A Soluble Assembly

Abstract

The invention relates to a water soluble electrical device assembly which may comprise at least a housing comprising a soluble material 116, preferably a thermoplastic polymer such as polyvinyl alcoho

Description

The invention relates generally to a soluble assembly. More particularly, but not exclusively, the invention relates to a soluble electronics assembly comprising a watersoluble printed circuit board partially covered with a non-water-soluble coating. Background Printed circuit boards (PCBs) are fundamental components in a majority of electronic devices, providing mechanical support and electrical connectivity for various electronic components. Traditional PCBs are formed of non-biodegradable materials such as fiberglass and epoxy resins, which pose significant environmental challenges at the end of their lifecycle. As electronic waste (e-waste) continues to grow globally, the disposal and recycling of PCBs have become critical environmental and economic issues. The typical methods of disposing of PCBs, such as incineration or landfill, lead to the release of hazardous substances, including heavy metals and brominated flame retardants, into the environment. Moreover, the physical recovery of valuable metals from PCBs is complex, energy-intensive, and often not economically viable, resulting in a large portion of PCB material ending up as waste. One approach to tackle these issues is the development of soluble PCBs, which are designed to dissolve under specific conditions at the end of their useful life. This technology aims to facilitate easier and more environmentally friendly recycling processes by allowing for the recovery of electronic components and metals while significantly reducing the volume of waste that needs to be managed. Soluble PCBs typically utilize materials that can break down or dissolve in aqueous solutions, leaving behind recoverable components without the need for harsh chemical treatments or high-temperature processes. Despite these advancements, there are several challenges that need to be addressed to make soluble PCBs a viable alternative to traditional PCBs. Currently, many soluble PCBs are not truly biodegradable. For example, PCBs formed of polylactic acid (PLA) require specific, hard-to-maintain conditions, including high temperatures and oxygenrich environments, in order to properly break down. Currently, the use of truly biodegradable PCBs which break down relatively quickly under standard conditions is limited by the lack of suitable materials which exhibit sufficient strength and rigidity. Further, PCBs which dissolve easily face problems when in use, as they begin to break down upon exposure to humid environments. Electronic devices often comprise casings which are configured to protect circuitry contained therein. These casings, which protect PCBs and the electronic components disposed thereon, also contribute to e-waste when the devices are at the end of their life cycle. The casings must have sufficient mechanical strength so as to protect the contents. The casings must also be resistant a range of external environments, for example, they should be waterproof so as to prevent water and moisture from affecting the circuitry. These requirements for the casings make them difficult to easily disposable in a sustainable manner. The present invention was devised with the foregoing issues in mind. Summary of Invention According to a first aspect of the invention there is provided an assembly. The assembly may comprise: a housing, wherein the housing is formed of, or comprises, a soluble material; and a non-soluble coating which covers the outer surface of the housing. The housing may be formed of, or comprise, a biodegradable material. The coating may be formed of, or comprise, a biodegradable material. The housing being soluble may enable the assembly to be completely disassembled at the end of its lifecycle. This provides the benefit of enabling valuable items within the housing, such as electronic components, to be easily extracted for subsequent reuse or recycling. The housing may be formed of, or comprise, a water-soluble material. The coating may be non-water-soluble. The housing being water-soluble may enable it to be disposed of easily without requiring specialist materials. This may provide the benefit of reducing the waste created when the assembly is no longer in use. The housing may be formed of, or comprise, a material which is soluble in a non-water solvent. The housing may be formed of, or comprise, a material which becomes watersoluble after exposure to a non-water solvent. The non-water-soluble coating may seal the housing such that that the housing is watertight. The non-water-soluble coating may hermetically seal the housing. The housing may be configured such that a user can break the seal formed by the non-water-soluble