GB2478641A

GB2478641A - Masking means and methods of use

Info

Publication number: GB2478641A
Application number: GB1103888A
Authority: GB
Inventors: John Tinker
Original assignee: Radio Design Ltd
Current assignee: Radio Design Ltd
Priority date: 2010-03-12
Filing date: 2011-03-08
Publication date: 2011-09-14
Anticipated expiration: 2031-03-08
Also published as: GB201004091D0; GB201103888D0; GB2478641B

Abstract

At least a part of one or more surfaces 6 of an object is provided with mask means thereon and at least a part of one or more other surfaces 4 of the object has at least one coating applied thereto, said mask means comprising polytetrafluoroethvlene (PTFE) or a PTFE-based material, and said at least one coating being or including a plating deposition coating or layer. The surfaces of the object may be formed from one or more base materials, which may comprise a metal that is preferably aluminium. The at least one coating preferably includes one or more of an electrically conductive material, a noble metal, copper or silver. The object may be a radio frequency (RF) filter housing 2. Also disclosed is a method (figure 2) of using mask means comprising polytetrafluoroethvlene (PTFE) or a PTFE-based material for masking one or more parts or surfaces of an object. Detachable cover means (14, figure 1b) are preferably applied to or over one or more surfaces that are not to have the mask means applied thereto. The mask means may be applied by dipping, spraying, submerging or coating onto said object.

Description

Masking Means and a Method of Using Masking Means This invention relates to masking means and a method of using masking means, and particularly to masking means and a method of using masking means suitable for use as part of a selective plating process.

Although the following description refers almost exclusively to masking means and a method of using masking to allow the selective plating of a radio frequency (RF) filter unit, it will be appreciated by persons skilled in the art that the present invention could be used as masking means and a method of using masking means for allowing selective plating or a coating application to be applied to any suitable item or items or for use in any process where masking of an item or items is required.

Conventional RF filter units typically include an aluminium body housing the RF filter components. The aluminium body is typically plated with a noble metal, such as silver, to improve the electrical performance of the unit in use. One or more paint layers can be applied on top of the silver plated surface on exterior surfaces to provide protection from environmental conditions, such as rain, heat, snow and/or salt spray, to provide an improved aesthetic appearance to the housing and/or the like. In the past, one or more Chromium VI based paint layers have been used to form an external environmental protection layer. However, due to the introduction of the EU Directive on the Restriction of Haarc1ous Substances (RoHS), use of Chromium VI is now prohibited. Other possible replacements for Chromium VI which would meet the requirements for RoHS, such as Chromium III or Non Chromate Passivate (NCP), do not appear to be as effective as Chromium VI and have been found to fail in harsh environmental conditions during testing. This can result in galvanic corrosion of the underlying noble metal (i.e. silver) and/or the base metal (i.e. aluminium), which can in turn result in failure of the RF filter unit. In an attempt to avoid this problem, it is known to use a mask on areas of the unit that are likely to be exposed to environmental conditions, such as the exterior surfaces of the unit for example, in order to prevent noble metal plating deposition on these surfaces and to prevent galvanic corrosion.

In addition, due to the expense associated with the purchase of noble metals, there is a need to reduce the surface area of the aluminium housing on which the noble metal is applied to in use.

One example of a known masking technique is the use of electroplating/anodising tape. The tape is applied as a mask to surfaces of the unit on which plating deposition is not required.

It is a manual operation that is difficult to perform successfully and/or with any consistent reproducibility. This is because many of the surfaces to which the tape is applied have been machined or cast in particular shapes which are not flat. Furthermore, since the tape is normally supplied in roll form of different widths, care and skill is required on the part of the user before and during application of the tape to the unit to ensure the correct areas are covered. Care also has to be taken to ensure a sealed bond is formed between the edges of the tape and the surface of the unit being masked so that the plating chemicals cannot penetrate underneath the tape and allow deposition of plating material. The care and skill required by the user results in an increase in the cost of labour and time for undertaking the process. In addition, the adhesive bond formed between the tape and the surface of the unit to which the tape is applied can be compromised above a relatively low temperature (i.e. typically in the region of 77°C or 170°F). This is of particular concern in a noble metal deposition plating process, where the process typically takes place within a temperature range of 86-90°C and results in a high proportion of units failing and having to be reworked (i.e. stripped of the noble metal, re-masked and re-plated).

