In-mold electronic integration structure and method of intelligent surface

Abstract

The invention relates to the field of electronic integration structures, discloses an in-mold electronic integration structure and method of an intelligent surface, and aims to solve the problems of large circuit printing positioning error, low interface bonding strength and poor compatibility between a bio-based material and electronic integration in the prior art. The method comprises the following steps: precisely printing a silver nanowire capacitor matrix on the surface of a cavity of an injection mold and carrying out hot air curing; covering the cured circuit pattern with an IMD functional film containing an electrochromic layer, and performing staged pressing after vacuum adsorption positioning; ultraviolet laser is used for drilling, and a micro LED array and a lead zirconate titanate piezoelectric feedback unit are mounted in a through hole in a surface mounting manner. According to the technical scheme, ultrahigh process integration precision and reliability can be achieved, the problem of compatibility of bio-based materials and electronic integration is solved, and excellent multifunctional interaction performance is provided.

Description

Technical Field

[0001] This invention belongs to the field of electronic integrated structure technology, specifically relating to an in-mold electronic integrated structure and method for an intelligent surface. Background Technology

[0002] With the rapid development of smart cockpits and human-computer interaction technologies, automotive interior surfaces are evolving from traditional decorative functions to intelligent interfaces integrating perception, display, and feedback. As a key carrier integrating electronic functions and aesthetic design, smart surfaces require manufacturing processes that simultaneously meet multiple stringent requirements, including high-precision circuit integration, multi-material composite molding, and environmental reliability. Current mainstream smart surface manufacturing solutions mainly include film embedding molding (FIM), in-mold decoration (IMD), and post-installation of electronic modules. However, these methods still face significant bottlenecks in achieving high-density electronic integration and structural integration.

[0003] Among these technologies, In-Mold Electronic Integration (IME) is considered the most promising solution because it allows flexible circuits to be directly embedded inside injection-molded parts. Its core lies in constructing functional electronic patterns on the surface of the mold cavity and then integrating them with functional film layers through hot pressing or injection molding. However, existing IME processes generally suffer from insufficient positioning accuracy, low interface bonding strength, and poor circuit impedance stability, making it difficult to reliably integrate high-resolution touchscreens, micro-optoelectronic devices, and piezoelectric feedback units. These shortcomings are further amplified in automotive-grade applications, where the requirements for temperature cycling, mechanical vibration, and long-term bending durability exacerbate these deficiencies.

[0004] In existing technologies, silver nanowire printing often suffers from large linewidth fluctuations and node spacing deviations exceeding ±0.2mm due to improper matching of screen mesh count, squeegee angle, and printing speed, resulting in a decrease in touch signal-to-noise ratio. If the lamination process of the IMD functional film and substrate is not effectively controlled in terms of venting and the melting interface state, bubbles or delamination are easily generated, making it difficult to achieve a bonding strength exceeding 5MPa. Furthermore, insufficient laser drilling precision or hole misalignment severely affects the mounting yield of micro-LEDs and PZT units. Traditional bio-based materials, due to their strong insulation properties, cannot directly support precision circuits, forcing the introduction of additional conductive layers in the process, increasing cost and thickness. These problems are particularly prominent in next-generation intelligent interior systems that pursue lightweight, environmentally friendly, and highly interactive performance, urgently requiring a new in-mold electronics manufacturing method that combines high precision, high strength, low environmental impact, and supports the direct integration of multifunctional devices. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an intelligent surface substrate for automotive interiors and its preparation method, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for in-mold electronic integration of an intelligent surface includes the following steps:

[0008] Step S1: Print a nano-silver wire capacitor matrix on the surface of the injection mold cavity to form a circuit pattern with a preset line width and node spacing, and perform hot air curing treatment on the circuit pattern.

[0009] Step S2: Cover the cured circuit pattern with the IMD functional film containing the electrochromic layer, and perform staged pressing after positioning by vacuum adsorption to achieve interface fusion of the functional film, circuit pattern and mold cavity to form a composite structure.

