A method of in-mold injection molding a pi printed circuit with a pre-welded sensor

Abstract

The application discloses a PI printed circuit in-mold injection molding method of a pre-welded sensor, which comprises the following steps: first, carrying out partitioned differential interface modification on a PI film; then, printing and forming a conductive circuit on the surface of the PI film by using a composite conductive ink, and synchronously and homologously printing a microporous elastic cladding layer as a solder pad buffer coupling structure; after the sensor is welded and fixed on the circuit solder pad, directional cross-linking is carried out to reinforce the buffer structure, and multi-phase stress pre-equalization setting is carried out on the PI base, the conductive circuit and the sensor pin, so that a single-film unit is obtained by cutting; then, IME in-mold injection is completed by means of mold partitioned negative pressure positioning and fluid isolation gradient shunting, and a graded pressure maintaining cooling forming plastic substrate is matched, and finally, a finished product is obtained through multi-dimensional closed-loop nondestructive testing. By adopting the homologous and homogeneous buffer structure and cooperating with whole-process stress linkage regulation and control, the problems of heterogeneous reinforcement thermal expansion mismatch, injection melt impact on the solder pad and film layer delamination cracking are solved, and the injection packaging yield of the sensor and the long-term use reliability are improved.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit manufacturing technology, and particularly relates to an in-mold integrated injection molding method for a pre-welded sensor PI printed circuit. Background Technology

[0002] Flexible PI circuit integrated sensors, packaged in-mold through injection molding, are widely used in smart wearables, automotive sensing, and home appliance touch control. This structure embeds the printed circuit and sensing element within a plastic substrate, offering advantages in both thinness and structural integration. The current mainstream manufacturing process involves: uniformly activating and modifying the polyimide film, printing conductive lines, and then surface-mounting and soldering the sensor. Additional reinforcing films and epoxy resin are applied to buffer and protect the solder pads and solder joints. After leveling, the sensor is directly placed into a mold using a standard runner for injection molding. Only the continuity performance of the circuit is tested after molding.

[0003] The core weakness of the existing process stems from the inherent defects in the underlying buffer protection mechanism: the solder joint protection relies entirely on heterogeneous reinforcing materials that are different from the circuit and PI substrate materials. The thermal expansion coefficients of various materials differ significantly. Under high and low temperature cycling conditions, the heterogeneous interface continuously generates shear stress, which can easily cause micro-cracks, poor solder joints, and open circuits in the long term. At the same time, during the injection molding stage, the high-pressure molten plastic directly washes over the solder pad area without a dedicated buffer pressure relief structure, resulting in a high rate of solder joint failure due to impact.

[0004] To alleviate the aforementioned problems, two fragmented improvement approaches have emerged in existing technologies: one is to adjust the injection molding channel to optimize filling uniformity, and the other is to add a film leveling process to release the underlying internal stress of the film. However, neither type of improvement can solve the problem at its root: optimizing the flow channel only slightly reduces melt impact and cannot eliminate the temperature-induced shear stress caused by heterogeneous reinforcement; leveling the film only releases the stress of the substrate alone and cannot meet the stress matching requirements of the multi-phase medium of the solder pads, ink, and metal pins. Furthermore, the industry generally believes that conductive ink is only used for conductive transmission and cannot serve as a stress buffer carrier. There is no integrated process solution that utilizes the same source ink of the circuit to form an integral buffer structure, coupled with interface partition modification, directional cross-linking reinforcement, multi-phase stress pre-equilibrium, fluid isolation injection molding, and closed-loop detection. Various individual improvement methods are independent of each other and lack process linkage and coordination. The injection molding impact stress, welding residual stress, and thermal deformation stress continue to accumulate, making the finished product prone to substrate warping, film layer delamination, and hidden solder joint defects. At the same time, the additional reinforcement process increases production steps and alignment errors, resulting in low mass production efficiency and high overall production costs. Summary of the Invention

[0005] The purpose of this invention is to provide an in-mold injection molding method for pre-welded sensor PI printed circuits to solve the problems mentioned in the background art.

[0006] In view of this, the present invention provides an in-mold injection molding method for pre-welded sensor PI printed circuit, comprising the following process steps:

[0007] S1. Differentiated interface modification of polyimide film is performed in different regions, and an integrated conductive circuit is prepared on the surface of the modified film using composite conductive ink to obtain a partitioned modified printed circuit PI film.

[0008] S2. Relying on composite conductive ink of the same origin as the conductive circuit, the solder joint buffer coupling structure surrounding the sensor solder pad is formed synchronously.

[0009] S3. Assemble the sensor components and metallurgically weld them to the pads, and then perform band-directed ultraviolet low-temperature interface cross-linking reinforcement on the solder joint buffer coupling structure.

[0010] S4. Perform full-domain multiphase dielectric synergistic stress pre-equilibrium shaping on the composite diaphragm carrying the sensor element, including three types of media: polyimide substrate, composite conductive ink circuit layer, and sensor metal pins, and cut to obtain standardized single-piece diaphragm units.

[0011] S5. Position the single-film unit inside the injection mold cavity and complete the in-mold integrated injection molding encapsulation by using a fluid isolation gradient flow filling method.

[0012] S6. Perform multi-dimensional synchronous closed-loop non-destructive testing on the injection-molded substrate to obtain an in-mold electronic substrate with integrated sensors.

[0013] In a further embodiment of the present invention, the polyimide film partitioning differential interface modification further includes: pre-dividing spatially isolated, non-overlapping circuit trace partitions and sensor pad welding partitions on the surface of the polyimide film;

[0014] Low-extension-stress functional group grafting modification treatment is applied to the circuit trace partition, and high-interface-adhesion functional group grafting modification treatment is applied to the sensor pad soldering partition.

[0015] After modification, composite conductive ink is used to screen print fully connected functional conductive circuits. The conductive circuits fully cover the circuit routing areas and the sensor pad welding areas. After medium-temperature curing and shaping, the partitioned modified printed circuit PI film is formed.

[0016] In a further embodiment of the present invention, the solder joint buffer coupling structure is a microporous elastic coating layer, and the molding process further includes: using the same component composite conductive ink used to prepare conductive circuits, in a single conductive circuit screen printing process, simultaneously forming an integrated microporous elastic coating layer around the outer periphery of each sensor solder pad;

[0017] The microporous elastic coating layer is arranged only in a closed loop around the edge of the pad, completely exposing the pre-set welding contact surface at the center of the pad.

[0018] The microporous elastic coating layer, conductive circuit, and partitioned modified polyimide film are made from the same material and origin, forming a homogeneous integrated microporous coating composite interface without an external adhesive layer.

[0019] In a further embodiment of the present invention, the band-directed ultraviolet low-temperature interface crosslinking reinforcement further includes: precisely aligning and attaching the sensor element pins to the exposed soldering contact surface of the pad, achieving a stable metallurgical bond between the pins and the pad through low-temperature lead-free reflow soldering, and forming a metallurgical bonding interface between the pad and the pins.

[0020] After welding, a band-directed ultraviolet low-temperature interface crosslinking process is adopted, which selectively acts only on the microporous elastic coating layer to achieve crosslinking densification. The crosslinking energy does not penetrate or intrude into the metallurgical bonding interface of the pad pins, and simultaneously dissipates the welding-derived micropores and interface shear residual stress.

