Compression molding method of laminated board

Abstract

A pressing forming method of a laminated board comprises the following steps that a board prefabricated material is put into a pressing machine, and the pressing machine is closed; in the temperature rise starting stage, the pressure of the press is increased to the closing pressure and kept, and the plate prefabricated material is pressed under the closing pressure; increasing the pressure of the press from the closing pressure to a first boosting pressure set value, then reducing the pressure, then increasing the pressure to the first boosting pressure set value, and maintaining the pressure; s4, increasing the pressure of the press from the nth boosting pressure set value to the (n + 1) th boosting pressure set value (n = 1, 2, 3,...), then reducing the pressure, then increasing to the (n + 1) th boosting pressure set value and maintaining the pressure, repeating until the pressure of the press reaches the curing pressure set value, and executing the step S4; when the pressure of the press is increased to the curing pressure set value from the (n + 1) th boosting pressure set value, reducing the pressure to a curing pressure-reducing pressure set value, then increasing to the curing pressure set value and maintaining the pressure, and keeping the temperature at high temperature during pressure-maintaining curing; and cooling and reducing the pressure to obtain the press-molded laminated board.

Description

Technical Field

[0001] The present invention belongs to the technical field of laminate processing, and more specifically, relates to a method for pressing and forming a copper-clad laminate. Background Art

[0002] Copper-clad laminates are the basic materials for manufacturing printed circuit boards, which are widely used in various industries such as electronic equipment, communication devices, computers, automotive electronics, and household appliances. With the booming development of the global electronic information industry and the environmental protection automotive industry, various assembly technologies are changing with each passing day, and the component assembly density per unit area is getting higher and higher, especially in the aspects of packaging modules and BGA technology. Therefore, higher requirements are put forward for the flatness and dimensional stability of PCBs, which correspondingly requires the base material of PCB boards, namely copper-clad laminates, to have higher flatness and higher dimensional stability. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for pressing and forming a laminate that can improve the flatness and dimensional stability of the board.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A method for pressing and forming a laminate, the steps are as follows: Put the prefabricated board material into a press and close the press;

[0006] S1. Start the heating stage, raise the pressure of the press to the closing pressure and hold the pressure, and press the prefabricated board material under the closing pressure;

[0007] S2. Raise the pressure of the press from the closing pressure to the first pressure increase setting value, then reduce the pressure to the first pressure reduction setting value, and then raise the pressure of the press to the first pressure increase setting value and hold the pressure. The first pressure reduction setting value is less than the first pressure increase setting value and greater than the closing pressure;

[0008] S3. Raise the pressure of the press from the nth pressure increase setting value to the (n + 1)th pressure increase setting value, n = 1, 2, 3,..., then reduce the pressure to the (n + 1)th pressure reduction setting value, and then raise it to the (n + 1)th pressure increase setting value and hold the pressure. The (n + 1)th pressure reduction setting value is less than the (n + 1)th pressure increase setting value and greater than the nth pressure increase setting value. Repeat step S3 until the pressure of the press reaches the curing pressure setting value, and execute step S4;

[0009] S4. When the pressure of the press decreases while rising from the (n + 1)-th pressure rising set value to the curing pressure set value, the pressure of the press is decreased to the curing pressure decreasing set value, then rises to the curing pressure set value again and is kept under pressure at the constant temperature curing temperature. The curing pressure decreasing set value is greater than the (n + 1)-th pressure rising set value and less than the curing pressure set value.

[0010] S5. Cool and depressurize to obtain the laminated board formed by pressing.

[0011] For the method for forming the laminated board as described above, optionally, a stepped heating method is adopted during heating. The stepped heating method is divided into several sections. At the beginning of each section, the temperature is raised by a heater. When the temperature reaches the upper limit of the temperature of this section, the heating stops and heat preservation is carried out until the end of the time of this section, and then enters the next section, repeating the process of heating - constant temperature - heating until the temperature reaches the constant temperature curing temperature value.

