PCB manufacturing method and PCB

Abstract

The application discloses a PCB manufacturing method, comprising the following steps: humidifying or absorbing moisture on a local area of a prepreg; and pressing the humidified or moisture-absorbed prepreg and a target core plate, wherein the local area of the prepreg after the humidification or moisture absorption forms a cavity during the pressing process. The application realizes the purpose of embedding a cavity in a PCB by humidifying a local area of a prepreg, wherein, during the pressing process, the humidified area of the prepreg has more water vapor, and the water vapor evaporates to form bubbles under high temperature; after the target core plate is attached to the surface of the prepreg, the bubbles cannot be discharged in time, and thus regular cavities are formed in the prepreg. In addition, the application further provides a PCB prepared by the above method.

Description

Technical Field

[0001] The present invention relates to the field of PCB (Printed Circuit Board) production, and in particular to a method for producing a PCB buried cavity. Background Art

[0002] PCBs with built-in cavities have two main uses: one is for high-speed rigid boards, which utilize the low dielectric constant of air to reduce signal loss; the other is for multi-layer flexible boards and rigid-flex boards, where there is no adhesive material between the flexible layers to enhance their flexural performance.

[0003] Conventional PCB cavities are usually formed by opening windows in the prepreg at the location where the cavity needs to be buried before lamination. This method of burying the cavity can cause collapse due to the lack of support at the cavity location, and the prepreg near the window melts and flows into the cavity location, destroying the formation of the cavity.

[0004] To address the issue of prepreg melt flow, low-flow or no-flow prepregs are typically used for window lamination in buried cavities. This effectively controls prepreg flow. However, due to the poor resin flow of low-flow or no-flow prepregs, other areas of the same layer are prone to poor filling. As for the collapse problem, there is currently no direct solution. Summary of the Invention

[0005] The present invention aims to provide a PCB manufacturing method and a PCB to solve one or more technical problems existing in the prior art and at least provide a beneficial option or create conditions.

[0006] The technical solutions adopted to solve the above technical problems are:

[0007] In one aspect, the present invention provides a PCB manufacturing method, comprising the following steps: humidifying or absorbing moisture in a localized area of ​​a prepreg; and laminating the humidified or absorbing prepreg to a target core board, wherein a cavity is formed in the humidified or absorbing localized area of ​​the prepreg during the lamination process.

[0008] The beneficial effects of the present invention are as follows: a local area of ​​the prepreg is humidified. During the pressing process, due to the large amount of water vapor in the humidified area of ​​the prepreg, the water vapor will evaporate under high temperature to form bubbles. After the target core board is bonded to the surface of the prepreg, the bubbles cannot be discharged in time, thereby forming regular cavities in the prepreg, thereby achieving the purpose of burying the PCB cavity. In addition, this manufacturing method avoids the problems of cavity collapse and prepreg melt flow.

[0009] As a further improvement of the above technical solution, the following steps are included: S10, providing two waterproof sheets, and processing line grooves on the two waterproof sheets; S20, overlapping the two waterproof sheets and the semi-cured sheets to form a multi-layer combination, and the semi-cured sheet is sandwiched between the two waterproof sheets; S30, placing the multi-layer combination in a humid environment to absorb moisture, and the position of the semi-cured sheet corresponding to the line groove is exposed to the humid environment; S40, after moisture absorption, separating the two waterproof sheets from the semi-cured sheet, and then pressing the semi-cured sheet after moisture absorption with the target core board, and forming a cavity in the moisture absorption area of ​​the semi-cured sheet during the pressing process.

[0010] By overlapping the slotted waterproof sheet with the prepreg, the portion of the prepreg exposed to the slot is subjected to moisture absorption treatment, thereby achieving the purpose of humidifying the local area of ​​the prepreg.

[0011] As a further improvement to the above technical solution, prior to laminating the waterproof sheet and the prepreg, positioning structures are fabricated on the waterproof sheet and the prepreg. These positioning structures help position the waterproof sheet and the prepreg relative to each other during lamination. The positioning structures prevent the waterproof sheet and the prepreg from sliding during lamination, which could alter the moisture absorption area. This allows the cavity to be formed at a predetermined location.