Furthermore, once the plating deposition process has been completed, the masking tape then has to be manually removed, exposing the originally masked surface. In harsh environmental conditions, this re-exposed surface will require a secondary coating or painting process to protect the same. The requirement for this additional protection coating increases both the cost of the process and the time taken to complete the process. The end result is that the use of tape to successfully mask RF filter units is not considered to be cost effective, is difficult to apply and maintain, is not consistently reproducible and has high labour costs associated with the same.

It is therefore an aim of the present invention to provide mask means for selectively masking one or more surfaces or areas of an object.

It is a further aim of the present invention to provide a method of using mask means for selectively masking one or more surfaces or areas of an object.

It is a yet further aim of the present invention to provide a selective plating method that uses mask means.

It is a yet further aim of the present invention to provide an object having mask means provided thereon.

According to a first aspect of the present invention there is provided an object, at least a part of one or more surfaces of the object provided with mask means thereon, at least a part of one or more other surfaces of the object that do not have the mask means provided thereon having at least one coating applied thereto, characterised in that the mask means includes or comprises polytetrafluoroethylene (PTFE) or a PTFE based material and the at least one coating is or includes a plating deposition coating or layer.

Thus, the present invention provides an object including a PTFE or Teflon (Brand name of E. I. du Pont de Nemours and Company (Dupont)) containing mask selectively applied to one or more surfaces of the object, and one or more other non-masked surfaces of the object having a coating or layer that has been applied by a plating deposition process (i.e. the non-masked surfaces are plated). The PTFE is easy and quick to apply, does not require removal after application, is substantially inert and therefore does not readily react with other processes that may be applied to the object, does not require a secondary coating to be applied to the same to provide environmental protection, and is cost effective. Use of the PTFE or PTFE based material as a mask also removes the requirement for a coating that could be applied by a plating process, such as a noble metal coating, to be applied to all exposed surfaces of the object in use. The PTFE or PTFE based material provides a durable surface coating that can withstand harsh environmental conditions. It can provide the object surfaces to which it is applied with an improved aesthetic appearance. The viscosity of the PTFE or PTFE based material is such that it provides a substantially even chemical coating providing accurate and consistently reproducible masking means. The PTFE or PTFE based material preferably becomes an integral part of the component and remains permanently attached to the object surfaces, even after the object has undergone a plating process. Furthermore, the use of PTFE removes the requirement for the design and manufacture of expensive and complex jigs used in prior art techniques to withstand the harsh chemical conditions of a plating process.

The object can be formed from a conductive material and/or a non-conductive material.

Preferably at least the surfaces of the object are formed from one or more base materials and said mask means are applied to said one or more base materials. The base material can be formed from a conductive material and/or a non-conductive material.

In one embodiment the base material is or includes a metal, and preferably the base material is or includes aluminium.

Preferably the one or more coatings and/or layers include any or any combination of an electrically conductive material, copper, a metal or metal alloy, a noble metal, such as for example silver and/or the like.

Preferably the object is for use outside or in an environment subject to extremes of environmental conditions.

Preferably the mask means is applied to a part or whole of the one or more substantially external surfaces of the object.

Preferably the one or more coatings and/or layers applied to one or more non-masked surfaces of the object include a part or whole of one or more substantially interior or internal surfaces of the object. For example the object can include a channel, aperture, cavity, recess and/or the like defined therein which are defined by one or more substantially interior surfaces.

