An auxiliary film for PCB lamination and a PCB lamination method

Abstract

The application relates to the technical field of PCB manufacturing, in particular to an auxiliary film for PCB pressing, a PCB pressing method and a PCB. The auxiliary film for PCB pressing is suitable for being peelably laminated on a metal foil of a PCB and comprises a cover type film and a viscous film. The cover type film comprises a first release film and a supporting layer. The viscous film, the supporting layer and the first release film are sequentially laminated in the thickness direction. The Tg of the thermosetting material of the viscous film is lower than the lowest temperature during hot pressing, and the Tg of the thermoplastic material of the supporting layer is higher than the highest temperature during hot pressing. The cover type film is used for bearing external pressing force. When the viscous film is in a low-temperature flow state, the viscous film flows and fills recessed positions of the metal foil. When the viscous film is in a high-temperature solidification state, the viscous film solidifies and bonds the supporting layer and the metal foil. The auxiliary film can be peeled off after pressing is completed, does not affect the use of the original material system of the PCB and is compatible with the existing PCB process design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of PCB manufacturing, and particularly relates to an auxiliary film for PCB pressing and a PCB pressing method. BACKGROUND

[0002] For a printed circuit board (PCB) integrated with a high-power device, high current carrying capacity, heat dissipation performance and insulation reliability need to be considered. However, the increase of the working environment frequency of the high-power device will cause the insulation performance of the dielectric layer of the PCB to deteriorate significantly, especially under the action of a high-frequency electric field, the polarization effect of the organic insulating material of the dielectric layer is intensified, the dielectric strength is intensified to decrease, and breakdown and insulation failure are easily caused.

[0003] In addition, the PCB integrated with the high-power device needs to use thick copper (the interlayer copper thickness is usually greater than or equal to 3 oz) design to meet the current carrying and heat dissipation requirements, but the thick copper layer has a circuit, and in the lamination process of the thick copper layer and the dielectric layer, the dielectric layer is not uniformly filled due to the gap between the circuits, so that the dielectric thickness control is difficult. In the conventional process, the dielectric layer thickness is usually difficult to stably reach more than 135 microns, and a weak area with a local dielectric thickness of less than 100 microns is easily formed, further intensifying the insulation failure risk.

[0004] The existing solution is to increase the number of dielectric layers or use high dielectric performance materials. For the solution of increasing the number of dielectric layers, the multi-layer dielectric layer stack will cause the overall thickness of the PCB to increase, which is contrary to the trend of PCB miniaturization. For the solution of using high dielectric performance materials, the adjustment of the material composition is limited by process compatibility, and the cost is high.

[0005] Therefore, how to realize precise control of dielectric thickness and insulation improvement under the existing material system has become a technical bottleneck to be solved. SUMMARY

[0006] The present application provides an auxiliary film for PCB pressing and a PCB pressing method to realize precise control of dielectric thickness and insulation improvement under the existing material system.

[0007] To solve the above problems, on the one hand, the present application provides an auxiliary film for PCB pressing, which is suitable for being laminated on a metal foil of a PCB in a peelable manner, comprising a cover type film and a viscous film, the viscous film is a film formed by a layer of thermosetting material, the cover type film comprises a first release film and a support layer, the support layer is formed by a layer of thermoplastic material, and the viscous film, the support layer and the first release film are sequentially laminated in the thickness direction.

[0008] The Tg of the thermosetting material is lower than the lowest temperature of the PCB during hot pressing, and the Tg of the thermoplastic material is higher than the highest temperature of the PCB during hot pressing;

[0009] The cover type film is used to bear external compression force, the viscous flow film has a low temperature flow state and a high temperature curing state, when the viscous flow film is in the low temperature flow state, the viscous flow film flows and fills the recessed position of the surface of the metal foil, and when the viscous flow film is in the high temperature curing state, the viscous flow film cures and bonds the support layer and the metal foil.

[0010] Optionally, the cover type film further comprises a second release film, and the surface of the support layer towards the viscous flow film is divided into an isolated area and a bonding area;

[0011] The second release film is attached to the isolated area of the support layer, and the viscous flow film in the high temperature curing state can bond the metal foil and the bonding area.

[0012] Optionally, the cross-sectional area of the second release film is smaller than the cross-sectional area of the support layer, the isolated area is located on the inner side of the surface of the support layer towards the viscous flow film, and the bonding area is arranged on the outer side of the isolated area.

[0013] Optionally, the thickness of the cover type film is greater than the thickness of the viscous flow film, the thickness t1 of the cover type film is 150-250 μm, and the thickness t2 of the viscous flow film is 20-50 μm.