[0012] For the method for forming the laminated board as described above, optionally, during heating, first preheat to 90 - 100 °C, then raise the temperature to 135 - 155 °C, then raise the temperature to 165 - 180 °C, and then raise the temperature to the constant temperature curing temperature.

[0013] For the method for forming the laminated board as described above, optionally, a tracking heating method is adopted during heating. The tracking heating method adopts a continuous heating method, and the actual heating rate is adjusted based on the heating rate curve drawn according to the heating rate required by the product, and the temperature is raised to the constant temperature curing temperature within the set time.

[0014] For the method for forming the laminated board as described above, optionally, during heating, first preheat to 90 - 100 °C and raise the temperature to the constant temperature curing temperature in 40 - 60 minutes.

[0015] For the method for forming the laminated board as described above, optionally, the constant temperature curing temperature is 180 - 250 °C; and / or, the curing pressure set value is 28 - 40 kg / cm 2 ; and / or, during cooling, the temperature is decreased to ≤120 °C.

[0016] For the method for forming the laminated board as described above, optionally, during the cooling process, the temperature is decreased at a rate of 0.5 - 3.5 °C per minute from the constant temperature curing temperature value.

[0017] For the method for forming the laminated board as described above, optionally, during the cooling process, when the temperature reaches the Tg value of the laminated board, the pressure is decreased and then pressurized again, and finally the pressure is decreased.

[0018] For the method for forming the laminated board as described above, optionally, during the cooling stage, when the temperature reaches the Tg value of the laminated board, the pressure is decreased from the curing pressure set value to 15 - 20 kg / cm2 and then pressurize to 23 - 30 kg / cm 2 and then reduce the pressure to the closing pressure.

[0019] For the laminate pressing and forming method as described above, optionally, in the cooling stage, the pressure is reduced at a rate of 0.5 - 1.5 kg / cm per minute from the curing pressure setting value 2 When the pressure drops to 22 - 25 kg / cm 2 rapidly reduce the pressure, and the rate at this time is greater than 0.5 - 1.5 kg / cm per minute 2 reduce the pressure to 15 - 20 kg / cm 2 and then increase it to 23 - 30 kg / cm 2 and then reduce the pressure to the closing pressure at a rate of 0.5 - 1.5 kg / cm per minute 2

[0020] It can be seen from the above technical solutions that the present invention adjusts the pressurization method in the pressing and forming process. Through operations of pressurization, pressure relief, and then re - pressurization, the inter - layer gaps and voids of the laminate are more fully filled in the molten state of the polymer resin polymer, thereby improving the density of the board and improving the resin voids of the base material. In addition, the internal stress generated by the polymer resin polymer in the laminate during the high - temperature curing process, and the stress generated by the inconsistent expansion and contraction of the two different materials, namely the inorganic material and the polymer resin polymer in the laminate during the temperature change process, these residual internal stresses are stretched and released through the pressurization method of pressurization, pressure relief, and then re - pressurization in the pressing and forming process, thereby improving the flatness and dimensional stability of the board. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a schematic diagram of the pressure change during the pressing and forming process of the laminate using the conventional process;

[0023] Figure 2 It is a schematic diagram of the pressure change during the pressing and forming process of the laminate using the method of the present invention;

[0024] Figure 3 It is a schematic diagram of the stepped temperature - rising method during the pressing and forming process of the laminate;

[0025] Figure 4 ​It is a schematic diagram of the tracking heating method during the pressing process of the laminate. Detailed implementation mode