[0010] Step S3: Use an ultraviolet laser to drill through holes of a preset diameter on the fused composite structure, and attach a micro LED array and a lead zirconate titanate piezoelectric feedback unit in the through holes to complete the in-mold integrated manufacturing of the intelligent surface.

[0011] Furthermore, in step S1, the injection mold comprises the following components by weight: 50-70 wt% polylactic acid resin; 15-45 wt% reinforcing phase; 5-8 wt% conductive filler; 8-12 wt% toughening agent; and 0.5-1.5 wt% hydrolysis resistant agent. The reinforcing phase is alkali-treated hemp fiber, the conductive filler is carbon fiber fragments, the toughening agent is ethylene-methyl acrylate-glycidyl methacrylate, and the hydrolysis resistant agent is carbodiimide. The injection mold material has a surface sheet resistance of less than 5 Ω, thus overcoming the shortcomings of traditional materials that have strong insulation but cannot directly support precision circuits, supporting direct printing and integration of circuits with linewidths of 50 μm.

[0012] Furthermore, in step S1, the precision printing of the nano-silver wire capacitor matrix on the surface of the injection mold cavity specifically includes: using a 250 mesh screen, setting the squeegee angle to 70°, and performing the squeegee printing operation of the nano-silver wire conductive paste at a constant printing speed of 10mm / s. The line width of the circuit pattern is within 40-60μm, the node spacing is 5.0±0.1mm, and the positioning error is ±0.05mm.

[0013] Furthermore, in step S1, the hot air curing process for the circuit pattern specifically involves placing the printed mold cavity in a hot air circulation environment at 80-90℃ for 5-10 minutes. This curing process allows the organic solvents in the nano-silver wire paste to fully evaporate, and the silver wire network forms a stable conductive path. After curing, the change rate of the circuit impedance relative to the initial design value is less than 1%, ensuring the stability and consistency of subsequent capacitive touch signal acquisition.

[0014] Furthermore, in step S2, the vacuum adsorption positioning specifically involves: after the IMD functional film is laid flat on top of the circuit pattern in the mold cavity, the vacuum system is activated to create a vacuum of -95 kPa between the mold cavity and the functional film. This negative pressure environment allows the functional film to adhere tightly to the surface of the mold cavity, eliminating initial gaps and limiting the planar displacement error of the functional film relative to the circuit pattern to the micrometer level, providing precise initial positioning for subsequent pressing.

[0015] Furthermore, in step S2, the staged pressing specifically includes the following steps: First, a uniform pressure of 20 MPa is applied at ambient temperature and maintained for 30 seconds to expel residual air between the functional film and the mold cavity and circuit pattern interface; second, under heating conditions of 150°C, the pressure is increased to 120 MPa and maintained for 60 seconds to bond the IMD functional film to the silver nanowire circuit and the mold cavity surface. The above steps ensure that the interfacial bonding strength between the functional film and the silver nanowire circuit and mold cavity exceeds 8 MPa.

[0016] Furthermore, in step S3, the ultraviolet laser drilling specifically involves using a 355nm ultraviolet laser to drill through holes with a diameter of 100±5μm at preset positions at a processing speed of 200 holes per second. The cold processing characteristics of ultraviolet lasers can effectively avoid damage to surrounding circuits and functional films caused by the heat-affected zone, and the positional accuracy of the holes is controlled within ±8μm, ensuring the precise mounting of micro-devices.

[0017] Furthermore, in step S3, mounting the micro-LED array specifically involves precisely mounting micro-LED chips with a pixel density of not less than 120 PPI onto the laser-drilled through-holes using conductive adhesive or reflow soldering, and electrically connecting them to the underlying circuitry printed in step S110. The brightness of the micro-LEDs is not less than 1000 nits to ensure sufficient visibility even in bright automotive lighting conditions.

