Air permeable membrane, in particular for the protection of MEMS packages, its manufacturing method and die-cut parts made with such air permeable membrane

Abstract

Disclosed is a breathable composite membrane, corresponding manufacturing method, and resulting parts, comprising a support woven fabric fabric made from woven polymer monofilaments and a membrane attached to the support fabric, the support woven fabric being at least partially embedded in the membrane, the membrane being a polymer membrane having a solidified porous microstructure.

Description

[Technical field]

[0001] The present invention relates to a venting device having a reinforced membrane, particularly intended for the protection of MEMS devices, and to die cut parts containing such a venting device. [Background technology]

[0002] As is known, in many technical fields there is a need to provide a venting device that allows the passage of a gaseous fluid, usually air, while preventing the passage of other fluids, dust, or other small particulate elements.

[0003] The particular field mentioned below is consumer electronics, but this should not be considered as limiting the application of the invention, which may be advantageously used in fields where it is necessary to design venting devices that offer good protection from external factors while ensuring acoustic (low frequency) or signal transparency, high mechanical performance and heat resistance (medical equipment, sealed containers, automobiles, etc.).

[0004] The field of consumer electronics is special in equipping various devices, such as smartphones or tablets, with small sensors for a wide range of applications. Such sensors are usually based on MEMS (Micro Electrical Mechanical System) architectures and are intended to measure quantities that are acoustic (e.g. microphones), physical (e.g. accelerometers), or environmental (e.g. temperature and pressure sensors and their gradients, etc.). Some types of MEMS do not require a direct connection to the outside and can therefore be properly sealed, while many others instead require an unobstructed path through which perturbations from the outside can reach the inside. In the second category there are, for example, microphones, which have a dedicated acoustic port in smartphones, and ambient pressure sensors (which can also be used as altimeters / climbers), which also need to be connected to the outside atmosphere through a dedicated opening in the device body.

[0005] 1 is a schematic perspective view of an example of a smartphone with water resistance (IP68 waterproof rating). One end of the smartphone housing is provided with multiple openings that allow access to the electronic devices behind it. For example, an ambient pressure sensor MEMS is located in opening 101, and a MEMS microphone is located in opening 102.

[0006] The openings in the smartphone housing must be adequately protected with a barrier that is permeable to air and pressure but prevents at least the ingress of dust.

[0007] In the vast majority of devices, especially smartphones, the sensor port consists of a hole with a diameter of 1-2 mm and is usually protected by a metal mesh or a synthetic fabric with an open mesh, which ensures a certain level of protection against larger contaminants (over 100 microns), but does not protect against the ingress of micrometer particles (usually less than 5 microns) as well as pressurized water.

[0008] The shielding problem becomes rather complicated as smartphone manufacturers increasingly demand the production of waterproof devices according to IPX7-X8 standards, i.e. devices that can withstand submersion to a certain depth (usually 1-10 meters for 30 seconds). In effect, it is necessary to prevent external liquids from penetrating the sensor port and reaching the MEMS sensor itself and damaging it.

[0009] In these types of applications, there is an urgent need to protect the MEMS from the ingress of external liquids and solid contaminants (dust), even if this is not achieved at the expense of the sensitivity and responsiveness of the sensor.

[0010] Similar significant problems already occur during the manufacturing and assembly of the MEMS sensor itself inside the electronic device, where there is a risk of particle or liquid ingress. During this step of the assembly process, the MEMS sensor, not yet integrated in the device and usually unprotected, is subjected to reflow soldering processes and other operations, where it is exposed to high temperatures and solid and even liquid contaminants (flux, solder paste). There is therefore a real risk of such substances ingressing into the MEMS port, which is usually 0.5-1 mm in size. Meanwhile, it is usually not possible to close this opening during the process, both for access reasons and because of the need to leave a vent for the heated air to expand in the MEMS cavity. All this currently leads to a certain percentage of waste during production due to contamination.

[0011] This processing step is crucial for air vent filters because it is performed at high temperatures. The reflow process involves a standardized thermal cycle with three cycles of 260°C peak for 40 seconds. Clearly, surviving the reflow cycle is a stringent requirement for a protection device that is integrated into a MEMS circuit from the start of production.

[0012] In the state of the art, solutions have already been proposed to protect MEMS microphones, consisting of an acoustic membrane that ensures proper protection and sound transmission. In particular, MEMS devices used as microphones can be protected by free-standing membranes in the form of expanded PTFE or nanofibers.

[0013] Such solutions are not entirely satisfactory, both in terms of heat resistance and mechanical behavior. In particular, the membranes are not suitable for MEMS pressure or ambient temperature sensors, since the materials mentioned above, which vibrate and exhibit a strong reactive acoustic behavior, are too sensitive to high-frequency disturbances of dynamic pressure stress. Even when the membrane is supported by a nonwoven fabric, it does not completely solve the above demands, since the discontinuous configuration may create preferential paths for air leakage (with accompanying degradation of the sensor performance) or for liquid ingress in case of waterproofing requirements.

[0014] Therefore, an optimal solution does not yet exist, especially for critical ventilation applications such as protection of MEMS ambient sensors.

[0015] This type of application requires simultaneous fulfillment of different demands, both in terms of the manufacture of the specific membranes and the assembled components, which are currently not yet fully met by the market.

[0016] When it comes to protecting devices while in use, there is demand for: Protection against splashes / jet or other liquid ingress (IPx4-x5 level), -Waterproof when submerged (level IPx7-x8, 1-10m depth for over 30 minutes) Protection against the ingress of solid particles; given the sensitivity of MEMS sensors, the critical size threshold for such contaminants goes down to 5 microns. Furthermore, taking into account the functional requirements, each protective element placed between the MEMS sensor and the external environment must in any case guarantee a sufficient air passage. Among the requirements to be fulfilled there is therefore also an air permeability function suitable for the transfer of the pressure signal to the cavity in which the MEMS sensor itself is mounted, guaranteeing at least the typical values ​​given below:

[0017] At the assembly level, as already mentioned, it is necessary to ensure the expansion of the internal air that becomes superheated during the reflow process.

[0018] Instead, at the intended level of use, the breathability of the protective component directly influences the performance of the MEMS pressure sensor. In fact, the pressure sensor measures the pressure in the cavity, which corresponds to the pressure outside the venting device, only after a sufficient time for pressure equalization has elapsed. Since the equalization of the internal and external pressures is accompanied by a small amount of air movement, the permeability of the intervening venting material influences this flow. A high breathability of the protective material allows to minimize the response time of the MEMS sensor and keep it in line with the required design specifications.