coating. The assembly may be an electronics assembly. The assembly may comprise one or more electronics components within the housing. The assembly may comprise a circuit board, wherein the circuit board is formed from, or comprises, a soluble material. The circuit board being soluble may enable the assembly to be completely disassembled at the end of its lifecycle. This provides the benefit of enabling valuable items such as electronic components to be easily extracted for subsequent reuse or recycling. The circuit board may be formed from, or comprise, a water-soluble material. The circuit board being water-soluble may enable it to be disposed of easily. This may provide the benefit of reducing the waste created when the electronics assembly is no longer in use. The circuit board may be formed of, or comprise, a material which is soluble in a non-water solvent. The circuit board may be formed of, or comprise, a material which becomes water-soluble after exposure to a non-water solvent. The assembly may comprise a non-soluble coating. The non-soluble coating may partially cover a surface of the circuit board. The non-soluble coating of the circuit board may be non-water-soluble. The use of a non-water-soluble coating may prevent the circuit board from dissolving when in use and ensures that the circuit board will only dissolve when a non-coated portion of the circuit board is exposed to the appropriate solvent. The use of a coating may also provide the advantage of improving the strength and rigidity of the circuit board. Having a non-water-soluble coating which only partially covers the circuit board provides the effect of improving the mechanical properties of the circuit board whilst ensuring the circuit board can still be dissolved. The circuit board may be formed of, or comprise, a biodegradable material. The circuit board may be formed of, or comprise, a biodegradable material. The assembly may comprise one or more electronic components disposed on the circuit board. The electronic components may be disposed on the portion of the surface of the circuit board which is covered by the non-water-soluble coating. The water-soluble coating may be positioned between the circuit board and the electronic components. The water-soluble coating may cover the electronic components. The circuit board may be substantially planar. The portion of the surface of the circuit board covered by the non-water-soluble coating may be a first side of the circuit board. The second side of the planar circuit board may not be covered by the coating. The circuit board and the housing may be formed of the same material. The circuit board coating and the housing coating may be formed of the same material. Having the circuit board and housing formed of the same soluble material may provide the advantage that they can both be dissolved under the same conditions. This simplifies the process of disposing of the electronics assembly. The circuit board may be formed of, or comprise, a water-soluble polymer. The circuit board may be formed from, or comprise, a thermoplastic water-soluble polymer. The water-soluble polymer may be, or comprise, polyvinyl alcohol. The housing may be formed from, or comprise, a water-soluble polymer. The housing may be formed from, or comprise, a thermoplastic water-soluble polymer. The watersoluble polymer may be, or comprise, polyvinyl alcohol. Using a thermoplastic polymer to form the circuit board and / or the housing may enable the manufacturing of said components to be performed using injection moulding. This provides the advantage of simplifying manufacturing. Using polyvinyl alcohol to form the housing and / or the circuit board may ensure said components are water-soluble whilst having appropriate mechanical properties. The non-water-soluble coating of the housing may be, or comprise, a hydrophobic material. The non-water-soluble coating of the housing may be, or comprise, a polysiloxane. The non-water-soluble coating of the housing may be, or comprise, polydimethylsiloxane. The non-water-soluble coating of the housing may be, or comprise, polyurethane. The non-water-soluble coating of the housing may be, or comprise, a polyester resin. The non-water-soluble coating of the housing may be, or comprise, an epoxy resin. The non-water-soluble coating of the housing may comprise polydimethylsiloxane and polyurethane. The non-water-soluble coating of the housing may comprise polydimethylsiloxane and a polyester resin. The non-water-soluble coating of the housing may comprise polydimethylsiloxane and an epoxy resin. The use of polyurethane may provide the effect of enabling polydimethylsiloxane (or any other polysiloxane) to adhere to the polyvinyl alcohol housing. The non-water-soluble coating of the housing may comprise first layer and a second layer. The first layer may be formed from, or comprise, a first