Preferably the object is in the form of any or any combination of a housing, unit or component for use in a base station, with a mast of a mobile phone or satellite network, with an antenna line device and/or the like. Further preferably the object is a radio frequency (RF) filter unit or housing, a tower mounted amplifier (TMA) unit or housing, a combiner unit or housing, a bias-T unit or housing and/or the like.

According to a second aspect of the present invention there is provided a method of using mask means for masking one or more parts and/or surfaces of an object, said method including the steps of selectively applying mask means to at least a part of one or more surfaces of the object, thereby leaving at least part of one or more other surfaces of the object with no mask means provided thereon, applying at least one coating to at least part of said one or more other unmasked surfaces, characterised in that the mask means includes or comprises polytetrafluoroethylene (PTFE) or a PTFE based material and the at least one coating is or includes a plating deposition coating or layer.

Preferably the mask means is a chemical mask means applied to one or more surfaces of the object.

Preferably a part of one or more surfaces of the object are cleaned prior to application of the mask means thereon. The cleaning step typically allows the surfaces of the object to be cleaned and/or degreased prior to application of the mask means thereto.

In one embodiment the cleaning step includes applying clegreasing means or one or more clegreasing agents to one or more parts or surfaces of the object. The degreasing means or agents can be applied to the object in the form of a vapour. For example, the object can be located in a chamber and degreasing vapour can be released into the chamber to cover said one or more surfaces. Alternatively, one or more surfaces of the object can be submerged and/or covered in degreasing means or agents. For example, the object could be submerged in a solvent based or aqueous based wash solution. In either case, the object could then be subjected to one or more rinsing and/or drying steps if required as part of the cleaning process.

Preferably detachable cover means are applied to or over the part or whole of the one or more other surfaces which are not to have the mask means applied thereto. The detachable cover means typically acts as a mechanical mask to provide a temporary and removable mask over the one or more surfaces of the object on which one or more coatings and/or layers or plating deposition is to be applied. This prevents the mask means from being applied to the object surfaces on which a plating material may be required or one or more coatings and/or layers are to be applied.

The detachable cover means are preferably applied to the object before application of the mask means, and further preferably after the cleaning step.

Thus, in one embodiment the process includes a two stage masking procedure; a first stage for masking the one or more surfaces/areas of the object that will eventually be plated; and a second stage for masking the one or more surfaces/areas of the object that do not require plating thereon.

The detachable cover means can include attachment means to allow the detachable cover means to be detachably attached to said one or more object surfaces. The attachment means can include one or more screws, thumb screws, nuts and bolts, clamps, ties, straps, adhesive, friction fit, inter-engaging members and/or the like.

Preferably the detachable cover means can include a metal or plastic lid or cover, such as for example an aluminium plate, a silicon bung and/or the like. In one embodiment the detachable cover means could include any conventional detachable masking means, such as masking tape and/or the like. The detachable cover means is preferably of such a form to be able to withstand high temperatures that might be used in one or more heating stages of the mask means.

In one embodiment the at least one part or whole of the one or more surfaces to which the mask means is to be applied undergoes a grit blasting treatment step before the mask means is applied. Preferably the grit blasting treatment step takes place after location of the detachable cover means to the object. The grit blasting treatment step typically increases the surface area of the object to which the mask means is to be applied, thereby increasing the ease to which the mask means can adhere to said object surfaces. The grit blasting treatment step can include the application of any suitable form of grit onto one or more surfaces of the object, typically at high pressure. For example, a glass based grit could be blasted at said one or more object surfaces.

In one embodiment the at least one part or whole of the one or more surfaces to which the mask means is to be applied undergoes a priming step and/or a phosphating step.

In the priming step, one or more priming materials are applied to the one or more surfaces of the object prior to applying the mask means. This typically increases the adhesion of the mask means to said surfaces in use.

In the phosphating step, one or more phosphate materials are applied to the one or more surfaces of the object prior to applying the mask means. This typically improves the corrosive resistance and/or adhesion of the mask means of the one or more surfaces.