[0019] Depending on the geometry of the system (volumes involved and area of ​​the venting device) and the desired reaction time, the air permeability of the venting device itself is typically between 5 and 50 L / m at a pressure of 1 kPa. 2 must be within the range.

[0020] It should be noted that the performance required of this measurement system is more complex than a simple reproduction and measurement of the pressure signal. In practice, one desires to reduce the high-frequency components of external stresses that are not related to sudden changes in the environment, but to disruptive factors such as excess pressure due to turbulence near the device, pressure waves generated by mid-frequency sound, or very powerful and short sound pulses that are unrelated to the size of the object. In all such cases, it is important that the venting material placed to protect the MEMS also acts as a low-pass filter, significantly cutting the components of the pressure signal above the maximum frequency of interest (which is always relatively low in any case).

[0021] In this regard, it is shown that a protective venting device that behaves in a more reactive manner, such as an unsupported vibrating membrane, will transmit an unattenuated high frequency pressure signal if that frequency is close to the resonant frequency of the protective venting device itself.

[0022] Currently, there exists a series of solutions using different technologies, which are still not satisfactory in the above mentioned situations. Some important examples are given here.

[0023] (synthetic or metallic fabrics) To protect the MEMS cavity, synthetic fabrics (made of polymers that can withstand the high temperatures typical of the reflow cycle) or precision fabrics of metal monofilaments may be used. Indeed, by choosing an appropriate filament diameter (preferably between 24 and 100 μm) and an appropriate number of filaments / yarns, it is possible to adjust the permeability of the venting device to the desired value, for example to ensure a fast pressure equalization and therefore minimize the response time of the sensor. An example of this technology is described in EP 2 566 183 in the name of the same applicant.

[0024] However, current technological limitations do not allow periodic apertures with a characteristic size of less than 5 μm to be obtained, and therefore a filtration efficiency of 99.99% for particles in the range of 1-5 μm cannot be guaranteed.

[0025] In addition, the fabric is not functional for applications requiring waterproofing at a depth of 1 meter for 30 minutes (IPX7) or waterproofing at depths of more than 1 meter for 30 minutes (IPX8, preferably at depths of more than 5m for 30 minutes). In fact, even taking into account surface treatments that minimize the surface energy of the material, characteristic openings of more than 1 μm allow water to pass through at pressures much lower than 100 mbar. Ultimately, this class of protective ventilation device is currently unable to achieve IP67 / 68 waterproofing classes.

[0026] (Expanded PTFE or nanofiber membrane) Thin (less than 300 μm) unsupported membranes, obtained by stretching of heat-resistant polymers (such as the material called ePTFE) or by electrospinning, can be produced with pores of 1 μm or less. This method gives excellent performance against particle ingress (99.99% of 1-5 μm) and protection against the ingress of pressurized liquids. However, unsupported membranes with a thickness of less than 300 μm, and even less than 100 μm, suffer from reduced stiffness values ​​and reactive behavior towards the passage of air. As already mentioned, these membranes may transmit high frequency pressure signals unattenuated if their frequency is close to the resonant frequency of the protective venting device itself, thereby impairing the sensor readings.

[0027] (Supported (non-embedded) PTFE or nanofiber membranes) The support membrane is obtained by expanding (ePTFE) or electrospinning a heat-resistant polymer, followed by lamination to a support layer such as a fabric or synthetic nonwoven, a metallic fabric, a perforated film, etc. Examples of this technology are described in EP 2 561 131 in the name of the same applicant.

[0028] These membranes make it possible to overcome problems related to high frequency vibrations, but other problems related to the assembly of the membrane arise. The venting component is in fact attached to the MEMS opening using an adhesive circular (acrylic or silicon-based) rim placed between the protective venting device and the MEMS cavity. In this way, lateral leakage from the outside into the MEMS sensor package can occur, since the membrane support layer is not sealed around and cannot waterproof itself. Thus, this type of solution helps to overcome problems with the reaction behavior of some types of membranes, but has the drawback of not being able to meet waterproof requirements (IPX7.8).

[0029] (Polyimide film) A last known solution is to use films of synthetic heat-resistant materials (especially PI and PEEK polymers, e.g. Kapton® film from DuPont). This family of ventilated devices is good in terms of protection against the ingress of liquids and particles, but on the other hand does not guarantee air permeability, since it is a continuous film with no air permeability. This property is problematic both during the MEMS process step (expansion due to heating) and for the operation of the ambient sensor.

[0030] As can be seen from the above, an optimal solution currently does not yet exist that meets all process and functional requirements of a venting device for protecting a MEMS sensor, such as an ambient temperature sensor. Summary of the Invention

[0031] It is therefore an object of the present invention to provide a venting device which overcomes the limitations of the prior art and which may be used in particular for protecting MEMS sensors.

[0032] This object is achieved by a reinforced membrane for a ventilation device, and a die-cut part containing said membrane, as described in the essential features of the appended claims.

[0033] The proposed invention relates to a hybrid ventilating device consisting of a polymer membrane obtained by phase inversion on a support layer (preferably a heat-resistant polymer monofilament fabric), which is partially or completely embedded in the membrane itself.

[0034] The function of the support layer is to strengthen and reinforce the membrane in a controlled way, so that a purely reactive behavior is achieved to the passage of air through the medium, with a porous structure with very small pores but high permeability, while avoiding as far as possible any resonance or uncontrolled vibration phenomena.

[0035] The support layer is at least partially embedded in the membrane and integrated therewith, which ensures excellent workability of the venting device and avoids peeling problems between the membrane and the support layer, among other things not affecting the waterproofing of the components assembled in the MEMS sensor package port by the adhesive circular rim.

[0036] The membrane is obtained from a polymer appropriately selected to withstand the high temperatures involved in the reflow soldering cycle. The membrane may have a very small pore size to ensure a good level of protection against the ingress of particles and pressurized liquids, and must also be sufficiently open to ensure an adequate level of air permeability, and therefore is characterized by sufficiently small pores, in particular less than 5 μm to ensure protection against particles, 1 μm to ensure watertightness against a pressure of 1 meter water column, and less than 1 μm to ensure watertightness against higher pressures, but at the same time a high porosity (expressed as the ratio of pore volume to material volume) of at least 40% of the volume of the membrane.

