Auxiliary film for PCB lamination, PCB lamination method and PCB

Abstract

The invention relates to the technical field of PCB manufacturing, in particular to an auxiliary film for PCB pressing, a PCB pressing method and a PCB. An auxiliary film for PCB lamination is suitable for being laminated on a metal foil of a PCB in a peelable manner and comprises a covering film and a viscous flow film, the covering film comprises a first release film and a supporting layer, and the viscous flow 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 flow 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 covering film is used for bearing external pressing force, and when the viscous flow film is in a low-temperature flow state, the viscous flow film flows and fills the concave position of the metal foil. When the viscous flow film is in a high-temperature curing state, the viscous flow film is cured and adheres to the supporting layer and the metal foil. The auxiliary thin film can be peeled off after pressing is completed, an original material system used by the PCB is not affected, and the auxiliary thin film is compatible with an existing PCB process design.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB production, and in particular to an auxiliary film for PCB lamination, a PCB lamination method and a PCB. Background Art

[0002] Printed circuit boards (PCBs) integrating high-power devices must balance high current carrying capacity, heat dissipation, and insulation reliability. However, the increasing frequency of high-power devices' operating environments can significantly degrade the insulation performance of the PCB's dielectric layer. This is especially true when exposed to high-frequency electric fields, which intensify the polarization effect of the organic insulating material in the dielectric layer, further reducing dielectric strength and potentially leading to breakdown and insulation failure.

[0003] Furthermore, PCBs integrating high-power devices require thick copper (typically ≥3oz between layers) to meet current-carrying and heat-dissipating requirements. However, these thick copper layers form circuits. During the lamination process, gaps between the circuits can lead to uneven dielectric filling, making dielectric thickness control more difficult. Conventional processes often struggle to consistently achieve dielectric layer thicknesses exceeding 135μm, and weak areas with thicknesses less than 100μm can easily form, further exacerbating the risk of insulation failure.

[0004] The existing solutions are to increase the number of dielectric layers or use high dielectric performance materials. For the solution of increasing the number of dielectric layers, the stacking of multiple dielectric layers will lead to an increase in the overall thickness of the PCB, which is contrary to the trend of PCB miniaturization. For the solution of using high dielectric performance materials, the adjustment of material composition is limited by process compatibility and is costly.

[0005] Therefore, how to achieve precise control of dielectric thickness and improve insulation properties under the existing material system has become a technical bottleneck that needs to be solved urgently. Summary of the Invention

[0006] The present invention provides an auxiliary film for PCB lamination, a PCB lamination method and a PCB, so as to achieve precise control of dielectric thickness and improvement of insulation properties under the existing material system.

[0007] To address the above-mentioned issues, embodiments of the present invention provide, on the one hand, an auxiliary film for PCB lamination, suitable for being releasably laminated on a metal foil of a PCB, comprising a laminating film and a viscous film. The viscous film is a film formed of a layer of thermosetting material. The laminating film comprises a first release film and a support layer formed of a layer of thermoplastic material. The viscous film, support layer, and first release film are sequentially laminated along the thickness direction. 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 coating film is used to withstand external pressure. The viscous film has a low-temperature fluid state and a high-temperature solidified state. When the viscous film is in the low-temperature fluid state, the viscous film flows and fills the concave positions on the surface of the metal foil; when the viscous film is in the high-temperature solidified state, the viscous film solidifies and bonds the support layer and the metal foil.

[0008] Optionally, the laminating film further comprises a second release film, and the surface of the support layer facing the adhesive film is divided into an isolation area and a bonding area; The second release film is attached to the isolation area of the support layer, and the viscous film in the high-temperature cured state can adhere to the metal foil and the bonding area.

[0009] Optionally, the cross-sectional area of the second release film is smaller than that of the support layer, the isolation area is located on the inner side of the surface of the support layer facing the adhesive film, and the bonding area is arranged around the outer side of the isolation area.

[0010] Optionally, the thickness of the coating film is greater than the thickness of the viscous flow film; the thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous flow film is 20-50 μm.