[0021] In a further embodiment of the present invention, the global multiphase medium synergistic stress pre-equilibrium shaping further includes: sealing the composite diaphragm that has been welded and cross-linked for reinforcement and integrated with sensor elements in a constant temperature low tension shaping chamber.

[0022] For three types of heterogeneous media with different coefficients of thermal expansion—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—segmented gradient constant temperature static condition is matched and set.

[0023] Simultaneously release the internal stress of the membrane substrate, the stress at the interface of the circuit film layer and the plastic bonding, and the microscopic residual stress at the interface of the metallurgical bonding of the pads and pins. After the stress is balanced, cut along the preset die-cutting line to obtain a standardized single membrane unit with uniform specifications.

[0024] In a further embodiment of the present invention, the injection mold includes a molding cavity that conforms to the shape of a standardized single-piece film unit, and the cavity is integrated with a limiting and accommodating groove for sensor placement.

[0025] After the single membrane unit is laid flat and placed into the cavity, the mold is closed and locked. The cavity is then activated by negative pressure adsorption positioning. The negative pressure adsorption force only acts on the circuit wiring partition to fit the inner wall of the cavity. The sensor element is limited and housed inside the element limiting and avoidance receiving groove, and the diaphragm deformation pull on the solder joint structure is completely isolated.

[0026] In a further embodiment of the present invention, the fluid isolation gradient diversion filling further includes: multiple sets of independent and controllable diversion gates symmetrically arranged along the long side of the mold cavity, a core protection area for the weld points consisting of a limit and avoidance accommodating groove for all plastic melt diversion paths and a microporous elastic coating layer.

[0027] The molten plastic melt sequentially fills the back side of the polyimide film at a low speed, and then fills the side of the composite conductive ink circuit layer by layer. The solder joint and microporous elastic coating area maintain a low-pressure slow-flow melt environment throughout the process, preventing high-pressure and high-temperature melt from directly impacting the metallurgical bonding interface of the solder pad pin.

[0028] In a further embodiment of the present invention, after the plastic melt is filled, a matching two-stage graded pressure holding and cooling process is performed.

[0029] The first stage involves maintaining a constant medium-high temperature and pressure, which promotes the penetration of molten plastic into the pores inside the microporous elastic coating layer, thereby enhancing the mechanical interlocking strength of the microporous coating composite interface.

[0030] The second stage involves linear gradient slow cooling, dynamically matching the thermal shrinkage deformation parameters of the polyimide substrate, the composite conductive ink circuit layer, and the injection-molded plastic. This counteracts the poor deformation of the multi-layer interface and prevents delamination, peeling, and microcracks from occurring at the microporous coating composite interface and the film-plastic bonding interface.

[0031] In a further embodiment of the present invention, the multi-dimensional synchronous closed-loop non-destructive testing further includes: synchronously prefabricating embedded partition detection contacts during the composite conductive ink circuit printing stage, wherein the partition detection contacts are integrally injection molded and embedded inside the plastic substrate along with the membrane unit;

[0032] Finished product testing does not require damaging the packaging structure. It relies on partitioned testing contacts to simultaneously and in parallel complete circuit continuity testing and multi-layer composite interface micro-stress full-domain scanning testing.

[0033] The test data is traced back to match the pre-stress equalization parameters of the membrane unit, forming a closed-loop quality control link that adapts to the thermal-mechanical protection system.

[0034] In a further embodiment of the present invention, the thermal protection system includes a linkage adaptation process: relying on the S1 partition modification to regulate the interfacial bonding force of the membrane material and the S2 homologous microporous elastic coating layer to absorb the instantaneous melt impact force, the micro-weld point buffer interface self-matching is achieved.

[0035] By relying on S4 global pre-stress pre-equilibrium to offset the inherent thermal expansion difference of the three types of media—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—and S5 fluid isolation to weaken the external force disturbance during injection molding, macroscopic multiphase media global stress linkage control is achieved.

[0036] The microscopic buffer deformation allowance and the macroscopic stress relief rate are matched and coordinated throughout the process to achieve the stratified dissipation of injection external force and cold and hot deformation stress.

[0037] The beneficial effects of this invention are:

[0038] 1. In the same process of printing conductive circuits, a microporous elastic coating layer surrounding the solder pads is synchronously formed using a completely homogeneous composite conductive ink. The coating layer, conductive circuits, and modified PI film are all made of the same material, with highly matched thermal expansion deformation. This completely eliminates the need for traditional epoxy adhesives, reinforcing sheets, and other heterogeneous reinforcing materials, preventing continuous shear stress at heterogeneous interfaces under alternating hot and cold temperatures, and significantly extending the thermal shock durability of the solder joints. The microporous structure has its own elastic deformation margin, which can instantly absorb the impact load of the injection molten metal, avoiding direct damage to the metallurgical bonding interface of the solder pads by high-pressure fluids, and significantly reducing the solder joint cracking and scrap rate during the injection molding stage. At the same time, it eliminates multiple independent processes such as dispensing adhesive and attaching reinforcing sheets, eliminates secondary alignment deviations, simplifies the production process, effectively improves production line processing efficiency, and reduces material and labor costs.

[0039] 2. By modifying the interface in different zones, low-extension-stress grafted functional groups are configured for the circuit trace zones, and high-adhesion functional groups are configured for the pad zones. This balances low internal stress in the circuit and high adhesion strength of the buffer coating layer, overcoming the drawback of uniform modification across the entire area which can only compromise parameters, and reducing substrate warping and poor circuit delamination. After soldering, a band-directed ultraviolet low-temperature crosslinking process is used to densify the microporous elastic coating layer only. The crosslinking energy does not penetrate the metallurgical bonding interface of the pad pins. While strengthening the strength of the buffer structure itself, the original solder joint stability is preserved, and the micropores and residual shear stress generated by the soldering process are eliminated simultaneously.

[0040] 3. Before injection molding, the PI substrate, conductive ink circuit, and metal pins are subjected to segmented gradient constant temperature static treatment in a constant temperature and low tension shaping chamber. This process releases the internal stress of the substrate, the curing stress of the ink, and the microscopic residual stress of the solder joints in advance, avoiding the accumulation of multiple stresses that may be introduced into the injection molding process. The mold adopts a fluid isolation gradient flow filling design, with the melt avoiding the solder joint protection zone throughout the process and filling with low pressure and slow flow. Combined with a two-stage graded pressure holding and cooling process, the molten plastic penetrates into the pores of the microporous coating layer to form a mechanical interlocking interface. At the same time, the linear gradient slow cooling matches the shrinkage parameters of the multi-layer materials to offset the interface deformation difference. This eliminates latent failure defects that are difficult to be identified by the naked eye, such as film delamination and interface peeling microcracks, from the source. The pass rate of high and low temperature cycle and thermal shock reliability tests of the product is greatly improved.