composition, and the second layer may be formed from, or comprise, a second composition which is different to the first composition. The second layer may be more hydrophobic than the first layer. The ratio of polydimethylsiloxane to polyurethane may be greater in the second layer than the first layer. The first layer may comprise a higher density of polyurethane than the second layer. Having a higher density of polyurethane may improve the strength and rigidity of the layer. The second layer may comprise a higher density of polydimethylsiloxane than the second layer. Having higher density of polydimethylsiloxane may improve the water resistance of the layer. The non-water-soluble coating of the circuit board may be, or comprise, a hydrophobic material. The non-water-soluble coating of the circuit board may be, or comprise, a polysiloxane. The non-water-soluble coating of the circuit board may be, or comprise, polydimethylsiloxane. The non-water-soluble coating of the circuit board may be, or comprise, polyurethane. The non-water-soluble coating of the circuit board may be, or comprise, a polyester resin. The non-water-soluble coating of the circuit board may be, or comprise, an epoxy resin. The non-water-soluble coating of the circuit board may comprise polydimethylsiloxane and polyurethane. The non-water-soluble coating of the circuit board may comprise polydimethylsiloxane and a polyester resin. The non-water-soluble coating of the circuit board may comprise polydimethylsiloxane and an epoxy resin. The use of polyurethane may provide the effect of enabling polydimethylsiloxane (or any other polysiloxane) to adhere to the polyvinyl alcohol circuit board. The non-water-soluble coating of the circuit board may comprise first layer and a second layer. The first layer may be formed from, or comprise, a first composition, and the second layer may be formed from, or comprise, a second composition which is different to the first composition. The second layer may be more hydrophobic than the first layer. The ratio of polydimethylsiloxane to polyurethane may be greater in the second layer than the first layer. The first layer may comprise a higher density of polyurethane than the second layer. Having a higher density of polyurethane may improve the strength and rigidity of the layer. The second layer may comprise a higher density of polydimethylsiloxane than the second layer. Having higher density of polydimethylsiloxane may improve the water resistance of the layer. The use of two layers in the coating of the housing and / or the circuit board may improve the properties of the coating. For example, a first (inner) layer of the coating may have good mechanical properties but poor water-resistant properties whilst the second (outer) layer may be the opposite. By combining the layers, the beneficial properties of each layer can be combined. According to a second aspect of the invention, there is provided a method of forming an assembly. The method of the second aspect may be used to form the assembly of the first aspect. The method may comprise providing a water-soluble housing. The housing may be configured to enclose a circuit board. The method may comprise applying a non-water-soluble coating to cover an outer surface of the housing. The method may comprise providing a water-soluble circuit board. The method may comprise applying a non-water-soluble coating to partially cover the circuit board. The non-water-soluble coating may be applied to a portion of the surface of the circuit board which is configured to have one or more electronic components disposed thereon. Providing the water-soluble circuit board may comprise injection moulding a watersoluble material. Providing the water-soluble housing may comprise injection moulding a water-soluble material. The water-soluble material may be, or comprise, polyvinyl alcohol. Applying a non-water-soluble coating to the circuit board may comprise using a spray gun to spray a solution onto the circuit board. Applying a non-water-soluble coating to the housing may comprise using a spray gun to spray a solution onto the housing. The method may comprise curing the non-water-soluble coating of the circuit board. The method may comprise curing the non-water-soluble coating of the housing. Curing may comprise UV curing. According to a third aspect of the invention, there is provided a method for disassembling an assembly. The assembly may be the assembly of the first aspect, or an assembly formed using the method of the second aspect. The method may comprise: opening a housing; and exposing an inner surface of the housing to water to dissolve the housing; and extracting the non-water-soluble coating from the dissolved housing. The method may comprise exposing a non-coated region of a circuit board to water to dissolve the circuit board. The method may comprise extracting non-water-soluble