Patent Description:
Thin film heaters are used for a wide range of applications which generally require a flexible, low profile heater which can conform to a surface or object to be heated. One such application is within the field of aerosol generating devices such as reduced risk nicotine delivery products, including e-cigarettes and tobacco vapour products. Such devices heat an aerosol generating substance within a heating chamber to produce a vapour. One means to heat the consumable is to use a heater assembly comprising a thin film heater which conforms to a surface of a heating chamber to ensure efficient heating of an aerosol-generating substance within the chamber.

Thin film heaters generally comprise a resistance heating element enclosed in a sealed envelope of flexible dielectric thin film with contact points to the heating element for connection to a power source, the contact points usually soldered on to exposed parts of the heating element.

Such thin film heaters are generally manufactured by depositing a layer of metal onto the dielectric thin film support, etching the metal layer supported on the thin film into the required shape of the heating element, applying a second layer of dielectric thin film onto the etched heating element and heat pressing to seal the heating element with the dielectric thin film envelope. The dielectric thin film is then die cut to create openings for contacts which are soldered on to the portions of the heating element exposed by the openings.

These conventional thin film heaters, formed of a planar heating element sealed within an insulating thin film envelope, must then be attached to a surface to be heated. In the context of aerosol generating devices, this involves attaching the thin film heater to the outer surface of a heating chamber to form a heater assembly so as to transfer heat to an aerosol generating consumable placed within the chamber. This is generally achieved by attaching the thin film heater with an adhesive or other fastening means to hold the thin film heater against the heating chamber during use. Other techniques use additional pieces of thin film to wrap around the heater assembly to hold the thin film heater against the heating chamber. The thin film heater must then be connected to a power source when assembled in the device.

Such conventional thin film heaters and heater assemblies suffer from a number of disadvantages. Existing thin film heaters comprise a significant amount of insulating material surrounding the heating element which results in an increased thermal mass and reduces the efficiency of heat transfer to the heating chamber. This issue is made worse by the conventional method of attaching the thin film heater to a heating chamber involving the application of additional adhesive and/or additional wrapping layers. The attachment method, which generally must be carried out by hand, is an awkward procedure in which it is difficult to securely attach the heater and reliably position it with the correct alignment relative to the heating chamber. The latter is a particularly significant problem given the heating element usually needs to be placed accurately at a specific position along the heating element to align with the portion of a heating chamber to be heated.

The present invention aims to make progress in addressing these issues to provide an improved heater assembly and method of fabricating a heater assembly.

Document <CIT> forms part of the relevant background art and discloses a heat-shrinkable article comprising a heat-shrinkable layer of polymeric material, a laminar heater which comprises a conductive polymer layer sandwiched between apertured metal electrodes and which is secured to the inner surface of the layer, and a member which is secured to the inside of the heater and which protects a substrate from damage caused by the heater when the layer shrinks.

Document <CIT> also forms part of the relevant background art and discloses a heating embedded within an electric heating mat, and more particularly, to an electric heating element for an electric heating mat securing the uniformity of heat and shielding electromagnetic waves by forming an improved placement structure fixing heating lines on a stacked fabric and locating the heating lines at a predetermined distance away from each other by means of the placement structure.

Document <CIT> also forms part of the relevant background art and discloses an apparatus configured to heat smokeable material to volatilize at least one component of the smokeable material. The apparatus comprises a heater comprising a heat-shrink material. The heater is configured to progressively heat the smokeable material upon constriction of the heat-shrink material.

According to a first aspect of the invention, there is provided a method of fabricating a heater assembly comprising: providing a heating element supported on a surface of a flexible dielectric backing film; and attaching a layer of heat shrink film onto the surface of the dielectric backing film so as to at least partially enclose the heating element between the heat shrink film and the dielectric backing film.

In this way, the number of thin film layers is reduced since the layer of heat shrink film provides both the function of sealing the heating element with the flexible backing film and also the means of attaching the heating element to a heating chamber. Therefore the thermal mass of the heater assembly is reduced and the efficiency of heat transfer is enhanced. Furthermore a secure attachment is provided by the heat shrink film in a simplified method in which sealing of the heating element and attachment may be carried out simultaneously. Heat shrinking provides a reliable close contact between the thin film heater and heating chamber to ensure effective heat transfer. The method further allows the heater to be placed accurately at the desired position on a heating chamber before heating to shrink the film and attach the heater at that position. The method therefore makes improvements over other attachment methods, such as using an adhesive, which do not reliably secure the heater at a required position.

The term "dielectric" used to define the backing film is intended to be interpreted broadly as meaning "electrically insulating".

The heating element is preferably a flexible heating element, preferably a flexible substantially planar heating element.

The assembled dielectric backing film, heating element and heat shrink film layer may be referred to as a thin film heater assembly or subassembly.