Preferably the mask means are applied by dipping, spraying, submerging, coating and/or the like the PTFE or PTFE based material onto the part or whole of the one or more surfaces of the object. The thickness to which the PTFE material is applied to the object surfaces depends on a number of possible factors, such as the composition of the base material, the environmental conditions the object will be exposed to in use and/or the like.

The thickness of the PTFE on the object is typically such that the base material or resulting object is or becomes substantially non-porous. This can be tested by any suitable means, such as an electrical sponge test and/or the like. Multiple layers of the PTFE can be applied to the object surfaces to achieve the required thickness if required.

The mask means can be applied in the form of a powder, dispersion, solution, vapour and/or the like. Application of the mask means can be via conventional spraying, electrostatic means, manually, automatic, such as via robotic means and/or the like.

For example, the object could be placed in a fluidised bed, wherein the object is placed into a tank or chamber of PTFE powder fluidised by passing low pressure air through the tank or chamber, thereby causing the powder to flow onto the object like a liquid.

Preferably the object is rotated during the mask means application process to reduce the effects of thermoplastic melt flow.

Preferably the one or more surfaces of the object are heated to a temperature sufficient to allow heat curing of the PTFE or PTFE based material following application of the same to the object. The temperature of the heat curing depends on the working characteristics of the PTFE or PTFE based material used, the base material, the length of time the heat curing is to take place and/or the like. If multiple layers of PTFE are to be applied to the object, the heat curing step typically takes place after the last or outermost layer of PTFE is applied to the object.

Once the mask means has been successfully applied, the object then preferably undergoes a plating process and/or further coating process to allow application of the one or more layers or coatings of a suitable material to the one or more non-masked surfaces of the object.

Preferably the detachable cover means are removed from the object prior to the plating and/or further coating process. This exposes the one or more surfaces on which the plating deposition and/or further coating(s) are to be applied. It also means that detachable cover means cannot become loose or detached from the object during a plating deposition process and/or further coating process.

The plating deposition process can include an electrolytic or an electro-less plating deposition process. The plating deposition process typically provides the object with improved electrical performance and/or the like.

It will be appreciated that the surface area of the object to which the plating material and/or further coating is applied to is significantly reduced compared to some prior art procedures where the whole of the object is coated in the plating material and/or further coating. This significantly reduces the costs associated with plating one or more surfaces of the object.

Furthermore, no hazardous chemicals are required to provide the masking and/or plating process and the method and final object therefore complies with RoHS standards.

According to a third aspect of the present invention there is provided a selective plating process for an object including the use of mask means.

According to a fourth aspect of the present invention there is provided a radio frequency filter housing having one or more surfaces provided with a PTFE or PTFE based coating thereon.

According to a fifth aspect of the present invention there is provided a method of selectively plating a radio frequency filter housing including the use of mask means.

According to a sixth aspect of the present invention there is provided mask means for selectively masking one or more surfaces of an object, said mask means including one or more PTFE or PTFE based layers or coatings for application to said one or more surfaces of said object in use.

An embodiment of the present invention will now be described with reference to the accompanying figures, wherein: Figures la-Ic show three stages involved in a masking method according to one embodiment of the present invention; Figure 2 is a flow diagram illustrating the steps involved in a masking method according to an embodiment of the present in ye ntio n.

Referring to the figures, there is illustrated a radio frequency filter housing 2, the surfaces of which require selective plating using the noble metal silver. The silver provides the filter housing with improved electrical performance when deployed in

the field in use.

Housing 2 is typically a machined body formed from a base material of aluminium. The silver typically needs to be applied to the interior surfaces 4 of the housing only. In addition, the exterior surfaces 6 of the housing are typically exposed to extreme environmental conditions in use and therefore the exterior surfaces need to be provided with a protective layer thereon. The protective outer layer is also preferably aesthetically pleasing to provide the external appearance with a commercially acceptable aesthetic appearance. In order to achieve the selective plating of the interior surfaces 4 of the housing 2, whilst providing the exterior surfaces 6 of the housing 2 with a robust, durable and aesthetically pleasing coating, a masking process according to the present invention is used.