coatings from a dissolved solution. The method may comprise extracting electronic components from a dissolved solution. According to a fourth aspect of the invention, there is provided an electronics assembly. The electronics assembly may comprise a circuit board. The circuit board may be soluble. The circuit board may be water-soluble. The electronics assembly may comprise one or more electronic components disposed on the circuit board. The electronic assembly may comprise a coating which partially covers the circuit board. The coating may be non-water-soluble. Optional features of any of the above aspects may be combined with the features of any other aspect, in any combination. For example, features described in connection with the assembly of the first aspect may have corresponding features definable with respect to the method of the second aspect, and vice versa, and these examples are specifically envisaged. Features which are described in the context or separate aspects and examples of the invention may be used together and / or be interchangeable wherever possible. Similarly, where features are, for brevity, described in the context of a single example, those features may also be provided separately or in any suitable sub-combination. Brief description of the drawings The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an assembly comprising a housing; Figure 2 shows an electronics assembly comprising a circuit board and a housing; Figure 3 shows an electronics assembly comprising a circuit board and a housing, wherein the housing and circuit board each comprise a two-layer coating; Figure 4 shows an electronics assembly comprising a circuit board; Figures 5(a)-(d) show a disassembly process for an electronics assembly; Figure 6 shows a flowchart representing a method for forming an assembly; and Figure 7 shows a flowchart representing a method for forming an electronics assembly; and Detailed description Figure 1 shows an assembly 10. The assembly 10 comprises a housing 16. The housing 16 is formed from, or comprises, a water-soluble material. The housing 16 comprises a coating 18. The coating 18 is non-water-soluble. The coating 18 covers the outer surface of the housing 16. In some examples, the coating 18 hermetically seals the housing 16. Coating the outer surface of the housing 16 also prevents the housing 16 from dissolving when the assembly is exposed to water or moisture during normal use. Coating the outer surface of the housing 16 also prevents the ingress of water and moisture into the housing, thereby protecting the contents within the housing. In other examples, the housing 16 is formed of, or comprises a material which is not soluble in water but is soluble in non-water solvents. In other examples, the housing 16 is formed of, or comprises a material which becomes water-soluble after exposure to a particular solvent or type of solvent. The housing 16 can be configured such that a user can break the seal formed by the coating 18. For examples, the housing 16 may be configured to be readily breakable when force is applied to a specific section of the housing 16. Alternatively, or additionally, the housing 16 may configured to be open / closed by a user, for example, using a hinge and a latch. Figure 2 shows an electronics assembly 100. The electronics assembly 100 comprises a housing 116 with a coating 118. The housing 116 and coating 118 are substantially similar to the housing 16 and coating 18 of the assembly 10 of Figure 1. The assembly 100 of Figure 2 is an electronics assembly. The electronics assembly 100 comprises a circuit board 112. The circuit board 112 is formed of, or comprises, a watersoluble material. In other embodiments, the assembly 100 comprises electronics components without requiring a circuit board. In other examples, the circuit board 112 is formed of, or comprises a material which is not soluble in water but is soluble in non-water solvents. In other examples, the circuit board 112 is formed of, or comprises a material which becomes water-soluble after exposure to a particular solvent or type of solvent. The electronics assembly 10 comprises a coating 114. The coating 114 is non-water-soluble. The coating 114 partially covers a surface of the circuit board 112. The coating 114 covers the surface of the circuit board 112 such that a portion of the circuit board 112 is exposed (i.e., not covered by the coating). The circuit board 112 is substantially planar. The portion of the surface of the circuit board 112 covered by the coating 114 is a first side of the planar circuit board 112. In the example of Figure 2, the coating 114 covers the entire first side of the circuit board 112. In other embodiments, the coating 114 partially covers the first side of the circuit board 112. The second side of the planar circuit board 112 is not covered by the coating. Electronic components 