[0012] As a further improvement to the above technical solution, in step S20, the surfaces of the two waterproof sheets and the prepreg bonded together are sealed around the circuit grooves and the outer edges of the bonding surfaces to prevent moisture from entering the non-hygroscopic areas. In other words, the prepreg is sealed in all areas except the moisture-absorbing areas.

[0013] As a further improvement of the above technical solution, the sealing treatment is to apply adhesive, which can simultaneously play the role of sealing and bonding and fixing.

[0014] As a further improvement of the above technical solution, in step S30, the temperature of the humid environment is set to ≤23°C, and the humidity is set to 85±10% R / H. In the humid environment, the multilayer combination is placed for 8h to 12h to fully absorb moisture.

[0015] As a further improvement to the above technical solution, the size of the circuit slot is set to be consistent with the width of the circuit on the target core board that needs to form a cavity. By calculating the expansion ratio of water evaporation and the water absorption rate of the prepreg under different times and environments (weight change before and after treatment), the corresponding relationship between the size of the cavity and the circuit slot on the aluminum plate can be obtained. In an environment with an ambient temperature of ≤23°C and an ambient humidity of 85±10%R / H, the prepreg absorbs moisture for 8h to 12h and can form a cavity approximately 2 to 2.5 times the size of the slot, with a flat spherical shape. The size of the formed cavity can meet the use requirements, that is, the size of the circuit slot on the aluminum sheet is set to be consistent with the size of the circuit on the PCB that needs to form a cavity, which can meet the use requirements.

[0016] As a further improvement of the above technical solution, in step S40, the semi-cured sheet is pressed with the target core board within 8 hours after separation. This can avoid the moisture absorption area of ​​the semi-cured sheet 200 from diffusing to other areas, causing void failure in other areas and evaporation of absorbed water vapor, resulting in the cavity effect being less than expected.

[0017] As a further improvement of the above technical solution, in step S40, the heating rate of the pressing program is set to ≥3.0℃ / min, and the pressing ambient temperature is between 80℃ and 140℃, so as to avoid the problem of irregular shape of the cavity and too small cavity formed due to too slow heating.

[0018] As a further improvement of the above technical solution, the prepreg is at least partially filled with pure glue. The prepregs used to make multilayer printed circuit boards are mostly made of glass fiber cloth as a reinforcing material. When the area of ​​the prepreg that needs to form a cavity is filled with pure glue (without glass fiber), a better cavity effect can be achieved due to the lack of constraint of the fiber bundle.

[0019] As a further improvement of the above technical solution, the copper thickness of the circuit on the target core board that needs to form a cavity is set to ≤1oz. If the copper thickness is too thick, the cavity may not be formed during the pressing process.

[0020] On the other hand, the present invention further provides a PCB, wherein the PCB comprises at least one cavity; and the PCB is manufactured according to any of the above manufacturing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0022] Figure 1 is a flow chart of a method for manufacturing a buried cavity in a PCB according to embodiment 1 of the present invention;

[0023] Figure 2 1 is a schematic diagram of the lamination process of the method for manufacturing a buried cavity in a PCB according to Example 1 of the present invention;

[0024] Figure 3 1 is a schematic diagram of the pressing process of the method for manufacturing a buried cavity in a PCB according to Example 1 of the present invention;

[0025] Figure 4 Schematic diagram of the structure of the waterproof sheet of the PCB buried cavity manufacturing method according to embodiment 1 of the present invention. DETAILED DESCRIPTION

[0026] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it should not be understood as a limitation on the scope of protection of the present invention.