[0018] Furthermore, in step S3, mounting the lead zirconate titanate (PZT) piezoelectric feedback unit specifically involves mounting a PZT piezoelectric sheet with an adjustable resonant frequency within the range of 50-200Hz at a designated through-hole location. When the capacitive matrix detects a touch signal, the control unit drives the PZT piezoelectric sheet to operate near its resonant frequency, generating perceptible mechanical vibration feedback with a feedback force of up to 1.55N, thereby providing a clear tactile interactive response.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. Achieved ultra-high process integration precision and reliability. Through precise matching of 250-mesh screen, 70° squeegee, and 10mm / s speed, the circuit printing positioning error was controlled within ±0.05mm, far superior to the ±0.2mm level of existing technologies. Through vacuum adsorption and two-stage pressing processes, the interfacial bonding strength between the IMD functional film and the substrate exceeded 8MPa, significantly higher than the bottleneck of existing technologies that are generally below 5MPa, ensuring long-term reliability in automotive-grade environments.

[0021] 2. Overcame the challenge of compatibility between bio-based materials and electronic integration. By introducing recycled carbon fiber fragments to construct conductive paths, the surface sheet resistance of PLA / hemp fiber composite materials was reduced to below 5Ω, allowing them to be directly used as substrates for precision circuits. This eliminates the need for additional insulating or conductive layers, achieving both environmental friendliness and lightweight design while ensuring excellent electronic compatibility.

[0022] 3. It offers superior multi-functional interactive performance. The integrated high-precision capacitive matrix supports high recognition rate and low latency touch operation, including stable operation under gloves and strong light conditions; combined with an electrochromic layer with adjustable transmittance, a high pixel density micro-LED array, and a frequency-tunable PZT piezoelectric feedback unit, it achieves deep integration of visual display, tactile feedback, and environmental adaptive adjustment, meeting the requirements of the next-generation smart cockpit for high-interactive surfaces.

[0023] 4. It possesses significant advantages in both economy and durability. The raw material cost of the bio-based composite material is 53% lower than that of traditional carbon fiber composite materials; after the integrated electronic system passes 100,000 bending tests (ISO 6722), the circuit resistance change rate is only 2.8%, demonstrating excellent mechanical durability and signal stability, and reducing the total life cycle usage and maintenance costs. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of the in-mold electronic integration structure of the intelligent surface in this invention.

[0025] Explanation of reference numerals in the attached figures: 1, substrate layer; 2, silver nanowire capacitor matrix layer; 3, IMD functional film layer; 4, photoelectric surface layer. Detailed Implementation

[0026] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments according to the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0027] Example

[0028] This embodiment provides an in-mold electronics integration method for intelligent surfaces, including the following steps:

[0029] Step S1: Print a nano-silver wire capacitor matrix on the surface of the injection mold cavity to form a circuit pattern with a preset line width and node spacing, and perform hot air curing treatment on the circuit pattern.

[0030] Specifically, in this embodiment, the substrate material of the injection mold cavity comprises the following components by weight: 50-70 wt% polylactic acid resin; 15-45 wt% reinforcing phase; 5-8 wt% conductive filler; 8-12 wt% toughening agent; and 0.5-1.5 wt% hydrolysis resistant agent. The specific composition is 52 wt% polylactic acid resin; 33 wt% reinforcing phase; 7 wt% conductive filler; 8 wt% toughening agent; and 1 wt% hydrolysis resistant agent. The reinforcing phase is alkali-treated hemp fiber, the conductive filler is carbon fiber fragments, the toughening agent is ethylene-methyl acrylate-glycidyl methacrylate, and the hydrolysis resistant agent is carbodiimide. The substrate material has a measured density of 1.18 g / cm³, a tensile strength of 61 MPa, a notched impact strength of 53 kJ / m², a surface sheet resistance of 4.3 Ω, and a heat distortion temperature of 86℃. Its performance fundamentally overcomes the inherent defects of bio-based materials, which cannot directly support precision circuits due to their strong insulation and poor strength. This allows precision circuits with a linewidth of 50 μm to be stably printed and integrated directly on its surface without the need for additional insulating or conductive layers, simplifying the process, reducing costs, and improving environmental friendliness.

