WO2016139687A1

WO2016139687A1 - Apparatus and method for making a photosensitive film adhere to a multilayer sheet in order to obtain a printed circuit board

Info

Publication number: WO2016139687A1
Application number: PCT/IT2015/000087
Authority: WO
Inventors: Osvaldo Novello; Francesco Parrinello
Original assignee: Automatic Lamination Technologies S.R.L.
Priority date: 2015-03-05
Filing date: 2015-03-30
Publication date: 2016-09-09

Abstract

The invention refers to an apparatus for making a photosensitive film (2) adhere to a multilayer sheet (3) on which the film (2) has been previously extended at at least one face of the sheet, in order to obtain a printed circuit board. The apparatus (1) comprises a movable lower plate (4) at which the sheet (3) is housable with the film (2), a fixed upper plate (5) and a double-acting pneumatic cylinder (7) for moving the lower plate. The lower plate (4) is sealingly couplable with the upper plate to delimit a compartment (6) that is hermetically isolated from the outside environment. A compressor (15) communicates with said compartment (6) in order to create, within the same, an overpressure with respect to the outside environment. Said overpressure presses the film (2) against the sheet (3), causing the mutual adhesion of the same. The invention also refers to a method for making a photosensitive film (2) adhere to a multilayer sheet (3).

Description

Apparatus and method for making a photosensitive film adhere to a multilayer sheet in order to obtain a printed circuit board

Field of application of the invention

The present invention has application in the field of the art regarding the manu- facturing of printed circuit boards (also known with the acronym "PCB"). More precisely, the present invention refers to apparatuses employed for making at least one film adhere to at least one sheet on which the film has been previously extended at one or both faces of the sheet.

Said sheet is, by way of example, a "multilayer sheet", i.e. sheet from whose processing a printed circuit board is obtainable. A multilayer sheet preferably comprises multiple layers made of dielectric material, superimposed on each other and covered on one or both faces by a layer of laminated copper. So as to facilitate the exposition, hereinbelow in the present description, reference will be made to a multilayer sheet in order to illustrate the invention.

The film is preferably polymeric and, by way of example, photosensitive, i.e. suitable for predisposing the copper lamina of the multilayer sheet to photo- etching. More precisely, the photosensitive film (obtained, for example, with the technology well-known to those skilled in the art as photoresist technology) allows chemically removing the "excess" copper in a manner so as to transform the copper lamina into a network of circuit connections. So as to facilitate the description, hereinbelow in the following present description, reference will be made to a photosensitive film in order to illustrate the invention. The non- removed film portion together with the excess copper becomes a layer of protection for circuit connections, i.e. of the printed circuit. Said protective layer is usually identified with the expression "welding mask". For this reason, between the apparatuses referred to by the present invention, those employed for mak- ing a photosensitive film adhere to a multilayer sheet, on which the film has been previously extended in order to obtain a printed circuit board, can be defined "welding mask applicators".

The present invention also regards a method (actuatable, by way of example, by means of the apparatus that is the subject of the invention) for making at least one film adhere to a sheet on which the film has been previously extended at one or both faces of the sheet, in order to obtain a printed circuit board.

Review of the prior art

The surface of a multilayer sheet on which a photosensitive film is extendable in order to obtain a printed circuit board is generally non-uniform. This is due to the presence of microscopic and/or macroscopic reliefs and/or depressions resulting from the manufacturing process of the multilayer sheet. Due to this non- uniformity, when the photosensitive film is extended on the multilayer sheet, air inclusions are formed which remain trapped between the film and the sheet. It is essential to remove said inclusions before the photosensitive film starts to ad- here to the multilayer sheet. Indeed, if the film is not made to completely adhere to the sheet opposed thereto, the air inclusions would compromise the photo- etching process and consequently the structure of the network of circuit connections.

An apparatus and a method for making a photosensitive film adhere to a multi- layer sheet in a manner so as to remove possible air inclusions remained trapped between the film and the sheet are described in the industrial invention Italian patent No. 1250461 , which is completely known in the art.

