A method for controlling PP overflow in the manufacture of high-speed rigid-flex plates

Abstract

This invention belongs to the field of printed circuit board manufacturing technology and discloses a method for controlling the flowability of PP glue overflow in the manufacturing of high-speed rigid-flex boards. The method includes the following steps: during low-pressure heating, the displacement of the pressure head of the hot press equipment is continuously monitored, and the displacement rate and displacement acceleration are calculated; the moment when the displacement acceleration reaches a negative peak value is taken as the point of lowest resin viscosity, and transient pressure cycling is performed to remove microscopic voids; then the moment when the displacement rate crosses zero is taken as the resin gelation inflection point, triggering high pressure application until curing is completed. This invention uses the mechanical response of the hot press equipment itself as the basis for closed-loop control of process nodes, no longer relying on externally set temperature or time parameters, and directly binds the timing of high pressure application with the physical phase change point of the resin from the completion of microscopic wetting to the start of curing. Thus, in terms of process timing, the two mutually restrictive goals of microscopic filling and glue overflow suppression are transformed into a continuous process that occurs sequentially.

Description

Technical Field

[0001] This invention relates to a method for controlling the flowability of PP adhesive overflow in the manufacturing of high-speed rigid-flex boards, belonging to the field of printed circuit board manufacturing technology. Background Technology

[0002] Currently, in the manufacturing of high-density, high-frequency, and high-speed printed circuit boards, the hot-pressing lamination between multilayer conductive patterns and insulating dielectric layers is a core process that determines the electrical performance and reliability of the final product. This is especially true in the manufacturing of rigid-flex boards containing flowable prepreg, i.e., prepreg (PP), epoxy resin. A common approach is to use preset temperature, pressure, and time process curves to control the curing and molding of the laminated structure during hot pressing. This method, relying on extensive preliminary experiments to determine a fixed set of process parameters, is a widely used production strategy in the industry. However, as circuit boards move towards higher integration and higher signal strength… As transmission rates continue to improve, the requirements for internal pattern precision and dielectric layer thickness uniformity are increasing. The aforementioned open-loop control method, which relies on fixed parameters, also has inherent technical limitations. The root of these limitations lies in the fact that the external process parameters applied by the hot press and the actual physical state of the prepreg resin inside the laminated structure, especially the dynamic changes in viscosity after melting, are not synchronous and linear. Delays in heat conduction and differences in the curing characteristics of different batches of materials can all lead to deviations between the external control rhythm and the actual internal physicochemical reaction process. Therefore, throughout the entire lamination process, there is always a set of mutually restrictive technical requirements.

[0003] On the one hand, to achieve sufficient filling of fine circuit patterns and eliminate any voids that may lead to delamination, the process requires the resin to have a sufficiently low viscosity in the initial stage of lamination. On the other hand, if the resin is still in this low-viscosity state when the final bonding high pressure is applied, uncontrollable overflow will occur, which will contaminate the board edge connection area or block the vias, resulting in uncontrolled impedance and thickness deviation in the finished product. Moreover, existing technologies generally adopt this open-loop control logic based on preset parameters at the process method setting level, failing to establish an effective insight into the true physical state of the resin. For example, Chinese invention patent CN103025081B discloses a manufacturing method for rigid-flex printed circuit boards. Although this method simplifies the steps through one-time lamination, its core control still relies on a set of fixed multi-stage temperature and pressure timing curves to complete the entire lamination process. This process is preset to a length of 180 minutes, with pressure from... Change to The fundamental flaw of this control logic is that it infers the internal physical state of the resin based on time, an indirect and imprecise external variable, completely ignoring the fluctuations in the curing characteristics of different batches of materials or the delay in heat conduction caused by uneven layered structures. Therefore, there will inevitably be an unavoidable random deviation between the high-pressure application point and the actual resin gelation inflection point, resulting in an extremely narrow process window and making it difficult to stably balance the full filling of micro-patterns with the suppression of macro-expansion.

[0004] Specifically, existing technologies suffer from the following inherent defects: 1. Existing process control methods lack the ability to directly identify the physical phase transition point where the resin viscosity inside the laminate has reached its minimum and begins to rise. Their decision-making is indirect and delayed. 2. To achieve both full filling and overflow suppression, the process requirements for the resin's physical state are conflicting. Existing processes can only find a compromise, but not always accurately reproducible, process window through repeated trials. Therefore, the technical problem this invention aims to solve is how to establish a method that can directly identify and capture the key process nodes from the completion of impregnation and filling to the start of viscosity recovery based on the changes in the physical state of the laminated structure during the pressing process, thereby controlling the timing of high-pressure application. Summary of the Invention

[0005] This invention provides a method for controlling the overflow of PP adhesive in the manufacturing of high-speed rigid-flex plates. Its main purpose is to solve the problem that existing processes cannot identify the phase transition point of the physical state of the resin inside the laminate in real time, and it is difficult to accurately determine the timing of applying high pressure between the opposing requirements of filling and overflow processes.

[0006] To achieve the above objectives, the present invention provides a method for controlling PP overflow during the manufacturing of high-speed rigid-flex plates, the method comprising the following steps:

[0007] Step 1: Place a laminated structure containing at least one layer of PP prepreg in a hot press, apply low pressure and start the heating process;

[0008] Step 2: During the execution of the heating program, continuously monitor the displacement of the pressure head of the hot pressing equipment along the pressure direction, and calculate a displacement rate and a displacement acceleration based on the pressure head displacement. The displacement rate is the first-order rate of change of the pressure head displacement, and the displacement acceleration is the second-order rate of change of the pressure head displacement.

