A sensor-computer integrated electronic skin based on a COF flexible substrate and its fabrication method

Abstract

This invention provides a sensing and computing integrated electronic skin based on a COF flexible substrate and its fabrication method, comprising a COF flexible substrate layer, a sensing layer, a chip layer, and an encapsulation layer. The COF flexible substrate layer includes a modified polyimide film substrate and a driving circuit layer. Laser-sensitive inorganic nanoparticles are uniformly dispersed within the modified polyimide film substrate. Laser-induced microporous circuit mounting sites are formed on the modified polyimide film substrate using laser-induced laser-sensitive inorganic nanoparticles. The driving circuit layer is disposed on the circuit mounting sites to ensure the connection strength between the driving circuit layer and the modified polyimide film substrate. This invention first flip-chip soldering, then forming the sensing element, and finally encapsulating with a flexible polymer, using a high-temperature followed by a low-temperature encapsulation sequence to avoid high-temperature damage to the sensing element caused by chip soldering.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a sensing and computing integrated electronic skin based on a COF flexible substrate and its preparation method. Background Technology

[0002] In existing robotic tactile skin, the sensor arrays mostly use traditional FPCs (flexible printed circuits) as the interconnect carrier, with electrodes mostly located at the edge of the substrate and complex internal interconnections. Furthermore, because the linewidth / spacing of FPC processes is typically above 50 micrometers, it is difficult to achieve "high-density" coverage of hundreds of sensor units in a small area, resulting in low resolution of the electronic skin (mostly single-point sensing), and the cumbersome FPC wiring makes the entire system bulky, with flexibility contradicting practical applications.

[0003] Furthermore, for bimodal skin that requires simultaneous acquisition of pressure and temperature, such as the graphene electronic skin mentioned in existing documents, the backend processing delay limits its ability to meet the real-time tactile closed-loop control requirements of robot dexterity hand with 0.2ms-level responsive force feedback.

[0004] In addition, in the traditional sequential process of "first mounting the passive sensing element and then reflow soldering the active chip", the high temperature of the active element soldering can cause irreversible melting or poor soldering of the already placed thermosensitive polymer sensing layer. The common ACF bonding method also has problems such as high contact resistance, poor consistency and easy breakage when bent, resulting in a low overall manufacturing yield of electronic skin.

[0005] In view of this, the inventor conducted in-depth research on the aforementioned deficiencies in the prior art, which led to the creation of this case. Summary of the Invention

[0006] The first objective of this invention is to address the above-mentioned shortcomings by providing an integrated electronic skin for sensing and computing based on a COF flexible substrate, in which the chip is first flip-chip soldered, then the sensing element is formed, and finally the chip is encapsulated by a flexible polymer. This method uses a high-temperature-then-low-temperature encapsulation sequence to avoid high-temperature damage to the sensing element caused by the soldering chip.

[0007] To achieve the above objectives, the first solution of the present invention is: an integrated electronic skin for sensing and computing based on a COF flexible substrate, comprising a COF flexible substrate layer, a sensing layer, a chip layer, and an encapsulation layer. The COF flexible substrate layer comprises a modified polyimide film substrate and a driving circuit layer. Laser-sensitive inorganic nanoparticles are uniformly dispersed within the modified polyimide film substrate. Laser-induced laser-sensitive inorganic nanoparticles form circuit mounting positions with micropore structures on the modified polyimide film substrate. The driving circuit layer is disposed on the circuit mounting positions to ensure the connection strength between the driving circuit layer and the modified polyimide film substrate. The sensing layer and the chip layer are both disposed on the driving circuit layer. The encapsulation layer covers the outer periphery of the COF flexible substrate layer, the sensing layer, and the chip layer.

[0008] Furthermore, the laser-sensitive inorganic nanoparticles are one or more of silicon dioxide, silicon carbide, titanium dioxide, zinc oxide, or MXene, and the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%.

[0009] The second objective of this invention is to address the above shortcomings by providing a method for preparing an integrated electronic skin for sensing and computing based on a COF flexible substrate, which involves first flip-chip bonding, then forming a sensing element, and finally encapsulating it with a flexible polymer. This method avoids high-temperature damage to the sensing element caused by chip bonding by using a high-temperature followed by a low-temperature encapsulation sequence.

