CN114266182A - Circuit board forming pressure optimization method and system, storage medium and equipment - Google Patents
Circuit board forming pressure optimization method and system, storage medium and equipment Download PDFInfo
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Abstract
The invention provides a method, a system, a storage medium and equipment for optimizing the molding pressure of a circuit board, wherein a finite element method is adopted, the maximum pressure at high temperature and high pressure in the circuit board press-molding process and the depressurization process specification are taken as decision variables, the minimization or on-demand control of the buckling deformation of the circuit board after the press-molding and mold opening cooling to room temperature is taken as an optimization objective function, the buckling deformation of the circuit board after the press-molding and cooling to the room temperature is rapidly and accurately simulated, and the improvement of the yield of circuit board manufacturing and the stability and reliability of the service process are facilitated.
Description
Technical Field
The invention belongs to the technical field of PCB (printed circuit board) molding and manufacturing, and particularly relates to a method and a system for optimizing molding pressure of a circuit board, a storage medium and equipment.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
With the development of mobile communication technology, the Printed Circuit Boards (PCBs for short) industry has also been rapidly developed. The PCB production integrates high and new technologies in the world, the printed circuit production technology can adopt new processes such as liquid photosensitive imaging, direct electroplating, pulse electroplating, laminated multilayer boards and the like, the manufacturing process of the printed circuit not only needs higher technology and equipment investment, but also needs experience accumulation of technicians and production personnel, and the PCB is more complex to manufacture and has higher requirements.
The process flow of the multilayer PCB is shown in fig. 1 and can be divided into eight parts: inner layer circuit, lamination, drilling, hole metallization, outer layer dry film, outer layer circuit, silk screen printing, surface process and post-process. The lamination is a process of bonding lines of all layers into a whole by utilizing the adhesiveness of a prepreg at high temperature, and the bonding is realized by mutual diffusion and permeation of macromolecules on an interface and further mutual interweaving. In the process production, materials such as copper foil, prepreg, inner layer plate, mirror surface stainless steel plate, isolation plate, kraft paper, outer layer steel plate and the like are laminated together from bottom to top through positioning holes according to the process requirements. Due to different physical and chemical properties of the materials of each layer of the PCB, residual internal stress can be generated after the materials are pressed together, so that the multilayer board is subjected to buckling deformation after demoulding. Meanwhile, after the PCB is pressed and molded, the PCB may pass through various processes such as high temperature, mechanical cutting, wet processing, etc., and these processes may also have an important influence on the deformation of the PCB. As described above, the reason why the warpage deformation occurs after the PCB is press-molded is complicated and various, and therefore, how to reduce or control the deformation caused by the difference in material characteristics or the processing becomes one of the most important problems facing PCB manufacturers.
Warpage of either the BGA package or the PCB itself can occur during PCB fabrication and surface mount components. If the BGA package is warped, the corner points of the BGA package can be maximally displaced in the thickness direction, which may cause a large amount of open circuits and bridging phenomena; if the PCB itself is warped, the board may bend up or down, pushing the solder paste inward, possibly causing an open or short circuit on the other component areas. The PCB with serious warpage even causes the problems of pillow effect, bridging and the like when the PCB is in reflow soldering with the BGA packaging chip, thereby failing.
In order to solve the problems, currently, researches on improving the warpage of the PCB and the chip in the packaging process by using a finite element method are more, but the researches mainly aim at the researches on the warpage deformation of the PCB in the service process and the reflow soldering process, and only relate to the researches in the PCB press-forming process, and have certain limitations in practical application.
Disclosure of Invention
The invention aims to solve the problems and provides a method, a system, a storage medium and equipment for optimizing the forming pressure of a circuit board.
According to some embodiments, the invention adopts the following technical scheme:
a circuit board forming pressure optimization method comprises the following steps:
establishing a simulation model of circuit board press-forming, taking the maximum pressure and the pressure reduction process specification of the circuit board at high temperature and high pressure in the press-forming process as decision variables, opening the die of the circuit board after press-forming and cooling to the minimum value of the warpage deformation of the circuit board to room temperature or controlling the minimum value as required as an optimization objective function, and numerically solving a stress strain field and a displacement field in the press-forming process of the circuit board under the conditions of different maximum pressures and different pressure reduction process specifications through thermal-chemical-mechanical coupling analysis to obtain the optimal pressure and the optimal pressure reduction process specification in the high temperature and high pressure stage of the press-forming process of the circuit board.