Housing 2 typically has a top 8, a base (not shown) and side walls 10 forming the exterior surfaces 6 of the housing. A machined recess 12 defined in top 8 defines interior surfaces 4 of the housing, as shown in figure Ia. The filter components are located in the interior recess 12 of the completed filter housing in use.

Temporary and detachable cover means in the form of a plate cover or lid 14 and silicone bungs 16 are located over the opening to recess 12 and in apertures 18 defined in one of the side walls 10 of the housing, respectively. Attachment means in the form of thumb screws 20 are used to clamp the lid 14 to housing 2 during the masking process, as shown in figure lb. The temporary and detachable cover means act as a temporary mechanical mask or members to cover the parts of the housing for which application of a permanent chemical or PTFE mask of the present invention is not required. These temporarily covered parts and surfaces typically correspond to the parts and interior surfaces 4 of the housing that require silver plating during a plating deposition process.

Mask means in the form of a chemical or PTFE mask 22 is applied to the exterior surfaces 6 of housing 2, as shown in figure lb. This mask becomes an integral part of the housing that does not require removal thereafter (i.e. it can be permanently attached). Once the mask is successfully applied, the detachable cover means can then be removed to allow the housing to undergo selective plating with silver, as shown in figure Ic.

The PTFE mask prevents application of silver to the exterior surfaces 6 of housing 2 but allows one or more silver coating layers to be applied to the interior surfaces 4 of housing 2.

A detailed example of the masking process steps will now be described below with reference to figure 2. It will be appreciated by persons skilled in the art that not all the steps are essential to the present invention and the order of some of the steps could vary.

The object 102 firstly undergoes a cleaning step involving the use of one or more degreasing agents 104 to degrease all the surfaces of the object. The application of degreasing agents to the object can take place via a vapour process 106, wherein the object is located in an atmosphere of one or more vapourised degreasing agents, or an in-line wash process 108, wherein the object is submerged in a solvent based wash solution. The object is then washed and dried before it is ready for the next stage.

Temporary and removable cover means are applied to one or more surfaces of the object which do not require the PTFE mask of the present invention to be applied, as shown by step 110. This then only leaves the surfaces to which the mask means are to be applied exposed. The exposed surfaces then undergo a grit blast process, as shown by step 112. The grit is fired at the exposed surfaces of the object under high pressure, thereby increasing the surface area of the surfaces to which the PTFE mask is to be applied. This increases the adherence of the PTFE mask to said surfaces during the PTFE application step.

The object can then undergo an optional phosphating step 114 which improves the corrosive resistance of the surfaces to which the PTFE mask is to be applied and can improve the adhesion of the PTFE mask to the object surfaces in some cases. The phosphate solution is typically sprayed onto the object surfaces but could be applied by other suitable means if required.

The object can undergo an optional priming step 116 to prime the surfaces of the object to which the PTFE mask is to be applied. The primer is typically sprayed onto the object surfaces but could be applied by other suitable means if required.

The PTFE mask is then sprayed onto the exposed object surfaces, as shown by step 118. One or more layers of the PTFE mask can be sprayed until a required thickness of the PTFE material is provided on the surfaces. The required thickness may depend on the environmental conditions the surfaces will be exposed to in use, the composition of the base material and/or the like. The object is preferably rotated during this spraying step so as to minimise the effects of thermoplastic melt flow.

The PTFE mask could be applied using a fluidised bed as an alternative application method to the spray method and/or any other suitable application method could be used.

The object with the mask selectively applied to the same is then placed in heating apparatus at a required temperature to allow the PTFE mask to be heat cured, as shown by step 120.