[0011] On the other hand, an embodiment of the present invention provides a PCB pressing method, comprising: Obtaining a core board, wherein a thick copper layer is formed on a surface of the core board; sequentially stacking a prepreg and a metal foil on the thick copper layer of the core board; An auxiliary film is laminated on the metal foil to form a temporary PCB lamination structure; wherein the auxiliary film includes a coating film and a viscous film, the viscous film being a film formed of a layer of thermosetting material, the coating film including a first release film and a support layer, the support layer being formed of a layer of thermoplastic material, the viscous film, the support layer, and the first release film being laminated sequentially along the thickness direction of the auxiliary film, and the viscous film being attached to the metal foil; the Tg of the thermosetting material being lower than the lowest temperature of the subsequent temporary PCB lamination structure during hot pressing, and the Tg of the thermoplastic material being higher than the highest temperature of the subsequent temporary PCB lamination structure during hot pressing; The temporary PCB pressing structure is hot pressed, sequentially reaching a first hot pressing stage and a second hot pressing stage; the laminating film is subjected to an external pressing force, and the prepreg melts and solidifies to form a dielectric layer; in the first hot pressing stage, the viscous film softens and flows, being in a low-temperature flow state, and the viscous film fills the concave positions on the surface of the metal foil to conform to the surface morphology of the metal foil; in the second hot pressing stage, the viscous film is in a high-temperature solidification state, and the viscous film solidifies and bonds the support layer and the metal foil; After the hot pressing is completed, the auxiliary film is peeled off to obtain the PCB.

[0012] Optionally, the laminating film further includes a second release film, and the surface of the supporting layer facing the viscous film is divided into an isolation area and a bonding area. The second release film is attached to the isolation area of the supporting layer. Subsequently, when the PCB temporary pressing structure is hot-pressed, the viscous film in the high-temperature cured state can bond to the metal foil and the bonding area.

[0013] Optionally, the cross-sectional area of the second release film is smaller than that of the support layer, the isolation area is located on the inner side of the surface of the support layer facing the adhesive film, and the bonding area is arranged around the outer side of the isolation area.

[0014] Optionally, the thickness of the coating film is greater than the thickness of the viscous flow film; the thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous flow film is 20-50 μm.

[0015] Optionally, the hot pressing temperature in the first hot pressing stage is between 110°C and 140°C, and the hot pressing temperature in the second hot pressing stage is between 140°C and 200°C.

[0016] On the other hand, an embodiment of the present invention provides a PCB, including a core board, a dielectric layer and a metal foil. A thick copper layer is formed on the surface of the core board, the dielectric layer is stacked on the thick copper layer, and the metal foil is stacked on the dielectric layer. The thickness deviation of the dielectric layer is controlled to be ±5μm.

[0017] An embodiment of the present invention provides an auxiliary film for PCB lamination. During the hot pressing process, the high modulus polymer of the support layer remains in a solid state before reaching the glass transition temperature, and the support layer maintains rigidity and can continuously withstand pressure. The viscous film softens and flows after initial heating, transforming into a low-temperature fluid state. The rigid support layer, when subjected to pressure, can resist the pressure of the undulating surface of the thick copper layer, providing a reaction force to force the thermosetting material of the viscous film to flow and fill the recessed positions of the metal foil, so that the viscous film completely replicates the surface morphology of the metal foil, achieving the viscous film's conformal effect. After further heating, the thermosetting material cross-links, solidifies, and sets, transforming into a high-temperature solidified state to bond the metal foil and the support layer, achieving the bonding effect of the viscous film, so that the metal foil, the viscous film, and the support layer are connected to form a whole. This facilitates the support layer to evenly transfer pressure to the dielectric layer through the viscous film and the metal foil, thereby improving the consistency and uniformity of the dielectric layer thickness and improving the insulation performance of the PCB. There is no need to replace high-cost special materials or increase the number of dielectric layers like in existing technologies. Moreover, the auxiliary film can be peeled off after lamination is completed, which does not affect the use of the original material system of the PCB. There is no need for complex parameter adjustments or additional equipment, and it is compatible with existing PCB process designs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 Schematic diagram of the explosion of an auxiliary film and a PCB during hot pressing for PCB lamination provided in one embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the core board of the PCB; Figure 3 for Figure 1 Schematic diagram of the explosion of the auxiliary film used for PCB lamination and the PCB before hot pressing.