[0026] The present invention will be described in detail below with reference to the accompanying drawings. When describing the embodiments of the present invention in detail, for the convenience of explanation, the drawings showing the device structure will be enlarged locally in a non-general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention here. It should be noted that the drawings are in a simplified form and all use non-precise proportions, only for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention. At the same time, in the description of the present application, terms such as "first" and "second" are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features; terms such as "front", "back", "bottom", "top", "bottom" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0027] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can also be the communication inside two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0028] The copper-clad laminate is also called copper-clad laminate. In the preparation process of the copper-clad laminate, first, reinforcing materials such as glass fiber cloth (inorganic material) are impregnated with resin adhesive (organic material) and then baked at high temperature. After high-temperature baking, the resin in the resin adhesive becomes a solid sheet material in a semi-cured state. After slicing, one or more semi-cured sheets (pp) obtained are stacked together, and copper foil and / or release film are covered on one or both sides to form a sheet preform. Then, these sheet preforms are put into a press for pressing to obtain a laminate.

[0029] The degree of crosslinking of the resin in the semi-cured sheet is not high. Under the combined action of high temperature and pressure during the pressing process in the press, the resin will remelt. The adhesive formed by the resin melting discharges the air inside, and the adhesive flows out in all directions; at the same time, the resin will continuously undergo crosslinking reactions, making the crosslinking density continuously increase and finally completely cured. The phenomenon that the adhesive discharges from the edge of the semi-cured sheet during this process is called bleeding.

[0030] The compression molding of the laminate is carried out under high temperature and pressure conditions. The conventional laminate pressing process will go through three stages: heating - curing - cooling. During heating, pressure is gradually applied, as Figure 1 shown. The purpose of setting three stages in the pressing process is to make the laminate have normal resin flow, uniform thickness, complete discharge of internal air, and no voids and microbubbles in the substrate during the compression molding process. However, since the prepreg is composed of organic materials (resin solution) and inorganic materials (glass fiber cloth), during the heating, curing, and cooling stages experienced by the conventional compression molding method during the compression molding process, the expansion and contraction of the organic materials and inorganic materials are not synchronized. At the same time, the externally applied process pressure causes internal stress in the substrate, which in turn affects the flatness and dimensional stability of the plate. Therefore, how to well control the resin flow, improve the resin voids in the substrate, and improve the internal stress of the substrate during the molding process of the laminate, so as to improve the flatness and dimensional stability of the plate is a problem to be solved.

[0031] In order to improve the flatness and dimensional stability of the plate, the present invention provides a compression molding method for a laminate. During the heating stage, a multi-step pressure application mode is used for pressure application. The steps of the method of the present invention are as follows: Put the plate preform into the press, close the press and close the press door. After the press starts the pressing program, the system automatically evacuates the air and starts heating; the plate preform is made by stacking prepregs into a core material according to the thickness requirement of the plate, and covering copper foil or release film on one or both surfaces of the core material as needed, such as covering copper foil on both surfaces, or covering release film on both surfaces, or covering copper foil on one surface and release film on the other surface to make the plate preform. The common number of laminations is 6 - 32 layers, but the number can be more or less, and no limitation is made here;

[0032] S1. At the beginning of the heating stage, set the pressure of the press to the closing pressure. After the pressure of the press rises to the closing pressure, hold the pressure for a period of time t 0 , t 0 can be 5 - 10 minutes, and press the plate preform under the closing pressure; the closing pressure refers to the minimum pressure at which the press can be closed. The closing pressure is related to the performance of the press itself and the number of prepreg laminations, and no limitation is made here;

[0033] S2. Raise the pressure of the press from the closing pressure to the first pressure increase setting value. The first pressure increase setting value is greater than the closing pressure. After the pressure of the press reaches the first pressure increase setting value, immediately reduce the pressure, reduce the pressure of the press to the first pressure reduction setting value, and then raise the pressure of the press to the first pressure increase setting value and hold the pressure at the first pressure increase setting value for a period of time t 1 , t 1 can be 1 - 15 minutes. The first pressure reduction setting value is less than the first pressure increase setting value but at the same time greater than the closing pressure;