[0037] To further ensure resistance to the penetration of water or any other liquid, its surface energy must be much smaller than the surface tension of the liquid in question. According to a preferred embodiment, the reinforced membrane according to the invention is also subjected to a treatment, preferably vacuum coating, capable of generating a low surface energy of less than 20 mN / m, preferably 10 mN / m, with a pore size of the order of 1 μm or less, so that it repels liquids with low surface tension (oil or alcohol, see 30-35 mN / m and 22-30 mN / m), returning contact angle values ​​with said liquids to greater than 90°, and withstands the penetration of pressurized water (greater than 100 mbar or 500 mbar), returning contact angle values ​​to greater than 120°, preferably greater than 130°.

[0038] According to another aspect of the invention, an assembled component is also provided, obtained from multi-layer die-cut parts incorporating an assembly adhesive, combined with a reinforced membrane based on a synthetic monofilament fabric, combined with a hydrophobic surface treatment to ensure the desired degree of waterproofing.

[0039] In particular, the present invention relates to a die-cut part of a size suitable for mounting on a MEMS sensor.Since the typical size of a MEMS port is 0.5-1 mm, a multi-layer die-cut part is provided with an active area size of 0.8-2 mm, which exposes a reinforced porous membrane that has been hydrophobically treated.

[0040] The outside of the active area is provided with a rim of dual pressure sensitive adhesive (PSA) covering an outer diameter of 2-3.5 mm. Such adhesive is preferably non-porous and is positioned to completely seal the space between the hydrophobic reinforced membrane and the MEMS port itself, thus avoiding side leakage and ensuring a watertight seal and heat resistance consistent with reflow applications.

[0041] Generally, the total thickness of the assembled device can vary from 60 to 300 microns, with ideal values ​​ranging from 80 to 150 microns. The thickness of the adhesive on the MEMS sensor side determines the internal volume between the reinforcement membrane and the MEMS port, and therefore the response time of the pressure measurement. Due to air permeability, the above thickness values ​​can minimize the response time of the sensor.

[0042] Depending on the geometry of the MEMS sensor package, the presence of a second layer of adhesive on the opposite side of the reinforced membrane may be required to keep it in the center of the sandwich configuration and also permanently seal the bond between itself and the external channel of the package, or in either case, the channel must be equipped with a compressible gasket suitable to completely seal the reinforced membrane during final assembly.

[0043] Finally, if a higher bending stiffness of the reinforced membrane is desired, a stiffer ring of continuous plastic material (reinforcement) can be attached to the die cut section, further involving a double PSA layer in its assembly.

[0044] The die cut parts may have a circular, square, rectangular, oval, or other simple convex shape, provided that the active area is equivalent to a circular surface having the above sizes.

[0045] There are several other contributions to porous membranes and filters in the prior art, such as US Patent Application Publication No. 2012 / 223014, WO 2017 / 014130, US Patent Application Publication No. 2017 / 128876, US Patent Application Publication No. 2019 / 052945, Korean Patent Publication No. 20090116564, WO 2021 / 083162, and US Patent Application Publication No. 2020 / 055006 by the same applicant.

[0046] Further features and advantages of the inventive solution will in any case become more apparent from the following detailed description of some preferred embodiments of the invention, given purely by way of non-limiting example and illustrated in the accompanying drawings, in which: [Brief description of the drawings]

[0047] [Figure 1] As previously mentioned, FIG. 1 is a schematic perspective view of an exemplary smartphone. [Diagram 2] FIG. 2 is a schematic diagram of a manufacturing process according to the present invention. [Figure 3A] FIG. 1 is a schematic diagram of the "slot die" technology. [Figure 3B] FIG. 1 is a schematic diagram of the "blade coating" technique. [Figure 4A] 1 is a schematic enlarged cross-sectional view of a reinforced membrane according to the present invention; [Figure 4B] 1 is a schematic enlarged cross-sectional view of a reinforced membrane according to the present invention; [Figure 4C] 1 is a schematic enlarged cross-sectional view of a reinforced membrane according to the present invention; [Diagram 5] FIG. 2 is an electron microscope view of a cross section of a venting device according to the present invention. [Figure 6] FIG. 2 is an enlarged plan view of the porous structure of the membrane according to the present invention. [Figure 7A] FIG. 1 is a plan view of a die cut part with a reinforced membrane and a PSA rim for attachment to a "top port" MEMS sensor package in accordance with the present invention. [Figure 7B] FIG. 1 is a cross-sectional view of a die cut part with a reinforced membrane and a PSA rim for attachment to a "top port" MEMS sensor package in accordance with the present invention. [Figure 8] 1 is a plot of complex acoustic impedance as a function of frequency comparing a die cut part of the present invention with a prior art example, both having active area diameters of 1.6 mm. [Figure 9] 1 is a plot of complex acoustic impedance as a function of frequency comparing a die cut part of the present invention with a prior art example, both having active area diameters of 1.6 mm. [Figure 10] 1 is a plot of complex acoustic impedance as a function of frequency comparing a die cut part of the present invention with a prior art example, both having active area diameters of 1.6 mm. [Figure 11] 1 is a plot of complex acoustic impedance as a function of frequency comparing a die cut part of the present invention with a prior art example, both having active area diameters of 1.6 mm. [Figure 12] 1 is a graph comparing the tensile stress stiffness values ​​of several prior art materials (free-standing membranes made of nanofibers and PTFE) with a supported, heat-resistant, hydrophobic membrane of the present invention. [Figure 13A] 1A-1C are schematic diagrams illustrating various combinations of die cut components according to the present invention with PSA rims and / or stiffening rings on the "top port" or "bottom port" of a MEMS sensor package. [Figure 13B] 1A-1C are schematic diagrams illustrating various combinations of die cut components according to the present invention with PSA rims and / or stiffening rings on the "top port" or "bottom port" of a MEMS sensor package. [Figure 13C] 1A-1C are schematic diagrams illustrating various combinations of die cut components according to the present invention with PSA rims and / or stiffening rings on the "top port" or "bottom port" of a MEMS sensor package. [Figure 13D] 1A-1C are schematic diagrams illustrating various combinations of die cut components according to the present invention with PSA rims and / or stiffening rings on the "top port" or "bottom port" of a MEMS sensor package. [Figure 13E] 1A-1C are schematic diagrams illustrating various combinations of die cut components according to the present invention with PSA rims and / or stiffening rings on the "top port" or "bottom port" of a MEMS sensor package. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Through extensive experimentation, the applicant identifies new configurations of composite devices, in particular reinforced membranes that have proven to be highly effective in meeting the above requirements and are particularly suitable as protection devices for MEMS sensor packages.