As an alternative embodiment, the specific process of establishing the simulation model of the circuit board press-fit molding includes: establishing a geometric model of the circuit board through a graphical interface of finite element software, or generating a data file by using the geometric modeling software, then introducing the data file into the finite element software, establishing the geometric model of the CCL substrate, the prepreg and the wiring layers of the circuit board layer by layer along the thickness direction according to the lamination sequence, and then geometrically partitioning each wiring layer according to the outline size of the circuit board.
As an alternative embodiment, the specific process of establishing the simulation model of the circuit board press-fit molding includes: establishing a material performance model of the circuit board, geometrically partitioning each wiring layer, defining uniform and equivalent material performance in the partition to simplify the model, and defining equivalent material performance parameters corresponding to the area according to different copper contents in each partition, thereby macroscopically representing the nonuniformity of the copper contents of the wiring layers in the in-plane and interlayer distribution and further reflecting the circuit characteristics of the wiring diagram.
As an alternative embodiment, the specific process of establishing the simulation model of the circuit board press-fit molding includes: establishing a unit cell model of the circuit board, establishing a series of copper-resin mixed unit cell models with copper content from 0% to 100% for geometric partitions of different copper contents of the wiring layer based on a mesomechanics theory, establishing periodic boundary conditions for the unit cell models according to the position characteristics of the unit cell models in a macroscopic geometric model of the circuit board, and calculating to obtain equivalent material performance parameters of the unit cell models with different copper contents.
As an alternative embodiment, the process of numerically solving the stress strain field and the displacement field in the circuit board press-forming process through thermal-chemical-mechanical coupling analysis includes: based on the geometric model, the material performance model and the unit cell model of the circuit board, establishing initial conditions and boundary conditions of mechanical displacement constraint and load and initial conditions and boundary conditions of heat transfer according to actual pressing process conditions; obtaining material performance parameters of the circuit board according to experimental tests, wherein the material performance parameters comprise density, specific heat capacity, heat conductivity coefficient, thermal expansion coefficient, chemical shrinkage, modulus, Poisson ratio and the like, then constructing a simulation model of the circuit board press-forming, and carrying out numerical solution on stress, strain and displacement of the circuit board in the press-forming process through finite element software.
As an alternative embodiment, the calculation process of the warpage deformation of the circuit board after the press-fit molding and after the mold opening and cooling to the room temperature comprises the following steps: based on the simulation model of the circuit board press-fit molding, initial conditions and boundary conditions of heat transfer and mechanics required by simulation and required material performance parameters, the composite material mesomechanics, the composite material thermal-elastic theory, the composite material structural mechanics and the generalized Maxwell viscoelasticity theory are adopted, the thermal-chemical-mechanical coupling stress strain field and the displacement field of the circuit board in the press-fit molding process are numerically solved, and then the maximum relative displacement of the surface of the circuit board in the thickness direction after the die sinking is finished through data processing and graphical interaction interfaces is obtained, namely the obtained buckling deformation.
As a further limitation, in the process of calculating the warpage deformation of the circuit board after the pressing and die sinking, the mechanical boundary condition, the thermal transmission boundary condition and other process parameters in the cold pressing stage are kept unchanged, the maximum pressure and the depressurization process specification in the constant-pressure constant-high-temperature stage in the circuit board hot pressing process are optimized, the stress, the strain and the displacement of the circuit board after the pressing and die sinking are cooled to the room temperature are obtained by utilizing a finite element simulation means under different maximum pressures and different depressurization process specifications, and the influence of the pressure condition in the circuit board pressing and molding process under high temperature and high pressure on the warpage deformation of the circuit board after the pressing and molding process is analyzed, so that the pressure optimization target in the circuit board pressing and molding process is achieved.
As an alternative, the depressurization process specification refers to the pressure relief rate and time requirements of the pressure relief stage of the press, including the total time for the different pressure relief stages, the pressure magnitude at each moment of the pressure relief stage, and the like.