[0010] To achieve the above objectives, the second solution of the present invention is: a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, comprising the following steps: (1) Dissolve laser-sensitive inorganic nanoparticles in a polar solvent, take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the laser-sensitive inorganic nanoparticle solution at a low temperature of -5℃ to 5℃ to mix, and form a film by casting. (2) The polyamic acid film is dried and then subjected to gradient thermal imidization to obtain a modified polyimide film. (3) A laser is used to scan and irradiate the modified polyimide film to perform surface treatment on the modified polyimide film, forming a microcrack / micropore structure on the surface of the modified polyimide film. The efficient absorption and photothermal conversion effect of the laser by the nanoparticles uniformly dispersed in the modified polyimide film is utilized to reduce the thermal impact of laser-induced modification and obtain a COF flexible substrate layer. (4) A driving circuit layer is formed in the laser irradiation area of ​​the modified polyimide film; (5) The chip is flip-chip soldered onto the driver circuit layer; (6) Integrate the sensing elements on the drive circuit layer; (7) A flexible polymer is used to form a packaging layer that includes the chip and sensing elements.

[0011] Furthermore, in step (1), the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%, and the laser-sensitive inorganic nanoparticles are one or more of silicon dioxide, silicon carbide, titanium dioxide, zinc oxide or MXene. The laser-sensitive inorganic nanoparticles are added before the polymerization reaction of the diamine monomer and the dianhydride monomer, or after the polymerization reaction of the diamine monomer and the dianhydride monomer is completed.

[0012] Furthermore, in step (2), the drying temperature of the drying treatment is 80-100°C and the drying time is 30-60 minutes. The gradient thermal imidization includes a primary thermal imidization treatment at a thermal imidization temperature of 120-180°C and a secondary thermal imidization treatment at a thermal imidization temperature of 180-220°C.

[0013] Furthermore, in step (3), the modified polyimide film is surface-treated using an ultraviolet nanosecond laser or a femtosecond laser with a laser density of 0.7 to 0.9 J / cm² and a scanning speed of 100 to 150 mm / s.

[0014] Furthermore, in step (4), a semiconductor-grade flip-chip thin film process is used to form the driving circuit layer. Specifically, a copper seed layer is sputtered on the modified polyimide thin film substrate, and then photolithography and pattern electroplating are performed to create a copper line with a line width and line spacing of only 10 micrometers. Finally, a nickel-gold protective film is chemically plated on the copper line to improve solderability and oxidation resistance.

[0015] Furthermore, in step (5), the gold-tin eutectic welding technology is used to weld the chip. Specifically, gold-tin bumps are prefabricated on the modified polyimide film substrate, the chip is precisely aligned using flip-chip welding equipment, and a certain pressure is applied to the chip while the temperature is rapidly increased to the peak temperature to complete the gold-tin fusion interconnection. Then, the chip is cooled at a rate of 10-20℃ / s to form a high-strength intermetallic compound solder joint.

[0016] Furthermore, in step (6), the sensing element formation process is as follows: functional ink is deposited onto the modified polyimide film substrate using a piezoelectric nozzle of an inkjet printer, aerosol jet printer, or electrohydrodynamic printer. Then, the substrate is sintered at 80-150°C using a hot plate or photonics for 30 minutes to allow the solvent to evaporate, the functional material to crosslink or sinter, and a sensing microstructure integrated with the bottom electrode is directly constructed at the target location.

[0017] Furthermore, in step (7), the flexible polymer is one or more of polydimethylsiloxane, platinum-catalyzed silicone rubber, polyurethane elastomer, parylene, silicone gel and flexible epoxy resin, and the encapsulation layer is an encapsulation layer with a thickness of 50 to 500 μm formed by spin coating, molding or vapor deposition.