In brief, the method, object of the aforesaid patent, comprises the following steps:

a) arranging a "vacuum laminator" having a fixed upper plate, a vertically- translatable lower plate and, interposed between the plates, an air- impermeable diaphragm, preferably elastically deformable and placed in proximity to the upper plate, and a conveyor belt placed in proximity to the lower plate;

b) placing, on the conveyor belt, a multilayer sheet on which a photosensitive film has been previously extended at one or both faces of the sheet, and driving the conveyor belt in a manner so as to position the sheet between the lower plate and the diaphragm of the laminator;

c) lifting the lower plate, sealingly coupling it with the diaphragm so as to create, within the laminator, a hermetically closed chamber in which the multilayer sheet is housed;

d) evacuating air both from the hermetically closed chamber in order to create a vacuum therein, and from the spatial region interposed between the diaphragm and the upper plate so as to maintain the diaphragm adherent to the latter;

e) after a first pre-established time period, making air at atmospheric pressure enter into the spatial region interposed between the diaphragm and the upper plate, so as to create a pressure difference between the two faces of the diaphragm, due to which the latter is deformed to the point of adhering to the face of the multilayer sheet opposite thereto;

f) after a second pre-established time period, making air at atmospheric pres- sure enter into the hermetically closed chamber;

g) lowering the lower plate of the laminator;

h) driving the conveyor belt in order to allow picking up the multilayer sheet from the apparatus.

The plates of the laminator are provided with heating devices which are acti- vated between the start of step d) and the end of step f) so as to suitably heat the multilayer sheet and the photosensitive film. In particular, the multilayer sheet and the photosensitive film are brought to a temperature such to optimize the sliding between the sheet and the film, and simultaneously facilitate the process of adhesion between the same.

The above-described method, by means of the triple application of vacuum, mechanical pressure and heat allows making the photosensitive film adhere to the multilayer sheet, removing possible air inclusions trapped therebetween. In- cidentally, the mechanical pressure is exerted by the diaphragm at one face of the multilayer sheet, and by the conveyor belt (as constraining reaction) at the other face of the multilayer sheet.

Even if this method is extremely effective, the heating of the multilayer sheet and of the photosensitive film can involve a premature adhesion between the same, before the vacuum and the mechanical pressure exerted by the diaphragm allow the expulsion of the air inclusions present between the film and the sheet. In addition, once the "lamination" of a first sheet on which a first film is extended has terminated, before being able to carry out the lamination of a second sheet on which a second film is extended, it is necessary to wait for the plates of the laminator to cool to the point of reaching temperatures such to not cause an adhesion between the second sheet and the second film before the air is evacuated from the hermetically closed chamber. The wait time can be relatively long if the plates of the laminator are brought to high temperatures. This of course slows the cycle of production of the printed circuit boards.

In order to overcome the aforesaid drawbacks, a new apparatus and a new method were conceived for making a photosensitive film adhere to a multilayer sheet; such apparatus and method were the subject of the industrial invention Italian patent No. 1313118, this too completely known in the art.

This second apparatus differs from the abovementioned apparatus substantially due to the fact that it comprises a second "conveyor belt" interposed between the lower plate of the laminator and the diaphragm. Each of the two conveyor belts possesses at least two sections arranged in a manner such that, when one section is positioned between the plates, the other section is situated far from the plates. Once the "lamination" of a first sheet on which a first film is extended has terminated, before carrying out the lamination of a second sheet on which a second film is extended, the conveyor belts are driven in a manner so as to move away from the plates the two sections currently interposed therebetween (hence having been heated during the just-concluded lamination cycle) and, simultaneously, to interpose between the plates the other two sections that are currently lying at a certain distance therefrom. For each section of a conveyor belt, there is therefore an alternation between a lamination cycle (during which the section is heated) and a "rest" cycle (during which the section is cooled). In such a manner, in the hermetically closed chamber, the multilayer sheet is always interposed between "cold" sections of the conveyor belts. These cold sections act as thermal screens which prevent a premature adhesion be- tween the sheet and the film, both before the creation of the vacuum and during the application of the vacuum and mechanical pressure of the diaphragm.

Notwithstanding the improvements brought by the above-described second apparatus, air inclusions are still present between the multilayer sheet and the photosensitive film at the outlet from the vacuum laminator.