[0034] S3. Increase the pressure of the press from the nth pressure increase set value to the (n + 1)th pressure increase set value, where n = 1, 2, 3, …. After the pressure of the press reaches the (n + 1)th pressure increase set value, immediately reduce the pressure, reduce the pressure of the press to the (n + 1)th pressure decrease set value, then increase the pressure of the press to the (n + 1)th pressure increase set value again and hold the pressure for a period of time t at the pressure of the (n + 1)th pressure increase set value. n+1 , the (n + 1)th pressure increase set value is greater than the nth pressure increase set value, the (n + 1)th pressure decrease set value is less than the (n + 1)th pressure increase set value but at the same time greater than the nth pressure increase set value. Repeat step S3 until the pressure of the press reaches the curing pressure set value, and execute step S4; Figure 2 The figure shows the pressure schematic diagram of the method of the present invention in the heating stage; the difference between the nth pressure increase set value and the (n + 1)th pressure increase set value can be 4 - 15 Kg / cm 2 , the difference between the nth pressure decrease set value and the (n + 1)th pressure decrease set value can be 4 - 10 Kg / cm 2 ;

[0035] S4. When the pressure of the press increases from the (n + 1)th pressure increase set value to the curing pressure set value, the heating stage transfers to the curing stage for constant temperature curing. When the pressure of the press reaches the curing pressure set value, immediately reduce the pressure, reduce the pressure of the press to the curing pressure decrease set value, then increase it to the curing pressure set value again, and hold the pressure at the curing pressure set value. When performing the holding and curing, use the high-temperature heat preservation method. When entering the constant temperature curing stage, the temperature rises to the constant temperature curing temperature value of 180 - 250 °C, and perform heat preservation, pressure holding and curing at the constant temperature curing temperature. The time for heat preservation and pressure holding can be 45 - 60 minutes; the curing pressure decrease set value is greater than the (n + 1)th pressure increase set value and less than the curing pressure set value, and the curing pressure set value can be 28 - 40 kg / cm 2 ; S5. After high-temperature heat preservation, perform cooling, reduce the temperature to ≤120 °C, and reduce the pressure while cooling to obtain the laminated board formed by pressing.

[0036] In the pressing process of high temperature and high pressure of the present invention, in the heating stage, the method of repeatedly pressurizing - depressurizing is adopted, and the pressure is reduced to the set low pressure value multiple times, so that the stress is continuously released, and the internal stress in the board is reduced. The base material of the laminated board produced by the method of the present invention has good compactness, no base material voids, better flatness, a greatly reduced warping probability, and obvious improvement in dimensional stability.

[0037] Furthermore, the present invention can adopt a step-by-step heating method or a tracking heating method. The step-by-step heating method divides the entire heating stage into several temperature sections. At the beginning of each temperature section, the heater is used to heat up. When the temperature reaches the upper limit of the temperature section, the heater is cut off to keep warm until the temperature section time ends and the next temperature section is heated up. Figure 3 As shown. That is, during the entire pressing process, the temperature control process is: heating-constant temperature-heating-constant temperature-heating (reaching the constant temperature curing temperature value)-constant temperature-cooling. When the heating stage is completed, the temperature is further raised to the constant temperature curing temperature value (180-250℃) and then constant temperature curing, and finally cooled (≤120℃). The step-by-step heating method does not control the heating rate.

[0038] The tracking heating method adopts a continuous heating method, raising the temperature to the constant temperature curing temperature value, then constant temperature curing, and finally cooling down. Figure 4 As shown. That is, during the entire pressing process, the temperature control process is: heating - constant temperature - cooling. The tracking heating method is to draw a heating rate curve according to the heating rate required by the product, compare the actual heating rate with the heating rate at the corresponding moment of the heating rate curve during the heating process, adjust the on-off time ratio of the heater, and continuously correct the on-off time ratio of the heater to make the actual heating rate track the heating rate curve.