[0020] The reference numerals in the specification are as follows: 100, core board; 200, auxiliary film; 1, thick copper layer; 2, support layer; 3, viscous flow film; 4, first release film; 5, second release film; 6, prepreg; 7, metal foil; 8, dielectric layer. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] like Figure 1 As shown, an embodiment of the present invention provides an auxiliary film for PCB lamination, which is suitable for being releasably laminated on a metal foil 7 of a PCB. The auxiliary film for PCB lamination (hereinafter referred to as auxiliary film 200) includes a laminating film and a viscous film 3. The viscous film 3 is a film formed of a layer of thermosetting material. The laminating film includes a first release film 4 and a support layer 2. The support layer 2 is formed of a layer of thermoplastic material. The viscous film 3, the support layer 2, and the first release film 4 are stacked in sequence along the thickness direction of the auxiliary film 200.

[0023] The Tg of the viscous film 3 is lower than the lowest temperature of the PCB during hot pressing, and the Tg of the supporting layer 2 is higher than the highest temperature of the PCB during hot pressing.

[0024] The coating film is used to withstand external pressure. The viscous film 3 has a low-temperature fluid state and a high-temperature solidified state. When the viscous film 3 is in the low-temperature fluid state, the viscous film 3 can flow and fill the concave positions on the surface of the metal foil 7; when the viscous film 3 is in the high-temperature solidified state, the viscous film 3 can solidify and bond the support layer 2 and the metal foil 7.

[0025] The so-called "low temperature" and "high temperature" are only relative definitions based on the fact that the hot pressing temperature when the viscous flow membrane 3 is in the "low temperature flow state" is lower than the hot pressing temperature when the viscous flow membrane 3 is in the "high temperature solidification state". It does not refer to the specific numerical value of the hot pressing temperature when the viscous flow membrane 3 is in the "low temperature flow state", nor does it refer to the specific numerical value of the hot pressing temperature when the viscous flow membrane 3 is in the "high temperature solidification state".

[0026] Existing PCBs that integrate high-power devices need to use thick copper (interlayer copper thickness is usually ≥3oz) to meet current carrying and heat dissipation requirements, such as Figure 1 As shown, the thick copper layer 1 of the core board 100 is formed with circuits, and gaps are formed between the circuits, resulting in an uneven surface of the core board 100. During the lamination process of the thick copper layer 1, the prepreg 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 prepreg 6 and concave positions on the surface of the copper foil. The resin of the prepreg 6 is difficult to evenly fill the concave areas between the circuits of the thick copper layer 1, resulting in uneven filling of the dielectric layer 8. In conventional processes, it is usually difficult for the thickness of the dielectric layer 8 to stably reach more than 135μm, and it is easy to form weak areas with a local dielectric thickness of less than 100μm, further exacerbating the risk of insulation failure.

[0027] The auxiliary film 200 in the present invention is used to assist in laminating the prepreg 6 and the metal foil 7 on the PCB, so as to accurately control the thickness of the dielectric layer 8 and improve the insulation performance of the PCB.

[0028] Specifically, such as Figure 3 As shown, the auxiliary film 200 is stacked on the metal foil 7 of the PCB before lamination. 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.

[0029] Because the laminating film's support layer 2 is made of a thermoplastic material with a Tg higher than the maximum temperature during PCB hot pressing, the high-modulus polymer in the support layer 2 remains solid before reaching its glass transition temperature during the hot pressing process, maintaining its rigidity and ability to withstand continuous pressure. Furthermore, the thermoplastic support layer 2 provides a certain cushioning effect, facilitating the uniform transfer of the pressing force to the adhesive film 3.