Preferably the method comprises attaching a layer of heat shrink film which extends beyond the surface area of the dielectric backing film in one or more directions. This allows for the extending portions of the heat shrink to be used to attach the heating element and supporting backing film to a surface. It further may allow for aligning of the heating element relative to a heating chamber by using one of the extending portions, where these portions extend by a predetermined distance beyond the heating element.

Preferably the layer of heat shrink film is attached directly against the heating element. In this way, the heating element is sealed directly between the flexible dielectric backing film and the layer of heat shrink such that an additional sealing layer is not required. In other words the heat shrink provides both a sealing layer and means of attachment.

Preferably the layer of heat shrink film is attached using an adhesive provided on the surface of the flexible dielectric layer which supports the heating element. The adhesive may be for example a silicon adhesive. The adhesive provides a straightforward means of reliably securing the heating element to the backing film. The flexible dielectric backing film may comprise a layer of adhesive, for example it may be polyimide film with a layer of Si adhesive. The heating element may be attached by subsequent heating of the flexible dielectric backing film, adhesive layer and positioned heating element to bond the heating element to the surface using the adhesive. The subsequent heating may be a heating step used to shrink the heat shrink film to attach the thin film heater to a heating chamber.

The backing film may comprise polyimide such as a polyimide film with a layer of Si adhesive. The backing film may alternatively or additionally comprise a fluoropolymer such as PTFE. When the backing film comprises a fluoropolymer it may comprise an at least partially defluorinated surface layer, formed for example by a surface treatment such as plasma and/or chemical etching. This allows for an adhesive to be applied to the treated surface which otherwise would not adhere given the extremely low friction surfaces provided by fluoropolymers. The backing film may additionally or alternatively comprise PEEK.

Preferably the flexible dielectric backing film has a thickness of less than <NUM> preferably less than <NUM>, and preferably a thickness of greater than <NUM>.

The heat shrink film may comprise one or more of polyimide, a fluoropolymer such as PTFE and PEEK. The heat shrink film is preferably a preferential heat shrink film arranged to shrink preferentially in one direction. For example the heat shrink film may be polyimide 208x tape manufactured by Dunstone. The heat shrink film may be in the form of an initially planar layer, i.e. a piece of heat tape arranged to be wrapped around the heating chamber or it may be in the form of a tube arranged to be passed around (i.e. sleeved on) a heating chamber and heated to shrink it to the surface of a heating chamber.

Preferably the heating element is a planar heating element comprising a heater track which follows a circuitous path over a heating area within the plane of the heating element; and two contact legs for connection to a power source, the contact legs extending away from the heater track in the plane of the heating element. Preferably the heater track is configured to provide substantially uniform heating over the heating area. The heater track path may be a serpentine or meandering path over the heating area and the heater track may have a substantially uniform width and thickness. Preferably the method comprises: attaching the layer of heat shrink film so as to enclose the heater track between the backing film and the heat shrink film layer, leaving the contact legs exposed. In this way the heater track is electrically insulated between the dielectric backing film and the heat shrink film whilst the contact legs are exposed such that they can be connected to a power source.

The contact legs may be sufficiently long to allow direct connection to a power source when the thin film heater is employed in the device. For example the length of the contact legs may be substantially equal or greater than one or both of the dimensions defining the heating area. The circuitous path may be configured to leave a vacant region within the heating area.

Preferably the layer of attached heat shrink film comprises an alignment region which extends beyond the heating element by a predetermined distance in a direction opposite to the direction of the extending contact legs. In particular the heat shrink film extends beyond the top edge of the heating element. In particular in an upward direction, i.e. a direction corresponding to towards the top, open end of the heating chamber when attached. By providing an alignment region which extends beyond the heating element and/or backing film by a chosen distance, the alignment region can be used to position the heating area of the heater at the required position. For example the method may further comprise aligning a top, marginal edge of the alignment region with an end of the heating chamber and attaching the thin film heater to the chamber using the heat shrink film. In this way, the heating area is positioned at a known location along the length of the heating chamber from the end of the chamber, without having to carefully measure or adjust the heating element to align it correctly. Preferably the predetermined distance is measured from the side of the heating area opposite the contact legs to the peripheral edge of the alignment region.

Preferably the method further comprises cutting a marginal part of the alignment region of the attached heat shrink film so that the distance in which the alignment region extends beyond the heater track is reduced to a predetermined distance. In this way, a precise distance between the edge of the heating area and the edge of the alignment region of the heat shrink can be provided so that the heating area can be accurately aligned relative to an edge of a heating chamber. The method may involve positioning and attaching a piece of heat shrink film which has dimensions larger than required and subsequently cutting the heat shrink film after attaching to provide a predetermined distance between the heating area and a peripheral edge of the alignment region. Precision stamping may be used to remove the excess marginal portion of the alignment region.