[0049] In particular, the protective ventilation device comprises a support layer formed by a monofilament fabric of synthetic material based on a polymer selected from PEEK, PEK, PEKK, PTFE, PI, PFA, FEP, PPS, PEI, PBI, PCTFE, ECTFE, PAI, PPSU. According to a particularly advantageous species, the preferred polymer is PEEK, which offers high heat resistance, good mechanical properties and good chemical inertness.

[0050] The open area percentage of the fabric (ratio of the open area of ​​the mesh to the area occupied by the filaments / yarns) should be more than 30%, preferably more than 50%, but less than 75% to avoid problems with dimensional stability and flatness of the fabric, as well as excessive loss of stiffness.

[0051] The square or rectangular mesh woven fabric is preferably a fabric with a flat wave mesh, but different interweavings between warp and weft filaments with an open area ratio of less than 50% are also theoretically usable, such as 2 / 1 twill, or 3 / 1, or 4 / 1, or 2 / 2 twill or panama. The fabric is made of polymer monofilaments, i.e. filaments / yarns extruded and stretched into a single thread. These types of monofilaments, unlike common multifilament yarns, are characterized by a very high uniformity of physical and geometrical properties by nature, which improves the dimensional uniformity of the final fabric (thickness, mesh opening, open area), which is advantageous for the effectiveness of the resulting composite product and for the manufacturing process (film deposition) described below. Other advantageous characteristics that can be obtained in the composite product are a high modulus of elasticity (helps to obtain high stiffness) and a low specific gravity, which allows the total weight of the composite product to be kept low.

[0052] The fabric thickness of this woven support layer (measured, for example, according to the ISO 5084 standard) is in the range of 40 to 120 μm, preferably 40 to 70 μm, in order to obtain sufficient bending rigidity of the fabric, and the thickness of each monofilament is 30 to 40 μm.

[0053] According to the present invention, a protective ventilation device is obtained from a woven support layer embedded in a porous polymer membrane obtained by a phase inversion process.

[0054] In particular, a porous membrane partially or completely embedding a support layer of monofilament fabric can be obtained by casting through a phase inversion process.

[0055] Although the phase inversion or solidification processes for obtaining porous membranes are known per se, according to the present invention a specific method is provided that allows for reliable embedding of the polymer monofilament fabric and exploitation of the unique characteristics of the resulting composite device.

[0056] Referring to FIG. 2, an exemplary diagram of a manufacturing plant for composite devices in accordance with the present invention is shown.

[0057] The starting solution for the phase inversion process consists of at least one polymer and one solvent, specifically including a heat-resistant polymer, process additives to modify the solution viscosity, additives useful for dyeing the membrane, organic and inorganic additives acting as pore formers, additives useful for imparting specific surface properties, and a solvent or solvent mixture capable of dissolving the used polymer or polymer mixture.

[0058] According to a preferred embodiment of the present invention, polyimide (PI) is used as the solution polymer. Alternatively, S-PEEK, PES, S-PES, PPS, PAI, PBI, and soluble fluorinated polymers may be selected depending on the specific chemical and thermal resistance required.

[0059] According to a preferred embodiment of the present invention, a water-soluble solvent for polyimide resins is used, such as Rodhiasolv® Polarclean HSP with "green" characteristics from Solvay. Alternatively, a solvent or solvent mixture selected from N-methyl-2-pyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), dihydrolevoglucosenone (Cyrene), Rodhiasolv® Polarclean HSP, gamma-butyrolactone (GBL), ethyl lactate, triethyl phosphate (TEP), gamma valerolactone (GVL), dimethyl lactamide, Tamisolve® NxG, acetonitrile, N,N-dimethyl lactamide (DML) may also be used.

[0060] The weight concentration of polymer (especially polyimide) in the starting solution can be as high as 25%, but it has been found that favorable results are obtained at weight concentrations of 6-12%. Thus, the solvent portion can be as high as 75%, but is preferably 94%-88%.

[0061] The solution may contain additives such as PEG, PEO, PVP, SiO2, metal oxides and hydroxides, carbon black, UV absorbers, HALS (hindered amine light stabilizers), etc., which may be added at 0.1-10% by weight. In a preferred species, functionalized carbon black is added at 2-8% and UV absorbers and HALS are added at 0.1-2%.

[0062] The starting solution viscosity can range from 300 to 10,000 cP, but experiments have shown that the most advantageous range for advantageously carrying out the casting process on the textile support layer is 500 to 2,000 cP. To keep the viscosity in the desired range, the solution temperature during the spreading stage is kept between 20 and 100°C, preferably between 20 and 60°C.

[0063] The monofilament fabric as described above is embedded in the starting solution by casting in the first part of the manufacturing plant (see Figure 2) using the "slot die" (Figure 3A) or "doctor blade" technique (Figure 3B), setting the spreading gap (between the spreading edge of the "die" / "blade" and the monofilament fabric) preferably to 50-100 µm, maximum 350 µm.

[0064] Spreading is preferably performed by sliding the support dough horizontally (as shown in Figures 2, 3A, and 3B), but can also be performed vertically using the "slot die" technique, especially when using highly viscous solutions (3000 cP or higher).

[0065] The woven fabric forming the support layer is supplied in a roll-to-roll line in a suitably tensioned roll (Figure 2). In the spreading area, a counter cylinder supports the fabric. In this spreading procedure, which involves sliding the fabric horizontally, the polymer solution is also passed on the side of the fabric opposite to the deposition face, passing through the mesh of the fabric by permeation. In this way, the fabric is more or less deeply embedded in the final membrane as it forms the final membrane (see the various final configurations shown diagrammatically in Figures 4A-4C). However, in order to avoid excessive penetration of the polymer solution under the woven fabric, it is preferred that the woven fabric is combined with a liner unwound from a corresponding roll in the area immediately upstream of the casting stage. The liner is, for example, a suitably tensioned polymer film with a thickness of 20-100 μm, which remains in close proximity to the fabric during the casting stage and the subsequent phase inversion stage forming the final membrane.

[0066] It should be noted that the degree of penetration between the membrane and the fabric (and thus at least partially contained or embedded in the membrane) depends on the combination of various parameters such as the viscosity of the polymer solution, the thickness of the fabric and its open area, the spread gap, the spread rate, etc. By appropriately adjusting said parameters, the desired configurations can be obtained among those shown diagrammatically in Figures 4A-4C.