[0018] Compared with the prior art, the present invention has the following advantages: (1) This invention utilizes the fine wiring capability of COF technology at the 10-micron level to achieve ultra-high density integration of more than 1200 sensing units (about 300 DPI) in a limited area, far exceeding the traditional FPC solution, and realizes "full-area high-density sensing". (2) This invention avoids damage to functional materials by high temperature from the source, solves the problems of poor soldering and melting loss, and improves the core manufacturing yield by about 25%; gold-tin eutectic solder replaces traditional ACF conductive adhesive, resulting in lower connection resistance and significantly improved bending life; (3) The present invention directly welds the preprocessing chip to the center of the sensing array to form a “sensing and computing integrated” architecture. The signal path is the shortest, and filtering and temperature drift compensation can be completed at the front end to achieve an end-to-end sensing-feedback delay of less than 1ms. Furthermore, the sensing layer and the driving circuit layer are merged into a single functional layer integrated on the modified polyimide film substrate, eliminating the complex stacking and connection layers in the traditional technology. Its overall thickness is thinner and its flexibility is better. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the structure of an integrated electronic skin for sensing and computing based on a COF flexible substrate.

[0020] In the figure: COF flexible substrate 1; sensing layer 2; chip layer 3; encapsulation layer 4. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1As shown, this invention provides a sensing and computing integrated electronic skin based on a COF flexible substrate, comprising a COF flexible substrate 1, a sensing layer 2, a chip layer 3, and an encapsulation layer 4. The COF flexible substrate 1 includes a modified polyimide film substrate and a driving circuit layer. Laser-sensitive inorganic nanoparticles are uniformly dispersed within the modified polyimide film substrate. Laser-induced laser-sensitive inorganic nanoparticles form circuit mounting positions with micropore structures on the modified polyimide film substrate. The driving circuit layer is disposed on the circuit mounting positions to ensure the connection strength between the driving circuit layer and the modified polyimide film substrate. The sensing layer 2 and the chip layer 3 are both disposed on the driving circuit layer. The encapsulation layer 4 covers the outer periphery of the COF flexible substrate 2, the sensing layer 3, and the chip layer 3.

[0023] In this invention, the laser-sensitive inorganic nanoparticles are one or more of silicon dioxide, silicon carbide, titanium oxide, zinc oxide or MXene, and the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%.

[0024] This invention also provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, comprising the following steps: (1) Dissolve laser-sensitive inorganic nanoparticles in a polar solvent, take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the laser-sensitive inorganic nanoparticle solution at a low temperature of -5℃ to 5℃ for mixing. Low temperature can prevent nanoparticles from agglomerating and polymerizing too quickly, ensure uniform dispersion, avoid local overheating or premature polymerization, achieve uniform bulk phase doping, and form a film by casting. (2) The polyamic acid film is dried and then subjected to gradient thermal imidization to obtain a modified polyimide film. (3) A laser is used to scan and irradiate the modified polyimide film to perform surface treatment on the modified polyimide film, forming a microcrack / micropore structure on the surface of the modified polyimide film. The efficient absorption and photothermal conversion effect of the laser by the nanoparticles uniformly dispersed in the modified polyimide film is utilized to reduce the thermal impact and obtain a COF flexible substrate layer. (4) A driving circuit layer is formed in the laser irradiation area of ​​the modified polyimide film using a semiconductor-grade flip-chip thin film process; (5) The chip is flip-chip bonded to the driver circuit layer using gold-tin eutectic bonding technology; (6) The sensing element is integrated on the drive circuit layer by inkjet printing, aerosol jetting or electrohydrodynamic printing. (7) A flexible polymer is used to form a packaging layer that includes the chip and sensing elements.

[0025] In this invention, in step (1), the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%, and the laser-sensitive inorganic nanoparticles are one or more of silicon dioxide (SiO2), silicon carbide (SiC), titanium dioxide (TiO2), zinc oxide (ZnO) or MXene. The laser-sensitive inorganic nanoparticles are added before the polymerization reaction of the diamine monomer and the dianhydride monomer, or after the polymerization reaction of the diamine monomer and the dianhydride monomer is completed. The mixture is then stirred and mixed by mechanical stirring and ultrasonic dispersion. The stirring speed of the mechanical stirring is 200 to 500 rpm, and the stirring time is 1 to 2 hours.

[0026] In this invention, in step (2), the drying temperature of the drying treatment is 80-100°C and the drying time is 30-60 minutes to remove most of the solvent. The gradient thermal imidization includes a first thermal imidization treatment with a thermal imidization temperature of 120-180°C and a heating time of 30-60 minutes and a second thermal imidization treatment with a thermal imidization temperature of 180-220°C and a heating time of 30-60 minutes.