Preferably the layer of attached heat shrink film comprises an attachment region which extends beyond the flexible backing film. Preferably the attachment region extends beyond the backing film in a direction approximately perpendicular to the direction of the extending contact legs. In particular, the heat shrink film may have a width such that it extends beyond the heating element and flexible dielectric backing film in one or both directions which are perpendicular to the direction of extension of the heater contact legs. This direction may be referred to as the wrapping direction and is a direction approximately perpendicular to an elongate axis of the heater chamber when the thin film heater is attached to the heater chamber. The attachment portion of the heat shrink is preferably arranged to extend around the heating chamber when attached to secure the heating element to the heating chamber.

Preferably the attachment region of the heat shrink may extend sufficiently such that it can circumferentially wrap around an outer surface of the heating chamber. For example, the attachment region may extend by a distance corresponding to at least the width of the heating area (i.e. the dimension perpendicular to that direction of extension of the contact legs).

The attachment region may be in the form of a tubular portion of heat shrink which is sleeved around the heating chamber. For example, the heating element and supporting backing film may be wrapped into a tube and sleeved within a tubular heat shrink. The tubular heat shrink and tubular thin film heater within may then be sleeved onto a heating chamber and heated to secure the thin film heater to the heating chamber.

Preferably the method further comprises attaching a temperature sensor to the surface of the flexible dielectric backing film adjacent to the heating element; and attaching the heat shrink layer over the heating element and the temperature sensor. In this way, a temperature sensor may be sealed with the heating element between the backing film and heat shrink such that the heating temperature can be measured accurately and used to control the power supplied to the heating element to precisely control the heater. The heater track of the heating element may be shaped so as to leave a vacant region in or adjacent to the heating area and the temperature sensor may be placed in the vacant region. The temperature sensor may comprise a sensor head and sensor connections (e.g. wires) for carrying the sensed signal from the sensor head. The sensor head may be positioned between the backing film and heat shrink with the connections extending out from between the heat shrink and backing film so as to be exposed. The temperature sensor may be arranged such that the connection wires lie adjacent to the extended contact legs of the heater element to allow for mutual support and/or ease of connection to a PCB. The backing film may comprise a through hole wherein the temperature sensor head lies on the through hole so as to be exposed on the underside of the backing film (the underside being the side opposite to the side holding the heating element).

Preferably the layer of heat shrink film is attached so as to leave an edge region of the flexible dielectric backing layer next to the temperature sensor exposed, the region comprising an adhesive and the region being folded over the heat shrink film so as to seal the edge of heat shrink film next to the temperature sensor. In particular the heat shrink film may be positioned such that it does not extend to the edge of the dielectric backing film. That is, in a direction opposition to the direction of extension of the attachment portion there may be a peripheral side portion of the backing film which remains exposed, where the edge region may carry an adhesive. This region may be folded over to cover the temperature sensor and to seal the edge of the heat shrink film.

Preferably the dielectric backing film and the heat shrink film both comprise a corresponding arrangement of through-holes; wherein the method comprises: positioning the heating element and dielectric backing film on a positioning fixture comprising a corresponding arrangement of pins with relative positions corresponding to those of the holes of the backing film, such that the pins extend through the holes of the backing film; and positioning the heat shrink film onto the heating element and backing film such that the pins of the positioning fixture enter the holes of the heat shrink film, thereby aligning the heat shrink film with the dielectric backing film. In this way the heat shrink film can be precisely aligned relative to the backing film and heating element. The corresponding holes of the backing film and heat shrink and the corresponding pins of the positioning fixture provide a reference with which the components can be aligned relative to each other with high precision.

The assembled dielectric backing film, heating element and shrink wrap layer may be referred to as a thin film heater assembly and preferably the method further comprises wrapping the thin film heater assembly around the outer surface of a tubular heating chamber, preferably with the dielectric backing film in contact with the outer surface of the heating chamber; and heating the thin film heater assembly to shrink the heat shrink layer, securing the thin film heater assembly against the tubular heating chamber. In this way, the heat shrink film will shrink under heating to secure the thin film heater assembly tightly against an outer surface of the heater chamber. Preferably the heat shrink material extends beyond the dielectric backing film sufficiently in the wrapping direction such that the extending portion covers the heater track twice when wrapped around the heating chamber. Preferably the preferential heat shrink direction of the heat shrink film corresponds to the wrapping direction. By wrapping a layer of preferential heat shrink tape around the thin film heater to secure it to the heating chamber with the direction of the preferential heat shrink aligned with the wrapping direction, upon heating, the heat shrink layer contracts to hold the thin film heater tightly against the heater chamber. Preferably the thin film heater assembly is wrapped around the heating chamber such that the upper edge of the alignment region is aligned with the top of the heating chamber.

Preferably the heating chamber comprises one or more indentations in an outer surface and the thin film heater assembly is positioned relative to the heating chamber such that a temperature sensor, attached to the flexible dielectric backing film, is positioned within an indentation.

Preferably the method further comprises wrapping a further dielectric film around the attached thin film heater assembly. In some examples, the further dielectric film may have lower thermal conduction than the backing film.