115 are disposed on a portion of the surface of the circuit board 112 which is covered by the coating 114. In the example of Figure 2, the water-soluble coating 114 is positioned between the circuit board 112 and the electronic components 115. In other examples, the water-soluble coating 114 covers the electronic components 115. In some examples, the electronic components 115 are soldered to the circuit board 112. The electronic components 115 can comprise any standard electronic component, such as resistors, transistors, IC chips, inductors, I / O devices, or any other electronic component. In some examples, the circuit board 112 and the housing 116 are formed of the same material. In some examples, the circuit board 112 and / or the housing 116 are soluble in water at temperatures greater than 30°C. In some examples, the circuit board 112 and / or the housing 116 are soluble in water at temperatures greater than 60°C. In some examples, the circuit board 112 and / or the housing 116 are formed of, or comprise, a water-soluble polymer. In some examples, the circuit board 112 and / or the housing 116 are formed of, or comprise, a thermoplastic water-soluble polymer. In some examples, the circuit board 112 and / or the housing 116 are formed of, or comprise, polyvinyl alcohol (PVOH). In some embodiments, the circuit board 112 and / or the housing 116 are formed of, or comprise, a copolymer comprising vinyl alcohol monomers. In some examples, the circuit board 112 and / or the housing 114 are formed via injection moulding. In some examples, the circuit board coating 114 and the housing coating 118 are formed of the same material. In some examples, the circuit board coating 114 and / or the housing coating 118 are non-water-soluble in water at temperatures between 0-100°C. In some examples, the circuit board coating 114 and / or the housing coating 118 are formed of, or comprise, a polysiloxane. In some examples, the circuit board coating 114 and / or the housing coating 118 are formed of, or comprise, polydimethylsiloxane (PDMS). In some examples, the circuit board coating 114 and / or the housing coating 118 are formed of, or comprise, polydimethylsiloxane (PDMS) and polyurethane (PU). In some examples, the circuit board coating 114 and / or the housing coating 118 are formed of, or comprise, polydimethylsiloxane (PDMS) and a polyester resin. In some examples, the circuit board coating 114 and / or the housing coating 118 are formed of, or comprise, polydimethylsiloxane (PDMS) and an epoxide resin. In some examples, the circuit board coating 114 and / or the housing coating 118 are formed using Poly(dimethylsiloxane), bis(3-aminopropyl) terminate. Figure 3 shows an electronics assembly 100’. The assembly 100’ is similar to the assembly 100 of Figure 2, but the circuit board coating 114’ and the housing coating 118’ each comprise two layers. The circuit board coating comprises an inner layer 114-1' and an outer layer 114-2’. In some examples, the outer layer 114-2’ is more water resistant than the inner layer 114-1’. In some examples, the inner layer 114-1’ is more rigid than the outer layer 114-2'. In some examples, the inner layer 114-1’ has a greater tensile strength than the outer layer 114-2’. In some examples, the inner layer 114-1’ is tougher than the outer layer 114-2’. In some examples, the inner layer 114-1’ comprises a greater proportion of PU than the outer layer 114-2’. In some examples, the outer layer 114-2’ comprises a greater proportion of PDMS than the inner layer 114-1’. The housing coating comprises an inner layer 118-1’ and an outer layer 118-2’. In some examples, the outer layer 118-2’ is more water resistant than the inner layer 118-1’. In some examples, the inner layer 118-1’ is more rigid than the outer layer 118-2’. In some examples, the inner layer 118-1’ has a greater tensile strength than the outer layer 118-2’. In some examples, the inner layer 118-1’ is tougher than the outer layer 118-2’. In some examples, the inner layer 118-1’ comprises a greater proportion of PU than the outer layer 118-2’. In some examples, the outer layer 118-2’ comprises a greater proportion of PDMS than the inner layer 118-1’. In some examples, the inner 114-1’ 118-1’and outer 114-2’ 118-2’layers ofthe coatings are the same for the circuit board and the housing. In other examples, only one of the circuit board coating 114 or the housing coating 118 comprises two layers. In other examples, the circuit board coating 114 and / or the housing coating 118 can comprise any plurality of layers. Figure 4 shows an electronics assembly 200. The electronics assembly 200 comprises a circuit board 212 partially covered with a coating 214, similarly to the circuit board 112 and coating 114 shown in Figure 2. The assembly 200 of Figure 4 is substantially similar to the electronics assembly of Figure 2, but without the housing 