[0041] 4. Embedded zone detection contacts are prefabricated simultaneously during the circuit printing stage. The finished product can complete circuit continuity testing and multi-layer interface full-area micro-stress scanning testing in parallel without damaging the packaging. It can accurately detect solder joint micro-cracks and local delamination risks that cannot be identified by conventional continuity testing. The test data can be traced back to and matched with the preceding process parameters such as zone modification, stress pre-equilibrium, and injection filling, forming a closed-loop quality control link adapted to the thermal-mechanical protection system of this invention. The process conditions are dynamically optimized according to the differences in batch materials, stabilizing the consistency of mass production and greatly reducing the rate of missed defects and after-sales repair costs.

[0042] 5. The six-step process has a strict progressive dependency relationship. The partitioned modification provides an adaptation interface for the homogeneous buffer structure, the directional cross-linking strengthens the performance of the buffer layer, the pre-stress equalization reduces the stress load in the injection stage, the fluid isolation injection protects the buffer structure from melt damage, the closed-loop detection reverse iterative optimization of the entire set of process parameters, the micro-buffer deformation margin and the macro-wide stress relief rate are matched throughout the process, and the layered dissipation of two types of loads: injection external force and cold and hot deformation. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the process steps. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0045] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0046] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0047] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0048] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0049] This embodiment provides an in-mold injection molding method for a pre-welded sensor PI printed circuit, comprising the following process steps:

[0050] S1. Differentiated interface modification of polyimide film is carried out in different regions, and integrated conductive circuit is prepared on the surface of the modified film using composite conductive ink to obtain a PI film with regional modification for printed circuit. Conventional existing processes only perform whole-domain indiscriminate plasma activation and single functional group grafting modification on the whole roll of polyimide film. There is a long-standing technical bias in the industry: it is believed that the interface modification of PI film requires a uniform interface energy, and that regional modification will cause uneven adhesion and line breakage in circuit printing. There is no motivation to differentiate the modification conditions for traces and pads.

[0051] However, there are irreconcilable contradictions in uniform modification of the entire area: if high-adhesion grafted functional groups are used as the whole, the internal stress of the film layer will rise sharply after the ink in the circuit trace area is cured, and the circuit will crack and the film will warp over a large area under the injection molding hot and cold cycle; if the interface adhesion is reduced to adapt to the low stress requirements of the trace, the bonding strength of the conductive ink in the pad area and the subsequent solder joint buffer structure will be insufficient, and ink peeling and pad delamination will easily occur.

[0052] To address this, this embodiment employs a segmented plasma radio frequency generator, coupled with a partitioned light-shielding mask fixture to isolate the PI film in different zones. The mask completely isolates the diffusion of functional groups in different modification regions, enabling independent grafting reactions in different spatial zones. During the modification process, an online interface energy detector monitors the surface energy of each zone in real time. The surface energy of the circuit trace zone is controlled at 32–38 mN / m, and the surface energy of the pad soldering zone is controlled at 55–62 mN / m, forming a stable and differentiated interface substrate. After modification, no primer or bonding transition layer is added. Instead, silver-carbon composite elastic conductive ink is used for full-process screen printing. Micron-sized elastic resin particles are added to the ink, and the printing thickness is uniformly controlled at 12–18 μm. The ink is then cured in segments at 130°C to form an integrated conductive circuit. Therefore, the partitioned interface can accurately match the usage requirements of two types of areas. The low interface in the trace area can significantly release the internal stress of ink curing, and reduce the overall warpage deformation of the substrate after injection molding. The high interface in the pad area can provide a strong adhesive substrate for the subsequent homogeneous microporous elastic coating layer, and reduce the failure rate of the buffer structure and PI film peeling. No additional adhesive additives are required, simplifying the process while avoiding the shear stress caused by the interface of multiple additives.

[0053] S2. Relying on composite conductive ink of the same origin as the conductive circuit, a solder joint buffer coupling structure surrounding the sensor solder pads is simultaneously formed. In the existing industry, conductive ink only has the function of conductive transmission. After curing, the ink has high hardness and no elastic buffering capacity, and cannot be used to absorb the impact load of injection molding melt. The buffer structure must use heterogeneous materials such as insulating elastic glue and independent film. Moreover, heterogeneous reinforcement solutions have underlying physical defects: the difference in the coefficient of thermal expansion (CTE) between epoxy glue, PI reinforcing sheet, plastic protective part and composite conductive ink, PI substrate and solder pin exceeds 6ppm / ℃. Under high and low temperature alternating conditions, the heterogeneous interface continuously generates reciprocating shear stress, and the metallurgical interface of the solder joint is very prone to micro-cracks. After 500 cold and hot shocks, the failure rate exceeds 40%. At the same time, heterogeneous reinforcement is an independent post-processing process, which adds at least 3 manual alignment, bonding and curing steps, resulting in poor positioning and a significant increase in production costs.

[0054] This step uses a composite conductive ink with the same components and proportions as the conductive circuit. No changes to the ink paste, printing plate, or multiple printing passes are required. Only one set of screen printing plates is used to simultaneously create interconnected microporous dam patterns in the circuit graphic area and around the solder pads. A single screen printing process forms the entire conductive circuit and the solder joint buffer coupling structure surrounding the pads in one step, eliminating the need for secondary printing, secondary adhesive application, or secondary bonding fixtures. The screen mesh is uniformly 300 mesh, and the microporous dams contain interconnected pore structures with diameters of 5–15 μm. After ink curing, the ink retains a porous elastic deformation allowance, forming a microporous elastic coating layer that can absorb instantaneous impacts. This step ensures that the buffer structure, conductive traces, and PI film are made of the same material, with perfect CTE matching, completely eliminating the continuous shear stress caused by heterogeneous reinforcement. The thermal shock durability of the solder joint is improved by more than 3 times. The circuit and buffer structure are formed simultaneously in a single printing process, eliminating the need for a whole set of post-processing steps for heterogeneous reinforcement, increasing production line efficiency by 40% and reducing the material cost per unit by 28%. The microporous structure reserves elastic buffer space, which can absorb the instantaneous impact load of the injection molten metal, blocking the direct transmission of high-pressure fluid impact force to the metallurgical interface of the solder pad at the microscopic level, reducing the cracking scrap rate of injection molded solder joints from 42% to less than 5%.

[0055] S3. Assemble the sensor components and metallurgically weld them to the pads. Then, perform band-directed ultraviolet low-temperature interface cross-linking reinforcement on the solder joint buffer coupling structure. Existing processes use full-area high-temperature baking and full-band ultraviolet irradiation to reinforce the solder joint reinforcement layer. High-temperature and broad-spectrum ultraviolet light can penetrate the buffer layer and directly act on the solder metallurgical interface of the pads. The tin layer oxidizes and intermetallic compounds grow excessively, resulting in increased brittleness of the solder joint and drift of conductive contact resistance. At the same time, full-area curing cannot specifically eliminate the local micropores and shear residual stress generated by welding.

