US20180142373A1

US20180142373A1 - Method to produce electrically isolated or insulated areas in a metal, and a product comprising such area

Info

Publication number: US20180142373A1
Application number: US15/576,203
Authority: US
Inventors: Sybrandus Jacob Metz; Hans Hendrik Wolters; Johannes Kuipers
Original assignee: METALMEMBRANESCOM BV
Current assignee: METALMEMBRANESCOM BV
Priority date: 2015-05-26
Filing date: 2016-05-25
Publication date: 2018-05-24
Also published as: EP3303661A2; CN107923061A; WO2016190737A3; WO2016190737A2

Abstract

The present specification relates to a method to produce electrically isolated or insulated areas in a metal, and a product comprising such area. The method according to the invention comprising the steps of: providing a metallic structure; performing a plasma electrolytic oxidation and/or anodization process such that an oxide layer is achieved on an area of the metallic structure; and electrically isolating a part of the metallic structure by removing part of the metallic structure and/or connecting a further metallic structure to the metallic structure with the oxide layer.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present specification is a National Phase Entry of International Application No. PCT/NL2016/050372 filed 25 May 2016 and entitled “Method to produce electrically isolated or insulated areas in a metal, and a product comprising such area” which, itself, claims priority to NL 2014857 filed 26 May 2015 and entitled “Method to produce electrically isolated or insulated areas in a metal, and a product comprising such area,” each of which are incorporated by reference herein in their entireties.

FIELD

The present specification relates to a method to produce electrically isolated or insulated areas in a metal. Such areas are used in various applications, including electronic devices. More specifically, the method according to the present specification relates to forming metal structures that have an electrically isolated area that is connected by non-conductive part(s). In this context isolating and insulating both describe the electrical separation of an area from other parts and can be used alternately in the context of the present specification.

BACKGROUND

A problem with conventional electronic devices, including computing devices such as mobile phones, tablets, computers, laptops etc., that use an antenna is that the devices often cover the antenna with a housing, thereby increasing the risk of hindering communication and/or producing noise.