Objects of the invention

The object of the present invention is to overcome the aforesaid drawbacks and to indicate an apparatus and a method for making a photosensitive film adhere to a multilayer sheet, removing air inclusions possibly present between the film and the sheet in a more effective manner than the apparatuses and methods of the aforementioned previously known type.

Summary of the invention

The subject of the present invention is an apparatus for making at least one film adhere to at least one sheet on which the film has been previously extended at at least one face of the sheet in order to obtain a printed circuit board, the appa- ratus comprising:

• at least one compartment in which the sheet with the film extended thereon is housable;

wherein, according to the invention, the apparatus also comprises:

• pneumophorous means communicating with said compartment and suitable for creating, within said compartment, an overpressure with respect to an environment outside said compartment.

Incidentally, with the expression "creating an overpressure" it is intended to increase the pressure within said compartment, bringing it to a value greater than that present in the environment outside the compartment. By "overpressure" it is therefore intended a difference of pressure between, in the current case, the pressure within said compartment and the pressure in the environment outside the compartment. By way of example, the pressure in the environment outside the compartment is the atmospheric pressure.

The overpressure that is created in said compartment makes the film adhere to the sheet, causing the expulsion of the air inclusions possibly present between the same. This is confirmed by several tests conducted by the Applicant, which demonstrated that the apparatus, subject of the invention, allows obtaining a near-total elimination of said air inclusions.

In addition, in the apparatus, subject of the invention, the film is pressed against the sheet, on which it is extended by a gaseous fluid. This involves a triple advantage. First, given that the pressure is exerted by a fluid, there cannot be zones of the film which the pressing fluid cannot reach. This ensures the compression of the entire film on the sheet. Second, the applied pressure is uniform over the entire surface of the film. Consequently, this ensures a uniform adhesion of the film to the sheet. Third, since the pressure is not exerted by means of a solid means (such as a diaphragm), there is no risk that an impression is imparted by the pressing means on the film. Indeed, even if smooth and extremely deformable, a diaphragm still has microscopic reliefs and depressions that are impressed on the film. This would compromise the surface "planarity" of the film, with clear negative consequences on a possible subsequent process of photo-etching. Clearly, this risk does not arise in the apparatus, subject of the invention.

Further innovative characteristics of the present invention are described in the dependent claims.

According to one aspect of the invention, the apparatus comprises first means for heating the air present within said compartment.

Advantageously, the heat spreads from the air to the sheet and film, heating them. This improves the sliding between the sheet and the film, and simultaneously facilitates the adhesion therebetween.

According to another aspect of the invention, the apparatus comprises:

• a lower plate at which the sheet is housable with the film;

· an upper plate, said plates being movable with respect to each other;

• means for moving at least one of the plates with respect to the other between at least one first position at which the plates are coupled with fluid seal to each other, and a second position at which the plates are not sealing coupled with each other, the plates at least partially delimiting said compartment when they are in said first position.

According to another aspect of the invention, at least one of the plates com- prises second means for heating the plates.

Advantageously, the heat spreads from the plates to the air within the compartment and hence to the sheet and film, heating them.

According to another aspect of the invention, the lower plate comprises an abutment base for the sheet with the film. Preferably, the abutment base is elas- tically deformable and is made of polymer material. Still more preferably, the abutment base is made of silicone.

If the film is extended on both faces of the sheet, when the latter rests on said base, there are portions of the film that cannot be reached by the pressing fluid, since they are interposed between the sheet and the abutment base. Neverthe- less, when the overpressure between the two plates is created, the gaseous fluid advantageously presses the sheet against the abutment base. Due to a constraining reaction, it is thus the abutment base to press the film against the sheet at the face of the sheet opposite the lower plate.

According to another aspect of the invention, the lower plate comprises at least one relief at which the sheet can be rested or connected, the sheet and the film being lifted from the lower plate by means of said relief when housed in said compartment.

Advantageously, if the film is extended on both faces of the sheet, by resting or connecting the sheet on the/to the relief at a portion of the sheet on which the film is not extended, due to the presence of the relief, the gaseous fluid is capable of pressing the film on the sheet at both faces thereof and for the entire surface of the film.