[0056] This step uses a high-precision visual positioning placement machine to precisely press the sensor metal pins onto the exposed soldering contact surface at the center of the pad, with a positioning tolerance controlled within ±0.03mm. Low-temperature lead-free solder paste is used for reflow soldering, with a peak temperature of up to 185℃ to avoid high-temperature damage to the porous elastic skeleton of the microporous buffer structure. After reflow soldering, a narrow-band directional ultraviolet light source of 320-365nm is used, along with a light-shielding positioning fixture, to project ultraviolet energy only onto the microporous elastic coating area around the pad. The metallurgical soldering area at the center of the pad is completely blocked by the light-shielding plate, preventing cross-linking energy from penetrating or invading the metallurgical interface between the pin and the pad. The cross-linking environment is kept at a constant low temperature of 45℃, and the cross-linking time is controlled within 60-90s. This step offers unique technical benefits: it cross-links and densifies only the microporous buffer layer, enhancing the elastic strength and wear resistance of the microporous structure itself, while simultaneously eliminating micropores generated inside the buffer layer during the reflow soldering process and residual interfacial shear stress accumulated at the edges of the solder pads; it protects the metallurgical bonding interface of the solder pads from damage by ultraviolet rays and high temperatures throughout the process, reducing the fluctuation range of solder joint contact resistance by 90% and significantly improving resistance stability under high and low temperature cycling; the directional narrow-band low-temperature cross-linking method differs from existing full-domain curing solutions and does not sacrifice the reliability of solder joint welding.

[0057] S4. For composite films carrying sensor elements, a pre-equilibrium shaping process is carried out using a multiphase medium synergistic stress, encompassing three types of media: polyimide substrate, composite conductive ink circuit layer, and sensor metal pins. Standardized single-piece film units are then cut. Existing film leveling processes only perform single-tension flattening on bare PI films without components, releasing only the internal stress of the single substrate and completely ignoring the superimposed stress caused by the CTE differences of the multiphase media after sensor integration. The welded composite film contains multiple media with different coefficients of thermal expansion, including the PI substrate, conductive ink, solder layer, and metal pins. All the residual stress at the multi-layer interface generated during curing and welding is retained. After being introduced into the injection molding process, multiple stresses are superimposed, inducing film delamination, circuit breakage, and hidden microcracks in the solder joints. Conventional leveling methods cannot achieve multiphase medium synergistic stress relief.

[0058] This step involves a comprehensive multi-phase stress pre-balancing process: The entire composite membrane sheet, after welding and directional cross-linking reinforcement, is laid flat and placed in a sealed, constant-temperature, low-tension shaping chamber. Flexible silicone pressure strips are installed inside the chamber to provide uniform low-tension clamping, with tensile tension controlled between 0.8 and 1.2 N / cm to prevent membrane deformation from pulling on the weld joints. Three-stage gradient constant-temperature static conditioning is applied to three different media: the first stage is 60℃ for 30 minutes to release internal stress in the PI film substrate; the second stage is 90℃ for 40 minutes to release residual stress from the curing of the composite conductive ink circuit layer; and the third stage is 120℃ for 25 minutes to eliminate shear stress at the interface between the sensor metal pins and the buffer layer and solder pads. The three-stage gradient heating is performed without sudden cooling or heating, and the humidity inside the chamber remains stable at 35%RH throughout to suppress ink moisture absorption and deformation. After stress balancing, a die-cutting blade is used to cut the membrane sheet along a pre-set cutting line in one pass, resulting in a standardized single-piece membrane unit with completely uniform shape, size, and stress state. This step pre-injection releases all residual stress from the three types of media in a layered manner, preventing the accumulation of multiple stresses and significantly reducing substrate warping and film layer delamination defects after injection molding. Low-tension flexible clamping avoids pulling on solder joints throughout the process, preventing pin misalignment and solder joint cracking during the shaping process. The standardized single film unit has high stress consistency, eliminating the need to adjust the injection filling, pressure holding, and cooling process parameters for each piece, significantly improving the stability of mass production. Existing technologies do not have a shaping scheme for segmented gradient isothermal coordinated stress release for the three types of media: PI, conductive ink, and metal pins, and ordinary leveling equipment cannot achieve differentiated stress release for multiphase media.

[0059] S5. The single-film unit is positioned in the injection mold cavity, and the in-mold integrated injection encapsulation is completed by using a fluid isolation gradient flow filling method. The conventional in-mold injection mold uses a symmetrical universal flow gate, and the melt fills the film surface at high speed without obstruction. The high-pressure and high-temperature plastic melt directly impacts the pads and buffer structure. The microporous elastic coating layer collapses and tears under the impact of high-speed fluid, losing its buffer protection capability. The existing gradient flow only pursues the uniform filling rate of multiple cavities, without fluid isolation and pressure relief buffer design for the core protection area of ​​the sensor solder joint, and does not combine the same microporous buffer structure with low-pressure filling logic. This step involves a complete practical approach to mold structure and fluid isolation filling: The injection mold cavity is machined to a 1:1 scale to the shape of the single-piece diaphragm unit. A milled groove is integrally formed in the cavity corresponding to the sensor mounting position to limit and avoid obstruction of the sensor element. The groove depth is 0.3mm greater than the sensor element thickness, allowing for clearance. After the diaphragm is placed in the cavity, the mold is closed and locked. The cavity-wide negative pressure adsorption system is activated, maintaining a stable negative pressure value of -0.06MPa. Adsorption channels are only created on the cavity wall corresponding to the circuit wiring area. There is no negative pressure adsorption at sensor solder joints or element areas to avoid negative pressure pulling on the diaphragm. Solder joint deformation; 4 to 8 sets of independent and controllable branch gates are symmetrically arranged along the long side of the cavity. An arc-shaped melt pressure relief buffer section is added at the front end of each set of gates. All melt branch paths avoid the core protection area of ​​the solder joint composed of component limit avoidance receiving groove and microporous elastic coating layer in advance. The injection filling process controls the melt flow rate in stages: the first stage is low-speed filling along the back side of the PI film with a flow rate of 5cm / s. The second stage is layered filling along the side of the conductive line with a flow rate of 2cm / s. The solder joint and buffer structure maintain a low-pressure slow-flow melt environment throughout, and the melt pressure is controlled within 30bar. In this step, negative pressure adsorption only fixes the wiring area, and the sensor element is housed entirely in the clearance groove, completely isolating the diaphragm deformation from pulling the solder joint structure; after the melt is depressurized in the pressure relief buffer section, it is slowly filled at low pressure, preventing the high-pressure and high-temperature melt from directly impacting the microporous elastic coating layer and the metallurgical interface of the solder pad, protecting the homogeneous buffer structure formed in the previous process from being damaged by the injection fluid; the layered back-side filling scheme avoids the melt front from scouring the solder pad, and together with the S2 microporous buffer structure, it forms a dual protection system of "micro-buffering + macro-fluid isolation".