[0009] Step 3: The moment when the displacement acceleration reaches its negative peak value is taken as the first process moment when the resin viscosity in the PP prepreg is at its lowest point. At the first process moment, a transient pressure cycle is performed to briefly reduce and then restore the pressure applied to the laminate structure.

[0010] Step 4: After performing the transient pressure cycle, continue to monitor the displacement rate, and take the moment when the displacement rate value changes from positive to negative and crosses zero as the second process moment when the resin viscosity in the PP prepreg starts to rise from the lowest point. At the second process moment, increase the pressure applied to the laminated structure from low pressure to high pressure, and maintain the high pressure for a preset time to complete the curing.

[0011] Preferably, in step one, the applied low pressure includes a constant pressure base value and a periodic pressure perturbation with a preset frequency superimposed on the constant pressure base value; and the determination of the second process time in step four is based on the change in the amplitude of the response signal of the pressure head displacement to the periodic pressure perturbation, wherein the change in the amplitude of the response signal satisfies the following determination rule: Where R(t) is the real-time amplitude of the response signal, This is a threshold value used to determine the magnitude of gelation.

[0012] Preferably, the method further includes: recording the transient response of the pressure head displacement during the transient pressure cycle of step three; determining a response characteristic parameter characterizing the effect of internal gas discharge based on the transient response; and determining whether to repeat the transient pressure cycle before proceeding to step four, based on the comparison result of the response characteristic parameter and a preset benchmark, until the response characteristic parameter meets the preset benchmark.

[0013] Preferably, the response characteristic parameters include the pressure reduction phase of the transient pressure cycle, the rebound amplitude of the indenter displacement, and the steady-state recovery time of the indenter displacement during the pressure recovery phase.

[0014] Preferably, the hot pressing device applies pressure to the laminated structure through multiple pressure actuation units; the method further includes: during the heating process, monitoring the pressure feedback value associated with each pressure actuation unit in real time; and determining a non-uniformity index characterizing the uniformity of the gelation process inside the laminated structure based on the standard deviation between multiple pressure feedback values.

[0015] Preferably, the triggering of the increase to high voltage in step four also depends on the non-uniformity index satisfying a preset uniformity condition, wherein the uniformity condition is that the non-uniformity index is less than a preset uniformity threshold.

[0016] Preferably, the low-pressure setting range in step one is: .

[0017] Preferably, the continuous monitoring in step two is achieved through the displacement sensor built into the hot pressing equipment.

[0018] Preferably, the preset frequency range of the periodic pressure perturbation is 0.5 Hz to 2 Hz.

[0019] Preferably, the transient pressure cycle in step three includes: removing the pressure applied to the laminated structure to the background pressure within 1 to 2 seconds, and then restoring the pressure to a low pressure level within 1 to 2 seconds.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This method treats the displacement of the pressure head of the hot pressing equipment along the pressure direction as a continuous process quantity that directly reflects the physical state of the resin inside the laminated structure. By continuously calculating the first-order rate of change of this displacement, i.e., the displacement rate, and defining the moment when the rate value crosses zero as the gelation inflection point where the resin viscosity starts to rise from the lowest point, the application of high pressure is triggered. This establishes a closed-loop control mode of process nodes based on the mechanical response of the laminated structure itself. This makes the timing of high pressure application no longer dependent on externally set temperature or time parameters that have a delay or deviation from the actual internal state of the material, but directly tied to the physical phase transition point of the resin from the completion of micro-impregnation to the start of curing. From the process sequence, the two mutually restrictive goals of fully filling the micro-circuit gaps and suppressing the overflow of adhesive at the board edge are transformed into a continuous process that occurs naturally in sequence.

[0022] 2. The applied low pressure includes periodic pressure perturbations of a preset frequency, and the change in the amplitude of the response signal corresponding to the preset frequency in the pressure head displacement signal is used as the basis for judging the gelation inflection point. When the resin inside the laminated structure begins to undergo cross-linking reaction and its mechanical modulus increases, its displacement response to the pressure perturbation of the specific frequency decreases accordingly. Thus, the system can identify the effective signal characterizing the material state change from the background vibration noise. This avoids misjudgment caused by spurious signals introduced by equipment vibration or environmental interference when directly performing differential calculations on the original displacement signal, and improves the reliability of inflection point judgment.

[0023] 3. This method utilizes the second-order change in pressure head displacement, i.e., displacement acceleration, to identify the moment when the resin viscosity reaches its minimum. At this moment, a transient pressure cycle is performed, briefly reducing and then restoring the pressure. This is because this moment represents the point of least resistance to gas escape from the laminated structure. The sudden pressure drop causes the trapped gas to expand, facilitating its active release. The subsequent pressure recovery allows the liquid resin to backfill the voids left after venting. This micro-process, performed before the final application of high pressure, leverages the separation between the resin viscosity minimum and the gelation inflection point on the time axis, solving the problem of how to pre-remove micro-void precursors within a control framework that suppresses overflow. Simultaneously, During the transient pressure cycle, the transient response curve of the pressure head displacement is recorded. Based on the characteristic parameters of the response curve, such as the displacement rebound amplitude during the pressure reduction phase or the steady-state recovery time during the pressure recovery phase, the effect of internal gas discharge is determined. If the characteristic parameter does not reach the preset stable state, the pressure cycle is repeated until the condition is met, and then the gelation inflection point is waited for to arrive before applying the final high pressure. This transforms an open venting action into a closed-loop subprocess with online verification and compensation capabilities. By treating the venting action itself as a process diagnosis of the internal residual gas content, a process-based confirmation of the microscopic quality of the final product is provided. Attached Figure Description

[0024] Figure 1 This is a diagram of the process closed-loop control logic based on mechanical response of the present invention.