A circuit board forming pressure optimization system, comprising:
the model building module is used for building a simulation model of the circuit board press-fit molding, and comprises a circuit board geometric model, a material performance model of the circuit board and a unit cell model of the circuit board;
the parameter setting module is used for setting parameters required by numerical solution of a thermal-chemical-mechanical coupling stress strain field and a displacement field in the circuit board press-fit molding process, and comprises the steps of establishing initial conditions and boundary conditions of mechanical displacement constraint and load, and initial conditions and boundary conditions of heat transfer according to actual press-fit process conditions; the material performance parameters of the circuit board obtained according to experimental tests comprise a plurality of density, specific heat capacity, heat conductivity coefficient, thermal expansion coefficient, chemical shrinkage rate, modulus and Poisson ratio;
and the optimization solving module is used for taking the maximum pressure and the depressurization process specification of the circuit board at high temperature and high pressure in the circuit board press-forming process as decision variables, and minimizing or controlling the warpage deformation of the circuit board after press-forming and mold opening and cooling to room temperature as an optimization objective function as required.
An electronic device comprising a memory and a processor and computer instructions stored on the memory and executed on the processor, the computer instructions, when executed by the processor, performing the steps of the above method.
A computer readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the above method.
Compared with the prior art, the invention has the beneficial effects that:
the invention establishes a finite element simulation method of the PCB press-fit molding process, which is used for improving the buckling deformation of the PCB after press-fit molding, namely, the buckling deformation of the PCB after press-fit molding is reduced by changing the maximum pressure in the press-fit stage and the pressure reduction process specification without repeatedly testing and improving the process through experiments, thereby effectively reducing the cost, further providing theoretical guidance for the design of PCB products and improving the stability of the subsequent processing process of the PCB.
The invention establishes a mathematical model of multilayer PCB press-fit molding, which is used for providing theoretical support for finite element simulation in the process of PCB press-fit molding with larger size, and takes the minimum warpage deformation amount of the PCB press-fit molding die-sinking cooling to room temperature or the control as an objective function as required by means of computer software and a numerical calculation method to complete the objective of pressure optimization in the process of PCB press-fit molding.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a process flow diagram of a multi-layer PCB manufacturing process;
FIG. 2 is a technical route of a PCB press-fit molding finite element simulation according to the present invention;
FIG. 3 is a graph of temperature, resin cure, and time, as simulated during a PCB lamination stage according to one embodiment;
FIG. 4 is a pressure history applied to the upper platen by the four-component bonding process according to one embodiment;
fig. 5 is a simulation result and an experimental result of the relative warpage deformation amount of the PCB when the PCB is opened and cooled to room temperature under different maximum pressures in the thermal compression stage according to the four embodiments of the first embodiment;
FIG. 6 is a graph of the surface temperature of the PCB in the bonding stage according to the three embodiments of the second embodiment;
FIG. 7 is a pressure history applied to the upper platen during the pressing stage by the three embodiments related to the second embodiment;
fig. 8 is a simulation result and an experimental result of the relative warpage deformation of the PCB when the PCB is opened and cooled to room temperature under different pressure reduction process specifications in the thermal compression stage according to the three embodiments of the second embodiment.
The specific implementation mode is as follows:
the invention is further described with reference to the following figures and examples.
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The method adopts a finite element method, takes the maximum pressure at a high-temperature high-pressure stage in the PCB press-fit molding process and the depressurization process specification thereof as decision variables, minimizes the warpage deformation of the PCB after press-fit molding after mold opening and cooling to room temperature or controls the PCB to be an optimized objective function as required, quickly and accurately simulates the warpage deformation of the PCB after press-fit and cooling to room temperature, verifies the warpage deformation result with an experimental test of the PCB under the same condition, and then uses the warpage deformation result to improve the press-fit molding process specification in the actual production process, thereby achieving the purposes of improving the yield of the PCB in the manufacturing process and ensuring the reliability and stability of the PCB in the service process.