[0060] S6. Perform multi-dimensional synchronous closed-loop non-destructive testing on the injection-molded substrate to obtain an in-mold electronic substrate with integrated sensors. Existing finished product testing only tests the conductivity of the circuit, which is a single-point testing method. It cannot identify latent defects that are not visible to the naked eye, such as delamination of the micropore coating interface, microcracks inside the solder joint, and excessive residual stress between multilayer films. Moreover, the test data is only used to screen defective products and cannot be used for reverse feedback, optimization of front-end modification, stress shaping, and injection filling processes. There is no closed-loop quality control link throughout the entire process. Stress fluctuations caused by batch material differences cannot be controlled in advance, and the cost of repairing hidden failures after sales remains high. This step involves simultaneously printing embedded zoned detection contacts during the S2 process of screen printing. The contacts are integrally formed with the conductive lines and microporous buffer structure, and are pre-embedded inside the plastic substrate along with the membrane unit, eliminating the need for subsequent welding of detection terminals. Finished product testing employs electromagnetic micro-stress scanning equipment and a continuity tester operating in parallel, without the need for grinding, cutting, or damaging the encapsulation plastic layer. Two sets of core data are collected simultaneously: one is the continuity resistance data of the entire circuit zone, and the other is the full-domain micro-stress distribution scanning spectrum of the multi-layer composite interface. The testing system has a built-in data traceability program that binds product data with excessive stress and abnormal resistance to the corresponding membrane unit pre-zone modification parameters, stress equalization constant temperature conditions, and injection molding shunt pressure parameters, automatically generating process optimization instructions and feeding them back to the front-end printing, shaping, and injection molding equipment to dynamically adjust the operating conditions, forming a closed-loop quality control link adapted to the entire thermal-mechanical protection system.

[0061] This step involves simultaneous dual-dimensional testing, which can detect interface delamination and latent micro-cracks in solder joints that cannot be identified by conventional continuity testing, resulting in a near-zero factory miss rate. The test data is used to iteratively optimize the entire process, dynamically matching stress relief and injection filling parameters to batch differences in PI film and plastic raw materials, continuously stabilizing the thermal-mechanical balance of batch products. The pre-embedded detection contacts are integrally molded, eliminating the need for subsequent welding of detection terminals and simplifying the testing process.

[0062] In this embodiment, the polyimide film partitioning differential interface modification further includes: pre-dividing spatially isolated, non-overlapping circuit trace partitions and sensor pad welding partitions on the surface of the polyimide film;

[0063] Low-extension-stress functional group grafting modification is applied to the circuit trace partitions, while high-interfacial-adhesion functional group grafting modification is applied to the sensor pad soldering partitions. After modification, a fully connected functional conductive circuit is screen-printed using composite conductive ink, completely covering both the circuit trace partitions and the sensor pad soldering partitions. After medium-temperature curing, the partition-modified printed circuit PI film is formed. Existing modifications lack clear boundary delineation standards, resulting in overlapping modification areas in the trace and pad regions, cross-diffusion of functional groups, and loss of differentiated interface control. This solution employs a high-precision CCD vision positioning and cutting fixture. Laser scribing is used to pre-define the boundaries of two types of zones on the unmodified PI film surface, with a 0.5mm isolation blank zone reserved between the boundaries. This ensures complete spatial isolation and prevents cross-regional diffusion of modified functional groups. Low-strength functional groups are selected from long-chain alkyl acrylic groups, which, after grafting, reduce the cross-linking density on the film surface and suppress internal stress generated by the stretching and shrinkage after ink curing. High-interface adhesion functional groups are selected from epoxy silane grafting groups, significantly increasing the number of active sites on the film surface and enhancing the adhesion strength between the composite conductive ink and the microporous elastic coating layer. Screen printing uses an integrated steel mesh, ensuring uninterrupted connection of lines and pad patterns, resulting in uniform ink thickness. Medium-temperature curing is achieved through two stages: pre-baking at 80℃ for 15 minutes to remove ink solvent, followed by main curing at 130℃ for 30 minutes. Slow heating avoids rapid ink shrinkage and delamination.

[0064] This embodiment refines the partition boundaries, selects differentiated functional groups, and employs segmented curing processes, thoroughly solving the technical challenge of compromise in global modification. The two types of partition interfaces are stable and controllable, providing a differentiated interface basis for the S2 homologous microporous buffer structure.

[0065] In this embodiment, the solder joint buffer coupling structure is a microporous elastic coating layer. The molding process also includes: using the same component composite conductive ink used to prepare the conductive circuit, in a single conductive circuit screen printing process, simultaneously forming an integrated microporous elastic coating layer around the outer periphery of each sensor solder pad.

[0066] The microporous elastic coating layer is arranged in a closed loop around the edge of the pad, completely exposing the pre-set welding contact surface at the center of the pad. The microporous elastic coating layer, conductive lines, and partitioned modified polyimide film are all made of the same material and origin, forming a homogeneous integrated microporous coating composite interface without an external adhesive layer. The industry generally believes that conductive inks, mainly composed of conductive metal fillers, are hard and lack elastic porous structures after curing, thus lacking buffering and energy absorption capabilities. Therefore, all buffer layers must use insulating elastic colloids or independent film heterogeneous materials, and there is no homogeneous conductive ink microporous buffer structure. Existing reinforcement structures all cover the entire area of ​​the pad, obstructing the welding contact surface, requiring secondary grooving and grinding before welding sensor pins, increasing process complexity and positioning errors. In this embodiment, a closed-loop dam pattern is individually designed for each sensor pad using a wire mesh. The dam is 0.4mm wide, and interconnected micro-holes are arranged in an array inside the dam. After printing, the ink naturally leaves gaps between the holes to form a microporous elastic coating layer. The dam only surrounds the edges of the pad, and a 1.2mm diameter fully exposed circular welding contact surface is reserved in the center of the pad. No secondary grinding or grooving is required, and it can be directly bonded to the sensor metal pins for reflow soldering. The composite conductive ink has completely uniform components. The ratio of metallic silver powder, elastic resin carrier, and diluent solvent is no different from that of conductive trace ink. There is no ink switching or intermediate cleaning process in a single printing. After curing, the three components fuse to form a homogeneous integrated interface. There are no additional adhesive layers such as epoxy glue or pressure-sensitive adhesive in the middle, completely eliminating multi-layer heterogeneous bonding interfaces.

[0067] Therefore, it brings the following advantages: 1. The microporous structure retains elastic deformation space, which can absorb the instantaneous impact load of injection molding. The homogeneous material has no CTE shear stress source, solving the long-term fatigue cracking defect of heterogeneous reinforcement; 2. The center of the pad is completely exposed, eliminating the need for post-processing, simplifying the welding process, and eliminating the pad damage and open circuit hazards caused by grinding; 3. No external adhesive layer is added, reducing the number of multi-layer interfaces and reducing the probability of delamination failure; 4. Single co-printing eliminates the need for a complete set of tooling and processes for heterogeneous reinforcement, greatly improving production efficiency and reducing material costs. In a further embodiment of the present invention, the band-directed ultraviolet low-temperature interface cross-linking reinforcement also includes: accurately aligning and attaching the sensor element pins to the exposed welding contact surface of the pad, and achieving a stable metallurgical bond between the pins and the pad through low-temperature lead-free reflow soldering, forming a metallurgical bonding interface between the pad and the pins;

[0068] In this embodiment, after welding, a band-directed ultraviolet low-temperature interface crosslinking process is adopted, which selectively acts only on the microporous elastic coating layer to achieve crosslinking densification. The crosslinking energy does not penetrate or intrude into the metallurgical bonding interface of the pad pins, and simultaneously dissipates the welding-derived micropores and interface shear residual stress. This solution details the supporting tooling and process parameters: the positioning accuracy of the vision placement machine is ±0.02mm, the sensor pins are fully attached to the exposed contact surface of the solder pads, the peak temperature profile of the reflow oven is 180℃, the holding time is 60s, and bismuth silver lead-free low-temperature solder paste is used to avoid high-temperature oxidation of the microporous elastic coating layer; the UV curing station is equipped with a contoured metal light-shielding fixture, which is fully attached to the center of the solder pad, 100% shielding the metallurgical bonding area of ​​the solder pad pins, with only the microporous elastic coating layer fully exposed to the UV light source; the UV light source is limited to a narrow wavelength band of 330-350nm to exclude short-wave UV light that will oxidize tin, and the curing environment temperature is controlled in a low-temperature range of 40-50℃; during the crosslinking process, the micropores inside the micropores slowly close under the action of low-temperature UV light, and the welding shear stress at the junction of the buffer layer edge and the solder pad is gradually released.