[0014] In another aspect, the embodiment of the present application provides a PCB pressing method, comprising:

[0015] Obtaining a core board, and a thick copper layer is formed on the surface of the core board;

[0016] Stacking a prepreg and a metal foil on the thick copper layer of the core board in sequence;

[0017] Stacking an auxiliary film on the metal foil to form a temporary PCB pressing structure, wherein the auxiliary film comprises a cover type film and a viscous flow film, the viscous flow film is a film formed by a layer of thermosetting material, the cover type film comprises a first release film and a support layer, the support layer is formed by a layer of thermoplastic material, the viscous flow film, the support layer and the first release film are sequentially stacked in the thickness direction of the auxiliary film, and the viscous flow film is attached to the metal foil; the Tg of the thermosetting material is lower than the lowest temperature of the subsequent temporary PCB pressing structure during hot pressing, and the Tg of the thermoplastic material is higher than the highest temperature of the subsequent temporary PCB pressing structure during hot pressing;

[0018] The PCB temporary lamination structure is hot-pressed to sequentially reach a first hot-pressing stage and a second hot-pressing stage; the cover type film bears external lamination force, and the prepreg is fused and solidified to form a dielectric layer; in the first hot-pressing stage, the viscous flow film softens and flows in a low-temperature flow state, fills the recessed positions on the surface of the metal foil, and is attached to the surface topography of the metal foil; in the second hot-pressing stage, the viscous flow film is in a high-temperature solidification state, and the viscous flow film is solidified and bonded to the support layer and the metal foil.

[0019] The hot-pressing is ended, and the auxiliary film is peeled off to obtain a PCB.

[0020] Optionally, the cover type film further comprises a second release film, the surface of the support layer facing the viscous flow film is divided into an isolated area and a bonding area, and the second release film is attached to the isolated area of the support layer; subsequently, when the PCB temporary lamination structure is hot-pressed, the viscous flow film in the high-temperature solidification state can bond the metal foil and the bonding area.

[0021] Optionally, the cross-sectional area of the second release film is smaller than the cross-sectional area of the support layer, the isolated area is located on the inner side of the surface of the support layer facing the viscous flow film, and the bonding area is arranged on the outer side of the isolated area.

[0022] Optionally, the thickness of the cover type film is greater than the thickness of the viscous flow film; the thickness t1 of the cover type film is 150-250 μm; and the thickness t2 of the viscous flow film is 20-50 μm.

[0023] Optionally, the hot-pressing temperature of the first hot-pressing stage is 110-140℃, and the hot-pressing temperature of the second hot-pressing stage is 140-200℃.

[0024] This invention provides an auxiliary film for PCB lamination. During hot pressing, the high-modulus polymer of the support layer remains solid until it reaches its glass transition temperature, maintaining rigidity and continuous pressure resistance. The viscous flow film softens and transforms into a low-temperature flow dynamic after initial heating. The rigid support layer, under pressure, resists the pressure undulations on the thick copper layer surface, providing a reaction force that compels the thermosetting material of the viscous flow film to flow and fill the depressions in the metal foil, allowing the viscous flow film to completely replicate the surface morphology of the metal foil, thus achieving the conformal function of the viscous flow film. Upon further heating, the thermosetting material cross-links, cures, and solidifies, transforming into a high-temperature cured state to bond the metal foil and support layer, achieving the bonding effect of the viscous flow film. This connects the metal foil, viscous flow film, and support layer into a unified whole, facilitating the uniform transfer of pressure from the support layer to the dielectric layer through the viscous flow film and metal foil, thereby improving the consistency and uniformity of the dielectric layer thickness and enhancing the insulation performance of the PCB. Unlike existing technologies, it does not require replacing high-cost special materials or increasing the number of dielectric layers. Moreover, the auxiliary film can be peeled off after lamination without affecting the original material system of the PCB. It does not require complex parameter adjustments or additional equipment and is compatible with existing PCB process designs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the explosion of the auxiliary film for PCB lamination and the PCB during hot pressing, provided in one embodiment of the present invention.

[0027] Figure 2 for Figure 1 A schematic diagram of the core board of the PCB.

[0028] Figure 3 for Figure 1 The diagram shows the auxiliary film used for PCB lamination and the explosion of the PCB before hot pressing.