116 and coating 118. Figures 5a-d show an examples process for disassembling and disposing of the electronics assembly 100 of Figure 2. Figure 5a shows the electronics assembly 100 when in use. The housing 116 isolates the circuit board 112 from contaminants, such as water and water vapour in the air. The coating 118, which covers the outer surface of the housing 116, prevents the housing 116 from being in contact with the water. The coating 114 on the circuit board 112 increases the strength and rigidity of the circuit board 112. Once the electronics assembly 100 is no longer in use, it can be disassembled and disposed of, as described with reference to Figures 5b-d. In Figure 5b, the housing 116 is disassembled. In some examples, disassembly of the housing comprises removing a lid from the housing 116 or opening the housing 116 via one or more fasteners. In some examples, disassembling the housing 116 comprises breaking the housing by breaking a seal of the housing. In some embodiments, the housing 116 comprises a structural weak point to enable a user to break the housing 116 at the end of use. The skilled person will recognise that any suitable method for disassembling the housing 116 can be used. After disassembly of the housing 116, the assembly 100 is exposed to water. In some examples, exposing the assembly 100 to water comprises submerging the assembly in a water bath. Upon exposure of the assembly 100 to water, water contacts the inner surface of the housing 116 and the exposed portion of the circuit board 112 (the portion of the surface of the circuit board 112 not covered by the coating 114). Because both the circuit board 112 and the housing 116 are water-soluble, they begin to dissolve when brought into contact with the water. Figure 5(c) shows the electronics assembly 100 after exposure to water. The circuit board 112 and the housing 116 are partially dissolved in the water. As the circuit board 112 dissolves, the circuit board coating 114 detaches from the circuit board 112. As the housing 116 dissolves, the housing coating 118 detaches from the housing 116. Figure 5(d) shows the electronics assembly 100 after prolonged exposure to water such that the housing 116 and the circuit board 112 are fully dissolved in the water. The coatings 114, 118 do not dissolve in the water. In some examples, the coatings 114, 118 form a gel-like substance. The coatings 114, 118 and the water comprising the dissolved circuit board 112 and housing 116 can be disposed of. In some examples, the dissolved circuit board 112 and housing 116 can be conveyed into a sewage system, or specialist treatment system. In some examples, the dissolved circuit board 112 and housing 116 are biodegradable. In some examples, the coatings 114, 118 are biodegradable. In some examples, the coatings 114, 118 can be removed from the dissolved circuit board 112 and housing 116 and subsequently recycled. Electronics components 115 detach from the circuit board 112 as the circuit board dissolves. Once the circuit board 112 is fully dissolved, the electronic components 115 can be extracted from the dissolved solution for reuse, or recycling. As such, the electronics assembly can be disassembled in such a way so as to minimise environmental waste. Figure 6 shows a flowchart 300 representing a method of forming an assembly. The method comprises providing 310 a housing. In some embodiments, providing 310 a housing comprises forming a housing. In some embodiments, forming a housing comprises injection moulding a water-soluble polymer to form a housing. In some embodiments, forming a housing comprises injection moulding a material comprising PVOH to form a housing. The method comprises providing 320 a coating solution. In some examples, providing 320 a coating solution comprises forming a coating solution. In some examples, the coating solution is formed to create a solution comprising PDMS and PU. In some examples, known methods for forming a coating solution comprising PDMS and PU can be used. In some such examples, the coating solution can be formed by combining Poly(dimethylsiloxane), bis(3-aminopropyl) terminate with hexamethylene diisocyanate trimer and glycerol propoxylate. In some such examples, the coating solution can be formed by combining Poly(dimethylsiloxane), bis(3-aminopropyl) terminate with hexamethylene diisocyanate trimer and glycerol propoxylate as described in Vijay Pandian, “IMPROVED WATER RESISTANCE AND BARRIER PROPERTIES OF POLYVINYL ALCOHOL WITH POLYURETHANE SILOXANE COATING FOR PACKAGING APPLICATIONS”, Thesis, 2018 In one example, forming the coating solution comprises: 1. Combining Poly(hexamethylene diisocyanate) with a solvent to form a first solution; 2. Combining Poly(dimethylsiloxane), bis(3-aminopropyl) terminate with a solvent to form a second solution; 3. Combining the first and second solutions to form a mixture; 4. Heating the mixture; 5. Adding glycerol propoxylate to the mixture; 6. Allowing the mixture to cool; 7. Adding dimethyl carbonate to the mixture; and 8. Bubbling nitrogen gas through the mixture to form the coating solution (sparging). In a more specific example, forming a solution comprises: 1. To a 22.8 mL vial, adding 2.2 mL of Poly(hexamethylene diisocyanate) and 2 mL of Tetrahydrofuran (THF) at ambient temperature and stir until mixed using magnetic stirring. 