[0069] Therefore, a dual protection of the solder pad metallurgical interface is achieved by directional shading and narrow-band low-temperature cross-linking, and the mechanical strength and conductivity of the solder joint are not damaged by the cross-linking process; the elastic buffer strength of the microporous elastic coating layer is increased by 2 times after cross-linking and densification, and the shock absorption capacity is further enhanced; at the same time, the micropores generated by the welding process are eliminated to avoid water vapor penetration and interface corrosion.

[0070] In this embodiment, the global multiphase medium synergistic stress pre-equilibrium shaping also includes: sealing the composite diaphragm that has been welded and cross-linked reinforced and integrated with sensor elements in a constant temperature low tension shaping chamber;

[0071] For three types of heterogeneous media with different coefficients of thermal expansion—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—segmented gradient constant temperature static condition is set up to simultaneously release the internal stress of the film substrate, the stress at the interface between the circuit film layer and the plastic film, and the microscopic residual stress at the interface between the metallurgical bonding of the pads and pins. After the stress is balanced, the film is cut along the preset die-cutting line to obtain a standardized single film unit with uniform specifications.

[0072] This embodiment details the hardware and temperature control process of the shaping chamber: the shaping chamber is sealed and insulated, filled with dry nitrogen to isolate moisture, and two sets of flexible silicone pressure strips are arranged at the top and bottom of the chamber, with a stable clamping tension of 1N / cm on one side, and the flexible contact will not scratch the circuit or pull the solder joint; the three-stage gradient constant temperature precisely matches the stress release characteristics of three types of media: the 60℃ low temperature stage is suitable for the slow release of the molding internal stress of the PI film substrate, the 90℃ medium temperature stage is suitable for the composite conductive ink to eliminate the curing shrinkage stress, and the 120℃ medium-high temperature stage is suitable for the shear stress relief at the interface between the metal pin and the microporous coating layer, with a three-stage heating rate of 1℃ / min, without sudden heating and cooling; the stress relief process is monitored in real time by an online infrared stress sensor for the warpage of the film, and the stress balance is determined to be completed when the warpage is less than 0.1mm / m; the die cutting adopts a hard alloy die, and the cutting is carried out in one go along the pre-preset laser cutting line, and the shape and stress state of the single film unit are completely standardized.

[0073] By using segmented gradient temperature control to precisely adapt to the stress release requirements of three types of heterogeneous media, residual stress accumulated at multi-layer interfaces is completely eliminated before injection molding; the low-tension flexible clamping structure protects the solder joints throughout the process, and there is no pin offset or solder joint cracking during the shaping process; the standardized single-piece film unit has high batch consistency, and subsequent injection molding processes do not require parameter adjustments for each piece, greatly expanding the mass production process window.

[0074] In this embodiment, the injection mold includes a molding cavity that conforms to the shape of a standardized single-piece film unit, and an integrally molded element limiting and avoiding receiving groove corresponding to the sensor placement position.

[0075] After the single membrane unit is laid flat and placed into the cavity, the mold is closed and locked. The cavity is then activated by negative pressure adsorption positioning. The negative pressure adsorption force only acts on the circuit wiring partition to fit the inner wall of the cavity. The sensor element is limited and housed inside the element limiting and avoidance receiving groove, and the diaphragm deformation pull on the solder joint structure is completely isolated.

[0076] Preferably, the inner wall of the molding cavity is machined to conform to the front and back contours of the standardized single-piece diaphragm unit in a 1:1 ratio, so that there is no gap after the diaphragm is laid flat; the corresponding position of the sensor is integrally milled to form a component limiting and avoidance receiving groove with a depth greater than the component height by 0.35mm, and the corner of the groove is rounded with a radius of 0.2mm to avoid scratching the sensor shell; the negative pressure adsorption air channel is only opened on the cavity wall surface corresponding to the circuit wiring partition, and there is no adsorption air channel in the solder pad and sensor area, the negative pressure value is stable at -0.05 to -0.07MPa, and the adsorption pull is evenly applied to the wiring film; after molding, the sensor element is completely housed inside the avoidance groove, the diaphragm deformation only occurs in the wiring area, and the pull will not be transmitted to the solder joints or micropore buffer coupling structure. This resulted in a dual-protection structure for the sensor and solder joints using a contoured cavity and an independent clearance groove. The negative pressure adsorption only fixes the wiring area, completely isolating the solder joints from diaphragm deformation and preventing damage to the buffer layer and solder joints caused by the pre-injection positioning process. The rounded clearance grooves prevent scratches and damage during sensor assembly and injection molding, thus improving the yield of finished products.

[0077] In this embodiment, the fluid isolation gradient diversion filling also includes: multiple sets of independent and controllable diversion gates symmetrically arranged along the long side of the mold cavity, and a core protection area for the weld points consisting of a limit and avoidance accommodating groove for all plastic melt diversion paths and a microporous elastic coating layer.

[0078] The molten plastic melt sequentially fills the back side of the polyimide film at a low speed, and then fills it in layers along the sides of the composite conductive ink circuit. The solder joints and microporous elastic coating area maintain a low-pressure, slow-flowing melt environment throughout the process, preventing high-pressure, high-temperature melt from directly impacting the metallurgical bonding interface of the solder pads and leads. Conventional gradient flow gates lack independent pressure relief buffer sections, and the high-speed melt directly impacts the front solder pad area of ​​the film. The microporous elastic coating layer collapses due to the high-speed fluid scouring, and the pore structure fails, losing its buffering and energy absorption function. Existing flow channel designs only pursue uniform filling and do not set up isolation and avoidance paths for the homogeneous microporous buffer structure.

[0079] Preferably, six sets of independent and controllable branch gates are symmetrically arranged along the long side of the cavity. Each set of gates is equipped with an arc-shaped pressure relief buffer channel at the front end, and the melt is pre-pressurized before entering the cavity. All branch gates are routed to bypass the component avoidance groove and the microporous elastic coating layer around the solder pads in advance, and no melt path passes through the core protection area of ​​the solder joint. The injection filling process is divided into two-stage flow rate control: the first stage of filling is carried out at a low speed along the back side of the PI film, with a melt flow rate of 4-6 cm / s. The plastic supports the film from the back side of the film to avoid front scouring. After the back side is filled, the second stage of side layering and surrounding filling is started, and the flow rate is reduced to 1.5-2.5 cm / s. The melt pressure in the solder joint area is stabilized in the low pressure range of 20-35 bar. The melt temperature is controlled at 210-220℃ to avoid softening of the resin skeleton of the microporous elastic coating layer at ultra-high temperature.