[0067] The final thickness of the resulting reinforced membrane (in which the fabric is at least partially embedded) is in the range of 50-130 μm, preferably 50-80 μm.

[0068] In an alternative cast configuration, the solution may be symmetrically placed on both sides of the fabric while sliding the fabric vertically without any liner, embedding the fabric to the desired depth in the resulting reinforced membrane. In contrast, in a horizontal scroll, the same application method may be performed by double passing the fabric under a spreading head or blade, spreading the polymer solution on both sides of the woven fabric, achieving double-sided coating and partial embedding of the monofilaments in the solution.

[0069] The desired porous membrane is formed downstream of casting and after further processing leading to phase inversion and solvent-nonsolvent exchange in and out of the solution.

[0070] Referring to FIG. 2, after the casting step, the assembly of fabric and polymer solution is subjected to a phase inversion precipitation procedure to form a porous membrane, specifically, carried out in two subsequent steps: VIPS (vapor induced phase separation) followed by NIPS (non-solvent induced phase separation).

[0071] According to the present invention, a VIPS phase is provided in order to define the desired morphology and size of the membrane pores, but it is also possible to use only the NIPS process under different conditions.

[0072] After the casting station, the properly tensioned fabric web containing the polymer solution is advanced and passes through a climate controlled chamber (denoted T, RH in FIG. 2), a temperature and humidity controlled area, to carry out the VIPS process. The temperature in the climate chamber is kept at 15-60°C, preferably 20-30°C, the humidity is kept at RH 30-95%, preferably 50-70%, and the residence time is 30 seconds to 10 minutes, preferably 1-4 minutes.

[0073] The fabric web, combined with the polymer solution and possibly the liner, then advances and enters a coagulation bath, preferably filled with a non-solvent (polymer), such as water (optionally dissolving a small amount of solvent, for example Rodhiasolv® Polarclean HSP, 0-10%). The ideal temperature in the bath is maintained at 20-60°C, preferably 20-30°C, and the formation of the porous structure is completed while the composite advances through the bath. Thus, the phase inversion process is completed in the coagulation bath, forming a stable porous film firmly attached to the textile fabric.

[0074] This process can advantageously yield membranes with asymmetric porosity, i.e. a porous structure with a denser skin and a gradient of pore size along the thickness. The side with the outer denser skin is the side that remains outside in the final application (e.g. MEMS packaging), i.e. the side that determines the barrier to liquids. It is not excluded that membrane species with symmetric porosity can also be used in many applications.

[0075] The choice of asymmetric or symmetric membranes must be tailored to the specific end use of the membrane within a MEMS (microelectromechanical systems) sensor or microphone.

[0076] especially, For MEMS microphones, the hole size and porosity should be equal on both sides of the membrane, which gives the same air permeability and the same acoustic impedance, and balances the insertion loss over the entire period of the sound wave. This makes it possible to avoid undesirable distortions, especially the even-order harmonic distortions associated with asymmetric resistance. For MEMS sensors, such as barometers or altimeters in smartphones, this need does not exist since there is no need to transmit a rapidly changing periodic sound pressure signal. On the other hand, the material may be required to be asymmetric in terms of air permeability, since it needs to rapidly release any internal pressure that builds up (high air permeability from inside to outside) and protect the device from external overpressure in case of rupture (low air permeability from outside to inside).

[0077] Therefore, the above process can be customized to provide a desired micropore structure.

[0078] According to a preferred embodiment, the membrane has a mean pore size MFP (mean flow pore) between 0.3 μm and 0.7 μm and a thickness between 50 μm and 80 μm, whereby the total weight of the composite including the textile fabric is between 20 and 50 g / m 2 The range is as follows.

[0079] The asymmetric porous structure of the reinforced composite membrane is created by taking advantage of the different separation / phase inversion kinetics on the two sides of the coated fabric. As can be seen from the above, the main factors that can control the different kinetics and therefore the different levels of asymmetry are the presence of a supporting liner on one of the two sides of the fabric and the entrance angle of the fabric into the phase inversion / coagulation bath.

[0080] Furthermore, due to the way in which its porous structure is obtained, it should also be considered that the membrane has a specific morphological design resulting from the action of the solvent migrating outwards through the polymer solution and the precipitation / solidification of the polymer material, so that the membrane thus obtained can also be defined as having a solidified porous structure.

[0081] In the "roll-to-roll" process, the composite reinforced membrane web exiting the coagulation bath enters one or more successive washing baths filled with water to remove solvent and / or contaminant residues. Washing is carried out at temperatures between 20 and 60°C, preferably between 40 and 50°C, for periods between 30 seconds and 10 minutes, preferably between 1 and 4 minutes.

[0082] The liner is removed before the composite reinforced membrane web is rewound onto the reinforced membrane reel, or the liner can be removed immediately after the NIPS stage and the composite reinforced membrane web is dried at a temperature between 60 and 130°C in a drying station equipped with a fan oven or IR lamps for the time it takes for the wash water to evaporate.

[0083] Figures 5 and 6 are high magnification photographs of the finished composite reinforced membrane. In the cross section of Figure 5, the polymer monofilament embedded in the porous matrix of the polymer membrane obtained by phase inversion can be perfectly discerned. It should be noted that the reinforced composite membrane has an asymmetric porosity: on one side (left side of the figure), the porous body above the monofilament is thickened and ends in a denser skin, while on the other side, the thickness is thinner and the pore size is larger.

[0084] According to a preferred embodiment of the present invention, the thus obtained reinforced composite membrane is then surface treated by plasma deposition of a nanometer thick polymer coating onto the exposed surfaces of the membrane.

[0085] In particular, the composite reinforced membrane is placed in a plasma treatment chamber in the presence of a gas that forms the coating described above. To meet the requirements described herein, gases based on fluorocarbon acrylates, such as heptadecafluorododecyl acrylate, perfluorooctyl acrylate, etc., have proven to be advantageous. To meet the requirements described herein, gases based on fluorocarbon acrylates, such as heptadecafluorododecyl acrylate, perfluorooctyl acrylate, etc., have proven to be advantageous. In particular, this selection of gases for the plasma treatment allows the deposition of fluorocarbon acrylates on the composite membrane, resulting in excellent water and oil repellency. In the plasma treatment described above, a carrier gas may also be used, as known in the literature.