[0027] In this invention, in step (3), a UV nanosecond laser or femtosecond laser is used to perform surface treatment on the modified polyimide thin film metal conductive circuit or functional sensing material setting area, with a laser density of 0.7 to 0.9 J / cm² and a scanning speed of 100 to 150 mm / s.

[0028] In this invention, in step (4), a semiconductor-grade flip-chip thin film process is used to form the driving circuit layer. Specifically, a copper seed layer is sputtered on a modified polyimide thin film substrate, and then photolithography and pattern electroplating are performed to produce a copper line with a line width and line spacing of only 10 micrometers. Finally, a nickel-gold protective film is chemically plated on the copper line to improve solderability and oxidation resistance.

[0029] In this invention, in step (5), the gold-tin eutectic welding technology is used to weld the chip. Specifically, gold-tin bumps are prefabricated on the modified polyimide film substrate, the chip is precisely aligned using flip-chip welding equipment, and a certain pressure is applied to the chip while the temperature is rapidly increased to the peak temperature to complete the gold-tin fusion interconnection. Then, the chip is cooled at a rate of 10-20℃ / s to form a high-strength intermetallic compound solder joint.

[0030] In this invention, in step (6), the sensing element is formed as follows: functional ink is deposited onto sensing reserved pads with a spacing of about 10 to 50 μm using a piezoelectric nozzle of an inkjet printer, aerosol jet printer, or electrohydrodynamic printer. Then, the ink is sintered at 80 to 150°C using a hot plate or photonics for 30 minutes to allow the solvent to evaporate, the functional material to crosslink or sinter, and a sensing microstructure integrated with the bottom electrode is directly constructed at the target location.

[0031] In this invention, in step (7), the flexible polymer is one or more of polydimethylsiloxane, platinum-catalyzed silicone rubber, polyurethane elastomer, parylene, silicone gel and flexible epoxy resin, and the encapsulation layer is an encapsulation layer with a thickness of 50 to 500 μm formed by spin coating, molding or vapor deposition.

[0032] In this invention, the bulk-doped nanoparticles, when irradiated with laser, not only assist in the formation of surface microstructures but also induce the formation of a three-dimensional interconnected network of microcracks / micropores (within a controllable range) in the shallow layer of the polyimide matrix. Subsequently deposited metals or sensing materials can then infiltrate within this network, forming a truly "embedded" mechanically interlocked structure. Peel strength tests (referencing ASTM D903) show that the peel strength between the modified polyimide film of this invention and the electroplated copper layer after laser activation can reach over 1.6 N / mm, which is more than 3 times higher than the control sample (approximately 0.5 N / mm) treated with laser without polyimide doping. Compared to the surface coating scheme of Lee et al. (where the coating itself carries the risk of peeling off), this invention, because the nanoparticles are firmly embedded in the polyimide matrix, has no peeling problem, and the peel strength retention rate is >85% after long-term bending (>100,000 times, bending radius 2 mm).

[0033] In this invention, bulk doping significantly improves laser energy utilization efficiency, reducing the required laser flux to 30%–50% of that required for traditional direct polyimide processing. Under femtosecond laser conditions, the heat-affected zone (HAZ) can be controlled within 100 nm; even with ultraviolet nanosecond lasers, the HAZ is still significantly smaller than that of undoped polyimide. This characteristic makes this invention particularly suitable for integrating temperature-sensitive layers or thermoplastic stretchable materials into flexible electronic skin (without functional layer failure due to thermal diffusion). Furthermore, laser selective activation is a completely dry, mask-free process, enabling selective interface enhancement with micron-level resolution without the need for chemical etching.

[0034] In this invention, by adjusting laser parameters (energy density, scanning speed, pulse number) and the type / content of nanoparticles, the surface morphology can be independently designed in different areas of the same polyimide film: in the chip welding or electrode lead-out area, a recessed micro-pit array can be formed to assist in precise solder wetting and positioning, improving welding reliability; in the sensor area, a fingerprint-like micro-groove structure can be constructed, which not only enhances the bonding force with sensitive materials but also simulates the friction / tactile characteristics of real skin; in non-functional areas, the original surface is maintained to ensure overall flexibility and insulation. This invention is the first to achieve, through a single laser process, simultaneous optimization of three properties—interface bonding force, tactile simulation, and solder wetting—on the same polyimide substrate, with each area being independently controllable. The material is highly adaptable and easy to industrialize. The inorganic nanoparticles used are all commercially available products, and the in-situ polymerization or blending method is compatible with traditional polyimide film manufacturing processes, requiring no additional complex equipment. The laser equipment can adopt a mature ultraviolet nanosecond laser direct writing system, which is cost-controllable and easy to achieve roll-to-roll continuous production.