[0080] This achieves fluid isolation and flow channel avoidance + two-stage low-speed layered filling, protecting the integrity of the homologous microporous elastic coating layer structure formed by S2 throughout the process, preventing it from being damaged by high-pressure melt; the back-side pre-filled diaphragm is supported by plastic, and the diaphragm does not bulge or vibrate during the injection molding process, greatly reducing the stress on the weld points; it forms a dual coupling protection mechanism of "microscopic energy absorption + macroscopic fluid isolation" with the homologous microporous buffer structure of S2.

[0081] In this embodiment, after the plastic melt is filled, a matching two-stage graded pressure holding and cooling process is performed.

[0082] Specifically, the first stage involves constant high-temperature and medium-pressure holding, which promotes the penetration of molten plastic into the pores of the microporous elastic coating layer, enhancing the mechanical interlocking strength of the microporous coating composite interface. The second stage involves linear gradient slow cooling, dynamically matching the thermal shrinkage deformation parameters of the polyimide substrate, the composite conductive ink circuit layer, and the injection-molded plastic, offsetting the poor deformation of the multi-layer interface, and preventing delamination, peeling, and microcracks at the microporous coating composite interface and the film-plastic bonding interface. Existing injection molding only uses a single constant pressure holding and rapid uniform cooling, which prevents the plastic from penetrating into the pores of the microporous elastic coating layer, resulting in only a surface bonding interface with low bonding strength. Under rapid cooling, the shrinkage rates of the three materials are mismatched, generating huge internal stress at the interface, leading to delamination, peeling, and microcracks. This step details the complete parameters for the two-stage graded holding pressure and cooling: After the melt is filled, the first stage of high-temperature holding pressure is entered, with the mold temperature maintained at 140℃, the holding pressure at 40 bar, and the holding time at 25 seconds. Under constant pressure, the molten plastic fully penetrates the interconnected pores inside the microporous elastic coating layer. After the plastic solidifies, it forms a locking mechanical interlocking interface with the micropores, which greatly improves the bonding strength between the buffer layer and the plastic encapsulation layer. After the holding pressure is completed, the second stage of linear gradient slow cooling is entered, with a constant cooling rate of 0.4℃ / min for slow cooling. Throughout the process, the thermal shrinkage deformation rates of the PI film, composite conductive ink, and injection-molded plastic are matched synchronously to gradually offset the shrinkage difference of the multi-layer interface until the mold temperature drops to 60℃ and the mold is opened.

[0083] This enables a two-stage graded pressure holding and cooling process specifically adapted to the homogeneous microporous elastic coating layer structure, forming a mechanical interlocking interface between the plastic and the micropores, thus improving the interface peel strength; linear gradient slow cooling eliminates the poor shrinkage deformation of multi-layer materials, and prevents delamination and micro-peeling cracks at the microporous coating interface and the film-plastic bonding interface.

[0084] In this embodiment, the multi-dimensional synchronous closed-loop non-destructive testing further includes: synchronously prefabricating embedded partition detection contacts during the composite conductive ink circuit printing stage, wherein the partition detection contacts are integrally injection molded and embedded inside the plastic substrate along with the membrane unit;

[0085] Finished product testing does not require damaging the packaging structure. It relies on partitioned testing contacts to simultaneously and in parallel complete circuit continuity testing and multi-layer composite interface micro-stress full-domain scanning testing. The test data is traceable and matched with the pre-stress equalization working parameters of the membrane unit, forming a closed-loop quality control link that is compatible with the thermal-mechanical protection system.

[0086] Preferably, the S2 screen-printed circuit synchronously prints rectangular partition detection contacts. The contact material, ink, and conductive lines are completely homologous. These contacts are distributed at the four corners of the membrane unit and at the segment nodes of the circuit. They are pre-embedded into the plastic substrate along with the membrane unit. Corresponding contact detection windows are reserved on the surface of the finished plastic. The detection station is equipped with a continuity resistance tester and an electromagnetic micro-stress scanning probe. Without grinding, cutting, or packaging the plastic, dual-dimensional parallel detection is completed non-destructively. The system has a built-in database that automatically binds the detected stress and resistance data of each substrate to the partition modification interface energy, stress equalization isothermal duration, and injection molding holding pressure parameters corresponding to the membrane unit. When the frequency of stress exceeding the threshold is higher than the threshold, the system automatically sends parameter correction instructions to the shaping chamber and injection molding machine to dynamically adjust the working conditions and continuously match the entire micro- and macro-coupled thermal-mechanical protection system.

[0087] This enables embedded, one-piece molded testing contacts to eliminate the need for subsequent terminal welding processes, thus eliminating the risk of exposed terminals failing due to impacts; dual-dimensional synchronous non-destructive testing can detect hidden interface defects that conventional continuity testing cannot identify; data traceability and closed-loop feedback enable adaptive optimization of the process, offsetting stress fluctuations caused by batch differences in PI film and plastic raw materials, and stabilizing mass production yield.

[0088] In this embodiment, the thermal protection system includes a linkage adaptation process: relying on the S1 partition modification to regulate the interfacial bonding force of the membrane material and the S2 homologous microporous elastic coating layer to absorb the instantaneous melt impact force, the micro-weld point buffer interface self-matching is achieved.

[0089] By relying on S4 global pre-stress pre-equilibrium to offset the inherent thermal expansion difference of the three media—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—and S5 fluid isolation to weaken the external force disturbance during injection molding, macroscopic multiphase medium global stress linkage control is achieved; microscopic buffer deformation margin and macroscopic stress release rate are linked and matched throughout the process to achieve layered dissolution of injection external force and cold and hot deformation stress.

[0090] Preferably, the entire thermal protection system is divided into two layers of linkage control logic: microscopic and macroscopic. Each process is interdependent and indispensable: 1. Microscopic stress control (S1+S2+S3 synergy): S1 partitioned differential modification constructs a partitioned interface energy substrate to ensure stable adhesion of the S2 homogeneous microporous elastic coating layer; S2 single co-printing of a homogeneous microporous buffer structure provides microscopic elastic deformation margin to absorb the instantaneous melt impact during injection molding; S3 directional low-temperature cross-linking strengthens the microporous buffer skeleton, while protecting the metallurgical interface of the solder pads, completing the self-matching buffer of microscopic solder joint stress, and blocking the transmission of impact load to the solder joint from the source.

[0091] 2. Macroscopic stress control (S4+S5+two-stage graded pressure holding and cooling synergy): S4 full-domain multiphase medium segmented gradient constant temperature pre-equilibrium, releases all inherent thermal expansion residual stress of the three types of media in advance before injection molding; S5 fluid isolation gradient diversion filling + two-stage graded slow cooling, weakens the external force disturbance of injection molding high pressure, dynamically matches the shrinkage deformation difference of multi-layer materials, and realizes macroscopic full-domain multiphase medium stress slow release.

[0092] 3. Closed-loop adaptive control (S6 supporting linkage): Multi-dimensional synchronous closed-loop non-destructive testing collects microscopic interface and macroscopic global stress data in real time, and reversely corrects the core parameters of S1 partition modification, S4 stress shaping and S5 injection filling, so that the microscopic buffer deformation margin and macroscopic stress relief rate are continuously and dynamically matched, and the two different loads of instantaneous injection impact force and long-term high and low temperature cold and hot deformation stress are resolved in layers.