According to another aspect of the invention, the apparatus comprises conveyor means suitable for introducing and picking up the sheet and the film into/from said compartment.

According to another aspect of the invention, the conveyor means comprise a conveyor belt at least partially interposed between said plates, the sheet and the film being restable on the abutment base by means of the conveyor belt. In other words, if a conveyor belt is present, the sheet and the film are restable on the conveyor belt which in turn is restable on the abutment base of the lower plate. The conveyor belt is thus at least partially comprised in said compart- ment.

Another object of the invention is a method for making at least one film adhere to at least one sheet on which the film has been previously extended at at least one face of the sheet. Said method, actuatable, by way of example, by using the apparatus, subject of the invention, comprises the steps of:

a) housing the sheet with the film extended thereon, within a compartment that can be isolated from an environment situated outside thereto;

b) creating, within said compartment, an overpressure with respect to said outside environment;

c) waiting a first time period;

d) bringing the pressure within said compartment back to nearly the same pressure as the outside environment;

e) picking up, from said compartment, the sheet with the film adhered thereto. According to one of the invention, in step b), said overpressure is preferably comprised between 0.005 MPa and 5 Pa, and still more preferably between 0.01 MPa and 3 MPa.

According to another aspect of the invention, in step c), said first time period is preferably comprised between 1 sec and 600 sec, and still more preferably between 3 sec and 200 sec.

According to another aspect of the invention, between the start of step b) and the end of step d), the sheet and the film are heated, for a second time period, in a manner so as to reach a temperature preferably comprised between 25 °C and 200 °C, and still more preferably between 60 °C and 180 °C.

According to another aspect of the invention, said second time period is preferably comprised between 10 sec and 1000 sec, and still more preferably be- tween 20 sec and 800 sec.

Brief description of the figures

Further objects and advantages of the present invention will be clearer from the following detailed description of embodiments thereof and from the enclosed drawings, given as merely exemplifying and non-limiting, in which:

- figure 1 shows, in schematic cross section, an apparatus according to the present invention in a stage in which the plates of the apparatus are mutually uncoupled;

- figure 2 shows, in schematic cross section, the apparatus of figure 1 in a stage in which the plates of the apparatus are coupled together with hermetic seal coupling;

- figure 3 shows, in schematic cross section, a first variant of the apparatus of figure 1 in a stage in which the plates of the apparatus are mutually coupled;

- figure 4 shows, in schematic cross section, a second variant of the apparatus of figure 1 in a stage in which the plates of the apparatus are mutually coupled;

- figures 5 to 7 show, in schematic cross section, a variant of the apparatus of figure 4, in three consecutive operation stages.

Detailed description of several preferred embodiments of the invention

As mentioned above, in order to facilitate the exposition, reference is only made in the present description to a preferred embodiment of the invention in which the apparatus and the method are employed for adhering, to a multilayer sheet, a photosensitive film previously extended on one or both faces of the sheet, in order to obtain a printed circuit board. It must be clear that the described apparatus and the method are not limited to the aforesaid embodiment but can be employed for making any one film adhere to any one sheet on which the film has been previously extended at one or both faces of the sheet, in order to ob- tain a sheet covered with a film firmly adhered thereto.

Hereinbelow in the present description, a figure can also be illustrated with reference to elements not expressly indicated in that figure but in other figures. The scale and proportions of the various depicted elements do not necessarily correspond to the actual scale and proportions.

Figures 1 and 2 show an apparatus 1 for making a film 2 adhere to a sheet 3 on which the film 2 has been previously extended at both faces of the sheet 3. By way of example, the sheet 3 is a multilayer sheet for printed circuits and the film 2 is a photosensitive film. The apparatus 1 comprises a movable lower plate 4 and a fixed upper plate 5 facing each other and preferably arranged horizontally. The plates 4 and 5 delimit a compartment 6 at which the sheet 3 is housable, preferably horizontally, with the film 2. The compartment 6 is there- fore a portion of space comprised between the plates 4 and 5.