[0025] Figure 2 This is a schematic diagram of the response characteristic parameters for online exhaust effect verification of the present invention;

[0026] Figure 3 This is a schematic diagram of the timing stages and control nodes of a pressing process according to the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. However, those skilled in the art will understand that this invention can be implemented in other specific forms without changing the spirit and basic characteristics of this invention. The following embodiments are intended to explain and illustrate, rather than to limit the scope of protection of this invention.

[0028] This invention discloses a method for controlling PP overflow in the manufacturing of high-speed rigid-flex printed circuit boards (PCBs). The mechanical response of the hot-pressing equipment during lamination is treated as a process quantity characterizing the internal physical state of the laminated structure. Based on real-time calculation and analysis of this process quantity, two key process moments are determined. The first process moment corresponds to the state where the resin viscosity in the PP prepreg inside the laminated structure reaches its lowest point, used to execute a transient pressure cycle to remove the precursor of internal voids. The second process moment corresponds to the gelation inflection point where the resin viscosity begins to rise from its lowest point, used to trigger the application of the final bonding high pressure. By separating the filling of the microstructure and the suppression of overflow at the board edge in a temporal sequence, separate control of both is achieved. In a specific implementation scenario, this method is applied to the manufacturing process of a ten-layer rigid-flex printed circuit board containing impedance-controlled microstrip lines with a linewidth spacing of less than 75 micrometers and micro-blind vias with an aspect ratio greater than 1:1. The hot-pressing equipment used in implementing this method is a laminator with multi-point independent pressure monitoring capabilities. Its control system integrates data acquisition and real-time calculation functions, and the pressure control accuracy of this laminator is no less than... The displacement sensor configured on its pressure head has a resolution of no less than 1 micrometer, and the control system can acquire displacement data at a frequency of no less than 10Hz. Before the process begins, a threshold for a gelation non-uniformity index needs to be calibrated through pressing tests on similar products. This index is determined by the standard deviation of the pressure values ​​fed back by each pressure actuator. To characterize this, the threshold is set to a stable value that can characterize the temperature distribution within the plate as having tended to be uniform, for example, 0.05 MPa.

[0029] The specific implementation steps of this method are as follows: First, in step one, the laminated structure containing at least one layer of PP prepreg is placed in a hot press, the heating program is started, and a preset low pressure is applied. This low pressure is set to ensure close contact between the layers in the laminated structure to facilitate uniform heat conduction, while avoiding overflow caused by excessive pressure when the resin melts to its lowest viscosity. For the laminated structure in this implementation scenario, this low pressure is set as follows: Then, proceeding to step two, during the heating process, the control system of the hot press equipment uses its built-in displacement sensor to continuously monitor the displacement Z(t) of the pressure head along the pressure direction at a frequency of 10Hz. Based on the collected continuous displacement data, it performs real-time calculations to obtain the displacement rate V(t) and displacement acceleration A(t); the calculation relationship here is: Where Z(t) is the head displacement at time t, V(t) is the displacement rate at time t, and A(t) is the displacement acceleration at time t. In specific engineering implementations, to suppress high-frequency noise in the raw displacement sensor data that may be amplified after differential operations, a digital filtering preprocessing step is usually performed on the acquired discrete displacement time series Z(t) before calculating the displacement rate V(t). This preprocessing step can, for example, use a 5-point window moving average algorithm, that is, generate a smoothed displacement series Z'(t) by the arithmetic mean of 5 consecutive sampling points. The subsequent calculations of displacement rate V(t) and displacement acceleration A(t) are based on this smoothed displacement series Z'(t), thereby obtaining a sequence that can characterize... The dynamic response curve of the morphology of the laminated structure during the physical compression process is stable. For the control program, the criterion for determining the first process moment, namely the negative peak value of the displacement acceleration A(t), is determined in the algorithm as the local minimum point where A(t) is less than its adjacent points A(t-1) and A(t+1) within the monitoring time window corresponding to resin melting. The criterion for determining the second process moment, namely the displacement rate V(t) crossing the zero point, is triggered when V(t-1) is detected to be negative and V(t) is non-negative, and this non-negative state continues for at least two consecutive sampling cycles. This avoids the instantaneous zero-crossing pseudo-signals caused by equipment micro-vibration, thereby accurately determining the high-pressure application action at the gelation physical inflection point. For example, if in The displacement collected at each moment is ,exist The displacement at time t is Then the average displacement velocity V(t) during this time interval can be approximately calculated as (2.048-2.050) / (150.1-150.0)=-0.02mm / s; by performing the same difference operation on a series of continuous V(t) values, the real-time value of acceleration A(t) can be obtained.

[0030] Next, step three is executed. This step is triggered when the displacement acceleration A(t) reaches its negative peak value. The physical process is as follows: as the temperature rises, the PP resin changes from a solid to a liquid state, and its viscosity decreases. Under constant low pressure, the laminated structure is compressed, and the absolute value of the displacement rate V(t) gradually increases. When the resin is completely melted and has finished wetting and filling the internal circuit pattern, the compression process is nearing completion, and the absolute value of the displacement rate V(t) begins to decrease. The moment when the absolute value of V(t) changes from increasing to decreasing corresponds to the moment when its rate of change A(t) reaches its negative peak value. This moment is defined as the first process moment when the resin viscosity is at its lowest. Once the system detects this characteristic, it immediately executes a transient pressure cycle. Specifically, this cycle involves changing the pressure applied to the laminated structure from... Quickly release the background pressure to the compression chamber, and then restore the pressure to normal within 1 to 2 seconds. The pressure drop causes the residual gas trapped in the micro-blind holes or dense circuits to expand and be expelled due to the pressure difference. The subsequent pressure recovery allows the low-viscosity liquid resin to backfill the voids left after the venting.