In a further aspect of the invention there is provided an aerosol generating device manufactured according to the method as defined above or in any of the appended claims. In particular there is provided an aerosol generating device comprising a thin film heater assembly comprising a heating element supported on a surface of a flexible dielectric backing film and a layer of heat shrink film attached to the surface of the dielectric backing film so as to at least partially enclose the heating element between the heat shrink film and the dielectric backing film; and a tubular heating chamber; wherein the thin film heater assembly is secured against an outer surface of the heating chamber with the heat shrink film.

<FIG> schematically illustrates a method of fabricating a heater assembly <NUM> according to the present invention. The method includes providing a heating element <NUM> supported on a surface of a flexible dielectric backing film <NUM> and attaching a layer of heat shrink film <NUM> onto the surface of the dielectric backing film <NUM> so as to at least partially enclose the heating element <NUM> between the heat shrink film <NUM> and the dielectric backing film <NUM>. The thin film heater assembly <NUM> may then be attached directly to a surface to be heated, such as the outer surface of the heating chamber of an aerosol generating device. The method provides a much more efficient, more precise and consistent method of assembling a heater which requires fewer parts. Since the heater assembly <NUM> requires fewer thin film layers then the conventional approach, the thermal mass of the heating arrangement is reduced, allowing for a greater efficiency of heat transfer to a surface to be heated. Furthermore, the heater assembly method requires only one heating step in order to bond the layers and secure the thin film heater assembly <NUM> to a heating chamber <NUM>.

As shown in <FIG>, the first step involves providing a heating element <NUM> supported on a surface of a flexible dielectric backing film <NUM>. This may be achieved in a number of different ways. In particular, the heating element <NUM> may be etched from a thin metal sheet of around <NUM>, for example a sheet of stainless steel such as 18SR or SUS304, although other materials and heater thicknesses may be selected depending on the application. The specific metal and thickness of the metal sheet are selected such that the resulting heating element <NUM> is flexible so that it can deform with the supporting flexible thin film <NUM> in order to conform to the shape of a surface to be heated. The metal sheet may be deposited initially on the surface flexible dielectric backing film <NUM>, before being etched whilst supported on the film to form the heater track <NUM> pattern. Alternatively, the heating element <NUM> may be etched from a metal sheet independently of the flexible dielectric backing film. For example a free standing metal foil may be chemically etched from both sides in order to provide one or more connected heating elements <NUM> which are subsequently detached and positioned on the surface of a dielectric backing film <NUM>.

The heating element is a planar heating element <NUM> including a heater track <NUM> which follows a circuitous path over a heating area <NUM> within the plane of the heating element <NUM>. The heating element has two contact legs <NUM> allowing connection to a power source, the contact legs <NUM> extending away from the heater track <NUM> in the plane of the heating element <NUM>. The heater track is preferably shaped so as to provide substantially uniform heating over the heating area <NUM>. In particular, the heater track is shaped such that it contains no sharp corners and has a uniform thickness and width, with the gaps between neighbouring parts of the heater track <NUM> being substantially constant to minimise increased heating at specific points within the heating area <NUM>. The heater track <NUM> in the example of <FIG> follows a serpentine path over the heater area <NUM> and is split into two parallel track paths 21a and 21b, each connected to both contact legs <NUM>. The heater layer <NUM> may be soldered at connection point <NUM> on each contact leg <NUM> to allow for the connection of the heater to a PCB and power source.

The flexible dielectric backing film <NUM> must have suitable properties provide a flexible substrate to support and electrically insulate the heating element <NUM>. Appropriate materials include polyimide, PEEK and fluoropolymers such as PTFE. In this case the heating element comprises a heater track pattern <NUM> etched from a layer of <NUM> stainless steel 18SR which is supported on a single sided polyimide/Si adhesive film comprising a <NUM> polyimide film with a <NUM> silicon adhesive layer. The heating element <NUM> is supported on the adhesive to allow the heating element to be attached to the backing film. The thin film heater <NUM> of <FIG> may be prepared in advance and stored with a release layer which is attached to the adhesive surface supporting the heating element <NUM> to preserve the adhesive layer until it is ready for use. The release layer may be provided for example by polyester or similar material. The release layer can then be peeled off to uncover the sticky adhesive layers supporting the heating element in order to proceed to the next assembly steps shown in <FIG>.

The next crucial step in the method of fabricating a heater assembly <NUM> is the application of a layer of heat shrink film <NUM> directly onto the surface of the dielectric backing film <NUM> so as to at least partially enclose the heating element <NUM> between the heat shrink film <NUM> and the backing film <NUM>. The heat shrink film <NUM> can be attached with the adhesive directly onto the surface of the heater element <NUM> so as to enclose the heating area <NUM> between the backing film <NUM> and the heat shrink <NUM>. In particular, the heater track <NUM> is insulated within a sealed envelope formed by the flexible backing film <NUM> and the heat shrink <NUM>, while the contact legs <NUM> remain exposed to allow connection to a power source.