The plate 4 is translatable, preferably vertically, by means of a linear actuator 7 integrally connected with the frame of the apparatus 1. By way of example, the linear actuator 7 is a double-acting pneumatic cylinder comprising a translating stem 8 integrally connected, at one end, to the plate 4. In the configuration shown in figure 1 , the stem 8 is at the lower end stop and the plate 4 is maintained by the pneumatic cylinder 7 at a distance from the plate 5 such to allow the passage of the sheet 3 with the film 2 between the two plates 4 and 5.

The plate 4 comprises a central section 4A placed at a height slightly lower than a peripheral section 4B. The section 4A therefore lies, from the plate 5, at a dis- tance greater than the distance at which the section 4B lies. The plate 4 is covered, at the section 4A, by a base 9 at which the sheet 3 is restable with the film 2. The base 9 is preferably made of polymer material, and still more preferably silicone. The height difference between the two sections 4A and 4B is sufficiently large to ensure that, when the sheet 3 and the film 2 rest on the base 9 (as shown in figure 1 ), they do not project towards the plate 5 beyond the section 4B.

When the stem 8 is at the upper end stop, as in the configuration shown in figure 2, the section 4B of the plate 4 is in contact with the plate 5. In this configuration, the compartment 6 is enclosed between the plate 5, the section 4A and a wall 10 whose presence is due to the projection of the section 4B with respect to the section 4A. The coupling between the section 4B and the plate 5 is substantially with fluid seal, in particular with air seal, so as to hermetically isolate the compartment 6, and the section 4A therewith, from the environment outside the compartment 6. The hermetic seal is ensured by the presence of a gasket 11 interposed between the section 4B and the plate 5, by way of example connected to the section 4B. Incidentally, when the sheet 3 and the film 2 rest on the base 9 (as shown also in figure 2), the sheet 3 and the film 2 not projecting towards the plate 5 beyond the section 4B, a space portion 12 of the compartment 6 is interposed between the plate 5 and the portion of film 2 that covers the upper face of the sheet 3.

With reference to figures 1 and 2, it is possible to observe that the apparatus 1 also comprises a compressor 15 communicating with the compartment 6 in order to create therein, when the plates 4 and 5 are sealingly coupled, an overpressure with respect to the environment outside the compartment 6. The compressor 15 is capable of introducing air into the compartment 6 through ducts 16 by way of example interposed between the sections 4A and 4B of the plate 4. In an alternative embodiment of the apparatus 1 not shown in the figures, the apparatus, subject of the invention, also comprises means suitable for heating the air introduced into the compartment 6 by the compressor 15.

In another alternative embodiment of the apparatus 1 , not shown in the figures, the apparatus, subject of the invention, also comprises means suitable for heat- ing the plate 5 and/or the section 4A of the plate 4.

Figure 3 shows an apparatus 20 that differs from the apparatus 1 of the preceding figures due to the fact that it comprises, in place of the abutment base 9, a relief 21 projecting from the section 4A towards the plate 5, on which the sheet 3 is restable at a portion 22 thereof, preferably not covered with the film 2. The relief 21 has a height such that, when the sheet 3 and the film 2 are housed in the compartment 6 (as shown in figure 3), they lie at a certain distance from the section 4A. A space portion 23 of the compartment 6 is therefore interposed between the section 4A and the film portion 2 that covers the lower face of the sheet 3. Analogous to that stated in reference to the apparatus 1 , also in the apparatus 20 the height difference between the two sections 4A and 4B is sufficiently large to ensure that, when the sheet 3 and the film 2 are housed in the compartment 6 and the plates 4 and 5 are sealingly coupled (as shown in figure 3), such sheet 3 and film 2 do not project towards the plate 5 beyond the section 4B and hence there is a space portion 24 of the compartment 6 interposed between the plate 5 and the film portion 2 that covers the upper face of the sheet 3.

In an alternative embodiment of the apparatus 20 not shown in the figures, the sheet 3, rather than only being restable on the relief 21 , is connectable and dis- connectable to the/from the same at a portion of the sheet 3, preferably not covered with the film 2.