The invention adopts the basic idea of 'isotropy in equal-length partitions and partitions' to establish a geometric model and a material performance model of the PCB, and the specific contents comprise: the method comprises the steps of establishing a geometric model layer by layer of a CCL substrate, a prepreg and wiring layers of the PCB according to a lamination sequence, carrying out geometric partitioning on each wiring layer, then establishing equivalent material performance parameters in partitions according to the volume content of copper in each partition, and carrying out numerical simulation on warping deformation evolution in the PCB press-molding process, wherein a specific numerical simulation technical route is shown in FIG. 2.
A pressure optimization method for reducing warping deformation in a PCB lamination molding process comprises the following steps:
(1) establishing a geometric model of PCB press-fit molding: according to the invention, a partitioned and layered modeling idea is adopted, a CCL substrate, a prepreg and wiring layers (mixed layers with copper and resin) of a PCB are built into a geometric model layer by layer according to a lamination sequence, then geometric partitioning is carried out on each wiring layer according to the outline size of a circuit board, and an upper pressing plate and a lower pressing plate are used as a mold structure.
(2) Establishing an equivalent material performance model in a PCB partition: and defining uniform and equivalent material performance for the geometric subarea of each wiring layer to simplify the model, and defining different equivalent performance parameters of the area according to different copper contents in the subarea, thereby showing the nonuniformity of the distribution of the copper contents of the wiring layers in the surface and among the layers macroscopically. Based on a mesomechanics theory, a series of copper-resin hybrid unit cell models with different copper contents are established for partitions with different copper contents of the wiring layer, meanwhile, periodic boundary conditions are established for the unit cell models according to the position characteristics of the unit cell models in the PCB macroscopic finite element model, and equivalent performance parameters of the unit cell models with different copper contents are obtained through calculation.
(3) Establishing a simulation model of PCB press-forming: based on a geometric model, a material performance model and a unit cell model of the PCB, establishing initial conditions and boundary conditions of mechanical displacement constraint and load and initial conditions and boundary conditions of heat transfer according to actual pressing process conditions; the material performance parameters of the circuit board, including density, specific heat capacity, thermal conductivity, thermal expansion coefficient, chemical shrinkage, modulus, Poisson's ratio, etc., are obtained according to experimental tests and are input into finite element software.
The simulation model of the circuit board press-fit molding comprises a unit cell model of the circuit board and a geometric model of the circuit board, wherein the unit cell model of the circuit board is firstly constructed to obtain equivalent material performance parameters corresponding to the unit cell models with different copper contents, then the material attributes are given to the geometric model of the circuit board in finite element software, and finally the simulation model of the circuit board press-fit molding is jointly constructed.
(4) And (3) numerical solution calculation: the simulation model based on the PCB press-fit molding adopts the composite material mesomechanics, the composite material thermal-elastic theory, the composite material structural mechanics and the generalized Maxwell viscoelasticity theory, numerically solves the stress, strain and displacement in the PCB press-fit molding process through the thermal-chemical-mechanical coupling analysis, and further obtains the buckling deformation of the PCB after the press-fit is finished, and the PCB is subjected to die sinking and cooling to the room temperature through data processing and graphical interactive interface calculation.
(5) Pressure optimization at high temperature and high pressure in the PCB press-forming process: based on a PCB press-fit molding simulation model and a numerical calculation method, the mechanical boundary condition, the heat transfer boundary condition and other process parameters in the cold press-fit stage are kept unchanged, and the pressure conditions (maximum pressure and depressurization process specification) in the constant-temperature constant-pressure stage in the PCB hot press-fit process are optimized.
The method can utilize a finite element simulation means and an experimental test under the same condition, obtain a warping amount simulation result and an experimental result of the PCB in the thickness direction when the PCB is opened and cooled to room temperature under different maximum pressures and different pressure reduction process specifications, analyze the influence of the pressure conditions at the constant-temperature and constant-pressure stage in the PCB press-forming process on the warping deformation of the PCB after press-forming through comparison and verification, and determine the optimal pressure conditions and the optimal pressure reduction process in the PCB press-forming process so as to improve the actual press-forming process.