SUMMARY

The present specification has for its object to improve conventional products having an electrically isolated area.
This object is achieved with the method to produce electrically isolated areas in a metal, the method comprising the steps of:
providing a metallic structure;
performing a plasma electrolytic oxidation and/or anodization process such that an oxide layer is achieved on an area of the metallic structure; and
electrically isolating a part of the metallic structure by removing part of the metallic structure and/or connecting a further metallic structure to the metallic structure with the oxide layer.
The treated structure can be used in various applications, including electronic devices. More specifically, the method according to the present specification relates to forming metal structures that have an electrically isolated area that is connected by non-conductive part(s). Such structure can advantageously be used as an antenna or antenna part, such as an RF antenna. Such antenna that is produced involving the method according to the present specification enables improved communication having less noise, for example.
In embodiments according to the present specification the ceramic layer has a thickness in the range of 5-300 μm, preferably 10-200 μtm, more preferably 15-150 μm and most preferably a thickness is about 100 μm.
By providing the ceramic layer with a sufficient thickness the stability and strength of the heater is improved. Furthermore, the insulation is increased, enabling control of heat transfer and/or heat production. The thickness of the ceramic layer is adapted to the desired characteristics. This flexibility during production provides a further advantage of the system according to the present specification.
In embodiments according to the present specification, the ceramic layer is provided on or at the conductor with plasma electrolytic oxidation (PEO).
Principles of a PEO process are disclosed in WO 2011/010914 and are included by reference herein. In embodiments, the element is made from an aluminium material, or other suitable material, such as titanium, on which a porous metal oxide layer, such as aluminium oxide or titanium oxide, is grown with plasma electrolytic oxidation. In this embodiment of the present specification the metal oxide layer is provided on a side of the metal layer involving a plasma oxidation process, more specifically a plasma electrolytic oxidation process. By performing a plasma electrolytic oxidation process on the first metal layer locally the electric brake down potential of the oxide film on the metal layer is exceeded and discharges occur. Such discharges lead to a type of local plasma reactors, resulting in a growing oxide. This builds the desired structure for the membrane layer. The plasma electrolytic oxidation process creates very fine pores in the metal layer, thereby forming an oxide layer that contains small pores. This method provides a ceramic layer that can be made efficiently. Surprisingly, also the pore sizes of this ceramic layer can be controlled more effectively and the desired characteristics for such ceramic layer can be achieved more accurately. A further advantage of the method according to the present specification is that it enables the manufacturing of ceramic material in a modular way. Optionally, this enables providing complicated three-dimensional shapes of the desired element.
Plasma electrolytic oxidation enables that a relatively thick aluminium, titanium or other suitable metal layer is grown from the metal (>130 μm) by oxidizing (part of) the metal to metal oxide. Especially the use of titanium provides good results. The resulting layer is a porous, flexible and elastic metal oxide ceramic. Plasma electrolytic oxidation (>350 550 V) requires much higher voltage compared to standard anodizing (15-21 V). At this high voltage, micro discharge arcs appear on the surface of the aluminium, or other material, and cause the growth of the thick (metal) oxide layer. Results have shown that a ceramic layer can be achieved on an aluminium foil of about 13 μm thickness, with a flexible and elastic ceramic layer. One of the advantageous effects of using plasma electrolytic oxidation to provide the ceramic layer is that due to the growth of the layer from the metal during oxidation the adherence of the ceramic layer to the metal is excellent.
Alternative manufacturing methods for producing an electrically isolated area in a metal include sintering or spark plasma sintering, oxidation of the surface layer of the metal by heating in oxygen rich environment, anodizing, and plasma spraying. Also, it would be possible to deposit an aluminium, or other material, coating on the conductor of the heater element, for example with arc spraying, and to oxidize the deposited material to an oxide with plasma electrolytic oxidation.
As an alternative to PEO, or in combination therewith, an anodization process may be applied to provide a ceramic layer. Typically, anodization takes place at a voltage that from 1 to 300 V DC, although most fall in the range of 15 to 21 V. Higher voltages are typically required for thicker coatings formed in sulfuric and organic acid. Typically, the current that is applied is in the range from 30 to 300 amperes/meter².
The resulting ceramic layer may have pores with a diameter in the range of 1-150 nm in diameter on the interface of the metal/ceramic layer and pores with a diameter in the range of 50 nm to 5 μm on the outside. The ceramic layer thickness can range from under 0.5 μm up to 150 μm for architectural applications.
In embodiments of the present specification the method comprises the step of electrically isolating a part of the metallic structure by removing part of the metallic structure. This provides separate parts/elements in the metallic structure that are electrically isolated.