[0027] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0028] In the description of this invention, terms such as "greater than," "less than," and "exceed" are understood to exclude the number itself, while terms such as "above," "below," and "within" are understood to include the number itself. The use of terms such as "first" and "second" is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0029] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0030] Example 1:

[0031] Reference Figures 1 to 3 The PCB manufacturing method according to an embodiment of the present invention includes:

[0032] Step S10: Prepare two aluminum sheets 100. In this embodiment, the thickness of the aluminum sheet 100 is between 0.15mm and 1mm, and the aluminum sheet 100 is square. The outer dimensions of the aluminum sheet 100 can be approximately 25mm larger on one side than the outer dimensions of the prepreg 200. Then, by analyzing the design requirements, the layer position and size of the cavity to be buried are determined, and the milling cutter path data is designed. Based on the above milling cutter path data, the same-sized circuit slots 110 are machined on the two aluminum sheets 100. It can be understood that the circuit slots 110 completely penetrate the aluminum sheet 100 and have the same slot width. In addition, positioning holes (not shown in the drawings) are punched out at the four corners of the aluminum sheet 100 using a punching machine. For example, the aperture of the positioning holes is 3mm. These positioning holes are used for subsequent fixation with the prepreg 200 to be pressed.

[0033] The processed aluminum sheet 100 is then cleaned, deburred and polished to keep the surface of the aluminum sheet smooth and clean.

[0034] Step S20: Prepare the prepreg 200. The prepreg 200 is also square in shape, and positioning holes that are consistent with the positioning holes of the aluminum sheet 100 are punched out at its four corners. The aperture is also 3 mm. Usually, the materials of the prepreg mainly include resin and reinforcing materials. The reinforcing materials are divided into several types such as glass fiber cloth, paper base, and composite materials. The prepregs used to make multi-layer printed circuit boards mostly use glass fiber cloth as the reinforcing material. In this embodiment, the prepreg is filled with pure glue (no glass fiber) as a whole, thereby ensuring a better effect of subsequent cavity formation. Of course, in some other embodiments, only local areas can be filled with pure glue, while other areas are still filled with glass fiber materials; this can ensure the overall stability of the prepreg.

[0035] After the aluminum sheet 100 and the prepreg 200 are processed, apply 1mm-2mm wide epoxy resin glue on the inner periphery of the aluminum sheet 100 corresponding to the outer edge of the prepreg 200 and around the circuit groove 110; then overlap the two aluminum sheets 100 and the prepreg 200 to form a multi-layer combination. When overlapping, the prepreg 200 is sandwiched between the two aluminum sheets 100. The two aluminum sheets 100 and the prepreg 200 are positioned by positioning pins, and lightly pressed on the outer edge of the aluminum sheet 100 and around the circuit groove 110, so that the epoxy resin glue can fit tightly between the aluminum sheet 100 and the prepreg 200, thereby increasing the sealing effect between the two.

[0036] Step S30: The laminated multilayer assembly is placed in a humid environment and allowed to stand for 8 to 12 hours, allowing the area of ​​the prepreg corresponding to the circuit slot 110 to be exposed to the humid environment and fully absorb moisture. The humid environment temperature is set to ≤ 23°C and the humidity is set to 85±10% R / H. The aluminum sheet 100 is waterproof, and the contact surface between the aluminum sheet 100 and the prepreg 200 is sealed with epoxy resin around the circuit slot and the outer edge of the contact surface. Therefore, only the area of ​​the prepreg 200 corresponding to the circuit slot absorbs moisture from the humid environment, while the rest of the prepreg 200, covered by the aluminum sheet 200 and the epoxy resin, cannot absorb moisture.

[0037] By calculating the expansion ratio due to water evaporation and the water absorption rate of the prepreg at different times and environments (weight change before and after treatment), the corresponding relationship between the cavity size and the circuit slot on the aluminum plate can be determined. In the environment of this embodiment, the temperature is ≤23°C, which is for the purpose of facilitating the storage of PP. When the temperature is too high, PP is prone to deformation. The humidity is 85±10% R / H. After the prepreg absorbs moisture for 8 to 12 hours, a cavity approximately 2 to 2.5 times the size of the slot is formed, which is a flattened spherical shape. The resulting cavity size meets the application requirements. Therefore, in step S10, the circuit slot on the aluminum plate is sized to match the width of the circuit to be formed on the PCB. Of course, in other embodiments, the size of the circuit slot can be adjusted according to actual production requirements.

[0038] As shown in the table below, the final size of the cavity formed in the circuit grooves varies under different moisture absorption environments.