[0086] The nanometer-thick polymer coatings obtained by plasma deposition techniques can be up to 500 nm thick and, thanks to the special techniques used, result in a continuous film structure that is coatable even on complex, 3D surfaces such as the reinforced porous membranes of the invention. Depending on the chemicals used, the polymer coatings can be endowed with hydrophobic and oleophobic as well as antistatic properties.

[0087] As noted above, it has been found that the most advantageous plasma treatment gases are obtained from the following compounds: 1H,1H,2H,2H-Heptadecafluorodecyl acrylate (CAS no. 27905-45-9, H2C=CHCO2CHCH2(CF2)7CF3) 1H,1H,2H,2H-Perfluorooctyl acrylate (CAS no. 17527-29-6, H2C=CHCO2CH2CH2(CF2)5CF3)

[0088] For the particular application of the vent device contemplated herein, the coating thickness is preferably kept in the range of 15-60 nm to avoid excessive coating thickness that would unduly restrict the membrane pores and prevent the desired air permeability.

[0089] Tests were carried out comparing the composite reinforced membrane by itself with a similar membrane that had been plasma treated. The measured air permeability was the same before and after plasma treatment, at 18 l / m at 1000 Pa. 2 However, the presence of the coating obtained by plasma treatment significantly increases both the contact angle with water (from 90° to 130°) and with oil (from 50° to 120° for oils such as corn oil, which has a surface tension of 32 mN / m). The contact angles are measured on water or oil droplets using the sessile drop method with a Kruss tensiometer (deposition of a droplet and measurement of the contact angle with a high-resolution camera).

[0090] According to a further embodiment of the present invention, after the manufacture of the reinforced composite membrane and the deposition of the polymeric coating by plasma treatment, a second stage of plasma treatment is provided, in which the reinforced membrane coated with the polymeric layer is exposed only to the carrier gas, and thus in the absence of forming gases of said polymeric coating. This method can provide the membrane with a desirable degree of water and oil repellency, as well as at the same time an excellent adhesion level with the subsequent PSA layer (provided in the subsequent assembly of the die-cut components).

[0091] For this second stage of plasma treatment, an appropriate working pressure of approximately 10-400 mTorr, electrode power of 100-2000 W, and exposure time of 5 s-5 min are set in the treatment chamber using only a carrier gas, best selected from nitrogen, helium, argon, or oxygen.

[0092] In this second stage, due to the inert nature of the gases used, the material that constitutes the membrane does not undergo any further coating processes. The carrier gas ions generated during the plasma treatment bombard the surface of the coating deposited in the previous stage with a certain amount of energy, resulting in a partial etching and reactivation process at the surface of the coating, generating surface irregularities, for example in the form of microcorrugations or nanogrooves, which facilitate the adhesion of the polymer coating to the next PSA layer.

[0093] Ion attack on this polymer coating causes a loss of the continuity of the coating, resulting in a change in the surface energy value, which slightly reduces the level of water- and oil-repellency of the reinforced composite membrane, but on the contrary, significantly improves the adhesion of the same reinforced membrane to the PSA layer required for the assembly of the die-cut parts. Thus, a satisfactory compromise between the water- and oil-repellency behavior of the reinforced membrane and the processability is obtained, and it is possible to obtain die-cut parts and corresponding venting devices with excellent performance, taking into account that in the assembled product the adhesion between the die-cut parts and the MEMS sensor package contributes significantly to the overall performance of the venting and protection device.

[0094] Reinforced membranes without supplemental treatment have very high contact angles with oil (130-135°) and prior art coatings typically have very poor adhesion to PSAs, compromising precision adhesion and ease of assembly of die-cut parts.

[0095] Conversely, the enhanced membranes produced according to the present invention provide superior results. The table below shows contact angle and adhesion values ​​for a PSA with only a plasma polymer coating and a PSA with a second etching plasma treatment using helium as the carrier gas, at a vacuum level of 100 mTorr, electrode power of 700 W, and exposure time of 2 minutes.

[0096] [Table 1]

[0097] Here, "gf / 20mm" is the adhesive force in grams of the reinforced composite membrane to a 20 mm wide PSA sample.

[0098] These results show that downstream of the second, i.e. supplementary, stage of plasma reactivation of the polymer coating formed in the previous stage, the reinforced composite membrane thus obtained is able to achieve both very high contact angle values ​​with oil (>110°) and adhesion levels with PSA much higher than the required minimum of 100 gf / 20 mm.

[0099] According to a further embodiment of the invention, the fabric of polymer monofilaments undergoes reactivation of the monofilament surface by plasma treatment in the presence of carrier gas only, before the casting stage. For example, the treatment is carried out in a chamber maintained at a pressure of about 10-400 mTorr, with a power of 100-2000 W at the electrodes and an exposure time of 5 seconds to 5 minutes, in the presence of a gas carrier, preferably selected from nitrogen, helium, argon or oxygen. Depending on the type of gas used, the exposure time and the power, a more or less pronounced etching effect is obtained, which creates a nano / micro roughness on the monofilament surface, which results in improved adhesion with the subsequent polymer solution that forms the porous membrane at the end of the phase inversion process.

[0100] The materials obtained after plasma treatment shown here have a WCA (water contact angle) of over 130°, an OCA (oil contact angle) of over 115° measured at an oil surface tension of 32 mN / m, and a surface free energy of less than 10 mN / m.

[0101] The composite reinforced composite membrane according to the invention can be advantageously assembled into a die-cut part, as shown in Figures 7A and 7B. In the practical case shown, a composite device 210 formed by the hydrophobic reinforced membrane described above is cut into a circle and bonded with a circular rim 211 made of a waterproof double adhesive layer suitable to withstand high temperatures (usually above 250°C), applied to the side of the membrane intended to be glued to the inlet port of the MEMS sensor package.

[0102] Exemplary features of the die cut parts include: a reinforced composite membrane according to the invention having a thickness of 70 microns, A circular active area of ​​reinforced composite membrane with a diameter of 1.6 mm, · Dual PSA layer for HT ("high temperature") applications: cellulose-based acrylic or 50 micron thick nonwoven, Dual PSA single rim with 2.6mm outer diameter, It is.

[0103] The components are preferably bonded to easily removable liners to ensure simple final assembly operations even in automated processes (using "pick-and-place" robots).

[0104] The present invention, in the embodiments described herein, has been subjected to laboratory measurements to verify its performance characteristics.