The heat shrink <NUM> is larger than the backing film <NUM> and heating element <NUM> such that it extends beyond the heating element <NUM> by predetermined distance in two orthogonal directions <NUM>, <NUM>. This alignment of the heat shrink <NUM> relative to the heating element <NUM> allows for the later alignment of the heating area <NUM> relative to the heating chamber <NUM>. Therefore, careful control of the size of these extending portions of the heat shrink <NUM>, <NUM> at this stage allows for the heater assembly <NUM> to be attached to a heating chamber <NUM> in a straightforward manner to provide precise alignment. The relative alignment of the heat shrink and thin film heater <NUM> can be achieved in a number of different ways. The heat shrink <NUM> may be pre-cut to correct size and then aligned to an edge of the flexible dielectric backing film <NUM> to provide the correct predetermined distances <NUM>, <NUM> of the extending portions. Alternatively, as will be described below, a particular alignment apparatus may be used to achieve this precise alignment.

The heat shrink <NUM> extends beyond the heating area <NUM> in a direction opposite to the contact legs <NUM> to provide an alignment region <NUM> of the heat shrink <NUM>. This alignment region <NUM> can be aligned with the top edge of a heating chamber <NUM> such that the heating area <NUM> is positioned at a position along the length of the heating chamber corresponding to the predetermined length <NUM> of the alignment region from the top edge of the heater track <NUM>. In this way, the heater element <NUM> can be provided at a correct position along the heating chamber <NUM>. The heat shrink <NUM> also has an attachment region <NUM> which extends past the heater track <NUM> and backing film <NUM> in a direction perpendicular to the direction of extension of the contact legs <NUM> to provide an attachment region <NUM>. The direction of extension of the attachment region <NUM> may be referred to as the "wrapping direction" since this portion of the heat shrink <NUM> allows for it to be wrapped around a tubular heating chamber <NUM> and subsequently heat shrunk to provide the required tight connection. Similarly, the direction opposite to the heater legs <NUM> in the direction that the alignment region <NUM> extends from the heating element <NUM> may be referred to as the upward or alignment direction which corresponds with the elongate axis of the heating chamber <NUM>, directed towards the top open end. These extension distances <NUM>, <NUM> may be configured by cutting the heat shrink <NUM> to the correct dimensions either before or after attaching to the surface of the dielectric backing film <NUM>.

<FIG> illustrate a method of attaching the thin film heater assembly <NUM> (formed of the heating element <NUM> supported on the dielectric backing film <NUM> with the attached heat shrink <NUM>) to the outer surface of the heating chamber <NUM>. <FIG> illustrates the positioning of the heat shrink <NUM> relative to the heating element <NUM> with the upwardly extending alignment portion <NUM> and the wrapping portion <NUM> extending away from the heating element <NUM> in the wrapping direction <NUM>. The heat shrink film <NUM> may be attached at this stage by the adhesive provided on the surface of the backing film <NUM> or this may be achieved in a subsequent heating step which bonds the heat shrink <NUM> to the backing film <NUM>.

Next, as shown in <FIG>, a temperature sensor <NUM> is attached to the heater assembly <NUM> between the flexible backing film <NUM> and the heat shrink <NUM>. The temperature sensor <NUM> in this case is a thermistor with a sensor head <NUM> configured to detect the local temperature and temperature sensor connections <NUM> configured to carry the sensed signal from the sensor head <NUM> to the PCB. The heater track <NUM> is preferably shaped so as to leave a vacant region 22v within the heating area <NUM>, as most clearly shown in <FIG> and <FIG>. The sensor head <NUM> is positioned in this vacant area 22v between the backing film <NUM> and the heat shrink <NUM> such that it is in close proximity with the heater track <NUM>.

By positioning the sensor head <NUM> in close proximity to the heating element <NUM> between the heat shrink <NUM> and the backing film <NUM> the temperature sensor <NUM> is sealed in close proximity to the heating element to provide accurate temperature readings of the heating area <NUM>. The sensor connections <NUM> preferably extend in the same direction as the contact legs <NUM> of the heating element <NUM>, which assists with the connection of the heater legs <NUM> and the sensor connection <NUM> to the PCB.

As shown in <FIG> the heat shrink <NUM> is preferably positioned so as to leave a free edge region <NUM> of the backing film <NUM> exposed. As illustrated in <FIG>, this free edge region <NUM> is folded over onto the heat shrink film <NUM> to seal an edge of the backing film <NUM> and heat shrink <NUM>. In particular, as the free edge region <NUM> comprises an adhesive on the surface this can be used to fold over the heat shrink <NUM> to seal this edge region. This can also be used to fold over the temperature sensor head <NUM> to secure it within the fold.