[0039]

[0040] After moisture absorption is complete in step S40, the two aluminum sheets 100 are separated from the prepreg 200. In this embodiment, epoxy resin is used for bonding, and epoxy resin glue requires more than 24 hours to fully cure at room temperature. Therefore, after the 8-12 hours of moisture absorption in step S30, the epoxy resin glue has not yet fully cured. Therefore, the aluminum sheets 100 and prepreg 200 can be separated manually without the aid of tools. After separation, the epoxy resin generally adheres to the aluminum sheets 100, so it does not affect the subsequent use of the prepreg 200.

[0041] Reference Figure 3The prepreg 200, which has been separated from the aluminum sheet 100 after absorbing moisture, is pressed together with two target core boards 300. The prepreg 200 is sandwiched between the two target core boards 300, one of which is provided with a circuit 400 in which a cavity is to be formed. During the pressing process, the moisture-absorbing area of ​​the prepreg 200 absorbs moisture, causing water vapor to evaporate and form bubbles during the pressing process. At the same time, because the extra gas cannot be removed in time by the vacuum pump, regular pressed bubbles are formed in this area, which eventually become the desired cavity. The other areas of the prepreg 200 are covered by the aluminum sheet during the moisture absorption process, making it difficult for them to absorb water. They are relatively dry and do not generate bubbles during the pressing process.

[0042] Furthermore, in order to improve the molding quality of the cavity, the semi-cured sheet 200 is pressed with the target core board 300 within 8 hours after being separated from the aluminum sheet 100. This can prevent the moisture absorption area of ​​the semi-cured sheet 200 from diffusing to other areas and causing voids in other areas.

[0043] Furthermore, the heating rate of the pressing program is set to ≥3.0°C / min, and the pressing environment temperature is between 80°C and 140°C. This can avoid the problem of irregular shape of the cavity and too small cavity formed due to slow heating.

[0044] Furthermore, the copper thickness of the circuits on the target core board 300 that need to form cavities is preferably ≤1oz, and more preferably ≤0.5oz. If the copper thickness is too thick, it may result in the inability to form cavities during the pressing process.

[0045] The present invention overlaps an aluminum sheet with circuit slots with a prepreg, and performs a moisture absorption treatment on the portion of the prepreg exposed to the slots, so that the prepreg can achieve humidification treatment in a local area, while other areas remain dry. The prepreg after moisture absorption is then pressed together with the core board. During the pressing process, the moisture absorption area in the prepreg contains a lot of water vapor, which will evaporate under high temperature to form bubbles. After the target core board is bonded to the surface of the prepreg, the bubbles cannot be removed in time, thereby forming regular cavities in the prepreg, thereby achieving the purpose of burying the PCB cavity. Compared with the traditional method of opening windows in the prepreg to form cavities before pressing, the advantages of the present invention are:

[0046] 1. Due to the high temperature gasification volume increases, there is sufficient support to solve the collapse problem during lamination;

[0047] 2. The water vapor in the prepreg evaporates and expands in volume, squeezing the resin in the original position to flow to the nearby area, while blocking the nearby resin from flowing into the cavity;

[0048] 3. Ordinary flow rate prepreg can be used to solve the problem of poor filling in other non-cavity areas.

[0049] In this embodiment, positioning holes are machined at the four corners of the aluminum sheet 100 and the prepreg 200, and the aluminum sheet and the prepreg are positioned using positioning pins. In other embodiments, the number of positioning holes and positioning pins is not limited to four, and the number and position of positioning holes and positioning pins can be adaptively changed according to actual conditions.

[0050] In some other embodiments, the positioning structure of the aluminum sheet and the semi-cured sheet can also be formed in other ways, such as a protruding limiting boss punched out on the aluminum sheet, and a positioning hole corresponding to the limiting boss punched out on the semi-cured sheet. When the aluminum sheet and the semi-cured sheet are superimposed, the limiting boss on the aluminum sheet is inserted into the positioning hole on the semi-cured sheet.

[0051] In some other embodiments, the sealing process in step S20 can also be to add a flexible rubber gasket between the aluminum sheet and the semi-cured sheet, and process an opening on the rubber gasket with the same size as the circuit groove on the aluminum sheet. When stacking, the multi-layer combination is placed in the order of aluminum sheet-rubber gasket-semi-cured sheet-rubber gasket-aluminum sheet from bottom to top. The stacked multi-layer combination is pressed to deform the rubber gasket, and then the operation of step S30 is continued.