[0035] Traditional packaging processes, which do not employ the reverse-order approach of "high-temperature chip soldering followed by low-temperature sensor integration," face several technical challenges: First, it is difficult to pattern sensing materials with micron-level precision around the already soldered raised chip and ensure accurate alignment between the sensing unit and the COF pre-reserved pads; second, the adhesion and electrical stability of functional inks used in low-temperature additive processes (such as inkjet printing) with the PI substrate are insufficient; third, the subsequent low-temperature curing process inevitably affects the already soldered chip and its interconnects; and fourth, it is difficult to avoid ink overflow leading to short circuits between the chip and the sensing unit. This invention overcomes these challenges through a specific combination of processes and material systems, achieving reverse-order packaging. The present invention overcomes the above problems. Specifically, the present invention selects a modified polyimide film substrate, using a polyimide (PI) film with a thickness of about 25-50 micrometers as a flexible substrate, and uses a semiconductor-grade flip-chip (COF) process. Specifically, a copper seed layer is first sputtered on the PI film, followed by photolithography and pattern electroplating to create a high-density copper interconnect line with a linewidth / spacing of only 10 micrometers. These lines not only include the signal lines and ground lines of the sensing unit, but also include micrometer-level precision pads (reserved positions) for subsequent connection of chips. Finally, a layer of nickel-gold is chemically plated on the copper lines or an organic solderable protective film is directly generated to improve solderability and oxidation resistance. Thus, the independent functions of the "substrate" and "circuit board" in the traditional solution are combined into this one thin film.

[0036] This step is crucial, as the entire design framework is established here. First, there's the design and layout: during the circuit diagram design phase of the chip PCB, an area for placing the chip is planned at the center or a specific location of the sensor array. Within this area, a series of tiny pads are designed, their arrangement, size, and spacing precisely corresponding to the bumps on the chip to be packaged. Second, there's the patterning: this layout pattern, along with all interconnect lines, is written into a photomask. When finely wiring on the PI film using the "chip-on-film process," we don't etch complex lines in the chip placement area; instead, we leave only a blank area and directly fabricate the exposed copper / gold micro-pad array for connecting the chip on the polyimide substrate in this area. These pads are called "reserved positions." Third, there's the surface treatment: the pads on these reserved positions undergo special surface treatments (such as chemical gold plating) to ensure excellent flatness, cleanliness, and wettability, preparing optimal conditions for subsequent gold-tin eutectic bonding.

[0037] Next, the chip is soldered using gold-tin eutectic solder (Au80Sn20) with a eutectic temperature of 280℃ and a reflow peak temperature controlled at 300-330℃ for 5-15 seconds. The specific operation involves: first, pre-fabricating gold-tin bumps on the micron-level pads of the pre-reserved positions on the COF substrate chip; then, using precision flip-chip bonding equipment (commercially available flip-chip bonding machines such as Finetech, SET, or similar thermo-press flip-chip bonding machines, which can be used directly with existing semiconductor packaging equipment), precisely aligning the front-end pre-processed chip and applying pressure while rapidly heating it to the peak temperature to complete the gold-tin fusion interconnection. Subsequently, it is cooled at a rate of 10-20℃ / s to form high-strength intermetallic compound solder joints. During the soldering process, the COF substrate can be preheated to 100-150℃ to reduce thermal shock. This step completely achieves the electrical and mechanical connection between the front-end processing chip and the high-density circuitry of the PI substrate layer. Furthermore, because the PI film is heat-resistant to over 400℃, the soldering process will not damage the substrate.