2. Separately preparing a solution containing 0.05 mL of Poly(dimethylsiloxane), bis(3-aminopropyl) terminated and 0.2 mL of THF in a 5 mL vial at ambient temperature and stir until mixed using magnetic stirring. 3. Adding the solution prepared in the 5 mL vial to the solution prepared in the 22.8 mL vial dropwise under magnetic stirring at ambient temperature. 4. Heating the solution in the 22.8 mL vial to 60 degrees Celsius in a silicone oil bath, then add 0.68 mL of Glycerol propoxylate and stir for 20 minutes with magnetic stirring. 5. Removing the vial from heat source and stirring and allow to cool to room temperature 6. Adding 6mL of dimethyl carbonate (DMC) to the 22.8 mL vial and stir at ambient temperature for 2 minutes using a magnetic stirrer; and 7. Bubbling nitrogen gas through the solution for 1 minute using a silicone tube immersed in the solution. In the example above, the measurements are provided by way of example only, and the skilled person will recognise that the amounts and ratios of various substances can be varied. In some examples, the first solution stabilises the isocyanate in the chosen reactive medium (THF in the example method above) and the second solution stabilises the PDMS. In some embodiments, if PDMS is simply added to the isocyanate it will react immediately to form clumps of PDMS linked by nitrile bridges, so the THF solvent spaces these reagents out and provides sufficient time for the coating solution to be used. In some examples, the propoxylate will react with the diisocyanate to form polyurethane. In some examples, the DMC is used to dilute and replace the THF from the reaction mixture, as THF can be carcinogenic and can form explosive peroxides. In some examples, the nitrogen bubbling / sparging step assists with removing residual THF. In some examples, THF is used in the first instance because DMC does not work well as a solvent for the initial reaction between HDIT, PDMS and GP. In other examples, the polyurethane within the coating solution can be formed using different isocyanate starting materials. In other examples, the PDMS can be functionalised differently in order to form a different type of bond with the polyurethane in the solution. In other examples, forming a solution comprises a method similar those discussed above, but with different solvents. In other examples, forming a solution comprises a method similar those discussed above, but with different volumes. In other examples, forming a solution comprises alternative methods to those discussed above. The method comprises coating 330 the housing with the coating solution. In some examples, coating 330 the housing comprises submerging the housing in the coating solution. In some examples, coating 330 the housing with the coating solution comprises using a spray gun to spray a solution onto the housing. In some examples, the method of forming an electronics assembly further comprises curing the coating. In some examples, curing comprises UV curing. Figure 7 shows a flowchart 400 representing a method of forming an assembly. The method 400 is substantially similar to the method represented by the flowchart 300 of Figure 6, but a circuit board is provided in step 410 and coated in step 430. The step of providing a solution 420 can be identical to the step of providing a solution 320 in Figure 6. In some embodiments, coating the circuit board 430 with the solution comprises partially submerging the circuit board in the solution. In some embodiments, coating the circuit board 430 with the solution comprises partially spraying the circuit board with the solution. From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of water-soluble material and non-water-soluble coatings, and which may be used instead of, or in addition to, features already described herein. Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. Features which are described in the context of separate examples may also be provided in combination in a single example. Conversely, various features which are, for brevity, described in the context of a single example, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom. For the sake of completeness, it is also stated that the term "comprising" does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several means recited in the claims and any reference signs in the claims shall not be construed as limiting the scope 5 of the claims.