[0031] In an implementation requiring higher reliability, an online verification and compensation sub-process can be introduced to confirm the exhaust effect of step three. Specifically, during the transient pressure cycle, the system records the transient response curve of the pressure head displacement Z(t) with higher time resolution and extracts two response characteristic parameters from this curve: the rebound amplitude of the pressure head displacement during the pressure reduction phase and the steady-state recovery time of the pressure head displacement during the pressure recovery phase. The system compares the extracted characteristic parameters with a benchmark established through prior experiments. If the comparison result exceeds the benchmark range, it indicates that there is still a significant amount of residual gas inside. The system then decides to repeat the transient pressure cycle until the response characteristic parameters of the latest cycle meet the preset benchmark. Only after this is the exhaust process confirmed to be complete. After the exhaust process is completed, the method proceeds to step four, which is triggered by the moment when the displacement rate V(t) changes from positive to negative and crosses zero. The physical process is that as the heat preservation time increases, the molecular chains of PP resin undergo a cross-linking reaction, the system changes from liquid to solid, and the viscosity increases. This change in internal state generates a supporting force against the downward pressure of the pressure head, eventually causing the compression of the laminated structure to stop completely, that is, the displacement rate V(t) decelerates to zero. Therefore, the moment when V(t) crosses zero is defined as the second process moment of the gelation inflection point where the resin viscosity begins to rise from its lowest point. Under normal operating conditions, once the system determines that V(t) has reached this characteristic, it immediately reduces the pressure applied to the laminated structure from... The low pressure was raised to Apply high pressure and maintain that high pressure until curing is complete.

[0032] Considering the large size or uneven distribution of internal copper foil in the laminated structure, and to address the issue of asynchronous gelation processes in different areas within the plane, the triggering mechanism for increasing the pressure in step four also adds a collaborative judgment condition; specifically, the control system of the hot pressing equipment monitors the pressure feedback values ​​of multiple pressure execution units in real time throughout the entire heating process. Based on the standard deviation between these pressure feedback values, a non-uniformity index characterizing the uniformity of the internal gelation process is determined. At this point, the triggering of the increase to high pressure depends not only on the displacement rate V(t) crossing zero, but also on the non-uniformity index. The pressure is less than the preset uniformity threshold of 0.05 MPa; if V(t) already meets the condition, but If the pressure exceeds this threshold, it indicates a curing difference within the board. At this point, the system will pause pressure increases and enter a brief temperature homogenization and holding phase, pending further monitoring. The pressure drops below the uniformity threshold before finally triggering the application of high pressure. Additionally, in production scenarios with strong equipment vibration or environmental interference, an alternative implementation method can be used to improve the reliability of the gelation inflection point determination. In this method, the low pressure applied in step one includes a... The system uses a constant pressure baseline and a periodic pressure perturbation with a preset frequency (e.g., 1.0 Hz) superimposed on that baseline. Correspondingly, in step four, the determination of the second process time is based on the change in the amplitude of the response signal to this periodic pressure perturbation caused by the pressure head displacement. The system extracts the response signal amplitude R(t) with the same frequency as the 1.0 Hz excitation signal from the displacement signal using a synchronous demodulation algorithm. When the resin inside the laminated structure begins to undergo a cross-linking reaction and its mechanical modulus increases, its displacement response to this specific frequency pressure perturbation will decrease accordingly. Therefore, the system decays R(t) to a preset amplitude threshold. The moment when the gelation inflection point occurs is used as the criterion for determining the occurrence of the gelation inflection point, i.e., when the determination rule is met. When high voltage is applied, it is triggered; where R(t) is the real-time amplitude of the response signal. A preset amplitude threshold is used to determine the occurrence of gelation. This threshold can be calibrated experimentally, for example, set to 30% of the amplitude of the stable liquid phase region.

[0033] Example 1: This example is a specific operational instance of the described technical solution in a particular industrial application scenario. In a scenario of manufacturing high-density rigid-flex boards for spaceborne communication modules, this batch of products not only contains a large area of ​​asymmetrically distributed copper foil within the laminated structure, but also, after inspection, the resin flow characteristics of a batch of PP prepregs showed a 3% deviation in curing kinetics compared to the standard batch. If a pressing process based on a fixed time-temperature curve is used, under the conditions of batch fluctuations and uneven laminated structure, excessive resin flow is likely to occur in areas with sparse copper foil due to localized overheating, or insufficient resin filling in areas with dense copper foil due to delayed temperature rise. To address this situation, the pressing method claimed in this invention is used. First, the laminated structure is placed in a hot press equipped with four independently monitorable pressure actuation units, and pressure is applied... The system lowers the pressure and initiates a heating process; during the initial heating phase, in addition to monitoring the global pressure head displacement Z(t), the control system also simultaneously records the pressure feedback values ​​of the four pressure actuators. And calculate its standard deviation in real time to obtain the heterogeneity index. During the first 120 seconds of the heating process, The value once climbed to 0.1 MPa due to the difference in heat capacity in different areas within the plate. When the system judges... When the pressure exceeds a preset threshold of 0.05 MPa, it automatically enters a temperature homogenization and holding phase. By maintaining the current temperature for 20 seconds, it provides heat compensation to the densely packed copper foil areas that heat up more slowly, until the temperature is detected. The pressure dropped to 0.04 MPa before the system confirmed that the conditions for synchronous gelation within the plate had been met. After confirming the uniformity of the thermal field within the plate, subsequent decisions regarding the process flow were based on the analysis of the mechanical response of the laminated structure itself. The system continuously calculated the first-order rate of change of displacement V(t) and the second-order rate of change of displacement A(t). At t=185s, the acceleration A(t) was monitored to reach... The negative peak value indicates that the system recognizes this state as the resin viscosity inside the entire laminated structure has reached its lowest point. The system then triggers a transient pressure cycle with a total duration of 3 seconds to relieve and restore the pressure, and uses the expansion effect of the gas trapped in the micro-blind holes to expel it. The execution of this step, using the displacement acceleration A(t) information, provides a triggering basis based on the physical state of the material for the action of clearing void defects.