[0029] The reference numerals in the accompanying drawings are as follows:

[0030] 100. Core board; 200. Auxiliary film; 1. Thick copper layer; 2. Support layer; 3. Flow film; 4. First release film; 5. Second release film; 6. Prepreg; 7. Metal foil; 8. Dielectric layer. Detailed Implementation

[0031] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0032] As shown in the drawings, Figure 1 An embodiment of the present application provides an auxiliary film for PCB pressing, which is suitable for being releasably laminated on a metal foil 7 of a PCB, and the auxiliary film for PCB pressing (hereinafter referred to as auxiliary film 200) comprises a cover type film and a flowable film 3, the flowable film 3 is a film formed by a layer of thermosetting material, the cover type film comprises a first release film 4 and a support layer 2, the support layer 2 is formed by a layer of thermoplastic material, and the flowable film 3, the support layer 2 and the first release film 4 are sequentially laminated in the thickness direction of the auxiliary film 200.

[0033] The Tg of the flowable film 3 is lower than the lowest temperature of the PCB during hot pressing, and the Tg of the support layer 2 is higher than the highest temperature of the PCB during hot pressing.

[0034] The cover type film is used to bear external pressing force, the flowable film 3 has a low-temperature flow state and a high-temperature curing state, when the flowable film 3 is in the low-temperature flow state, the flowable film 3 can flow and fill the recessed positions on the surface of the metal foil 7, and when the flowable film 3 is in the high-temperature curing state, the flowable film 3 can cure and bond the support layer 2 and the metal foil 7.

[0035] Said "low temperature" and "high temperature" are only relative definitions according to the fact that the hot pressing temperature when the flowable film 3 is in the "low-temperature flow state" is lower than the hot pressing temperature when the flowable film 3 is in the "high-temperature curing state", and are not intended to refer to the specific value of the hot pressing temperature when the flowable film 3 is in the "low-temperature flow state" or the specific value of the hot pressing temperature when the flowable film 3 is in the "high-temperature curing state".

[0036] At present, the PCB integrated with high-power devices needs to adopt thick copper (the copper thickness between layers is usually ≥3oz) design to meet the current-carrying and heat dissipation requirements, as shown in the drawings, Figure 1 But the thick copper layer 1 of the core board 100 forms a circuit, and gaps are formed between the circuits, resulting in uneven surface of the core board 100. During the lamination process of the thick copper layer 1, the semi-cured sheet 6 and the copper foil, the uniform pressure of the hot pressing equipment will be preferentially borne by the "high points", resulting in uneven pressure on the semi-cured sheet 6, recessed positions on the surface of the copper foil, and difficulty of the resin of the semi-cured sheet 6 to uniformly fill the recessed areas between the circuits of the thick copper layer 1, which leads to uneven filling of the dielectric layer 8. In the conventional process, the thickness of the dielectric layer 8 is usually difficult to stably reach more than 135μm, and weak areas with local dielectric thickness less than 100μm are easily formed, further increasing the risk of insulation failure.

[0037] The auxiliary film 200 in the application is used for assisting the pressing when the PCB is pressed with the prepreg 6 and the metal foil 7, so as to precisely control the thickness of the dielectric layer 8 and improve the insulation performance of the PCB.

[0038] Specifically, as shown in the figure, Figure 3 the auxiliary film 200 is laminated on the metal foil 7 of the PCB before pressing. When the PCB is pressed, the steel plate of the hot pressing equipment is pressed on the first release film 4, and the first release film 4 has an interface isolation function. The first release film 4 remains solid during the hot pressing process, so as to avoid the pollution of the support layer 2 to the steel plate during the hot pressing.

[0039] Since the support layer 2 of the cover film is formed of a thermoplastic material, the Tg of the thermoplastic material is higher than the highest temperature during the hot pressing of the PCB. Therefore, during the hot pressing process, the high modulus polymer of the support layer 2 does not reach the glass transition temperature and remains solid, so that the support layer 2 remains rigid and can continuously bear pressure. Moreover, the support layer 2 formed of the thermoplastic material has a certain buffering effect, which is conducive to uniformly transmitting the pressing force to the viscous flow film 3.

[0040] Since the viscous flow film 3 is a film formed of a layer of thermosetting material, the Tg of the thermosetting material of the viscous flow film 3 is lower than the lowest temperature during the hot pressing of the PCB. Therefore, after the initial temperature rise, as shown in the figure, Figure 1 the viscous flow film 3 softens and flows into a low-temperature flow state. After the rigid support layer 2 is pressed, it can resist the pressure of the surface undulation of the thick copper layer 1 and provide a counterforce to force the thermosetting material of the viscous flow film 3 to flow and fill the recessed positions of the metal foil 7, so that the viscous flow film 3 completely replicates the surface topography of the metal foil 7 and realizes the shape-attaching effect of the viscous flow film 3. After continuous temperature rise, the thermosetting material is crosslinked, solidified and shaped into a high-temperature solidification state, so as to bond the metal foil 7 and the support layer 2, realize the bonding effect of the viscous flow film 3, and make the metal foil 7, the viscous flow film 3 and the support layer 2 connected to form a whole, which is conducive to the support layer 2 uniformly transmitting the pressure to the dielectric layer 8 through the viscous flow film 3 and the metal foil 7. At the same time, the physical support effect of the cover film can offset the influence of the unevenness of the thick copper layer 1 on the uniformity of the pressure on the dielectric layer 8 during pressing, so as to improve the consistency and uniformity of the thickness of the dielectric layer 8.