[0039] Optionally, the cooling stage of step S5 uses a tracking cooling method, and the speed of cooling is controlled by the cooling rate, that is, the slope of the diagonal line. The tracking cooling method of this embodiment is to cool from a constant temperature curing temperature of 180-250°C to 120°C at a rate of 0.5-3.5°C / minute. Furthermore, a tracking decompression method can be used in the cooling stage. When the temperature reaches the Tg value (glass transition temperature) of the laminate, a pressure relief operation is performed to reduce the pressure from the curing pressure setting value to 15-20kg / cm 2 Then pressurize to 23-30kg / cm 2 And then slowly reduce the pressure to the closing pressure. The operation of pressure relief - pressurization - pressure relief during the pressure reduction process can further release the internal stress of the plate, avoid stress concentration inside the plate, thereby reducing the warping of the plate and improving the flatness of the plate.

[0040] The present invention is further described below by specific examples. Unless otherwise specified, the reagents, materials and instruments used in the following description are all conventional reagents, conventional materials and conventional instruments, which can be commercially obtained, and the reagents involved can also be synthesized by conventional synthesis methods.

[0041] Example 1

[0042] The laminate sheet preform of this embodiment is a core material composed of 8 layers of prepregs stacked together. Copper foils are covered on both side surfaces of the core material. The sheet preform is placed in a press, the press is closed, the press door is shut, and the temperature starts to rise. In this embodiment, a stepped temperature rise method is adopted for temperature rise. Table 1 is a list of pressure and temperature during the entire pressing process of this embodiment;

[0043] S1. During the temperature rise stage, set the pressure of the press to the closing pressure = 6 Kg / cm 2 , raise the pressure of the press to the closing pressure, press the core material under the closing pressure, and keep the pressure for 5 minutes; When the temperature rise stage starts, the equipment is preheated to 100 °C, then raised to 140 °C, the temperature rise time is 5 minutes, and keep the pressure for 5 minutes at 140 °C and the closing pressure;

[0044] S2. Raise the pressure of the press from the closing pressure to the first pressure increase set value = 14 Kg / cm 2 , when the pressure rises to 14 Kg / cm 2 , start to reduce the pressure, reduce it to the first pressure reduction set value = 8 Kg / cm 2 , then raise the pressure again to the first pressure increase set value of 14 Kg / cm 2 , keep the pressure for 10 minutes at the pressure of the first pressure increase set value; During this process, the temperature rises from 140 °C to 175 °C, the temperature rise time is 10 minutes, and keep the pressure for 20 minutes at 175 °C;

[0045] S3. Raise the pressure of the press from the first pressure increase set value to the second pressure increase set value = 20 Kg / cm 2 , when the pressure rises to 20 Kg / cm 2 , start to reduce the pressure, reduce it to the second pressure reduction set value = 16 Kg / cm 2 , then raise the pressure again to the second pressure increase set value of 20 Kg / cm 2 , keep the pressure for 8 minutes at the pressure of the second pressure increase set value; Continue to keep the pressure at 175 °C;

[0046] The set value of the curing pressure in this embodiment is 35 Kg / cm 2 , if the pressure of the press does not reach the set value of the curing pressure, repeat step S3 to continue raising the pressure. Raise the pressure of the press from the second pressure increase set value to the third pressure increase set value = 25 Kg / cm 2 , when the pressure rises to 25 Kg / cm 2 , immediately reduce the pressure after that, reduce it to the third pressure reduction set value = 22 Kg / cm 2 , then raise the pressure again to the third pressure increase set value of 25 Kg / cm 2 , keep the pressure for 15 minutes at the pressure of the third pressure increase set value; Continue to keep the pressure at 175 °C;

[0047] At this time, the pressure of the press still has not reached the set value of the curing pressure, which is 35 Kg / cm 2 , repeat step S3 to continue boosting the pressure, boost the pressure of the press from the third pressure boosting set value to the curing pressure set value. At this time, the pressure of the press has reached the curing pressure set value, and the pressure boosting process in the heating stage ends and transfers to the curing stage;