Certainly, in this embodiment, the constant high temperature in the PCB lamination process is the maximum temperature of the PCB surface layer at the thermal lamination stage in the analog simulation process of 200 ℃; the constant high voltage in the PCB laminating process is 2.89MPa of the highest voltage of the PCB in the hot laminating stage in the analog simulation process; the pressure and the pressure reduction process specification of the constant high pressure and the constant high temperature stage in the hot pressing process are changed into the maximum pressure, the pressure reduction rate and the pressure value under the high temperature and the high pressure in the hot pressing stage.
In other embodiments, however, other settings for the high pressure, high temperature values may be made.
A warpage-reducing pressure optimization system for a press-in molding process of a PCB, comprising:
the model building module is used for building a PCB geometric model including a mould structure, an equivalent material performance model in a PCB wiring layer partition, a single cell model of the PCB and a mathematical model for numerical calculation, and the models jointly form a simulation model of a PCB press-fit molding process;
the parameter acquisition module is used for acquiring process parameters such as specific temperature, pressure, time and the like in a pressing stage in the PCB production process, initial conditions and boundary conditions of actual mechanical constraint and load, initial conditions and boundary conditions of heat transfer, and material performance parameters of the PCB, including density, specific heat capacity, heat conductivity coefficient, thermal expansion coefficient, chemical shrinkage rate, modulus, Poisson ratio and the like;
the numerical simulation module is used for carrying out numerical simulation on the processes from press-forming to die sinking and cooling to room temperature based on a simulation model of the PCB press-fitting process, and firstly solving the chemical reaction heat release and the PCB temperature field of the resin by utilizing chemical-thermal coupling analysis; then solving the chemical shrinkage strain and the thermal expansion and cold contraction strain of the composite material through the mesomechanics of the composite material and the thermal-elastic theory of the composite material; then, utilizing thermal-chemical-mechanical coupling analysis to solve the strain, strain and displacement of the PCB in the laminating process; and finally, solving the warpage deformation of the PCB after the pressing and the die sinking and the cooling to the room temperature through the composite material structure mechanics, the anisotropic visco-elastic mechanics and the thermal-visco-elastic mechanics theory of the composite material structure.
The parameter optimization module is used for changing pressure process parameters in the pressing process, including changing the highest pressure and depressurization process specification in the constant high temperature and constant high pressure stage in the hot pressing process, and other pressing process parameters are not changed, respectively performing numerical simulation on the PCB pressing process, obtaining a buckling deformation sensitivity curve of opening the mold and cooling to room temperature after the PCB pressing under different highest pressures and different depressurization process specifications is finished, and determining the influence degree of the pressure process parameters on the numerical simulation result, thereby achieving the purposes of pressure optimization of PCB high temperature and high pressure molding and reduction of the buckling deformation after PCB pressing molding.
The first embodiment is as follows:
in this embodiment, a mobile phone motherboard with an outline size of 260mm × 160mm is used as a research object, a geometric model is first built on the PCB in a layered and partitioned manner, irregular geometric features such as bumps and pits are ignored during the modeling process, a wiring layer of the PCB is equally partitioned into 20 geometric regions in a 4 × 5 manner, the PCB has 8 wiring layers in total, the CCL substrate layer, the prepreg and the wiring layer are geometrically modeled respectively, and different equivalent performance parameters are defined according to copper contents corresponding to the positions of the partitions.
In the finite element software, mechanical and thermal initial conditions and boundary conditions are set according to actual pressing process parameters, and corresponding material performance parameters are respectively given to each layer according to actual different laminated layers. The numerical simulation process comprises the following steps: firstly, calling a program containing a resin curing reaction kinetic equation and a composite material viscoelasticity constitutive equation to calculate the temperature and resin curing degree evolution of the PCB in the process of opening the mold and cooling to room temperature after lamination; and then calling a program containing a composite material thermal-elastic theory, composite material structure mechanics and a generalized Maxwell viscoelasticity theory to calculate the stress, strain and displacement of the PCB in the pressing process, and simulating the material behaviors of the PCB such as curing reaction shrinkage, thermal expansion and cold contraction and the like and the mechanical response under pressure, such as the stress, the strain state, the PCB buckling deformation state and the like. The pressing process comprises a hot pressing process of 16400s, a cold pressing process of 3800s and a process of 3000s of opening the die and cooling to room temperature. FIG. 3 is a graph of temperature and resin cure versus time obtained from PCB simulation during the lamination stage. In the experiment process corresponding to the simulation, the technological parameters and the like in the pressing process are ensured to be consistent with the set parameters of the simulation, and the obtained experiment result is compared with the simulation result.