[0041] Therefore, the auxiliary film 200 can eliminate the problem of uneven filling of the dielectric layer 8 caused by the line gap of the thick copper layer 1, improve the uniformity of the thickness of the dielectric layer 8, and reduce the thickness error to ±5 μm, so as to avoid the risk of insulation failure and dielectric breakdown caused by local insufficient thickness.

[0042] Compared with the PCB formed by the existing PCB pressing process, the thickness of the dielectric layer 8 is difficult to stably reach more than 135 mu m, and there is a situation of forming a local dielectric thickness insufficient (<100 mu m) weak area, the thickness of the dielectric layer 8 of the PCB formed by the auxiliary film 200 assisted pressing can be accurately controlled within 150 mu m+5 mu m range, so as to significantly increase the insulation distance, reduce the high frequency electric field strength, suppress the polarization effect and the dielectric layer 8 breakdown risk.

[0043] In the present application, without changing the high-cost special material or increasing the number of dielectric layers in the prior art, the material cost of the auxiliary film 200 is less than 5%, and the auxiliary film 200 can be completely peeled off after pressing, without affecting the use of the original material system of the PCB, without complex parameter adjustment or additional equipment, and can be compatible with the existing PCB process design.

[0044] It should be noted that the viscous film 3 has low viscosity, so that the auxiliary film 200 can be peeled off from the metal foil 7 after the hot pressing is completed.

[0045] In an embodiment, as shown in Figure 1 The cover type film further includes a second release film 5, and the surface of the support layer 2 facing the viscous film 3 is divided into an isolation area and an adhesive area.

[0046] The second release film 5 is attached to the isolation area of the support layer 2, and the viscous film 3 in the high-temperature solidification state can bond the metal foil 7 and the adhesive area.

[0047] The second release film 5 has an interface isolation function and remains solid during hot pressing, and the adhesive area of the support layer 2 is not attached to the second release film 5 and can directly contact the viscous film 3, so that the viscous film 3 in the high-temperature solidification state can bond the metal foil 7 and the adhesive area, so that the metal foil 7, the viscous film 3 and the support layer 2 are connected to form a whole. The isolation area of the support layer 2 and the viscous film 3 are isolated by the second release film 5, which can ensure that the cover type film can be peeled off after hot pressing without residue.

[0048] In an embodiment, as shown in Figure 1 The cross-sectional area of the second release film 5 is smaller than the cross-sectional area of the support layer 2, the isolation area is located on the inner side of the surface of the support layer 2 facing the viscous film 3, and the adhesive area is arranged on the outer side of the isolation area, so that the viscous film 3 in the high-temperature solidification state is bonded to the outer side area of the support layer 2, so as to increase the bonding area of the support layer 2 and the viscous film 3, and improve the bonding force of the support layer 2 and the viscous film 3.

[0049] In an embodiment, the thickness of the cover film is greater than the thickness of the adhesive flow film 3. The cover film needs to have enough rigidity to withstand high pressure during hot pressing and resist the pressure of the surface relief of the thick copper layer 1, providing uniform support and uniformly transmitting the pressing force to the dielectric layer 8. Therefore, the cover film is designed to be thicker to ensure its rigidity.

[0050] As shown in FIG. 1, the thickness t1 of the cover film is 150-250 μm; and the thickness t2 of the adhesive flow film 3 is 20-50 μm. Figure 1

[0051] When the thickness of the cover film is too small (t1 < 150 μm), it cannot guarantee enough rigidity. When the thickness of the cover film is too large (t1 > 250 μm), although the cover film has enough rigidity, its thickness is too thick, the thermal resistance is large, the heating time of the steel plate of the hot pressing equipment on the PCB is prolonged, the lamination efficiency is reduced, and the material cost is increased. Therefore, the thickness t1 of the cover film is designed to be 150-250 μm.