[0034] After completing the transient pressure cycle, the timing of applying high pressure is determined by monitoring the displacement rate V(t). The system continuously judges the changing trend of the V(t) value. At t=210s, the system detects that the V(t) value changes from -0.01mm / s crossing zero to +0.001mm / s. This zero-crossing point is confirmed as the gelation inflection point where the resin has completed impregnation and filling and the viscosity begins to rise. At this moment, the system immediately increases the pressure from... Upgraded to High pressure is applied and maintained until curing is complete; this anchors the application of high pressure to a physical state point where the resin's fluidity has decreased but it still retains plasticity, thus avoiding the possibility of resin overflow at the board edge caused by applying high pressure at low viscosity. Ultimately, the high-density rigid-flexible bonded board of this batch, which had material property deviations and structural inhomogeneities, showed no internal voids or defects after cross-sectional analysis and electrical performance testing, and no resin overflow contamination in the gold finger area at the board edge. The product yield was higher than that of the traditional fixed process curve method. In this embodiment, the entire process first uses the negative peak value of displacement acceleration to identify the lowest viscosity point to perform venting, and then uses the zero-crossing point of displacement rate to identify the gelation inflection point to apply high pressure. This judgment sequence based on different orders of mechanical response characteristics decomposes the suppression of voids and the control of resin overflow into two independent steps driven by the physical state of the material itself and executed at different time points.

[0035] To further verify the fundamental role of the step of identifying the lowest viscosity point based on the negative peak value of displacement acceleration A(t) and performing transient pressure cycling in improving the internal quality of the final product in the method claimed in this invention, the following comparative example is established.

[0036] Comparative Example 1: The test vehicle, hot pressing equipment, and basic process parameters (such as low pressure value) used in this comparative example. High voltage value The sampling frequency of the equipment and the evaluation method of the final quality are completely consistent with those in Example 1. The fundamental difference from the method claimed in this invention is that the pressing control logic of this comparative example removes the step of using the negative peak value of displacement acceleration A(t) as the first process moment and executing transient pressure cycle to clear voids accordingly. Instead, this method only executes some features of the technical solution of this invention, namely: in the low-pressure heating stage, although the system continuously monitors the pressure head displacement Z(t) and calculates the displacement rate V(t), it does not judge or make any process response to the change of acceleration A(t); the system only waits until the value of displacement rate V(t) changes from negative to positive and crosses zero, and then takes this as the only process inflection point, directly triggering the application of high pressure until curing is completed; after the pressing process is completed, the sample of this comparative example is subjected to the same slice analysis and electrical performance test as in Example 1, and the statistical results of its key performance indicators are shown in Table 1.

[0037] Table 1: Comparison of key performance indicators between Comparative Example 1 and Example 1.

[0038]

[0039] The experimental results show that, since the method in this comparative example also utilizes the displacement rate V(t) to trigger high pressure through the gelation inflection point, its effect on suppressing glue overflow at the edge of the plate is basically at the same level as that in Example 1, with an average glue overflow distance of only 0.46 mm. However, in terms of internal quality, since this method omits the key venting step of performing transient pressure cycling at the point of lowest resin viscosity (i.e., the moment indicated by the negative peak of displacement acceleration A(t)), the gas trapped inside the laminated structure due to resin flow cannot be effectively discharged within the optimal time window. Ultimately, cross-sectional analysis confirmed that the internal void ratio of the micro-blind hole array region was as high as 0.24%, which is nearly an order of magnitude lower than that of the aforementioned embodiment using the complete technical solution. Moreover, this void ratio level is close to that of the process using the traditional preset time-temperature curve, where the void ratio of the control group is 0.25%. This comparative result confirms that in the method claimed in this invention, identifying the lowest viscosity point of the resin based on the negative peak value of displacement acceleration A(t) and identifying the gelation inflection point based on the zero-crossing point of displacement rate V(t) are two functionally synergistic and indispensable technical steps. Simply binding the timing of high pressure application with the gelation inflection point can effectively suppress macroscopic glue overflow, but it cannot solve the microscopic void problem. Only by using the former as the trigger for active venting can the internal void defects be specifically eliminated within the framework of suppressing glue overflow.