On the basis of the simulation result, the pressing force (the pressure changing along with the time) applied on the upper pressing plate is changed, the mechanical boundary condition, the thermal conductivity boundary condition and the process parameters in the cold pressing stage are not modified, the temperature field of the PCB is calculated firstly, then the temperature field is used as a predefined field for stress-strain calculation, the displacement and the distribution of the thickness direction of the PCB when the PCB is opened and cooled to the room temperature are further calculated and output, and the buckling deformation of the PCB when the PCB is opened and cooled to the room temperature is obtained.
This example relates to four sets of equations. One group is a control group, namely the maximum constant temperature and pressure of the PCB in the thermal compression stage is set to be 2.89MPa, and the other three groups are used for keeping other conditions unchanged, and only the maximum constant temperature and pressure of the thermal compression stage is respectively changed to be 1.45MPa, 2.00MPa and 3.20 MPa. The temperature field of the PCB is calculated firstly and then used as a predefined field for stress strain field calculation, so that the warpage deformation of the PCB when the PCB is opened and cooled to room temperature is obtained through data processing, a simulation result is compared with an experiment result, and the actual press-forming process is improved, so that the production cost is reduced, and the yield of products is improved. Fig. 4 is a pressure history of the upper platen during four exemplary pressing operations. Fig. 5 shows the simulation result and the experimental result of the maximum pressure PCB relative warpage deformation at the thermal compression stage with four embodiments. Table 1 is a table (partial) of time-pressure data for the upper platen for a four-component example lamination process.
TABLE 1 time-pressure data sheet (local) of upper platen in four-group arithmetic example press-fitting process
From the above results, it is known that under the same other conditions, the warpage deformation amount of the PCB is gradually decreased as the maximum pressure at high temperature and high pressure is increased; the higher the maximum pressure at high temperature and high pressure is, the more remarkable the strain (pure mechanical strain) which can not cause the PCB buckling deformation is than the strain (mainly chemical shrinkage strain) which can cause the PCB buckling deformation is, and accordingly, the influence degree of the strain (mainly chemical shrinkage strain) which can cause the PCB buckling deformation on the PCB buckling deformation is weakened in the viscoelastic deformation process with larger strain. The maximum pressure of the high temperature and the high pressure is continuously increased, and the safe production pressure and the manufacturing cost are increased, so that it is not desirable to extend an excessive time in the actual production process. The scheme of reducing the warpage deformation of the PCB in the press-fit molding process is feasible by properly improving the maximum pressure under high temperature and high pressure in the hot-press-fit stage, so that the warpage deformation of the PCB after the press-fit is finished and the mold-opening cooling is carried out to the room temperature can be reduced according to the optimized design system and method.
Example two:
in this embodiment, the same PCB as in the first embodiment is used as a research object, and the modeling scheme, the material parameter definition, and the like are the same as in the first embodiment. The embodiment includes three sets of calculation examples, wherein one set of calculation examples is to simultaneously release pressure and reduce temperature in a hot-pressing state with high temperature and high pressure, the simultaneous release and reduction of temperature refers to reducing the temperature of the PCB from a certain pressure of 0.69MPa to 774Pa in a hot-pressing stage, reducing the temperature from a certain temperature of 198 ℃ to 25 ℃, and the hot-pressing process parameters used by the other two sets of calculation examples are the same, and the two sets of calculation examples are respectively to release the pressure from the high temperature of 198 ℃ to 1Pa and reduce the temperature from 0.1Pa in the hot-pressing stage when the pressure of the PCB is 687055 Pa. Only the pressure reduction specification of the hot pressing stage is changed, the convective heat transfer coefficient and the process parameters of the cold pressing stage are not changed, the temperature field of the PCB is calculated firstly, and then the temperature field is used as a predefined field for stress strain calculation, so that the displacement distribution and the size of the PCB in the thickness direction when the mold is opened and cooled to the room temperature are calculated and output. Tables 2, 3 and 4 are the setting data tables (local) of time-temperature and time-pressure of the temperature fields of the current three groups of calculation examples and the corresponding time tables of each stage. Fig. 6 is a graph of the surface temperature of a PCB over time for three exemplary formulations during the bonding stage. FIG. 7 is a pressure history applied to the upper platen during three exemplary compression phases. Fig. 8 is a simulation result and an experimental result of the relative warpage deformation of the PCB corresponding to three calculation examples by changing the depressurization process specification of constant high temperature and constant high pressure at the thermal compression stage.