In the method of <FIG> the next step is to attach two pieces of adhesive tape 35a, 35b to attach the thin film heater assembly <NUM> to the heating chamber <NUM> at the correct position before heating the assembly to shrink the heat shrink. The sticky tape 35a, 35b may be provided by pieces of polyimide adhesive tape, for example <NUM> inch polyimide tape with <NUM> micrometre polyimide and <NUM> micrometre silicon adhesive. The sticky attachment tape 35a, 35b is positioned along each edge of the heat shrink at the extremities in the wrapping direction. As shown in <FIG>, the thin film heater <NUM> may then be attached to the heating chamber <NUM> by aligning the top edge <NUM> of the heat shrink <NUM> with the top edge <NUM> of the heating chamber <NUM>. Given the distance <NUM> of the alignment region has been carefully selected this alignment step allows for the heating area <NUM> to be placed at the correct position along the heating chamber <NUM>. Certain consumables will contain a charge of aerosol generating substance at a particular position so it is important that the correct portion of the heater chamber is heated to efficiently release the vapour from the consumable.

The thin film heater assembly <NUM> is initially attached to the heating chamber using the adhesive tape 35a. The heating chamber <NUM> is a tubular heating chamber arranged to accept a consumable to be heated in order to generate a vapour to be inhaled by a user. The heating chamber <NUM> preferably has one or more indentations <NUM> on an outer surface which provide internal protrusions which assist with the positioning and heat transfer to a consumable received within the chamber <NUM>. The circumference of the heating chamber <NUM> preferably closely matches the width of the heating element <NUM> (the length in a direction perpendicular to the direction of extension of the contact legs) such that the heating element provides one complete circumferential loop around the chamber <NUM>. In other examples the heater element might be sized to wrap more than once around the circumference of the heating chamber, i.e. the heating element may be sized so as to provide an integral number of circumferential loops around the heating chamber so as not to produce any variation in the heating temperature around the circumference of the heating chamber. The thin film heater assembly <NUM> is positioned and attached such that the temperature sensor head <NUM> lies within an indentation <NUM> on the outer surface on the heating chamber <NUM> to provide a more accurate reading of the internal temperature of the heating chamber <NUM>.

Once attached with first adhesive tape portion 35a, the thin film heater assembly <NUM> is then rolled around the heating chamber <NUM> with the extended attachment portion <NUM> of the heat shrink <NUM> wrapping circumferentially around the chamber <NUM> to cover the heating element <NUM> again before being attached by the second piece of attachment tape 35b to provide the attached heater assembly <NUM> (including the heater element <NUM>, backing film <NUM>, heat shrink film <NUM>, thermistor <NUM> and heater chamber <NUM>) shown in <FIG>. Since the length of the attachment region <NUM> is approximately the same as the length of the heating area <NUM> (and the circumference of the heating chamber <NUM>), the attachment portion <NUM> wraps around to cover the heating area <NUM> once, such that the heater element is insulated by two layers of heat shrink film in the attached heater assembly <NUM> in <FIG>. The attachment region may be sized to provide more than one additional covering of the heating element <NUM>. For example the attachment region <NUM> may extend beyond the heating element by a distance corresponding to an integer multiple of the outer circumference of the heating chamber <NUM>.

As can be seen in <FIG> the temperature sensor connections <NUM> and the heater leg <NUM> are positioned such that they are aligned following this rapid step for ease of connection to the PCB. The attached heater assembly <NUM> is then heated to shrink the heat shrink <NUM> tight against the heating chamber <NUM> as shown in <FIG>. For example, the assembly <NUM> can be heated in an oven at around <NUM> for ten minutes to shrink the film, although the time and temperature can be adapted for other varieties of heat shrink. This process allows large numbers of units to be heat treated in a small oven at the same time. This is the only heating step which can both simultaneously seal the thin film heater to the heating chamber and bond the backing film to the heat shrink.

Finally, although not essential, a final layer of dielectric film <NUM> may be added around the outside of the heating element to complete the heating assembly as shown in <FIG>. This final dielectric layer may be for example a further layer of adhesive polyimide such as <NUM> inch polyimide tape with <NUM> micrometre polyimide and <NUM> micrometres silicon adhesive. This outer layer of dielectric film <NUM> provides a further layer of insulation and further secures the attachment of the thin film heater to the heating chamber <NUM>. The thickness and/or material of the backing film <NUM>, heat shrink <NUM> and final insulating layer <NUM> may be selected to enhance heat transfer to the heating chamber, for example with lower thermal conductivity layers provided outside the heating element (i.e. for the heat shrink 50and insulating layer <NUM> in this example) and a higher thermal conductivity layer provided as the backing film. Once the outer insulating layer of dielectric film <NUM> has been applied, the assembly <NUM> may again be heated. This second heating step allows for further outgassing of the outer layer of dielectric film <NUM>, as well as the other layers. For example, in the second heating stage, the heating temperature may be taken up to a higher temperature than the heat shrinking stage, closer to the operating temperature of the device. This allows for further outgassing, for example of the Si adhesive, that may not have taken place during the heat shrinking step at the lower temperatures. It is also beneficial to expose the heat shrink to a temperature closer to the operating temperature prior to heating during first use of the device.