[0040] Example 2: To objectively verify the effectiveness of the method claimed in this invention in suppressing resin overflow and internal voids, and the synergistic effect between its core steps, this comparative experiment was conducted. The test carrier used in the experiment was a standardized eight-layer rigid-flex plate containing patterns with a minimum linewidth spacing of 75 micrometers and an array of micro-blind holes with a diameter of 100 micrometers. The PP prepreg used was from the same batch of epoxy resin material. The test platform was a hot press with closed-loop pressure control and displacement monitoring functions, and its pressure control accuracy was [insert accuracy here]. The displacement sensor has a resolution of 1 micrometer, and the sampling frequency of the data acquisition system is set to 20Hz. This sampling frequency setting aims to balance the ability to capture physical changes during resin melting with the data processing load of the system. Three sample groups were set up in this experiment, each containing 10 identical test carrier samples. All samples were stacked under the same temperature and humidity environment to eliminate differences in initial conditions. The control group used an industry-standard two-stage thermo-pressing process, with a pre-set process curve of: applying pressure at 120℃... Maintain the pressure for 15 minutes, then raise the temperature to 185°C and increase the pressure to [unclear]. The process involves curing; some characteristic sample groups utilize certain technical features from the method of this invention, namely, determining the applied force solely by utilizing the characteristic of the displacement rate V(t) crossing zero. The timing of high pressure is described, but the step of judging based on displacement acceleration A(t) and executing transient pressure cycling is omitted; the sample group of this invention adopts the complete technical solution mentioned above, that is, sequentially executing the first process timing judgment and transient pressure cycling based on the negative peak value of A(t), and the second process timing judgment and high pressure application based on the zero crossing point of V(t); after all sample groups have completed the pressing process, each sample is quantitatively evaluated. The method for measuring the average distance of glue overflow at the plate edge is to use a tool microscope with a micrometer at the midpoint of the four plate edges of the sample to measure the distance from the plate edge baseline to the end of the resin overflow front, and take the arithmetic mean of the four measurements; the method for measuring the internal void ratio is to slice the central region of the micro-blind hole array of each sample, acquire cross-sectional images through a metallographic microscope, and calculate the void ratio using image analysis software. The percentage of the total area of ​​all cavities within the statistical area to the statistical area; the statistical results of the key performance indicators for each sample group are shown in Table 2.

[0041] Table 2: Comparison of key performance indicators of pressing quality for each sample group.

[0042]

[0043] According to the data in Table 1, the control group, due to its fixed timing of high-pressure application, failed to adapt to the actual flow state of the resin, exhibiting more obvious overflow and internal voids. Some characteristic sample groups, by binding the timing of high-pressure application with the gelation inflection point, showed a reduction in the average distance of overflow at the plate edge compared to the control group. This indicates that identifying the gelation inflection point is an effective step in controlling overflow, but due to the lack of a targeted venting step, their internal void rate was no different from the control group. The sample group of this invention, while effectively controlling overflow, showed an order-of-magnitude reduction in its internal void rate compared to the other two groups. The experimental results show that in the method claimed in this invention, the step of identifying the lowest viscosity point based on the negative peak value of displacement acceleration A(t) and performing transient pressure cycling, and the step of identifying the gelation inflection point based on the zero-crossing point of displacement rate V(t) and applying high pressure, have a functional synergy. The former provides an opportunity to address the internal void problem, while the latter provides a decision basis for suppressing overflow at the plate edge. The combined application of the two allows for targeted solutions to these two quality problems in the same pressing process, thereby achieving a comprehensive pressing quality superior to that obtained by using a single fixed process or some technical features.

[0044] Example 3: This example combines Figures 1 to 3 This document describes a method for controlling PP overflow during the manufacturing of a high-speed rigid-flex plate, such as... Figure 1As shown, the process begins with a laminated structure as input and produces a high-quality rigid-flex plate as the final output. In step one, low pressure is applied to the laminated structure and a heating program is initiated to facilitate uniform heat conduction. The subsequent step two involves a continuous monitoring phase, where the displacement of the pressure head Z(t) is monitored in real time, and the displacement rate V(t) and displacement acceleration A(t) are calculated based on this. The first key decision point of this method is to continuously determine whether the displacement acceleration A(t) reaches its negative peak. When this condition is met, the first process time is reached, and the system executes a transient pressure cycle. Its goal is to remove microscopic void precursors. After the transient pressure cycle is completed, the process enters the continuous monitoring of the displacement rate V(t). When it is determined that V(t) crosses the zero point, that is, the second process time corresponding to the gelation inflection point, the high-pressure curing action is triggered. The goal is to suppress macroscopic glue overflow. To improve the accuracy and reliability of control, the process also integrates two key modules. The first is to selectively perform online venting effect verification after the first process time to confirm the internal gas venting effect. The second is to perform a gelation uniformity judgment before triggering high pressure at the second process time to ensure that high pressure is finally applied only when the internal gelation process is uniform.

[0045] like Figure 2 As shown in the figure, a bar chart quantifies the relationship between two key response characteristic parameters exhibited by different material types during transient pressure cycling: displacement rebound amplitude and steady-state recovery time. The chart clearly reveals that, compared to standard materials, high-volatile materials exhibit increased displacement rebound amplitude due to greater internal gas expulsion, while high-viscosity materials experience a correspondingly longer steady-state recovery time due to slower resin backfilling. Figure 3 As shown, from the perspective of process timing, the entire pressing process is divided into stages and activities. The entire process starts at time T0 and ends at T3 when curing is completed. It is divided into three core process stages: stage one is low-pressure heating, stage two is gelation inflection point monitoring, and stage three is high-pressure curing. The transient pressure cycle event that occurs at time T1, based on the lowest resin viscosity, is the dividing point between stage one and stage two. The switching to high pressure event that occurs at time T2, based on the resin gelation inflection point, is the dividing point between stage two and stage three. In this timing view, the calculation of indenter displacement and derived parameters runs through the first two stages, while gelation uniformity monitoring is a parallel monitoring activity that provides a collaborative judgment basis for the final decision at time T2.