[0030] Since the viscous film 3 is a thin film formed by a layer of thermosetting material, the Tg of the thermosetting material of the viscous film 3 is lower than the lowest temperature of the PCB during hot pressing. Therefore, after the initial temperature rise, Figure 1 As shown, the viscous film 3 softens and flows into a low-temperature flow state. The rigid support layer 2, when under pressure, can resist the pressure of the undulating surface of the thick copper layer 1, providing a reaction force to force the thermosetting material of 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, achieving the shape-adhering effect of the viscous film 3. After further heating, the thermosetting material cross-links and solidifies, setting, and transforms into a high-temperature solidified state to bond the metal foil 7 and the support layer 2, achieving the bonding effect 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, which facilitates the support layer 2 to evenly 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 laminating film can offset the impact of the unevenness of the thick copper layer 1 on the pressure uniformity of the dielectric layer 8 during lamination, thereby improving the consistency and uniformity of the thickness of the dielectric layer 8.

[0031] 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, thereby improving the uniformity of the thickness of the dielectric layer 8 and reducing the thickness error to ±5μm, avoiding the risk of insulation failure and dielectric breakdown caused by insufficient local dielectric thickness.

[0032] Compared to PCBs formed by existing PCB lamination processes, in which the thickness of the dielectric layer 8 is difficult to stably reach above 135μm, and weak areas with insufficient dielectric thickness (<100μm) are formed locally, the thickness of the dielectric layer 8 of the PCB formed by the present invention through auxiliary lamination assisted by the auxiliary film 200 can be precisely controlled within the range of 150μm±5μm, thereby significantly increasing the insulation distance, reducing the high-frequency electric field strength, and suppressing the polarization effect and the risk of dielectric layer 8 breakdown.

[0033] In the present invention, there is no need to replace high-cost special materials or increase the number of dielectric layers as in the prior art. The material cost of the auxiliary film 200 accounts for <5%. Moreover, the auxiliary film 200 can be completely peeled off after the lamination is completed, without affecting the use of the original material system of the PCB. There is no need for complex parameter adjustments or additional equipment, and it is compatible with existing PCB process designs.

[0034] 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.

[0035] In one embodiment, if Figure 1 As shown, the laminating film further includes a second release film 5, and the surface of the support layer 2 facing the adhesive film 3 is divided into an isolation area and a bonding area.

[0036] The second release film 5 is attached to the isolation area of the support layer 2 , and the adhesive film 3 in a high-temperature solidified state can adhere to the metal foil 7 and the adhesive area.

[0037] The second release film 5 provides an interfacial barrier function and remains solid during the hot pressing process. The adhesive area of the support layer 2, unattached with the second release film 5, can directly contact the adhesive film 3, allowing the adhesive film 3, in its high-temperature cured state, to adhere to the metal foil 7 and the adhesive area, thereby connecting the metal foil 7, adhesive film 3, and support layer 2 to form a single entity. The second release film 5 separates the isolation area of the support layer 2 from the adhesive film 3, ensuring that the laminating film can be peeled off without residue after the hot pressing is completed.

[0038] In one embodiment, if Figure 1 As shown, 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 bonding area is arranged around the outer side of the isolation area, so that the viscous film 3 in the high-temperature cured state is bonded to the outer area of the support layer 2, so as to increase the bonding area between the support layer 2 and the viscous film 3 and enhance the bonding strength between the support layer 2 and the viscous film 3.

[0039] In one embodiment, the thickness of the mold film is greater than that of the adhesive film 3. The mold film must be sufficiently rigid to withstand the high pressure during the hot pressing process and resist the pressure of the surface fluctuations of the thick copper layer 1, providing uniform support and evenly transferring the pressing force to the dielectric layer 8. Therefore, the mold film is designed to be thicker to ensure its rigidity.

[0040] like Figure 1 As shown, the thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous film 3 is 20-50 μm.

[0041] If the lamination film thickness is too small (t1 < 150μm), it cannot guarantee sufficient rigidity. If the lamination film thickness is too large (t1 > 250μm), although the lamination film has sufficient rigidity, its thickness is too thick and the thermal resistance is large, which will prolong the time it takes for the steel plate of the hot press to heat the PCB, reduce lamination efficiency, and increase material costs. Therefore, the lamination film thickness t1 is designed to be 150-250μm.