[0048] S4. When the pressure of the press rises from the third pressure boosting set value to the curing pressure set value of 35 Kg / cm 2 , immediately reduce the pressure, reduce the pressure of the press to the set value of the curing pressure reduction, which is 27 Kg / cm 2 , then raise it to the curing pressure set value and hold the pressure for 55 minutes. At this time, it is in the curing stage, and the temperature rises from 175 °C to the constant temperature curing temperature value of 205 °C. Keep the pressure and temperature constant at the high temperature (constant temperature curing temperature value of 205 °C) in the curing stage;

[0049] S5. After the high-temperature pressure and temperature holding are completed, carry out cooling and pressure reduction. The temperature drops to 120 °C and the pressure drops to the closing pressure. In this embodiment, when reducing the pressure in the cooling stage, from the highest pressure of 35 kg / cm 2 reduce the pressure at a rate of 0.5 - 1.5 kg / cm per minute 2 . When the pressure drops to 25 kg / cm 2 , immediately reduce the pressure rapidly, and the rate at this time is greater than 0.5 - 1.5 kg / cm per minute 2 , reduce the pressure to 18 kg / cm 2 , then raise it to 25 kg / cm 2 , and then keep the original rate of 0.5 - 1.5 kg / cm per minute 2 to reduce the pressure to 6 kg / cm 2 .

[0050] Table 1

[0051]

[0052] In this embodiment, when boosting the pressure in step S1, press and bond the core material under the closing pressure, which can make each layer of prepreg bond tightly, strengthen the heat conduction between layers. At the same time, under the combined action of the closing pressure and temperature, drive out the residual gas existing between the copper foil and the prepreg, between the release film and the prepreg, or between two prepregs during the operation process.

[0053] When the pressure of the press rises from the closing pressure to the first pressure increase set value in step S2, then the pressure is immediately reduced, and then increased again. During this process, under the combined action of temperature and pressure, the prepreg on the surface begins to melt when heated. At the same time, a small amount of residual solvent in the prepreg is expelled. Pressurizing, depressurizing, and then pressurizing in the pressure operation can further expel the residual gas and residual solvent during the operation process;

[0054] In step S3, the pressure of the press rises from the first pressure reduction set value to the second pressure increase set value, then immediately reduces and then increases the pressure. During this process, under the combined action of temperature and pressure, the prepreg completely melts, the viscosity reaches the lowest point, and the voids that appear after the solvent is expelled begin to be filled at this stage. Pressurizing, depressurizing, and then pressurizing in the pressure operation at this time can control the bleeding of the base material and expel the residual solvent;

[0055] In step S3, the pressure of the press rises from the second pressure reduction set value to the third pressure increase set value, then reduces and then increases the pressure. During this process, under the combined action of temperature and pressure, the prepreg of the base material in the middle of each press opening completely melts, the viscosity reaches the lowest point, and the voids that appear after the solvent is expelled continue to be filled at this stage. Pressurizing, depressurizing, and then pressurizing in the pressure operation at this time can control the bleeding of the base material, improve the void filling effect, and improve the voids in the base material;

[0056] After the pressure of the press in step S3 reaches the curing pressure set value, it then enters the curing stage. During the pressing process, the adhesive liquid changes from solid to molten and then begins to cure. The thermal expansion of the organic material and the thermal expansion of the inorganic material are not synchronized and internal stress is generated. These internal stresses experience pressurizing, depressurizing, and then pressurizing in the pressure operation during the curing stage, which can effectively release the internal stress, avoid the concentration inside the base material, thereby reducing the warpage degree of the base material and improving the flatness.

