating at 350°C for 30 minutes. Next, the substrates were subjected to an electroless deposition process as disclosed in Example 9. A 100 nm thick layer of copper was deposited on the substrates after the electroless deposition process. The substrates were then heated at 350°C for 30 minutes in forming gas. The substrates passed the 3N/cm cross hatched tape test, showing that sufficient results were achieved with a separate silane coupling agent layer.

[00135] Example 13

[00136] In this example, six glass substrates (13A, 13B, 13C, 13D, 13E, and 13F) were coated with polyimide and copper coatings similar to the process disclosed in Example 9. Thus, the process of this example did not include the electroplating steps. Furthermore, the process of this example included an additional heating step during the electroless deposition.

[00137] The polyimide coating was prepared by mixing 15% PMDA-ODA PAA solution from Aldrich with an NMP solvent in a volume ratio of 1:7. The glass substrates of Example 13 were each comprised of EAGLE XG® Glass. The same spray-coating process as in Example 9 was applied on a surface of the substrates, which produced a polyimide coating thickness of about 1.5 microns.

[00138] The substrates were then dried in an oven at 150°C for 30 minutes, followed by heating at 350°C for 30 minutes. Next, the substrates were subjected to an electroless deposition process in which about 600 nm was of copper was deposited on each substrate. Then, during an intermediate heating step, the substrates were heated to either 250°C or to 350°C with a ramp rate of 2°C/min for a duration of 30 minutes in forming gas. After this heating step, the electroless deposition process continued and a 3.4 microns thick layer of copper was then deposited on each substrate via the electroless deposition.

[00139] The substrates were then heated at 350°C for 30 minutes in forming gas. Substrates 13 A, 13B, 13C, 13D, 13E, and 13F all had a peel strength of about 2N/cm, showing that sufficient results were achieved with a relatively thick copper layer that was applied via electroless deposition and with the additional heating step. Additionally, all six substrates (13 A, 13B, 13C, 13D, 13E, and 13F) passed the 3N/cm cross hatched tape test. However, it is noted that in this example, 6 microns of copper was deposited on each substrate via electroplating only so that the metal layers would be sufficiently thick for the peel strength test.

[00140] Example 14

[00141] This example is similar to the process disclosed in Example 13, except it is directed to a comparative example that did not include the intermediate heating step.

[00142] In this example, four samples (14A, 14B, 14C, and 14D) were coated with polyimide and copper coatings. The process of this example did not include the electroplating steps. Furthermore, the process of this example did not include the intermediate heating step during the electroless deposition.

[00143] The polyimide coating was prepared by mixing 15% PMDA-ODA PAA solution from Aldrich with an NMP solvent in a volume ratio of 1:7. The glass substrates of Example 14 were each comprised of EAGLE XG® Glass. The same spray-coating process as in Example 9 was applied on a surface of the substrates, which produced a polyimide coating thickness of about 1.5 microns.

[00144] The substrates were then dried in an oven at 150°C for 30 minutes, followed by heating at 350°C for 30 minutes. Next, the substrates were subjected to an electroless deposition process in which about 600 nm was of copper was deposited on each substrate. After this initial deposition of the copper layer, the electroless deposition process continued and 3.4 microns of copper was then deposited on each substrate via the electroless deposition.

[00145] The substrates were then heated at 350°C for 30 minutes in forming gas. Substrates 14A, 14B, 14C, and 14D all had failed the 3N/cm cross hatched tape test. [00146] As discussed above, the polyimide coatings of the present disclosure advantageously promote metal-to-glass adhesion. Additionally, the polyimide coatings provide increased damage resistance and improved strength and durability of the glass substrate, even with exposure at elevated temperatures.

[00147] The description of the embodiments of the present disclosure is not intended to be exhaustive or to limit the disclosure. While specific embodiments and examples of the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize. Such modifications may include, but are not limited to, changes in the dimensions and/or the materials shown in the disclosed embodiments.

Claims

WHAT IS CLAIMED IS:

1. A coated substrate comprising: a substrate comprised of glass, glass ceramic, or a silicon wafer and having a surface; a polyimide layer disposed on the surface; and a metal layer disposed directly on the polyimide layer, wherein the polyimide layer promotes adhesion of the metal layer to the substrate.

2. The coated substrate of claim 1, wherein the polyimide layer has a thickness in a range from about 5 nm to about 50 microns.

3. The coated substrate of claim 2, wherein the polyimide layer has a thickness in a range from about 0.3 microns to about 10 microns.

4. The coated substrate of claim 3, wherein the polyimide layer has a thickness in a range from about 0.5 microns to about 3 microns.

5. The coated substrate of any one of claims 1-4, wherein the polyimide layer is coupled to the substrate with a silane coupling agent.

6. The coated substrate of any one of claims 1-5, wherein the metal layer comprises copper, magnesium, titanium, tin, indium, chromium, molybdenum, aluminum, niobium, tantalum, vanadium, zinc, silver, nickel, gold, platinum, palladium, or combinations thereof.

7. The coated substrate of claim 6, wherein the metal layer comprises copper.

8. The coated substrate of any one of claims 1-7, wherein the metal layer has a thickness in range from about 50 nm to about 20 microns.