[0042] If the thickness of the adhesive film 3 is too small (t2 < 20 μm), the softened film 3 will have insufficient volume and may not be able to fill the recessed areas of the metal foil 7, nor fully replicate the surface topography of the metal foil 7. If the thickness of the adhesive film 3 is too large (t2 > 50 μm), the thermal resistance will be high, which will increase the time it takes for the steel plate in the hot press to heat the PCB, reduce lamination efficiency, and increase material costs. Therefore, the thickness t2 of the adhesive film 3 is designed to be between 20 and 50 μm.

[0043] Figure 1The thickness t1 of the laminating film shown is the sum of the thicknesses of the first release film 4 , the second release film 5 and the support layer 2 .

[0044] In one embodiment, the adhesive film 3 is a thin film composed of a PI film (polyimide film) and epoxy adhesive.

[0045] In one embodiment, the first release film 4 and the second release film 5 are made of 100% polyimide.

[0046] In other embodiments, the second release film 5 may be omitted. Since the thermosetting material of the adhesive film 3 has low viscosity, the support layer 2 can be easily removed from the PCB even if combined with the adhesive film 3 .

[0047] In one embodiment, the thermoplastic material of the support layer 2 is PS (polystyrene).

[0048] In addition, an embodiment of the present invention provides a PCB lamination method, which utilizes the auxiliary film 200 to assist in lamination of the prepreg 6 and the metal foil 7 on the PCB, thereby precisely controlling the thickness of the dielectric layer 8 and improving the insulation performance of the PCB. The PCB lamination method includes: S1: If 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.

[0049] Specifically, a copper clad laminate with a corresponding copper thickness is selected, and a circuit pattern is formed on the copper clad laminate through an image transfer-flash etching-film stripping process. The copper surface at the non-circuit pattern position is removed to expose the corresponding substrate surface to form a core board 100 with a thick copper layer 1. The so-called thick copper refers to the interlayer copper thickness usually ≥3oz.

[0050] S2: If 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 .

[0051] S3: If Figure 3 As shown, an auxiliary film 200 is laminated on the metal foil 7 to form a temporary PCB lamination structure. The auxiliary film 200 includes a molded film and a viscous film 3. The viscous film 3 is a film formed of a thermosetting material. The molded film includes a first release film 4 and a support layer 2. The support layer 2 is formed of a thermoplastic material. The viscous film 3, support layer 2, and first release film 4 are laminated sequentially along the thickness direction of the auxiliary film 200. The viscous film 3 is attached to the metal foil 7.

[0052] 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.

[0053] S4: As Figure 1As shown, the temporary PCB pressing structure undergoes hot pressing, sequentially progressing through the first and second hot pressing stages. The laminating film withstands the external pressing force, and the prepreg 6 melts and solidifies to form the dielectric layer 8. During the first hot pressing stage, the viscous film 3 softens and flows, entering a low-temperature flow state. It fills the recessed areas on the surface of the metal foil 7, conforming to its surface topography. In the second hot pressing stage, the viscous film 3 enters a high-temperature solidification state, solidifying and bonding the support layer 2 and the metal foil 7.

[0054] S5: Finish the hot pressing, peel off the auxiliary film 200, and obtain the PCB.

[0055] It should be noted that the first hot pressing stage and the second hot pressing stage are only the division of the entire hot pressing process according to the stages when the viscous flow film 3 is in the low-temperature fluid state and the high-temperature solidification state. In the entire hot pressing process, the stage when the viscous flow film 3 is in the low-temperature fluid state belongs to the first hot pressing stage, and the stage when the viscous flow film 3 is in the high-temperature solidification state belongs to the second hot pressing stage. The first hot pressing stage and the second hot pressing stage are not a distinction between the process means.

[0056] Specifically, it can be seen from step S3 that the auxiliary film 200 is stacked on the metal foil 7 of the PCB before lamination. 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.

[0057] Because the laminating film's support layer 2 is made of a thermoplastic material with a Tg higher than the maximum temperature during PCB hot pressing, during the hot pressing process in step S4, the high-modulus polymer in support layer 2 remains solid before reaching its glass transition temperature. This maintains its rigidity and ability to withstand continuous pressure. Furthermore, the thermoplastic support layer 2 provides a certain cushioning effect, facilitating the uniform transfer of the pressing force to the adhesive film 3.