<FIG> and <FIG> illustrate a further optimised method of fabricating a heater assembly according to the present invention including a number of additional features which assist with the accurate alignment of the heat shrink film <NUM> relative to the heating element <NUM> and backing film <NUM>. In this method, as shown in <FIG>, a series of alignment holes <NUM>, <NUM> are provided in both the backing film <NUM> and heat shrink <NUM> which can be used for the relative alignment of the backing film <NUM> and heat shrink <NUM>.

<FIG> schematically illustrates a thin film heater <NUM> in which the first step of providing a heating element <NUM> on the surface of a flexible dielectric backing film <NUM> has been carried out. This thin film heater <NUM> differs from the previous embodiments in that the backing film <NUM> is provided with a number of alignment holes 34a, 34b, 34c, 34d positioned in the backing film so as to be provided around the heating element <NUM>. In particular, in this example the backing film <NUM> comprises two alignment holes 34a, 34b provided along a top edge of the backing film <NUM> as to be positioned above the heating element <NUM> when it is attached to the backing film <NUM>. Two further align the holes 34c, 34d are provided below the heating area <NUM> of the heating element <NUM>. Thermistor hole 37b, discussed below, many in some example provide an additional alignment hole. Similarly, the heat shrink film <NUM> has a corresponding number of alignment holes <NUM> which correspond in relative position to those alignment holes <NUM> of the backing film <NUM>. The alignment holes <NUM>, <NUM> are arranged such that when the holes of the backing film <NUM> are brought into alignment with the alignment holes <NUM> of the heat shrink <NUM>, the heat shrink <NUM> is positioned at precisely the correct position relative to the thin film heater <NUM> such that the heat shrink <NUM> extends beyond the heating area <NUM> by the correct lengths <NUM>, <NUM> to allow for precise alignment of the heating element <NUM> relative to the heating chamber <NUM> when attached.

The flexible dielectric backing film <NUM> has two further holes 37a, 37b on which the thermistor sensor head <NUM> is positioned, so as to expose the temperature sensing head <NUM> of the thermistor <NUM> through the backing film <NUM>, as will be described in more detail below. As with the previous example, the backing film <NUM> may be any appropriate flexible electrically insulating material, for example a fluoropolymer such as PTFE, or PEEK or polyimide. In this case, the backing film <NUM> is provided by a <NUM> polyimide film with a <NUM> silicon adhesive layer, the heating element <NUM> being supported on the adhesive layer. The holes <NUM>, <NUM> may be of any appropriate size, in this case <NUM>, such that they may be used with alignment pins on an alignment fixture to co-locate the alignment holes <NUM> of the backing film with those <NUM> of the heat shrink <NUM>.

<FIG> illustrates a method of preparing the thin film heater assembly <NUM> ready for attachment to a heating chamber <NUM>. As described above, the heating element <NUM> is firstly provided on the adhesive surface of the flexible dielectric backing film <NUM> so as to be positioned between the alignment holes <NUM> of the backing film <NUM>. The heating element <NUM> is generally as described above although two <NUM> holes <NUM> are provided in the solder <NUM> on the heating legs <NUM> to enhance the welding strength when the heating element contact legs <NUM> are attached to the PCB.

The first step in the process is to initially attach the thermistor <NUM> as shown in <FIG>. As clear from <FIG> the flexible dielectric backing film <NUM> additionally includes a foldable portion <NUM> in the form of the tab <NUM> formed by two cuts in the backing film allowing the tab <NUM> to fold over on itself into the vacant region 22v into which the thermistor <NUM> is positioned. In this example the tab <NUM> is at an intermediate position along the free edge region <NUM> but it might equally be formed by one cut to provide a bottom part of the free edge region which can fold over the thermistor <NUM> when positioned. In this example the tab <NUM> includes thermistor hole 37b which aligns with the thermistor hole 37a provided in the flexible dielectric backing film <NUM> in the vacant region 22v left by the shape of the heating track <NUM>. The thermistor hole 37b is not essential and the tab <NUM> may an uninterrupted surface portion which does not contain a hole, such that it folds over the thermistor leaving the thermistor only visible through the thermistor hole 37a. Thermistor hole 37b may also be used for alignment with the positioning fixture <NUM> in some examples, The thermistor sensor head <NUM> is positioned on the thermistor hole 37a in the vacant region 22v of the backing film <NUM> such that the sensor head is exposed through the backing film <NUM> to the opposing side of the thin film heater. Since the thin film heater is attached to the heating chamber <NUM> with the backing film in direct contact, the thermistor hole 37a allows for the thermistor sensor head <NUM> to be in direct contact with the heating chamber <NUM>.

The backing film tab <NUM> is then folded over the thermistor <NUM> such that the thermistor hole 37b (if present) aligns with thermistor hole 37a and is attached via the silicon adhesive provided on the attachment surface of the backing film <NUM>. In this way, the thermistor is attached to the backing film with the sensor head <NUM> attached between the backing film <NUM> and the folded tab <NUM> of the backing film which is glued in place, with the thermistor connection <NUM> extending in the direction approximately corresponding to that of the heater contact legs <NUM>. This process serves to initially attach the thermistor <NUM> in position before the heat shrink <NUM> is aligned and attached with the thin film heater <NUM>.