Figure 4 shows an apparatus 30 that differs from the apparatus 1 due to the fact that it comprises a conveyor belt 31 for introducing and picking up the sheet 3 and the film 2 into/from the compartment 6. In particular, the apparatus 30 comprises a cover structure (not visible in the figures) having a first opening (not visible in the figures) for the entrance into the compartment 6 of the sheet 3 with the film 2 extended thereon, and a second opening (not visible in the fig- ures) for the exit from the compartment 6 of the sheet 3 and the film 2 adhered to each other. The conveyor belt 31 traverses the apparatus 30, being extended from the first to the second opening and, preferably, projects outside the covering structure at both openings. Proceeding from the first opening towards the second opening, the conveyor belt 31 traverses the compartment 6 in an inter- mediate position between the plates 4 and 5. In particular, in figure 4, the belt 31 traverses the compartment 6 in a direction orthogonal to the plane of the sheet. When the sheet 3 and the film 2 rest on the belt 31 and simultaneously lie within the compartment 6 (as shown in figure 4), the belt 31 is restable on the base 9. The sheet 3 and the film 2 are therefore restable on the base 9 by means of the belt 31. The belt 31 has a width such to not obstruct (or to not completely obstruct) the ducts 16 with which the compressor 15 introduces air into the compartment 6. In addition, the belt 31 has a thickness such that, when the sheet 3 and the film 2 are housed in the compartment 6 and the plates 4 and 5 are sealingly coupled (as shown in figure 4), they do not project towards the plate 5 beyond the section 4B and therefore there is a space portion 32 of the compartment 6 interposed between the plate 5 and the film portion 2 that covers the upper face of the sheet 3.

Since the belt 31 completely traverses the compartment 6, when the plates 4 and 5 are sealingly coupled, the portions of the belt 31 interposed between the gasket 11 and the plate 5 are shut with fluid seal therebetween. The presence of the belt 31 therefore does not compromise the hermetic seal of the compartment 6 when the plates 4 and 5 are sealingly coupled. The conveyor belt 31 is an element that is substantially known in this technology, hence further details will not be provided thereon.

Figures 5 to 7 show a modified apparatus 40 according to a different embodiment of the invention. In particular, the apparatus 40 differs from the apparatus 30 due to the fact that it also comprises:

• an air-impermeable diaphragm 41 , preferably elastically deformable and opposite the plate 5 at least at the portion of plate 5 facing the base 9. The diaphragm 41 is sufficiently wide to be sealingly shuttable between the gasket 1 1 (or, if present, the conveyor belt 31 ) and the plate 5 when the stem 8 is at the upper end stop, and is connected to the plate 5 at a region 42 of the diaphragm 41 outside the gasket 1 1. The coupling between the section 4B and the plate 5 therefore hermetically isolates not only the compartment 6, but also a space portion 43 delimited by the plate 5 and by the diaphragm 1 1. By way of example, when there is no pressure difference between the two faces of the diaphragm 41 , the latter is opposite the plate 5;

• a first vacuum pump 44 communicating with the space portion 43 in order to create a high vacuum inside the same;

• a second vacuum pump 45 communicating with the compartment 6 in order to create a high vacuum inside the same.

Incidentally, when the plates 4 and 5 are sealingly coupled (as shown in figures 5 to 7), the plate 5 on the upper part delimits the compartment 6 by means of the diaphragm 41 .

In the configuration shown in figure 5, a high vacuum is present both in the spatial region 43, and in the compartment 6.

In the configuration shown in figure 6, a high vacuum is still present in the compartment 6, while in the spatial region 43 air was made to enter at atmospheric pressure. In such a manner, a pressure difference was created between the two faces of the diaphragm 41 due to which the latter is deformed to the point of adhering to the film 2 that covers the upper face of the sheet 3, pressing the film 2 against the sheet 3.

In the configuration shown in figure 7, air at atmospheric pressure is still present in the spatial region 43, while in the compartment 6 an overpressure was ere- ated with respect to the region 43. In such a manner, a pressure difference is created between the two faces of the diaphragm 41 due to which the latter is deformed to the point of adhering to the plate 5.

In the configuration shown in figure 7, as an alternative to that stated above, in- stead of air at atmospheric pressure being present in the spatial region 43, a high vacuum was created therein.

In an alternative embodiment of the apparatus 40, not shown in the figures, the apparatus, subject of the invention, comprises a second compressor communicating with the spatial region 43 in order to create therein, when the plates 4 and 5 are sealingly coupled, an overpressure with respect to the compartment 6 and/or to the environment outside the compartment 6.