[0057] Example 2

[0058] The difference between this example and Example 1 is that this example uses a tracking heating method for heating. In the tracking heating method of this example, after the equipment is preheated to 100 °C, it is heated to 205 °C in 43 minutes, maintained at 205 °C for 55 minutes in the curing stage, and then cooled to 120 °C in 50 minutes in the cooling stage. The pressure control process is the same as that in Example 1; Table 2 is the pressure and temperature list of this example during the entire pressing process;

[0059] S1. Heating stage, set the pressure of the press to the closing pressure = 6 Kg / cm 2 , the pressure of the press rises to the closing pressure, and the core material is pressed at the closing pressure and held for 5 minutes;

[0060] S2. Raise the pressure of the press from the closing pressure to the first pressure increase set value = 14 Kg / cm 2 , and when the pressure reaches 14 Kg / cm 2 , immediately reduce the pressure to the first pressure reduction set value = 8 Kg / cm 2 , then raise the pressure again to the first pressure increase set value of 14 Kg / cm 2 , and hold the pressure for 10 minutes at the pressure of the first pressure increase set value;

[0061] S3. Raise the pressure of the press from the first pressure increase set value to the second pressure increase set value = 20 Kg / cm 2 , and when the pressure reaches 20 Kg / cm 2 , immediately reduce the pressure to the second pressure reduction set value = 16 Kg / cm 2 , then raise the pressure again to the second pressure increase set value of 20 Kg / cm 2 , and hold the pressure for 8 minutes at the pressure of the second pressure increase set value;

[0062] Repeat step S3 to continue increasing the pressure. Raise the pressure of the press from the second pressure increase set value to the third pressure increase set value = 25 Kg / cm 2 , and when the pressure reaches 25 Kg / cm 2 , immediately reduce the pressure to the third pressure reduction set value = 22 Kg / cm 2 , then raise the pressure again to the third pressure increase set value of 25 Kg / cm 2 , and hold the pressure for 15 minutes at the pressure of the third pressure increase set value;

[0063] Raise the pressure of the press from the third pressure increase set value to the curing pressure set value of 35 Kg / cm 2 , and the heating stage ends and transfers to the curing stage;

[0064] S4. When the pressure of the press rises from the third pressure increase set value to the curing pressure set value of 35 Kg / cm 2 , immediately reduce the pressure and reduce the pressure of the press to the curing pressure reduction set value of 27 Kg / cm 2 , then raise it to the curing pressure set value and hold the pressure for 55 minutes. At this time, it is in the curing stage, and high-temperature heat preservation and pressure holding are carried out during the curing stage;

[0065] S5. After high-temperature heat preservation, carry out cooling and pressure reduction. The temperature drops to 120 °C and the pressure drops to the closing pressure.

[0066] Table 2

[0067]

[0068]

[0069] The warpage and expansion rate of the plates prepared in Example 1 and Example 2 were detected, and at the same time, they were compared with the plates prepared by using the traditional pressing method. The pressure change of the traditional pressing method is as follows Figure 1 . The warpage of the plates prepared by the traditional pressing method is between 0.25% and 0.65%, and the dimensional expansion rates in the transverse and longitudinal directions of the plates are 260 - 350 ppm. The warpage of the plates prepared in Example 1 and Example 2 is between 0.15% and 0.35%, and the dimensional expansion rates in the transverse and longitudinal directions of the plates are 240 - 320 ppm. The flatness and dimensional stability of the plates are improved.

[0070] In the process of heating up and turning into the curing stage of the present invention, every time the pressure goes up one step, a pressure relief operation is carried out. The pressure relief operation during pressure increase can control the resin flow of the substrate, improve the void filling effect and the denseness of the substrate, and improve the voids and dimensional stability of the substrate.

[0071] 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 the above embodiments, those of ordinary skill in the art should understand that the specific implementation manners of the present invention can still be modified or equivalently replaced. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the present invention.