[0046] Example 4: This example illustrates a calibration procedure for determining key process control parameters involved in the method of this invention, providing a basis for setting relevant thresholds when dealing with a new rigid-flex plate product. In a scenario of setting a pressing procedure for a new twelve-layer high-frequency rigid-flex plate, since its laminated structure and material system are different from previous products, a calibration process is used in the small-batch trial production stage to obtain its unique set of process parameters. The initial objects used in the calibration process are three test samples with the same laminated structure as the final product, and the equipment used is a production-type hot press that meets the functional specifications. First, to reduce the noise in the original displacement sensor data Z(t) on subsequent... To mitigate interference from differential calculations, before entering the core calculation steps, the control system is configured to perform a moving average filter on the acquired Z(t) sequence. In this embodiment, the average value of a 5-point window is used to replace the instantaneous value at the center point to obtain a smoothed displacement sequence. All subsequent rate and acceleration calculations are based on this smoothed sequence. After the calibration process is initiated, the system runs according to a complete process method, the purpose of which is data recording and parameter extraction. When the process enters the transient pressure cycle stage triggered by the negative peak value of displacement acceleration A(t), the system records the transient response curve of the pressure head displacement Z(t) in this cycle and extracts the displacement rebound amplitude during the pressure reduction stage. The value is 0.008 mm, and the steady-state recovery time during the pressure recovery phase is also considered. The time was 2.1 seconds. After the entire calibration process was completed, the test sample was sliced ​​and analyzed. Microscopic examination confirmed that the internal micro-blind holes were well filled and there were no voids. Based on this, the system assigned this set of response characteristic parameters. The value of the void removal effect, along with its fluctuation range of 5%, is stored in the process database of the new product model. This database will serve as a benchmark for online verification of whether the void removal effect meets the standards during subsequent mass production.

[0047] Simultaneously, during this calibration operation, the system applied low pressure while superimposing a 1.0Hz periodic pressure perturbation, and continuously demodulated the displacement response to obtain the response signal amplitude R(t). After the system determined, based on the trend of the displacement rate V(t), that the resin had entered the stable liquid phase region where it was fully melted but had not yet begun to gel, the system automatically calculated and recorded the average value of the response signal amplitude R(t) within that time window, obtaining... The value is 0.015 mm; based on this, the gelation inflection point determination threshold is used for alternative implementation methods. Through calculation formula The value was determined to be 0.0045 mm, and this parameter was also stored in the process database. By performing the above-mentioned complete calibration process, a set of process control parameters with a clear source was established for this new rigid-flex plate product, including a response characteristic benchmark for verifying the venting effect and a response amplitude threshold for judging the gelation inflection point under interference environment. This allows the method of the present invention to complete parameter setting through a standardized engineering procedure when applied to new products.

[0048] Example 5: This example illustrates the built-in procedures of the method of the present invention when dealing with two boundary conditions; in one condition, when pressing a laminated structure with an abnormally high volatile content in the PP prepreg material, after the system performs the first transient pressure cycle at the first process moment, the displacement rebound amplitude is monitored. The value exceeds the calibrated reference range. Based on this, the system determines that a single cycle is insufficient to complete the exhaust and automatically triggers a second cycle. If the response characteristic parameters still do not enter the reference range after the second cycle, the system will continue to execute a compensation cycle, but this repetition will be within the preset maximum number of repetitions, such as 3 times. If the response characteristic parameters still fail to meet the reference after reaching the maximum number of repetitions, the control system will record a process alarm and execute a preset compensatory action, that is, when the gelation inflection point is subsequently detected, the high pressure originally scheduled to be applied immediately will be delayed by 0.5 seconds before being applied, thus reserving an additional window for the escape of residual gas. In another operating condition, when pressing a backplate with a large size and uneven distribution of internal copper foil, the difference in heat capacity in different regions causes a continuous temperature gradient, which makes the non-uniformity index characterizing the uniformity of the internal gelation process increase when the global displacement rate V(t) is close to zero. The pressure remains 0.05 MPa above the preset threshold. At this point, the system will automatically enter and maintain a temperature homogenization phase, during which the system not only monitors... The absolute value of the value is also calculated, along with its rate of change; if The continuous decrease indicates that the temperature inside the plate is becoming more uniform, so the system will continue to maintain this state until... Falling within the threshold range; but if detected If the non-uniformity stops decreasing at a relatively high value and remains there for more than a preset duration, such as 60 seconds, the system determines that the non-uniformity is an unrecoverable process anomaly and, according to the preset program, chooses to terminate the current pressing process or record the alarm and continue execution.

[0049] In another operating condition, when the method of the present invention is applied to a production workshop with continuous ground micro-vibrations transmitted from nearby large stamping equipment, directly performing first and second-order differential operations on the acquired raw displacement signal Z(t) will generate multiple false zero-crossings in the calculated displacement rate V(t) due to the amplification effect of background noise. This will cause the control system to prematurely trigger erroneously before the actual gelation inflection point arrives. To address this challenge, the system is switched to the alternative implementation method described above, i.e., in On the low-pressure base value, a periodic pressure perturbation with a frequency of 1.0 Hz is superimposed. In this mode, the decision basis of the control system is no longer the absolute value of V(t), but the response signal amplitude R(t) corresponding to the 1.0 Hz excitation frequency is extracted from the displacement signal through a synchronous demodulation algorithm. Since the demodulation algorithm has narrowband filtering characteristics, all random vibration noises that are independent of the excitation frequency and transmitted from the external environment are suppressed, making the demodulated R(t) curve smooth. Its cliff-like drop when the resin gels is clearly discernible. Based on this, the system captures the gelation inflection point and triggers high pressure, thus obtaining the same pressing quality as in the interference-free environment under strong noise background.