[0052] When the thickness of the adhesive flow film 3 is too small (t2 < 20 μm), the volume of the softened adhesive flow film 3 is insufficient, which can not fill the recessed position of the metal foil 7 and can not completely reproduce the surface topography of the metal foil 7. When the thickness of the adhesive flow film 3 is too large (t2 > 50 μm), the thermal resistance is large, the heating time of the steel plate of the hot pressing equipment on the PCB is prolonged, the lamination efficiency is reduced, and the material cost is increased. Therefore, the thickness t2 of the adhesive flow film 3 is designed to be 20-50 μm.

[0053] Figure 1 As shown in FIG. 1, the thickness t1 of the cover film is the sum of the thicknesses of the first release film 4, the second release film 5 and the support layer 2.

[0054] In an embodiment, the adhesive flow film 3 is a thin film composed of a PI film (polyimide film) and an epoxy glue.

[0055] In an embodiment, the first release film 4 and the second release film 5 are composed of 100% polyimide.

[0056] In other embodiments, the second release film 5 can be cancelled, because the thermosetting material of the adhesive flow film 3 has low viscosity, the support layer 2 can be easily removed from the PCB even if it is combined with the adhesive flow film 3.

[0057] In an embodiment, the thermoplastic material of the support layer 2 is PS (polystyrene).

[0058] In addition, an embodiment of the present application provides a PCB pressing method, which uses the above-mentioned auxiliary film 200 to assist in pressing the semi-cured sheet 6 and the metal foil 7 during PCB pressing, to accurately control the thickness of the dielectric layer 8 and improve the insulation performance of the PCB. The PCB pressing method comprises the following steps: ​

[0059] S1: As Figure 2 As shown, a core board 100 is obtained, and a thick copper layer 1 is formed on the surface of the core board 100.

[0060] Specifically, a copper-clad laminate with appropriate copper thickness is selected, and a circuit pattern is formed on the copper-clad laminate through an image transfer-flash etching-film removal process. The copper surface at the non-circuit pattern position is removed to expose the corresponding substrate surface, so as to form a core board 100 with a thick copper layer 1. The thick copper refers to the interlayer copper thickness, which is usually ≥3oz.

[0061] S2: As Figure 3 As shown, a prepreg 6 and a metal foil 7 are sequentially stacked on the thick copper layer 1 of the core board 100.

[0062] S3: As Figure 3 As shown, an auxiliary film 200 is laminated on a metal foil 7 to form a temporary PCB bonding structure. The auxiliary film 200 includes a cover film and a flow film 3. The flow film 3 is a film formed of a thermosetting material. The cover film includes a first release film 4 and a support layer 2. The support layer 2 is formed of a thermoplastic material. The flow film 3, the support layer 2, and the first release film 4 are sequentially laminated along the thickness direction of the auxiliary film 200. The flow film 3 is attached to the metal foil 7.

[0063] The Tg of thermosetting materials is lower than the lowest temperature of the subsequent PCB temporary lamination structure during hot pressing, while the Tg of thermoplastic materials is higher than the highest temperature of the subsequent PCB temporary lamination structure during hot pressing.

[0064] S4: As Figure 1 As shown, the temporary hot-pressed PCB structure sequentially reaches the first and second hot-pressing stages. The overlay film withstands external pressure, and the prepreg 6 melts and solidifies to form the dielectric layer 8. In the first hot-pressing stage, the viscous flow film 3 softens and flows, operating at a low temperature. The viscous flow film 3 fills the depressions on the surface of the metal foil 7 to conform to the surface morphology of the metal foil 7. In the second hot-pressing stage, the viscous flow film 3 is in a high-temperature solidified state, solidifying and bonding the support layer 2 and the metal foil 7.

[0065] S5: End the hot pressing, peel off the auxiliary film 200, and obtain the PCB.

[0066] It should be noted that the first hot pressing stage and the second hot pressing stage are only a division of the entire hot pressing process based on the stage in which the viscous flow film 3 is in a low-temperature flow dynamic state and a high-temperature curing state. In the entire hot pressing process, the stage in which the viscous flow film 3 is in a low-temperature flow dynamic state belongs to the first hot pressing stage, and the stage in which the viscous flow film 3 is in a high-temperature curing state belongs to the second hot pressing stage. The first hot pressing stage and the second hot pressing stage are not a distinction between process methods.

[0067] Specifically, in step S3, the auxiliary film 200 is laminated on the metal foil 7 of the PCB before pressing. In step S4, when the PCB is pressed, the steel plate of the hot pressing equipment is pressed on the first release film 4. The first release film 4 has an interface isolation function. The first release film 4 remains solid during the hot pressing process, which can prevent the support layer 2 from contaminating the steel plate during hot pressing.