[0038] Then, and this is the core step, the innovation of this invention, is that since the chip has already been soldered at high temperature, there are no longer high-temperature restrictions in subsequent processes after the chip soldering is completed. Low-temperature additive manufacturing technologies are used, such as inkjet printing, aerosol jetting, or electrohydrodynamic printing. The printer nozzle, according to a pre-set CAD drawing, forms a piezoresistive or capacitive temperature- and pressure-sensitive composite material array in situ on the pre-reserved electrode pairs on the COF substrate around the chip. The principle of this "in-situ formation" is as follows: using a piezoelectric nozzle, functional nano-inks (such as pressure-sensitive inks made of carbon nanotube / polymer composites, or temperature-sensitive inks made of PEDOT) are precisely applied according to a pre-programmed pattern. The ink droplets are deposited onto the sensor pads with a spacing of approximately 10-50 μm. The hydrophilic or hydrophobic patterning of the PI surface or physical barriers confine the ink droplets within the electrode area. Subsequently, the ink is sintered at 80-150°C (preferably 120°C) using a hot plate or photonics method for 30 minutes to allow solvent evaporation, cross-linking or sintering of functional materials. This directly constructs a sensor microstructure that is integrated with the underlying electrode at the target location, forming the final piezoresistive or thermistor unit. This eliminates the need for transfer or assembly. This in-situ forming method avoids high temperatures and achieves seamless integration of the sensor unit and interconnect circuitry, eliminating subsequent alignment errors. By controlling the ink formulation and printing parameters, the pressure sensitivity and temperature coefficient can be customized.

[0039] Finally, a flexible polymer is used for encapsulation. In addition to PDMS (polydimethylsiloxane), the flexible polymer can also be one or a combination of the following materials: Ecoflex (platinum-catalyzed silicone rubber, which is ultra-soft and highly tensile), polyurethane elastomers (such as the Dragon Skin series), parylene (Parylene C, vapor-deposited ultrathin insulating layer), silicone gel, or flexible epoxy resin (such as SU-8 modified material). Spin coating, molding, or vapor deposition methods are preferred to form a uniform encapsulation layer with a thickness of 50~500μm, which protects the chip and sensor array while maintaining overall flexibility. After encapsulation, the device can withstand more than 100,000 bends without functional degradation.

[0040] The beneficial technical effects of the modified polyimide film used in this invention will be explained below through several examples and comparative examples.

[0041] Example 1 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 0.5% zinc oxide nanoparticles (average particle size 50 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0042] Example 2 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 2% by mass of zinc oxide nanoparticles (average particle size 50 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0043] Example 3 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 5% by mass of zinc oxide nanoparticles (average particle size 50 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0044] Example 4 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 2% by mass silica nanoparticles (average particle size 30 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0045] Example 5 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 2% by mass of silicon carbide nanoparticles (average particle size 50 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0046] Example 6 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 2% by mass titanium dioxide nanoparticles (average particle size 25 nm) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0047] Example 7 This embodiment provides a method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate, which employs a blending method to form a film and includes the following steps: (1) Dissolve 2% by mass of MXene nanoparticles (sheets) in a polar solvent; (2) Take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the solution obtained in step (1) at a low temperature of -5℃ to mix them, and form a film by casting. (3) The polyamic acid film obtained in step (3) is dried at 100°C for 30 minutes. (4) The dried polyamic acid film is subjected to preliminary thermal imidization treatment at a temperature of 150°C. (5) The polyamic acid film that has undergone preliminary thermal imidization is subjected to a second thermal imidization treatment at a temperature of 200°C to obtain a modified polyimide film with a thickness of 75 μm. (6) A laser is used to scan and irradiate the modified polyimide film. The laser density is 0.8 J / cm² and the scanning speed is 150 mm / s. The modified polyimide film is surface treated to form microcrack / micropore structure on the surface of the modified polyimide film, which improves the adhesion of metal conductive lines or functional sensing materials on the modified polyimide film. The high efficiency absorption and photothermal conversion effect of laser-sensitive inorganic nanoparticles uniformly dispersed in the modified polyimide film reduce the thermal impact of laser-induced modification.

[0048] Comparative Example 1 This embodiment provides a method for preparing a polyimide-based thin film without laser-sensitive inorganic nanoparticles. The film is prepared by a blending method and includes the following steps: (1) Take diamine monomers and dianhydride monomers in an organic solvent and form a film by casting; (2) The polyamic acid film obtained in step (1) is dried at 100°C for 30 minutes. (3) The dried polyamic acid film was subjected to thermal imidization treatment to obtain a polyimide-based film with a thickness of 75 μm; (4) The polyimide film was scanned and irradiated with an ultraviolet nanosecond laser (355 nm) at a laser density of 1.5 J / cm² and a scanning speed of 100 mm / s.