[0031] In the actual printing process, a 250 mesh screen is used as the printing template. The mesh size of this screen matches the particle size of the nano-silver wire conductive paste, ensuring that the paste can pass smoothly and form uniform lines. The squeegee angle is set to 70°, which facilitates the paste being fully squeezed through the mesh during the printing process, while reducing the dragging effect on the already printed pattern. During the printing process, the squeegee is controlled to perform unidirectional squeegee operation at a constant speed of 10mm / s. This speed parameter, together with the paste viscosity, screen tension, and squeegee pressure, ensures that the nano-silver wire conductive paste is uniformly and continuously transferred to the mold cavity surface. The final printed circuit pattern has a linewidth of 52μm, and the spacing between each capacitor node in the pattern is precisely controlled within 5mm, with a tolerance of only ±0.1mm. More importantly, the positioning error of the entire circuit pattern relative to the pre-set geometric reference of the mold cavity is strictly limited to within ±0.05mm. This level of precision is far higher than the ±0.2mm error range commonly found in existing technologies, laying a crucial foundation for the precise alignment of subsequent functional films and the accurate mounting of micro-devices.

[0032] Immediately after printing, the circuit enters the hot air curing stage. The mold cavity carrying the uncured circuit pattern is transferred to a hot air circulation curing device. The curing temperature is set to 80℃ and maintained at this temperature for 10 minutes. 80℃ is sufficient to allow the organic solvents and dispersants in the conductive paste of the silver nanowires to fully evaporate, but it is not too high, which would cause excessive agglomeration of the silver nanowires in the paste or thermal deformation of the substrate material. After the curing process, the circuit performance needs to be tested. The test results show that the DC impedance of the cured circuit changes by less than 1% relative to the initial theoretical design value. This extremely low impedance change rate indicates that the curing process successfully stabilized the conductivity of the circuit, ensuring the stability of signal acquisition and consistency between nodes when used as a capacitive touch sensor, avoiding touch signal drift or misjudgment caused by impedance unevenness.

[0033] Step S2: Cover the cured circuit pattern with the IMD functional film containing the electrochromic layer, and perform staged pressing after positioning by vacuum adsorption to achieve interface fusion of the functional film, circuit pattern and mold cavity to form a composite structure.

[0034] Specifically, the IMD functional film containing an electrochromic layer is a pre-prepared multilayer composite film. Its structure includes at least: an outermost polycarbonate substrate layer, a middle electrochromic functional layer, and an innermost hot melt adhesive layer or protective coating. The electrochromic functional layer is a key functional layer; when different DC voltages are applied to it, a reversible electrochemical oxidation-reduction reaction occurs within the layer, causing a change in its optical absorption characteristics, thereby achieving continuous adjustment of its transmittance. In this embodiment, the functional layer is a 0.3mm IMD-PC film, and the transmittance of the electrochromic layer can be adjusted within a wide range of 15-75%, providing the intelligent cockpit with dynamic environmental adaptive adjustment capabilities.

[0035] During vacuum adsorption positioning, the pre-cut IMD functional film is laid flat above the surface of the mold cavity where the circuit printing has been completed, ensuring that it roughly covers the target area. Subsequently, the vacuum system extracts air between the functional film and the cavity surface through a pre-set micro-pore array on the back of the mold cavity, rapidly creating a negative pressure environment in this sealed space. In this embodiment, this negative pressure value is stably maintained at -95 kPa, allowing the IMD functional film to be uniformly and tightly adsorbed and adhered to the mold cavity surface and the circuit pattern. This process not only eliminates initial installation gaps but also limits the displacement error of the functional film relative to the precision-printed circuit pattern below in the planar direction to the micrometer level, providing a perfect starting point for subsequent lamination processes and avoiding short circuits, functional layer misalignment, or appearance defects caused by alignment deviations.

[0036] After precise positioning via vacuum adsorption, a staged pressing process is immediately performed. This process consists of two consecutive steps. The first step is degassing pressing: the mold and the entire IMD functional membrane are kept at ambient temperature, and the pressing equipment applies a uniform pressure of 20 MPa to the surface of the functional membrane and maintains this pressure for 30 seconds. Using this uniform high pressure, the trace amounts of air remaining between the hot melt adhesive layer of the functional membrane and the surface of the mold cavity, as well as between the functional membrane and the nano-silver wire circuit, are thoroughly expelled.