[0058] Since the viscous film 3 is a thin film formed by a layer of thermosetting material, the Tg of the thermosetting material of the viscous film 3 is lower than the lowest temperature of the PCB during hot pressing. Figure 1As shown, during the hot pressing process of step S4, after the initial temperature rise, the viscous film 3 softens and flows, and the rigid support layer 2 is able to resist the pressure of the undulating surface of the thick copper layer 1 after being compressed, providing a reaction force to force the viscous film 3 to flow and fill the concave position of the metal foil 7, so that the viscous film 3 completely replicates the surface morphology of the metal foil 7, and realizes the shape-attaching effect of the viscous film 3. After continuing to heat up, the thermosetting material cross-links and solidifies, and sets to bond the metal foil 7 and the support layer 2, realizing the bonding effect 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, which is conducive to 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 effect of the laminating 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, so as to ensure the consistency and uniformity of the thickness of the dielectric layer 8.

[0059] Compared to PCBs formed by existing PCB lamination processes, in which the thickness of the dielectric layer 8 is difficult to stably reach above 135μm, and weak areas with insufficient dielectric thickness (<100μm) are formed locally, the thickness of the dielectric layer 8 of the PCB formed by the present invention through auxiliary lamination assisted by the auxiliary film 200 can be precisely controlled within the range of 150μm±5μm, thereby significantly increasing the insulation distance, reducing the high-frequency electric field strength, and suppressing the polarization effect and the risk of dielectric layer 8 breakdown.

[0060] Moreover, as can be seen from step S5, the auxiliary film 200 can be peeled off after the lamination is completed, which does not affect the use of the original material system of the PCB, does not require complex parameter adjustments or additional equipment, and is compatible with existing PCB process designs.

[0061] It should be noted that the viscous film 3 has low viscosity, so that the auxiliary film 200 can be easily peeled off from the metal foil 7 after the hot pressing is completed.

[0062] In one embodiment, if Figure 3 As shown, the laminated coating film in step S2 also includes a second release film 5. The surface of the support layer 2 facing the viscous film 3 is divided into an isolation area and a bonding area. The second release film 5 is attached to the isolation area of the support layer 2. Subsequently, when the PCB temporary pressing structure is hot-pressed, the viscous film 3 in a high-temperature cured state can bond to the metal foil 7 and the bonding area.

[0063] The second release film 5 provides an interfacial barrier function and remains solid during the hot pressing process. The adhesive area of the support layer 2, unattached with the second release film 5, can directly contact the adhesive film 3, allowing the adhesive film 3, in its high-temperature cured state, to adhere to the metal foil 7 and the adhesive area, thereby connecting the metal foil 7, adhesive film 3, and support layer 2 to form a single entity. The second release film 5 separates the isolation area of the support layer 2 from the adhesive film 3, ensuring that the laminating film can be peeled off without residue after the hot pressing is completed.

[0064] In one embodiment, if Figure 3 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 mucosal film 3, and the bonding area is arranged around the outer side of the isolation area, so that the mucosal film 3 in the high-temperature cured state is bonded to the outer peripheral area of the support layer 2, so as to increase the bonding area between the support layer 2 and the mucosal film 3 and enhance the bonding strength between the support layer 2 and the mucosal film 3.

[0065] 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 opened on the second release film 5. When the viscous film 3 flows, it can adhere to the support layer 2 through the holes. The positions on the surface of the support layer 2 facing the viscous film 3 corresponding to the plurality of holes are bonding areas, and the remaining positions on the support layer 2 are isolation areas.

[0066] In one embodiment, the thickness of the mold film is greater than that of the adhesive film 3. The mold film must be sufficiently rigid to withstand the high pressure during the hot pressing process and resist the pressure of the surface fluctuations of the thick copper layer 1, providing uniform support and evenly transferring the pressing force to the dielectric layer 8. Therefore, the mold film is designed to be thicker to ensure its rigidity.

[0067] The thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous film 3 is 20-50 μm.