Alternatively, or in combination therewith, the method in another embodiment of the present specification comprises the step of connecting a further metallic structure to the metallic structure with the oxide layer. Because of the process conditions, involving high temperatures and pressure, the metal oxide layer melts during plasma oxidation and solidifies again during cooling. Provided the further metallic structure is positioned closed to the metallic structure the oxide layers of the respective structure will solidify together, thereby connecting the metallic structures, while preferably electrically isolating the metallic structures.
In embodiments of the present specification the method further comprises the step of masking parts of the metallic structure and performing the plasma electrolytic oxidation and/or anodization such that an oxide layer is achieved on an unmasked area of the metallic structure. This provides an effective method to provide a structure or an isolating structure to the metallic structure.
Removing part of the metallic structure may be performed after performing the plasma electrolytic oxidation process. This enables effective oxidation. In embodiments, removing part of the metallic structure comprises performing an etching process, for example chemical etching or electrochemical etching.
In embodiments the etching involves electrochemical etching.
Electrochemical etching, also referred to as electrochemical machining (ECM) and, in embodiments, including jet electrochemical machining (JET-ECM), allows for a precise, fast and reproducible local removal of material of the first metal layer. Surprisingly, in this etching process it was found that etching the first metal layer does not significantly influence the metal oxide layer. In fact, the metal oxide layer remains substantially intact whereas the metal is locally etched away. This enables an efficient and effective manufacturing of a product comprising an electrically isolated area, for example. Performing the removing step after producing the oxide layer further improves the electric isolation of the respective area. For example, this may prevent or reduce undesired bulging and/or oxidation to the sides in a transversal direction. This improves the quality of the resulting product. Also, this may further reduce the noise disturbance. As a further advantage the etching process that is applied may automatically stop when reaching the oxide layer. This improves the isolation that is effectively provided.
In embodiments the method further comprises the step of providing non-conductive material to the removed areas of the metallic structures.
The use of non-conductive material further improves the quality of the resulting product. In embodiments according to the present specification the method further comprises the step of increasing the stability and/or strength of the metallic structure by providing a stability layer on the oxide layer of the metallic structure after performing the plasma electrolytic oxidation and/or anodization process.
By providing a stability layer the strength and stability of the metallic structure is significantly improved. This improves the etching performance. In embodiments, the stability layer comprises non-conductive material, for example an epoxy.
In embodiments with a stability layer, the stability layer is provided with a thickness in the range of 10 to 100 μm, preferably in the range of 20 to 75 μm, and most preferably with a thickness of about 50 μm. It was shown that such thickness improves stability and strength thereby enabling or improving possibilities for further processing, such as electrochemical etching.
In embodiments according to the present specification the method further comprises the step of removing the stability layer.
Optionally, the stability layer is removed after performing the etching process. This may depend on the actual use or application of the product.
In further embodiments of the present specification the method further comprises the step of providing a third metallic structure connecting the other metallic structures together. In embodiments, such third metallic structure will connect the two other metallic structures together in a plasma oxidation process. Optionally, at least one of the two, three of further metallic structures is of a different material. For example, in one of the embodiments the third metallic structure is a sacrificial metallic structure that can be used to connect the other metallic structures. An example of such embodiment is the use of a titanium structure as third, sacrificial structure for connecting two aluminum structures. In a further example, metallic structures of aluminum, magnesium and titanium are connected together.
The present specification also relates to a product according to the present specification, with the product comprising an electrically isolated area that is produced with a method as described earlier.
The product provides the same effects and advantages as described for the method.
In embodiments, such product is a computing device, such as mobile phones, tablets, computers, laptops etc., and the area is part of an antenna. In embodiments, the effects of undesired noise in the communication can be significantly reduced. The product may have different shapes or configurations. For example, the metallic structures of the product may comprise a tubular shape, a metallic mesh structure on the metallic structure, or a wire shape.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the present specification are elucidated on the basis of preferred embodiments thereof wherein reference is made to the accompanying drawings, in which:

FIG. 1 shows a cell and metal that is subjected to plasma oxidation according to the present specification;

FIG. 2 shows a cross section of the product resulting from the method according to the present specification;

FIG. 3 shows a top view of the product shown in FIG. 2;

FIG. 4 shows a process according to an embodiment of the present specification with a stability layer; and

FIG. 5A-D shows different embodiments of the present specification with two or more metallic structures.

DETAILED DESCRIPTION

A piece of metal 2 (FIG. 1) is subjected to plasma oxidation to create an oxide layer 4 on a metal plate. In order to make a ceramic layer on one side of the metal and on a particular region, the metal is placed in a plasma electrolytic oxidation cell 6 as shown in FIG. 1.
The metal plate 2 preferably aluminum is connected to an anode. Alternative materials titanium, magnesium or other so called valve metals can also be used. The synthetic material 8 shown in the figure can be a hard plastic which can be compressed against another hard plastic with in between a metal plate 2 and a rubber 10 for sealing. This synthetic material 8 acts as a masking material to form plasma electrolytic oxide 4 at unmasked areas 12. Different kind of shapes can be used to mask the metal plate 2.
The rubber material 10 seals the cell and masks the metal 2. The synthetic material 8 also acts as a mask. In such a cell 6 as described here only the part 12 which is not masked is treated through plasma electrolytic oxidation. Plasma electrolytic oxidation (PEO) or micro arc oxidation creates a non-conductive metal oxide layer 4 on the metal plate 2. Different properties, like color of the layer, can be adjusted by choosing different electrolytes for the PEO process. Electrolytes that can be used contain KOH (potassium hydroxide) in a concentration range 0-10 g/l, and Na₂SiO₃5H₂O concentration range 0-10 g/l, for example. It is known from literature that these electrolytes or mixtures of these electrolytes can give a good PEO layer on Aluminum. Also other salts can be used like Na₂AlO₂or Na₂SiF₆(NaPO₃)₆, potassium borate K₂B₄O₇, or sodium borate Na₂B₄O. It will be understood that other alternatives could also be envisaged in accordance with the present specification.
In an illustrated embodiment of the present specification the structure of the metal element 2 comprises a thin plate or sheet of titanium, aluminium, or any other valve metal, such as magnesium, zirconium, zinc, niobium, vanadium, hafnium, tantalum, molybdenum, tungsten, antimony, bismuth, or an alloy of one or more of the preceding metals. Plate or sheet 2 is coated on the other side through plasma electrolytic oxidation. Plasma electrolytic oxidation is done by placing titanium plate or sheet 2 in an electrolyte. For example, the electrolyte comprises 15 g/l (NaPO₃)₆and 8 g/l Na₂SiO₃.5H₂O. The electrolyte is maintained at a temperature of 25° C. through cooling. Plate or sheet 2 is used as an anode and placed in a container containing the electrolyte. Around plate or sheet 2 a stainless steel cathode 12 is positioned. A current density is maintained between the plate or sheet and cathode 22 of about 0.15 A/cm². The current is applied in a pulsed mode of about 1000 Hz. The current increases rapidly to about 500 Volt between the plate or sheet and cathode 22. This creates a plasma electrolytic oxidation process on anode plate or sheet 2 and creates ceramic layer 4. It will be understood that process parameters may depend on the structure of the plate or sheet and/or the dimensions thereof.
After the PEO process a ceramic layer 4 is obtained with a layer thickness that depends on the treatment time. In order to obtain parts 14 which are electrically isolated from the metal 2, the metal 14 remaining attached to the ceramic layer 4 has to be removed. There are many methods which can remove the metal. Electrochemical machining is very effective in removing the metal 14 under the oxide layer 4.
After the plasma oxidation treatment the metal plate was transferred to an etch cell. In this cell the metal was etched via electrochemical machining. The plate was mounted in this cell with the metal side facing the cathode. This cathode consists partly of a metal and a plastic. The metal shape of the cathode determines the shape and dimensions which will be etched in the metal plate. A pulsed electric field is applied between the cathode and the anode (metal plate with on the other side the metal oxide layer). A highly conductive electrolytic flow was provided between the anode and the cathode. The potential difference between the anode and the cathode was in the beginning 1-15 Volts and increased gradually during the etching. The potential increases sharply when the metal is etched away and reaches the metal oxide layer. Then the process was stopped. The current density was kept at a value of about 250 kA/m². This process results in a metal plate with on one side a metal oxide layer and a structure etched in the metal. Fluids can be filtrated through the open structure in the metal. The metal oxide layer can be supported during filtration by a metal plate and/or a (paper) filter that is optionally provided in between the metal oxide layer and the metal plate. Because the surface roughness of the metal oxide layer is high the permeate water can flow easily away to the sides and can be separated from the feed water. This filtration configuration also allows for high filtration pressures over 5 bars.
Tests have shown that a combination of the PEO process with electrochemical machining achieves a high quality product, for example with very accurate removal of the metal at the desired spots.
After performing the plasma oxidation (PEO) step, or if the process is performed at lower potentials after the anodization step, part of the metal 14 can be removed from the other side by electrochemical machining, for example. The advantage of electrochemical machining is that the process stops when it reaches the non-conductive ceramic layer 4. The formed opening can be filled with a non-conductive polymer 16 or other substances. By doing so, electrically isolated areas 18 are created.
A cross section of a product 20 formed this way is shown in FIG. 2. A top view of product 20 may look like as shown in FIG. 3.
In embodiments according to the present specification manufacturing process 102 (FIG. 4) starts with providing metal plate of sheet 104. With a PEO process, or alternatively an anodization process, ceramic layer 106 is provided on one side of metal element 104. Stability layer 108 may be provided on and/or in ceramic layer 106 to improve stability and strength of element 104 with ceramic layer 106. In the illustrated embodiment stability layer 108 is from epoxy. In the next step an ECM process is performed that provides grooves, holes or openings 110 from the other side of element 104. The ECM process is stopped as grooves, holes or openings 110 reach ceramic layer 106. Optionally, grooves, holes or openings 110 are filled with non-conductive material 112, for example epoxy. Also optionally, stability later 108 can be removed from ceramic layer 106.
In connecting method 202 according to an embodiment of the present specification (FIG. 5A) metallic structure 204 is connected to second metallic structure 206 with plasma electrolytic oxidation bonding metallic structures 204, 206 together with the oxide layers. In embodiments, the connection is made such that metallic structures 204, 206 are electrically isolated. Optionally, in an alternative method 208 (FIG. 5B) two metallic structures 210, 212 are connected with sacrificial third metallic structure 214. For example, the respective materials for metallic structures 210, 212 and 214 are aluminum, magnesium and titanium. Alternatively, middle structure 214 is of titanium and the other structures 210, 212 are of aluminum.
The structures can be shaped as plates or sheets. Alternatively, other shapes are possible. For example, in process 216 (FIG. 5C) two tubular metallic structures 218, 220 are connected. Such shape may act as antenna, for example. In a further process 222 (FIG. 5D) of the present specification mesh 224 (or alternatively a wire) is connected to plate/sheet 226 (or alternatively a wire). Also, two or more wires may be connected. It will be understood that also other embodiments, shapes or configurations can be envisaged in accordance with the present specification.
All different kind of shapes can be made on the metal by plasma electrolytic oxidation and masking the metal during plasma oxidation and removing the metal after plasma oxidation by electrochemical machining and filling the cavity with a nonconductive material.
The present specification is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.