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9. The coated substrate of any one of claims 1-8, wherein the metal layer is deposited on the polyimide layer only by electroless deposition.

10. The coated substrate of claim 9, wherein the metal layer comprises copper and has a thickness in a range from about 500 nm to about 20 microns.

11. The coated substrate of claim 10, wherein the metal layer has a thickness in a range from about 1 micron to about 10 microns.

12. The coated substrate of claim 9, wherein a resistivity of the metal layer is between about 2x10'⁸ Q/m to about 40x10'⁸ Q/m.

13. The coated substrate of any one of claims 1-12, further comprising a transition region between the polyimide layer and the metal layer, the transition region having a width between about 1 nm and about 10 nm.

14. The coated substrate of any one of claims 1-13, wherein the substrate is a ring-shaped member.

15. The coated substrate of claim 14, wherein the ring-shaped member is a spacer for a hard disk.

16. The coated substrate of claim 15, wherein the ring-shaped member has a thickness in range from about 100 microns to about 10 mm.

17. The coated substrate of any one of claims 1-13, wherein the substrate comprises a via, the surface being an inner surface of the via.

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18. The coated substrate of claim 17, wherein a diameter at a top portion and a diameter at a bottom portion of the via are each greater than a diameter at a middle portion of the via, the middle portion being disposed between the top portion and the bottom portion.

19. The coated substrate of claim 18, wherein the diameter at the top portion and the diameter at the bottom portion are each in range from about 80 microns to about 200 microns.

20. The coated substrate of any one of claims 1-19, wherein the polyimide layer has a surface roughness in a range from about 2 nm to about 3 microns.

21. A method of coating a substrate, the method comprising: depositing a polyimide layer on a substrate comprised of glass, glass ceramic, or a silicon wafer; depositing a metal layer on the polyimide layer; and after depositing the polyimide layer and the metal layer on the substrate, heating the substrate at a temperature in a range from about 150°C to about 400°C.

22. The method of claim 21, wherein the metal layer comprises copper, magnesium, titanium, tin, indium, chromium, molybdenum, aluminum, niobium, tantalum, vanadium, zinc, silver, nickel, gold, platinum, palladium, or combinations thereof.

23. The method of claim 22, wherein the metal layer comprises copper.

24. The method of any one of claims 21-23, further comprising after depositing the polyimide layer on the substrate, heating the polyimide layer at a temperature in a range from about 200°C to about 400°C.

25. The method of claim 24, further comprising after depositing the polyimide layer on the substrate, heating the polyimide layer at a temperature of about 400°C for about 0.5 hours to about 2 hours.

26. The method of claim 24, wherein the heated polyimide layer has a thickness in a range from about 5 nm to about 50 microns.

27. The method of any one of claims 21-26, wherein the polyimide layer comprises a silane coupling agent.

28. The method of any one of claims 21-27, further comprising depositing a silane coupling agent layer on the substrate.

29. The method of claim any one of claims 21-28, further comprising after depositing the polyimide layer on the substrate, catalyzing the polyimide layer.

30. The method of any one of claims 21-29, further comprising depositing the metal layer on the polyimide layer using electroless deposition.

31. The method of claim 30, wherein the metal layer has a thickness in a range from about 50 nm to about 800 nm.

32. The method of claim 30, wherein the thickness of the metal layer is in a range from about 600 nm to about 800 nm.

33. The method of claim 30, further comprising heating the metal layer at a temperature in a range from about 200°C to about 400°C.

34. The method of claim 30, wherein the metal layer is a first metal layer and further comprising depositing a second metal layer on the first metal layer using electroplating.

35. The method of claim 34, wherein the second metal layer has a thickness in a range from about 3 microns to about 12 microns.

36. The method of claim 34, further comprising heating the second metal layer at a temperature in a range from about 300°C to about 375 °C.

37. The method of any one of claims 21-36, further comprising: after depositing the polyimide layer on the substrate, heating the polyimide layer at about 400°C in a nitrogen environment; and after depositing the metal layer on the polyimide layer, heating the metal layer in a forming gas.

38. The method of any one of claims 21-37, wherein the resistivity of the metal layer is between about 2x1 O'⁸ Q/m to about 40x1 O'⁸ Q/m.

39. The method of any one of claims 21-38, wherein the step of depositing the metal layer on the polyimide layer does not include an electroplating process.

40. The method of any one of claims 21-39, wherein the step of depositing the metal layer on the polyimide layer further comprises: depositing a first electroless deposition metal layer on the polyimide layer; heating the first electroless deposition metal layer; and depositing a second electroless deposition metal layer on the first electroless deposition metal layer.

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41. The method of claim 40, wherein a thickness of the first electroless deposition metal layer is from about 50 nm to about 1000 nm.

42. The method of claim 41, wherein the thickness of the first electroless deposition metal layer is from about 50 nm to about 600 nm.

43. The method of claim 40, wherein a thickness of the first electroless deposition metal layer is less than a thickness of the second electroless deposition metal layer.

44. The method of claim 40, wherein the first electroless deposition metal layer is heated to a temperature within a range of from about 150°C to about 400°C.

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