[0068] If the lamination film thickness is too small (t1 < 150μm), it cannot guarantee sufficient rigidity. If the lamination film thickness is too large (t1 > 250μm), although the lamination film has sufficient rigidity, its thickness is too thick and the thermal resistance is large, which will prolong the time it takes for the steel plate of the hot press to heat the PCB, reduce lamination efficiency, and increase material costs. Therefore, the lamination film thickness t1 is designed to be 150-250μm.

[0069] If the thickness of the adhesive film 3 is too small (t2 < 20 μm), the softened film 3 will have insufficient volume and may not be able to fill the recessed areas of the metal foil 7, nor fully replicate the surface topography of the metal foil 7. If the thickness of the adhesive film 3 is too large (t2 > 50 μm), the thermal resistance will be high, which will increase the time it takes for the steel plate in the hot press to heat the PCB, reduce lamination efficiency, and increase material costs. Therefore, the thickness t2 of the adhesive film 3 is designed to be between 20 and 50 μm.

[0070] Figure 1 The thickness t1 of the laminating film shown is the sum of the thicknesses of the first release film 4 , the second release film 5 and the support layer 2 .

[0071] In one embodiment, the hot pressing temperature of the first hot pressing stage is 110° C.-140° C., and the hot pressing temperature of the second hot pressing stage is 140° C.-200° C.

[0072] Specifically, the hot pressing process in step S4 utilizes staged heating, staged pressurization, and gradient cooling control. The staged heating includes a first, second, and third stage, which are performed sequentially. In the first stage, the temperature is raised to 110°C (held at this temperature for 10 minutes) to initially soften the prepreg 6 and fill the gaps between the lines of the thick copper layer 1. In the second stage, the temperature is raised to 140°C (held at this temperature for 15 minutes), the temperature at which the viscosity of the prepreg 6 is lowest, to promote the flow of the prepreg 6 and expel bubbles. In the third stage, the temperature is raised to 200°C (held at this temperature for 30 minutes) to fully cure the prepreg 6.

[0073] At the same time, a pre-compression pressure of 300 psi (continuously up to 140°C) is applied in the first stage to remove interlayer bubbles and preliminarily compact the dielectric layer 8. In the second and third stages, the main pressure is increased to 450 psi (continuously up to 200°C) to ensure the density and thickness uniformity of the dielectric layer 8.

[0074] The gradient cooling is carried out at a rate of ≤3℃ / min, from 200℃→120℃→80℃, to avoid thickness rebound or interlayer delamination due to thermal stress.

[0075] In addition, an embodiment of the present invention provides a PCB, which is formed by the above-mentioned PCB pressing method, including a core board 100, a dielectric layer 8 and a metal foil 7. A thick copper layer 1 is formed on the surface of the core board 100, the dielectric layer 8 is stacked on the thick copper layer 1, and the metal foil 7 is stacked on the dielectric layer 8. The thickness deviation of the dielectric layer 8 is controlled to be ±5μm.

[0076] Compared to PCBs formed by existing PCB lamination processes, in which the thickness of the dielectric layer 8 is difficult to stably reach above 135μm, and weak areas with insufficient dielectric thickness (<100μm) are formed locally, resulting in large thickness deviations in the dielectric layer 8. In the PCB formed by the PCB lamination method of the present invention, the thickness of the dielectric layer 8 can be precisely controlled within a range of ±5μm of the target dielectric thickness, significantly improving the uniformity and consistency of the dielectric layer 8. There is no need to replace high-cost special materials or increase the number of dielectric layers as in the existing technology. The material cost of the auxiliary film 200 accounts for less than 5%.

[0077] Moreover, the auxiliary film 200 can be completely peeled off after the lamination is completed, without affecting the original material system used in the PCB, without the need for complex parameter adjustments or additional equipment, and is compatible with existing PCB process designs.