TABLE 2 three calculation examples time-temperature setting data table (local) of thermocompression bonding stage
TABLE 3 data sheet for time-pressure setting of three sets of arithmetic upper press plates (partial)
TABLE 4 corresponding time tables for each stage
From the above results, it is understood that the simulated warpage deformation of the PCB is reduced by 10.76% and 10.88% in the thermal compression stage, in which the pressure is released at high temperature and high pressure and the temperature is reduced, respectively, as compared with the case where the pressure is released to 0.1Pa and 1Pa first and then the temperature is reduced. This is probably because the mechanical equilibrium state of the PCB under high temperature and high pressure is destroyed by the large pressure relief at high temperature, and the residual thermal stress is not completely relaxed, so that the warpage of the PCB is increased, and therefore the pressure relief specification at constant high temperature and constant time has a large influence on the warpage deformation of the PCB. According to the results of the embodiment, the decompression standard at high temperature and high pressure in the hot pressing stage can affect the warpage deformation of the PCB after the pressing and molding, the scheme of reducing the warpage deformation of the PCB in the pressing and molding process by simultaneously releasing pressure and cooling in the hot pressing stage is feasible, the decompression standard in the hot pressing stage can be properly adjusted, and the warpage deformation of the PCB after the pressing and molding is finished and the mold opening and the cooling are reduced to the room temperature according to the optimized design system and the optimized design method.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A circuit board forming pressure optimization method is characterized by comprising the following steps: the method comprises the following steps:
establishing a simulation model of circuit board press-forming, taking the maximum pressure and the pressure reduction process specification of the circuit board at high temperature and high pressure in the press-forming process as decision variables, opening the die of the circuit board after press-forming and cooling to the minimum value of the warpage deformation of the circuit board to room temperature or controlling the minimum value as required as an optimization objective function, and numerically solving a stress strain field and a displacement field in the press-forming process of the circuit board under the conditions of different maximum pressures and different pressure reduction process specifications through thermal-chemical-mechanical coupling analysis to obtain the optimal pressure and the optimal pressure reduction process specification in the high temperature and high pressure stage of the press-forming process of the circuit board.
2. The circuit board forming pressure optimization method according to claim 1, wherein: the specific process for establishing the circuit board press-fit molding simulation model comprises the following steps: establishing a geometric model of the circuit board through a graphical interface of finite element software, or generating a data file by using the geometric modeling software, then introducing the data file into the finite element software, establishing the geometric model of the CCL substrate, the prepreg and the wiring layers of the circuit board layer by layer according to the lamination sequence, and then geometrically partitioning each wiring layer according to the outline size of the circuit board.
3. The circuit board forming pressure optimization method according to claim 1, wherein: the specific process for establishing the circuit board press-fit molding simulation model comprises the following steps: establishing a material performance model of the circuit board, geometrically partitioning each wiring layer, defining uniform and equivalent material performance in the partition to simplify the model, and defining equivalent material performance parameters corresponding to the area according to different copper contents in each partition, thereby macroscopically representing the nonuniformity of the copper contents of the wiring layers in the in-plane and interlayer distribution and further reflecting the circuit characteristics of the wiring diagram.
4. The circuit board forming pressure optimization method according to claim 1, wherein: the specific process for establishing the circuit board press-fit molding simulation model comprises the following steps: establishing a unit cell model of the circuit board, establishing a series of copper-resin mixed unit cell models with different copper contents for the geometric partitions of the wiring layer with different copper contents based on a mesomechanics theory, establishing periodic boundary conditions for the unit cell models according to the position characteristics of the unit cell models in the macroscopic geometric model of the circuit board, and calculating to obtain equivalent material performance parameters of the unit cell models with different copper contents.