[0037] The second stage is fusion bonding: the temperature of the interface between the mold and the functional membrane is rapidly increased and stabilized at 150°C, while the applied pressure is increased from 20MPa to 120MPa and maintained at this temperature and pressure for 60 seconds. Under the synergistic effect of temperature and pressure, molecular-level diffusion, entanglement, and chemical bonding occur between the material of the functional membrane, the mold substrate material, and the coupling agent on the surface of the silver nanowires. After bonding, the membrane is cooled and shaped, and the interfacial bonding strength is tested according to the international standard ISO8510-2, with a result exceeding 8MPa. This strength value is significantly higher than the bonding strength of existing technologies, which is generally below 5MPa. This means that the composite structure can withstand the harsh thermal cycling, vibration, and impact stresses in the smart cockpit environment, ensuring long-term reliability in automotive-grade environments.

[0038] Step S3: Use an ultraviolet laser to drill through holes of a preset diameter on the fused composite structure, and attach a micro LED array and a lead zirconate titanate piezoelectric feedback unit in the through holes to complete the in-mold integrated manufacturing of the intelligent surface.

[0039] Specifically, ultraviolet laser drilling is an ideal process for achieving micron-sized through-holes without damaging surrounding sensitive structures. A 355nm ultraviolet laser is used, and the laser processing path and through-hole position are controlled by a computer numerical control system. At a processing speed of 200 holes / s, micro-through-holes are drilled on the composite structure at preset coordinate points corresponding to the future installation of micro-LEDs and piezoelectric units, penetrating the functional film layer and exposing the underlying silver nanowire circuit pads. In this embodiment, the through-hole diameter is 102μm, with a positional accuracy of ±8μm.

[0040] After drilling, the micro-LED array and lead zirconate titanate (PZT) piezoelectric feedback unit need to be mounted. In this embodiment, the micro-LED array uses Samsung ML0806 micro-LEDs with a pixel density ≥120 PPI and a brightness of 1000 nits. The lead zirconate titanate (PZT) piezoelectric feedback unit is a PZT-5H piezoelectric sheet with a feedback force of 1.55N. Before mounting, a layer of conductive adhesive or solder paste needs to be pre-coated or printed on the bottom of the laser-drilled through-hole, i.e., on the exposed nano-silver wire circuit pads. Using a pick-and-place machine, the micro-LED array is precisely picked up and placed into the through-hole, aligning its electrodes with the bottom circuit pads.

[0041] The mounted lead zirconate titanate piezoelectric feedback unit provides physical confirmation for touch operations, enhancing the interactive experience. This piezoelectric feedback unit uses a lead zirconate titanate piezoelectric ceramic sheet, whose resonant frequency can be adjusted within the range of 50-200Hz through design dimensions and electrodes. The mounting process is similar to that of a miniature light-emitting diode, where the piezoelectric sheet is mounted at a laser-guided via specifically designed for feedback and connected to the underlying control circuitry via conductive bonding material. This completes the integrated manufacturing process.

[0042] Through the precise execution of the above steps, the final fabricated intelligent surface in-mold electronic integration structure is shown in the attached figure. Figure 1 As shown, the structure includes a substrate layer 1, a silver nanowire capacitor matrix layer 2, an IMD functional film layer 3, and a photoelectric surface layer 4, arranged in that order. After 1000 interactive tests, the above structure showed the following results: single-finger touch recognition rate of 99.1%, response latency of 38ms, and false trigger rate due to environmental interference of 0.07%; two-finger swipe recognition rate of 98.3%, latency of 45ms, and false trigger rate of 0.12%; recognition rate of 97.5% with gloves on, latency of 51ms; and a recognition rate of 98.8% with a latency of 41ms even under strong light.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method of in-mold electronics integration for an intelligent surface, the method comprising: Includes the following steps: ​ Step S1: Print a nano-silver wire capacitor matrix on the surface of the injection mold cavity to form a circuit pattern with a preset line width and node spacing, and perform hot air curing treatment on the circuit pattern. Step S2: Cover the cured circuit pattern with the IMD functional film containing the electrochromic layer, and perform staged pressing after positioning by vacuum adsorption to achieve interface fusion of the functional film, circuit pattern and mold cavity to form a composite structure. Step S3: Use an ultraviolet laser to drill through holes of a preset diameter on the fused composite structure, and attach a micro LED array and a lead zirconate titanate piezoelectric feedback unit in the through holes to complete the in-mold integrated manufacturing of the intelligent surface.