The heat shrink <NUM> is then aligned relative to the thin film heater <NUM> using a positioning fixture <NUM>. The positioning fixture <NUM> comprises a supporting surface <NUM> with four upstanding alignment pins <NUM> which correspond in their relative displacement to the positions of the alignment holes <NUM>, <NUM> on the backing film <NUM> and the heat shrink <NUM>. The thin film heater <NUM> (comprising the heating element <NUM> on the backing film <NUM>) is first positioned on the surface of the alignment fixture <NUM> such that the alignment pins <NUM> extend through the backing film alignment holes <NUM>. The heat shrink <NUM> is then positioned over the thin film heater <NUM> such that the pins <NUM> further extend through the alignment holes <NUM> of the heat shrink <NUM>. This process ensures that the heat shrink <NUM> is aligned precisely relative to the heating element <NUM> and backing film <NUM>. In particular, when the alignment holes <NUM> and <NUM> are aligned this positions the heat shrink such that the heat shrink <NUM> extends beyond the heating element <NUM> in a direction opposite to the contact legs to provide a specific predetermined length of the alignment portion <NUM> and a specific predetermined length of extension of the wrapping portion <NUM>.

Once the heat shrink <NUM> is correctly positioned as shown in <FIG>, the peripheral edge region <NUM> of the backing film <NUM> which is left free by the positioning of the heat shrink <NUM> is folded over on top of the heat shrink as shown in <FIG> to seal this edge of the backing film <NUM> and heat shrink <NUM> layers. This secures the heat shrink <NUM> to the backing film <NUM> and additionally secures the thermistor connections <NUM> in position. The assembled thin film heater sub-assembly <NUM> shown in <FIG> can then be attached to the heating chamber <NUM> as described above in reference to <FIG>. In particular, by aligning the top edge <NUM> of the heat shrink <NUM> with the top edge <NUM> of the heating chamber <NUM> the heating area provided by the heating track <NUM> is positioned at the required point on the heating chamber <NUM> to provide efficient heating to a consumable received within the chamber <NUM>. The wrapping of the thin film heater sub-assembly <NUM> onto the chamber can be performed by hand as shown in <FIG> or equally this can be carried out in an automated process by a device which rotates the heating chamber <NUM> relative to the thin film heater to secure it in place. As described above, the thin film heater assembly <NUM> is sealed to the heating chamber <NUM> via heating to shrink the heat shrink <NUM> to secure the heater tightly against the outer surface of the heating chamber <NUM>.

As described above it is important to guarantee a precise distance between the top edge of the heat shrink layer <NUM> and the heating track <NUM> such that the heating area <NUM> can be reliably positioned on the heating chamber. The fact that the flexible backing film is thin and soft it can undergo tensile deformation during the process of assembling the heater assembly <NUM> which can alter the prescribed distance of this alignment region <NUM>. In order to ensure that this predefined distance <NUM> is provided reliably and reproducibly, the method can further include a number of additional steps to guarantee this. Firstly, the heat shrink <NUM> is made slightly longer in the vertical, alignment direction (the direction opposite to the direction of extension of the contact legs <NUM> when attached to the backing film). For example, the heat shrink film <NUM> can be increased in length by <NUM>. The distance between the top of the heater track <NUM> and the top of the heat shrink film will then be <NUM> more than the required size to provide the heater track <NUM> in the correct position. Once the heat shrink has been attached as shown in <FIG>, the heat shrink layer <NUM> is then punched, for example using precision stamping, to cut the heat shrink to size and remove this excess part. In this way, if the heat shrink has deformed or moved during the initial assembly steps, this subsequent cutting step guarantees the accuracy in the distance between the heater track <NUM> and the top edge <NUM> of the heat shrink <NUM> which can provide a precision of around <NUM> sufficient to achieve accurate placement of the heater area <NUM>.

As described above the thermistor is placed with the sensor head in the thermistor hole 37a and hole 37b in the tab <NUM> of the backing film <NUM> is folded over onto the sensor head <NUM>. This ensures the thermistor is always placed accurately relative to the heating element <NUM> and it also means that the sensor head <NUM> of the thermistor <NUM> is directly in contact with the outer surface of the heating chamber <NUM> so there is no intervening insulating material, thereby increasing precision in the temperature reading provided by the thermistor <NUM>.

Claim 1:
A method of fabricating an aerosol generating device with a heater assembly (<NUM>) and a heating chamber (<NUM>), comprising:
providing a heating element (<NUM>) supported on a surface of a flexible dielectric backing film (<NUM>);
attaching a layer of heat shrink film (<NUM>) onto the surface of the dielectric backing film so as to at least partially enclose the heating element between the heat shrink film and the dielectric backing film; and
attaching the heating element to a heating chamber with the heat shrink film.