[0068] Since the support layer 2 of the coating film is formed of a thermoplastic material, the Tg of which is higher than the highest temperature during PCB hot pressing, the high modulus polymer of the support layer 2 remains solid before reaching its glass transition temperature during the hot pressing process in step S4. The support layer 2 maintains its rigidity and can continuously withstand pressure. Furthermore, the support layer 2 formed of thermoplastic material has a certain buffering effect, which helps to uniformly transfer the pressing force to the viscous flow film 3.

[0069] Since the viscous flow film 3 is a thin film formed of a thermosetting material, and the Tg of the thermosetting material of the viscous flow film 3 is lower than the minimum temperature of the PCB during hot pressing, therefore, as Figure 1 As shown, during the hot pressing process in step S4, after the initial heating, the viscous film 3 softens and flows. The rigid support layer 2, under pressure, can resist the pressure of the uneven surface of the thick copper layer 1, providing a reaction force to force the viscous film 3 to flow and fill the recessed positions of the metal foil 7, so that the viscous film 3 completely replicates the surface morphology of the metal foil 7, realizing the conforming function of the viscous film 3. After further heating, the thermosetting material cross-links, cures, and sets, bonding the metal foil 7 and the support layer 2, realizing the bonding function of the viscous film 3, so that the metal foil 7, the viscous film 3, and the support layer 2 are connected to form a whole. This facilitates the support layer 2 to uniformly transfer pressure to the dielectric layer 8 through the viscous film 3 and the metal foil 7. At the same time, the physical support of the coating film can offset the influence of the unevenness of the thick copper layer 1 on the pressure uniformity of the dielectric layer 8 during pressing, ensuring the consistency and uniformity of the thickness of the dielectric layer 8.

[0070] Compared to existing PCB lamination processes, where the thickness of the dielectric layer 8 is difficult to consistently reach 135μm or more and weak areas with insufficient dielectric thickness (<100μm) are formed, the present invention achieves precise control of the dielectric layer 8 thickness within the range of 150μm±5μm in PCBs formed by auxiliary lamination with auxiliary film 200. This significantly increases the insulation distance, reduces the high-frequency electric field intensity, and suppresses polarization effects and the risk of dielectric layer 8 breakdown.

[0071] Moreover, as can be seen from step S5, the auxiliary film 200 can be peeled off after lamination without affecting the original material system of the PCB. It does not require complex parameter adjustments or additional equipment and is compatible with existing PCB process designs.

[0072] It should be noted that the viscous flow film 3 has low viscosity, thereby assisting the thin film 200 to be easily peeled off from the metal foil 7 after the hot pressing is completed.

[0073] In an embodiment, as shown in FIG. 2, the laminated cover-type film in the S2 step further comprises a second release film 5, and the surface of the support layer 2 facing the viscous flow film 3 is divided into an isolated area and a bonding area, and the second release film 5 is attached to the isolated area of the support layer 2. Subsequently, when the PCB temporary compression structure is hot-pressed, the viscous flow film 3 in the high-temperature solidification state can bond the metal foil 7 and the bonding area. Figure 3

[0074] The second release film 5 has an interface isolation function and remains in a solid state during the hot pressing process. The bonding area of the support layer 2 is not attached to the second release film 5 and can directly contact the viscous flow film 3, so that the viscous flow film 3 in the high-temperature solidification state can bond the metal foil 7 and the bonding area, thereby connecting the metal foil 7, the viscous flow film 3, and the support layer 2 to form an integral whole. The isolated area of the support layer 2 is isolated from the viscous flow film 3 by the second release film 5, which can ensure that the cover-type film can be peeled off after the hot pressing is completed without residue.

[0075] In an embodiment, as shown in FIG. 2, the cross-sectional area of the second release film 5 is smaller than the cross-sectional area of the support layer 2, the isolated area is located on the inner side of the surface of the support layer 2 facing the viscous flow film 3, and the bonding area is arranged on the outer side of the isolated area, so that the viscous flow film 3 in the high-temperature solidification state is bonded to the peripheral side area of the support layer 2, thereby increasing the bonding area of the support layer 2 and the viscous flow film 3 and improving the bonding force of the support layer 2 and the viscous flow film 3. Figure 3

[0076] In other embodiments, the cross-sectional area of the second release film 5 can be the same as the cross-sectional area of the support layer 2, and a plurality of holes can be formed in the second release film 5. The viscous flow film 3 can bond the support layer 2 through the holes when flowing, the positions on the surface of the support layer 2 facing the viscous flow film 3 corresponding to the plurality of holes are the bonding areas, and the remaining positions on the support layer 2 are the isolated areas.