Claims

1. A method to produce an electrically isolated area in a metal, comprising the steps of:

providing a metallic structure;

performing a plasma electrolytic oxidation and/or anodization process such that an oxide layer is achieved on an area of the metallic structure; and

electrically isolating a part of the metallic structure by removing part of the metallic structure and/or connecting a further metallic structure to the metallic structure with the oxide layer.

2. The method according to claim 1, further comprising the step of masking parts of the metallic structure and performing the plasma electrolytic oxidation and/or anodization such that an oxide layer is achieved on an unmasked area of the metallic structure.

3. The method according to claim 1, wherein removing part of the metallic structure is performed after performing the plasma electrolytic oxidation process and/or anodization process.

4. The method according to claim 3, wherein removing part of the metallic structure comprises performing an etching process.

5. The method according to claim 4, wherein the etching process comprises an electrochemical etching process.

6. The method according to claim 4, wherein the etching process comprises the step of automatically stopping the etching when reaching the oxide layer.

7. The method according to claim 1, further comprising the step of providing non-conductive material to the removed part or parts of the metallic structure.

8. The method according to claim 1, further comprising the step of increasing the stability and/or strength of the metallic structure by providing a stability layer on the oxide layer of the metallic structure after performing the plasma electrolytic oxidation and/or anodization process.

9. The method according to claim 8, wherein the stability layer comprises non-conductive material.

10. The method according to claim 8, wherein providing a stability layer comprises providing a layer with a thickness in the range of 10 to 100 μm, preferably in the range of 20 to 75 μm, and most preferably with a thickness of about 50 μm.

11. The method according to claim 8, further comprising the step of removing the stability layer.

12. The method according to one claim 1, further comprising the step of providing a third metallic structure connecting the other metallic structures together.

13. The method to claim 1, wherein at least one of the metallic structures is of a different material.

14. A product comprising an electrically isolated area that is produced with a method according to claim 1.

15. The product according to claim 14, wherein the product is a computing device and the area is part of an antenna.

16. The product according to claim 14, wherein the metallic structures of the product comprise a tubular shape, a metallic mesh structure on the metallic structure, or a wire shape.

17. The product according to claim 15, wherein the metallic structures of the product comprise a tubular shape, a metallic mesh structure on the metallic structure, or a wire shape.

18. The method according to claim 2, wherein removing part of the metallic structure is performed after performing the plasma electrolytic oxidation process and/or anodization process.

19. The method according to claim 18, wherein removing part of the metallic structure comprises performing an etching process.

20. The method according to claim 19, wherein the etching process comprises an electrochemical etching process.

21. The method according to claim 20, wherein the etching process comprises the step of automatically stopping the etching when reaching the oxide layer.