The temporary and removable cover is then removed from the object, as indicated by a de-masking step 122 in figure 2. This exposes the surfaces of the object to which a plating coating is required. The object is then ready to enter a plating process with the PTFE mask in place. Since the PTFE mask offers both environmental protection and aesthetic improvements to the object, there is no requirement to remove the PTFE mask after the plating process. The mask also reduces the surface area of the object that needs to undergo plating, thereby reducing the costs associated with the plating procedure.

The plating deposition process is not an essential element of the present invention but is an optional step that can take place once the mask means have been applied. The plating deposition process can be an electrolytic plating process or an electro-less plating process to deposit one or more layers of one or more materials to the areas not provided with the PTFE mask.

Claims

Claims: 1. An object, at least a part of one or more surfaces of the object provided with mask means thereon, at least a part of one or more other surfaces of the object that do not have the mask means provided thereon having at least one coating applied thereto, characterised in that the mask means includes or comprises polytetrafluoroethylene (PTFE) or a PTFE based material and the at least one coating is or includes a plating deposition coating or layer.
2. An object according to claim I characterised in that the surfaces of the object are formed from one or more base materials to which the mask means and at least one coating is applied, said base material formed from or including a metal.
3. An object according to claim 2 characterised in that the metal is aluminium.
4. An object according to claim I characterised in that the one or more plating deposition coatings or layers include any or any combination of an electrically conductive material, a noble metal, copper or silver.
5. An object according to claim I characterised in that the mask means is provided on a part or whole of one or more substantially external surfaces of the object.
6. An object according to claim I characterised in that the one or more plating deposition coatings or layers is provided on a part or whole of one or more substantially interior surfaces of the object.
7. An object according to claim I characterised in that the object is any or any combination of a housing, unit or component of a base station, mobile phone or satellite network, a radio frequency filter unit or housing, a tower mounted amplifier unit or housing a combiner unit or housing or a biasT unit or housing.
8. A method of using mask means for masking one or more parts and/or surfaces of an object, said method including the steps of selectively applying mask means to at least a part of one or more surfaces of the object, thereby leaving at least part of one or more other surfaces of the object with no mask means provided thereon, applying at least one coating to at least part of said one or more other unmasked surfaces, characterised in that the mask means includes or comprises polytetrafluoroethylene (PTFE) or a PTFE based material and the at least one coating is or includes a plating deposition coating or layer.
9. A method according to claim 8 characterised in that the method includes cleaning a part or one or more surfaces of the object prior to applying the mask means to said object, said cleaning including applying one or more degreasing agents to said object part or surfaces.
10. A method according to claim 8 characterised in that detachable cover means are applied to or over the part or whole of the one or more other surfaces which are not to have the mask means applied thereto.
11. A method according to claim 8 characterised in that a part or whole of the one or more surfaces to which the mask means is to be applied undergoes a grit blasting treatment step prior to applying the mask means thereto.
12. A method according to claim 8 characterised in that a part or whole of the one or more surfaces to which the mask means is to be applied undergoes a priming step including applying one or more priming materials to said part or surfaces and/or a phosphating step including applying one or more phosphate materials to said part or surfaces, prior to applying the mask means thereto.
13. A method according to claim 8 characterised in that the mask means is applied by dipping, spraying, submerging or coating the PTFE or PTFE based material onto the part or whole of the one or more surfaces of the object, followed by a heating step at a temperature sufficient to cure the PTFE or PTFE based material
14. A method according to claim 8 characterised in that the object is rotated during application of the mask means thereto.
15. A method according to claim 10 characterised in that the detachable cover means are removed from the object prior to plating the unmasked surfaces of the object using a plating deposition process.
16. A method according to claim 8 characterised in that mask means is applied to a part or whole of one or more substantially external surfaces of the object.
17. A method according to claim 8 characterised in that the one or more plating deposition coatings or layers is applied to one or more substantially interior surfaces of the object.