[0077] In an embodiment, the thickness of the cover-type film is greater than the thickness of the viscous flow film 3. The cover-type film needs to have sufficient rigidity to withstand high pressure during the hot pressing process and resist the pressure of the surface undulation of the thick copper layer 1, provide uniform support, and uniformly transmit the compression force to the dielectric layer 8. Therefore, the cover-type film is designed to be thicker during design, which is beneficial to ensure its rigidity.

[0078] The thickness t1 of the cover-type film is 150-250 μm, and the thickness t2 of the viscous flow film 3 is 20-50 μm.

[0079] ​​When the thickness of the cover film is too small (t1 < 150 μm), it cannot guarantee sufficient rigidity. When the thickness of the cover film is too large (t1 > 250 μm), although the cover film has sufficient rigidity, its thickness is too thick, the thermal resistance is large, the heating time of the steel plate of the hot pressing equipment on the PCB is prolonged, the lamination efficiency is reduced, and the material cost is increased. Therefore, the thickness t1 of the cover film is designed to be 150-250 μm.

[0080] When the thickness of the viscous flow film 3 is too small (t2 < 20 μm), the softened volume of the viscous flow film 3 is insufficient, which may not be able to fill the recessed position of the metal foil 7, and cannot completely reproduce the surface topography of the metal foil 7. When the thickness of the viscous flow film 3 is too large (t2 > 50 μm), the thermal resistance is large, which prolongs the heating time of the steel plate of the hot pressing equipment on the PCB, reduces the lamination efficiency, and increases the material cost. Therefore, the thickness t2 of the viscous flow film 3 is designed to be 20-50 μm.

[0081] Figure 1 The thickness t1 of the cover film shown is the sum of the thicknesses of the first release film 4, the second release film 5 and the support layer 2.

[0082] In an embodiment, the hot pressing temperature of the first hot pressing stage is 110-140℃, and the hot pressing temperature of the second hot pressing stage is 140-200℃.

[0083] Specifically, in the hot pressing process of S4 step, segmented temperature rise, segmented pressure rise and gradient cooling control are adopted. The segmented temperature rise includes first stage, second stage and third stage which are performed in turn. In the first stage, the temperature is raised to 110℃ (10 min of holding), so that the prepreg 6 is preliminarily softened and fills the line gap of the thick copper layer 1. In the second stage, the temperature is raised to 140℃ (15 min of holding), which is the lowest temperature point of the viscosity of the prepreg 6, to promote the flow of the prepreg 6 and discharge the bubbles; in the third stage, the temperature is raised to 200℃ (30 min of holding) to realize complete curing of the prepreg 6.

[0084] At the same time, in the first stage, a pre-pressing pressure of 300 psi is applied (until 140℃), to exclude interlayer bubbles and preliminarily compact the dielectric layer 8, and in the second and third stages, the main pressing pressure is increased to 450 psi (until 200℃), to ensure the density and thickness uniformity of the dielectric layer 8.

[0085] The gradient cooling is at a rate of ≤3℃ / min, from 200℃ to 120℃ to 80℃, to avoid rebound of the dielectric thickness or interlayer delamination caused by thermal stress.

[0086] The PCB formed by the PCB laminating method comprises a core plate 100, a dielectric layer 8 and a metal foil 7, the surface of the core plate 100 is formed with a thick copper layer 1, the dielectric layer 8 is laminated on the thick copper layer 1, the metal foil 7 is laminated on the dielectric layer 8, and the thickness deviation of the dielectric layer 8 is controlled to be ±5 μm.

[0087] Compared with the PCB formed by the existing PCB laminating process, the thickness of the dielectric layer 8 is difficult to be stably controlled to be greater than 135 μm, and there is a weak area with a local insufficient thickness (<100 μm), and the thickness deviation of the dielectric layer 8 is large, the PCB formed by the PCB laminating method of the present application can accurately control the thickness of the dielectric layer 8 within the target thickness ±5 μm, greatly improve the uniformity and consistency of the dielectric layer 8, and does not need to replace the high-cost special material or increase the number of dielectric layers as in the prior art, the material cost of the auxiliary film 200 accounts for less than 5%.

[0088] Moreover, the auxiliary film 200 can be completely peeled off after lamination, does not affect the use of the original material system of the PCB, does not need complex parameter adjustment or additional equipment, and can be compatible with the existing PCB process design.