[0049] Comparative Example 2 This embodiment provides a method for preparing a polyimide-based thin film coated with zinc oxide, which uses a blending method and includes the following steps: (1) Take diamine monomers and dianhydride monomers in an organic solvent and form a film by casting; (2) The polyamic acid film obtained in step (1) is dried at 100°C for 30 minutes. (3) The dried polyamic acid film was subjected to thermal imidization treatment to obtain a polyimide-based film with a thickness of 75 μm; (4) A ZnO nanoparticle dispersion was spin-coated onto the surface of a polyimide-based film and dried to form a coating with a thickness of about 80 nm. (5) The polyimide film was scanned and irradiated with an ultraviolet nanosecond laser (355 nm) at a laser density of 0.6 J / cm² and a scanning speed of 150 mm / s.

[0050] The performance of the polyimide-based film materials prepared in Examples 1-7 and Comparative Examples 1-6 was tested: Table 1 Performance parameters of polyimide-based film materials in various embodiments and comparative examples

[0051] Peel strength: According to ASTM D903 standard, a 90° peel test was performed on a universal testing machine, and the copper layer thickness was approximately 18μm (due to the thickening effect of chemical copper plating).

[0052] Bending test: Cyclic bending tester, bending radius 2 mm, frequency 1 Hz, peel strength was retested after 100,000 cycles.

[0053] Heat-affected zone: The width of the microstructure change zone in the cross section was observed using scanning electron microscopy (SEM), and the extent of structural damage was defined by Raman spectroscopy.

[0054] Microstructure depth: Surface roughness Rz and average pit depth were measured using laser confocal microscopy.

[0055] Comparative Example 1 is a pure polyimide film without laser-sensitive inorganic nanoparticles, which was treated with a UV nanosecond laser (355 nm), energy density of 1.5 J / cm², scanning speed of 100 mm / s, peel strength (for electroplated copper, ASTM D903): 0.52 N / mm, peel strength retention rate after 100,000 bends (bending radius of 2 mm): 48%, heat-affected zone (nanosecond laser): approximately 2.5 μm.

[0056] Comparative Example 2: ZnO nanoparticle dispersion was spin-coated onto the surface of a polyimide film. After drying, a coating with a thickness of about 80 nm was formed. The coating was then treated with a UV nanosecond laser with an energy density of 0.6 J / cm² (due to the low absorption threshold of the coating). The peel strength was 0.87 N / mm. After 100,000 bends, the peel strength retention rate was 51% (the coating peeled off in some areas). The heat-affected zone after laser treatment was about 1.8 μm.

[0057] In Examples 1-3, the nanoparticles were all ZnO (average particle size 50 nm), and the laser conditions were the same as those in Comparative Example 1 (energy density 0.8 J / cm², scanning speed 150 mm / s). The peel strength of all examples was >1.6 N / mm, the bending retention rate was >85%, and the heat-affected zone was reduced by more than 4 times compared with Comparative Example 1.

[0058] The preparation conditions for Examples 4-7 were the same as above, and the laser energy density was finely adjusted according to the particle photothermal efficiency (0.7-0.9 J / cm²). The peel strength of all examples was >1.6 N / mm, the bending retention rate was >85%, and the heat-affected zone was reduced by more than 4 times compared with Comparative Example 1.

[0059] The above embodiments and comparative data show that the present invention can achieve a peel strength increase of more than 3 times at an extremely low content of 0.5% to 5% by bulk doping with laser-sensitive inorganic nanoparticles. At the same time, it has excellent bending durability and a very small heat-affected zone, and is applicable to a variety of nanoparticles, with good process versatility.

[0060] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A COF flexible substrate-based electrodermal sensing integrated electronic skin, characterized in that: The device comprises a COF flexible substrate, a sensing layer, a chip layer, and a packaging layer. The COF flexible substrate includes a modified polyimide film substrate and a driving circuit layer. Laser-sensitive inorganic nanoparticles are uniformly dispersed within the modified polyimide film substrate. Laser-induced laser-sensitive inorganic nanoparticles form microporous circuit mounting positions on the modified polyimide film substrate. The driving circuit layer is disposed on the circuit mounting positions to ensure the connection strength between the driving circuit layer and the modified polyimide film substrate. The sensing layer and the chip layer are both disposed on the driving circuit layer. The packaging layer covers the outer periphery of the COF flexible substrate, the sensing layer, and the chip layer. 2.The COF flexible substrate-based sensory and computing integrated electronic skin of claim 1, wherein: The laser-sensitive inorganic nanoparticles are one or more of silicon dioxide, silicon carbide, titanium oxide, zinc oxide, or MXene, and the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%.