With reference to this alternative embodiment, in the configuration shown in figure 6, as an alternative to that stated above, instead of air at atmospheric pressure being present in the spatial region 43, an overpressure was created with respect to the environment outside the compartment 6.

Having described the apparatus, subject of the invention, a method will now be described which is also the subject of the invention; such method is actuatable for example by means of said apparatus for making a film 2 adhere to a sheet 3 on which the film 2 has been previously extended at both faces of the sheet 3. With reference to the apparatus 1 , starting from a configuration in which the stem 8 is at the lower end stop, the method, subject of the invention, comprises the following steps:

a) abutting the sheet 3 with the film 2 extended thereon, against the base 9 of the plate 4;

b) driving the pneumatic cylinder 7 so as to lift the plate 4, sealingly coupling it to the plate 5;

c) driving the compressor 15, creating within the compartment 6 an overpressure with respect to the environment outside the compartment 6;

d) waiting a first time period;

e) bringing the pressure within the compartment 6 back to nearly the same pressure as the outside environment;

f) driving the pneumatic cylinder 7 so as to lower the plate 4; g) picking up, from the compartment 6, the sheet 3 with the film 2 adhered thereto.

The overpressure created in step c) is preferably comprised between 0.005 MPa and 5 MPa, and still more preferably between 0.01 MPa and 3 MPa.

Said first wait time period in step d) is preferably comprised between 1 sec and 600 sec, and still more preferably between 3 sec and 200 sec.

If the apparatus 1 comprises the means for heating the air inserted in the compartment 6 by the compressor 15 and/or the means for heating one or both plates 4 and 5, according to a variant of the above-described method, between the start of step c) and the end of step e), the sheet 3 and the film 2 are heated, for a second time period, in a manner so as to reach a temperature preferably comprised between 25 °C and 200 °C, and still more preferably between 60 °C and 180 °C. Said second time period is preferably comprised between 10 sec and 1000 sec, and still more preferably between 20 sec and 800 sec.

With reference to the apparatus 20, the method, subject of the invention, is substantially identical to that described in reference to the apparatus 1 , except that the sheet 3, rather than being abutted and removed from the base 9, is abutted (or connected) and removed (or disconnected) from the relief 21.

With reference to the apparatus 30, the method, subject of the invention, is sub- stantially identical to that described in reference to the apparatus 1 , with the following exceptions:

• step a) consists of the following sub-steps:

a1 ) abutting the sheet 3 with the film 2 extended thereon, against the portion of conveyor belt 31 projecting at the first opening of the apparatus 30; a2) driving the belt 31 so as to bring the sheet 3 and the film 2 within the compartment 6, between the plates 4 and 5, and to lay the sheet 3 and the film 2 down on the base 9 (with the belt 31 interposed therebetween);

• step g) consists of the following sub-steps:

g1 ) driving the belt 31 so as to bring the sheet 3 and the film 2 outside the compartment 6, at the belt portion 31 projecting from the second opening of the apparatus 30;

g2) removing, from the belt 31 , the sheet 3 with the film 2 adhered thereto. With reference to the apparatus 40, starting from a configuration in which the stem 8 is at the lower end stop and in the region 43 and in the compartment 6, air is present at atmospheric pressure, the method, subject of the invention, comprises the following steps:

a) abutting the sheet 3 with the film 2 extended thereon, against the portion of conveyor belt 31 projecting at the first opening of the apparatus 40;

b) driving the belt 31 so as to bring the sheet 3 and the film 2 within the compartment 6, between the plates 4 and 5, and to lay the sheet 3 and the film 2 down on the base 9 (with the belt 31 interposed therebetween);

c) driving the pneumatic cylinder 7 so as to lift the plate 4, sealingly coupling it to the plate 5;

d) driving the vacuum pumps 44 and 45 so as to create a high vacuum both in the spatial region 43, and in the compartment 6. At the end of this step, the apparatus 40 is in the configuration shown in figure 5;

e) waiting a time period preferably comprised between 2 sec and 300 sec, and still more preferably between 5 sec and 150 sec;

f) making air at atmospheric pressure enter into the spatial region 43. At the end of this step, the apparatus 40 is in the configuration shown in figure 6; g) waiting a time period preferably comprised between 0.1 sec and 1000 sec; h) driving the compressor 15, creating within the compartment 6 an overpressure with respect to the region 43. At the end of this step, the apparatus 40 is in the configuration shown in figure 7;

i) waiting a time period preferably comprised between 1 sec and 600 sec, and still more preferably between 3 sec and 200 sec;

j) bringing the pressure within the compartment 6 back to atmospheric pressure;

k) driving the pneumatic cylinder 7 so as to lower the plate 4;