[0089] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. An auxiliary film for use in PCB lamination, adapted to be peelably laminated on a metal foil of a PCB, characterized in that, The cover type film includes a first release film and a support layer formed by a layer of thermoplastic material, and the adhesive flow film, the support layer and the first release film are sequentially stacked along the thickness direction; the thermosetting material is composed of a polyimide film and an epoxy glue, and the thermoplastic material is polystyrene; The Tg of the thermosetting material is lower than the lowest temperature of the PCB during hot pressing, and the Tg of the thermoplastic material is higher than the highest temperature of the PCB during hot pressing; the temperature of the PCB during hot pressing is 110-200℃; The cover type film is used to bear external pressure, the adhesive flow film has a low-temperature flow state and a high-temperature curing state, when the adhesive flow film is in the low-temperature flow state, the adhesive flow film flows and fills the recessed position on the surface of the metal foil; when the adhesive flow film is in the high-temperature curing state, the adhesive flow film cures and bonds the support layer and the metal foil.

2. The auxiliary film for PCB pressing according to claim 1, wherein, The cover type film further includes a second release film, and the surface of the support layer facing the adhesive flow film is divided into an isolated area and a bonding area; The second release film is attached to the isolated area of the support layer, and the adhesive flow film in the high-temperature curing state can bond the metal foil and the bonding area.

3. The auxiliary film for PCB pressing according to claim 2, wherein, The cross-sectional area of the second release film is smaller than the cross-sectional area of the support layer, the isolated area is located on the inner side of the surface of the support layer facing the adhesive flow film, and the bonding area is arranged on the outer side of the isolated area.

4. The auxiliary film for PCB pressing according to claim 1, wherein, The thickness of the cover type film is greater than the thickness of the adhesive flow film; the thickness t1 of the cover type film is 150-250μm; the thickness t2 of the adhesive flow film is 20-50μm.

5. A PCB pressing method, characterized by, It includes: An acquisition core plate, the surface of which is formed with a thick copper layer; A semi-cured sheet and a metal foil are sequentially stacked on the thick copper layer of the core plate; An auxiliary film is stacked on the metal foil to form a temporary PCB pressing structure; wherein the auxiliary film includes a cover type film and an adhesive flow film, the adhesive flow film is a film formed by a layer of thermosetting material, the cover type film includes a first release film and a support layer, the support layer is formed by a layer of thermoplastic material, the adhesive flow film, the support layer and the first release film are sequentially stacked along the thickness direction of the auxiliary film, and the adhesive flow film is attached to the metal foil; the Tg of the thermosetting material is lower than the lowest temperature of the subsequent PCB temporary pressing structure during hot pressing, and the Tg of the thermoplastic material is higher than the highest temperature of the subsequent PCB temporary pressing structure during hot pressing; the thermosetting material is composed of a polyimide film and an epoxy glue, and the thermoplastic material is polystyrene; the temperature of the PCB during hot pressing is 110-200℃; The PCB temporary lamination structure is hot-pressed to reach a first hot-pressing stage and a second hot-pressing stage in sequence, the cover type film bears external lamination force, and the prepreg is fused and solidified to form a dielectric layer; in the first hot-pressing stage, the viscous flow film softens and flows in a low-temperature flow state, fills the recessed positions on the surface of the metal foil, and is attached to the surface topography of the metal foil; in the second hot-pressing stage, the viscous flow film is in a high-temperature solidification state, and the viscous flow film is solidified and bonded to the support layer and the metal foil; The hot-pressing is ended, and the auxiliary film is peeled off to obtain a PCB.

6. The PCB pressing method of claim 5, wherein, The cover type film further comprises a second release film, a surface of the support layer facing the viscous flow film is divided into an isolated area and a bonding area, and the second release film is attached to the isolated area of the support layer, and the viscous flow film in the high-temperature solidification state can bond the metal foil and the bonding area when the PCB temporary lamination structure is subsequently hot-pressed.

7. The PCB pressing method of claim 6, wherein, The cross-sectional area of the second release film is smaller than the cross-sectional area of the support layer, the isolated area is located on the inner side of the surface of the support layer facing the viscous flow film, and the bonding area is arranged on the outer side of the isolated area.

8. The PCB pressing method of claim 5, wherein, The thickness of the cover type film is greater than the thickness of the viscous flow film; the thickness t1 of the cover type film is 150-250 μm; and the thickness t2 of the viscous flow film is 20-50 μm.

9. The PCB pressing method of claim 5, wherein, The hot-pressing temperature of the first hot-pressing stage is 110-140℃, and the hot-pressing temperature of the second hot-pressing stage is 140-200℃.

Images