[0050] Example 6: In a scenario where a lamination process is set for a flexible circuit board using a high-flow PP prepreg, the material is sensitive to initial pressure. Too low a pressure will result in poor interlayer adhesion, while too high a pressure will cause excessive adhesive overflow. Therefore, a gradient experiment is used to determine the low-pressure setting value. The procedure first prepares a set of six identical test samples. During lamination, all process steps are kept consistent except for the initial low-pressure value. The low-pressure values ​​for these six samples are set sequentially as follows: After lamination, each sample was evaluated in two ways: first, ultrasonic scanning was used to detect any delamination areas caused by poor interlayer bonding; second, the distance of excess adhesive at the edge of the sample was measured. The experimental results showed that the low-pressure value... The sample showed localized poor bonding, and the low-pressure value was greater than or equal to... The sample showed excess glue exceeding specifications; Within the specified pressure range, the sample maintained good internal bonding quality while keeping adhesive overflow at a low level. To allow for a processing window while ensuring quality, the initial low pressure for this product was ultimately determined to be [value missing]. .

[0051] After determining the low pressure value, the threshold for the gelation inhomogeneity index was then determined. Calibration is performed; the procedure selected is the aforementioned gradient experiment, in... A sample was successfully pressed under low pressure, and pressure data records from multiple pressure actuators throughout the pressing process were retrieved. Analysis of this data revealed that in the initial heating stage... The value will rise due to uneven thermal expansion, then enter a plateau period, and finally reach a peak near the gelation inflection point due to the difference in the curing process of different regions; the value occurring during this dynamic process before the global displacement rate V(t) crosses zero is recorded. The maximum value of the batch of multiple successful samples. The average of the maximum values, plus a 20% safety margin, is used to determine the uniformity threshold for this product in mass production. This provides a quantitative standard with statistical significance and physical process basis for judging non-uniformity.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling flowable PP overflow in high speed rigid-flex board manufacturing, characterized in that, The method comprises the following steps: Step one, place a stack structure comprising at least one layer of PP prepreg into a hot-pressing device, apply a low pressure and start a heating program; Step two, during the execution of the heating program, continuously monitor the ram displacement of the hot-pressing device along the pressure direction, and based on the ram displacement, calculate a displacement rate and a displacement acceleration, wherein the displacement rate is the first-order change rate of the ram displacement, and the displacement acceleration is the second-order change rate of the ram displacement; Step three, take the time when the value of the displacement acceleration reaches the negative peak value as the first process time of the lowest point of the resin viscosity in the PP prepreg, and at the first process time, perform a transient pressure cycle of temporarily reducing and then restoring the pressure applied to the stack structure; Step four, after performing the transient pressure cycle, continue to monitor the displacement rate, and take the time when the value of the displacement rate crosses zero from positive to negative as the second process time of the gelation inflection point of the resin viscosity starting to rise from the lowest point in the PP prepreg, and at the second process time, increase the pressure applied to the stack structure from the low pressure to the high pressure, and maintain the high pressure for a preset time length to complete the curing; And, in step one, the applied low pressure comprises a constant pressure base value and a periodic pressure perturbation with a preset frequency superimposed on the constant pressure base value; and the determination of the second process time in step four is based on the change of the response signal amplitude of the head displacement to the periodic pressure perturbation, wherein the change of the response signal amplitude satisfies the following determination rule: wherein, is the real-time amplitude of the response signal, is an amplitude threshold value for determining the occurrence of gelation.

2. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The method further comprises: during the execution of the transient pressure cycle of step three, recording the transient response of the ram displacement; based on the transient response, determining a response characteristic parameter representing the internal gas discharge effect; and according to the comparison result of the response characteristic parameter with the preset reference, deciding whether to repeat the transient pressure cycle before entering step four until the response characteristic parameter meets the preset reference.

3. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 2, characterized in that, The response characteristic parameter includes the rebound amplitude of the ram displacement in the pressure reduction stage of the transient pressure cycle, and the steady-state recovery time of the ram displacement in the pressure recovery stage.

4. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The hot-pressing device applies pressure to the stack structure through multiple pressure execution units; the method further comprises: in the heating program, real-time monitoring the pressure feedback value associated with each pressure execution unit; and based on the standard deviation between multiple pressure feedback values, determining a non-uniformity index representing the uniformity of the gelation process inside the stack structure.

5. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 4, characterized in that, The trigger of increasing to the high pressure in step four also depends on whether the non-uniformity index meets the preset uniformity condition, wherein the uniformity condition is that the non-uniformity index is less than the preset uniformity threshold.

6. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The low pressure in step one is set in the range of .

7. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The continuous monitoring in step two is realized by the displacement sensor built-in the hot-pressing device.

8. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The preset frequency of the periodic pressure perturbation ranges from 0.5 Hz to 2 Hz.

9. The method for controlling flowability of PP overflow glue in high-speed rigid-flex board manufacturing according to claim 1, characterized in that, The transient pressure cycle of step three comprises: in 1-2 seconds, remove the pressure applied to the stack structure to the background pressure, and then in 1-2 seconds, restore the pressure to the level of the low pressure.

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