I) driving the belt 31 so as to bring the sheet 3 and the film 2 outside the compartment 6, at the belt portion 31 projecting from the second opening of the apparatus 30;

m) removing, from the belt 31 , the sheet 3 with the film 2 adhered thereto.

According to a variant of the method described above in reference to the appa- ratus 40, step h), in addition to driving the compressor 15, consists of driving the vacuum pump 44 so as to create a high vacuum in the spatial region 43.

If the apparatus 40 comprises the second compressor communicating with the spatial region 43, according to another variant of the method described above in reference to the apparatus 40, step f), instead of or in addition to making air at atmospheric pressure enter into the spatial region 43, consists of driving the second compressor, creating, in the spatial region 43, an overpressure with respect to the environment outside the compartment 6.

On the basis of the description provided for a preferred embodiment, it is obvi- ous that several changes can be introduced by the man skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims

C L A I M S

1. Apparatus (1 , 20, 30, 40) for making at least one film (2) adhere to at least one sheet (3) on which said film has been previously extended at at least one face of said sheet (3), said apparatus (1 , 20, 30, 40) comprising:

· at least one compartment (6) in which said sheet (3) is housable with the film (2) extended thereon;

said apparatus (1 , 20, 30, 40) being characterized in that it comprises:

• pneumophorous means (15) communicating with said compartment (6) and suitable for creating, within said compartment (6), an overpressure with respect to an environment outside said compartment (6).

2. Apparatus according to claim 1 , characterized in that it comprises first means for heating the air present within said compartment (6).

3. Apparatus (1 , 20, 30, 40) according to claim 1 , characterized in that it comprises:

· a lower plate (4, 4A, 4B) at which said sheet (3) is housable with said film (2);

• an upper plate (5), said plates (4, 4A, 4B, 5) being movable with respect to each other;

• means (7, 8) for moving at least one (4, 4A, 4B) of said plates with re- spect to the other (5) between at least one first position at which said plates (4, 4A, 4B, 5) are coupled with fluid seal to each other, and a second position at which said plates (4, 4A, 4B, 5) are uncoupled from each other, said plates (4, 4A, 4B, 5) at least partially delimiting said compartment (6) when they are in said first position.

4. Apparatus according to claim 3, characterized in that at least one of said plates comprises second means for heating said plates.

5. Apparatus (30, 40) according to claim 1 , characterized in that it comprises conveyor means (31) suitable for introducing and picking up said sheet (3) and said film (2) into/from said compartment (6).

6. Method for making at least one film (2) adhere to at least one sheet (3) on which said film (2) has been previously extended at at least one face of said sheet (3), said method being characterized in that it comprises the steps of: a) housing said sheet (3) with said film (2) extended thereon, within a compartment (6) that can be isolated from an environment situated outside thereto;

b) creating, within said compartment (6), an overpressure with respect to said outside environment;

c) waiting a first time period;

d) bringing the pressure within said compartment (6) back to nearly the same pressure as said outside environment;

e) picking up, from said compartment (6), said sheet (3) with said film (2) adhered thereto.

Method according to claim 6, characterized in that, in step b), said overpressure is comprised between 0.005 MPa and 5 MPa.

Method according to claim 6, characterized in that, in step c), said first time period is comprised between 1 sec and 600 sec.

. Method according to claim 6 characterized in that, between the start of step b) and the end of step d), said sheet (3) and said film (2) are heated, for a second time period, in a manner so as to reach a temperature comprised between 25 °C and 200 °C.

0. Method according to claim 9, characterized in that said second time period is comprised between 10 sec and 1000 sec.