[0105] Hydrophobic plasma-treated die-cut parts made with the reinforced composite film of the present invention showed resistance to pressurized water of over 500 mbar for 30 minutes, making them suitable for application in devices such as IP68 waterproof smartphones. Furthermore, an air flow rate of 36 ml / min was measured at 1 kPa, which is sufficient to ensure pressure equalization during the reflow cycle and also provides fast pressure equalization for instant sensor response when in use, consistent with the desired requirements.

[0106] Finally, due to the placement of the reinforcing film according to the invention and its excellent adhesion to the PSA, the stiffness of the die cut parts can reach more than 25 N / mm (in a 10×10 mm test piece), which is a high bending stiffness calculated for a circular part with a diameter of 1.5 mm (bending stiffness 10 -6 mm 3 / Pa).

[0107] This last feature, while a desirable requirement in itself, is further examined in terms of its effect on the acoustic impedance of the die-cut part.

[0108] For this reason, the complete die-cut part was measured in terms of complex acoustic impedance and its performance was verified in terms of pressure signal transmission, with the aim of verifying that its excellent stiffness contributes to significantly reducing the signal transmission due to the vibration of the membrane itself, making it possible to reduce mid- and high-frequency disturbances (something that cannot be guaranteed with conventional ventilation components).

[0109] In complex acoustic impedance measurements performed with a dedicated impedance tube, a die-cut part made with a protective composite reinforced membrane according to the invention was stressed by a sound source close to one of two sides over the entire frequency range of interest (in the specific case, 20 Hz to 10 kHz). A pair of microphones was positioned to measure the pressure signal in front of and behind the membrane, and the transfer function through the membrane was calculated to derive the complex acoustic impedance.

[0110] In the ventilation application considered here, it is desirable for the resistive behavior to be as constant as possible with changing frequency in order to effectively attenuate high-frequency disturbances. On the other hand, the reactive part of the impedance (imaginary part, i.e. reactance) must be as limited as possible and not dominate the overall behavior of the membrane. Otherwise the material will show strong resonances and high-frequency disturbances will not be attenuated.

[0111] Figures 8 through 11 show graphs of the complex acoustic impedance measured as a function of frequency for a die cut part of the invention with an active area having a diameter of 1.6 mm, compatible with typical mounting in a MEMS sensor package. These results are compared to curves obtained from measurements of a prior art sample having the same active area and made of a free-standing nanofiber membrane. The acoustic impedance data is expressed as both absolute values ​​(magnitude) and the real and imaginary components of the complex acoustic impedance.

[0112] In more detail, the plot refers to the following: FIG. 8 - Amplitude values ​​of the hydrophobic reinforced membrane of the present invention; Figure 9 - Amplitude values ​​of the free-standing membrane of the prior art, FIG. 10 - Real (solid line) and imaginary (dashed line) parts of the hydrophobic enhanced membrane of the present invention; Figure 11 - Real (solid line) and imaginary (dashed line) parts of a free-standing membrane of the prior art.

[0113] From these results, the effectiveness of the invention can be clearly inferred. The first two plots (magnitude) show that when the frequency is increased to 1 kHz, the membrane according to the invention does not change its impedance value, whereas the prior art drops to about 30% of the initial value, significantly losing its ability to attenuate disturbances in the pressure signal. In fact, at 10 kHz, the conventional component loses about 99% of its acoustic impedance and attenuation capacity, operating at a frequency close to resonance. Under the same conditions, the die-cut part of the invention loses only 20-30% of its acoustic impedance and maintains adequate attenuation properties of high-frequency disturbances. This is due mainly to its resistive behavior, associated with the excellent bending stiffness guaranteed by the novel composite structure of the reinforced membrane.

[0114] A graph of the real and imaginary acoustic impedance components illustrates the above details. It should be noted that the die-cut part of the present invention maintains the dominance of resistance over reactance even at high frequencies, with the imaginary part close to zero up to 1 kHz. All this makes it ideal for use as a protective venting device for MEMS pressure sensors. In contrast, the prior art part clearly shows a resonance near 10 kHz, where the imaginary part of the impedance approaches zero and then becomes positive at higher frequencies, with the real part also decreasing to a minimum. In these conditions, the prior art die-cut part is unable to effectively attenuate unwanted disturbances to the pressure signal. Therefore, when used in combination with a MEMS pressure sensor, it gives unsatisfactory results, contrary to the case of the membrane according to the present invention.

[0115] The graph in Figure 12 compares stiffness values ​​of several prior art venting devices with the preferred embodiment venting device of the present invention made with Peek fabric and PI polymer solution, the latter shown in the last two data points on the right side of the graph exhibiting significantly higher values ​​at operating temperatures but not softening at reflow conditions.

[0116] Figures 13A-13E show various ways of assembling the die cut part of the present invention to the port of a MEMS sensor package, with the numerical references indicating the same elements as in Figures 7A and 7B. In particular, 200 refers to the die cut part having a reinforced hydrophobic membrane made in accordance with the present invention, 201 refers to the MEMS sensor, 202 refers to the MEMS flex / PCB, 203 refers to the location of the external channel of the electronic device, 210 refers to the heat resistant hydrophobic reinforced composite membrane, 211 refers to the heat resistant PSA dual rim, and 212 refers to the high temperature polymer reinforcement.

[0117] Thus, the die-cut venting device may be equipped with a PSA rim on one or both sides of the reinforced composite membrane. The polymer reinforcement preferably has a thickness of less than 100 microns and does not cover the active area of ​​the membrane that performs the venting function, i.e. the non-fitting area. If necessary, an additional layer of synthetic or metallic fabric with mesh openings of more than 20 microns may be provided, mainly for aesthetic function or as a coarser protection against particles, and a corresponding additional PSA rim may be provided.

[0118] As can be seen from the above description, the composite membrane and the corresponding venting device according to the invention make it possible to fully achieve the object mentioned at the outset. The materials used in its manufacture, the geometrical and spatial structure as well as the specific manufacturing and treatment processes result in a venting device that exhibits excellent performance in the important applications considered. In particular, the reinforced membrane can be optimally assembled to provide die-cut parts, which are perfectly used as protective venting devices for MEMS pressure sensors, an area with particularly high requirements.