2. The method for in-mold electronic integration of intelligent surfaces according to claim 1, characterized in that: In step S1, the injection mold comprises the following components by weight: 50-70 wt% polylactic acid resin; 15-45 wt% reinforcing phase; and 5-8 wt% conductive filler. 8-12wt% toughening agent; 0.5-1.5wt% hydrolysis resistant agent, wherein the reinforcing phase is alkali-treated hemp fiber, the conductive filler is carbon fiber fragments, the toughening agent is ethylene-methyl acrylate-glycidyl methacrylate, and the hydrolysis resistant agent is carbodiimide.

3. The method for in-mold electronic integration of intelligent surfaces according to claim 2, characterized in that: In step S1, the precision printing of the nano-silver wire capacitor matrix on the surface of the injection mold cavity specifically includes: using a 250 mesh screen, setting the squeegee angle to 70°, and performing the squeegee printing operation of the nano-silver wire conductive paste at a constant printing speed of 10mm / s. The line width of the circuit pattern is within 40-60μm, the node spacing is 5.0±0.1mm, and the positioning error is ±0.05mm.

4. The method for in-mold electronic integration of intelligent surfaces according to claim 3, characterized in that: In step S1, the hot air curing process for the circuit pattern specifically involves placing the printed mold cavity in a hot air circulation environment at 80-90℃ and curing it continuously for 5-10 minutes.

5. The method for in-mold electronic integration of intelligent surfaces according to claim 1, characterized in that: In step S2, the vacuum adsorption positioning specifically involves: after the IMD functional film is laid flat on the circuit pattern of the mold cavity, the vacuum system is activated to create a vacuum of -95 kPa between the mold cavity and the functional film.

6. The method for in-mold electronic integration of intelligent surfaces according to claim 5, characterized in that: In step S2, the staged pressing specifically includes the following steps: First, apply a uniform pressure of 20 MPa at ambient temperature and hold for 30 seconds to expel the residual air between the functional film and the mold cavity and circuit pattern interface; second, under the heating condition of 150°C, increase the pressure to 120 MPa and hold for 60 seconds to bond the IMD functional film with the nano-silver wire circuit and the surface of the mold cavity.

7. The method for in-mold electronic integration of intelligent surfaces according to claim 1, characterized in that: In step S3, drilling with ultraviolet laser specifically involves using an ultraviolet laser with a wavelength of 355nm to drill through holes with a diameter of 100±5μm at a preset position at a processing speed of 200 holes per second.

8. The method for in-mold electronic integration of intelligent surfaces according to claim 7, characterized in that: In step S3, mounting the micro LED array specifically involves precisely mounting micro LED chips with a pixel density of not less than 120 PPI onto the laser-drilled through-holes using conductive adhesive or reflow soldering, and electrically connecting them to the underlying circuitry printed in step S110.

9. The method for in-mold electronic integration of intelligent surfaces according to claim 8, characterized in that: In step S3, mounting the lead zirconate titanate piezoelectric feedback unit specifically involves mounting a PZT piezoelectric sheet with an adjustable resonant frequency in the range of 50-200Hz onto the designated through-hole position.

10. The intelligent surface in-mold electronic integration structure prepared by the integration method according to any one of claims 1-9, characterized in that: The integrated structure includes a substrate layer, a silver nanowire capacitor matrix layer, an IMD functional film layer, and a photoelectric surface layer arranged in that order. The substrate layer has a thickness of 1.5±0.2mm, the sheet resistance of the silver nanowire capacitor matrix layer is 4.5±0.3Ω, and the photoelectric surface layer has an integrated micro-LED matrix and a piezoelectric element.

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