[0078] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. An auxiliary film for PCB lamination, suitable for being peelably laminated on a metal foil of a PCB, characterized in that: The invention comprises a coating film and a viscous film, wherein the viscous film is a film formed of a layer of thermosetting material, the coating film comprises a first release film and a support layer, wherein the support layer is formed of a layer of thermoplastic material, and the viscous film, the support layer and the first release film are sequentially stacked in the thickness direction; 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 coating film is used to withstand external pressure. The viscous film has a low-temperature fluid state and a high-temperature solidified state. When the viscous film is in the low-temperature fluid state, the viscous film flows and fills the concave positions on the surface of the metal foil; when the viscous film is in the high-temperature solidified state, the viscous film solidifies and bonds the support layer and the metal foil.

2. The auxiliary film for PCB lamination according to claim 1, characterized in that: The laminating film further includes a second release film, and the surface of the support layer facing the adhesive film is divided into an isolation area and a bonding area; The second release film is attached to the isolation area of the support layer, and the viscous film in the high-temperature cured state can adhere to the metal foil and the bonding area.

3. The auxiliary film for PCB lamination according to claim 2, characterized in that: The cross-sectional area of the second release film is smaller than that of the support layer. The isolation area is located on the inner side of the surface of the support layer facing the adhesive film. The bonding area is arranged around the outer side of the isolation area.

4. The auxiliary film for PCB lamination according to claim 1, characterized in that: The thickness of the coating film is greater than that of the viscous film; the thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous film is 20-50 μm.

5. A PCB pressing method, characterized in that: include: Obtaining a core board, wherein a thick copper layer is formed on a surface of the core board; sequentially stacking a prepreg and a metal foil on the thick copper layer of the core board; An auxiliary film is laminated on the metal foil to form a temporary PCB lamination structure; wherein the auxiliary film includes a coating film and a viscous film, the viscous film being a film formed of a layer of thermosetting material, the coating film including a first release film and a support layer, the support layer being formed of a layer of thermoplastic material, the viscous film, the support layer, and the first release film being laminated sequentially along the thickness direction of the auxiliary film, and the viscous film being attached to the metal foil; the Tg of the thermosetting material being lower than the lowest temperature of the subsequent temporary PCB lamination structure during hot pressing, and the Tg of the thermoplastic material being higher than the highest temperature of the subsequent temporary PCB lamination structure during hot pressing; The temporary PCB pressing structure is hot pressed, sequentially reaching a first hot pressing stage and a second hot pressing stage, wherein the laminating film is subjected to an external pressing force, and the prepreg melts and solidifies to form a dielectric layer; in the first hot pressing stage, the viscous film softens and flows, being in a low-temperature flow state, and the viscous film fills the concave positions on the surface of the metal foil to conform to the surface morphology of the metal foil; in the second hot pressing stage, the viscous film is in a high-temperature solidification state, and the viscous film solidifies and bonds the support layer and the metal foil; After the hot pressing is completed, the auxiliary film is peeled off to obtain the PCB.

6. The PCB pressing method according to claim 5, characterized in that: The laminating film also includes a second release film. The surface of the support layer facing the viscous film is divided into an isolation area and a bonding area. The second release film is attached to the isolation area of the support layer. When the PCB temporary pressing structure is subsequently hot-pressed, the viscous film in the high-temperature cured state can adhere to the metal foil and the bonding area.

7. The PCB pressing method according to claim 6, characterized in that: The cross-sectional area of the second release film is smaller than that of the support layer. The isolation area is located on the inner side of the surface of the support layer facing the adhesive film. The bonding area is arranged around the outer side of the isolation area.

8. The PCB pressing method according to claim 5, characterized in that: The thickness of the coating film is greater than that of the viscous film; the thickness t1 of the coating film is 150-250 μm; the thickness t2 of the viscous film is 20-50 μm.

9. The PCB pressing method according to claim 5, wherein: The hot pressing temperature of the first hot pressing stage is 110° C. to 140° C., and the hot pressing temperature of the second hot pressing stage is 140° C. to 200° C.

10. A PCB formed by the PCB lamination method according to any one of claims 5 to 9, characterized in that: It includes a core board, a dielectric layer and a metal foil. A thick copper layer is formed on the surface of the core board. The dielectric layer is stacked on the thick copper layer. The metal foil is stacked on the dielectric layer. The thickness deviation of the dielectric layer is controlled to be ±5μm.

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