Claims

1. A method for pressing a laminate, characterized in that: The steps are as follows: placing the sheet material prefabricated into the press and closing the press; S1, starting the temperature rise stage, raising the pressure of the press to the closing pressure and maintaining the pressure, and pressing the plate prefabricated material under the closing pressure; S2, raising the pressure of the compressor from the closing pressure to the first boost pressure setting value, then reducing the pressure to the first depressurization pressure setting value, and then raising the pressure of the compressor to the first boost pressure setting value and maintaining the pressure, the first depressurization pressure setting value is less than the first boost pressure setting value and greater than the closing pressure; S3, raising the pressure of the press from the nth boost pressure setting value to the n+1th boost pressure setting value, n=1, 2, 3, ..., then reducing the pressure to the n+1th depressurization pressure setting value, then raising it to the n+1th boost pressure setting value and maintaining the pressure, the n+1th depressurization pressure setting value is less than the n+1th boost pressure setting value and greater than the nth boost pressure setting value, repeating step S3 until the pressure of the press reaches the curing pressure setting value, and executing step S4; S4, when the pressure of the compressor is increased from the n+1th boost pressure setting value to the curing pressure setting value and then decreased, the pressure of the compressor is decreased to the curing pressure setting value, and then increased to the curing pressure setting value and maintained at the constant curing temperature, and the curing pressure setting value is greater than the n+1th boost pressure setting value and less than the curing pressure setting value; S5, cooling and reducing the pressure to obtain a pressed laminate.

2. The method for pressing a laminate as claimed in claim 1, wherein: When heating up, a step-by-step heating method is adopted. The step-by-step heating method is divided into several sections. At the beginning of each section, the temperature is increased by the heater. When the temperature reaches the upper limit of the section, the heating is stopped and kept warm until the end of the section time, and then enters the next section, repeating the process of heating-constant temperature-heating until the temperature reaches the constant temperature curing temperature value.

3. The method for pressing a laminate as claimed in claim 2, wherein: When heating, first preheat to 90-100°C, then increase to 135-155°C, then increase to 165-180°C, and then increase to the constant temperature curing temperature.

4. The method for pressing a laminate as claimed in claim 1, wherein: When heating up, a tracking heating method is adopted. The tracking heating method adopts a continuous heating method. The actual heating rate is adjusted based on the heating rate curve drawn according to the heating rate required by the product, and the temperature is raised to the constant temperature curing temperature within the set time.

5. The method for pressing a laminate as claimed in claim 4, characterized in that: When heating up, preheat to 90-100°C and use 40-60 minutes to reach the constant temperature curing temperature.

6. The method for pressing a laminate as claimed in claim 1, wherein: The constant temperature curing temperature is 180-250°C; and / or the curing pressure setting value is 28-40 kg / cm 2 ; and / or, reducing the temperature to ≤120°C during cooling.

7. The method for press-forming a laminate according to claim 1, wherein: During the cooling process, the temperature is lowered from the constant temperature curing temperature at a rate of 0.5 to 3.5°C / min.

8. The method for press-forming a laminate as claimed in claim 1, characterized in that: During the cooling process, when the temperature reaches the Tg value of the laminate, the pressure is reduced and then increased, and finally reduced.

9. The method for pressing a laminate as claimed in claim 8, wherein: During the cooling stage, when the temperature reaches the Tg value of the laminate, reduce the pressure from the curing pressure setting value to 15-20 kg / cm 2 Then pressurize to 23-30kg / cm 2 , then reduce the pressure to the closing pressure.

10. The method for pressing a laminate as claimed in claim 9, wherein: During the cooling stage, the pressure increases from the solidification pressure setting value to 0.5-1.5 kg / cm per minute. 2 When the pressure drops to 22-25 kg / cm 2 Rapid blood pressure reduction, at a rate greater than 0.5-1.5 kg / cm per minute 2 , reduce the pressure to 15-20kg / cm 2 Then increase to 23-30kg / cm 2 , then at 0.5~1.5kg / cm per minute 2 The pressure is reduced to the closing pressure at a rate of

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