[0052] In addition to the above-mentioned local humidification treatment method, the prepreg can also be used to make anti-plating patterns, copper electroplating, remove the anti-plating film / press the copper foil, etch the pattern, absorb moisture, protect the pattern, etch copper, or apply a waterproof sheet, control the depth of the milling pattern, and then process the edge to make the same prepreg.

[0053] In some other embodiments, the number of prepregs is not limited to one, and the number of prepregs can be adaptively changed through moisture absorption tests.

[0054] In other embodiments, the aluminum sheet may be replaced by other waterproof sheets, such as steel sheets, hard plastic sheets, etc.

[0055] In some other embodiments, a waterproof sheet may not be required. Instead, a waterproof membrane may be attached to the prepreg and then processed (e.g., laser cutting) to partially remove material from the membrane, thereby creating grooves similar to those for circuits. The membrane can then be removed after absorbing moisture. Alternatively, in some other embodiments, the material of the waterproof membrane can be changed so that the membrane does not need to be removed without affecting the normal operation of the PCB. During the lamination process, the waterproof membrane can be bonded to the target core board.

[0056] In some other embodiments, the semi-cured sheet can also be immersed in water to absorb moisture. For example, by analyzing the design requirements and determining the hierarchical position and size of the cavity to be buried, the boundary of the area to be humidified is directly marked on the semi-cured sheet, and a circle of waterproof tape is pasted around the boundary. A circle of water retaining ring is set on the waterproof tape. The water retaining ring can be used to form a water storage tank, and then a certain amount of water is injected into the water retaining ring. In this way, the area to be humidified of the semi-cured sheet can be immersed in water for moisture absorption. After moisture absorption is completed, the water retaining ring and waterproof tape are removed.

[0057] In some other embodiments, an automatic water spraying system can be used to spray water intermittently into the water retaining ring, which makes the operation more intelligent and convenient.

[0058] The above specifically describes the preferred embodiments of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A PCB manufacturing method, characterized in that: A local area of ​​the prepreg is humidified or moisture-absorbed, and the humidified or moisture-absorbed prepreg is pressed onto a target core board, wherein a cavity is formed in the humidified or moisture-absorbed local area of ​​the prepreg during the pressing process, specifically comprising the following steps: S10, providing two waterproof sheets, and processing circuit grooves on the two waterproof sheets; S20, stacking the two waterproof sheets and the prepreg to form a multi-layered body, with the prepreg sandwiched between the two waterproof sheets, and sealing the surfaces of the two waterproof sheets and the prepreg around the circuit grooves and the outer edges of the surfaces; S30, placing the multilayer combination in a humid environment to absorb moisture, with the prepreg corresponding to the circuit slot exposed to the humid environment, the temperature of the humid environment being set to ≤ 23° C., and the humidity being set to 85±10% R / H, and the multilayer combination being placed in the humid environment for 8 hours to 12 hours; S40, after moisture absorption, separate the two waterproof sheets from the prepreg, and then press the prepreg after moisture absorption with the target core board within 8 hours after separation, and form a cavity in the moisture absorption area of ​​the prepreg during the pressing process.

2. The PCB manufacturing method according to claim 1, wherein: Before the waterproof sheet and the prepreg are superimposed, a positioning structure is processed on the waterproof sheet and the prepreg, and the waterproof sheet and the prepreg are positioned relative to each other by the positioning structure during superposition.

3. The PCB manufacturing method according to claim 1, wherein: In step S40, the heating rate of the pressing process is set to ≥3.0°C / min, and the pressing environment temperature is between 80°C and 140°C.

4. The PCB manufacturing method according to claim 1, wherein: The prepreg is at least partially filled with pure glue.

5. The PCB manufacturing method according to claim 1, wherein: The copper thickness of the circuits on the target core board that need to form cavities is set to be ≤1oz.

6. A PCB comprising at least one cavity; characterized in that: The PCB is manufactured according to any one of the manufacturing methods of claims 1 to 5.

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