5. The circuit board forming pressure optimization method according to claim 1, wherein: the process of numerically solving the stress strain field and the displacement field in the press-forming process of the circuit board through thermal-chemical-mechanical coupling analysis comprises the following steps: based on the geometric model, the material performance model and the unit cell model of the circuit board, establishing initial conditions and boundary conditions of mechanical displacement constraint and load and initial conditions and boundary conditions of heat transfer according to actual pressing process conditions; obtaining material performance parameters of the circuit board according to experimental tests, wherein the material performance parameters comprise a plurality of density, specific heat capacity, heat conductivity coefficient, thermal expansion coefficient, chemical shrinkage rate, modulus and Poisson ratio, then constructing a simulation model of the circuit board press-forming, and carrying out numerical solution on stress, strain and displacement of the circuit board in the press-forming process through finite element software.
6. The circuit board forming pressure optimization method according to claim 1, wherein: the calculation process of the buckling deformation of the circuit board after the press molding and after the mold opening and the cooling to the room temperature comprises the following steps: based on the simulation model of the circuit board press-fit molding, initial conditions and boundary conditions of heat transfer and mechanics required by simulation and required material performance parameters, the composite material mesomechanics, the composite material thermal-elastic theory, the composite material structural mechanics and the generalized Maxwell viscoelasticity theory are adopted, the thermal-chemical-mechanical coupling stress strain field and the displacement field of the circuit board in the press-fit molding process are numerically solved, and then the maximum relative displacement of the surface of the circuit board in the thickness direction after the die sinking is finished through data processing and graphical interaction interfaces is obtained, namely the obtained buckling deformation.
7. The circuit board forming pressure optimization method according to claim 6, wherein: in the process of calculating the warpage deformation of the circuit board after the pressing and the die sinking, keeping the mechanical boundary condition, the thermal transmission boundary condition and other process parameters in the cold pressing stage unchanged, obtaining the stress, strain and displacement of the circuit board after the pressing and the die sinking and cooling to room temperature by using a finite element simulation means under different maximum pressures and different pressure reduction process specifications, analyzing the influence of the pressure condition in the circuit board pressing and forming process under high temperature and high pressure on the warpage deformation of the circuit board after the pressing and the forming process, and optimizing the circuit board hot pressing process, thereby achieving the aim of optimizing the pressure in the circuit board forming process.
8. The utility model provides a circuit board shaping pressure optimizing system which characterized by: the method comprises the following steps:
the model building module is used for building a simulation model of the circuit board press-fit molding, and comprises a circuit board geometric model, a material performance model of the circuit board and a unit cell model of the circuit board;
the parameter setting module is used for setting parameters required by numerical solution of a thermal-chemical-mechanical coupling stress strain field and a displacement field in the circuit board press-forming process, and comprises the steps of establishing initial conditions and boundary conditions of mechanical displacement constraint and load, and initial boundary value initial conditions and boundary conditions of heat transfer according to actual press-forming process conditions; the material performance parameters of the circuit board obtained according to experimental tests comprise a plurality of density, specific heat capacity, heat conductivity coefficient, thermal expansion coefficient, chemical shrinkage rate, modulus and Poisson ratio;
and the optimization solving module is used for taking the maximum pressure and the depressurization process specification of the circuit board at high temperature and high pressure in the press-fit molding process as decision variables, and minimizing or controlling the warpage deformation of the circuit board after the press-fit molding after the mold opening and cooling to room temperature as an optimization objective function according to needs.
9. An electronic device, characterized by: comprising a memory and a processor and computer instructions stored on the memory and executed on the processor, which when executed by the processor, perform the steps of the method of any one of claims 1 to 7.
10. A computer-readable storage medium characterized by: for storing computer instructions which, when executed by a processor, perform the steps of the method of any one of claims 1 to 7.
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| JP2007110051A (en) * | 2005-09-15 | 2007-04-26 | Denso Corp | Device for adjusting warpage amount of circuit board |
| US20140285979A1 (en) * | 2013-03-25 | 2014-09-25 | International Business Machines Corporation | Minimizing printed circuit board warpage |
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