3. A preparation method of a COF flexible substrate-based sensing and computing integrated electronic skin, characterized in that: Includes the following steps: (1) Dissolve laser-sensitive inorganic nanoparticles in a polar solvent, take diamine monomers and dianhydride monomers in an organic solvent, and slowly add the laser-sensitive inorganic nanoparticle solution at a low temperature of -5℃ to 5℃ to mix, and form a film by casting. (2) The polyamic acid film is dried and then subjected to gradient thermal imidization to obtain a modified polyimide film. (3) A laser is used to scan and irradiate the modified polyimide film to perform surface treatment on the modified polyimide film, forming a microcrack / micropore structure on the surface of the modified polyimide film. The efficient absorption and photothermal conversion effect of the laser by the nanoparticles uniformly dispersed in the modified polyimide film is utilized to reduce the thermal impact of laser-induced modification and obtain a COF flexible substrate layer. (4) A driving circuit layer is formed in the laser irradiation area of ​​the modified polyimide film; (5) The chip is flip-chip soldered onto the driver circuit layer; (6) Integrate the sensing elements on the drive circuit layer; (7) A flexible polymer is used to form a packaging layer that includes the chip and sensing elements.

4. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (1), the mass fraction of the laser-sensitive inorganic nanoparticles is 0.5% to 5%, and the laser-sensitive inorganic nanoparticles are one or more of silicon dioxide, silicon carbide, titanium dioxide, zinc oxide or MXene. The laser-sensitive inorganic nanoparticles are added before the polymerization reaction of diamine monomers and dianhydride monomers, or after the polymerization reaction of diamine monomers and dianhydride monomers is completed.

5. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (2), the drying temperature of the drying treatment is 80-100℃ and the drying time is 30-60 minutes. The gradient thermal imidization includes a primary thermal imidization treatment at a thermal imidization temperature of 120-180℃ and a secondary thermal imidization treatment at a thermal imidization temperature of 180-220℃.

6. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (3), the modified polyimide film is surface treated with an ultraviolet nanosecond laser or a femtosecond laser, with a laser density of 0.7 to 0.9 J / cm² and a scanning speed of 100 to 150 mm / s.

7. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (4), a semiconductor-grade flip-chip thin film process is used to form the driving circuit layer. Specifically, a copper seed layer is sputtered on the modified polyimide thin film substrate, and then photolithography and pattern electroplating are performed to create a copper line with a line width and line spacing of only 10 micrometers. Finally, a nickel-gold protective film is chemically plated on the copper line to improve solderability and oxidation resistance.

8. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (5), the gold-tin eutectic welding technology is used to weld the chip. Specifically, gold-tin bumps are prefabricated on the modified polyimide film substrate, the chip is precisely aligned using flip-chip welding equipment, and a certain pressure is applied to the chip while the temperature is rapidly increased to the peak temperature to complete the gold-tin fusion interconnection. Then, the chip is cooled at a rate of 10-20℃ / s to form a high-strength intermetallic compound solder joint.

9. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (6), the sensing element is formed by depositing functional ink onto a modified polyimide film substrate using a piezoelectric nozzle from an inkjet printer, aerosol jet printer, or electrohydrodynamic printer. Then, the substrate is sintered at 80–150°C using a hot plate or photonics for 30 minutes to allow the solvent to evaporate, the functional material to crosslink or sinter, and a sensing microstructure integrated with the bottom electrode is directly constructed at the target location.

10. The method for fabricating an integrated electronic skin for sensing and computing based on a COF flexible substrate according to claim 3, characterized in that: In step (7), the flexible polymer is one or more of polydimethylsiloxane, platinum-catalyzed silicone rubber, polyurethane elastomer, parylene, silicone gel or flexible epoxy resin, and the encapsulation layer is an encapsulation layer with a thickness of 50 to 500 μm formed by spin coating, molding or vapor deposition.

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