[0119] The monofilament mesh has a very defined shape compared to the multifilament fabric. This allows the monofilament mesh to provide optimal geometric characteristics for the attachment of the phase inversion membrane. In particular, The thickness of the monofilament woven mesh is approximately equal to twice the diameter of the monofilament yarn. This choice determines the required thickness of the membrane in which the mesh is embedded, which can be optimized for this task. · In combination with the thickness, the shape of the mesh openings determines the amount of solution the mesh can accommodate and the characteristics of the final membrane obtained. Only in the case of monofilament mesh, the open area value can be mathematically obtained from the mesh number and mesh opening measured in both warp and weft directions. Therefore, by appropriately selecting the mesh number and the yarn diameter, it is possible to obtain the ideal open area for embedding the phase inversion membrane.

[0120] For multifilament fabrics, none of the above characteristics can be precisely defined and therefore cannot be optimized for the above processes.

[0121] In particular, the solution provided by the present invention satisfies the above process and functional requirements, namely: Resistance to liquid ingress, class IPx7, IPx8, 99.99% resistance to particle intrusion from 1 to 5 μm; Air permeability of 10 l / m at 1000 Pa, which is necessary to ensure fast pressure equalization times considering MEMS package ports with diameters of 0.5 to 2 mm 2 Super, Air permeability of 10 l / m at 1000 Pa, necessary to compensate for the pressure increase caused by heating of the internal air during the reflow cycle in the assembly of MEME 2 Super, A purely resistive (passage of air) and non-reactive (vibration of components) behavior towards the transmission of pressure signals, which is necessary to ensure the correct functioning of the pressure sensor; · Bending stiffness of 10 at design size (diameter 1.6 mm) in the MEMS field -6 mm 3 / Pa or less Sensor response time of less than 0.2 seconds under MEMS design conditions (port area 2mm 2, internal volume 0.4mm 3 ), This makes it possible to completely satisfy the above requirements.

[0122] It should also be noted that according to a preferred embodiment of the present invention, it is possible to obtain excellent adhesion of the membrane body to the support layer made of monofilament fabric, as well as excellent adhesion of the composite device with PS adhesive, thereby avoiding problems of delamination and / or air leakage and achieving the desired breathability performance and excellent life span.

[0123] It should be understood, however, that the present invention is not limited to the particular configurations shown, which are non-limiting examples of the scope of the invention, and that several variations are possible within the understanding of those skilled in the art without departing from the scope of the invention itself, as defined in the appended claims.

Claims

1. Support fabric made by weaving polymer monofilaments, A membrane attached to the aforementioned support fabric, Equipped with, The support fabric is at least partially embedded in the membrane. The aforementioned film is a polymer film having a solidified porous microstructure. Breathable composite membrane.

2. The breathable composite membrane according to claim 1, wherein the monofilament of the supporting fabric is made from a polymer selected from PEEK, PEK, PEKK, PTFE, PI, PFA, FEP, PPS, PEI, PBI, PCTFE, ECTFE, PAI, PPSU, preferably PEEK.

3. The breathable composite membrane according to claim 1 or 2, wherein the ratio of the opening area of ​​the supporting woven fabric is at least 30% and less than 75%.

4. The breathable composite membrane according to claim 1 or 2, wherein the thickness of the supporting fabric is in the range of 40 to 120 μm, preferably 40 to 70 μm, and the thickness of each monofilament is 30 to 40 μm.

5. The breathable composite membrane according to claim 1 or 2, wherein the polymer film is based on a polymer selected from polyimide (PI), S-PEEK, PES, S-PES, PPS, PAI, and PBI.

6. The breathable composite membrane according to claim 1 or 2, wherein the polymer membrane having a porous microstructure has asymmetric porosity and a dense outer layer on only one side.

7. The permeable composite membrane according to claim 1 or 2, wherein the polymer film has an average flow pore size (MFP) of 0.3 to 0.7 μm, a thickness of 50 to 80 μm, and a weight of 20 to 50 g / m2.

8. A method for manufacturing a ventilation device having a composite structure, wherein at least, - A step of bonding a support fabric made of polymer monofilaments to a polymer porous membrane. Includes, this is, • Prepare a solution of the polymer and solvent, - To obtain an assembly by casting the solution onto the support fabric and spreading it, thereby allowing the solution to at least partially penetrate the mesh of the support fabric. - The assembly of the support fabric and the polymer solution is subjected to a phase inversion solidification process in a tank containing at least a non-solvent to obtain a reinforced film having a solidified porous microstructure. - The reinforced film having a solidified porous microstructure is subjected to surface treatment by plasma deposition of a polymer coating having a nanometer thickness in the range of 15 to 60 nm, thereby giving the surface of the reinforced film the properties of a contact angle with water of 90° to 130° and a contact angle with oil of 50° to 120°. Giving and including, A method for manufacturing a ventilation device having a composite structure.

9. The aforementioned solution is - A polymer selected from polyimide (PI), S-PEEK, PES, S-PES, PPS, PAI, and PBI, The method for producing the product according to claim 8, comprising: a solvent selected from solvents for water-soluble resins, namely N-methyl-2-pyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), dihydrolevoglucocenone (Cyrene), Rodhiasolv® Polarclean HSP, γ-butyrolactone (GBL), ethyl lactate, triethyl phosphate (TEP), gamma valerolactone (GVL), dimethyllactamide, Tamisolv® NxG, acetonitrile, and N,N-dimethyllactamide (DML).

10. The manufacturing method according to claim 8, wherein the solution of the polymer and the corresponding solvent has an initial polymer weight of up to 25%, preferably 6% to 12%.

11. The manufacturing method according to claim 8, wherein the casting step is performed on one side of the support fabric to which the liner is attached on the opposite side.

12. The manufacturing method according to claim 8, wherein the phase inversion solidification step is carried out in two stages: a VIPS phase (vapor-induced phase separation) and a subsequent NIPS phase (non-solvent-induced phase separation).

13. The manufacturing method according to claim 8, wherein the second step of plasma treatment is performed by exposing the reinforced film to a carrier gas only in a treatment chamber set to a working pressure of about 10 to 400 mTorr, an electrode power of 100 to 2000 W, and an exposure time of 5 seconds to 5 minutes, the carrier gas being selected from nitrogen, helium, argon, or oxygen.

14. A ventilation device for application to a MEMS sensor package, comprising a reinforced film manufactured by the method of any one of claims 8 to 13, die-cut according to a desired shape, and bonded to at least one PSA rim.

15. The ventilation device according to claim 14, wherein the PSA rim is bonded to a ring-shaped reinforcing layer of polymer material less than 100 microns thick that does not cover the active region of the reinforcing film.

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