[0093] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for in-mold integral injection molding of a pre-welded sensor PI printed circuit, characterized in that, The process includes the following steps: S1. Differentiated interface modification of polyimide film is performed in different regions, and an integrated conductive circuit is prepared on the surface of the modified film using composite conductive ink to obtain a partitioned modified printed circuit PI film. S2. Relying on composite conductive ink of the same origin as the conductive circuit, the solder joint buffer coupling structure surrounding the sensor solder pad is formed synchronously. S3. Assemble the sensor components and metallurgically weld them to the pads, and then perform band-directed ultraviolet low-temperature interface cross-linking reinforcement on the solder joint buffer coupling structure. S4. Perform full-domain multiphase dielectric synergistic stress pre-equilibrium shaping on the composite diaphragm carrying the sensor element, including three types of media: polyimide substrate, composite conductive ink circuit layer, and sensor metal pins, and cut to obtain standardized single-piece diaphragm units. S5. Position the single-film unit inside the injection mold cavity and complete the in-mold integrated injection molding encapsulation by using a fluid isolation gradient flow filling method. S6. Perform multi-dimensional synchronous closed-loop non-destructive testing on the injection-molded substrate to obtain an in-mold electronic substrate with integrated sensors.

2. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The polyimide film partitioning differential interface modification also includes: pre-dividing spatially isolated, non-overlapping circuit trace partitions and sensor pad welding partitions on the surface of the polyimide film. Low-extension-stress functional group grafting modification treatment is applied to the circuit trace partition, and high-interface-adhesion functional group grafting modification treatment is applied to the sensor pad soldering partition. After modification, composite conductive ink is used to screen print fully connected functional conductive circuits. The conductive circuits fully cover the circuit routing areas and the sensor pad welding areas. After medium-temperature curing and shaping, the partitioned modified printed circuit PI film is formed.

3. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The solder joint buffer coupling structure is a microporous elastic coating layer. The molding process also includes: using the same component composite conductive ink used to prepare the conductive circuit, in the single conductive circuit screen printing process, to simultaneously surround the outer periphery of each sensor solder pad with an integrated microporous elastic coating layer. The microporous elastic coating layer is arranged only in a closed loop around the edge of the pad, completely exposing the pre-set welding contact surface at the center of the pad. The microporous elastic coating layer, conductive circuit, and partitioned modified polyimide film are made from the same material and origin, forming a homogeneous integrated microporous coating composite interface without an external adhesive layer.

4. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The band-directed ultraviolet low-temperature interface cross-linking reinforcement also includes: precisely aligning and attaching the sensor element pins to the exposed soldering contact surface of the pad, and achieving a stable metallurgical bond between the pins and the pad through low-temperature lead-free reflow soldering to form a metallurgical bonding interface between the pad and the pins. After welding, a band-directed ultraviolet low-temperature interface crosslinking process is adopted, which selectively acts only on the microporous elastic coating layer to achieve crosslinking densification. The crosslinking energy does not penetrate or intrude into the metallurgical bonding interface of the pad pins, and simultaneously dissipates the welding-derived micropores and interface shear residual stress.

5. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The full-domain multiphase medium synergistic stress pre-equilibrium shaping also includes: sealing the composite diaphragm that has been welded and cross-linked reinforced and integrated with sensor elements in a constant temperature low tension shaping chamber; For three types of heterogeneous media with different coefficients of thermal expansion—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—segmented gradient constant temperature static condition is matched and set. Simultaneously release the internal stress of the membrane substrate, the stress at the interface of the circuit film layer and the plastic bonding, and the microscopic residual stress at the interface of the metallurgical bonding of the pads and pins. After the stress is balanced, cut along the preset die-cutting line to obtain a standardized single membrane unit with uniform specifications.

6. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The injection mold includes a molding cavity that conforms to the shape of a standardized single-piece film unit, and an integral molding element limiting and avoiding receiving groove corresponding to the sensor placement position. After the single membrane unit is laid flat and placed into the cavity, the mold is closed and locked. The cavity is then activated by negative pressure adsorption positioning. The negative pressure adsorption force only acts on the circuit wiring partition to fit the inner wall of the cavity. The sensor element is limited and housed inside the element limiting and avoidance receiving groove, and the diaphragm deformation pull on the solder joint structure is completely isolated.

7. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The fluid isolation gradient diversion filling also includes: multiple sets of independent and controllable diversion gates symmetrically arranged along the long side of the mold cavity; a core protection area for weld points consisting of limit and avoidance accommodating grooves for all plastic melt diversion paths and microporous elastic coating layers. The molten plastic melt sequentially fills the back side of the polyimide film at a low speed, and then fills the side of the composite conductive ink circuit layer by layer. The solder joint and microporous elastic coating area maintain a low-pressure slow-flow melt environment throughout the process, preventing high-pressure and high-temperature melt from directly impacting the metallurgical bonding interface of the solder pad pin.

8. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, After the plastic melt is filled, a matching two-stage graded pressure holding and cooling process is performed. The first stage involves maintaining a constant medium-high temperature and pressure, which promotes the penetration of molten plastic into the pores inside the microporous elastic coating layer, thereby enhancing the mechanical interlocking strength of the microporous coating composite interface. The second stage involves linear gradient slow cooling, dynamically matching the thermal shrinkage deformation parameters of the polyimide substrate, the composite conductive ink circuit layer, and the injection-molded plastic. This counteracts the poor deformation of the multi-layer interface and prevents delamination, peeling, and microcracks from occurring at the microporous coating composite interface and the film-plastic bonding interface.

9. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The multi-dimensional synchronous closed-loop non-destructive testing also includes: synchronously prefabricated embedded partition detection contacts during the composite conductive ink circuit printing stage, with the partition detection contacts being integrally injection molded and embedded inside the plastic matrix along with the membrane unit; Finished product testing does not require damaging the packaging structure. It relies on partitioned testing contacts to simultaneously and in parallel complete circuit continuity testing and multi-layer composite interface micro-stress full-domain scanning testing. The test data is traced back to match the pre-stress equalization parameters of the membrane unit, forming a closed-loop quality control link that adapts to the thermal-mechanical protection system.

10. The in-mold injection molding method for the PI printed circuit of the pre-welded sensor according to claim 1, characterized in that, The thermal protection system includes a linkage adaptation process: relying on the S1 partition modification to regulate the interfacial bonding force of the membrane material and the S2 homogeneous microporous elastic coating layer to absorb the instantaneous melt impact force, the micro-weld point buffer interface self-matching is achieved. By relying on S4 global pre-stress pre-equilibrium to offset the inherent thermal expansion difference of the three types of media—polyimide substrate, composite conductive ink circuit layer, and sensor metal pins—and S5 fluid isolation to weaken the external force disturbance during injection molding, macroscopic multiphase media global stress linkage control is achieved. The microscopic buffer deformation allowance and the macroscopic stress relief rate are matched and coordinated throughout the process to achieve the stratified dissipation of injection external force and cold and hot deformation stress.

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