Claims

1. An assembly comprising:a housing, wherein the housing is formed of, or comprises, a water-soluble material; anda non-water-soluble coating which covers the outer surface of the housing to prevent ingress of water and moisture into the housing.

2. The assembly of claim 1, wherein the non-water-soluble coating hermetically seals the housing, and wherein the housing is configured such that a user can break the hermetic seal formed by the non-water-soluble coating.

3. The assembly of claim 1 or claim 2, further comprising:a circuit board, wherein the circuit board is formed of, or comprises, a watersoluble material, and wherein the circuit board is contained within the housing; anda non-water-soluble coating which partially covers a surface of the circuit board.

4. The assembly of claim 3, further comprising one or more electronic components disposed on the circuit board, wherein the electronic components are disposed on the portion of the surface of the circuit board which is covered by the non-water-soluble coating, and wherein the water-soluble coating is positioned between the circuit board and the electronic components.

5. The assembly of claim 3, further comprising one or more electronic components disposed on the circuit board, wherein the electronic components are disposed on the portion of the surface of the circuit board which is covered by the non-water-soluble coating, and wherein the water-soluble coating covers the electronic components.

6. The assembly of any of claims 3-5, wherein the circuit board is substantially planar, and wherein the portion of the surface of the circuit board covered by the non-water-soluble coating is a first side of the circuit board.

7. The assembly of any preceding claim, wherein the circuit board and / or the housing is formed of, or comprises, a water-soluble polymer.

8. The assembly of claim 7, wherein the circuit board and / or the housing is formed of, or comprises, a thermoplastic water-soluble polymer.

9. The assembly of claim 7 or claim 8, wherein the water-soluble polymer is, or comprises, polyvinyl alcohol.

10. The assembly of any of claims 3-9, wherein the housing and the circuit board are formed of, or comprise, the same material.

11. The assembly of any preceding claim, wherein the non-water-soluble coating of the housing and / or circuit board is, or comprises, a polysiloxane.

12. The assembly of claim 11, wherein the non-water-soluble coating of the housing and / or circuit board is, or comprises, polydimethylsiloxane.

13. The assembly of claim 12, wherein the non-water-soluble coating of the housing and / or circuit board is, or comprises, polydimethylsiloxane and polyurethane.

14. The assembly of any preceding claim, wherein the non-water-soluble coating of the housing and / or circuit board comprises:a first layer formed of a first composition; anda second layer formed of a second composition, wherein the second composition is different to the first composition.

15. The assembly of claim 14, wherein the second layer is an outer layer, and the second layer is more hydrophobic than the first layer.

16. The assembly of claim 15, wherein the ratio of polydimethylsiloxane to polyurethane is greater in the second layer than the first layer.

17. A method of forming an assembly, the method comprising:providing a water-soluble housing; andapplying a non-water-soluble coating to cover an outer surface of the housing so as to prevent ingress of water and moisture into the housing.

18. The method of claim 17, further comprising: providing a water-soluble circuit board; and applying a non-water-soluble coating to partially cover the circuit board;19. The method of claim 17 or claim 18, wherein providing the water-soluble circuit board and / or housing comprises injection moulding a water-soluble material.

20. The method of claim 19, wherein the water-soluble material is, or comprises, polyvinyl alcohol.

21. The method of any preceding method claim, wherein applying a non-water-soluble coating to the circuit board and / or housing comprises spraying a solution onto the circuit board and / or housing via a spray gun.

22. The method of any preceding method claim, further comprising: curing the non-water-soluble coating of the circuit board and / or housing.

23. The method of claim 22, wherein curing comprises UV curing.

24. A method of disassembling the assembly of any of claims 1-16, the method comprising:opening the housing;exposing an inner surface of the housing to water to dissolve the housing; and extracting the non-water-soluble coating from the dissolved housing.

25. The method of claim 24, further comprising:exposing a non-coated region of the circuit board to water to dissolve the circuit board; andextracting the electronic components from the dissolved circuit board.

Images